### For Official Use E NV/JM/TG/RD(2006)1/REV

Organisation de Coopération et de Développement Economiques
Organisation for Economic Co-operation and Development 05-Apr-2006

___________________________________________________________________________________________

_____________ English - Or. English

ENVIRONMENT DIRECTORATE
JOINT MEETING OF THE CHEMICALS COMMITTEE AND THE WORKING PARTY ON CHEMICALS, PESTICIDES AND BIOTECHNOLOGY



### Test Guidelines Programme

PROJECTS FOR DEVELOPING TEST GUIDELINES ON PHOTOTRANSFORMATION IN WATER

AND ON SOIL SURFACES

18th Meeting of the Working Group of National Coordinators of the Test Guidelines Programme

16-18 May 2006, Bern, Switzerland

Ms. Laurence MUSSET Tel: +33 (0)1 45 24 16 76; Fax: +33 (0)1 45 24 16 75; Email: laurence.musset@oecd.org

JT03207035

Document complet disponible sur OLIS dans son format d'origine Complete document available on OLIS in its original formatENV/JM/TG/RD(2006)1/REVFor Official UseEnglish - Or. EnglishENV/JM/TG/RD(2006)1/REV

2 This room document is provided for information, to facilitate the discussion of the projects related to the phototransformation of chemicals in water and on the soil. It includes six annexes:

Annex 1 is Part 1: Direct Photolysis of the second revised draft of the Test Guideline Phototransformation of Chemicals in Water (November 2004);

Annex 2 is Part 2: Indirect Photolysis of the second revised draft Test Guideline Phototransformation of

Chemicals in Water (November 2004);

Annex 3 is the compilation of comments received before revising the draft Test Guideline Phototransformation of Chemicals in Water (November 2004);

Annex 4 is the second draft of the Test Guideline Phototransformation of Chemicals on Soil Surface (February 2004)

Annex 5 is the compilation of comments received before the preparation of the second draft Test Guideline Phototransformation of Chemicals on Soil Surface (February 2004)

Annex 6 is a third draft of the Test Guideline Phototransformation of Chemicals on Soil Surface prepared by BIAC (July 2005)ENV/JM/TG/RD(2006)1/REV

3 

### DRAFT DOCUMENT

November 2004 August 2000

ANNEX 1



## OECD GUIDELINE FOR TESTING OF CHEMICALS

PROPOSAL FOR A NEW GUIDELINE

Phototransformation of Chemicals in Water

- – Part 1: Direct and Indirect Photolysis

INTRODUCTION

1. This guideline provides guidance for conducting phototransformation in water studies to determine the potential effects of solar irradiation on chemical pollutants in surface water. Such studies determine phototransformation kinetics, products, and product pathways resulting from both either direct and (as an option or if applicable) or indirect aqueous photolysis. It is based on current and /or proposed methods (references 1 through 10) and on relevant literature on environment al aqueous photochemistry. Part 1 of this guideline deals with direct photolysis.

2. A glossary of definitions (11) and symbols/units are provided in Annexes 1 and 2

, respectively.

ENVIRONMENTAL SIGNIFICANCE AND USE

3. Chemical pollutants and/or their transformation products that are potentially susceptible to direct and/or indirect photolysis include those that are transported to surface water by direct point discharge and/or by runoff from urban and/or rural areas. Chemical pollutants in surface water also often originate from transformation of other chemicals via hydrolysis, photolysis, and biotransformation.

4. Direct photolysis in natural water involves th e transformation of a chemical resulting from the direct absorption of a solar photon (references 12 through 18). Indirect photolysis in natural water

sometimes involves the transformation of a chemical due to energy transfer from naturally occurring photosensitizers in electronically excited triplet states (12)(13)(19)(20). However, indirect photolysis more often involves the transformation of a chemical due to reactions with transient oxidants such as hydroxyl radicals, molecular oxygen in a singlet electronic state (“singlet oxygen”), and peroxy radicals (references 12 and 22 through 32). Both triplet state photosensitizers and transient oxidants result from the absorption of solar photons by chromophoric dissolved organic matter (CDOM) and nitrate ion (12)(21)(32)(33)(34).

5. Direct photolysis can be an important dissipation pathway for some chemical pollutants that exhibit significant light absorption above the 29 0 5 nm cutoff of solar irradiation at the earth’s surface. Indirect photolysis can also be an important dissipatio n pathway for some chemical pollutants that come in contact with photosensitizers in electronically excited triplet states or with short-lived photochemically generated oxidants such as hydroxyl radicals and singlet oxygen. In some cases both direct and indirect photolysis can contribute significantly to the dissipation of a chemical in natural waters.

6. The direct and indirect phototransformation of chemicals in natural water bodies is a complex process which depends on a number of factors such as:ENV/JM/TG/RD(2006)1/REV

4 (a) the chemical structure and electronic absorption spectrum of the chemical; (b) the concentration, composition, and absorption spectra of CDOM (from which photosensitizers and singlet oxygen arise); (c) the concentration of nitrate (the primary source of hydroxyl radicals); and (d) the solar photon flux spectrum to which the chemical, CDOM and nitrate are exposed.

7. The solar photon flux spectrum to which a chemical, CDOM, and nitrate are exposed depend on numerous factors including the latitude, season, and the physical and chemical properties of the water body (12)(18)( 41 35 )( 42 36 ). Important properties of the water body which contribute to the attenuation of solar irradiation with depth include the concentration and composition of CDOM and suspended particulates. The mixing and stratification properties of the water will help determine the horizontal and vertical distribution of the chemical, CDOM, and nitrate.

8. The results of phototransformation in water studies are used in conjunction with physical chemical properties and data from other studies (abiotic hydrolysis; biotransformation; adsorption/desorption) to help assess the overall environmental transformation and transport of chemical pollutants. The results of phototransformation in water studies are also used to help develop inputs for environmental fate computer models, and to help develop protocols for conducting other aquatic laboratory and/or aquatic field studies.

PRINCIPLE OF THE STUDY

Scope and approach

9. This part of the test guideline is designed to provide some or all of the following data and/or information depending upon specific needs:

• The quantum yield and resulting estimated direct photolysis rate constants for test chemical test
substance s for various types of water bodies (defined by depth and light attenuation), seasons, and

latitudes of interest.

• Direct photolysis rate constants for test chemical test substance s determined in the laboratory using filtered xenon arc lamp or sunlight irradiation and extrapolated to natural water. A xenon arc lamp

filtered to remove irradiation < 29 0 5 nm will be referred to throughout the rest of the document as a filtered xenon arc lamp.

• The net (combined direct and indirect) and indirect photolysis rate constants of one or more test chemicals

in a stan dard simulated natural water (containing humics as a surrogate for CDOM and in some cases, nitrate) and/or in one or more natural waters.

• The transformation pathway and the identities, concentrations, and rates of formation and decline of major phototransformation products resulting from direct photolysis

. and/or indirect photolysis

.

10. This guideline is designed as a tiered approach. Each tier is triggered by the results of the previous

tier. The t T iered approach es are proposed separately for direct a nd indirect photolysis tests a i s shown in Figures 1 and 2, respectively (see Annex 3 )

.ENV/JM/TG/RD(2006)1/REV

5 Pseudo first-order kinetics of direct and indirect photolysis

11. The rate of decline of a test chemical test substance in either a direct or indirect photolysis studyis generally assumed to follow pseudo first-order kinetics (e.g., time series data are fit to a pseudo firstorder kinetics model):



### d C

dt k C [ ] [ ] = − [eq. 1]

The integrated form of equation 1 is:

[ ] [ ]exp( )

C C kt = − 0 [eq. 2] The ln transformed version of equation 2 is:



# ln[ ] ln[ ] C C kt = − 0 [eq. 3]

where

c C = test chemical test substance concentration at time t (mol/L)

c 0 C 0 = initial test chemical test substance concentration at time t = 0 k = pseudo first-order rate constant (1/unit of time)

t = time

t 1/2 = half

- life

The pseudo first-order rate constant is determin ed by using non-linear regression to fit data to equation 2 or using linear regression to fit data to equation 3.

The half-life can be determined by substituting the pseudo first-order rate constant into the following equation:



### t k d i 1 2 

### 2

/
( ) 

### ln

=

or [eq. 4]

where where

k d is the direct photolysis rate constant and k i is the indirect photolysis rate constant

t 1/2 = half-life

. Other kinetic models may be applied if they better fit the kinetic data.

Note : In the equations provided in this guideline, units for half-lives, pseudo first- order rate constants and photon fluxes are (for illustrative purposes) given in days, 1/day, and photons/cm 2 • day, respectively. However, other units of time such as hours or seconds may be used as long as there is consistency within the same equation. Units of concentration are given in mol/L.

Direct photolysis

12. To undergo transformation via direct photolysis, a chemical molecule must first absorb a photon

. of light. The absorption of a photon by a molecule results in a transition from an electronic ground state toENV/JM/TG/RD(2006)1/REV

6 an electronically excited state of the molecule. To be absorbed by the molecule, the energy of the photon (which is inversely proportional to its wavelength ) must correspond to the difference between the ground and a possible excited electronic state of the molecule (12). Within the UV-Visible wavelength of interest (29 0 5 -800 nm), photons energies range from 150 kJ/mol at 800 nm to slightly greater than 400 kJ/mol at

29 0 5 nm (11)( 43 37 ).

13. The absorption of a photon is a necessary, but often not a sufficient condition, for a molecule to undergo transformation via direct photolysis (12)(14)( 43 37 ). The absorbed energy must first be sufficient to cause the transformation via bond cleavage, rearrangement, oxidation, or reduction. Then, phototransformation to form new molecular structures must compete with other possible deactivation processes such as quenching, other radiationless processes, and radiative processes. Consequently, the fraction of photon excited molecules that actually undergo phototransformation ( i.e. e.g. the quantum yield) is generally much less than 1 (usually < 0.1 and sometimes < 0.01) (14)(2 3 1 ). The mechanistic aspects of phototransformation reactions at a molecular level are beyond the scope of this guideline (see

reference 44 38 for further information).

14. It can be shown that for an optically dilute solution (absorbance A < 0.02) of a chemical in pure water exposed to polychromatic irradiation above the cutoff of solar irradiation at the earth’s surface of

29 0 5 nm, the direct photolysis rate constant (assuming the quantum yield is independent of wavelength) is given by (12)(14through 18) (See Annex 4: Derivation of selected equations):



### k j l

D I d

sys



### = 

# ∑ 2 3

0

295 800



### . φ ε λ λ [eq. 5]

where:

k d = direct photolysis rate constant (1/day) φ = the quantum yield (independent of wavelength)

ε λ = molar absorption coefficient (L/mol • cm; M -1 •cm -1 ) at wavelength λ

I 0 λ = photon flux (photons/cm 2 • day) over a 1 nm interval centered at wavelength λ

D sys = depth of irradiated system (cm) = volume of irradiated system/incident area l = light pathlength (cm) j = conversion factor to make units consistent with the L/mol • cm unit of the molar absorption coefficient and the mol/L unit of concentration = 6.02 x 10 20

(L/cm 3 )(photons/mol)

Note : The term (l/D sys ) in equation 5 approximately cancels out for rectangular photolysis cells exposed to irradiation from a filtered xenon arc lamp and for which D sys = D cell . However, that would not be true for cylindrical photolysis cells or for any photolysis cells exposed to solar irradiation where the pathlength l has a more complicated dependency on D cell. Methods for determining the pathlength of cylindrical cells exposed to filtered xenon-arc lamps are discussed in references 12 and 17. Pathlength determinations as a function of the depth of a system, D sys exposed to solar irradiation are discussed in references 12 and 18. In addition, note that if the quantum yield is not independent of wavelength, it must remain inside of the summation in equation 5.

15. Equation 5 is applicable to solar as well as filtered xenon arc lamp irradiation. However, the following equation is often used to determine the di rect photolysis rate constant for optically dilute

solutions of test chemical test substance s in pure water in photolysis cells or in near surface, clear natural water exposed to solar irradiation (2)(12) (See Annex 4: Derivations of selected equations):ENV/JM/TG/RD(2006)1/REV

7 

### k L

d solar

( ) 

### = 

# ∑ φ ε λ λ

295 800



### [eq. 6]

where:

k d 

### = direct photolysis rate constant (1/day) φ = quantum yield (independent of wavelength)

ε λ 

### = molar absorption coefficient (L/mol • 

### cm) at wavelength λ

L λ 

### = average daily solar photon flux irradiance (mmol photons/cm 2

• 

### day) over wavelength interval ∆λ centered at wavelength λ

16. Equations 1, 5 and 6 show that direct photolysis kinetics are theoretically pseudo-first order only if the photon flux remains constant over time. Photon fluxes from filtered xenon arc lamps at any given wavelength remain, in general, relatively constant over time. This is one of the primary advantages in using filtered xenon arc lamps. However, solar photon fluxes at any given wavelength vary cyclically over 24- hour periods. Nevertheless, the data obtained from studies conducted in natural sunlight (in which the rate constant reflects an average over the entire study duration) generally do fit a single, pseudo-first order rate constant model reasonably well. The reason is that changes in the average pseudo first-order rate constant over time as the study progresses is generally relatively small and not systematic. This is particularly valid for studies conducted for one to several weeks or for 2-4 hours mid-day. It may not be as valid for studies lasting 4 hours to several days or for those conducted beyond 30 days.

Summary of the proposed tiered approach for direct photolysis

Tier 1: Theoretical screen

17. Estimate a maximum possible direct photolysis rate constant for the test chemical test substance

in the near surface of a clear natural water as follows. Measure the test chemical test substance molar absorption coefficients from 29 0 5 nm to 800 nm, and use tabular solar irradiance for summer and 40 0 or 50 0 latitude over the same wavelength interval. Estimate a maximum possible direct photolysis rate by assuming the quantum yield in equation 6 is equal to one and by substituting the molar absorption
coefficients and tabular solar irradiance values, L λ

, into the equation (2)(12). Determine if the estimated maximum possible direct photolysis rate constant would theoretically result in estimated direct photolysis losses greater than 50% of an initial concentration over 30 days /nights. If maximum possible losses are < 50%, no further direct photolysis work is performe d, but proceed to Indirect Photolysis Tier 1 (experimental /theoretical screen)

. , if required . If the maximum possible losses > 50%, proceed to Direct Photolysis Tier 2 (experimental screen ) and range finding) or to Direct Photolysis Tier 3 (determination of the quantum yield).

Tier 2 - Experimental screen and range finding

18. Approximately determine the rate of decline in the concentration of the test chemical test
substance and corresponding direct photolysis rate constant in buffered pure water exposed to a filtered xenon arc lamp (recommended) or sunlight. Determine if the approximate direct photolysis rate constant would result in estimated direct photolysis losses equal to or greater than to 20% of an initial concentration

over a period equivalent to 30 days /nights in the near surface of a clear natural water body exposed to summer sunlight. If estimated losses are < 20%, no further direct photolysis work is performed, but proceed to Indirect Photolysis Tier 1 (experimental /theoretical screen

. ), if required. If estimated losses

≥ 20%, proceed to Direct Photolysis Tier 3 (determination of the quantum yield). If the determination ofENV/JM/TG/RD(2006)1/REV

8 the quantum yield is not required, proceed to Direct Photolysis Tier 4 (kinetics study).

Tier 3 - Determination of the quantum yield and its use to estimate direct photolysis rate constants

19. Determine the quantum yield for direct photolysis of the test chemical test substance in buffered pure water using monochromatic irradiation (12), polychromatic artificial irradiation (8) or sunlight (2). The pseudo first-order rate constant for direct phototransformation and thus the life-time of a test substance in water can be calculated from the quantum yield (18)(52). Once the quantum yield has been determined, use it as input to c C omputer programs such as GCSOLAR (18) or ABIWAS ( 41 35 )( 42 36 ) to may help to estimate direct photolysis rates for the test chemical test substance applicable to any types of surface waters (defined by depth and light attenuation), seasons, and latitudes of interest (2). If the Direct Photolysis Tier 4 study is potentially applicable, d D etermine if the direct photolysis rate constants estimated from the quantum yield would result in estimated direct photolysis losses greater than or equal to 20% of the initial

concentration over a period equivalent to 30 days /nights in the near surface of a clear natural water body exposed to sunlight. If the estimated losses are < 20%, no further direct photolysis work is required but proceed to Indirect Photolysis Tier 1 (experimental /theoretical screen)

. , if required . If the estimated losses

are > 20%, proceed to the Direct Photolysis Products Tier 4

. kinetics study.

Tier 4

- – Identification ofKinetics study on the parent and, if applicable, major transformation products

20. Estimate Determine the rate of formation and decline of phototransformation products in the

concentration of the test chemical test substance and corresponding direct photolysis rate constant in buffered pure water exposed to a filtered xenon arc lamp (recommended) or sunlight. If applicable, also

Isolate and identify /quantify and determine the rates of formation and decline of the major transformation products. In this guideline, major transformation products are defined as those accounting for ≥ 10% of the applied test substance chemical in an individual sample at any sampling time.

Indirect Photolysis

21. To undergo transformation via indirect photolysis, the test substance must:

• receive energy from a photosensitizer in an excited electronic triplet state such as va rious ones generated from the solar irradiation of CDOM (12)(14)(19)(20), or

• react with a photochemically generated oxidant such as a hydroxyl free radical, a singlet oxygen, or a alkylperoxy free radical (references 12 and 21 through 32). Singlet oxygen a nd alkylperoxy free radicals appear to be generated primarily from the solar irradiation of CDOM in oxygenated natural waters. Some hydroxyl free radicals also appear to originate from the solar irradiation of CDOM. However, the major source of the hydrox yl free radical in natural waters appears to generally be the solar irradiation of nitrate (21).

22. In infrequent cases where the nitrate to nitrite ratio is less than 100 in aerobic surface waters, the photolysis of nitrite (which is present in much low er concentrations than nitrate) may also contribute significantly to the formation of hydroxyl radicals because “nitrite photoproduces OH radicals about 50 times more rapidly than nitrate” (39).

23. The transformation of chemical pollutants in surface wat ers may also occur via photoredox reactions with soluble and insoluble Fe (III) species, which are commonly present at significant concentrations in many surface waters (40)(41).

24. Indirect photolysis kinetics are actually closer to being second

- order t han first

- order because the rate of decline of the test chemical is generally proportional to the product of the test chemical andENV/JM/TG/RD(2006)1/REV

9 sensitizer or photooxidant concentrations (12)(20) (21). However, although transient photooxidant and excited photosensitizer concentrations are very low (typically below 1 x 10

- 10 M), they can quickly attain quasi steady

- state concentrations in irradiated solutions thereby leading to pseudo first

- order kinetics (12)(20)(21).

25. In many cases, the net pseudo first

- order rate co nstant for indirect photolysis will reflect the reaction of different molecules with more than one type of sensitizer and/or oxidant:



# ( ) k k S or

indirect j nd j ss 

### = 

# ∑

( ) () 2 

### Ox j(ss) j=1 j=n



### [eq. 7]

where:

k indirect 

### = net pseudo first

- order indirect photolysis rate constant (1/day)

k

j(2nd) 

### = secon d order rate constant for the reaction with sensitizer j or oxidant j (L/mol • 

### d)

S j(ss) 

### = steady state concentration of sensitizer j (mol/L)

Ox j(ss) 

### = steady state concentration of oxidant j (mol/L)

Summary of the proposed tiered approach for indirect photolysis

Tier 1

- Experimental and/or theoretical screen

26. Perform an experimental screen in simulated natural water (SNW) containing humics as a surrogate for CDOM, and/or in a simulated natural water containing nitrate as well as humics (SNW

- N)

a nd/or in one or more natural waters (NW) and in buffered pure water (PW) (3). Specifications for PW appear in paragraph 68

- a. Approximately determine the rate of decline in the concentration of the test chemical in SNW, and/or SNW

- N, and/or NW exposed to s unlight to determine if indirect photolysis represents a potentially significant transformation pathway. The use of a xenon lamp light source for indirect photolysis studies is not recommended at this time. Determine if the estimated indirect (not net) ph otolysis losses over the equivalent of 30 days/nights of sunlight exposure is greater than or equal to 20% of an initial concentration of the test chemical. If the estimated indirect photolysis losses are < 20%), no further indirect photolysis work is perf ormed. If the estimated indirect photolysis losses are > 20%, proceed to the Indirect Photolysis Tier 2 (kinetics study).

27. In some cases, it may be possible to supplement the Tier 1 experimental screen with a theoretical screen based on using structur e activity relationships (SARs) to estimate rate constants for reaction with photooxidants and information on the typical concentrations of photooxidants in surface water (21).

Tier 2

- Kinetics study on the parent and (if applicable) major transformation products

28. Determine the rate of decline in the concentration of the test chemical and its corresponding net and indirect photolysis rate constants in SNW, and/or SNW

- N and/or one or more NWs irradiated with sunlight and in PW. If data on transformatio n products for indirect photolysis are applicable, identify/quantify major transformation products and determine their rates of formation and decline. In this guideline, major transformation products are defined as those accounting for > 10% of the applied test chemical (percent of applied radioactivity or molar basis) during any part of the study.ENV/JM/TG/RD(2006)1/REV

10 APPLICABILITY OF THE TEST GUIDELINE

21. 29 . This test guideline is applicable to chemical substances for which analytical methods with sufficient accuracy and precision are available and validated (if required). If data are needed on transformation products, adequate quantitative analytical methods must also be available/developed for

them.

22. 30. If a non-ionic test chemical test substance is somewhat susceptible to hydrolysis, the test may still be applicable as long as a dark control is used to account for the hydrolysis rate (2)(4)(5). However, photolysis tests should be conducted at a pH at which the hydrolysis rate of the chemical is minimized (5)( 45 42 ). The rate constant determined from the dark controls should be identical to the hydrolysis rate

constant and can be subtracted from the overall rate constant determined from the irradiated solutions to give the direct photolysis rate constant. However, in some cases, the desired test substance chemical may undergo rapid hydrolysis (i.e., hydrolysis half-life of < 1 day) within the environmentally relevant pH range of 4 5 -9 at 20-25 o C (46) . In such cases, the photolysis study should instead be conducted on e ach the major hydroly sis tic product (s) (> 10% of applied ) as the test substance )

.

23. 31. The test is not applicable to highly volatile compounds such as fumigants and some organic solvents. However, in some cases, where the Henry’s Law constant of the tes t chemical test substance and/or anticipated transformation products may indicate the potential for fairly substantial volatilization rates from water, the study may still be applicable provided that precautions are taken. Such precautions include using minimal head-space, adequate sealing in the photolysis cells to minimize volatile losses during the study (2)(4) or trapping. Trapping volatiles becomes more difficult, but preferred, when employing sacrificial sampling on numerous small photolysis cells than when employing aliquot sampling on a smaller number of much larger test vessels. However, with the proper equipment and experimental set-up, it can be done as shown by Ruzo (4 7 3 ).

INFORMATION ON THE TEST SUBSTANCE

24. Unlabelled or labelled test substances can be used to measure the rate of phototransformation. Labelled mareial is required for studying the pathway of phototransformation and for establishing a mass balance. 14 C-labelling is recommended but other isotopes, such as 13 C,

15 N, 32 P, may also be useful. As far as possible, the label should be positioned in the most stable part(s) of the molecule 1 . The chemical and radiochemical purity of the test substance should be at

least 95 %.

25. 32. Before carrying out any of the phototransformati on tests, the following information on the test

substance should be known, if available:

(a) Solubility in water [OECD Guideline 105]. (b) Solubility in organis solvents ( c b) Vapor pressure [OECD Guideline 104] ( d c ) Henry’s Law Constant 2 *

1 For example, if the test substance contains one ring, labelling on this ring is required; if the test substance contains two or more rings, separate studies may be needed to eval uate the fate of each ring and to obtain suitable information on formation of phototransformation products.

2 * Henry’s Law constant estimated from solubility in water and vapour pressure or measured. Henry’s Law constants for some chemicals may also be found in: http://webbook.nist.gov/chemistryENV/JM/TG/RD(2006)1/REV

11 ( e d ) Abiotic hydrolysis as a function of pH [OECD Guideline 111] ( f e ) n -octanol/water partition coeffici ent [OECD Guidelines 107 and 117] ( g f ) pK

a (s) of ionisable substances [OECD Guideline 112] (g) Chemical nomenclature (IUPAC and CAS) (h) Chemical Abstract Registry Number of the test substance (i) Common name(s), if any (j) Chemical structure (k) Position(s) of radiolabelled atom(s) or other molecular tags (if applicable) (l) Isomer purity (if applicable)

Note : The temperatures at which the physical chemical properties listed above in the previous paragraph were determined should generally be reported. within the range of (25 ± 5) ° C and should be specified.

33. If available, the solubility in non

- aqueous solvents may be useful in selecting a co

- solvent or

ex tractant. Also, the following optional information may be useful for indirect photolysis studies conducted

in natural water:

- Aerobic

- Anaerobic Transformation in Aquatic Sediment Systems [OECD draft Guideline 308]

- Adsorption / Desorption [OECD Guideline 106]

26. 34. The n-octanol/water partition coefficient and aqueous solubility supply some information on the potential of the test chemical test substance to significantly adsorb to glassware and reaction vessels. However, any additional information on the glassware adsorption potential of the test chemical test
substance should be known to ensure that such characteristics are taken into account in preparing glassware and reaction vessels for the study.

27. An appropriate analytical method of known accuracy, precision and sensitivity for the quantification and identification of the test substance and its phototransformation products should be available. The analytical detection limit for the test substance and its phototransformation products should also be known (see paragraph 31).

ANALYTICAL METHODS AND QUALITY CRITERIA

35. The experimenter should develop methods with appropriate accuracy (recovery), precision (reproducibility), and adequate limits of detection (LOD) and quantification (LOQ). In many instances, validation of the analytical methodology may be requi red. In those cases, the experimenter should be responsible for ensuring that the analytical methods have been validated.

36. The analytical methods that may be used include liquid s cintillation counting (LCS) and radiochromatography (radiolabelled substances), high

- performance liquid chromatography (HPLC), gas chromatography (GC), gas

- liquid chromatography (GLC), and capillary electrophoresis (CE), etc. TLC can

also be used for radio labelled test chemicals, but only if adequate resolution can be achieved and there is no decomposition of the reference standards in the silica plates.

37. When necessary to identify and/or confirm transformation products, the separation methods listed

in the preceding paragraph may be coupled with spectrometric methods such as mass spectrometry (MS)

and/or Fourier

- Transform Infrared spectroscopy (FT

- IR). Examples of such couplings include as GC/MS,
HPLC/MS, LC/MS

- MS, GC/FT

- IR or any other adequate techniq ues.ENV/JM/TG/RD(2006)1/REV

12 38. Reference chemicals of potential transformation products may be used for identification (e.g. by

co

- chromatography). When radiolabelled test substance is used, it may be necessary to use radiolabelled reference chemicals. However, as indicated in the previous paragraph, the identities of major transformation products need to be confirmed preferab ly by an independent analytical chemistry method such as with MS. Transformation products that cannot be identified from reference chemicals should be

e lucidated using, for example, MS, NMR and infrared spectroscopy.

39. Parameters that can influence the accuracy and/or precision of the determination of chemical concentrations in aqueous media include the stability of the chemicals in samples during stor age, extraction efficiency, analytical separation efficiency in mixtures, and the magnitude of the concentrations with respect to analytical detection and quantification limits.

40. Analytical instrumentation should be periodically calibrated within appl icable concentration ranges according to the manufacturer’s specifications. If samples are stored prior to analysis, storage stability tests may need to be performed depending upon the storage method and duration. The accuracy and precision of the analyti cal method should be checked within the expected concentration range. Accuracy can be determined from the recovery percenta ges of spiked samples. Precision can be determined by replicate analyses of an appropriate percentage of the samples.

41. Regardless of the chosen analytical method, analytical recoveries for radiolabelled test chemicals should fall within 90% and 110% of the applied radioactivity. For non

- radiolabelled test chemicals, analytical recoveries of 85 to 115% are desirable.

42. For radiola belled materials, total mass balance should fall within that range 90% to 110% of the total applied radioactivity (42).

REFERENCE SUBSTANCES

28. Reference substances should be used for the characterisation and/or identification of phototransformation products by spectroscopic and chromatographic methods.

QUALITY CRITERIA

Recovery

29. Extraction and analysis of, at least, duplicate samples immediately after the addition of the test substance gives a first indication of the repeatability of the analytical method and of the initial recoveries for the test substance. Recoveries for later stages of the experiments are given by the respective mass balance obtained with labelled material. Recoveries should range from 90 to 100 % for labelled chemicals (48) and from 70 to 110 % for non-labelled chemicals (7).

Repeatability and sensitivity of analytical method

30. Repeatability of the analytical method (excluding the initial extraction efficiency) to quatify test substance and phototransformation products can be checked by duplicate analysis of the same extract , incubated long enough for formation of phototransformation products.ENV/JM/TG/RD(2006)1/REV

13 31 The limit of detection (LOD) of the analytical method for the test substance and for the phototransformation products should be at least 0.01 mg/kg water (as test substance) or 1 % of the applied dose whichever is lower. The limit of quantification (LOQ) should also be specified.

Accuracy of transformation data

32 Regression analysis of the concentration of the test substance as a function of time gives the appropriate information on the reliability of the photo transformation curve and allows the calculation of the confidence limits for half-lives (in case of pseudo first-order kinetics) or DT 50 values and, if appropriate, DT 90 values.

TEST MATERIALS

Test vessels

33. 43. All glassware and reaction vessels/photolysis cells used in the photolysis studies should must be sterilized by autoclaving (2)(3)(4)(12) or any other suitable non-chemical method

. (2). Chemical sterilization is not recommended since chemical reagents may leave residues that could absorb in the 29 0 5 to 800 nm region and/or behave as photosensitizers.

Test substance application

34. The test substance should be directly dissolved in the aqueous media at a concentration which should not exceed half its solubility. For test substances with low aqueous solubility, a co-solvent may be used to prepare the test solution. However, the amount of co-solvent used must be as little as possible and preferably not exceed 1% by volume in the test solution (45). Co-solvent percentages up to 10% may be used, but if more than 10% co-solvent is required to dissolve the test substance, the study should not be performed. The selected co-solvent must not solvolyse the test substance, must not absorb in the 290 to 800 nm region, and must not be a photosensitizer. Acetone is an example of a solvent that is a photosynthesizer, and should not be used. Acetonitrile is a generally recommended co-solvent.

35. The initial concentration of the test substance for quantum yield determinations and direct photolysis studies should be such that the absorbance at any wavelength above 290 nm (maximum absorption wavelength included) is less than 0.02. These optically dilute, also referred to as “optically thin” solutions generally have a concentration of < 10 -4 M. Nevertheless, the initial concentration of the test substance should be at least 10 times greater than the quantification limit of the analytical method.

36 Because oxygen can affect the rates and even pathways of photodegradation reactions, test solutions should be saturated with air at the beginni ng of the study (4). A buffer solution that has been autoclaved should be given sufficient time to aerate prior to dispensing into the vessels. It is not recommended to autoclave small amounts of buffer in individual vessels because driving the air out may change the volume.

44. If radiolabelling is used, test chemicals should be labelled at one or more atoms within each stable or relatively sta ble portion of the molecule. For chemicals containing one or more aromatic rings, one or more atoms in each ring are usually labelled. In addition, one or more atoms on both sides of any linkage thought to be readily susceptible to cleavage should be radio labelled (42). Radiolabelling is particularly important when there is the need to identify transformation pahtways. Radiolabelling does not have to be limited only to 14 C. For example, in some cases, 32 P can be used in place of or in addition to 14 C (42). If mass spectroscopy is used, stable isotopes such as 15 N can also be used as molecular tags.ENV/JM/TG/RD(2006)1/REV

14 45. Radiolabelled test substances should have radiochemical and chemical purities of 95% or greater (42). Non

- radiolabelled test substances should have a chemi cal purity of 95% or greater (42).

46. If the test chemical consists of more than one geometrical and/or optical isomer, the percentage represented by each isomer should be provided.

47. Pesticide testing should generally be conducted with the active i ngredient. The same generally applies to pharmaceutical chemicals. However, in some instances it may be more appropriate to use a formulated product.

48. If the potential loss of the test chemical by volatilization or adsorption to test vessels is of

conc ern or if the identification and quantification of major transformation products are of interest, radiolabeling should be used.

Test media for direct photolysis studies

37. 49. Guidance for preparing test media for direct and indirect photolysis respecti vely is provided in

Annex 5.

Test media for direct photolysis

38. 50. For direct photolysis studies, the test media should be sterilized aqueous buffer solutions at the appropriate pH (for sterilisation methods see paragraph 33) . The water should be “pure water” (PW). The buffers should be identical or comparable to those used in the hydrolysis studies (46) and should not absorb

between 29 0 5 and 800 nm or be photosensitizers. Also, the buffers should not adversely affect the solubility of the test substance. chemical.

39. 51. For If the non-ionisable test substances the tests should be conducted at a pH at which the test substance is hydrolytically most stable in the pH range 4-9. chemical is non

- ionizable and is approximately stable to abiotic hydrolysis at pH 7, the buffer used in the direct photolysis study should maintain a pH of approximately 7. However, if the hydrolysis rate of a non

- ionizable test chemical at pH 7 is significant, but its hydrolysis rate at pH 5 or 9 is much lower, the buffer used sh ould maintain a pH (within the 5 to 9 range) at which the hydrolysis rate is minimized (42).

40. 52. If the test chemical test substance is appreciably ionic anywhere within a 4 5 to 9 pH range, the study should be conducted in one or more aqueous buffers at any of the pH 4 5 , 7, and/or 9. Selection of the pH (s) at which the study should be conducted depends on the electronic absorption spectra at each pH. Spectra showing absorption bands between 29 0 5 and 800 nm or shorter wavelengths tailing above 29 0

5 nm together with estimates of maximum photolysis rates (Tier 1: Direct Photolysis) are the criteria for selecting the pH(s). Refer to Tier 1, Direct Photolysis for further details.

53. For test chemicals with low aqueous solubility, a co

- solvent may be u sed to prepare the test solution. However, the amount of co

- solvent used must be as little as possible and preferably not exceed 1% by volume in the test solution (42). Co

- solvent percentages up to 10% may be used, but if more than

10% co

- solvent is requir ed to dissolve the test chemical, the study should not be performed. The selected

co

- solvent must not solvolyse the test chemical, must not absorb in the 295 to 800 nm region, and must not be a photosensitizer. Acetone is an example of a solvent that is a photosynthesizer, and should not be used. Acetonitrile is a generally recommended co

- solvent.

Test media for indirect photolysis studiesENV/JM/TG/RD(2006)1/REV

15 54. The selection of test media for indirect photolysis studies depends on the purpose of the study. The preparation of test media is based on the procedure given in OPPTS 835.5270 guideline (3). Three test media may be used for these studies: (1) SNW (Simulated Natural Water); SNW

- N (Simulated Natural Water with Nitrate); and (3) NW (Natural Water). SNW

- N may be approp riate for areas where surface waters show strong evidence of nitrate pollution associated with the use of fertilizer and other nitrate

bearing substances. Nitrate has been known to photochemically produce hydroxy radical (21)(22)(26). NW may be important i n situations when the understanding of the photochemical behavior of chemicals in

actual natural surface waters is of interest.

55. Humic acid or other humic materials may be obtained commercially (Aldrich, Fluka, etc.).

Humic and fulvic acid extracted fr om soils or natural surface water may be used as surrogates for aquatic humic acids (23)(44). Composite data for typical humic acids are available from the International Humic Substances Society (45). The UV

- VISIBLE spectra of the selected humic materials in the test media (natural water and/or buffered SNW) should be provided. The absorption spectra of some humic materials

are shown in reference 46

.

Light sources

41. 56. For direct photolysis studies the recommended light source should be a filtered xenon arc lamp capable of simulating natural sunlight in the 29 0 5 to 800 nm region or sunlight (4 9 7 ). For indirect photolysis studies, the only recommended light source at this time is sunlight. The photon flux of the filtered xenon arc lamp as a function of wavelength should be determined at least at the beginning and the end of the study using one or more actinometers or and a spectral radiometer

. if available. If sunlight is used, average daily solar photon fluxes (L λ ) as a function of wavelength should be determined for the season and latitude closest to those of the experiment using solar irradiance tables and a spectral

radiometer

. , if available.

42. 57. If a filtered xenon arc lamp is used, the irradiation photon flux incident on the test vessels should be adequate to cause substantial decline of the test substance chemical over a several day experimental period. The transformation rate constant and corresponding half-life obtained with a filtered xenon arc lamp can be adjusted to solar equivalents from a comparison of solar photon flux to lamp photon flux because of the linear relationship between the transformation rate and photon flux (see equation 14).

43. 58. If sunlight is used, the study should be conducted during the season when and at the latitude

where the concentration of the test substance chemical is expected to be highest in the environment. For pesticides, that would be the season when and the latitude where it is typically applied.

44. 59. If a filtered xenon arc lamp (see Annex 6) and sacrificial sampling of multiple test vessels are used, an appropriate experimental set-up should be used to ensure that all of the test vessels receive the same incident irradiation flux. Self-contained, commercially available xenon photolysis units in the projection or “working plane” configuration produce uniform fluxes ( 50 48 )( 51 49 a). A commonly used configuration is the “merry-go-round” photochemical reactor (12). Merry-go-round photochemical reactors are commercially available ( 51 49 a)( 51 49 b). Another example of an experimental set-up is shown reference

5 2 0 (see Annex 6). . An experimental set-up that includes trapping of volatiles appears in reference s (4 7 3 )

and is also shown in Annex 6

.

Other photolytic equipment and reagents

45. 60. Photolytic equipment includes:ENV/JM/TG/RD(2006)1/REV

16 • Optical cells of appropriate material (generally qua r tz) and path length for measuring UV-VIS spectra.

• Appropriate optical filters to cut-off radiation below 29 0 5 nm and above 800 nm.

• When monochromatic irradiation is used in the determination of the quantum yield, the appropriate filter systems must be used to isolate the desired wavelength (12)(4 9 7 ). Monochromatic irradiation at the desired wavelength can also be achieved with a monochromator in conjunction with a suitable polychromatic light source such as a mercury or xenon arc lamp. An example of a useful optical bench

is shown in Annex 6. (Filters for isolating the 313 and 366 nm wavelengths from a mercury arc lamp are discussed in reference 12).

• Specially designed reaction cuvettes/photolysis cells to contain test solutions (exposed and dark control) and chemical actinometers, when needed. The recommended material is quartz.

• Appropriate apparatus designed to contain the light source, filters, sample, holders, reaction vessels/actinometers such as the photochemical “merry-go-round” reactor. Several appropriate designs

are commercially available to accommodate specific needs. shown in Part 1, Annex 6.

• Photometer or spectral radiometer to meas ure photon flux as a function of wavelength.

46. 61. Photolytic reagents include:

• All of the water used in the direct photolysis tests must be of high purity and free of any absorbing or photosensitizing chemical species. For example, the U.S.EPA OPPTS 835.2210 (2) recommends using reagent water meeting ASTM Type IIA standard s, as described in ASTM D1193-99 Standard Specification for Reagent Water (see Annex 5: Test Media). “Milli-Q” water is one example of high purity water. In this guideline, the water used in the preparation of stock, test and buffer solutions is referred as “pure water”.

• Appropriate chemical reagents to be used as actinometers.

• Commercially available, certified humic material for indirect photolysis studies (Fluka; Aldrich).

• Analytical grade NaNO 3

• Appropriate aqueous buffers such as phosphate for pH 7, acetate for pH 4 5 and borate for pH 9 for compatibility with hydrolysis studies. Phosphate buffers are usually recommended for direct photolysis studies(2)(12) but only cover

. pH range 5 to 8. Caution should be applied when using phosphate buffers because they might promote catalytic effects.

Analytical equipment and chemical reagents

47. 62. In addition to standard laboratory equipment, the following is required:

• Spectrophotometer to acquire spectral data in the UV-VIS range. For example, single beam, diode array instruments that allow sensitive, rapid acquisition of digitized spectral absorbance data.

• Appropriate analytical instrumentation to measure the concentration of the test substance in exposed and dark control samples, such as HPLC, GLC, TLC, etc.

• Suitable instrumentation for identification purpos es, such as MS, HPLC/MS, GC/MS, LC/MS, GCFTIR, NMR, etc.

• When radiolabelled test substances are used, liquid scintillation counters (LSC) and instrumentation for radiochromatography should be available.

• Appropriate extraction apparatus.

• Equipment to sterilise reaction vessels and other glassware used in the preparation of stock and test

solutions.

48. 63. Chemical reagents include:

• Reagent grade chemicals and solvents free of any photosensitizer.ENV/JM/TG/RD(2006)1/REV

17 • Scintillation liquid (for radiolabelled chemicals).

64. Analytical references include:

• Test substance reference standards for co

- chromatography and/or for other analytical methods.

• Potential transformation products (including hydrolysi s products) reference standards for the determination of products, if applicable.

TEST METHODOLOGY

Test conditions

49. 65. The temperature during photolysis studies may vary by as much as 10 degrees but should be maintained within the range of 20 to 30 C. (25 ± 5) o C and monitored periodically

.

50. 66 . The pH of buffered solutions should be maintained within + 0. 1 5 pH units. The pH should be checked during the course of the study, if feasible.

51. 67. Dark control solutions should be used for all quantum yield determinations and for all direct and

indirect photolysis studies and should be kept at the same temperature as the irradiated samples

.

68. The concentration of the chemical in the test media should never exceed half its solubility. When

a co

- solven t is needed, it should preferably not exceed 1% by volume in the test solution and never exceed 10% by volume.

69. The initial concentration of the test chemical for quantum yield determinations and direct photolysis studies should be such that the absor bance at any wavelength above 295 nm (maximum absorption wavelength included) is less than 0.02. These optically dilute, also referred to as “optically thin”, solutions generally have a concentration of < 10

- 4 M. Nevertheless, the initial concentration of the test chemical should be at least 10 times greater than the quantification limit of the analytical method.

70. The concentration of the test chemical in simulated (SNW, SNW

- N) or natural water (NW) test media should be equivalent to that of optically dilute test solutions in pure water/buffer solutions required for direct photolysis studies.

71. Because oxygen can affect the rates and even pathways of photodegradation reactions, test solutions should be saturated with air at the beginning of the study (4). A buffer solution that has been autoclaved should be given sufficient time to aerate prior to dispensing into the vessels. It is not recommended to autoclave small amounts of buffer in individual vessels because driving the air out may change the vol ume.

Study duration, sampling, and replication

52. 72. The study duration should be sufficient to determine the DT 75 (two half-lives if decline is firstorder) of the test chemical test substance and (if applicable) the formation and decline of major transformation products until they have declined to < 25% of their maximum concentration. However, the maximum study duration should not exceed the equivalent of 30 days/nights of sunlight exposure during an appropriate season and at an appropriate latitude. The “DT 75 " is defined as the time required for 75% of the

initial concentration of test chemical to disappear.ENV/JM/TG/RD(2006)1/REV

18 53. 73. Based upon equating photons absorbed by the test chemical test substance per unit volume, the maximum direct photolysis study duration (using continuous filtered xenon arc lamp irradiation) that is equivalent to 30 days /nights of sunlight exposure will be only a few days and is given by (see Annex 4) :

.

Max direct photolysis duration days j D

l L

I cell

xenon

xenon . ()

( ) = 

### ∑

∑ 30 295 800

0

ε

ε λ λ

λ λ [eq. 7 8 ]

where:

30 = 30 days/nights of solar irradiation

D cell = depth of irradiated cell (cm) = volume of irradiated cell/incident area

l

xenon = light pathlength in cell exposed to a filtered xenon arc lamp j = conversion factor (for details see eq. 9)

and other terms same as defined for equations 5 and 6.

Note : For rectangular box cells, the term D cell /l

xenon cancels out because l

xenon = D cell . However, that will not be true for cylindrical cells (12).

54. 74. Although equation 7 8 allows for flexibility in choosing an experimental photon flux from a filtered xenon arc lamp, practical considerations somewhat limit the range of experimental fluxes that should be used. In general, it is recommended that the experimental photon flux from a filtered xenon lamp be adjusted to be somewhat comparable to that of sunlight (at noon for short several hour studies or 24 hour average for several day to weeks studies). The reason is the experimental flux should not be so intense that photolytic processes other than those that would occur under natural sunlight are initiated. Also, if the parent is susceptible to hydrolysis at the experimental pH and the hydrolytic products are susceptible to direct photolysis, time should be allowed for them to form.

55. 75. A preliminary range-finding study should be performed to help determine the number of samples to be collected and the timing of their collection. For linear and non-linear regressions on test chemical test
substance data in definitive or upper tier tests, the minimum number of samples collected should be five and seven, respectively. The greatest number of samples taken should generally be during the first part of the study where the slope of the concentration versus time series for the test chemical test substance is generally greatest. If an accurate determination of the rates of formation and decline of major transformation products is desired, the number of samples taken should generally be greater and somewhat more dispersed throughout the study duration. The number of sampling times can be less in range finding

or lower tier tests.

56. 76. Either aliquot or sacrificial sampling can be used. Sacrificial sampling of entire photolysis cells at each sampling time is often preferred over withdrawing aliquots of test solutions at each sampling time. The reason is that it helps to maintain aseptic conditions and allows for mass balance determinations at each sampling time. The use of sacrificial sampling is particularly necessary in cases where mass balance

determinations are needed such as when the test chemical test substance and/or its transformation products are volatile and/or adsorb strongly to the photolysi s cells (5). Future sampling descriptions in this document will be for the generally preferred sacrificial sampling, but aliquot sampling from larger irradiated and dark control reaction vessels is acceptable as long as the resulting mass balance is adequate and aseptic conditions are properly maintained.

57. 77. Replicates (preferably a minimum of two three ) of each experimental determination of kinetic parameters are recommended to determine variability and reduce uncertainty in the determination ofENV/JM/TG/RD(2006)1/REV

19 kinetic parameters. However, the uncertainty in the determination of kinetic parameters can also be reduced by increasing the number of sampling intervals within each experiment, particularly when the rates of formation and decline of major transformation products are being determined. In such cases, a minimum of two replicate determinations of kinetic parameters may be adequate. With generally limited resources, the researcher needs to weigh the pros and cons of experimental replication versus increased numbers of sampling times per experiment in designing the study.

Calculations

58. 78. Basic calculations/equations, including the foll owing one used to determine whether going to higher tiers is triggered, are included within the body of the guideline:



### ( ) 

# [ ] 

# { } % loss over 30 days / nights solar = −− = 100 1 30 exp ( ) 

### k td

solar [eq. 8 9 ]

where:

k solar = pseudo first-order direct or indirect photolysis rate constant for test chemical test
substance exposed to solar irradiation (1/day)

59. 79. Calculations/equations for the kinetics of the formation and decline of major photoproducts , and accounting for photobleaching are optional

. The necessary non-linear regressions can be readily performed with the use of commercially available spreadsheets and/or statistical software.

Determination of the photon flux from a filtered xenon arc lamp

60. 80. The photon flux from a filtered xenon arc lamp can be determined with the use of low and/or high optical density actinometers alone or preferab ly in conjunction with a spectral radiometer (5 3 1 ). The advantage in using a spectral radiometer to determine the photon flux is convenience, as it avoids changing actinometers. However, spectral radiometers are expensive and are not always readily available. Furthermore, even if a spectral radiometer is generally used to determine the photon flux, it should be periodically calibrated against photon fluxes determined with actinometers. Calibration is necessary because of the difference between the exposure surface of a spectral radiometer and that of the photolysis cuvette or tubes used to contain the actinometers (5 3 1 ).

61. 81. By determining the monochromatic first-order direct photolysis rate constant for a low optical density actinometer of known quantum yield in PW in a photolysis cell irradiated with monochromatic irradiation, the incident photon flux at the wavelength of the irradiation can be determined from the following equation (5 3 1 ; see Annex 4 3 - Equation Derivations):



### I j D

l k

xenon cell

xenon d act

act act 0 

### 2 3 λ λ

λ 

### φ ε ( ) ( )

( ) 

### . = [eq. 9 10 ]

where :

I 0 λ (xenon) = photon flux (photons/cm 2 • day) over a 1 nm interval centered at wavelength j = conversion factor to make units consistent with the L/mol • cm unit of the molar absorption coefficient and the mol/L unit of concentration =

6.02 x 10 20 (L/cm 3 ) (photons/mol)ENV/JM/TG/RD(2006)1/REV

20 k d λ (act) = monochromatic direct photolysis rate constant (1/day, pseudo first-order)

of an actinometer exposed to monoc hromatic irradiation at wavelength λ
φ (act) = the quantum yield of the actinometer

ε λ = molar absorption coefficient (L/mol • cm; M -1 •cm -1 ) of the actinometer at wavelength λ

D cell = depth of irradiated cell (cm) = volume of irradiated cell/incident area

l

xenon = light pathlength in cell exposed to a filtered xenon arc lamp

62. 82. Equation 9 10 only gives the photon flux at one wavelength, but it can be used at different individual wavelengths wherever another monochromatic direct photolysis rate constant is determined for one or more low optical density actinometers. The determination of the photon flux at several different individual wavelengths spread throughout the waveleng th range in which an estimate of the photon flux is desired should be sufficient to determine the photon flux from a filtered xenon arc lamp as a continuous function of wavelength. Because photon flux irradi ation spectrum from a filtered xenon arc lamp is smooth, interpolation from known photon fluxes at several different wavelengths can be readily done (5 3

1 ).

63. 83. By determining the polychromatic zero order direct photolysis rate constant for a high optical density actinometer of known quantum yield in PW in a photolysis cell irradiated with a filtered xenon arc lamp, the sum of the incident photon flux over the absorption spectrum of the actinometer above 29 0 5 nm can be determined from the following equation (5 3 1 ) (see Annex 4):



### I jD k

xenon cell

act d act

initial final

0 λ
λ λ



### φ ( ) ( )( 

### =

= = 

# ∑

zero order) [eq. 1 0 1 ]

where:

( λ =initial) = initial wavelength of actinometer absorption (if > 29 0 5 nm)
( λ =final) = final wavelength of the actinonmeter absorption (if < 800 nm)

I 0 λ = photon flux over a 1 nm interval centered at wavelength λ (photons/cm 2

• day) j = conversion factor to make units consistent with the L/mol • cm unit of the

molar

absorption coefficient and the mol/L unit of concentration =

6.02 x 10 20 (L/cm 3 )(photons/mol)

k d_(act) (0 order) = monochromatic direct photolysis rate constant (zero order) of an actinometer exposed to monochromatic irradiation at wavelength λ
(mol/L • day)

D cell = depth of irradiated cell (cm) = volume of irradiated cell/incident area (cm) φ act = the quantum yield of the actinometer

64. 85. By using more than one high optical density actinometer with absorption bands at different wavelengths, the sum of the photon flux over any desired range including the entire range between 29 0 5 and 800 nm can be determined. Further experimental details of procedures for determining the photon flux from and for calibrating xenon arc lamps are provided in references ( 41 37 )(5 3 1 ).ENV/JM/TG/RD(2006)1/REV

21 Performance of direct photolysis study

Tier 1 - Theoretical screen.

65. 8 6 . For a test substance chemical which does not ionize significantly within a pH range of 4 5 to 9, a single UV-Visible absorption spectrum should be measured at a single pH within the 4 5 to 9 range where the hydrolysis rate, if any, is minimized. If the chemical is stable to abiotic hydrolysis, the spectrum should be measured at pH 7. The pH at which a direct photolysis study on a non-ionic test substance chemical is conducted should be the same as the pH at which the spectrum is determined. For a test substance chemical that is appreciably ionized anywhere within a 4 5 to 9 pH range, UV- Visible absorption spectra should be measured at pH 4 5 , 7, and 9.

66. 87. Electronic absorption spectra of the test substance chemica l should be obtained in appropriate solvent systems at desired pHs with a spectrometer capable of recording UV-VISIBLE spectra between

29 0 5 and 800 nm. Because the higher energy (shorter wavelength) bands of many chemicals may sometimes tail into wavelengths above 29 0 5 nm, it is recommended that the spectrum be recorded 30 to 40

nm below 29 0 5 nm. The procedure to record, assign absorption band maxima, band-widths and determine decadic molar absorption coefficients has been described elsewhere (OECD Guideline 101). To obtain an adequate absorption spectrum, it may sometimes be necessary to enhance the solubility of the test

substance chemical by using aqueous methanol, ethanol, or acetonitrile. It is recommended that UVVISIBLE spectra of test substance chemicals be also obtained in the pure ne at co-solvent.

67. 88. If the test substance chemical absorbs above the 29 0 5 nm cutoff of solar irradiation at the earth’s

surface with ε λ > 2 L/mol•cm (M -1 cm -1 ) over at least 15 nm, estimate a maximum possible direct photolysis rate by assuming that the quantum yield is equal to one in equation 6 (2):



## k L

d (max) 

## =

= = 

# ∑ ε λ λ
λ λ

295 800

[eq. 1 1 2 ]

where:

k d(max) = maximum possible direct photolysis rate constant (1/day)

ε λ = molar absorption coefficient (L/mol • cm; M -1 cm -1 ) at wavelength λ

L λ = average daily solar photon flux (mmol photons/cm 2 • day) over wavelength interval centered at wavelength λ

.

68. 89. In estimating the maximum possible photolysis rate constant, the average daily solar photon

fluxes L λ substituted into equation 1 1 2 should be those for summer at 40 ° or 50 ° latitude. Values of L λ can be readily obtained from tables (2)(12). As an alternative to the use of equation 1 1 2 and tables of L λ , the maximum direct photolysis rate constant can be readily estimated by inputting molar absorption coefficients and a quantum yield equal to one into computer programs such as GCSOLAR (18) or ABIWAS ( 41 35 )( 42 36 ).

Criteria for deciding whether to go to Direct Photolysis Tier 2 or Tier 3

69. 90. Determine if the maximum possible direct photolysis rate constant for the test substance chemical in the near surface of a clear natural water exposed to an average daily solar photon flux would result in estimated direct photolysis losses > 50% of an initial concentration over 30 days /nights of sunlight exposure by substituting k max(solar) for k (solar) in equation 8 9

.ENV/JM/TG/RD(2006)1/REV

22 70. 91. If estimated direct photolysis losses (assuming a maximum direct photolysis rate constant) are less than 50% of the initial concentration over a 30-day period direct photolysis is considered to be an insignificant process. In such a case, no further direct photolysis work is performed. If required, Go go to Indirect Photolysis Tier 1 (experimental /theoretical screen).

71. 92. If estimated direct photolysis losses (assuming a maximum direct photolysis rate constant) are greater than or equal to 50% of the initial concentrati on over a 30-day period, go to Direct Photolysis Tier 2 (experimental screen and range finding ) or Direct Photolysis Tier 3 (det ermination of the quantum yield).

Tier 2 - Experimental screen and range finding test for higher tiers

72. 93. Dissolve the test substance chemical in sterilized, buffered pure water and place an optically dilute solution in photolysis test vessels. Expose at least half of the test vessels to a filtered xenon arc lamp or sunlight and allow an equal number or fewer of the test vessels to serve as dark controls. To account for volatile losses of test substance and /or transformation products, test vessels should be attached to suitable traps for the collection of organic volatiles and CO 2

.

73. 94. Determine the concentrations of the test substance chemical in the irradiated test vessels and in the dark control test vessels at adequate enough sampling intervals to approximately determine the direct photolysis rate constant of the test substance. chemical.

74. 95. At each sampling interval, sacrifice an irradiated photolysis cell for analysis. The number of sampling intervals for which a dark control is also sacrificed for analysis should depend upon a prior knowledge of the rate of hydrolysis of the test substance chemica l at the experimental pH. For example, if

the test substance chemical is susceptible to appreciable rates of hydrolysis at the experimental pH, a dark control cell should be sacrificed for analysis each time an irradiated cell is sacrificed. However, if the test

substance chemical is stable to hydrolysis at the experimental pH, a minimum of 3 sampling intervals for the dark control will be adequate.

75. 96. If the data follow first-order kinetics, compute irradiated and dark control rate constants for the

test substance chemical by using linear regression on equation 3 or non-linear regression on equation 2.

76. 97. Once the irradiated and dark control rate constants for the test substance chemica l have been determined, compute the approximate laboratory direct photolysis rate constant from the following equation:



### kkk

d screen irradiated dark

( ) 

### = − [eq. 1 2 3 ]

Estimation of direct photolysis rate constants in near surface clear natural water from laboratory values

77. 98. Estimate a direct photolysis rate constant for the test chemical test substance in near surface clear natural water exposed to average daily solar photon fluxes L λ

_from the direct photolysis rate constant in a photolysis cell exposed to continuous photon fluxes from a filtered xenon arc lamp using the following equation (assuming D cell the pathlength l; see Annex 4):ENV/JM/TG/RD(2006)1/REV

23 

## k j D

l k L

I d solar cell d xenon

xenon

( ) ( )

( ) 

## . = 

# ∑

∑ 23 295 800

0 

## ε

ε λ λ

λ λ [eq. 1 3 4 ]

where:

k d(solar) = average daily direct photolysis rate constant (1/day) for the test chemical test substance

in the near surface of clear natural water exposed to average daily solar irradiation fluxes L λ k d(xenon) = direct photolysis rate constant (1/sec) for the test chemical test substance in buffered pure water in photolysis cells exposed to constant filtered xenon arc lamp fluxes I 0 λ

ε λ (chem) = molar absorptivity of the test chemical test substance (L/mol • cm; M -1 cm -1 )

D cell = depth of irradiated cell (cm) = volume of irradiated cell/incident area (cm)

l

xenon = light pathlength in cell exposed to a filtered xenon arc lamp

I 0_(xenon) = incident filtered xenon arc lamp photon flux (photons/cm 2 • day) over a 1 nm interval centered at wavelength λ

L λ = 24 hour average daily solar photon flux over wavelength interval λ centered at 

### wavelength λ for the weakly absorbing near surface of clear natural water

bodies in (mmol photons/cm 2

• 

### day) j = conversion factor = 6.02 x 10 20 

### (L/cm 3 

### )(photons/mol)

78. 99. To use equation 1 3 4 , the photon flux from the filtered xenon arc lamp that is incident on the photolysis cells (I 0 λ ) must be determined as a function of wavelength using actinometers or and (if available) a spectral radiometer. The solar photon fluxes as a function of wavelength for the near surface of
clear natural waters (L λ ) for various mid-seasons and latitudes are readily available (2)(12).



### Criteria for deciding whether to go to Direct Photolysis Tiers 3 and/or 4

79. 100. Determine if the screen direct photolysis rate constant for the test substance chemica l in the near surface of a clear natural water exposed to sunlight would result in estimated direct photolysis losses > 20% of an initial concentration over 30 days /nights of sunlight exposure by substituting k d(screen)(solar) for

k (solar) in equation 8 9

.

80. 101. If estimated direct photolysis losses (assuming the screen direct photolysis rate constant) are less than 20% of the initial concentration over a 30-day light/dark sunlight exposure period, direct photolysis is considered to be an insignificant process. In such a case, no further direct photolysis work is performed. If required, p P roceed to the Indirect Photolysis Tier 1 screen.

81. 102 . If estimated direct photolysis losses (assuming the approximate direct photolysis rate constant) are greater than or equal to 20% of the initial concentration over a 30-day light/dark sunlight exposure period, proceed to Direct Photolysis Tiers 3

. and/or 4. If determining the quantum yield of the test chemical and using it to estimate direct photolysis rate constants for types of water bodies, seasons, and

latitudes is required, proceed to Direct Photolysis Tier 3. Otherwise, proceed to direct photolysis Tier 4 to perform a more definitive kinetics study.ENV/JM/TG/RD(2006)1/REV

24 Tier 3 - Determination of the quantum yield and estimations of direct photolysis rate constants

82. 103. Determine the quantum yield of the test substance chemical in buffered solutions using monochromatic irradiation (12), filtered xenon-arc lamp polychromatic irradiation (8) or sunlight polychromatic irradiation (2). Each has advant ages and disadvantages compared to the others (see Annex 7)

.

104. The main advantage in using monochromatic irradiation to determine the test chemical quantum yield of the test chemical is that (as will be shown la ter by equations 19 through 21) it eliminates the need to directly mea sure the incident monochromatic irradiation. However, a disadvantage is that it will take longer to determine the quantum yield with monochromatic irradiation than with the use of polychromatic

irradiation because the actinometer and the test chemical are absorbing photon fluxes at just one wavelength instead of over multiple wavelengths.

105. The main advantage in using polychromatic irradiation (filtered xenon arc lamp or sunlight) instead of monochromatic irradiation to determine the test chemical qua ntum yield is that the time required to determine the quantum yield may be substantially shorter (8). The reason is due to the absorption of photon fluxes by the actinometer and test chemical over multiple wavelengths instead of just one wavelength. The main disadvantage in using polychromatic irradiation to determine the test chemical test
substance quantum yield is that unlike with monochromatic irradiation (as will be shown later by equations 20 and 21), its use requires the determination of the photon flux.

106. The advantage in using sunlight instead of a filtered xenon arc lamp, if polychromatic irradiation is used to determine the quantum yield, is that tables of average solar intensities as a function of season and latitude are readily available. Also, if sunlight is used, it eliminates the necessity of having a monochromatic or polychromatic artificial light source. However, if sunlight is used, an actinometer with an adjustable quantum yield is needed so the direct photolysis rate of the actino meter can be adjusted to be comparable to that of the test chemical under the same irradiation conditions (2)(12). Parallel exposure of the test chemical and actinometer to sunlight over comparable time frames minimizes errors due to changes

in solar flux caused by fog, varying cloud cover, etc. (12)(51).

107. An example of an adjustable quantum yield actinometer is the p

- nitroacetophenone

- pyridine (PNAP

- PYR) actinometer (52). For a 1.0 X 10

- 5 M p

- nitroacetophenone solution, the quantum yield of the

act inometer in experiments carried out with monochromatic irradiation at 313 nm can be adjusted by varying the concentration of pyridine in the solution according to the following equation (2)(12):



# φ

act 

# pyridine = • 0 0169

.[ ] [eq. 15]

where: φ act = quantum yield of the 1.0 X 1 0
- 5 M p

- nitroacetophenone [pyridine] = molar concentration of pyridine

108. Suitable chemical actinometers used in aqueous photochemical studies include the following:

Actinometer System Literature Citation (a) p

- nitroacetophenone/pyridine 52 (b) p

- n itroanisole/pyridine 26, 52 (c) valerophenone 53
(d) ferrioxalate 19, 23, 37, 54, 55ENV/JM/TG/RD(2006)1/REV

25 (e) o

- nitrobenzaldehyde 37, 52
(f) Reinecke’s salt 12 (g) aberchrome 540 56, 57

109. The first two actinometers listed in the above table have adjustable quantum yi elds and are therefore particularly useful when solar irradiation is used (12). The first three actinometers listed in the table are low optical density actinometers and the last four are high optical density actinometers. The

characteristics of those ac tinometers including the optimal wavelength range for their use are discussed in

references 12 and 58. Other chemical actinometers are described in the IUPAC document on chemical actinometers (58).

Determination of the quantum yield using monochromatic irradiation

83. 110. Place solutions of the test substance chemical and the selected optically low density actinometer in separate but identical photolysis cells. Irradiate at least half of the photolysis cells with monochromatic irradiation of wavelength λ and let an equal or fewer number (depending upon the hydrolytic stability of

the test chemical test substance ) serve as dark controls. Determine the concentration of the test substance in the irradiated cells and in the dark controls at adequate enough sampling intervals to determine the monochromatic direct photolysis rate constant of the test chemical test substance (k d_(chem) ) and of the
actinometer (k d λ (act) ) at the wavelength λ of irradiation. At each sampling interval, sacrifice an irradiated photolysis cell for analysis. The number of sampling intervals for which a dark control is also sacrificed for analysis should depend upon a prior knowledge of the rate of hydrolysis of the test substance chemical at the experimental pH.

84. 11. The decline of a test substance chemical or actinometer concentrations at low optical density should follow pseudo first-order kinetics so that the monochromatic irradiated and the dark control rate constants can be determined by using linear regression on equation 3 or non-linear regression on equation

2. The decline of a test substance chemical or actinometer at high optical density should follow zero-order kinetics so that the monochromatic irradiated and the dark control rate constants can be determined by using linear regression on the following zero-order kinetics equation:

C C kt

= − 0 [eq. 1 4 6 ]

85. 112. Once the monochromatic irradiated and dark control rate constants for the test substance

chemical and the actinometer have been determined, the monochromatic direct photolysis rate constant of

the test substance chemical (k d_(chem) ) and of the actinometer k d λ (act) at wavelength λ are given by:



# kk k

d chem or irradiated chem or act dark chem or act

λλ λ

( ) ( )( ) ( )( ) act 

# = − [eq. 1 5 7 ]

Note : In a sterilized aqueous buffer, the dark control rate constant (k dark ) should be equal to the hydrolysis rate constant at the pH of the buffer.

86. 113. Determine the molar absorption coefficients of the test substance chemical ( ε λ (chem) ) and (if a low optical density actinometer is being used) the actinometer ( ε λ (act) ) at the wavelength λ of the monochromatic irradiation using the Beer-Lambert law assuming that ε λ C is >> than the attenuation

coefficient α λ of the test medium:ENV/JM/TG/RD(2006)1/REV

26 

## ε

λ λ

( ( )

( ) 

## [ ] chem chem act

chem act 

## A

l C or act) or

or 

## =

[eq. 1 6 8 ]

where:

ε λ (chem) = molar absorption coefficient of the test substance chemical or actinometer

L/mol • cm; M -1 cm -1 )

A λ (chem or act) = absorbance of test substance chemical or actinometer solution at wavelength λ L = light pathlength (cm) generally equivalent to D cell [C (chem or act) ] = concentration of test substance chemical or actinometer solution (mol/L)

87. 1 14. The quantum yield of an optically dilute test substance chemical determined using monochromatic irradiation and a low optical density (low absorbance) actinometer is given by (12)(4 9 7 ) (See Annex 4):



## φ φ ε

ε λ λ

λ λ chem act d chem act

d act chem 

## k

k = ( )()

()( ) [eq. 1 7 9 ]

where:

φ chem = the quantum yield of the test substance chemical φ act = the quantum yield of the actinometer

k d λ (chem) = monochromatic direct photolysis rate constant (1/day, pseudo first-order) of a test

substance chemical exposed to monochromatic irradiation at wavelength λ

k d λ (act) = monochromatic direct photolysis rate constant (1/day, pseudo first-order) of an actinometer exposed to monochr omatic irradiation at wavelength λ

ε λ (chem) = molar absorption coefficient (L/mol • cm; M -1 cm -1 ) of the test substance chemical at wavelength λ

ε λ (act) = molar absorption coefficient (L/mol • cm; M -1 cm -1 ) of the actinometer at wavelength λ

88. 115. The quantum yield of an optically dilute test substance chemical determined using monochromatic irradiation and a high optical density (high absorbance) actinometer is given by (12)(4 9 7 )

. ( See Annex 4 ) :



## φ φ

ε

λ λ

λ chem act

chem cell d chem

d act zero 

## D k

k = 2 3

. ( ) ( )

( )( order) [eq. 18 20 ]

where:

φ chem = the quantum yield of the test chemical test substance φ act = the quantum yield of the actinometer

k d_(chem) = monochromatic direct photolysis rate constant (1/day, pseudo first-order) of a test chemical exposed to monochromatic irradiation at wavelength λ

k d_(act)(zero) = monochromatic direct photolysis rate constant (mol/L • day, zero-order) of anENV/JM/TG/RD(2006)1/REV

27 actinometer exposed to monochr omatic irradiation at wavelength λ

D cell = depth of irradiated cell (cm) = volume of irradiated cell/incident area (cm)

89. 116. The quantum yield of a test chemical test substance at high optical density (high absorbance) determined using monochromatic irradiation and a high optical density (high absorbance) actinometer is given by (12)(4 9 7 ). See Annex 4):

φ φ λ

λ chem act d chem zero

d act zero k

k = ( )( )

( )( ) [eq. 19 21 ]

where:

φ chem = the quantum yield of the test chemical test substance φ act = the quantum yield of the actinometer

k d_(chem)(zero) = monochromatic direct photolysis rate constant (mol/L • day, zero-order) of a test chemical exposed to monochromatic irradiation at wavelength λ

k d_(act)(zero) = monochromatic direct photolysis rate constant (mol/L • day, zero-order) of an actinometer exposed to monochr omatic irradiation at wavelength λ

90. 117 . As can be seen from equations 1 7 9

, 18 20 , and 19 21 , it is not necessary to determine the photon

flux if monochromatic irradiation is used to determine the test chemical test substance quantum yield.

Determination of the quantum yield using polychromatic irradiation (lamp or sunlight)

91. 118. The quantum yield of an optically dilute test chemical test substance using a low optical density (low absorbance) actinometer and sunlight or a polychromatic filtered xenon arc lamp can be determined from equations 2 0 2 and 2 1 3 , respectively (2)(6)(12)(See Annex 4):



### φ φ ε

ε λ λ
λ λ

λ λ
λ λ chem act d chem

d act act

nm nm

chem

nm nm 

### k

k L

L = 

  



 

     



    = =

= = 

# ∑

∑ ( )

( ) ( )

( ) 295 800

295 800

[eq. 2 0 2 ]



### φ φ ε

ε λ λ

λ λ chem act d chem

d act act xenon

chem xenon 

### k

k I

I = 

  

  

     

     

# ∑

∑ ( )

( ) () ( )

()( ) 0

295 800

0

295 800

[eq. 2 1 3 ]

where:

k d(chem) = direct photolysis rate constant (1/day, pseudo first-order) of the test chemical test
substance

k d(act) = direct photolysis rate constant (1/day, pseudo first-order) of the actinometer φ chem = quantum yield of the test chemical test substance (dimensionless ratio) φ act = quantum yield of the actinometer (dimensionless ratio)
ελ (chem) = molar absorption coefficient (L/mol • cm; M -1 cm -1 ) of the test chemical test substance

atENV/JM/TG/RD(2006)1/REV

28 wavelength λ

ελ (act) = molar absorption coefficient (L/mol • cm; M -1 cm -1 ) of the actinometer at wavelength λ

L λ = average daily solar photon flux (mmol photons/cm 2 • day) over wavelength interval

∆λ centered at wavelength λ

I 0 λ (xenon) = incident filtered xenon arc lamp photon flux (photons/cm 2 • day) over a 1 nm interval centered at wavelength λ

92. 119. As can be seen from equations 2 0 2 and 2 1 3 , it is necessary to independently and accurately determine the incident photon flux as a function of wavelength when polychromatic irradiation is used to

determine the test chemical test substance quantum yield.

93. 120 The determination of the test chemical test substance quantum yield using polychromatic irradiation and an actinometer are discussed in detail in (2) for the use of sunlight, and in (8) for the use of a filtered xenon arc lamp.

Dependence of the quantum yield on wavelength

121. Most of the direct photolysis equ ations involving polychromatic irradiation in this document and in the literature are presented with the quantum yield taken outside of the integral or summation over different wavelengths. The reason is that in aqueous solutions, the quantum yields of tes t chemical s are (in general) approximately independent of wavelength, even across different absorption bands. In aqueous solutions, molecules in higher excited electronic states tend to undergo radiationless decay to their first excited state before any ph otoreaction occurs (12). If photoreaction does occur, it generally occurs in competition with other deactivation processes while the molecule is in its first (not higher) excited

electronic state.

122. However, the quantum yield may sometimes differ betw een absorption bands (6)(14). Therefore, it may sometimes be necessary to determine the quantum yield at least one wavelength for each adsorption

band within the 295

- 800 nm range using monochromatic irradiation. The wavelength chosen for each absorption ba nd should correspond to the maximum absorption. In cases where the quantum yield varies with wavelength, the quantum yield should be br ought inside any integrals or summations over wavelengths.

123. In cases where the quantum yield remains constant withi n the same absorption band, but varies across different absorption bands, equations 5 and 6 for the direct photolysis rate constant can be modified to give:



## k I d i ii i begin

i end

i i n



## = 

# ∑ ∑

= = 

## φ ε λ λ
λ

λ

0 1 () ( )

[eq. 24]



# k L d i

i i n

i i i begin

i end



# =

= = 

# ∑ ∑ φ ε λ λ
λ

λ

1 () ( )

[eq. 25]

where:

φ I = quantum yield for absorption band iENV/JM/TG/RD(2006)1/REV

29 ε i λ = molar abs orption coefficient (L/mol • cm; M - 1 cm - 1 ) at wavelength λ within absorption band i

I 0i λ = photon flux per nm (photons/cm 2 • sec/nm) at wavelength λ within absorption

band i

λ I = wavelength interval in nm generally = 1 nm

L i λ = average daily sol ar photon flux irradiance (mmol photons/cm 2 • day) over wavelength interval ∆ λ centered at wavelength λ within absorption band i

I = indice for different absorption bands up to the maximum of n bands

i λ (begin) = wavelength at the beginning of absorpti on band i

i λ (end) = wavelength at the end of absorption band i

Use of the quantum yield to estimate direct photolysis rate constants

94. 124. The pseudo first-order rate constant for direct phototransformation and thus the life-time of a test substance in water can be calculated from the quantum yield (18)(52). Once the quantum yield of a test
chemical has been determined, it should be used as input into c C omputer programs such as GCSOLAR (18) or ABIWAS ( 41 35 )( 42 36 ) to estimate direct photolysis rate constants for seasons, latitudes, and water body depths and light attenuations of interest. GCSOLAR and ABIWAS can be used to estimate direct photolysis rate constants at any given time in near surface water or at any specified depth. The programs can also average rate constants over any given time and/or depth interval of interest.

95. 125. Although programs such as GCSOLAR or ABIWAS are readily available, equation 5 is often used to estimate the direct photolysis rate constant for optically dilute solutions of test chemical test
substance s in pure water in photolysis cells or in the near surface of clear natural water exposed to solar irradiation (2)(12).

Criteria for deciding whether to go to direct photolysis Tier 4

96. 126. A Direct Photolysis Tier 4 kinetics study should be performed if identification/kinetics data on the major transformation products are applicable and if the direct photolysis rate constant(s) for the parent

test chemical test substance (estimated from its quantum yield) indicate (s) that direct photolysis is a potentially significant process.

97. 127. Determine if the direct photolysis rate constant (estimated from the quantum yield) for the test
chemical test substance in shallow natural water exposed to sunlight would result in estimated direct photolysis losses > 20% of an initial concentration over 30 days /nights of sunlight exposure by substituting k d(solar) for k (solar) in equation 8 9

.

98. 128. If estimated direct photolysis losses are less than 20% of the initial concentration over a 30 day light/dark sunlight exposure period, direct photolysis is considered to be an insignificant process. In such a case, no further direct photolysis work is performed

. . If of interest, p P roceed to indirect photolysis Tier 1. Proceed to direct photolysis Tier 4 if the estimated direct photolysis losses are greater than or equal to 20% of the initial concentration over a 30 day sunlight exposure period. :

 Estimated direct photolysis losses are greater than or equal to 20% of the initial concent ration over a 30 day light/dark sunlight exposure period , and

• The identification of major transformation products and/or the determination of their rates of formation and decline are required.ENV/JM/TG/RD(2006)1/REV

30 Tier 4 Identification of

- Kinetics study on the test chemica l and (if applicable) major transformation products

Experimental determinations of direct photolysis rate constants in the laboratory

99. 129. In direct photolysis Tier 4

, the decrease in the concentrations of the test chemical the test

substance is deter mined in buffered pure water is exposed to a filtered xenon arc lamp or sunlight. If applicable, T t he rates of formation and decline of major transformation products are also determined , if possible. Major phototransformation products are isolated and identified.

. For the purposes of this guideline, a major transformation product is one accounting for > 10% of the applied radioactivity (or molar basis) in an individual sample at any time during the study.

100. 130. If a flow-through system is used to trap volatile test chemical test substance s and/or their major transformation products, the following considerations should be made. The air should be passed through microbial filters to keep the samples sterile. Moist air should be used to prevent evaporation. The system should be checked for sterility at the study termination.

101. 131 . Place the test solution in photolysis test vessels. At least half the test vessels should be exposed to a filtered xenon arc lamp or sunlight and an equal or fewer number of the test vessels should serve as

dark controls.

102. 132 . Determine the concentrations of the transformation products in the irradiated test vessels and in the dark control test vessels at adequate enough sampling intervals

. to determine the direct photo lysis rate

constant of the test chemical

.

103. 133. At each sampling interval, sacrifice an irradiated photolysis cell for analysis. The number of sampling intervals for which a dark control is also sacrificed for analysis should depend upon the rate of hydrolysis of the test chemical test substance at the experimental pH.

134. f the data follow first

- order kinetics, compute irradiated and dark control rate constants for the

test chemical by using linear regression on equation 3 or non

- linear regression o n equation 2.

135. Once the irradiated and dark control rate constants for the test chemical have been determined, compute the laboratory direct photolysis rate constant from the following equation:



### kk k

d irradiated dark



### = − [eq. 26]

136. If a filtered xenon arc lamp is used for irradiation, estimate an approximate average daily direct photolysis rate constant for the test chemical in shallow natural water exposed to average daily solar photon fluxes L λ from equation 14.

137. In direct photolysis Tier 4, the decrease in the concentrations of the test chemical is determined in buffered pure water exposed to a filtered xenon arc lamp or sunlight. If applicable, the rates of formation and decline of major transformation products are also determined. For the purposes of this guideline, a major transformation product is one accounting for > 10% of the applied radioactivity at any time during the study.

138. If a flow

- through system is used to trap volatile test chemical s and/or their major transformation products, the followin g considerations should be made. The air should be passed through microbial filters to keep the samples sterile. Moist air should be used to prevent evaporation. The system should be checkedENV/JM/TG/RD(2006)1/REV

31 for sterility at the study termination.

139. The following equa tion can be used to estimate the direct photolysis rate constant for the test
chemical in shallow natural water exposed to one or more different sunlight conditions from those in the study (see Annex 3

- Equation Derivations):

k k L

L sun shallow sun shallow water nm nm

nm nm ( ) ( )

( ) water)2 = = =

= = 

### ∑

∑ 1 2

295 800

1

295 800 ε

ε λ λ
λ λ

λ λ
λ λ
[eq. 27]

where:

k d(sun shallow water)2 = estimated direct photolysis rate constant in the near surface of clear natural water exposed to solar irradiation fluxes (L λ (2) ) different from solar irradiation
fluxes (L λ (1) ) used in the experiment.

k d(sun shallow water)1 = estim ated direct photolysis rate constant in the near surface of clear natural water exposed to the experimental solar irradiation fluxes.

L λ (2) = average daily solar photon fluxes different from those closest
(L λ (1) ) to the experimental conditions.

L λ (1) = average daily solar photon fluxes closest to the experimental ones based on the season and latitude at which the study was performed.

140. Compute direct photolysis half

- lives by substituting the estimated direct photolysis rate constants into equati on 4.

Major transformation products (if required)

104. 141. Identify and quantify major phototransformation products using analytical methods and criteria indicated in paragraph s 27. 39 t hrough 43.

105. 142. In cases where data follow first-order kinetics and the parent test chemical test substance rapidly transforms, use the same first-order methods applied to the test chemical test substance to also estimate first-order direct photolysis rate constants and corresponding half-lives for any major primary transformation products formed from the parent which are still at substantial concentrations (e.g. at > 10% of applied) after the parent has degraded to negligible levels.

143. Equation 14 for estimating sunlight rate constants from filtered xenon arc lamp rate constants and equation 27 for estimating a sunlight rate constant for a given season and latitude from a sunlight rate constant for a different season and/or latitude are also applicable to any first

- order photolysis rate constants determined for any major transformation products.

106. 144. In cases where primary or secondary transformation products are being substantially formed over the same time period they are being substantially lost, their direct photolysis rate constants and corresponding half-lives cannot be readily estimated as they were for the parent. However, as an option, attempts can be made to estimate first-order rate constants for the formation and decline of major transformation products using non-linear regression to fit concentration versus time series data to various equations derived from assumed transformation pathways.

Performance of indirect photolysis tiersENV/JM/TG/RD(2006)1/REV

32 Tier 1 for indirect photolysis

- Experimental and/or theoretical screen

145. Perform a screen in simulated water (con taining humics as a surrogate for CDOM and when applicable, nitrate) or natural water to determine if indirect photolysis represents a potentially significant transformation pathway.

146. Place solutions of the test chemical in simulated natural water (S NW) and/or simulated natural water with nitrate (SHW

- N) and/or natural water (NW) and in buffered pure water (PW) into equal numbers of photolysis cells. Expose at half of the photolysis cells containing each type of solution to sunlight and let an equal o r smaller number of the photolysis cells containing each type of solution serve as

dark controls.

147. The use of a filtered xenon arc lamp for indirect photolysis studies is not recommended at this time. The complexity of indirect photolysis processes do es not allow straightforward extrapolation of results from filtered xenon arc lamps to sunlight equivalents and may not be feasible (2)(12).

148. Determine the concentrations in the irradiated photolysis cells and in the dark control photolysis

cells at adequate enough sampling intervals to determine the irradiated and dark control rate constants of

the test chemical in SNW and/or SNW

- N and/or in NW and in PW. At each sampling time, sacrifice an irradiated photolysis cell. The number of sampling interval s for which a dark control is also sacrificed for analysis should depend upon the stability of the test chemical in the dark control at the experimental pH. Assuming the decline of the test chemical follows first

- order kinetics, determine the irradiated a nd dark control rate constants in the irradiated and dark control solutions by using linear regression on equation 3

or non

- linear regression on equation 2.

149. Once the irradiated and dark control rate constants for the test chemical in SNW and/or SNW

- N and/or NW and in PW have been determined, the net photolysis rate constants, the direct photolysis rate in PW, and the indirect photolysis rates constants can be respectively determined from the following equations:

kk k

pX X irrad X dark

= − ( ) () [eq. 28]

kk k

d PW PW irrad PW dark () ( ) ( ) = − [eq. 29]

k kk

iX approx pX d PW

( ) () = − [eq. 30]

where:

X = SNW, SNW

- N, or NW

Note : Equation 30 is only approximate because the direct photolysis rate constant in PW (k d(PW) ) will be greater than the direct photolysis rate constant in SNW, SNW

- N or NW (k dX ) due to light

attenuation (12). However, the approximation is adequate for a screen. Also, unlike indirect photolysis Tier 2, this indirect photolysis Tier 1 screen does not take into account the photobleaching of humic solutions in photolysis cells by sunlight as reported by Win terle and Mill (59).

150. Determine if the approximate indirect photolysis rate constant for the test chemical in shallow natural surface water would result in estimated indirect photolysis losses > 20% of an initial concentration over 30 days/nights of s unlight exposure by substituting k iX(approx) for k (solar) in equation 9.ENV/JM/TG/RD(2006)1/REV

33 151. If estimated indirect photolysis losses (assuming an approximate indirect photolysis rate constant) are less than 20% of the initial concentration over a 30 day/night sunlight e xposure period, indirect photolysis is considered to be an insignificant process. In such a case, no further indirect photolysis work is performed.

152. If estimated indirect photolysis losses (assuming an approximate indirect photolysis rate constant) ar e greater than or equal to 20% of the initial concentration over a 30

- day light/dark sunlight exposure period, indirect photolysis is considered to be a potentially significant process. Proceed to Indirect Photolysis Tier 2 to perform a more definitive kin etics study.

153. Mill (21) has summarized structural activity relations (SARs) for estimating second

- order rate constants for the reaction of organics with photooxidants in water. He also summarized typical concentrations of various photooxidants general ly found in the top layers of surface water exposed to sunlight. In some cases, it may be possible to supplement or even replace the experimental screen with a theoretical screen based on using structural activity relationships (SARs). These SARs estimate rate constants and information on the typical concentrations of photoxidants in surface water. Although a theoretical screen involving one or two potential photooxidants may indicate that going to Tier 2 is justified, it is doubtful that one can indicate t hat going to Tier 2 is not justified. The reason is that a theoretical screen will generally cover only one or two of the large number of possible types of indirect photolysis reactions. Further details on using structure activity relations for estimating rate constants for

the reaction of test chemical s with photoxidants in water such as the hydroxyl radical and singlet oxygen are provided in reference 51.

Tier 2

- Experimental determination of rate constants (and identification/quantification of major

t ransformation products, when required)

154. In the indirect photolysis Tier 2, the decrease in the concentration of the test chemical is determined in simulated natural water (SNW) an d/or simulated natural water with nitrate (SNW

- N) and/or

one or more nat ural surface waters (NW) and in buffered pure water (PW) exposed to sunlight. If applicable, the identities and rates of formation and decline of major transformation products are also determined. For the purposes of this guideline, a major transformation product is one accounting for > 10% of applied at any time during the study.

155. The performance of Tier 2 differs from that in Tier 1 in several ways including:

• The number of sampling times is greater.

• The direct photolysis constant in humic water is e stimated by inputing the chemical’s quantum yield and

the attenuation constants of the humic solution into GCSOLAR or ABIWAS.

• If applicable, the rates of formation and decline of major transformation products are determined.

• If a study lasts for several d ays or more such that “photobleaching” of the humic solutions in photolysis cells may be substantial in some cases, it can (as an option) be accounted for as indicated in Leifer (12) and OPPTS 835.5270(2).

156 Dissolve the test chemical in SNW and/or SNW

- N and/or NW and in PW and place the solutions in equal numbers of photolysis cells. Expose at least half of the photolysis cells containing each type of solution to sunlight and let an equal or lesser number of the photolysis cells containing each type of

solution serve as dark controls.

157. Determine the concentrations in the irradiated cells and in the dark controls at adequate enough sampling intervals to determine the irradiated and dark control rate constants of the test chemical in

simulated natur al water (SNW), and/or simulated natural water with nitrate (SNW

- N), and/or naturalENV/JM/TG/RD(2006)1/REV

34 surface water (NW), and in buffered pure water (PW). At each sampling interval, sacrifice an irradiated test vessel for analysis. Sacrifice dark controls for analysis at a n equal or fewer number of sampling

intervals

158. Determine the irradiated and dark control rate constants of the test chemical in SNW and/or

SNW

- N and/or NW and in PW by using linear regression on equation 3 or non

- linear regression on equation 2.

159

. Once the irradiated and dark control rate constants for the test chemical in SNW and/or SNW

- N and/or NW and in PW have been determined, the net photolysis rate constants in those waters and the direct photolysis rate constants in PW can be determined fro m equations 28 and 29.

160. If the same light source and photon flux, test vessels, and experimental set

- up are used for the definitive determination of the direct photolysis rate constant in PW in the Tier 4 Direct Photolysis study, a separate determinat ion of the direct photolysis rate constant in PW in the Tier 2 Indirect Photolysis study as just described is not necessary.



### Determination of direct photolysis rate constant in SNW, and/or SNWN, and/or NW from

one in PW

161. Determine attenuation const ants as a function of wavelength for all experimental waters (SNW,

SNW

- N, and/or NW and PW) from the following equation:

α λ λ

( ) ( )

= A

l 

### [eq. 31]

where:

α ( λ ) = light attenuation constant as a function of wavelength λ (1/cm)
A( λ ) = absorbance of test medium as a function of wavelength λ

l = light pathlength in cell (cm)

162. Estimate average daily direct photolysis rate constant for the test chemical in near surface PW

and in SNW and/or SNW

- N, and/or NW by inputting its quantum yield and attenuation const ants for PW and for SNW, and/or SNW

- N, and/or NW into GCSOLAR or AB IWAS. If the quantum yield of the test
chemical was determined in Direct Photolysis Tier 3, use it as input. Otherwise, estimate the quantum yield by substituting the experimental direct ph otolysis rate constant in PW and ε λ L λ into equation 6 and rearranging to solve for the quantum yield.

163. Estimate the direct photolysis rate constant in SNW and/or SNWN and/or NW in a photolysis cell from the following equation:

k k

k k dX dX GCSOLARorABIWAS

d PW GCSOLARorABIWAS d PW = ( )

( ) ( ) ( )(exp) 

### [eq. 31]

wh ere:

X = SNW, SNW

- N, or NWENV/JM/TG/RD(2006)1/REV

35 k dX = direct photolysis rate constant in SNW, SNWN, or NW in a photolysis cell

k dX(GCSOLAR) = GCSOLAR or ABIWAS estimated average da ily direct photolysis rate constant in near surface SNW, SNW

- N, or NW

k d(PW)(GCSOLAR) = GCSOLAR or ABIWAS estimated average da ily direct photolysis rate constant

in PW

k d(PW)(exp) = experimentally determined direct photolysis rate constant in PW in a photolysis

cell

164. Once the net and direct photolysis rate constants in SNW and/or SN W

- N and/or NW have been determined, the indirect photolysis rate constant in those waters can be estimated from the following equation:

kkk iX pX dX

= − [ eq. 32]

where X = SNW, SNW

- N, or NW

165. The methods used in the identification and kinetics analysis of transformation products formed during indirect photolysis studies are comparable to those formed during direct photolysis studies.

Method of accounting for “photobleaching”

166. If a study lasts for several days or more, the decline of the test chemical in irradiated SNW,

SNW

- N, or NW may not be first

- order due to the “photobleaching” of humic solutions. Photobleaching in photolysis cells that has been studied and reported by Winterle and Mill (54).

167. Photobleaching does not appear to be a significan t process in the actual environment because CDOM appears to be generated at much faster rates than the rates of its decline through photobleaching (51). However in the laboratory, the photobleaching of humic solutions in photolysis cells by sunlight

somew hat complicates a more definitive determination of the indirect photolysis rate. Because of photobleaching, the indirect photolysis rate constant for a test chemical in SNW, SNW

- N, or NW solutions in photolysis cells exposed to sunlight decreases over tim e. If that occurs, there are two options:



### 168. When photobleaching begins to become substantia l, the study can be terminated. In such cases, only data obtained from the study prior to substantial photobleaching should be used in the analysis. The study can be continued by accounting for photobleaching.

Extrapolation from cell or near surface to the same water over a deeper depth, and from experimental to other solar photon fluxes

169. Unfortunately, methods of extrapolation to greater depths and light attenuation and to other solar conditions are not as straightforward for indirect photolysis as they are for direct photolysis, even when irradiation is restricted to sunlight. The reason isthat indirect photolysis may involve the absorption of solar

flux by many different types of sensitizers with different absorption spectra and by nitrate. Therefore, the results of an indirect photolysis study conducted in cells exposed to natural sunlight are only applicable to

the near surface and the same set of sol ar conditions as the experimental ones.

REPORTING OF DATA AND RESULTS

170. The degree of presentation of results depends on the complexity and purpose of the study, that is,

the number of tiers. The reporting should follow the IUPAC recommendations (63).ENV/JM/TG/RD(2006)1/REV

36 Direct photolysis data and results

Tier 1

• Provide the UV-VISIBLE spectrum or spectra of the test chemical test substance as the molar absorption coefficients (L/mol • cm or M -1 cm -1 ) on the y-axis versus wavelengths (nm) on the x-axis.

• Report the estimated maximum photolysis rate constant and associated direct photolysis losses over a 30 days /nights sunlight exposure period. Provide the equations and calculations used to estimate them. Provide the rationale for selecting the season and latitude of the average daily solar photon
fluxes (L λ ) used in the calculations.Report whether or not the results of the calculations trigger Direct Photolysis Tiers 2 and/or 3.

Tier 2

• If a filtered xenon arc lamp was used, provide the incident photon flux in a graph as the photon flux (photons/cm 2 • sec) on the y-axis versus the wavelength (nm) on the x-axis.

• If sunlight was used, provide tabular values of solar photon fluxes for the season and latitude closest to those of the study.

• Provide table(s) and graph(s) which show the concentrations of the test chemical test substance in irradiated and dark control solutions versus time. Show the best fit regression lines on the graph(s) along with the data points.

• Report the irradiated, dark control, and approximate direct photolysis rate constant of the test
chemical test substance along with their corresponding half-lives. Provide the equations, calculations, and regression coefficients used to compute them together with regression n and r 2 values, and standard errors of coefficients (for example, slope, intercept).

• Based upon the approximate direct photolysis rate constant, report the associated estimated direct photolysis losses over a 30 days /nights sunlight exposure period. Provide the equations and

calculations used to estimate them. Provide the rati onale for selecting the season and latitude of the average daily solar photon fluxes (L λ ) used in the calculations. Report whether or not the results of the calculations trigger Direct Photolysis Tiers 3 and/or 4.

Tier 3

• For the determination of the test chemical test substance quantum yield with the use of an actinometer, provide table(s) and graph(s) showing the concentrations of the test chemical test substance and actinometer in irradiated and dark control solutions versus time. Show the best fit regression lines on the graph(s) along with the data points.

• Report the irradiated, dark control, and direct photolysis rate constants of the test chemical test
substance and actinometer. Provide the equations, calculations, and regression coefficients used to compute them together with regression n and r 2 values, and standard errors of coefficients (for example, slope, intercept).

• Report the quantum yield of the test chemical test substance . Provide the equation and calculation usedENV/JM/TG/RD(2006)1/REV

37 to compute it.

• Report estimated direct photolysis rate constants for the test chemical test substance in natural water

that are estimated from the test chemical test substance quantum yield for seasons, latitudes, and water body types of interest. Provide and/or describe the equations and calculations or computer program (e.g. GCSOLAR or ABIWAS) and inputs to estimate them.

Tier 4

• If a filtered xenon arc lamp was used, provide the incident photon flux in a graph as the photon flux (photons/cm 2 • sec) on the y

- axis versus the wavelength (nm) on the x

- axis.

• If sunlight was used, provide tabular values of solar photon fluxes for the season and latitude closest to those of the study.

• Provide table(s) and graph(s) showing the concentrations of the test chemical and (if applicable) major phototransformation product s concentrations and mass balance determinations in irradiated and dark

control solutions versus time. Show the best fit re gression lines on the graphs along with the data points.

• Report the irradiated, dark control, and direct photolysis rate constants of the test chemical along with their corresponding half

- lives. Provide the equations, calculations, and regression coefficients used to compute them together with regression n and r 2 valu es, and standard errors of coefficients.

• If applicable, report the rate constants for the formation and decline of the major transformation products. Report the identity of the major phototransformation products (> 10% of the applied dose). Provide the transformation pathway model (see next paragraph ) , equations, calculations, and regression coefficients used to compute them together with regression n and r 2 values, and standard

errors of coefficients.

• Provide chemical structures and names of the test che mical and (if applicable) major transformation products in both irradiated and dark control solutions. Provide graphical presentations of postulated transformation pathways in both the irradiated and dark control solutions.

Indirect photolysis data and r esults

Tier 1

• Assuming sunlight was used for indirect photolysi s as recommended, provide tabular values of solar photon fluxes for the season and latitude closest to those of the study.

• Provide important characteristics of all simulated and/or natural waters used including DOC, humic content (if simulated), pH, dissolved oxygen, nitrate. Include the UV

- VISIBLE spectrum of the test media from 295 to 800 nm. For natural water, include site of collection.

• Provide table(s) and graph(s) showing the concen trations of the test chemical in irradiated and dark

control solutions versus time. Show the best fit regression lines on the graph(s) along with the data points.

• Report the irradiated, dark control, and approximate net, direct, and indirect photolysis r ate constants ofENV/JM/TG/RD(2006)1/REV

38 the test chemical along with their corresponding half

- lives.. Provide the equations, calculations, and regression coefficients used to compute them together with regression n and r 2 values, and standard

errors of coefficients.

• Report the approximate indirect (or indirect plus hydroxyl) photolysis rate constant and associated indirect photolysis losses over a 30 days/nights sunlight exposure period. Provide the equations and

calculations used to estimate them. Provide the rationale for s electing the season and latitude of the average daily solar photon fluxes (L λ ) used in the calculations. Report whether or not the results of the calculations trigger Tier 2 Indirect Photolysis.

Tier 2

• Provide tabular values of solar photon fluxes for t he season and latitude closest to those of the study.

• Provide important characteristics of all simulated and/or natural waters used including DOC, humic content (if simulated), pH, dissol ved oxygen, and nitrate. The UV

- VISIBLE spectrum (295 to 800 nm)

o f the test media should be included. For natural water, include the site of collection.

• Provide table(s) and graph(s) showing the concentrations of the test chemical and (if applicable) major transformation product concentrations and mass balance determi nations in irradiated and dark control solutions versus time. Show the best fit regres sion lines on the graphs along with the data points.

• Report the irradiated, dark control, and net, direct, and indirect photolysis rate constants of the test
chemical along with their corresponding half

- lives. Provide the equations, calculations, and regression coefficients used to compute them together with regression n and r 2 values, and standard errors of coefficients. If applicable and possible, supply the same info rmation for major transformation products.

• If applicable, report the rate constants for the formation and decline of the major transformation products. Provide the transformation pathway model (see next paragraph), equations, calculations, and regressio n coefficients used to compute them together with regression n and r 2 values, and standard

errors of coefficients.

• Provide chemical structures and names of the test chemical and (if applicable) major transformation products in both irradiated and dark con trol solutions. Provide graphical presentations of postulated transformation pathways in both the irradiated and dark control solutions.

Additional reporting requirements

General information

• Title of the study, author(s), performing laboratory (name and address), laboratory report identification number, date of completion. In some instances, it may be necessary to identify who is submitting the study, their address and any other identification number.

• Name(s) of the test substance, chemical nomenclature, Chemical Abstracts Registry Number (CAS Reg. No.). A tabular format may be used to present this infomation, but it is optional.

• Physical and chemical properties applicable to th e test substance. As an option, these physical and chemical properties may be listed in a table.ENV/JM/TG/RD(2006)1/REV

39 • Report if the test substance is the primary chemical or any transformation product resulting from abiotic hydrolysis and/or biotransformation. Report if the test substance is an industrial chemical, a pharmaceutical chemical, a pesticide, etc.

• For radiolabelled test substances, the radiolabelled element and isotope, radiolabelling position(s), chemical and radiolabel purity, and specific activity should be reported.

Experimental information

• Standard laboratory equipment and reagents.

• Analytical method(s) used for identifying and quantifying the test substance. The report should include a brief description of the method, reference standards, instrumentation, accuracy and precision, LOD and LOQ. Results of independent laboratory validation (if required).

• Quality Control (QC) results such as analytical recoveries and relative percent standard deviations for replicate analyses.

Specific experimental information related to photolysis (60)

• Experimental conditions, reagents, reaction vessels and other information relevant to each of the tiers comprising the study. This may include:

- Temperature - Solvent and/or buffers used for preparing stock and test solutions for direct photolysis, including dark control samples. - Co-solvent and percent by volume used, if any.

- Nominal and actual concentration of test substance in the test media

• Absorption Spectroscopy:

- Description of instrumentation - Pathlength and material of optical cells - Spectral resolution

- Concentration of test chemical test substance in solution - Co-solvent and percent by volume used, if any - Temperature and pH

• Specific information on reaction vessels:

- Material (type of glass, quartz, etc) - Geometry of the reaction vessels and positioning of the reaction vessels with respect to the light source. - Any significant optical properties of the vessel material (wavelength cut-off, etc.) - Illustration of the reaction vessel(s) arrangement and/or a photograph is encouraged to be included in the report.ENV/JM/TG/RD(2006)1/REV

40 • Xenon-light source:

- Manufacturer, model - Filters and their purpose - Measured spectrum of the light source betw een 295 and 800 nm at at least the beginning and end of the study. - Comparison of the spectrum of the light with that of natural sunlight for the conditions required for specific tiers. - Intensity (radiant flux, fluence rate) at sample (J m -2 s -1 ; photons m -2 s -1 ) and area irradiated.

• Irradiation dose (fluence) (J m -2 ):

- State if continuous or intermittent irradiation was used - If continuous irradiation, state radiant flux (intensity) and time - If intermittent irradiation, state radiant flux, cycle duration and number of cycles

• Quantum Yields:

- Experimental conditions (temperature, test media, concentration of test substance in test

media - Description of reaction vessels (diagram and/or photograph) - Specify if monochromatic or polychromatic irradiation was used and source - Monochromatic wavelength and bandwidth used. - Intensity (radiance flux) - Photometric methods, if any - Chemical actinometer used (criteria for selec tion, concentration of actinometer in test media, absorption spectrum of the actinometer in the test media). - Positioning of the actinometer with respect to the test substance

• Computational methods for:

- Calculation of molar absorption coefficients ( ε λ ) utilizing Beer-Lambert’s relationship - Maximum photolysis reaction rate assuming φ = 1 (direct and/or indirect photolysis) - Experimental photolysis reaction rate (direct and/or indirect photolysis) - Quantum yield calculations (quantum yield should be expressed as a fraction and not as a percent) - GCSOLAR or ABIWAS calculation of reaction rates at different latitudes, seasons, time of the day, water bodies.

- Half-lives or DT 50 , DT 75 , and DT 90 values and appropriate associated confidence intervals.

Interpretation and Discussion of results

171. The purpose of conducting the study should be discussed in terms of the potential for the test
chemical to be present in surface water. For e xample, chemicals can be transported to surface water in numerous ways including by direct point discharge in to water bodies, runoff, spray drift or atmospheric deposition.

172. The depth of the discussion depends on the complexity of the study. Regardle ss of the complexity of the study, the discussion should be focused on the effect sunlight may have on the rate and pathway of transformation of the test chemical in aqueous environments.ENV/JM/TG/RD(2006)1/REV

41 173. The potential for the test chemical to undergo direct and/or i ndirect photolysis should be discussed. When applicable, the rate constants for irradiated and dark control test chemical should be compared to distinguish between hydrolytic and phot olytic transformations. When possible, discuss the

relative contributio n(s) of direct and indirect photolysis to the overall net photolysis rate.

174. When quantum yields are determined, the calculated rate constants at different latitudes, seasons and for water bodies with depths and light attenuation coefficients of intere st should be used to discuss how sunlight would affect the transformation rate of the test chemical at the time when the concentration of the chemical in surface water is expected to be the maximum.

175. When transformation products are identified and qua ntified in direct and indirect photolysis studies, photolytic products should be distinguished from hydrolytic products. When feasible, potential hydrolytic and/or photolytic stability of primary tran sformation products should be included in the results. When available, the rates of formation and decline of primary transformation products should be discussed. In turn, transformation products from direct and indirect photolysis studies should be compared to distinguish products unique to each.

176. When studies are conducted with both SNW and SNW

- N, the potential contribution of hydroxyl radical should be assessed by comparing the results in the two types of water.

177. Sources of error and uncertainty such as losses of the test chemical and/or transfor mation products due to volatilization and/or adsorption to glassware should be discussed.

LITERATURE

1. OECD. 1998. OECD Working Group for the Development of a Test Guideline on

Phototransformation of Chemicals in Water. Rome, 21- 22 September 1998.

2. U.S. EPA. 1998. OPPTS 835.2210 - Direct Photolysis Rate in Water by Sunlight. United States Environmental Protection Agency. Washington, DC. http://www.epa.gov/docs/OPPTS_Harmonized/835_Fate_Transport_Transformation_Test_Guideli

nes/Series/

3. U.S. EPA. 1998. OPPTS 835.5270 - Indirect Phot olysis Screening Test. United States Environmental Protection Agency. Washington, DC.

4. ASTM. 1987. E 896-87: Standard Test Method for Conducting Aqueous Direct Photolysis Tests. American Society for Testing and Materials. Philadelphia PA.

5. U.K. DOE. 1993. Determination of the Stability of Substance in Simulated Sunlight- A proposal for a Test Guideline. Submitted by the Department of the Environment, United Kingdom.

6. UBA. 1992. Direct Phototransformation of Chemical s in Water - A proposal for a Test Guideline. Submitted by UBA, Germany. Berlin.

7. SETAC. 1995. Procedures for Assessing the Environmental Fate and Ecotoxicity of Pesticides. Section 10 in Aqueous Photolysis (page 28- 30). Mark Lynch, Editor. SETAC - Europe

Publication.

8. ECETOC. 1984. The Phototransformation of Ch emicals in Water: Results of a Ring Test. ECETOC Technical Report N o 12. Brussels, BelgiumENV/JM/TG/RD(2006)1/REV

42 9. Van Henegouven B. 1990. Sunlight induced Degradation of Chemicals in Surface Water. Report of Centre for Bio-Pharmaceutical Sciences. Leiden, The Netherlands.

10. OECD. 1997. Guidance Document on Direct Photot ransformation of Chemicals in Water. OECD Environmental Health and Safety Publication. Series on Testing and Assessment No.7. Paris,

France.

21. 11. IUPAC. 1996. Glossary of terms used in photo chemistry (IUPAC Recommendations 1996) Pure & Appl. Chem. 68: pp 2223 - 2286.

22. 12. Leifer A. 1988. The Kinetics of Environmental Aquatic Photochemistry. Theory and Practice. ACS Professional Reference Book. Published by the American Chemical Society. Washington,

D.C.

23. 13. Mill T and Mabey W. 1985. Photodegradation in water. Chapter 8 in Environmental Exposure from Chemicals. Neely W and Blau G, editors. CRC Press. Boca Raton FL. pp. 175-216

24. 14. Harris J. 1982. Rates of Direct Aqueous Phot olysis. Chapter — in Handbook of Chemical Property Estimation Methods. Environmental Be havior of Organic Compounds. Lyman W, Reehl W, and Rosenblatt D, editors. McGraw-Hill Publishers. New York, NY.

25. 15. Mill T, Mabey W, Bomberger D, Chou T, Henry D, and Smith JH. 1982. Laboratory Protocols for Evaluation of the Fate of Organic Chemicals in Air and Water. U.S. Environmental Protection Agency. EPA 600/3-82-002. Washington, D.C.

26. 16. Mill T, Davenport J, Dulin D, Mabey W, and Bawol R. 1981. Evaluation and Optimization of Photolysis Screens. U.S. Environmental Pr otection Agency. EPA 560/5-81-003. Washington,

D.C.

27. 17. Zepp R. 1978. Quantum yields for reaction of pollutants in dilute aqueous solutions. Environ. Sci. & Technol. 12: pp. 327-329.

28. 18. Zepp R, and Cline D. 1977. Rate of direct photolysis in aquatic environment. Environ. Sci. & Technol. 11(4): pp. 359-366.

19. Boule P., Guyon C. and Lemaire J. 1982. Photochemistry and Environment IV : Photochemical behaviour of monochlorophenols in aqueous dilute solution. Chemosphere 11, 1179-1188.

20. Boule P., Guyon C., Tissot A. and Lemaire J. 1987. Specific phototransformation of xenobiotic compounds : chlorobenzene and chlorophenols. Photoc hemistry of Environmenta l Aquatic Systems (R.G. Zit % W: J. Cooper, eds.), Miami, 10-26.

29. 21. Zepp R, Schlotzhauer P, and Sink R. 1985. Phot osensitized transformations involving electronic energy transfer in natural waters: Role of humic substances. Environ. Sci. & Technol. 19: pp. 74-81.

30. 22. Zepp R, Baughman G, and Scholtzhauer P. 1981. Comparison of photochemical behavior of various humic substances in Water. I. Sunlight induced reactions of aquatic pollutants photosensitized by humic substances. Chemosphere 10: pp. 109-117.

31. 23. Mill T. 1999. Predicting photoreaction rates in surface water. Chemosphere 38(6): pp. 1379-ENV/JM/TG/RD(2006)1/REV

43 1390.

32. 24. Brezonik P and Fulkerson-Brekken J. 1998. Ni trate-induced photolysis in natural waters: Controls on concentrations of hydroxy radical photo-i ntermediates by natural scavenging agents. Environ.

Sci. & Technol. 32: 3004-3010.

33. 25. Vaughan P and Bough N. 1998. Photochemical formation of hydroxy radical by constituents of

natural waters. Environ. Sci. Technol. 32: 2947-2953.

34. 26. Blough N and Zepp R. 1995. Reactive oxygen species in natural waters. Chapter in Active Oxygen in Chemistry. Foote C, Valentine G, Gree nberg A, and Liebman J, editors. Published by Chapman and Hall. New York, NY. pp. 280-333.

35. 27. Mabury S and Crosby D. 1994. The relationship of the hydroxyl reactivity to pesticide persistence. Chapter 10 in Aquatic and Surface Photochemistry. G Helz, R Zepp, and D Crosby, editors. Lewis Publishers. Boca Raton, Florida, USA. pp. 149- 161.

36. 28. Zepp, R.G., Hoign é e , J. and Bader, H. 1987. Nitrate-induced photooxidation of trace organics in

water. Environ. Sci. Technol. 21: 443-450.

37. 29. Haag W and Hoign é e’ J. 1986. Singlet oxygen in surface waters. III. Steady state concentrations in various types of waters. Environ. Sci. & Technol. 20: 341-348.

38. 30. Haag W, Hoign é e’ J, Gassmann E, and Braun A. 1984. Singlet oxygen in surface waters. II. Quantum yields of its production by some natural humic materials as a function of wavelength. Chemosphere 13: pp. 641-650.

39. 31. Mill T, Hendry D, and Richardson H. 1980. Free radical oxidants in natural waters. Science 207: pp. 886-889.

40. 32. Draper W and Crosby D. 1981. Hydrogen peroxi de and hydroxyl radical: Intermediates in indirect photolysis reactions in water. J. Agric. Food Chem. 29: pp. 699.

41. 33. Wolff C, Halmans M and Van der Heijde H. 1981. The formation of singlet oxygen in surface waters. Chemosphere 10: pp. 59.

42. 34. Zepp R, Wolfe N, Baughman G, and Hollis R. 1977. Singlet oxygen in natural waters. Nature 267: pp. 421-423.

43. 35. Zhou, X. and Mopper, R. 1990. Determination of photochemically produced hydroxyl


### radicals in seawater and fresh water. Mar. Chem. 30: 71-88.

44. 36. Mopper, R. and Zhou, X. 1990. Hydroxyl radical photoproduction in the sea and its potential impact in marine processes. Science 250: 661-664.

37. Aguer J.P., Richard C. and Andreux F. 1997. Comparison of the photoinductive properties of commercial, synthetic and soil extracted humic s ubstances. J. Photochem. Photobiol. A 103, 163-168.

38. Vialaton D., Richard C., Baglio D. and Paya-P erez A. 1998. Phototransformation of 4-chloro-2- methylphenol in water; influence of humic substanc es on the reaction. J. Photochem. Photobiol. A 119, 39-

45.ENV/JM/TG/RD(2006)1/REV

44 39. Niessen R., Lenoir D. and Boule P. 1988. Phototransformation of phenol induced by excitation of nitrate ions. Chemosphere 17, 1977-1984.

40. Mailhot G., Astruc M. and Bolte M. 1999. Degradation of tributyltin chloride in water photoinduced by iron(III). Applied Organometallic Chem. 13, 53-61.

45. 41. Frank R and Klöpffer W. 1988. Spectral solar photo irradiance in Central Europe and the adjacent North Sea. Chemosphere 10: p. 985.

46. 42. Frank R and Klöpffer W. 1988. A convenient mode l and program for the assessment of abiotic degradation of chemicals in natural waters. Ecotox. Environ. Safety 17: pp. 323-332.

47. 43. Calvert, J.G. and Pitts, J.N., Jr. 1966. Photochemistry. Wiley, New York, USA.

48. 44. Turro N. 1991. Modern Molecular Photochemistry. Published by University Science Books. Sausalito, California, USA.

19. Zepp R. 1999. Personal communication (December 30, 1999).

20. Faust B. 1994. A review of the photochemical redox reactions of iron(III) species in atmospheric, oceanic, and surface waters: Influence on geochemical cycles and oxidant formation. Chapter 1 in Aqu atic and Surface Photochemistry. G Helz, R Zepp, and D Crosby, editors. Lewis Publishers. Boca Raton, Florida, USA. pp. 3

- 35

21. Su i zberger B, Laubscher H, and Karametaxas G. 1994. Photoredox reactions at the surface of iron (III) hydr(oxides). Chapter 3 in Aquatic and Surface Photochemistry. G Helz, R Zepp, and D Crosby, editors. Lewis Publishers. Boca Raton, Florida, USA. pp. 53

- 73.

52. 45. U.S. EPA. 1985. Hazard Evaluation Division. Standard Evaluation Procedure: Aqueous Photolysis Studies. Office of Pesticide Programs , U.S. Environmental Protection Agency. EPA-540/9-85-

014

46. OECD Test Guideline 111. 2003 Hydrolysis as a Function of pH.

53. 47. Ruzo L, Shepler K, and Toia R. 1995. Pesticide hydrolysis and photolysis studies: Guideline challenges and experimental approaches. Chapter 8 in Agrochemical Environmental Fate - State of the Art. M Leng, E Leovey, and P Zubkoff, editors. Lewis Publishers. Boca Raton, Florida, USA. pp 77- 91.

22. Gao H and Zepp R. 1998. Factors influencing photoreactions of diss olved organic matter in a coastal

area of the Southeastern United States. Environ. Sci. Technol. 32: 2940

- 2946.

23. IHSS. 1999. Typical Humic Acid Data Packet. In ternational Humic Substances Society (IHSS). Available from website http://ihss.gatech.edu/datah a.html.

24. Zepp R and Schlotzhauer P. 1981. Chemosphere 10: pp. 479

48. European Union (EU). 1995. Commission Dire ctive 95/36/EC amending Council Directive 91/414/EEC concerning the placing of plant protec tion products on the market. Annex I: Fate and

behaviour in the Environment.ENV/JM/TG/RD(2006)1/REV

45 57. 49. Zepp, R.G. 1982. Experimental Approaches to Environmental Photochemistry. Chapter in the Handbook of Environmental Photochemistry, edited by Hutzinger, O.; Springer-Verlag, New York 2, Part B: pp 19-40.

58. 50. Faust, B.C. 1993. Generation and use of simulated sunlight in photochemical studies of liquid solutions. Rev. Sci. Instrum. 64:(2) pp. 577- 578.

59. 51. (a) The Book of Photon Tools. 1999. Drozdowicz, Z., Editor. Oriel Instruments, Stratford, Connecticut 006615, USA. (b) Atlas Electric Devices Company, 114 Ravenswood Avenue, Chica go, Illinois 60613 USA.Oriel Instruments. 1999.

60. 52. Lema i r e ie , J., Guth, J. A., Klais, D., Leahey, J., Merz, W., Philp, J. Wilmes, R., and Wolff C.J.M. 1985. Chemosphere, 14: pp 53- 77.

61. 53. Mill T. 2000. Documents on Calibration of Lamp and Indirect Photoreaction Estimation Methods, prepared for and submitted to the U.S. Environmental Protection Agency, Office of Pesticide Programs under PR Number 9W-2901-NASA, February 22, 2000.

62. 54. Dulin D. and Mill T. 1982. Development and evalua tion of sunlight actinometers. Environ. Sci. Technol. 16(11): pp. 815-820.

63. 55. Zepp, R.G., Gumz, M.M., Miller, W., and Gao, H. 1998. Photoreaction of Valerophenone in Aqueous Solutions. J. Phys. Chem. A, 102: pp. 5716- 5722.

64. 56. Murov et al. 1993. Chemical Actinomet ry. In Handbook of Photochemistry. 2 nd ed. Marcel Decker Inc., New York. pp. 298-305.

65. 57. Millet et al. 1998. Abiotic Degradation of Halobenzonitriles: Investigations of the Photolysis in Solution. Ecotoxicol. Environ. Safety. 41: pp. 44-50.

66. 58. Heller, H. and Langan J. 1981. A new reusable chemical actinometer. EPA Newsletter 71.

67. 59. Bahnemann, D. 1993. Ultra-small metal oxide particles: preparation, photophysical characterization and photocatalytic properties. Isr. J. Chem. 33: pp. 115.

60. Gauglitz G. and Hubig S. 1984. Photokinetische Grundlagen moderner Aktinometer. Z. Phys. Chem. N. F. 139, 237-246.

61. Gauglitz G. and Hubig S. 1985. Chemical actinometry in the UV by azobenzene in concentrated

solutions: A convenient method. J. Photochem. 30. 121-125.

68. 62. IUPAC. 1989. Chemical Actinometry. Prepared fo r publication by H.J. Kuhn, S.E. Braslavsky, and R. Schmidt. Pure & Appl. Chem., Vol. 61, No. 2, (1989) pp. 187- 210.

25. Winterle J and Mill T. 1985. Toxic substances process data generation and protocol development. Work assignment 18: Indirect Photoreaction Protocol. Submitted to Office of Toxic Substances, U.S. Environmental Protection Agency. EPA Contract No. 68

- 03

- 2981.ENV/JM/TG/RD(2006)1/REV

46 70. 63. IUPAC. 1984. Recommended Standards for Re porting Photochemical Data (1984). Pure & Appl. Chem. 56: pp 939- 934.

26. AWWA. 1991. Standard Methods for the Analysis of Water and Wastewater. American Water Works Association, 6666 West Quincy Avenue, Denver, Colorado 80295, USA

. http://www.awwa.org/stanmeth/contents.htm

72. Mill T, Mabey W, Winterle J, Davenport J, Barich V, Dulin D, Tse D, and Lee G. 1982. Design and validation of screening and detailed methods for environmental processes. Final Report. Submitted to

Office of T oxic Substances, U.S. Environmental Protection Agency. EPA Contract No. 68

- 01

- 6325.ENV/JM/TG/RD(2006)1/REV

47 ANNEX 1

Definitions and Units

Test substance: any substance, whether the parent compound or relevant transformation products

Transformation products: all substances resulting from biotic or abiotic transformation reactions of the test substance including CO 2

.

Half-Life, t 0.5 is the time taken for 50% transformation of a test substance when the transformation can be described by first-order kinetics; it is independent of the concentration.

DT 50 (Disappearance Time 50) is the time within which the concentration of the test substance is reduced by 50%; it is different from the half-life t 0.5 when transformation does not follow first-order kinetics.

DT 75 (Disappearance Time 75) is the time within which the concentration of the test substance is reduced by 75%.

DT 90 (Disappearance Time 90) is the time within which the concentration of the test substance is reduced by 90%.

The limit of detection (LOD) is the concentration of a substance below which the identity of the substance cannot be distinguished from analytical artefacts.

The limit of quantification (LOQ) is the concentration of a substance below which the concentration cannot be determined with an acceptable accuracy.

The definitions and units thereafter are taken from the Glossary of terms used in photochemistry (IUPAC Recommendations 1996) published in Pure and Applied Chemistry, 68 , 2223-2286, 1996. Commonly used and SI units are provided. Cited with permission from the International Union of Pure and Applied Chemistry

Absorbance (A), [Dimensionless] - The logarithm to the base 10 of the ratio of the spectral radiant power of incident, essentially monochromatic radiation (I= ∫ λ I λ d λ ) to the radiant power of transmitted radiation (P λ ):

A = log(P λ o /P λ ) = -log T

In practice, absorbance is the logarithm to the base 10 of the ratio of the special radiant power of light transmitted through the reference sample to that of the light transmitted through the solution, both observed in identical cells. T is the (internal) transmittance. The terms “absorbancy”, “extinction” and “optical density” should no longer be used.

Absorption Coefficient (a) , [m -1 or cm -1 ] - Absorbance divided by the optical pathlength, l. The term “absorptivity” is not recommended

Actinometer - A chemical system or physical device which determines the number of photons in a beam integrally or per unit time and it is commonly applied to devices used in the ultraviolet and visible wavelength ranges. Examples of a chemical actinometers are iron(III) oxalate solutions. Examples of physical devices are bolometers, thermopiles and phot odiodes. Actinometers give a reading that can be correlated to the number of photons detected.ENV/JM/TG/RD(2006)1/REV

48 Beer-Lambert Law - The absorbance of a beam of collimated monochromatic radiation in a homogeneous isotropic medium is proportional to the absorption pathlength, l , and to the concentration, c. This law holds only under the limitations of the Lambert Law and for absorbing species exhibiting no concentration dependent aggregation. The law can be expressed as,

A = log(P λ o /P λ ) = ε c l

or
P λ

= P λ o 10
- ε cl

where the proportionality constant, ε , is called the molar (decadic) absorption coefficient.

Units: For l in cm and c in mol dm 3 or M, ε will result in dm 3 mol -1 cm -1 or M -1 cm -1 . These are the commonly used units. The SI units for ε is m 2 mol -1

.

Chromophore - That part of a molecular entity consisting of an atom or group of atoms in which the electronic transition responsible for a given spectral band is approximately localized.

Depth of Penetration (of light), [m] - The inverse of the absorption coefficient . If the decadic absorption coefficient, a , is used, the depth of penetration (1/ a ) is the distance at which the spectral radiant power, P l decreases to one tenth of its incident value, P λ o

.

Einstein - One mole of photons . It is not an IUPAC-sanctioned unit. It is sometimes defined as the energy of one mole of photons.

Energy Transfer - From a phenomenological point of view, the term is used to describe d the process by which a molecular entity absorbs light and a phenomenon originates from the excited state of another molecule. In mechanistic photochemistry, the term has been reserved for the photophysical process in which an excited state of a molecular entity (the donor) is deactivated to a lower-lying state by transferring energy to a second molecular entity (the acceptor), which is thereby raised to a higher energy state. The excitation may be electronic, vibrational, rotational or translational. The donor and acceptor may be two parts of the same molecule, in which case the process is called intramolecular energy transfer

.

Excited State - A state of higher energy than the ground state of a chemical entity. In photochemistry an electronically excited state is usually meant.

Frequency (v or ω ), [sec -1 or rad*sec -1 ] - The number of waveperiods per unit time. The linear frequency, v, is the number of cycles per unit time. For the angular frequency, the symbol ω (= 2 π v) is used.

Ground State - The lowest energy state of a chemical entity. In photochemistry, ground electronic state is usually meant.

Half-width (of a band) - The full width of a spectral band at a height equal to half of the height at the band

maximum. Also known as full width at half maximum (FWHM). The dimensions of band width should be either inverse length ( wavenumbers, ) or inverse time ( frequencies ) so that the values give an indication of the energies. Note the hyphen in half-width. Half bandwidth has the meaning of half -width at half

maximum.

Hyperchromic Effect - Increase in the intensity of a band due to substituents or interactions with the molecular environment. Hypochromic effect is the opposite to hyperchromic effect.

Intensity - Traditional term for photon flux, irradiance or radiant power (radiant flux) . In terms of an objectENV/JM/TG/RD(2006)1/REV

49 exposed to radiation, the term should now be used only for qualitative descriptions.

Intensity (l) (of a light source)- Same as radiant intensity.

Intensity (of a spectral feature)- Describes the magnitude of the particular feature in the spectrum.

Irradiance (E) , [W m -2 ] - The radiant flux or radiant power, P, of all wavelengths incident on an infinitesimal element of surface containing the point under consideration divided by the area of the element (d P /d S, , simplified expression: E= P/S when the radiant power is constant over the surface area
considered). E = ∫ E

λ d λ , where E λ is the spectral irradiance at wavelength λ . For a parallel and perpendicular incident beam not scattered or reflected by the target or its surrounding fluence rate (E o ) is an equivalent term.

Lambert Law - The fraction of light absorbed by a system is independent of the spectral radiant power (

P λ o ). This law holds only if P λ o is small, scattering is negligible, and multiphoton processes, excited state populations, and photochemical reactions are negligible.

Lamp - A source of incoherent radiation.

Molar Absorption Coefficient, Molar Decadic Absorption Coefficient - [dm 3 mol -1 cm -1 , M -1 cm -1 or dm 3 mol -1 mol -1 ]

Absorbance divided by the absorption pathlength, l, and the concentration,

. ε = [1 / c l ] log(P λ o /P λ ) = A / c l : The term molar absorptivity for molar absorption coefficient should be avoided.

Photochemical Reaction - This term is generally used to describe a chemical reaction caused by absorption of ultraviolet, visible, or infrared radiation.

Photochemistry - The branch of chemistry concerned with the chemical effects of light (far UV to IR).

Photodegradation - The photochemical transformation of a molecule into lower molecular weight fragments, usually in an oxidation process. This term is widely used in the destruction (oxidation) of pollutants by UV-based processes.

Photolysis - A light-induced bond cleavage.

Photon - The quantum of electromagnetic energy at a given frequency . This energy, E = hv is the product of the Planck ( h) constant and the frequency of the radiation (v).

Photooxidation - Reactions induced by light. Common process are:

• The loss of one or more electrons from a chemical species as a result of photexcitation of that species;

• The reaction of a substance with oxygen under the influence of light. When oxygen remains in the product this latter process is also called photooxygenation. Reactions in which neither the substrate nor the oxygen are electronically excited are sometimes called “photoinitiated oxidations”.

Photoreductions - Reduction reactions induced by light. Common process are:

• Addition of one or more electrons to a photoexcited species;

• The photochemical hydrogenation of a substance. Reactions in which the substrate is not electronically excited are sometimes called “photinitiated reductions”.ENV/JM/TG/RD(2006)1/REV

50 Photosensitization - The process by which a photochemical or photophysical alteration occurs in one molecular entity as a result of initial absorption of radiation by another molecular entity called a photosensitizer . In mechanistic photochemistry the term is limited to cases in which the photosensitizer is

not consumed in the reaction.

Primary Photochemical Process (Primary Photoreaction) - Any elementary chemical process undergone by an electronically excited molecular entity yielding a primary photoproduct.

Primary (Photo)product - The first observable chemical entity which is produced in the primary photochemical process and which is chemically different from the reactant.

Quantum (of radiation) - An elementary particle of electromagnetic energy in the sense of the waveparticle duality.

Quantum Yield ( φ ) - The number of defined events which occur per photon absorbed by the system. The integral quantum yield is:

φ = number of events/ number of photons absorbed

For a photochemical reaction,

φ = amount of reactant consumed or produ ct formed/amount of photons absorbed

The differential quantum yield is Φ = d[x]/dt /n, where d[x]/dt is the rate of change of a measureable quantity, and n is the amount of photos (mol or its equivalent einstein) absorbed per unit time. Φ can be used for photophysical processes or photochemical reactions.

Radiant Energy ( Q), [J]

- The total energy emitted, transferred or received as radiation of all wavelengths in a defined period of time ( Q= ∫ Q λ d λ ). It is the product of radiant power, and time, t:Q= P t when the radiant power is constant over the time considered.

Radiant Exposure (H) , [J m -2 ] - The irradiance, E, integrated over time of irradiation ( ∫ E d t , simplified expression H= E t when the irradiance is constant over the time considered).

Radiant Intensity (I), [W sr -1 ] - Radiant (energy) flux or radiation power, P, at all wavelengths per unit solid angle, ω . The radiant power emitted in a given direction by a source or an element of the source in an infinitestimal cone containing the given direction divided by the solid angle of the cone (dP/d ω , simplified expression: I = P/S when the radiant power is constant over the surface area considered).

Radiant Power (P) , [J s -1 , or W] - Power emitted, transferred or received as radiation.

Singlet Molecular Oxygen - The oxygen molecule (dioxygen), O 2 , in an excited singlet state. The ground

state of oxygen is a triplet 3 Σ g - ). The two metastable singlet states derived from the ground state configuration are 1 ∆ g and 1 Σ g -

. The IUPAC discourages the use of the term “singl et oxygen” alone, without mentioning the oxygen species (in this case, dioxygen) to avoid confusion with 1S and 1D excited states of the oxygen atom.

Singlet State - A state having a total electron spin quantum number equal to 0.

Solvent Shift - A shift in the frequency of a spectral band of a chemical species arising from its interactionENV/JM/TG/RD(2006)1/REV

51 with its solvent environment. Bathochromic shift , also known to as “red shift”, refers to the shift of a spectral band to lower frequencies (longer wavelenghts) as result of interaction with the solvent Hypsochromic shift , also known as “blue shift”, refers to the shift of a spectral band to higher frequencies (shorter wavelengths) as a result of interaction with the solvent..

Spectral Irradiance (E λ ) , [W m -3 , or W m -2 nm -1 ] - Irradiance, E, at wavelength λ per unit wavelength.

Triplet State - A state having a total soin quantum number of 1.

Wavelength ( λ ) - The distance, measured along the line of propagation, between two corresponding points on adjacent waves. The wavelength depends on the medium in which the wave propagates

Wavenumber ( σ
, υ ) , [m -1 or cm -1 ]- The reciprocal of the wavelength, λ , or the number of waves per unit length along the direction of propagation.

Xenon Lamp - An intense source of ultraviolet, visible a nd near-infrared light produced by electrical discharge in xenon under high pressure.ENV/JM/TG/RD(2006)1/REV

52 ANNEX 2

Symbols and Units Related to Photochemistry

Symbol Name SI Units Common Units

A Absorbance Dimensionless Dimensionless

a Decadic absorption

coefficient m -1 cm -1

D Attenuance Dimensionless Dimensionless

H

0 Fluence J m -2 Same

E

0 Fluence rate W m -2

E Irradiance W m -2

ε Molar (decadic) absorption coefficient m -2 mol -1 cm -1 dm 3 mol -1 or

cm 2 mmol -1

Sometimes L mol -1 cm -1

φ Quantum yield Dimensionless a Dimensionless a

Q Radiant energy J

H Radiant exposure J m -2

I Radiant intensity W sr -1

P W

I Spectral radiance intensity W sr -1 m -1 W sr -1 nm -1

λ Wavelength m nm

σ ; υ Wavenumber m -1 cm -1ENV/JM/TG/RD(2006)1/REV

53 ANNEX 3

Fig ure 1: Proposed test scheme for direct photolysis

Tier 1: Theoretical Screen

• Measurement of Absorbance

• Estimation of Max. Photolysis Rate

Decision Criteria: Photolysis Loss ≥ 50 % Over 30 Days?

yes 

### n

Tier 2: Experimental Screen (optional) Determination of Photolysis Rate Constant over 30 Days

Decision Criteria: Photolysis Loss ≥ 20% in 30 Days Sunlight Exposure?

yes n 

### o

Tier 3: Quantum Yield Determination and Calculation of Photolysis Rates and

Life

- Times

Decision Criteria: Photolysis Loss ≥ 20% in 30 Days Sunlight Exposure?

yes n 

### o

Go to Indirect Photolysis Tier 1 yes

Tier 4: Isolation / Identification of Major Phototransformation Products ( ≥ 10% of dose applied)ENV/JM/TG/RD(2006)1/REV

54 Tier 1

- Theoritical Screen

1. If the test chemical absorbs solar irridiation > 295 nm, estimate a maximum direct photolysis rate

constant K d(max) in shallow natural water by assuming the quantum yield φ = 1; K d(max) = Σ ε λ L λ 2. Determine if the maximum direct photolysis rate constant would result in estimated direct photolysis

losses of ≥ 20% of an initial concentration over a 30

- day/night sunlight exposure period using the

fol lowing equation: C/C 0 = exp [

- K d(max) (30

- days) ]

Yes ↓ → No → Quit or go to Tier 1 Indirect Photolysis

Tier 2

- Experimental Screen

1. Measure the decline of the test chemical in sterilised buffer exp osed to a xenon lamp or sunlight. If data fit a first order kinetics model, determine the apporximate direct photolysis rate.

2. Determine if approximate direct photolysis rate consta nt would result in estimated direct photolysis losses

of ≥ 10% of an initial concentration from the following equation: C/C 0 = exp [

- K d(max) (30 days)] If yes, go to next step; if no, quit or go to Tier 1 Indirect Photolysis.

3. Is there interest in determining the quantum yield and in estimating theoretical direct photolysis rate

con stant from the quantum yield?

Yes ↓ → No → Go to Tier 4 Direct Photolysis

Tier 3

- Quantum Yield and Estimation of Theoretical Rate constant

1. Determine the quantum yield and use it to estimate theoretical direct phot olysis rate constant for seasons, latitudes, elevations and types of water bodies of interest.

2. Is there interest in comparing experimental direct photolysis rate constants with theoretical ones and/or identifying/quantifying major transformation products?

Yes ↓ → No → Quit or go to Tier 1 Indirect Photolysis

Tier 4

- Determine the Direct Photolysis Rate Constant

1. Measure the decline of the test chemical (and if of interest) the formation and decline of maj or transformation products in sterilised buff ers exposed to a xenon lamp or sunlight.

2. If data fit a first order kinetics model, determine the direct photolysis rate constants and corresponding

half

- life. Otherwise, determine the DT 50 , DT 75 and DT 90 values from fitting data to a non

- first order model. If practical and of interest, determine the same parameters for major transformation products.

3. Is there interest in indirect photolysis? If yes, go to Tier 1 Indirect Photolysis; if no, quit.ENV/JM/TG/RD(2006)1/REV

55 Figure 2: Propos ed Test Scheme for Indirect Photolysis

Tier 1

- Screen

1. Measure the decline of the test chemical in synthetic water containing humics (and if applicable, nitrate) in buffered distilled water and estimate indirect photolysis rate constant K i(approx). 2. Det ermine if the approximate indirect photolysis rate constant would result in estimated indirect photolysis losses of ≥ 10% of an initial concentration over a 30

- day/night sunlight exposure period using the following equation: C/C 0 = exp [

- K i(approx) (30 day s)]

3. In some cases, it may be possible to supplement or even replace the experimental screen with a theoretical screen based on using structural activity relationships (SARs) to estimate second order rate constants and on information on the typical concentr ations of photooxidation in surface water.

Yes ↓ → No → Quit

Tier 2

- Definitive Indirect Photolysis Test

1. Measure the decline of the test chemical (and if of interest) the formation and decline of major transformation products in synthetic and/or natura l waters and in buffered distilled water exposure to a xenon lamp or sunlight.

2. If data fit a first order kinetics model, estimate net, indirect, and direct photolysis rate constants and corresponding half

- lives for the test chemical . Correct for photobleac hing and attenuation effects.

3. If data fit a non

- first order model, determine the DT 50 , DT 75 and DT 90 values for fitting data to a non

first order model. If practical and of interest, determine the same parameters for major transformation products.ENV/JM/TG/RD(2006)1/REV

56 ANNEX 4

Derivations of Selected Equations

Background equations from Leifer (12):



# d C

dt j I jD IF F

sys 

# [ ]     



=− =−

λ λ λλ λ 

# φ φ

(abs by chem) (abs by sys) (abs by chem) 0

[eq. 3 4 -1]



# d C

dt j I jD IF F

sys 

# [ ]

=− =− 

# ∑ ∑ φ φ

λ λλ λ

295 800

295 800

0 (abs by chem) (abs by sys) (abs by chem)

[eq. 3 4 -2]

where:

φ = quantum yield j = conversion factor to make units consistent with the L/mol • cm unit of the molar absorption

coefficient and the mol/L unit of concentration =

6.02 x 10 20 (L/cm 3 )(photons/mol)

I λ (abs by chem) = photon absorption rate by the chemical per unit volume over a 1 nm interval centered at wavelength λ (photons/cm 3 • day)

D sys = depth of irradiated system (cm) = volume of irradiated system/incident area

I 0 λ = incident photon flux over a 1 nm interval centered at wavelength λ
(photons/cm 2 • day)

F λ (abs by sys) = fraction of incident photon flux absorbed by the system

F λ (abs by chem) = fraction of incident photon flux absorbed by the chemical



# [ ]

F I I

I I

I t C l

C l
λ λ λ

λ λ α ε

λ α ε λ λ

λ λ (abs by sys) 

### = −

= −

= − − +

− + 0

0 0

0 

### 1 10 1 10 ( [ ])

( [ ])

[eq. 3 4 -3]



# F C

C λ λ

λ λ 

# ε

α ε (abs by chem) 

# = + [ ]

[ ]

[eq. 3 4 -4]

where:

α λ = attenuation coefficient of the system at wavelength λ (1/cm)ENV/JM/TG/RD(2006)1/REV

57 ε λ = molar absorption coefficient of the chemical at wavelength λ (L/mol • cm) l = light pathlength (cm)

Inserting equations 3 4 -3 and 3 4 -4 into equation 3 4 -1 gives:



# [ ] d C

dt jD I C

C

sys C l 

## [ ] [ ]

[ ] ( [] 

##     

 =− − • + 
  


 − +

λ λ α ε λ

λ λ 

## φ ε

α ε λ λ 0 

## 1 10

[eq. 3 4 -5]

Summing equation 3 4 -5 over all wavelengths from 29 0 5 nm to 800 nm gives:



## [ ] d C

dt jD I C

C

sys C l [ ] [ ]

[ ] ( [] =− − • + 
  


 − +

= = 

## ∑ φ ε

α ε λ α ε λ

λ λ λ λ

λ λ 0

295 800 1 10

[eq. 3 4 -6]

For solar irradiation on an aqueous system (12),



# I t It It solar d s 0 λ λλ ( ) 

# () () () = +

[eq. 3 4 -7]



# lD t

d sys 

# ≅ sec ( ) θ

[eq. 3 4 -8]



### l D

s sys 

### = 12

. [eq. 3 4 -9]

where:

I 0 λ (solar) = total incident solar photon flux as a function of time

I d λ (solar) = direct incident solar photon flux as a function of time

I 0 λ (solar) = sky radiation incident solar photon flux as a function of time

l d = average light pathlength for direct irradiation

l

s = average light pathlength for sky irradiation



# [ ] [ ] 

# { } dC

dt jD I I C

C

sys d C D

s C D sys 

### =− − + − + 
  
  − + − +

= = 

# ∑ φ ε

α ε λ αε θ

λ α ε λ

λ λ λ λ

λ λ λ λ 

### 1 10 1 10 1 2

295 800 ( [ ]) sec ( [ ]) . 

### [ ]

[ ]

[eq. 3 4 -10]ENV/JM/TG/RD(2006)1/REV

58 Derivation of equation 5 in the main text (12):

10 -y = exp(-2.3y) [eq. 3 4 -11]

Therefore, 

# { } 1 10 1 2 3 1

− =− − + =− − − +

( [ ]) 

# exp . ( [ ]) exp( )

α ε λ λ

λ λ 

# α ε C l 

# Cl x

[eq. 3 4 -12]

where: 

# ( ) x Cl A =+ = 23 23

. [] . α ε λ λ

[eq. 3 4 -13]

A = absorbance of the solution

A series expansion of the exponential in equation 3 4 -12 gives:



### 1 2 3 4 5 2345



### − − = + − + − + ⋅⋅⋅⋅⋅

exp( ) ! ! ! ! x x xxxx

[eq. 3 4 -14]

For an optically dilute solution of a test chemical test substance in pure water or in shallow water or in the near surface of natural water such that the absorbance of the system is < 0.02, all of the higher terms in equation 3 4 -14 are small compared to x such that equation 3 4 -14 reduces to:



# 1 − −≅ exp( ) x x

[eq. 3 4 -15]

Combining equations 3 4 -13 and 3 4 -15 with equation 3 4 -12 gives for an optically dilute solution of a test
chemical test substance in pure water or clear shallow water or in the near surface of natural water: 

# ( ) 1 10 2 3

− ≅+ − +

( [ ]) 

### . [] α ε λ λ

λ λ 

### α ε C l 

### C l

[eq. 3 4 -16]

Substituting equation 3 4 -16 into equation 3 4 -6 and canceling out the resulting identical terms in the numerator and denominator gives for an optically dilute solution of a test chemical test substance in pure

water or in clear shallow water or in the near surface of natural water:

d C

dt j l

D I C

sys [] . [ ] = − 

   

  

= = 

### ∑ 2 3

0

295 800 φ

ε λ λ
λ λ

[eq. 3 4 -17]

By comparing equation 3 4 -17 to equation 1 in the main text, it can be seen that for a test chemical test
substance in an optically dilute solution in pure water or in clear shallow water or in the near surface of natural water, the direct photolysis rate constant is given by:ENV/JM/TG/RD(2006)1/REV

59 k j l

D I d

sys

= 

### ∑

2 3

0

295 800

. φ ε λ λ
[eq. 3 4 -18]

where equation 3 4 -18 is identical to equation 5 of the main text

Derivation of equation 6 in the main text (12)

By analogy to equation 3 4 -16, it can be seen that for a solar irradiated, optically dilute solution of a test
chemical test substance in pure water or in clear shallow water or in the near surface of natural water such that the absorbance of the system is < 0.02,

1 10 2 3

− ≅+ − + ( [ ]) sec . ( [ ]) sec αε θ

λ λ λ λ αε θ C D

sys sys C D [eq. 3 4 -19]

1 10 2 3 12 1 2 − ≅+ − + ( [ ])( . ) . ( [ ])( . ) α ε
λ λ λ λ α ε C D

sys sys C D [eq. 3 4 -20]

Substituting equations 3 4 -19 and 3 4 -20 into equation 3 4 -10 and canceling out the resulting identical terms in the numerator and denominator gives:

d C

dt j Zt C [] . ()[ ] = − 

  

  

### ∑ 2 3

φ

ε λ λ

[eq. 3 4 -21]

where:

Zt I t I t d s λλ λ θ ( ) ( ) sec . ( ) = + 12
[eq. 3 4 -22]

Equation 3 4 -21 gives the direct photolysis rate as a function of time because the solar photon flux at any given wavelength varies over time as represented by Z(t) for an optically dilute solution.

Z Z t dt

hours λ λ

= 

### ∫ ( )

0 24

24 [eq. 3 4 -23]

Mill et al (1985) defined 24 hour average solar irradience values as:

L j Z

λ λ

= 2 3

. [eq. 3 4 -24]

Substituting equation 3 4 -24 into 3 4 -21 gives the average direct photolysis rate over a 24-hour period:

d C

dt L C [ ] [ ]      

= − 

  

  

### ∑ φ ε λ λ

[eq. 3 4 -25]ENV/JM/TG/RD(2006)1/REV

60 By comparing equation 3 4 -25 to equation 1 in the main text, it can be seen that for an optically dilute

solution of a test chemical test substance in pure water or clear shallow water or in the near surface of natural water exposed to sunlight, the 24 hour average direct photolysis rate constant is given by:

k L

d solar ( ) = 

### ∑ φ ε λ λ

295 800
[eq. 3 4 -26]

where equation 3 4 -26 is identical to equation 6 in the main text.

Derivation of equation 7 8 in the main text:

Rearranging equation 3 4 -2 gives the total photon absorption rate per unit volume by the test chemical test
substance :

I I jdC

dt abs by chem abs by chem () () [ ]

= =−



### ∑

λ φ 295 800
[eq. 3 4 -27]

where:

I λ (abs by chem) = photon absorption rate by the chemical per unit volume over a 1 nm interval centered at wavelength λ (photons/cm 3 • day)

I (abs by chem) = total photon absorption rate by the chemical per unit volume (photons/cm 3 • day)

Multiplying equations 3 4 -18 and 3 4 -25 by (-j / .) gives the total photon absorption rate per unit volume by

the test chemical test substance in an optically dilute solution exposed to xenon arc lamp or solar irradiation, respectively:

I l

D I C

sys xenon xenon ( xenon abs by chem)

=295 = 

   

   = 

### ∑ 2 3 0 800 . [] ( ) ε λ λ
λ λ

[eq. 3 4 -28]

I j LC solar (solar abs by chem) = 

  

  

### ∑ ε λ λ [ ] [eq. 3 4 -29]

The total number of photons absorbed per unit volume by a test chemical test substance in a low optical density solution over x days of xenon arc lamp irradiation or over 30 day/ nights of solar irradiation are given respectively by:



### ( ) Total # photons abs by chem / cm days xenon 3

= 

### ∑ X l

D I C

sys xenon xenon ( . )[ ] ( ) 2 3 0 ε λ λ [eq. 3 4 -30]



### ( ) Total # photons abs by chem / cm days / nights solar 3

= 

  

  

### ∑ 30 j LC solar ε λ λ [ ] [eq. 3 4 -31]

The number of days (X) of constant irradiation by a filtered xenon arc lamp that is equivalent to 30 days /nights of solar irradiation of a low absorbance water can be obtained by equating equations 3 4 -30 and

3 4 -31, assuming that the average concentration over 30 days /nights of solar irradiation is equal to the average concentration over X days of constant irradiation by a xenon arc lamp, and solving for X:

X days xenon = 
  
  

     

     = 
  
  

     

     

### ∑

∑ ∑

∑ 30

2 3 13

0 0 j D

l L

I j D

l L

I sys

xenon sys

xenon .
() () ε

ε ε

ε λ λ

λ λ λ λ

λ λENV/JM/TG/RD(2006)1/REV

61 [eq. 3 4 -32]

where equation 3 4 -32 is identical to equation 7 8 in the main text.

Derivation of equation 910 in the main text:

Substituting equation 3 4 -16 for an optically dilute solution (applicable to a low optical density actinometer solution) into equation 3 4 -5, rearranging and incorporating subscripts to designate the use of monochromatic irradiation from a xenon arc lamp (obtained with a monochromator) gives:

d C

dt j l

D I C act

sys act xenon [ ]

. [ ] () ( )      

= −

λ λ λ φ

ε 2 3

0 [eq. 3 4 -33]

By comparing equation 3 4 -33 to equation 1 in the main text, it can be seen that the monochromatic pse udo first order rate direct photolysis rate constant of a low optical density actinometer exposed to monochromatic irradiation from a xenon arc lamp is given by:

k j l

D I d act

sys act act xenon λ λλ φ ε () () ( ) .

= − 2 3

0
[eq. 3 4 -34]

Rearranging equation 4- 34 to solve for I 0_(xenon) gives:

I j D

l k

xenon sys d act

act act 0 2 3 λ λ

λ φ ε ( ) ( )

( ) . =

[eq. 3 4 -35]

where equation 3 4 -35 is identical to equation 9 10 in the text.

Derivation of equation 1 01 in the main text

For a high optical density actinometer solution,

10 0

− + ≅ ( [ ]) α ε λ λ C l [eq. 3 4 -36]

and

ε α λ λ

[ ] C > > [eq. 3 4 -37)]

such that

ε

α ε ε

ε λ

λ λ λ

λ [ ]

[ ] [ ]

[ ] C

C C

C + ≅ = 1 [eq. 3 4 -38]

Substituting equations 3 4 -36 and 3 4 -38 for a high optical density actinometer solution into equation 3 4 -6, summing only over the absorption spectrum of the actinometer above 29 0 5 nm, and using subscripts to designate the use of a filtered xenon arc lamp gives:

d C

dt jD I act

sys xenon initial final [ ]

( ) = −

= = 

### ∑ φ

λ
λ λ

0 [eq. 3 4 -39]ENV/JM/TG/RD(2006)1/REV

62 Equation 3 4 -39 is a zero order equation such that the zero order direct photolysis rate constant of the high optical density actinometer is given by:

k jD I d act zero order act

cell xenon initial final

( )( ) ( ) =

= = 

### ∑ φ

λ
λ λ

0 [eq. 3 4 -40)

Rearranging equation 3 4 -40 gives:

I jD k

xenon cell

act d act

initial final

0 λ
λ λ

φ ( ) ( )( =

= = 

### ∑

zero order) [eq. 3 4 -41]

where equation 3 4 -41 is identical to equation 1 0 1 of the main text

Derivation of equation 1 34 in the main text:

Dividing equation 3 4 -25 (for the pseudo first order rate constant of a test chemical test substance in an optically dilute solution exposed to sunlight) by equation 3 4 -18 (for the pseudo first order rate constant of a

test chemical test substance in an optically dilute solution exposed to a filtered xenon arc lamp) and rearranging gives:

k j D

l k L

I d solar cell d xenon

xenon ( ) ( )

( ) . = 

### ∑

∑ 2 3 295 800

0 ε

ε λ λ

λ λ [eq. 3 4 -42]

where equation 3 4 -42 is identical to equation 1 3 4 in the main text

Derivation of equation 1 79 in the main text:

By analogy to equation 3 4 -34 for a low optical density actinonmeter, the monochromatic pseudo first order direct photolysis rate constant of a test chemical test substance in an optically dilute solution exposed to monochromatic irradiation from a xenon arc lamp is given by:

k j l

D I d chem

sys chem chem xenon λ λλ φ ε ( ) ( )( ) .

= − 2 3

0 [eq. 3 4 -43]

Dividing equation 3 4 -34 by equation 3 4 -43, and rearranging gives:

φ φ ε

ε λ λ

λ λ chem act d chem act

d act chem k

k = ( )()

()( ) [eq. 3- 44 44 ]

where equation 3 4 -44 is identical to equation 1 7 9 of the main text

Derivation of equation 1820 in the main text:

Substituting equations 3 4 -36 and 3 4 -38 (for a high optical density actinometer solution exposed to monochromatic irradiation from a xenon arc lamp) into equation 3 4 -5 gives:

d C

dt jD I act

cell xenon [ ]

( )      

= −

λ λ φ

0 [eq. 3 4 -45]ENV/JM/TG/RD(2006)1/REV

63 Equation 3 4 -45 is a zero order equation such that the monochromatic zero order direct photolysis rate constant of a high optical density actinometer is given by:

k jD I

act zero order act

cell xenon λ λ φ

( )( ) ( ) = 0 [eq. 3 4 -46]

Dividing equation 3 4 -43 (for the monochromatic pseudo first order direct photolysis rate constant of a test
chemical test substance in an optically dilute solution exposed to monochromatic irradiation from a xenon arc lamp) by equation 3 4 -46 (for the monochromatic zero order direct photolysis rate constant of a high optical density actinometer exposed to monochromatic irradiation from a xenon arc lamp), and rearranging gives:

φ φ

ε λ λ

λ chem act

chem cell d chem

d act zero D k

k = 2 3

. ( ) ( )

( )( order) [eq. 3 4 -47]

where 3 4 -47 is identical to equation 18 20 in the main text

Derivation of equation 1921 in the main text:

By analogy to equation 3 4 -46 for a high optical density actinometer, the monochromatic zero order direct photolysis rate constant of a test chemical test substance at high optical density in a solution exposed to monochromatic irradiation from a xenon arc lamp is given by:

k jD I

chem zero order chem

cell xenon λ λ φ

( )( ) ( ) = 0 [eq. 3 4 -48]

Dividing equation 3 4 -48 by equation 3 4 -46 and rearranging gives:

φ φ λ

λ chem act d chem zero

d act zero k

k = ( )( )

( )( ) [eq. 3 4 -49]

where equation 3 4 -49 is identical to equation 19 21 in the main text

Derivation of equation 2 02 in the main text:

Dividing equation 3 4 -25 (for the pseudo first order rate constant of a test chemical test substance in an optically dilute solution exposed to sunlight) by equation 3 4 -25 (for the pseudo first order rate constant of a low optical density actinometer solution exposed to sunlight), and rearranging gives:

φ φ ε

ε λ λ

λ λ chem act d chem

d act act

chem k

k L

L = 

### ∑

∑ ( )

( ) ( )

( ) 295 800

295 800
[eq. 3 4 -50]

where equation 3-50 is identical to equation 2 0 2 in the main text

Derivation of equation 2 13 in the main text:

Dividing equation 3 4 -18 (for the pseudo first order rate constant of a test chemical test substance in an optically dilute solution exposed to a filtered xenon arc lamp) by equation 3 4 -18 (for the pseudo first orderENV/JM/TG/RD(2006)1/REV

64 rate constant of a low optical density actinometer solution exposed to a filtered xenon arc lamp), and rearranging gives:

φ φ ε

ε λ λ

λ λ chem act d chem

d act act xenon

chem xenon k

k I

I = 

### ∑

∑ ( )

( ) () ( )

( )( ) 0

295 800

0

295 800
[eq. 3 4 -51]

where equation 3 4 -51 is identical to equation 2 1 3 in the main text

Derivation of equation 27 In the main text:

Dividing equation 3

- 25 (for the pseudo first order rate constant for a test chemical in an optically dilute solution in shallow or near to the surface water exposed to sunlight conditions 2 by equation 3

- 25 (for sunlight conditions 1), and rearranging gives:

k k L

L d shallow solar d shallow solar chem

chem ( )( ) ( )( ) ( )

( ) 2 1 2

295 800

1

295 800 = 

### ∑

∑ ε

ε λ λ

λ λ [eq. 3

- 52]

where equation 3

- 52 is identical to equation 27 in the main textENV/JM/TG/RD(2006)1/REV

65 ANNEX 5

Preparation of Direct Photolysis Test Media

Water meeting ASTM Type IIA standards is recommended to prepare buffer solutions for direct photolysis studies. This water is described in ASTM D 1193-99- Standard Specification for Reagent Water. This document can be obtained from ASTM. In the USA, this document can be obtained from:

American Society for Testing and Materials (ASTM)

1961 Race Street Philadelphia, Pennsylvania 19103

For outside the USA, see http://www.astm.org/dist.htm

A recommended procedure for preparing buffers for direct photolysis studies is given in USEPA OPPTS 835.2210 Direct Photolysis Rate in Water by Sunlight (2). This guideline recommends:

Preparing all buffer solutions at 25 o C Using reagent grade chemicals free of impurities that could behave as photosensitizers For pHs in the range of 3 to 6, use NaH 2 PO 4 /HCl For pHs in the range of 6 to 8, use KH 2 PO 4 /NaOH For pHs in the range of 8 to 10, use H 3 BO 3 /Na OH Using procedures such as those described in the Handbook of Chemistry and Physics or by any

well establish method. Always checking the pH with a well calibrated pH meter Using the minimum concentration of buffer

To prepare the test solutions for the direct photolysis studies, add the buffer solution to the test
chemical test substance to attain the desired pH. If necessary, adjust the pH with 1 M HCl or NaOH. It is highly recommended that the actual concentration of the test chemical test substance in the test solution be determined prior to starting the study.

Preparation of Indirect Photolysis Study Test Media

1. SNW (Simulated Natural Water):

(a) Prepare an initial stock solution of humic acid, followed by filtration, preaging and dilution. The stock solution should have about 60 ppm DOC of humic acid and absorbance of approximately

1.7 at 313 nm and 0.7 at 370 nm. Aging can be accomplished by exposing the stock humi c acid

solution in a 2

- L flask for 3

- 4 days to direct sunlight (2). The absorbance of the solution is checked and used in estimating a dilution factor for preparing the test solution. (b) Buffer the SHW at pH 7 with 0.010 M phosphate solution. (c) The S NW test media should have an absorbance of 0.05 at 370 nm and a dissolved organic carbon concentration of about 5 mg/L or ppm. (d) The appropriate amount of the test chemical is introduced to the test media immediately prior to

irradiation.ENV/JM/TG/RD(2006)1/REV

66 2. SNW

- N (S imulated Natural Water with Added Nitrate):

(a) Prepare test media as for SNW, Steps a through c ; (b) Add nitrate as NaNO 3 or KNO 3 . In freshwater streams of the United States, average nitrate concentrations range from less than 0.1 mg/L to approximately 4 mg/L with the highest concentrations in agricultural followed by urban areas (USGS 1993). The mean nitrate concentration in some lakes may range up to 9 ppm (22). Nitrate concentrations in the agricultural and urban areas of Europe often exceed 9 mg/L ( German personal communication). (c) The test chemical is introduced immediately prior to irradiation.

3. NW (Natural Water):

Natural surface water may be taken from lakes, rivers, ponds, streams, creeks or coastal water

bodies where the test chemical is expected to be present. Proper water sample collection and characterization is required. The geographical location (including longitude and latitude), site

characteristics and date of collection should be recorded.

Collection and Sampling

(a) Sample c ontainers such as polyethylene bottles should be soaked in 10% HNO 3 overnight, thoroughly washed, and then rinsed with distilled water at least three times. (b) Samples are collected from the surface (top few centimeters) of the selected water body. (c) Wa ter samples that are not used shortly after collection should be stored at 4 o C.

Characterization

In the laboratory: The dissolved organic carbon (DOC), pH, and nitrate/nitrite need to be determined (61). As an option, additional factors that influenc e indirect photolysis can be determined including diisolved oxygen, redox potential, alkalinity, turbidity, other major major anions (HCO 3 - , Cl

- , SO 4 2

- ), major cations (Na + , K + , Ca 2+ , Mg 2+ ) and other metal ions such as iron and manganese (61).

All wate rs (SNW, SNW

- N, and NW) prepared for the indirect photolysis test should be filter

- sterilized

with a 0.2 μ m filter. The absorptivity should be computed at 350 nm (absorptivity =

2.303 x absorbance/pathlength). Computing the absortivity at 350 nm in SHW, SH W

- N, and NSW provides an estimate of CDOM. CDOM exhibits a much stronger correlation with indirect photolysis rates

than DOC.ENV/JM/TG/RD(2006)1/REV

67 ANNEX 6

EXAMPLE OF A SUNTEST APPARATUS EQUIPPED WITH A XENON ARC LAMPENV/JM/TG/RD(2006)1/REV

68 EXAMPLE OF A MERRY-GO-ROUND APPARATUS FOR DIRECT PHOTOLYSIS STUDIES

OPTICAL BENCH FOR QUANTUM YIELD DETERMINATIONSENV/JM/TG/RD(2006)1/REV

69 EXAMPLE OF A FLOW-TROUGH SYSTEM FOR DIRECT PHOTOLYSIS STUDIES

EXAMPLE OF A STATIC SYSTEM FOR DIRECT PHOTOLYSIS STUDIESENV/JM/TG/RD(2006)1/REV

70 ANNEX 7

Advantages and Disadvantages of Monochromatic and Polychromatic irradiation

1. The main advantage in using monochromatic irradiation to determine the test substance quantum yield of the test substance is that (as will be shown later by equations 19 through 21) it eliminates the need to directly measure the incident monochromatic irradiation. However, a disadvantage is that it will take longer to determine the quantum yield with monochromatic irradiation than with the use of polychromatic irradiation because the actinometer and the test substance are absorbing photon fluxes at just one wavelength instead of over multiple wavelengths.

2. The main advantage in using polychromatic irradiation (filtered xenon arc lamp or sunlight) instead of monochromatic irradiation to determine the test substance quantum yield is that the time required to determine the quantum yield may be substantially shorter (8). The reason is due to the absorption of photon fluxes by the actinometer and test substance over multiple wavelengths instead of just one wavelength. The main disadvantage in using polychromatic irradiation to determine the test substance quantum yield is that unlike with monochromatic irradiation (as will be shown later by equations 20 and 21), its use requires the determination of the photon flux.

3. The advantage in using sunlight instead of a filtered xenon arc lamp, if polychromatic irradiation is used to determine the quantum yield, is that tables of average solar intensities as a function of season and latitude are readily available. Also, if sunlight is used, it eliminates the necessity of having a monochromatic or polychromatic artificial light source. However, if sunlight is used, an actinometer with an adjustable quantum yield is needed so the direct photolysis rate of the actinometer can be adjusted to be comparable to that of the test substance under the same irradiation conditions (2)(12). Parallel exposure of the test substance and actinometer to sunlight over comparable time frames minimizes errors due to changes in solar flux caused by fog, varying cloud cover, etc. (12)(53).

4. An example of an adjustable quantum yield ac tinometer is the p-nitroacetophenone - pyridine (PNAP-PYR) actinometer (54). For a 1.0 X 10 -5 M p-nitroacetophenone solution, the quantum yield of the actinometer in experiments carried out with monochromatic irradiation at 313 nm can be adjusted by varying the concentration of pyridine in the solution according to the following equation (2)(12):



# φ

act 

# pyridine = • 0 0169

.[ ] [eq. 1]

where: φ act 

### = quantum yield of the 1.0 X 10 -5 

### M p-nitroacetophenone [pyridine] = molar concentration of pyridine

5. Suitable chemical actinometers used in aqueous photochemical studies include the following:ENV/JM/TG/RD(2006)1/REV

71 ANNEX 7 (continued)

Actinometer System Literature Citation (a)p-nitroacetophenone/pyridine 54 (b) p-nitroanisole/pyridine 28, 54 (c) valerophenone 55
(d) ferrioxalate 21, 25, 43, 56, 57 (e) o-nitrobenzaldehyde 43, 54 (f) Reinecke’s salt 12 (g) aberchrome 540 58, 59
(h) azobenzene 60, 61 (i) oxalic acid/uranyl sulphate 8

6. The first two actinometers listed in the above table have adjustable quantum yields and are therefore particularly useful when solar irradiation is used (12). The first three actinometers listed in the table are low optical density actinometers and the last four are high optical density actinometers. The characteristics of those actinometers including the optimal wavelength range for their use are discussed in

references 12 and 62. Other chemical actinometers are described in the IUPAC document on chemical actinometers (62).ENV/JM/TG/RD(2006)1/REV

72 

### DRAFT DOCUMENT

November 2004 August 2000

ANNEX 2



## OECD GUIDELINE FOR TESTING OF CHEMICALS

PROPOSAL FOR A NEW GUIDELINE

Phototransformation of Chemicals in Water

- – Part 2: Direct and Indirect Photolysis

INTRODUCTION

1. This guideline provides guidance for conducting phototransformation in water studies to determine the potential effects of solar irradiation on chemical pollutants in surface water. Such studies determine phototransformation kinetics, products, and product pathways resulting from both either direct and (as an option or if applicable) or indirect aqueous photolysis. It is based on current and /or proposed methods (references 1 through 10) and on relevant literature on environment al aqueous photochemistry. Part 2 of this guideline deals with indirect photolysis.

2. A glossary of definitions (11) and symbols/units are provided in Annexes 1 and 2 respectively.

ENVIRONMENTAL SIGNIFICANCE AND USE

3. Chemical pollutants and/or their transformation products that are potentially susceptible to direct and/or indirect photolysis include those that are transported to surface water by direct point discharge and/or by runoff from urban and/or rural areas. Chemical pollutants in surface water also often originate from transformation of other chemicals via hydrolysis, photolysis, and biotransformation.

4. Direct photolysis in natural water involves th e transformation of a chemical resulting from the direct absorption of a solar photon (references 12 through 20 18 ). Indirect photolysis in natural water

sometimes involves the transformation of a chemical due to energy transfer from naturally occurring photosensitizers in electronically excited triplet states (12)(13)( 21 19 )( 22 20 ). However, indirect photolysis

more often involves the transformation of a chemical due to reactions with transient oxidants such as hydroxyl radicals, molecular oxygen in a singlet electronic state (“singlet oxygen”), and peroxy radicals (references 12 and 2 4 2 through 3 4 2 ). Both triplet state photosensitizers and transient oxidants result from the absorption of solar photons by chromophoric dissolved organic matter (CDOM) and nitrate ion (12)(2 3 1 )(3 4 2 )(3 5 3 )(3 6 4 ) (37)(38)(39)(40)

.

5. Direct photolysis can be an important dissipation pathway for some chemical pollutants that exhibit significant light absorption above the 295 290 nm cutoff of solar irradiation at the earth’s surface. Indirect photolysis can also be an important dissipatio n pathway for some chemical pollutants that come in contact with photosensitizers in electronically excited triplet states or with short-lived photochemically generated oxidants such as hydroxyl radicals and singlet oxygen. In some cases both direct and indirect photolysis can contribute significantly to the dissipation of a chemical in natural waters.

6. The direct and indirect phototransformation of chemicals in natural water bodies is a complex process which depends on a number of factors such as:ENV/JM/TG/RD(2006)1/REV

73 (a) the chemical structure and electronic absorption spectrum of the chemical; (b) the concentration, composition, and absorption spectra of CDOM (from which photosensitizers and singlet oxygen arise); (c) the concentration of nitrate (the primary source of hydroxyl radicals); and (d) the solar photon flux spectrum to which the chemical, CDOM and nitrate are exposed.

7. The solar photon flux spectrum to which a chemical, CDOM, and nitrate are exposed depend on numerous factors including the latitude, season, and the physical and chemical properties of the water body (12)(18)( 41 35 )( 42 36 ). Important properties of the water body which contribute to the attenuation of solar irradiation with depth include the concentration and composition of CDOM and suspended particulates. The mixing and stratification properties of the water will help determine the horizontal and vertical distribution of the chemical, CDOM, and nitrate.

8. The results of phototransformation in water studies are used in conjunction with physical chemical properties and data from other studies (abiotic hydrolysis; biotransformation; adsorption/desorption) to help assess the overall environmental transformation and transport of chemical pollutants. The results of phototransformation in water studies are also used to help develop inputs for environmental fate computer models, and to help develop protocols for conducting other aquatic laboratory and/or aquatic field studies.

PRINCIPLE OF THE STUDY

Scope and approach

9. This part of the test guideline is designed to provide some or all of the following data and/or information depending upon specific needs:

• The quantum yield and resulting estimated direct photolysis rate constants for test chemicals for various types of water bodies (defined by depth and light attenuation), seasons, and latitudes of interest.

• Direct pho tolysis rate constants for test chemicals determined in the laboratory using filtered xenon arc lamp or sunlight irradiation and extrapolated to natural water. A xenon arc lamp filtered to remove

irradiation < 295 nm will be referred to throughout the rest of the document as a filtered xenon arc lamp.

• The net (combined direct and indirect) and indirect photolysis rate constants of one or more test
chemical test substance s in a standard simulated natural water (containing humics as a surrogate for CDOM and in some cases, nitrate) and/or in one or more natural waters using a filtered Xenon arc lamp or sunlight irradiation.

. A xenon arc lamp filtered to remove irradiation < 290 nm will be referred to throughout the rest of the document as a filtered Xenon arc lamp.

• The transformation pathway and the identities, concentrations, and rates of formation and decline of major phototransformation products resulting from direct photolysis and/or indirect photolysis.

10. This guideline is designed as a tiered approach. Each tier is triggered by the results of the previous

tier. The T t iered approach es are proposed separately for direct and indirect photolysis tests is as shown in Figures 1 and 2, respectively (see Annex 3

. ).ENV/JM/TG/RD(2006)1/REV

74 Pseudo first-order kinetics of direct and indirect photolysis

11. The rate of decline of a test chemical test substance in either a n direct or indirect photolysis studyis generally assumed to follow pseudo first-order kinetics (e.g., time series data are fit to a pseudo firstorder kinetics model):



### d C

dt k C [ ] [ ] = − [eq. 1]

The integrated form of equation 1 is:

[ ] [ ]exp( )

C C kt = − 0 [eq. 2] The ln transformed version of equation 2 is:



# ln[ ] ln[ ] C C kt = − 0 [eq. 3]

where

C = test chemical test substance concentration at time t (mol/L)

C 0 = initial test chemical test substance concentration at time t = 0 k = pseudo first-order rate constant (1/unit of time)

t = time

t 1/2 = half

- life

The pseudo first-order rate constant is determin ed by using non-linear regression to fit data to equation 2 or using linear regression to fit data to equation 3.

The half-life can be determined by substituting the pseudo first-order rate constant into the following equation:



### t k d i 1 2 

### 2

/
( ) 

### ln

=

or [eq. 4]

where t 1/2 = half-life and

k d is the direct photolysis rate constant an d k i is the indirect photolysis rate constant.

Note : In the equations provided in this guideline, units for half-lives, pseudo first- order rate constants and photon fluxes are (for illustrative purposes) given in days, 1/day, and photons/cm 2 • day, respectively. However, other units of time such as hours or seconds may be used as long as there is consistency within the same equation. Units of concentration are given in mol/L. Other kinetic models may be applied if they better fit the kinetic data.

Direct photolysis

12. To undergo transformation via direct photolysis, a chemical molecule must first absorb a photon of light. The absorption of a photon by a molecule results in a transition from an electronic ground state to an electronically excited state of the molecul e. To be absorbed by the molecule, the energy of the photonENV/JM/TG/RD(2006)1/REV

75 ( which is inversely proportional to its wavelength) must correspond to the difference between the ground and a possible excited electronic state of the molecule (12). Within the UV

- Visible wavelen gth of interest ( 295

- 800 nm), photons energies range from 150 kJ/mol at 800 nm to slightly greater than 400 kJ/mol at

295 nm (11)(37).

13. The absorption of a photon is a necessary, but often not a sufficient condition, for a molecule to undergo transform ation via direct photolysis (12)(14)(37). The absorbed energy must first be sufficient to cause the transformation via bond cleavage, rearrangement, oxidation, or reduction. Then, phototransformation to form new molecular structures must compete with other possible deactivation processes such as quenching, other radiationless processes, and radiative processes. Consequently, the fraction of photon excited molecules that actually undergo phototransformation (e.g. the quantum yield) is generally much less tha n 1 (usually < 0.1 and sometimes < 0.01) (14)(21). The mechanistic aspects of phototransformation reactions at a molecular level are beyond the scope of this guideline (see reference 38 for further information).

14. It can be shown that for an optically d ilute solution (absorbance A < 0.02) of a chemical in pure water exposed to polychromatic irradiation above the cutoff of solar irradiation at the earth’s surface of 295 nm, the direct photolysis rate constant (assuming the quantum yield is independent of wavelength) is given by (12)(14through 18) (See Annex 4: Derivation of selected equations):



### k j l

D I d

sys



### = 

# ∑ 2 3

0

295 800



### . φ ε λ λ [eq. 5]

where:

k d = direct photolysis rate constant (1/day) φ = the quantum yield (independent of wavelength)

ε λ = molar absorption coefficient (L/mo l • cm; M - 1 •cm - 1 ) at wavelength λ

I 0 λ = photon flux (photons/cm 2 • day) over a 1 nm interval centered at wavelength λ

D sys = depth of irradiated system (cm) = volume of irradiated system/incident area

l = light pathlength (cm) j = conversion factor to make units consistent with the L/mol • cm unit of the molar absorption coefficient and the mol/L unit of concentration = 6.02 x 10 20

(L/cm 3 )(photons/mol)

Note : The term (l/D sys ) in equation 5 approximately cancels out for rectangular photolysis cells expos ed to irradiation from a filtered xenon arc lamp and for which D sys = D cell . However, that would not be true for cylindrical photolysis cells or for any photolysis cells exposed to solar irradiation where the pathlength l has a more complicated dependency on D cell. Methods for determining the pathlength of cylindrical cells exposed to filtered xenon

- arc lamps are discussed in references 12 and 17. Pathlength determinations as a function of the depth of a system, D sys exposed to solar

irradiation are discu ssed in references 12 and 18. In addition, note that if the quantum yield is not independent of wavelength, it must remain inside of the summation in equation 5.

15. Equation 5 is applicable to solar as well as filtered xenon arc lamp irradiation. However , the following equation is often used to determine the di rect photolysis rate constant for optically dilute

solutions of test chemical s in pure water in photolysis cells or in near surface, clear natural water exposed to solar irradiation (2)(12) (See Ann ex 4: Derivations of selected equations):ENV/JM/TG/RD(2006)1/REV

76 

### k L

d solar

( ) 

### = 

# ∑ φ ε λ λ

295 800

[eq. 6]

where:

k d = direct photolysis rate constant (1/day) φ = quantum yield (independent of wavelength)

ε λ = molar absorption coefficient (L/mol • cm) at wavelength λ

L λ = average daily solar photo n flux irradiance (mmol photons/cm 2 • day) over wavelength interval ∆ λ centered at wavelength λ

16. Equations 1, 5 and 6 show that direct photolysis kinetics are theoretically pseudo

- first order only if the photon flux remains constant over time. Photon flu xes from filtered xenon arc lamps at any given wavelength remain, in general, relatively constant over time. This is one of the primary advantages in using filtered xenon arc lamps. However, solar photon fluxes at any given wavelength vary cyclically over 24

- hour periods. Nevertheless, the data obtained from studies conducted in natural sunlight (in which the rate constant reflects an average over the entire study duration) generally do fit a single, pseudo

- first order rate constant model reasonably well. The reason is that changes in the average pseudo first

- order rate constant over time as the study progresses is generally relatively small and not systematic. This is particularly valid

for studies conducted for one to several weeks or for 2

- 4 hours mid

- d ay. It may not be as valid for studies lasting 4 hours to several days or for those conducted beyond 30 days.

Summary of the proposed tiered approach for direct photolysis

Tier 1: Theoretical screen

17. Estimate a maximum possible direct photolysis ra te constant for the test chemical in the near

surface of a clear natural water as follows. Measure the test chemical molar absorption coefficients from

295 nm to 800 nm, and use tabular solar irradiance for summer and 40 0 or 50 0 latitude over the same

wave length interval. Estimate a maximum possible direct photolysis rate by assuming the quantum yield in equation 6 is equal to one and by substituting the molar absorption coefficients and tabular solar
irradiance values, L λ

, into the equation (2)(12). Deter mine if the estimated maximum possible direct photolysis rate constant would theoretically result in estimated direct photolysis losses greater than 50% of an initial concentration over 30 days/nights. If maximum possible losses are < 50%, no further direc t photolysis work is performed, but proceed to Indirect Photolysis Tier 1 (experimental/theoretical screen), if required. If the maximum possible losses > 50%, proceed to Direct Photolysis Tier 2 (experimental screen and range finding) or to Direct Photoly sis Tier 3 (determination of the quantum yield).

Tier 2

- Experimental screen and range finding

18. Approximately determine the rate of decline in the concentration of the test chemical and corresponding direct photolysis rate constant in buffered pure w ater exposed to a filtered xenon arc lamp (recommended) or sunlight. Determine if the approximate direct photolysis rate constant would result in estimated direct photolysis losses equal or greater than to 20% of an initial concentration over

30 days/night s in the near surface of a clear natural water body exposed to summer sunlight. If estimated

losses are < 20%, no further direct photolysis work is performed, but proceed to Indirect Photolysis Tier 1 (experimental/theoretical screen), if required. If esti mated losses ≥ 20%, proceed to Direct Photolysis

Tier 3 (determination of the quantum yield). If the determination of the quantum yield is not required, proceed to Direct Photolysis Tier 4 (kinetics study).ENV/JM/TG/RD(2006)1/REV

77 Tier 3

- Determination of the quantum yield and its use to estimate direct photolysis rate constants

19. Determine the quantum yield for direct photolysis of the test chemical in buffered pure water using monochromatic irradiation (12), polychromatic artificial irradiation (8) or sunlight (2). Once th e quantum yield has been determined, use it as input to com puter programs such as GCSOLAR (18) or ABIWAS (35)(36) to help estimate direct photolysis rates for the test chemical applicable to any types of surface waters (defined by depth and light attenuati on), seasons, and latitudes of interest (2). If the Direct Photolysis Tier 4 study is potentially applicable, determine if the direct photolysis rate constants estimated from the quantum yield would result in estimated direct photolysis losses greater th an or equal to 20% of the initial concentration over 30 days/nights in the near surface of a clear natural water body exposed to sunlight. If the estimated losses are < 20%, no further direct photolysis work is required but proceed to Indirect Photolysis T ier 1 (experimental/theoretical screen), if required. If the estimated losses are > 20%, proceed to the Direct Photolysis Tier 4 kinetics study.

Tier 4

- Kinetics study on the parent and, if applicable, major transformation products

20. Determine the ra te of decline in the concentration of the test chemical and corresponding direct photolysis rate constant in buffered pure water exposed to a filtered xenon arc lamp (recommended) or sunlight. If applicable, also identify/quantify and determine the rates o f formation and decline of major transformation products. In this guideline, major tr ansformation products are defined as those accounting

for ≥ 10% of the applied test chemical at any sampling time.

Indirect Photolysis

12. 21 . To undergo transformation via indirect photolysis, the test substance must:

• receive energy from a photosensitizer in an excited electronic triplet state such as various ones generated from the solar irradiation of CDOM (12)(14)( 21 19 )(2 2 0 ), or

• react with a photochemically generated oxidant such as a hydroxyl free radical, a singlet oxygen, or a alkylperoxy free radical (references 12 and 2 3 1 through 3 4 2 ). Singlet oxygen and alkylperoxy free radicals appear to be generated primarily from the solar irradiation of CDOM in oxygenated natural waters. Some hydroxyl free radicals also appear to originate from the solar irradiation of CDOM. However, the major source of the hydroxyl free radical in natural waters appears to generally be the solar irradiation of nitrate (2 3 1 ).

13 22. In infrequent cases where the nitrate to nitrite ratio is less than 100 in aerobic surface waters, the photolysis of nitrite (which is present in much lower concentrations than nitrate) may also contribute significantly to the formation of hydroxyl radicals because “nitrite photoproduces OH radicals about 50 times more rapidly than nitrate” ( 43 39 ).

14. 23. The transformation of chemical pollutants in surface waters may also occur via photoredox reactions with soluble and insoluble Fe (III) species, which are commonly present at significant concentrations in many surface waters (4 4 0 )(4 5 1 ).

15. 24. Indirect photolysis kinetics are actually closer to being second-order than first-order because the

rate of decline of the test chemical test substance is generally proportional to the product of the test
chemical test substance and sensitizer or photooxidant concentrations (12)(2 2 0 )(2 3 1 ). However, although transient photooxidant and excited photosensitizer concentrations are very low (typically below 1 x 10 -10
M), they can quickly attain quasi steady-state concentrations in irradiated solutions thereby leading to pseudo first-order kinetics (12)(2 2 0 )(2 3 1 ).ENV/JM/TG/RD(2006)1/REV

78 16. 25. In many cases, the net pseudo first-order rate constant for indirect photolysis will reflect the reaction of different molecules with more than one type of sensitizer and/or oxidant:



# ( ) k k S or

indirect j nd j ss 

### = 

# ∑

( ) () 2 

### Ox j(ss) j=1 j=n

[eq. 5 7 ]

where:

k indirect = net pseudo first-order indirect photolysis rate constant (1/day)

k j(2nd) = second order rate constant for the reaction with sensitizer j or oxidant j (L/mol • d)

S j(ss) = steady state concentration of sensitizer j (mol/L)

Ox j(ss) = steady state concentration of oxidant j (mol/L)

Summary of the proposed tiered approach for indirect photolysis

Tier 1 - Experimental and/or theoretical screen

17. 26

. Perform an experimental screen in simulated natural water (SNW) containing humics as a surrogate for CDOM, and/or in a simulated natural water containing nitrate as well as humics (SNW-N) and/or in one or more natural waters (NW)

. and in buffe red pure water (PW) (3). Specifications for PW appear in paragraph 68

- a

. Approximately determine the rate of decline in the concentration of the test
chemical test substance in SNW, and/or SNW-N, and/or NW exposed to sunlight or a Xenon arc lamp to determine if indirect photolysis represents a potentially significant transformation pathway . The use of a xenon lamp light source for indirect photolysis studies is not recommended at this time . Determine if the

estimated indirect (not net) photolysis losses over the equivalent of 30 days /nights of sunlight exposure is greater than or equal to 20% of an initial concentration of the test chemical test substance . If the estimated indirect photolysis losses are < 20%), no further indirect photolysis work is performed. If the estimated indirect photolysis losses are > 20%, proceed to the Indirect Photolysis Tier 2 (kinetics study).

27. In some cases, it may be possible to supplement the Tier 1 experimental screen with a theoretical screen based on using structure activity relationships (SARs) to estimate rate constants for reaction with photooxidants and information on the typical concentrations of photooxidants in surface water (21).

Tier 2 - Kinetics study on the test substance parent and (if applicable) major t ransformation products

18. 28. Determine the rate of decline in the concentration of the test chemical test substance and its corresponding net and indirect photolysis rate constants in SN W, and/or SNW-N and/or one or more NWs

irradiated with a Xenon lamp or sunlight

. and in PW. Determine if the indirect photolysis rate constants would result in estimated losses greater than or equal to 20% of the initial concentration over a period equivalent to 30 days in the near surface of a clear natural water body exposed to sunlight. If the estimated losses are <20%, no further indirect photolysis work is required. If the estimated losses are ≥ 20%, proceed

to Tier 3. If data on transformation products for indirect photolysis are applicable, identify/quantify major transformation products and determine their rates of formation and decline. In this guideline, major transformation products are defined as those accounting for > 10% of the applied test chemical (percent of applied radioactivity or molar basis) during any part of the study.ENV/JM/TG/RD(2006)1/REV

79 Tier 3 – Identification of major phototransformation products

19. Estimate the rates of formation and decline ofphototransformation products in SNW and/or SNWN and /or NW exposed to a filtered Xenon lamp or sunlight. Isolate and identify the major phototransformation products. In this guideline, major transformation products are defined as those acconting for ≥ 10% of the applied test substance in an individual sample at any sampling time.

APPLICABILITY OF THE TEST GUIDELINE

20. 29. This test guideline is applicable to chemical substances for which analytical methods with sufficient accuracy and precision are available and validated (if required). If data are needed on transformation products, adequate quantitative analytical methods must also be available/developed for

them.

21. 30. If a non-ionic test chemical test substance is somewhat susceptible to hydrolysis, the test may still be applicable as long as a dark control is used to account for the hydrolysis rate (2)(4)(5). However, photolysis tests should be conducted at a pH at which the hydrolysis rate of the chemical is minimized (5)(4 6 2 ). The rate constant determined from the dark cont rols should be identical to the hydrolysis rate

constant and can be subtracted from the overall rate constant determined from the irradiated solutions to give the direct photolysis rate constant. However, in some cases, the desired test chemical test substance may undergo rapid hydrolysis (i.e., hydrolysis half-life of < 1 day) within the environmentally relevant pH range of 4 5 -9 at 20-25 o C (47) . In such cases, the photolysis study should instead be conducted on each the major hydrolytic product (s) (> 10% of applied ) as the test substance )

.

22. 31. The test is not applicable to highly volatile compounds such as fumigants and some organic solvents. However, in some cases, where the Henry’s Law constant of the test chemica l test substance and/or anticipated transformation products may indicate the potential for fairly substantial volatilization rates from water, the study may still be applicable provided that precautions are taken. Such precautions include using minimal head-space, adequate sealing in the photolysis cells to minimize volatile losses during the study (2)(4) or trapping. Trapping volatiles becomes more difficult, but preferred, when employing sacrificial sampling on numerous small photolysis cells than when employing aliquot sampling on a smaller number of much larger test vessels. However, with the proper equipment and experimental set-up, it can be done as shown by Ruzo (4 8 3 ).

INFORMATION ON THE TEST SUBSTANCE

23. Unlabelled or labelled test substances can be used to measure the rate of photolysis. Labelled material is required for studying the pathway of phototransformation and for establishing a mass

balance. 14 C-labelling is recommended but other isotopes, such as 13 C, 15 N, 32 P, may also be useful. As far as possible, the label should be positioned in the most stable part(s) of the molecule 2 . The chemical and radiochemical purity of the test substance should be at least 95 %.

24. 32. Before carrying out any of the phototransformati on tests, the following information on the test

substance should be known, if available:

2 For example, if the test substance contains one ring, labelling on this ring is required; if the test substance contains two or more rings, separate studies may be needed to eval uate the fate of each ring and to obtain suitable information on formation of phototransformation products.ENV/JM/TG/RD(2006)1/REV

80 (a) Solubility in water [OECD Guideline 105]. (b) Solubility in organic solvents ( c b ) Vapor pressure [OECD Guideline 104] ( d c ) Henry’s Law Constant *

( e d ) Abiotic hydrolysis as a function of pH [OECD Guideline 111] ( f e ) n -octanol/water partition coeffici ent [OECD Guidelines 107 and 117] ( g f ) pK

a (s) of ionisable substances [OECD Guideline 112] (g) Chemical nomenclature (IUPAC and CAS) (h) Chemical Abstract Registry Number of the test substance (i) Common name(s), if any (j) Chemical structure (k) Position(s) of radiolabelled atom(s) or other molecular tags (if applicable) (l) Isomer purity (if applicable)

Note : The temperatures at which the physical chemical properties listed above in the previous paragraph were determined should generally be reported. within the range of (25 ± 5) ° C and

should be specified.

33. If available, the solubility in non

- aqueous solvents may be useful in selecting a co

- solvent or extractant. Also, the f ollowing optional information may be useful for indirect photolysis studies conducted

in natural water:

- Aerobic

- Anaerobic Transformation in Aquatic Sediment Systems [OECD draft Guideline 308]

- Adsorption / Desorption [OECD Guideline 106]

25. 34

. The n-octanol/water partition coefficient and aqueous solubility supply some information on the potential of the test chemical test substance to significantly adsorb to glassware and reaction vessels. However, any additional information on the glassware adsorption potential of the test chemical test
substance should be known to ensure that such characteristics are taken into account in preparing glassware and reaction vessels for the study.

26. An appropriate analytical method of known accuracy, precision and sensitivity for the quantification and identification of the test substance and its phototransformation products should be available. The analytical detection limit for the test substance and its phototransformation products should also be known (see paragraph 31).

ANALYTICAL METHODS AND QUALITY CRITERIA

35. The experimenter should develop methods with appropriate accuracy (recovery), precision (reproducibility), and adequate limits of detection (LOD) and quantification (LOQ). In many instances,

v alidation of the analytical methodology may be requi red. In those cases, the experimenter should be responsible for ensuring that the analytical methods have been validated.

36. The analytical methods that may be used include liquid scintillation countin g (LCS) and radiochromatography (radiolabelled substances), high

- performance liquid chromatography (HPLC), gas

* Henry’s Law constant estimated from solubility in water and vapour pressure or measured. Henry’s Law constants for some chemicals may also be found in: http://webbook.nist.gov/chemistryENV/JM/TG/RD(2006)1/REV

81 chromatography (GC), gas

- liquid chromatography (GLC), and capillary electrophoresis (CE), etc. TLC can

also be used for radiolabelled test chemic al s, but only if adequate resolution can be achieved and there is no decomposition of the reference standards in the silica plates.

37. When necessary to identify and/or confirm transformation products, the separation methods listed in the preceding parag raph may be coupled with spectrometric methods such as mass spectrometry (MS)

and/or Fourier

- Transform Infrared spectroscopy (FT

- IR). Examples of such couplings include as GC/MS,
HPLC/MS, LC/MS

- MS, GC/FT

- IR or any other adequate techniques.

38. Referenc e chemicals of potential transformation products may be used for identification (e.g. by

co

- chromatography). When radiolabelled test substance is used, it may be necessary to use radiolabelled reference chemicals. However, as indicated in the previous para graph, the identities of major transformation products need to be confirmed preferab ly by an independent analytical chemistry method such as with MS. Transformation products that cannot be identified from reference chemicals should be elucidated using, for example, MS, NMR and infrared spectroscopy.

39. Parameters that can influence the accuracy and/or precision of the determination of chemical concentrations in aqueous media include the stability of the chemicals in samples during storage, extraction

effi ciency, analytical separation efficiency in mixtures, and the magnitude of the concentrations with respect to analytical detection and quantification limits.

40. Analytical instrumentation should be periodically calibrated within applicable concentration ranges according to the manufacturer’s specifications. If samples are stored prior to analysis, storage stability tests may need to be performed depending upon the storage method and duration. The accuracy and precision of the analytical method should be checked within the expected concentration range. Accuracy can be determined from the recovery percenta ges of spiked samples. Precision can be determined by replicate analyses of an appropriate percentage of the samples.

41. Regardless of the chosen analy tical method, analytical recoveries for radiolabelled test chemical s should fall within 90% and 110% of the applied radioactivity. For non

- radiolabelled test chemical s, analytical recoveries of 85 to 115% are desirable.

42. For radiolabelled materials, to tal mass balance should fall within that range 90% to 110% of the total applied radioactivity (42).

REFERENCE SUBSTANCES

27. Reference substances should be used for the characterisation and/or identification of phototransformation products by spectroscopic and chromatographic methods.

QUALITY CRITERIA

Recovery

28. Extraction and analysis of, at least, duplicate samples immediately after the addition of the test substance gives a first indication of the repeatability of the analytical method and of the initial recoveries for the test substance. Recoveries for later stages of the experiments are given by the respective mass balance obtained with labelled material. Recoveries should range from 90 to 100 % for labelled chemicals (49) and from 70 to 110 % for non-labelled chemicals (7).ENV/JM/TG/RD(2006)1/REV

82 Repeatability and sensitivity of analytical method

29. Repeatability of the analytical method (excluding the initial extraction efficiency) to quatify test substance and phototransformation products can be checked by duplicate analysis of the same extract , incubated long enough for formation of phototransformation products.

30. The limit of detection (LOD) of the analytical method for the test substance and for the phototransformation products should be at least 0.01 mg/kg water (as test substance) or 1 % of the applied dose whichever is lower. The limit of quantification (LOQ) should also be specified.

Accuracy of transformation data

31. Regression analysis of the concentration of the test substance as a function of time gives the appropriate information on the reliability of the photo transformation curve and allows the calculation of the confidence limits for half-lives (in case of pseudo first-order kinetics) or DT 50 values and, if appropriate, DT 75 and DT 90 values.

TEST MATERIALS

Test vessels

32. 43. All glassware and reaction vessels/photolysis cells used in the photolysis studies must be sterilized by autoclaving (2)(3)(4)(12) or by any other suitable non-chemical method (2) . Chemical sterilization is not recommended since chemical reagents may leave residues that could absorb in the

295 290 to 800 nm region and/or behave as photosensitizers.

Test substance application

33. The test substance should be directly dissolved in the aqueous media at a concentration which should not exceed half its solubility. For test substances with low aqueous solubility, a co-solvent may be used to prepare the test solution. However, the amount of co-solvent used must be as little as possible and preferably not exceed 1% by volume in the test solution (46). Co-solvent percentages up to 10% may be used, but if more than 10% co-solvent is required to dissolve the test substance, the study should not be performed. The selected co-solvent must not solvolyse the test substance, must not absorb in the 290 to 800 nm region, and must not be a photosensitizer. Acetone is an example of a solvent that is a photosynthesizer, and should not be used. Acetonitrile is a generally recommended co-solvent.

34. The initial concentration of the test substance for indirect photolysis studies should be such that the absorbance at any wavelength above 290 nm (maximum absorption wavelength included) is less than 0. 02. These optically dilute, also referred to as “optically thin” solutions generally have a concentration of < 10 -4
M. Nevertheless, the initial concentration of the test substance should be at least 10 times greater than the quantification limit of the analytical method.

35. Because oxygen can affect the rates and even pathways of photodegradation reactions, test solutions should be saturated with air at the beginni ng of the study (4). A buffer solution that has been autoclaved should be given sufficient time to aerate prior to dispensing into the vessels. It is not recommended to autoclave small amounts of buffer in individual vessels because driving the air out may change the volume.ENV/JM/TG/RD(2006)1/REV

83 44. If radiolabelling is used, test chemical s should be labelled at one or more atoms within each stable or relatively stable portion of the molecule. For chemicals containing one or more aromatic rings, one or more atoms in each ring are usually labelled. In addition, one or more atoms on both sides of any linkage thought to be readily susceptible to cleavage should be radiolabelled (42). Radiolabelling is particular ly important when there is the need to identify transformation pahtways. Radiolabelling does not have to be limited only to 14 C. For example, in some cases, 32 P can be used in place of or in addition to 14 C (42). If mass spectroscopy is used, stable isotop es such as 15 N can also be used as molecular tags.

45. Radiolabelled test substances should have radiochemical and chemical purities of 95% or greater (42). Non

- radiolabelled test substances should have a chemical purity of 95% or greater (42).

46. If the test chemical consists of more than one geometrical and/or optical isomer, the percentage represented by each isomer should be provided.

47. Pesticide testing should generally be conducted with the active ingredient. The same generally applies to ph armaceutical chemicals. However, in some instances it may be more appropriate to use a formulated product.

48. If the potential loss of the test chemical by volatilization or adsorption to test vessels is of concern or if the identification and quantifica tion of major transformation products are of interest, radiolabeling should be used.

Test media

36. 49. Guidance for preparing test media for direct and indirect photolysis respectively is provided in

Annex 5.

Test media for direct photolysis

50. For d irect photolysis studies, the test media should be sterilized aqueous buffer solutions at the appropriate pH. The water should be “pure water” (PW). The buffers should be identical or comparable to those used in the hydrolysis studies and should not absorb between 295 and 800 nm or be photosensitizers. Also, the buffers should not adversely affect the solubility of the test chemical

.

51. If the test chemical is non

- ionizable and is approximately stable to abiotic hydrolysis at pH 7, the

buffer used in the direct photolysis study should maintain a pH of approximately 7. However, if the hydrolysis rate of a non

- ionizable test chemical at pH 7 is significant, but its hydrolysis rate at pH 5 or 9 is much lower, the buffer used should maintain a pH (within the 5 to 9 range) at which the hydrolysis rate is minimized (42).

52. If the test chemical is appreciably ionic anywhere within a 5 to 9 pH range, the study should be conducted in one or more aqueous buffers at any of the pH 5, 7, and/or 9. Selection of the pH (s) at which the study should be conducted depends on the electronic absorption spectra at each pH. Spectra showing absorption bands between 295 and 800 nm or shorter wavelengths tailing above 295 nm together with estimates of maximum photolysis rates (Tier 1: Direct Photolysis) are the criteria for selecting the pH(s). Refer to Tier 1, Direct Photolysis for further details.

53. For test chemical s with low aqueous solubility, a co

- solvent may be used to prepare the test solution. However, the amount of co

- solvent used must be as little as possible and preferably not exceed 1% by volume in the test solution (42). Co

- solvent percentages up to 10% may be used, but if more thanENV/JM/TG/RD(2006)1/REV

84 10% co

- solvent is required to dissolve the test chemical , the study should not be performed. The selected

co

- solvent must not solvolyse the test chemical , must not absorb in the 295 to 800 nm region, and must not be a photosensitizer. Acetone is an example of a solven t that is a photosynthesizer, and should not be used.

Acetonitril e is a generally recommended co

- solvent.

Test media for indirect photolysis studies

37. 54. The selection of test media for indirect photolysis studies depends on the purpose of the study. The preparation of test media is based on the procedure given in OPPTS 835.5270 guideline (3). Three test media may be used for these studies: (1) SNW (Simulated Natural Water); SNW-N (Simulated Natural Water with Nitrate); and (3) NW (Natural Water). SNW-N may be appropriate for areas where surfacewaters show strong evidence of nitrate pollution associated with the use of fertilizer and other nitratebearing substances. Nitrate has been known to photochemically produce hydroxy radical s (2 3 1 )(2 4 2 )(2 8 6 ) (50) . NW may be important in situations when the understanding of the photochemical

behavior of chemicals in actual natural surface waters is of interest.

38. 55. Humic acid or other humic materials may be obtained commercially (Aldrich, Fluka, etc.). Humic and fulvic acid extracted from soils or natural surface water may be used as surrogates for aquatic humic acids (2 5 3 )( 51 4 4 ). Composite data for typical humic acids are available from the International Humic Substances Society ( 52 45 ). The UV-VISIBLE spectra of the selected humic materials in the test media (natural water and/or buffered SNW) should be provided. The absorption spectra of some humic

materials are shown in reference 53 46

.

Light sources

39. 56. For in direct photolysis studies the recommended light source should be a filtered xenon arc lamp capable of simulating natural sunlight in the 295 290 to 800 nm region or sunlight ( 54 47 ). For indirect photolysis studies, the only recommended light source at this time is sunlight. The photon flux of the filtered xenon arc lamp as a function of wavelength should be determined at least at the beginning and the end of the study using one or more actinometers and or a spectral radiometer

. if available. If sunlight is used, average daily solar photon fluxes (L λ ) as a function of wavelength should be determined for the season and latitude closest to those of the experiment using solar irradiance tables and a spectral

radiometer

. , if available.

40. 57. If a filtered xenon arc lamp is used, the irradiation photon flux incident on the test vessels should be adequate to cause substantial decline of the test chemical test substance over a several day experimental period. The transformation rate constant and corresponding half-life obtained with a filtered xenon arc lamp can be adjusted to solar equivalents from a comparison of solar photon flux to lamp photon flux because of the linear relationship between the transformation rate and photon flux (see equation 14).

41. 58. If sunlight is used, the study should be conducted during the season when and at the latitude

where the concentration of the test chemical test substance is expected to be highest in the environment. For pesticides, that would be the season when and the latitude where it is typically applied.

42. 59. If a filtered xenon arc lamp (see part 1, Annex 6) and sacrificial sampling of multiple test vessels are used, an appropriate experimental set-up should be used to ensure that all of the test vessels receive the same incident irradiation flux. Self-contained, commercially available xenon photolysis units in the projection or “working plane” configuration produce uniform fluxes ( 55 48 )( 56 49 a). A commonly used configuration is the “merry-go-round” photochemical reactor (12). Merry-go-round photochemical reactors are commercially available ( 56 49 a)( 56 49 b). Another example of an experimental set-up is shown reference

5 7 0 (see part 1, Annex 6)

. An e E xperimental set-up s that includes trapping of volatiles appears in referenceENV/JM/TG/RD(2006)1/REV

85 (4 8 3 ) and are also shown in Part 1 Annex 6

.

Other photolytic equipment and reagents

43. 60. Photolytic equipment includes:

• Optical cells of appropriate material (generally qua r tz) and path length for measuring UV-VIS spectra.

• Appropriate optical filters to cut-off radiation below 295 290 nm and above 800 nm.

• When monochromatic irradiation is used in the determinat ion of the quantum yield, the appropriate filter systems must be used to isolate the desired wave length (12)(47). Monochromatic irradiation at the desired wavelength can also be achieved with a monochromator in conjunction with a suitable polychromatic li ght source such as a mercury or xenon arc lamp. (Filters for isolating the 313 and

366 nm wavelengths from a mercury arc lamp are discussed in reference 12).

• Specially designed reaction cuvettes/photolysis cells to contain test solutions (exposed and dark control) and chemical actinometers, when needed. The recommended material is quartz.

• Appropriate apparatus designed to contain the light source, filters, sample, holders, reaction vessels/actinometers such as the photochemical “merry-go-round” reactor. Several appropriate designs

are commercially available to accommodate specific needs. shown in Part 1, Annex 6.

• Photometer or spectral radiometer to meas ure photon flux as a function of wavelength.

44. 61. Photolytic reagents include:

• All of the water used in the direct photolysis tests must be of high purity and free of any absorbing or photosensitizing chemical species. For example, the U.S.EPA OPPTS 835.2210 (2) recommends using reagent water meeting ASTM Type IIA standard s, as described in ASTM D1193-99 Standard Specification for Reagent Water (see Annex 5: Test Media). “Milli-Q” water is one example of high purity water. In this guideline, the water used in the preparation of stock, test and buffer solutions is referred as “pure water”.

• Appropriate chemical reagents to be used as actinometers.

• Commercially available, certified humic material for indirect photolysis studies (Fluka; Aldrich).

• Analytical grade NaNO 3

• Appropriate aqueous buffers such as phosphate for pH 7, acetate for pH 5 and borate for pH 9 for compatibility with hydrolysis studies. Phosphate buffers are usually recommended for direct photolysis studies(2)(12).

• Analytical equipment and chemical reagents

45. 62. In addition to standard laboratory equipment, the following is required:

• Spectrophotometer to acquire spectral data in the UV-VIS range. For example, single beam, diode array instruments that allow sensitive, rapid acquisition of digitized spectral absorbance data.

• Appropriate analytical instrumentation to measure the concentration of the test substance in exposed and dark control samples, such as HPLC, GLC, TLC, etc.

• Suitable instrumentation for identification purpos es, such as MS, HPLC/MS, GC/MS, LC/MS, GCFTIR, NMR, etc.

• When radiolabelled test substances are used, liquid scintillation counters (LSC) and instrumentation for radiochromatography should be available.

• Appropriate extraction apparatus.

• Equipment to sterilise reaction vessels and other glassware used in the preparation of stock and test

solutions.ENV/JM/TG/RD(2006)1/REV

86 46. 63. Chemical reagents include:

• Reagent grade chemicals and solvents free of any photosensitizer.

• Scintillation liquid (for radiolabelled chemicals).

64. Analytical references include:

• Test substance reference standards for co

- chromatography and/or for other analytical methods.

• Potential transformation products (including hydrolysis products) reference standards for the determination of products, if applicable.

TEST METHODOLOGY

Test conditions

47. 65. The temperature during photolysis studies may vary by as much as 10 degrees but should be maintained within the range of 20 to 30  ̊ C. (25 ± 5) o C and periodically monitored.

.

48. 66. The pH of buffered solutions should be maintained within + 0. 1 5 pH units. The pH should be checked during the course of the study, if feasible.

49. 67. Dark control solutions should be used for all quantum yield determinations and for all direct and indirect photolysis studies and should be kept at the same temperature as the irradiated samples

.

68. The concentration of the chemical in the test media should never exceed half its solubility. When

a co

- solve nt is needed, it should preferably not exceed 1% by volume in the test solution and never exceed 10% by volume.

69. The initial concentration of the test chemical for quantum yield determinations and direct photolysis studies should be such that the abso rbance at any wavelength above 295 nm (maximum absorption wavelength included) is less than 0.02. These optically dilute, also referred to as “optically thin”, solutions generally have a concentration of < 10

- 4 M. Nevertheless, the initial concentration of the

test chemical should be at least 10 times greater than the quantification limit of the analytical method.

70. The concentration of the test chemical in simulated (SNW, SNW

- N) or natural water (NW) test media should be equivalent to that of optically dilute test solutions in pure water/buffer solutions required for direct photolysis studies.

71. Because oxygen can affect the rates and even pathways of photodegradation reactions, test solutions should be saturated with air at the beginning of the stud y (4). A buffer solution that has been autoclaved should be given sufficient time to aerate prior to dispensing into the vessels. It is not recommended to autoclave small amounts of buffer in individual vessels because driving the air out may change the vo lume.

Study duration, sampling, and replication

50. 72. The study duration should be sufficient to determine the DT 75 (two half-lives if decline is firstorder) of the test chemical test substance and (if applicable) the formation and decline of major transformation products until they have declined to < 25% of their maximum concentration. However, theENV/JM/TG/RD(2006)1/REV

87 maximum study duration should not exceed the equivalent of 30 days /nights of sunlight exposure during an appropriate season and at an appropriate latitude. The “DT 75 " is defined as the time required for 75% of the

initial concentration of test chemical to disappear.

73. Based upon equating photons absorbed by the test chemical per unit volume, the maximum direct photolysis study duration (using continuous filtered xenon arc lamp irradiation) that is equivalent to 30 days/nights of sunlight exposure will be only a few days and is given by (see Annex 4).

Max direct photolysis duration days j D

l L

I cell

xenon

xenon . ()

( ) = 

### ∑

∑ 30 295 800

0

ε

ε λ λ

λ λ [eq. 8]

where:

30 = 30 days/nights of solar irradiation

D cell = depth of irradiated cell (cm) = volume of irradiated cell/incident area

l

xenon = light pathlength in cell exposed to a filtered xenon arc lamp

and other terms same as defined for equations 5 and 6.

Note : For rectangular box cells, the term D cell /l

xenon cancels out because l

xenon = D cell . However, that will not be true for cylindrical cells (12).

51. 74. Although equation 8 allows for flexibility in choos ing an experimental photon flux from a filtered xenon arc lamp, practical considerations somewhat limit the range of experimental fluxes that should be

used. In general, it is recommended that the experimental photon flux from a filtered xenon lamp be adjusted to be somewhat comparable to that of sunlight (at noon for short several hour studies or 24 hour average for several day to weeks studies). The reason is the experimental flux should not be so intense that photolytic processes other than those that would occur under natural sunlight are initiated. Also, if the test
substance parent is susceptible to hydrolysis at the experimental pH and the hydrolytic products are susceptible to direct photolysis, time should be allowed for them to form.

52. 75. A preliminary range-finding study should be performed to help determine the number of samples to be collected and the timing of their collection. For linear and non-linear regressions on test chemical test
substance data in definitive or upper tier tests, the minimum number of samples collected should be five and seven, respectively. The greatest number of samples taken should generally be during the first part of the study where the slope of the concentration versus time series for the test chemical test substance is generally greatest. If an accurate determination of the rates of formation and decline of major transformation products is desired, the number of samples taken should generally be greater and somewhat more dispersed throughout the study duration. The number of sampling times can be less in range finding

or lower tier tests.

53. 76. Either aliquot or sacrificial sampling can be used. Sacrificial sampling of entire photolysis cells at each sampling time is often preferred over withdrawing aliquots of test solutions at each sampling time. The reason is that it helps to maintain aseptic conditions and allows for mass balance determinations at each sampling time. The use of sacrificial sampling is particularly necessary in cases where mass balance

determinations are needed such as when the test chemical test substance and/or its transformation products are volatile and/or adsorb strongly to the photolysi s cells (5). Future sampling descriptions in this document will be for the generally preferred sacrificial sampling, but aliquot sampling from larger irradiated and dark control reaction vessels is acceptable as long as the resulting mass balance is adequate and aseptic conditions are properly maintained.ENV/JM/TG/RD(2006)1/REV

88 54. 77. Replicates (preferably a minimum of two three ) of each experimental determination of kinetic parameters are recommended to determine variability and reduce uncertainty in the determination of kinetic parameters. However, the uncertainty in the determination of kinetic parameters can also be reduced by increasing the number of sampling intervals within each experiment, particularly when the rates of formation and decline of major transformation products are being determined. In such cases, a minimum

of two replicate determinations of kinetic parameters may be adequate. With generally limited resources, the researcher needs to weigh the pros and cons of experimental replication versus increased numbers of sampling times per experiment in designing the study.

Calculations

55. 78. Basic calculations/equations, including the foll owing one used to determine whether going to higher tiers is triggered, are included within the body of the guideline:



### ( ) 

# [ ] 

# { } % loss over 30 days / nights solar = −− = 100 1 30 exp ( ) 

### k td

solar [eq. 6 9 ]

where:

k solar = pseudo first-order direct or indirect photolysis rate constant for test chemical test
substance exposed to solar irradiation (1/day)

56. 79. Calculations/equations for the kinetics of the formation and decline of major photoproducts, and accounting for photobleaching are optional

. The necessary non-linear regressions can be readily performed with the use of commercially available spreadsheets and/or statistical software.

Determination of the photon flux from a filtered xenon arc lamp

57. 80. The photon flux from a filtered xenon arc lamp can be determined with the use of low and/or high optical density actinometers alone or preferab ly in conjunction with a spectral radiometer (5 8 1 ). The advantage in using a spectral radiometer to determine the photon flux is convenience, as it avoids changing actinometers. However, spectral radiometers are expensive and are not always readily available. Furthermore, even if a spectral radiometer is generally used to determine the photon flux, it should be periodically calibrated against photon fluxes determined with actinometers. Calibration is necessary because of the difference between the exposure surface of a spectral radiometer and that of the photolysis cuvette or tubes used to contain the actinometers (5 8 1 ).

58. 81. By determining the monochromatic first-order direct photolysis rate constant for a low optical density actinometer of known quantum yield in PW in a photolysis cell irradiated with monochromatic irradiation, the incident photon flux at the wavelength of the irradiation can be determined from the following equation (5 8 1 ; see Annex 4 3 - Equation Derivations):



### I j D

l k

xenon cell

xenon d act

act act 0 

### 2 3 λ λ

λ 

### φ ε ( ) ( )

( ) 

### . = [eq. 7 10 ]

where :

I 0 λ (xenon) = photon flux (photons/cm 2 • day) over a 1 nm interval centered at wavelength j = conversion factor to make units consistent with the L/mol • cm unit of the molarENV/JM/TG/RD(2006)1/REV

89 absorption coefficient and the mol/L unit of concentration =

6.02 x 10 20 (L/cm 3 ) (photons/mol)

k d λ (act) = monochromatic direct photolysis rate constant (1/day, pseudo first-order)

of an actinometer exposed to monoc hromatic irradiation at wavelength λ
φ (act) = the quantum yield of the actinometer

ε λ = molar absorption coefficient (L/mol • cm; M -1 •cm -1 ) of the actinometer at wavelength λ

D cell = depth of irradiated cell (cm) = volume of irradiated cell/incident area

l

xenon = light pathlength in cell exposed to a filtered xenon arc lamp

59. 82. Equation 10 only gives the photon flux at one wavelength, but it can be used at different individual wavelengths wherever another monochromatic direct photolysis rate constant is determined for one or more low optical density actinometers. The determination of the photon flux at several different individual wavelengths spread throughout the waveleng th range in which an estimate of the photon flux is desired should be sufficient to determine the photon flux from a filtered xenon arc lamp as a continuous function of wavelength. Because photon flux irradi ation spectrum from a filtered xenon arc lamp is smooth, interpolation from known photon fluxes at several different wavelengths can be readily done (5 8 1 ).

60. 83. By determining the polychromatic zero order direct photolysis rate constant for a high optical density actinometer of known quantum yield in PW in a photolysis cell irradiated with a filtered xenon arc lamp, the sum of the incident photon flux over the absorption spectrum of the actinometer above

295 290 nm can be determined from the following equation (5 8 1 ) (see Annex 4):



### I jD k

xenon cell

act d act

initial final

0 λ
λ λ



### φ ( ) ( )( 

### =

= = 

# ∑

zero order) [eq. 8 11 ]

where:

( λ =initial) = initial wavelength of actinometer absorption (if > 295 290 nm)
( λ =final) = final wavelength of the actinonmeter absorption (if < 800 nm)

I 0 λ = photon flux over a 1 nm interval centered at wavelength λ (photons/cm 2

• day) j = conversion factor to make units consistent with the L/mol • cm unit of the

molar

absorption coefficient and the mol/L unit of concentration =

6.02 x 10 20 (L/cm 3 )(photons/mol)

k d_(act) (0 order) = monochromatic direct photolysis rate constant (zero order) of an actinometer exposed to monochromatic irradiation at wavelength λ
(mol/L • day)

D cell = depth of irradiated cell (cm) = volume of irradiated cell/incident area (cm) φ act = the quantum yield of the actinometer

61. 85. By using more than one high optical density actinometer with absorption bands at different wavelengths, the sum of the photon flux over any desired range including the entire range between 295 290 and 800 nm can be determined. Further experimental details of procedures for determining the photon flux from and for calibrating xenon arc lamps are provided in references ( 58 37 )(5 9 1 ).ENV/JM/TG/RD(2006)1/REV

90 Performance of direct photolysis study

Tier 1

- Theoretical screen.

86. For a test chemical which does not ionize significantl y within a pH range of 5 to 9, a single UV

Visible absorption spectrum should be measured at a single pH within the 5 to 9 range where the hydrolysis rate, if any, is minimized. If the chemical is stable to abiotic hydrolysis, the spectrum should be

measur ed at pH 7. The pH at which a direct photolysis study on a non

- ionic test chemical is conducted should be the same as the pH at which the spectrum is determined. For a test chemical that is appreciably ionized anywhere within a 5 to 9 pH range, UV

- Visible absorption spectra should be measured at pH 5, 7,

and 9.

87. Electronic absorption spectra of the test chemical should be obtained in appropriate solvent systems at desired pHs with a spectrometer capable of recording UV

- VISIBLE spectra between 295 and

8 00 nm. Because the higher energy (shorter wavelength) bands of many chemicals may sometimes tail into wavelengths above 295 nm, it is recommended that the spectrum be recorded 30 to 40 nm below 295 nm. The procedure to record, assign absorption band maxima , band

- widths and determine decadic molar absorption coefficients has been described elsewhere (OECD Guideline 101). To obtain an adequate absorption spectrum, it may sometimes be necessary to enhance the solubility of the test chemical by using

aqueous me thanol, ethanol, or acetonitrile. It is recommended that UV

- VISIBLE spectra of test chemical s be also obtained in the neat co

- solvent.

88. If the test chemical absorbs above the 295 nm cutoff of solar irradiation at the earth’s surface

with ε λ > 2 L/mol•cm (M
- 1 cm - 1 ) over at least 15 nm, estimate a maximum possible direct photolysis rate by assuming that the quantum yield is equal to one in equation 6 (2):



## k L

d (max) 

## =

= = 

# ∑ ε λ λ
λ λ

295 800

[eq. 12]

where:

k d(max) = maximum possible direct photolysis rate constant (1/day)

ε λ = molar absorption coefficient (L/mol • cm; M - 1 cm - 1 ) at wavelength λ

L λ = average daily solar photon flux (mmol photons/cm 2 • day) over wavelength interval centered at wavelength λ

.

89. In estimating the maximum possible photolysis rate constant, th e average daily solar photon

fluxes L λ substituted into equation 12 should be those for summer at 40 ° or 50 ° latitude. Values of L λ can be readily obtained from tables (2)(12). As an alternative to the use of equation 12 and tables of L λ , the

maximum dire ct photolysis rate constant can be readily estimated by inputting molar absorption coefficients and a quantum yield equal to one into computer programs such as GCSOLAR (18) or ABIWAS (35)(36).

Criteria for deciding whether to go to Direct Photolysis Tier 2 or Tier 3

90. Determine if the maximum possible direct photolysis rate constant for the test chemical in the near surface of a clear natural water exposed to an average daily solar photon flux would result in estimated direct photolysis losses > 50% of an initial concentration over 30 days/nights of sunlight exposure by substituting k max(solar) for k (solar) in equation 9.ENV/JM/TG/RD(2006)1/REV

91 91. If estimated direct photolysis losses (assuming a maximum direct photolysis rate constant) are

less than 50% of the initial conce ntration over a 30

- day period direct photolysis is considered to be an insignificant process. In such a case, no further direct photolysis work is performed. If required, go to Indirect Photolysis Tier 1 (experimental/theoretical screen).

92. If estimate d direct photolysis losses (assuming a maximum direct photolysis rate constant) are greater than or equal to 50% of the initial concentration over a 30

- day period, go to Direct Photolysis Tier 2 (experimental screen and range finding) or Direct Photolysis Tier 3 (determination of the quantum yield).

Tier 2

- Experimental screen and range finding test for higher tiers

93. Dissolve the test chemical in sterilized, buffered pure water and place an optically dilute solution in photolysis test vessels. Expos e at least half of the test vessels to a filtered xenon arc lamp or sunlight and allow an equal number or fewer of the test vessels to serve as dark controls.

94. Determine the concentrations of the test chemical in the irradiated test vessels and in the dark control test vessels at adequate enough sampling intervals to approximately determine the direct photolysis

rate constant of the test chemical

.

95. At each sampling interval, sacrifice an irradiated photolysis cell for analysis. The number of sampli ng intervals for which a dark control is also sacrificed for analysis should depend upon a prior knowledge of the rate of hydrolysis of the test chemical at the experimental pH. For example, if the test
chemical is susceptible to appreciable rates of hydro lysis at the experimental pH, a dark control cell should be sacrificed for analysis each time an irradiated cell is sacrificed. However, if the test chemical is stable to hydrolysis at the experimental pH, a minimum of 3 sampling intervals for the dark co ntrol will be adequate.

96. If the data follow first

- order kinetics, compute irradiated and dark control rate constants for the

test chemical by using linear regression on equation 3 or non

- linear regression on equation 2.

97. Once the irradiated and dar k control rate constants for the test chemical have been determined, compute the approximate laboratory direct photolysis rate constant from the following equation:



### kkk

d screen irradiated dark

( ) 

### = − [eq. 13]

Estimation of direct photolysis rate constants in near surface clear nat ural water from laboratory values

98. Estimate a direct photolysis rate constant for the test chemical in near surface clear natural water exposed to average daily solar photon fluxes L

_ from the direct photolysis rate constant in a photolysis cell

expose d to continuous photon fluxes from a filtered xenon arc lamp using the following equation (assuming D cell the pathlength l; see Annex 4):



## k j D

l k L

I d solar cell d xenon

xenon

( ) ( )

( ) 

## . = 

# ∑

∑ 23 295 800

0 

## ε

ε λ λ

λ λ [eq. 14]ENV/JM/TG/RD(2006)1/REV

92 where:

k d(solar) = average daily direct photolysis rate constant (1/day) for the test chemical in t he near surface of clear natural water exposed to average daily solar irradiation fluxes L λ k d(xenon) = direct photolysis rate constant (1/sec) for the test chemical in buffered pure water in photolysis cells exposed to constant filtered xenon arc l amp fluxes I 0 λ

ε λ (chem) = molar absorptivity of the test chemical (L/mol • cm; M - 1 cm - 1 )

D cell = depth of irradiated cell (cm) = volume of irradiated cell/incident area (cm)

l

xenon = light pathlength in cell exposed to a filtered xenon arc lamp

I 0_(xenon) = incident filtered xenon arc lamp photon flux (photons/cm 2 • day) over a 1 nm interval centered at wavelength λ

L λ = 24 hour average daily solar photon flux over wavelength interval λ centered at wavelength λ for the weakly absorbing near surface of clear natural water bodies in (mmol photons/cm 2 • day) j = conversion factor = 6.02 x 10 20 (L/cm 3 )(photons/mol)

99. To use equation 14, the photon flux from the filtered xenon arc lamp that is incident on the photolysis cells (I 0 λ ) must be determined a s a function of wavelength using actinometers and (if available) a spectral radiometer. The solar photon fluxes as a function of wavelength for the near surface of clear
natural waters (L λ ) for various mid

- seasons and latitudes are readily available (2)(12 ).

Criteria for deciding whether to go to Direct Photolysis Tiers 3 and/or 4

100. Determine if the screen direct photolysis rate constant for the test chemical in the near surface of a clear natural water exposed to sunlight would result in estimated di rect photolysis losses > 20% of an initial concentration over 30 days/nights of sunlight exposure by substituting k d(screen)(solar) for k (solar) in equation 9.

101. If estimated direct photolysis losses (assuming the screen direct photolysis rate constan t) are less

than 20% of the initial concentration over a 30

- day light/dark sunlight exposure period, direct photolysis is considered to be an insignificant process. In such a case, no further direct photolysis work is performed. If required, proceed to th e Indirect Photolysis Tier 1 screen.

102. If estimated direct photolysis losses (assuming the approximate direct photolysis rate constant) are greater than or equal to 20% of the initial concentration over a 30

- day light/dark sunlight exposure period, pro ceed to Direct Photolysis Tiers 3 and/or 4. If determining the quantum yield of the test chemical and using it to estimate direct photolysis rate constants for types of water bodies, seasons, and latitudes is required, proceed to Direct Photolysis Tier 3. Otherwise, proceed to direct photolysis Tier 4 to perform a more definitive kinetics study.

Tier 3

- Determination of the quantum yield and estimations of direct photolysis rate constants

103. Determine the quantum yield of the test chemical in buffer ed solutions using monochromatic irradiation (12), filtered xenon

- arc lamp polychromatic irradiation (8) or sunlight polychromatic irradiation (2). Each has advantages and disadvantages compared to the others.

104. The main advantage in using monochromat ic irradiation to determine the test chemical quantum yield of the test chemical is that (as will be shown later by equations 19 through 21) it eliminates the need to directly measure the incident monochromatic irradiation. However, a disadvantage is that it will take longer to determine the quantum yield with monochromatic irradiation than with the use of polychromaticENV/JM/TG/RD(2006)1/REV

93 irradiation because the actinometer and the test chemical are absorbing photon fluxes at just one wavelength instead of over multiple wave lengths.

105. The main advantage in using polychromatic irradiation (filtered xenon arc lamp or sunlight)

instead of monochromatic irradiation to determine the test chemical quantum yield is that the time required to determine the quantum yield may be su bstantially shorter (8). The reason is due to the absorption of photon fluxes by the actinometer and test chemical over multiple wavelengths instead of just one wavelength. The main disadvantage in using polychromatic irradiation to determine the test ch emical quantum yield is that unlike with monochromatic irradiation (as will be shown later by equations 20 and 21), its use requires the determination of the photon flux.

106. The advantage in using sunlight instead of a filtered xenon arc lamp, if polyc hromatic irradiation is used to determine the quantum yield, is that tables of average solar intensities as a function of season and latitude are readily available. Also, if sunlight is used, it eliminates the necessity of having a monochromatic or polych romatic artificial light source. However, if sunlight is used, an actinometer with an adjustable quantum yield is needed so the direct photolysis rate of the actinometer can be adjusted to be comparable to that of the test chemical under the same irradiat ion conditions (2)(12). Parallel exposure of

the test chemical and actinometer to sunlight over comparable time frames minimizes errors due to changes in solar flux caused by fog, varying cloud cover, etc. (12)(51).

107. An example of an adjustable quant um yield actinometer is the p

- nitroacetophenone

- pyridine (PNAP

- PYR) actinometer (52). For a 1.0 X 10

- 5 M p

- nitroacetophenone solution, the quantum yield of the actinometer in experiments carried out with monochromatic irradiation at 313 nm can be adjuste d by varying the concentration of pyridine in the solution according to the following equation (2)(12):



# φ

act 

# pyridine = • 0 0169

.[ ] [eq. 15]

where: φ act = quantum yield of the 1.0 X 10

- 5 M p

- nitroacetophenone [pyridine] = molar concentration of pyridine

108. Suitable chem ical actinometers used in aqueous photochemical studies include the following :

Actinometer System Literature Citation (a) p

- nitroacetophenone/pyridine 52 (b) p

- nitroanisole/pyridine 26, 52 (c) valerophenone 53
(d) ferrioxalate 19, 23, 37, 54, 55
(e) o

- nitrobenzaldehyde 37, 52
(f) Reinecke’s salt 12 (g) aberchrome 540 56, 57

109. The first two actinometers listed in the above table have adjustable quantum yields and are therefore particularly useful when solar irradiation is used (12). The first three actinometers listed in the table are low optical density actinometers and the last four are high optical density actinometers. The characteristics of those actinometers including the optimal wavelength range for their use are discussed in

references 12 and 58. Other chemical actinometers are described in the IUPAC document on chemical actinometers (58).ENV/JM/TG/RD(2006)1/REV

94 Determination of the quantum yield using monochromatic irradiation

110. Place solutions of the test chemical and the selected optically low densit y actinometer in separate but identical photolysis cells. Irradiate at least half of the photolysis cells with monochromatic irradiation of wavelength λ and let an equal or fewer number (depending upon the hydrolytic stability of the test
chemical ) serve a s dark controls. Determine the concentration of the test substance in the irradiated cells and in the dark controls at adequate enough sampling intervals to determine the monochromatic direct photolysis rate constant of the test chemical (k d_(chem) ) and of the actinometer (k d λ (act) ) at the wavelength λ of irradiation. At each sampling interval, sacrifice an irradiated photolysis cell for analysis. The number of sampling intervals for which a dark control is also sacrificed for analysis should depend upon a prior knowledge of the rate of hydrolysis of the test chemical at the experimental pH.

11. The decline of a test chemical or actinometer concentrations at low optical density should follow pseudo first

- order kinetics so that the monochromatic irradiated a nd the dark control rate constants can be determined by using linear regression on equation 3 or non

- linear regression on equation 2. The decline of

a test chemical or actinometer at high optical density should follow zero

- order kinetics so that the

monoc hromatic irradiated and the dark control rate constants can be determined by using linear regression on the following zero

- order kinetics equation:

C C kt

= − 0 [eq. 16]

112. Once the monochromatic irradiated and dark control rate constants for the test che mical and the actinometer have been determined, the monochrom atic direct photolysis rate constant of the test chemical
(k d_(chem) ) and of the actinometer k d λ (act) at wavelength λ are given by:



# kk k

d chem or irradiated chem or act dark chem or act

λλ λ

( ) ( )( ) ( )( ) act 

# = − [eq. 17]

Note : In a sterilized aqueous buffer, the dark co ntrol rate constant (k dark ) should be equal to the hydrolysis rate constant at the pH of the buffer.

113. Determine the molar absorption coefficients of the test chemical ( ε λ (chem) ) and (if a low optical density actinometer is being used) the actinometer ( ε λ (act) ) at the wavelength λ of the monochromatic irradiation using the Beer

- Lambert law assuming that ε λ C is >> than the attenuation coefficient α λ of the

test medium:



## ε

λ λ

( ( )

( ) 

## [ ] chem chem act

chem act 

## A

l C or act) or

or 

## =

[eq. 18]

where:

ε λ (chem) = molar absorption coefficient of the test chemi cal or actinometer

L/mol • cm; M - 1 cm - 1 )

A λ (chem or act) = absorbance of test chemical or actinometer solution at wavelength λ

L = light pathlength (cm) generally equivalent to D cell [C (chem or act) ] = concentration of test chemical or actinometer solution (mol/L)

114. The quantum yield of an optically dilute test chemical determined using monochromaticENV/JM/TG/RD(2006)1/REV

95 irradiation and a low optical density (low absorbance) actinometer is given by (12)(47) (See Annex 4):



## φ φ ε

ε λ λ

λ λ chem act d chem act

d act chem 

## k

k = ( )()

()( ) [eq. 19]

where:

φ chem = the quantu m yield of the test chemical φ act = the quantum yield of the actinometer

k d λ (chem) = monochromatic direct photolysis rate constant (1/day, pseudo first

- order) of a test chemical exposed to monochromatic irradiation at wavelength λ

k d λ (act) = monochr omatic direct photolysis rate constant (1/day, pseudo first

- order) of an actinometer exposed to monochromat ic irradiation at wavelength λ

ε λ (chem) = molar absorption coefficient (L/mol • cm; M - 1 cm - 1 ) of the test chemical at wavelength λ

ε λ (act) = molar absorption coefficient (L/mol • cm; M - 1 cm - 1 ) of the actinometer at wavelength λ

115. The quantum yield of an optically dilute test chemical determined using monochromatic irradiation and a high optical density (high absorbance) actinometer is give n by (12)(47). See Annex 4:



## φ φ

ε

λ λ

λ chem act

chem cell d chem

d act zero 

## D k

k = 2 3

. ( ) ( )

( )( order) [eq. 20]

where:

φ chem = the quantum yield of the test chemical φ act = the quantum yield of the actinometer

k d_(chem) = monochromatic direct photolysis rate constant (1/day, pseudo first

- order) of a test

chemical exposed to monochromatic irradiation at wavelength λ

k d_(act)(zero) = monochromatic direct photolysis rate constant (mol/L • day, zero

- order) of an actinometer exposed to monochromat ic irradiation at wavelength λ

D cell = depth of irradiated cell (cm) = volume of irradiated cell/incident area (cm)

116. The quantum yield of a test chemical at high optical density (high absorbance) determined using monochromatic irradiation and a high optical density (high absorbance) actinometer is given by (12)(47).

Se e Annex 4):

φ φ λ

λ chem act d chem zero

d act zero k

k = ( )( )

( )( ) [eq. 21]

where:

φ chem = the quantum yield of the test chemical φ act = the quantum yield of the actinometer

k d_(chem)(zero) = monochromatic direct photolysis rate constant (mol/L • day, zero

- order) of a test chemical exposed to monochromatic irradiation at wavelength λENV/JM/TG/RD(2006)1/REV

96 k d_(act)(zero) = monochromatic direct photolysis rate constant (mol/L • day, zero

- order) of an actinometer exposed to monochromat ic irradiation at wavelength λ

117. As can be seen from equations 19, 20, an d 21, it is not necessary to determine the photon flux if

monochromatic irradiation is used to determine the test chemical quantum yield.

Determination of the quantum yield using polychromatic irradiation (lamp or sunlight)

118. The quantum yield of an o ptically dilute test chemical using a low optical density (low absorbance) actinometer and sunlight or a polychromatic filtered xenon arc lamp can be determined from equations 22 and 23, respectively (2)(6)(12)(See Annex 4):



### φ φ ε

ε λ λ
λ λ

λ λ
λ λ chem act d chem

d act act

nm nm

chem

nm nm 

### k

k L

L = 

  



 

     



    = =

= = 

# ∑

∑ ( )

( ) ( )

( ) 295 800

295 800

[eq. 22]



### φ φ ε

ε λ λ

λ λ chem act d chem

d act act xenon

chem xenon 

### k

k I

I = 

  

  

     

     

# ∑

∑ ( )

( ) () ( )

()( ) 0

295 800

0

295 800

[eq. 23]

where:

k d(chem) = direct photolysis rate constant (1/day, pseudo first

- order) of the test chemical

k d(act) = direct photolysis rate constant (1/day, pseudo first

- order) of the actinometer φ chem = quantum yield of the test chemical (dimensionless rati o) φ act = quantum yield of the actinometer (dimensionless ratio)

ε λ (chem) = molar absorption coefficient (L/mol • cm; M - 1 cm - 1 ) of the test chemical at wavelength λ

ε λ (act) = molar absorption coefficient (L/mol • cm; M - 1 cm - 1 ) of the actinometer at wavelength λ

L λ = average daily solar photon flux (mmol photons/cm 2 • day) over wavelength interval

∆ λ centered at wavelength λ

I 0 λ (xenon) = incident filtered xenon arc lamp photon flux (photons/cm 2 • day) over a 1 nm
interval centered at wavelen gth λ

119. As can be seen from equations 22 and 23, it is necessary to independently and accurately determine the incident photon flux as a function of wavelength when polychromatic irradiation is used to

determine the test chemical quantum yield.

120 Th e determination of the test chemical quantum yield using polychromatic irradiation and an actinometer are discussed in detail in (2) for the use of sunlight, and in (8) for the use of a filtered xenon arc lamp.

Dependence of the quantum yield on wavelen gthENV/JM/TG/RD(2006)1/REV

97 121. Most of the direct photolysis equations involving polychromatic irradiation in this document and in the literature are presented with the quantum yield taken outside of the integral or summation over different wavelengths. The reason is that in a queous solutions, the quantum yields of test chemical s are (in general) approximately independent of wavelength, even across different absorption bands. In aqueous solutions, molecules in higher excited electronic states tend to undergo radiationless decay to their first excited state before any photoreaction occurs (12). If photoreaction does occur, it generally occurs in competition with other deactivation processes while the molecule is in its first (not higher) excited

electronic state.

122. However, the quantum yield may sometimes differ between absorption bands (6)(14). Therefore, it may sometimes be necessary to determine the quantum yield at least one wavelength for each adsorption

band within the 295

- 800 nm range using monochromatic irradiation. T he wavelength chosen for each absorption band should correspond to the maximum absorption. In cases where the quantum yield varies with wavelength, the quantum yield should be br ought inside any integrals or summations over wavelengths.

123. In cases whe re the quantum yield remains constant within the same absorption band, but varies across different absorption bands, equations 5 and 6 for the direct photolysis rate constant can be modified to give:



## k I d i ii i begin

i end

i i n



## = 

# ∑ ∑

= = 

## φ ε λ λ
λ

λ

0 1 () ( )

[eq. 24]



# k L d i

i i n

i i i begin

i end



# =

= = 

# ∑ ∑ φ ε λ λ
λ

λ

1 () ( )

[eq. 25]

where:

φ I = quantum y ield for absorption band i

ε i λ = molar absorption coefficient (L/mol • cm; M - 1 cm - 1 ) at wavelength λ within absorption band i

I 0i λ = photon flux per nm (photons/cm 2 • sec/nm) at wavelength λ within absorption

band i

λ I = wavelength interval in nm generally = 1 nm

L i λ = average daily solar photon flux irradiance (mmol photons/cm 2 • day) over wavelength interval ∆ λ centered at wavelength λ within absorption band i

I = indice for different absorption bands up to the maximum of n bands

i λ (begin ) = wavelength at the beginning of absorption band i

i λ (end) = wavelength at the end of absorption band i

Use of the quantum yield to estimate direct photolysis rate constants

124. Once the quantum yield of a test chemical has been determined, it sho uld be used as input into computer programs such as GCSOLA R (18) or ABIWAS (35)(36) to estimate direct photolysis rate constants for seasons, latitudes, and water body depths and light attenuations of interest. GCSOLAR and

ABIWAS can be used to estimate di rect photolysis rate constants at any given time in near surface water or at any specified depth. The programs can also average rate constants over any given time and/or depthENV/JM/TG/RD(2006)1/REV

98 interval of interest.

125. Although programs such as GCSOLAR or ABIWAS are read ily available, equation 5 is often used to estimate the direct photolysis rate constant for optically dilute solutions of test chemical s in pure water in photolysis cells or in the near surface of clear natural water exposed to solar irradiation (2)(12).

Criteria for deciding whether to go to direct photolysis Tier 4

126. A Direct Photolysis Tier 4 kinetics study should be performed if identification/kinetics data on the major transformation products are applicable and if the direct photolysis rate consta nt(s) for the parent

test chemical (estimated from its quantum yield) indicate that direct photolysis is a potentially significant process.

127. Determine if the direct photolysis rate constant (estimated from the quantum yield) for the test
chemical in shallow natural water exposed to sunlight would result in estimated direct photolysis losses

> 20% of an initial concentration over 30 days/nights of sunlight exposure by substituting k d(solar) for k (solar) in equation 9.

128. If estimated direct photoly sis losses are less than 20% of the initial concentration over a 30 day light/dark sunlight exposure period, direct photolysis is considered to be an insignificant process. In such a case, no further direct photolysis work is performed. If of interest, p roceed to indirect photolysis Tier 1. Proceed to direct photolysis Tier 4 if:

• Estimated direct photolysis losses are greater than or equal to 20% of the initial concentration over a 30 day light/dark sunlight exposure period, and

• The identification of ma jor transformation products and/or the determination of their rates of formation and decline are required.

Tier 4

- Kinetics study on the test chemical and (if applicable) major transformation products

Experimental determinations of direct photolysis ra te constants in the laboratory

129. In direct photolysis Tier 4, the decrease in the concentrations of the test chemical is determined in buffered pure water exposed to a filtered xenon arc lamp or sunlight. If applicable, the rates of formation

and decli ne of major transformation products are also determined. For the purposes of this guideline, a major transformation product is one accounting for > 10% of the applied radioactivity (or molar basis) at any time during the study.

130. If a flow

- through sy stem is used to trap volatile test chemical s and/or their major transformation products, the following considerations should be made. The air should be passed through microbial filters to keep the samples sterile. Moist air should be used to prevent evap oration. The system should be checked for sterility at the study termination.

131. Place the test solution in photolysis test vessels. At least half the test vessels should be exposed to a filtered xenon arc lamp or sunlight and an equal or fewer number of the test vessels should serve as

dark controls.

132. Determine the concentrations in the irradiated test vessels and in the dark control test vessels at adequate enough sampling intervals to determine the direct photolysis rate constant of the test ch emical

.

133. At each sampling interval, sacrifice an irradiated photolysis cell for analysis. The number ofENV/JM/TG/RD(2006)1/REV

99 sampling intervals for which a dark control is also sacrificed for analysis should depend upon the rate of hydrolysis of the test chemical at the experimental pH.

134. f the data follow first

- order kinetics, compute irradiated and dark control rate constants for the

test chemical by using linear regression on equation 3 or non

- linear regression on equation 2.

135. Once the irradiated and dark co ntrol rate constants for the test chemical have been determined, compute the laboratory direct photolysis rate constant from the following equation:



### kk k

d irradiated dark



### = − [eq. 26]

136. If a filtered xenon arc lamp is used for irradiation, estimate an approximate avera ge daily direct photolysis rate constant for the test chemical in shallow natural water exposed to average daily solar photon fluxes L λ from equation 14.

137. In direct photolysis Tier 4, the decrease in the concentrations of the test chemical is determin ed in buffered pure water exposed to a filtered xenon arc lamp or sunlight. If applicable, the rates of formation and decline of major transformation products are also determined. For the purposes of this guideline, a major transformation product is one ac counting for > 10% of the applied radioactivity at any time during the study.

138. If a flow

- through system is used to trap volatile test chemical s and/or their major transformation products, the following considerations should be made. The air should be passed through microbial filters to keep the samples sterile. Moist air should be used to prevent evaporation. The system should be checked for sterility at the study termination.

139. The following equation can be used to estimate the direct photolysis rate constant for the test
chemical in shallow natural water exposed to one or more different sunlight conditions from those in the study (see Annex 3

- Equation Derivations):

k k L

L sun shallow sun shallow water nm nm

nm nm ( ) ( )

( ) water)2 = = =

= = 

### ∑

∑ 1 2

295 800

1

295 800 ε

ε λ λ
λ λ

λ λ
λ λ
[eq. 27]

where:

k d(sun shallow water)2 = estimated direct photolysis rate constant in the near surface of clear natural water exposed to solar irradiation fluxes (L λ (2) ) different from solar irradiation
fluxes (L λ (1) ) used in the experiment.

k d(sun shallow water)1 = estimated direct photolysis rate constant in the near su rface of clear natural water exposed to the experimental solar irradiation fluxes.

L λ (2) = average daily solar photon fluxes different from those closest
(L λ (1) ) to the experimental conditions.

L λ (1) = average daily solar photon fluxes closest to t he experimental ones based on the season and latitude at which the study was performed.

140. Compute direct photolysis half

- lives by substituting the estimated direct photolysis rate constants into equation 4.ENV/JM/TG/RD(2006)1/REV

100 Major transformation products (if required)

141. Identify and quantify major phototransformation products using analytical methods and criteria indicated in paragraphs 39 through 43.

142. In cases where data follow first

- order kinetics and the parent test chemical substance rapidly transforms, use the same first

- order methods applied to the test chemical to also estimate first

- order direct photolysis rate constants and corresponding half

- lives for any major primary transformation products formed from the parent which are still at substantial concent rations (e.g. at > 10% of applied) after the parent has degraded to negligible levels.

143. Equation 14 for estimating sunlight rate constants from filtered xenon arc lamp rate constants and equation 27 for estimating a sunlight rate constant for a given season and latitude from a sunlight rate constant for a different season and/or latitude are also applicable to any first

- order photolysis rate constants determined for any major transformation products.

144. In cases where primary or secondary transform ation products are being substantially formed over the same time period they are being substantially lost, their direct photolysis rate constants and corresponding half

- lives cannot be readily estimated as they were for the parent. However, as an option,

a ttempts can be made to estimate first

- order rate constants for the formation and decline of major transformation products using non

- linear regression to fit concentration versus time series data to various equations derived from assumed transformation path ways.

Performance of indirect photolysis tiers

Tier 1 for indirect photolysis

- Experimental and/or theoretical screen

62. 145. Perform a screen in simulated water (containing humics as a surrogate for CDOM and when applicable, nitrate) or natural water to determine if indirect photolysis represents a potentially significant transformation pathway.

63. 146. Place solutions of the test chemical test substance in simulated natural water (SNW) and/or simulated natural water with nitrate (SHW-N) and/or natural water (NW ). ) and in buffered pure water (PW) into equal numbers of photolysis cells. Expose at half of the photolysis cells containing each type of

solution to a Xenon arc lamp or sunlight and let an equal or smaller number of the photolysis cells containing each type of solution serve as dark controls.

147. The use of a filtered xenon arc lamp for indirect photolysis studies is not recommended at this time. The complexity of indirect photolysis processes does not allow straightforward extrapolation of results from filtered xenon arc lamps to sunlight equivalents and may not be feasible (2)(12).

64. 148. Determine the concentrations in the irradiated photolysis cells and in the dark control photolysis cells at adequate enough sampling intervals to determine the irradiated and dark control rate constants of

the test chemical test substance in SNW and/or SNW-N and/or in NW

. and in PW. At each sampling time, sacrifice an irradiated photolysis cell. The number of sampling intervals for which a dark control is also sacrificed for analysis should depend upon the stability of the test chemical test substance in the dark control at the experimental pH. Assuming the decline of the test chemical test substance follows first-order kinetics, determine the irradiated and dark control rate constants in the irradiated and dark control solutions by using linear regression on equation 3 or non-linear regression on equation 2.

65. 149. Once the irradiated and dark control rate constants for the test chemical test substance in SNWENV/JM/TG/RD(2006)1/REV

101 and/or SNW-N and/or NW and in PW have been determined, the net photolysis rate constants, the direct photolysis rate in PW, and the indirect photolysis rates constants can be respectively determined from the following equation s :

kk k

pX X irrad X dark

= − ( ) () [eq. 9 2 8 ]

kk k

d PW PW irrad PW dark () ( ) ( ) = − [eq. 29]

k kk

iX approx pX d PW

( ) () = − [eq. 30]

where:

X = SNW, SNW-N, or NW

Note : Equation 30 is only approximate because the direct photolysis rate constant in PW (k d(PW) ) will be greater than the direct photolysis rate constant in SNW, SNW

- N or NW (k dX ) d ue to light attenuation (12). However, the approximation is adequate for a screen. Also, u U nlike indirect photolysis Tier 2, this indirect photolysis Tier 1 screen does not take into account the photobleaching of humic solutions in photolysis cells by sunlight as reported by Winterle and Mill ( 60 59 ).

66. 150. Determine if the approximate indirect photolysis rate constant for the test chemical test substance in shallow natural surface water would result in estimated indirect photolysis losses > 20% of an initial concentration over 30 days /nights of sunlight exposure by substituting k pX k iX (approx) for k (solar) in equation 9. When a Xenon arc lamp is used its intensity of irradiation has to be related to natural sunlight (see Annex &).

67. 151. If estimated indirect photolysis losses (assuming an approximate indirect photolysis rate constant) are less than 20% of the initial concentration over a 30 day /night sunlight exposure period, indirect photolysis is considered to be an insignificant process. In such a case, no further indirect photolysis work is performed.

68. 152. If estimated indirect photolysis losses (assuming an approximate indirect photolysis rate constant) are greater than or equal to 20% of the initial concentration over a 30-day light/dark sunlight exposure period, indirect photolysis is considered to be a potentially significant process. Proceed to Indirect Photolysis Tier 2 to perform a more definitive kinetics study.

153. Mill (21) has summarized structural activity relations (SARs) for estima ting second

- order rate constants for the reaction of organics with photooxidants in water. He also summarized typical concentrations of various photooxidants generally found in the top layers of surface water exposed to sunlight. In some cases, it may be p ossible to supplement or even replace the experimental screen with a theoretical screen based on using structural activity relationships (SARs). These SARs estimate rate constants and information on the typical concentrations of photoxidants in surface wat er. Although a theoretical screen involving one or two potential photooxidants may indicate that going to Tier 2 is justified, it is doubtful that one can indicate that going to Tier 2 is not justified. The reason is that a theoretical screen will generall y cover only one or two of the large number of possible types of indirect photolysis reactions. Further details on using structure activity relations for estimating rate constants for

the reaction of test chemical s with photoxidants in water such as the hy droxyl radical and singlet oxygen are provided in reference 51.ENV/JM/TG/RD(2006)1/REV

102 Tier 2

- Experimental determination of rate constants (and identification/quantification of major transformation products, when required)

69. 154. In the indirect photolysis Tier 2, the decrease in the concentration of the test chemical test
substance is determined in simulated natural water (SNW ) and/or simulated natural water with nitrate (SNW-N) and/or one or more natural surface waters (NW) and in buffered pure water (PW) exposed to sunlight or a Xenon arc lamp. . If applicable, the identities and rates of formation and decline of major transformation products are also determined. For the purposes of this guideline, a major transformation product is one accounting for > 10% of applied at any time during the study.

70. 155. The performance of Tier 2 differs from that in Tier 1 in several ways including:

• The number of sampling times is greater.

• The direct photolysis constant in humic water is estimated by inputing the chemical’s quantum yield and

the attenuation constants of the humic solution into GCSOLAR or ABIWAS.

• If applicable, the rates of formation and decline of major transformation products are determined.

• If a study lasts for several days or more such that “photobleaching” of the humic solutions in photolysis cells may be substantial in some cases, it can (as an option) be accounted for as indicated in Leifer (12) and OPPTS 835.5270(2).

71. 156 Dissolve the test chemical test substance in SNW and/or SNW-N and/or NW and in PW and place the solutions in equal numbers of photolysis cells. Expose at least half of the photolysis cells containing each type of solution to sunlight or a Xenon arc lamp and let an equal or lesser number of the photolysis cells containing each type of solution serve as dark controls.

72. 157. Determine the concentrations in the irradiated cells and in the dark controls at adequate enough sampling intervals to determine the irradiated and dark control rate constants of the test chemical test
substance in simulated natural water (SNW), and/or simulated natural water with nitrate (SNW-N), and/or natural surface water (NW)

. , and in buffered pure water (PW). At each sampling interval, sacrifice an irradiated test vessel for analysis. Sacrifice dark controls for analysis at an equal or fewer number of sampling intervals

73. 158. Determine the irradiated and dark control rate constants of the test chemical test substance in

SNW and/or SNW-N and/or NW and in PW by using linear regression on equation 3 or non-linear regression on equation 2.

159. Once the irradiated and dark control rate constants for the test chemical in SNW and/or SNW

- N and/or NW and in PW have been determined, the net photolysis rate constants in those waters and the direct photolysis rate constants in PW can be determined from equations 28 and 29.

160. If the same light source and photon flux, test vessels, and experimental set

- up are used for the definitive determination of the direct photolysis rate constant in PW in the Tier 4 Direct Photolysis study, a separate determination of the direct photolysis rate constant in PW in the Tier 2 Indirect Photolysis study as just described is not necessary.

Determination of direct photolysis rate constant in SNW, and/or SNWN, and/or NW from one in PW

161. Deter mine attenuation constants as a function of wavelength for all experimental waters (SNW,

SNW

- N, and/or NW and PW) from the following equation:ENV/JM/TG/RD(2006)1/REV

103 α λ λ

( ) ( )

= A

l [eq. 31]

where:

α ( λ ) = light attenuation constant as a function of wavelength λ (1/cm)
A( λ ) = abs orbance of test medium as a function of wavelength λ

l = light pathlength in cell (cm)

162. Estimate average daily direct photolysis rate constant for the test chemical in near surface PW

and in SNW and/or SNW

- N, and/or NW by inputting its quantum yield and attenuation constants for PW and for SNW, and/or SNW

- N, and/or NW into GCSOLAR or ABIWAS. If the quantum yield of the test
chemical was determined in Direct Photolysis Tier 3, use it as input. Otherwise

, e stimate the quantum yield by substituting the experimental direct photolysis rate constant in PW and ε λ L λ into equation 6 and rearranging to solve for the quantum yield.

163. Estimate the direct photolysis rate constant in SNW and/or SNWN and/or NW in a photolysis cell from the following equation:

k k

k k dX dX GCSOLARorABIWAS

d PW GCSOLARorABIWAS d PW = ( )

( ) ( ) ( )(exp) [eq. 31]

where:

X = SNW, SNW

- N, or NW

k dX = direct photolysis rate constant in SNW, SNWN, or NW in a photolysis cell

k dX(GCSOLAR) = GCSOLAR or ABIWAS estimated average da ily direct photolysis rate constant in near surface SNW, SNW

- N, or NW

k d(PW)(GCSOLAR) = GCSOLAR or ABIWAS estimated average da ily direct photolysis rate constant

in PW

k d(PW)(exp) = experimentally determined direct photolysis rate constant in PW in a photolysis

cell

74. 164. Once the irradiated and dark control net and direct photolysis rate constants in SNW and/or SNW-N and/or NW have been determined, the indirect photolysis rate constant in those waters can be estimated from the following equation 9. :

kkk

iX pX dX

= − [ eq. 32]

where X = SNW, SNW

- N, or NW

75. Determine if the indirect photolysis rate constant for the test substance in shallow natural surface water would result in estimated indirect photolysis losses > 20% of an initial concentration over 30 days of sunlight exposure by substituting k pX for k (solar) in equation 9. When a Xenon arc lamp is used its intensity of irradiation has to be related to natural sunlight (see Annex 6).

76. If estimated indirect photolysis losses (assuming an indirect photolysis rate constant) are less than 20% of the initial concentration over a 30 day sunlight exposure period, indirect photolysis is considered to be an insignificant process. In such a case, no further indirect photolysis work is performed.ENV/JM/TG/RD(2006)1/REV

104 77. If estimated indirect photolysis losses (assuming an indirect photolysis rate constant) are greater than or equal to 20% of the initial concentration over a 30-day sunlight exposure period, indirect photolysis is considered to be a potentially significant process. Proceed to Indirect Photolysis Tier 3.

165. The methods used in the identification and kinetics analysis of transformation products formed during indirect photolysis studies are comparable to those formed during direct photolysis studies.

Method of accounting for “photobleaching”

78. 166. If a study lasts for several days or more, the decline of the test chemical test substance in irradiated SNW, SNW-N, or NW may not be first-order due to the “photobleaching” of humic solutions. Photobleaching in photolysis cells that has been studied and reported by Winterle and Mill ( 60 5 4 ).

79. 167. Photobleaching does not appear to be a significant process in the actual environment because CDOM appears to be generated at much faster rates than the rates of its decline through photobleaching (5 8 1 ). However in the laboratory, the photobleaching of humic solutions in photolysis cells by sunlight somewhat complicates a more definitive determination of the indirect photolysis rate. Because of photobleaching, the indirect photolysis rate constant for a test chemical test substance in SNW, SNW-N, or NW solutions in photolysis cells exposed to sunlight decreases over time. If that occurs, there are two options:

80. 168. When photobleaching begins to become substantial, the study can be terminated. In such cases, only data obtained from the study prior to substantial photobleaching should be used in the analysis. The study can be continued by accounting for photobleaching.

Extrapolation from cell or near surface to the same water over a deeper depth, and from experimental to other solar photon fluxes

81. 169. Unfortunately, methods of extrapolation to greater depths and light attenuation and to other solar conditions are not as straightforward for indirect photolysis as they are for direct photolysis, even when irradiation is restricted to sunlight. The reason is that indirect photolysis may involve the absorption of solar flux by many different types of sensitizers with different absorption spectra and by nitrate. Therefore, the results of an indirect photolysis study conducted in cells exposed to natural sunlight are only applicable to the near surface and the same set of solar conditions as the experimental ones.

Tier 3 Identification of major phototransformation products

82. In indirect photolysis Tier 3, the test substance in SNW and/or SNW-N and/or one or more natural waters is exposed to a filtered xenon arc lamp or sunlight. The rates of formation and decline of transformation products are determined, if possible. Major phototransformation products are isolated and identified. For the purposes of this guideline, a major transformation product is one accounting for > 10% of the applied radioactivity (or molar basis) in an individual sample at any time during the study.

83. If a flow-through system is used to trap volatile test substances and/or their transformation products, the following considerations should be made. The air should be passed through microbial filters to keep the samples sterile. Moist air should be used to prevent evaporation.

84. Place the test solution in photolysis test vessels. At least half the test vessels should be exposed to a filtered xenon arc lamp or sunlight and an equal or fewer number of the test vessels should serve as dark

controls.ENV/JM/TG/RD(2006)1/REV

105 85. Determine the concentrations of the transformation products in the irradiated test vessels and in the dark control test vessels at adequate enough sampling intervals.

86. At each sampling interval, sacrifice an irradiated photolysis cell for analysis. The number of sampling intervals for which a dark control is also sacrificed for analysis should depend upon the rate of hydrolysis of the test substance at the experimental pH.

87. Identify and quantify major phototransformation products using analytical methods and criteria indicated in paragraph 26.

88. In cases where data follow first-order kinetics and the parent test substance rapidly transforms, use the same first-order methods applied to the test substance to also estimate first-order photolysis rate constants and corresponding half-lives for any major transformation products formed from the parent which are still at substantial concentrations (e.g. at > 10% of applied) after the parent has degraded to negligible levels.

89. In cases where primary or secondary transformation products are being substantially formed over the same time period they are being substantially lost, their photolysis rate constants and corresponding half-lives cannot be readily estimated as they were for the parent. However, as an option, attempts can be made to estimate first-order rate constants for the formation and decline of transformation products using non-linear regression to fit concentration versus time series data to various equations derived from assumed transformation pathways.

REPORTING OF DATA AND RESULTS

90. 170. The degree of presentation of results depends on the complexity and purpose of the study, that is,

the number of tiers. Reporting should follow the IUPAC recommendations (61).

Direct photolysis data and results

Tier 1

• Provide the UV

- VISIBLE spectrum or spectra of the test chemical as the molar absorption coefficients
(L/mol • cm or M - 1 cm - 1 ) on the y

- axis versus wavelengths (nm) on the x

- axis.

• Report the estimated maximum photolysis rate constant and associated direct photolysis losses over a 30 days/nigh ts sunlight exposure period. Provide the equations and calculations used to estimate them. Provide the rationale for selecting the season and latitude of the average daily solar photon fluxes (L λ ) used in the calculations.Report whether or not the result s of the calculations trigger Direct Photolysis

Tiers 2 and/or 3.

Tier 2

• If a filtered xenon arc lamp was used, provide the incident photon flux in a graph as the photon flux (photons/cm 2 • sec) on the y

- axis versus the wavelength (nm) on the x

- axis.

• If sunlight was used, provide tabular values of solar photon fluxes for the season and latitude closest to those of the study.ENV/JM/TG/RD(2006)1/REV

106 • Provide table(s) and graph(s) which show the concentrations of the test chemical in irradiated and dark

control solutions versus ti me. Show the best fit regression lines on the graph(s) along with the data points.

• Report the irradiated, dark control, and approximate direct photolysis rate constant of the test chemical along with their corresponding half

- lives. Provide the equations , calculations, and regression coefficients used to compute them together with regression n and r 2 values, and standard errors of coefficients (for example, slope, intercept).

• Based upon the approximate direct photolysis rate constant, report the associat ed estimated direct photolysis losses over a 30 days/nights sunlight exposure period. Provide the equations and

calculations used to estimate them. Provide the rati onale for selecting the season and latitude of the average daily solar photon fluxes (L λ ) used in the calculations. Report whether or not the results of the calculations trigger Direct Photolysis Tiers 3 and/or 4.

Tier 3

• For the determination of the test chemical quantum yield with the use of an actinometer, provide table(s) and graph(s) sh owing the concentrations of the test chemical and actinometer in irradiated and dark

control solutions versus time. Show the best fit regression lines on the graph(s) along with the data points.

• Report the irradiated, dark control, and direct photolysis rate constants of the test chemical and actinometer. Provide the equations, calculations, and regression coefficients used to compute them together with regression n and r 2 values, and standard errors of coefficients (for example, slope, intercept).

• Repo rt the quantum yield of the test chemical . Provide the equation and calculation used to compute it.

• Report estimated direct photolysis rate constants for the test chemical in natural water that are estimated

from the test chemical quantum yield for seaso ns, latitudes, and water body types of interest. Provide and/or describe the equations and calculations or computer program (e .g. GCSOLAR or ABIWAS) and inputs to estimate them.

Tier 4

• If a filtered xenon arc lamp was used, provide the incident photon f lux in a graph as the photon flux (photons/cm 2 • sec) on the y

- axis versus the wavelength (nm) on the x

- axis.

• If sunlight was used, provide tabular values of solar photon fluxes for the season and latitude closest to those of the study.

• Provide table(s) an d graph(s) showing the concentrations of the test chemical and (if applicable) major phototransformation product concentrations and mass balance determinations in irradiated and dark control solutions versus time. Show the best fit regression lines on the graphs along with the data points.

• Report the irradiated, dark control, and direct photoly sis rate constants of the test chemical along with their corresponding half

- lives. Provide the equations, calculations, and regression coefficients used to

compute them together with regression n and r 2 values, and standard errors of coefficients.ENV/JM/TG/RD(2006)1/REV

107 • If applicable, report the rate constants for the formation and decline of the major transformation products. Provide the transformation pathway model (see next paragraph ), equations, calculations, and regression coefficients used to compute them together with regression n and r 2 values, and standard

errors of coefficients.

• Provide chemical structures and names of the test chemical and (if applicable) major transformation products in both irradiated and dark control solutions. Provide graphical presentations of postulated transformation pathways in both the irradiated and dark control solutions.

Indirect photolysis data and results

Tier 1

• When Assuming sunlight was used for indirect photolysis as recommended, provide tabular values of solar photon fluxes for the season and latitude closest to those of the study. When a Xenon arc lamp was used report intensities of irradiation of the lamp and relate it to sunlight (for details, see Annex 6).

• Provide important characteristics of all simulated and/or natural waters used including DOC (= Dissolved Organic Carbon) , humic acid content (if simulated), pH, dissolved oxygen, nitrate. Include the UV-VISIBLE spectrum of the test media from 295 290 to 800 nm. For natural water, include site

of collection.

• Provide table(s) and graph(s) showing the concentrations of the test chemical test substance in

irradiated and dark control solutions versus time. Show the best fit regression lines on the graph(s) along with the data points.

• Report the irradiated, dark control, and approximate net, direct, and indirect photolysis rate constants

of the test chemical test substance along with their corresponding half-lives.

. Provide the equations, calculations, and regression coefficients used to compute them together with regression n and r 2 values,

and standard errors of coefficients.

• Report the approximate indirect (or indirect plus hydroxyl) photolysis rate constant and associated indirect photolysis losses over a 30 days /nights sunlight exposure period. Provide the equations and

calculations used to estimate them. Provide the rati onale for selecting the season and latitude of the average daily solar photon fluxes (L λ ) used in the calculations. Report whether or not the results of the calculations trigger Tier 2 Indirect Photolysis.

Tier 2

• Provide tabular values of solar photon fluxes for the season and latitude closest to those of the study . If a Xenon arc lamp was used, report photon fluxes and/or intensities of irradiation of the lamp and relate it to sunlight (for details, see Annex 6)

.

• Provide important characteristics of all simulated and/or natural waters used including DOC, humic content (if simulated), pH, dissolved oxygen, and nitrate. The UV-VISIBLE spectrum ( 295 290 to 800 nm) of the test media should be included. For natural water, include the site of collection.

• Provide table(s) and graph(s) showing the concentrations of the test chemical test substance and (if applicable ) major transformation product concentrations and mass balance determinations in irradiatedENV/JM/TG/RD(2006)1/REV

108 and dark control solutions versus time. Show the best fit regression lines on the graphs along with the data points.

• Report the irradiated, dark control, and net , direct, and indirect photolysis rate constants of the test
chemical test substance along with their corresponding half-lives. Provide the equations, calculations, and regression coefficients used to compute them together with regression n and r 2 values, and

standard errors of coefficients. If applicable and possible, supply the same information for major transformation products.

• Report the indirect photolysis rate constant and associated indirect photolysis losses over a 30 days sunlight exposure period. Provide the equations and calculations used to estimate them. Provide the rationale for selecting the season and latitude of the average daily solar photon fluxes (L λ ) used in the calculations. Report whether or not the results of the calculations trigger Tier 3 Indirect Photolysis.

• If applicable, report the rate constants for the formation and decline of the major transformation products.

Provide the transformation pathway model (see next paragraph), equations, calculations, and regression coefficients used to compute them together with regression n and r 2 values, and standard

errors of coefficients.

• Provide chemical structures and names of the test chemical and (i f applicable) major transformation products in both irradiated and dark control solutions. Provide graphical presentations of postulated transformation pathways in both the irradiated and dark control solutions.

Tier 3

• Provide table(s) and graph(s) showing the conc entrations of the phototransformation product

concentrations and mass balance determinations in irradiated and dark control solutions versus time. Show the best fit regression lines on th e graphs along with the data points.

• If applicable, report the rate constants for the formation and decline of the transformation products. Provide the transformation pathway model, equations, calculations, and regression coefficients used to compute them together with regression n and r 2 values, and standard errors of coefficients.

• Provide chemical structures and names of the ma jor transformation products in both irradiated and dark control solutions. Provide graphical presentations of postulated transformation pathways in both

the irradiated and dark control solutions.

Additional reporting requirements

General information

• Title of the study, author(s), performing laboratory (name and address), laboratory report identification number, date of completion. In some instances, it may be necessary to identify who is submitting the study, their address and any other identification number.

• Name(s) of the test substance, chemical nomenclature, Chemical Abstracts Registry Number (CAS Reg. No.). A tabular format may be used to present this infomation, but it is optional.

• Physical and chemical properties applicable to th e test substance. As an option, these physical and chemical properties may be listed in a table.ENV/JM/TG/RD(2006)1/REV

109 • Report if the test substance is the primary chemical or any transformation product resulting from abiotic hydrolysis and/or biotransformation. Report if the test substance is an industrial chemical, a pharmaceutical chemical, a pesticide, etc.

• For radiolabelled test substances, the radiolabelled element and isotope, radiolabelling position(s), chemical and radiolabel purity, and specific activity should be reported.

Experimental information

• Standard laboratory equipment and reagents.

• Analytical method(s) used for identifying and quantifying the test substance. The report should include a brief description of the method, reference standards, instrumentation, accuracy and precision, LOD and LOQ. Results of independent laboratory validation (if required).

• Quality Control (QC) results such as analytical recoveries and relative percent standard deviations for replicate analyses.

Specific experimental information related to photolysis (60)

• Experimental conditions, reagents, reaction vessels and other information relevant to each of the tiers comprising the study. This may include:

- Temperature - Solvent and/or buffers used for preparing stock and test solutions for direct photolysis, including dark control samples. - Co-solvent and percent by volume used, if any.

- Nominal and actual concentration of test substance in the test media

• Absorption Spectroscopy:

- Description of instrumentation - Pathlength and material of optical cells - Spectral resolution

- Concentration of test chemical test substance in solution - Co-solvent and percent by volume used, if any - Temperature and pH

• Specific information on reaction vessels:

- Material (type of glass, quartz, etc) - Geometry of the reaction vessels and positioning of the reaction vessels with respect to the light source. - Any significant optical properties of the vessel material (wavelength cut-off, etc.) - Illustration of the reaction vessel(s) arrangement and/or a photograph is encouraged to be included in the report.

• Xenon-light source:

- Manufacturer, modelENV/JM/TG/RD(2006)1/REV

110 - Filters and their purpose - Measured spectrum of the light source between 295 290 and 800 nm at at least the beginning and end of the study. - Comparison of the spectrum of the light with that of natural sunlight for the conditions required for specific tiers. - Intensity (radiant flux, fluence rate) at sample (J m -2 s -1 ; photons m -2 s -1 ) and area irradiated.

• Irradiation dose (fluence) (J m -2 ):

- State if continuous or intermittent irradiation was used - If continuous irradiation, state radiant flux (intensity) and time - If intermittent irradiation, state radiant flux, cycle duration and number of cycles

• Quantum Yields:

- Experimental conditions (temperature, test media, concentration of test substance in test

media

- Description of reaction vessel s (diagram and/or photograph)

- Specify if monochromatic or polychr omatic irradiation was used and source

- Monochromatic wavelength and bandwidth used.

- Intensity (radiance flux)

- Photometric methods, if any

- Chemical actinometer used (criteria for selecti on, concentration of actinometer in test media, absorption spectrum of the actinometer in the test media).

- Positioning of the actinometer with respect to the test substance

• Computational methods for:

- Calculation of molar absorption coefficients ( ε λ ) utilizing Beer-Lambert’s relationship - Maximum photolysis reaction rate assuming φ = 1 ( direct and/or indirect photolysis) - Experimental photolysis reaction rate ( direct and/or indirect photolysis)

- Quantum yield calculations (quantum yield should be expressed as a fraction and not as a percent) - GCSOLAR or ABIWAS calculation of reaction rates at different latitudes, seasons, time of the day, water bodies (when applicable)

. - Half-lives or DT 50 , DT 75 , and DT 90 values and appropriate associated confidence intervals.

Discussion and interpretation of results

171. The purpose of conducting the study should be discussed in terms of the potential for the test
chemical to be present in surface water. For example, chemicals can be transported to surface water in numerous ways including by direct point dischar ge into water bodies, runoff, spray drift or atmospheric deposition.

172. The depth of the discussion depends on the complexity of the study. Regardless of the complexity of the study, the discussion should be focused on the effect sunlight may have on t he rate and pathway of transformation of the test chemical in aqueous environments.

173. The potential for the test chemical to undergo direct and/or indirect photolysis should be discussed. When applicable, the rate constants for irradiated and dark con trol test chemical should be compared to distinguish between hydrolytic and phot olytic transformations. When possible, discuss theENV/JM/TG/RD(2006)1/REV

111 relative contribution(s) of direct and indirect photolysis to the overall net photolysis rate.

174. When quantum yields are determined, the calculated rate constants at different latitudes, seasons and for water bodies with depths and light attenuation coefficients of interest should be used to discuss how sunlight would affect the transformation rate of the test chemical at t he time when the concentration of the chemical in surface water is expected to be the maximum.

175. When transformation products are identified and quantified in direct and indirect photolysis studies, photolytic products should be distinguished from hydr olytic products. When feasible, potential hydrolytic and/or photolytic stability of primary tran sformation products should be included in the results. When available, the rates of formation and decline of primary transformation products should be discusse d. In turn, transformation products from direct and indirect photolysis studies should be compared to distinguish products unique to each.

176. When studies are conducted with both SNW and SNW

- N, the potential contribution of hydroxyl

radical should be assessed by comparing the results in the two types of water.

177. Sources of error and uncertainty such as losses of the test chemical and/or transformation products due to volatilization and/or adsorption to glassware should be discussed.

LITERATURE

1. OECD. 1998. OECD Working Group for the Development of a Test Guideline on

Phototransformation of Chemicals in Water. Rome, 21- 22 September 1998.

2. U.S. EPA. 1998. OPPTS 835.2210 - Direct Photolysis Rate in Water by Sunlight. United States Environmental Protection Agency. Washington, DC. http://www.epa.gov/docs/OPPTS_Harmonized/835_Fate_Transport_Transformation_Test_Guideli

nes/Series/

3. U.S. EPA. 1998. OPPTS 835.5270 - Indirect Phot olysis Screening Test. United States Environmental Protection Agency. Washington, DC.

4. ASTM. 1987. E 896-87: Standard Test Method for Conducting Aqueous Direct Photolysis Tests. American Society for Testing and Materials. Philadelphia PA.

5. U.K. DOE. 1993. Determination of the Stability of Substance in Simulated Sunlight- A proposal for a Test Guideline. Submitted by the Department of the Environment, United Kingdom.

6. UBA. 1992. Direct Phototransformation of Chemical s in Water - A proposal for a Test Guideline. Submitted by UBA, Germany. Berlin.

7. SETAC. 1995. Procedures for Assessing the Environmental Fate and Ecotoxicity of Pesticides. Section 10 in Aqueous Photolysis (page 28- 30). Mark Lynch, Editor. SETAC - Europe

Publication.

8. ECETOC. 1984. The Phototransformation of Ch emicals in Water: Results of a Ring Test. ECETOC Technical Report N o 12. Brussels, BelgiumENV/JM/TG/RD(2006)1/REV

112 9. Van Henegouven B. 1990. Sunlight induced Degradation of Chemicals in Surface Water. Report of Centre for Bio-Pharmaceutical Sciences. Leiden, The Netherlands.

10. OECD. 1997. Guidance Document on Direct Photot ransformation of Chemicals in Water. OECD Environmental Health and Safety Publication. Series on Testing and Assessment No.7. Paris,

France.

21. 19. IUPAC. 1996. Glossary of terms used in photo chemistry (IUPAC Recommendations 1996) Pure & Appl. Chem. 68: pp 2223 - 2286.

22. 20. Leifer A. 1988. The Kinetics of Environmental Aquatic Photochemistry. Theory and Practice. ACS Professional Reference Book. Published by the American Chemical Society. Washington,

D.C.

23. 21. Mill T and Mabey W. 1985. Photodegradation in water. Chapter 8 in Environmental Exposure from Chemicals. Neely W and Blau G, editors. CRC Press. Boca Raton FL. pp. 175-216

24. 22. Harris J. 1982. Rates of Direct Aqueous Phot olysis. Chapter — in Handbook of Chemical Property Estimation Methods. Environmental Be havior of Organic Compounds. Lyman W, Reehl W, and Rosenblatt D, editors. McGraw-Hill Publishers. New York, NY.

25. 23. Mill T, Mabey W, Bomberger D, Chou T, Henry D, and Smith JH. 1982. Laboratory Protocols for Evaluation of the Fate of Organic Chemicals in Air and Water. U.S. Environmental Protection Agency. EPA 600/3-82-002. Washington, D.C.

26. 24. Mill T, Davenport J, Dulin D, Mabey W, and Bawol R. 1981. Evaluation and Optimization of Photolysis Screens. U.S. Environmental Pr otection Agency. EPA 560/5-81-003. Washington,

D.C.

27. 25. Zepp R. 1978. Quantum yields for reaction of pollutants in dilute aqueous solutions. Environ. Sci. & Technol. 12: pp. 327-329.

28. 26. Zepp R, and Cline D. 1977. Rate of direct photolysis in aquatic environment. Environ. Sci. & Technol. 11(4): pp. 359-366.

19. Boule P., Guyon C. and Lemaire J. 1982. Photochemistry and Environment IV : Photochemical behaviour of monochlorophenols in aqueous dilute solution. Chemosphere 11, 1179-1188.

20. Boule P., Guyon C., Tissot A. and Lemaire J. 1987. Specific phototransformation of xenobiotic compounds : chlorobenzene and chlorophenols. Photoc hemistry of Environmenta l Aquatic Systems (R.G. Zit % W: J. Cooper, eds.), Miami, 10-26.

29. 21. Zepp R, Schlotzhauer P, and Sink R. 1985. Phot osensitized transformations involving electronic energy transfer in natural waters: Role of humic substances. Environ. Sci. & Technol. 19: pp. 74-81.

30. 22. Zepp R, Baughman G, and Scholtzhauer P. 1981. Comparison of photochemical behavior of various humic substances in Water. I. Sunlight induced reactions of aquatic pollutants photosensitized by humic substances. Chemosphere 10: pp. 109-117.

31. 23. Mill T. 1999. Predicting photoreaction rates in surface water. Chemosphere 38(6): pp. 1379-

1390.ENV/JM/TG/RD(2006)1/REV

113 32. 24. Brezonik P and Fulkerson-Brekken J. 1998. Ni trate-induced photolysis in natural waters: Controls on concentrations of hydroxy radical photo-i ntermediates by natural scavenging agents. Environ.

Sci. & Technol. 32: 3004-3010.

33. 25. Vaughan P and Bough N. 1998. Photochemical formation of hydroxy radical by constituents of

natural waters. Environ. Sci. Technol. 32: 2947- 295 290 3.

34. 26. Blough N and Zepp R. 1995. Reactive oxygen species in natural waters. Chapter in Active Oxygen in Chemistry. Foote C, Valentine G, Gree nberg A, and Liebman J, editors. Published by Chapman and Hall. New York, NY. pp. 280-333.

35. 27. Mabury S and Crosby D. 1994. The relationship of the hydroxyl reactivity to pesticide persistence. Chapter 10 in Aquatic and Surface Photochemistry. G Helz, R Zepp, and D Crosby, editors. Lewis Publishers. Boca Raton, Florida, USA. pp. 149- 161.

36. 28. Zepp, R.G., Hoign é e , J. and Bader, H. 1987. Nitrate-induced photooxidation of trace organics in

water. Environ. Sci. Technol. 21: 443-450.

37. 29. Haag W and Hoign é e’ J. 1986. Singlet oxygen in surface waters. III. Steady state concentrations in various types of waters. Environ. Sci. & Technol. 20: 341-348.

38. 30. Haag W, Hoign é e’ J, Gassmann E, and Braun A. 1984. Singlet oxygen in surface waters. II. Quantum yields of its production by some natural humic materials as a function of wavelength. Chemosphere 13: pp. 641-650.

39. 31. Mill T, Hendry D, and Richardson H. 1980. Free radical oxidants in natural waters. Science 207: pp. 886-889.

40. 32. Draper W and Crosby D. 1981. Hydrogen peroxi de and hydroxyl radical: Intermediates in indirect photolysis reactions in water. J. Agric. Food Chem. 29: pp. 699.

41. 33. Wolff C, Halmans M and Van der Heijde H. 1981. The formation of singlet oxygen in surface waters. Chemosphere 10: pp. 59.

42. 34. Zepp R, Wolfe N, Baughman G, and Hollis R. 1977. Singlet oxygen in natural waters. Nature 267: pp. 421-423.

43. 35. Zhou, X. and Mopper, R. 1990. Determination of photochemically produced hydroxyl

radicals in seawater and fresh water. Mar. Chem. 30: 71-88.

44. 36. Mopper, R. and Zhou, X. 1990. Hydroxyl radical photoproduction in the sea and its potential impact in marine processes. Science 250: 661-664.

37. Aguer J.P., Richard C. and Andreux F. 1997. Comparison of the photoinductive properties of commercial, synthetic and soil extracted humic s ubstances. J. Photochem. Photobiol. A 103, 163-168.

38. Vialaton D., Richard C., Baglio D. and Paya-P erez A. 1998. Phototransformation of 4-chloro-2- methylphenol in water; influence of humic substanc es on the reaction. J. Photochem. Photobiol. A 119, 39-

45.ENV/JM/TG/RD(2006)1/REV

114 39. Niessen R., Lenoir D. and Boule P. 1988. Phototransformation of phenol induced by excitation of nitrate ions. Chemosphere 17, 1977-1984.

40. Mailhot G., Astruc M. and Bolte M. 1999. Degradation of tributyltin chloride in water photoinduced by iron(III). Applied Organometallic Chem. 13, 53-61.

45. 41. Frank R and Klöpffer W. 1988. Spectral solar photo irradiance in Central Europe and the adjacent North Sea. Chemosphere 10: p. 985.

46. 42. Frank R and Klöpffer W. 1988. A convenient mode l and program for the assessment of abiotic degradation of chemicals in natural waters. Ecotox. Environ. Safety 17: pp. 323-332.

47. 58. Calvert, J.G. and Pitts, J.N., Jr. 1966. Photochemistry. Wiley, New York, USA.

35. Turro N. 1991. Modern Molecular Photochemistry. Published by University Science Books. Sausalito, California, USA.

49. 43. Zepp R. 1999. Personal communication (December 30, 1999).

50. 44. Faust B. 1994. A review of the photochemical redox reactions of iron(III) species in atmospheric, oceanic, and surface waters: Influence on geochemical cycles and oxidant formation. Chapter 1 in Aquatic and Surface Photochemistry. G Helz, R Zepp, and D Crosby, editors. Lewis Publishers. Boca Raton, Florida, USA. pp. 3- 35

51. 45. Su l i zberger B, Laubscher H, and Karametaxas G. 1994. Photoredox reactions at the surface of iron (III) hydr(oxides). Chapter 3 in Aquatic and Su rface Photochemistry. G Helz, R Zepp, and D Crosby, editors. Lewis Publishers. Boca Raton, Florida, USA. pp. 53- 73.

52. 46. U.S. EPA. 1985. Hazard Evaluation Division. Standard Evaluation Procedure: Aqueous Photolysis Studies. Office of Pesticide Programs , U.S. Environmental Protection Agency. EPA-540/9-85-

014 47. OECD Test Guideline 111. 2003 Hydrolysis as a Function of pH.

53. 48. Ruzo L, Shepler K, and Toia R. 1995. Pesticide hydrolysis and photolysis studies: Guideline challenges and experimental approaches. Chapter 8 in Agrochemical Environmental Fate - State of the Art. M Leng, E Leovey, and P Zubkoff, editors. Lewis Publishers. Boca Raton, Florida, USA. pp 77- 91.

49. European Union (EU). 1995. Commission Dire ctive 95/36/EC amending Council Directive 91/414/EEC concerning the placing of plant protec tion products on the market. Annex I: Fate and

behaviour in the Environment.

50. Méallier, P. 1999. The handbook of Environmental Chemistry (C. Richard and G. Grabner, eds.),

240-260.

54. 51. Gao H and Zepp R. 1998. Factors influencing photoreactions of dissolved organic matter in a

coastal area of the Southeastern United States. Environ. Sci. Technol. 32: 2940-2946.

55. 52. IHSS. 1999. Typical Humic Acid Data Packet. International Humic Substances Society (IHSS). Available from website http://ihss.gatech.edu/dataha.html.

56. 53. Zepp R and Schlotzhauer P. 1981. Chemosphere 10: pp. 479ENV/JM/TG/RD(2006)1/REV

115 57. 54. Zepp, R.G. 1982. Experimental Approaches to Environmental Photochemistry. Chapter in the Handbook of Environmental Photochemistry, edited by Hutzinger, O.; Springer-Verlag, New York 2, Part B: pp 19-40.

58. 55. Faust, B.C. 1993. Generation and use of simulated sunlight in photochemical studies of liquid solutions. Rev. Sci. Instrum. 64:(2) pp. 577- 578.

59. 56. (a) The Book of Photon Tools. 1999. Drozdowicz, Z., Editor. Oriel Instruments, Stratford, Connecticut 006615, USA. (b) Atlas Electric Devices Company, 114 Ravenswood Avenue, Chica go, Illinois 60613 USA.Oriel Instruments. 1999.

60. 57. Lemarie, J., Guth, J. A., Klais, D., Leahey, J., Merz, W., Philp, J. Wilmes, R., and Wolff C.J.M. 1985. Chemosphere, 14: pp 53- 77.

61. 58. Mill T. 2000. Documents on Calibration of Lamp and Indirect Photoreaction Estimation Methods, prepared for and submitted to the U.S. Environmental Protection Agency, Office of Pesticide Programs under PR Number 9W-2901-NASA, February 22, 2000.

59. Calvert, J.G. and Pitts, J.N., Jr. 1966. Photochemistry. Wiley, New York, USA.

36. Dulin D. and Mill T. 1982. Development and eval uation of sunlight actinometers. Environ. Sci. Technol. 16(11): pp. 815

- 820.

37. Zepp, R.G., Gumz, M.M., Miller, W., an d Gao, H. 1998. Photoreaction of Valerophenone in Aqueous Solutions. J. Phys. Chem. A, 102: pp. 5716

- 5722.

38. Murov et al. 1993. Chemical Actinometry. In Handbook of Photochemistry. 2 nd ed. Marcel Decker Inc., New York. pp. 298

- 305.

39. Millet et al. 1998. Ab iotic Degradation of Halobenzonitriles: Investigations of the Photolysis in Solution. Ecotoxicol. Environ. Safety. 41: pp. 44

- 50.

40. Heller, H. and Langan J. 1981. A new reusable chemical actinometer. EPA Newsletter 71.

41. Bahnemann, D. 1993. Ultra

- small metal oxide particles: preparation, photophysical characterization and photocatalytic properties. Isr. J. Chem. 33: pp. 115.

42. IUPAC. 1989. Chemical Actinometry. Prepared for publication by H.J. Kuhn, S.E. Braslavsky, and R. Schmidt. Pure & Appl. Chem., Vol. 6 1, No. 2, (1989) pp. 187

- 210.

69. 60. Winterle J and Mill T. 1985. Toxic substances process data generation and protocol development. Work assignment 18: Indirect Phot oreaction Protocol. Submitted to Office of Toxic Substances, U.S. Environmental Protection Agency. EPA Contract No. 68-03-2981.

70. 61. IUPAC. 1984. Recommended Standards for Re porting Photochemical Data (1984). Pure & Appl. Chem. 56: pp 939- 934.

71. 62. AWWA. 1991. Standard Methods for the Analysis of Water and Wastewater. American Water Works Association, 6666 West Quincy Avenue, Denver, Colorado 80 295 290 , USA. http://www.awwa.org/stanmeth/contents.htmENV/JM/TG/RD(2006)1/REV

116 72. Mill T, Mabey W, Winterle J, Davenport J, Barich V, Dulin D, Tse D, and Lee G. 1982. Design and validation of screening and detailed method s for environmental processes. Final Report. Submitted to Office of Toxic Substances, U.S. Environmental Protection Agency. EPA Contract No. 68

- 01

- 6325.ENV/JM/TG/RD(2006)1/REV

117 ANNEX 1

Definitions and Units

Test substance: any substance, whether the parent compound or relevant transformation products

Transformation products: all substances resulting from biotic or abiotic transformation reactions of the test substance including CO 2

.

Half-Life, t 0.5 is the time taken for 50% transformation of a test substance when the transformation can be described by first-order kinetics; it is independent of the concentration.

DT 50 (Disappearance Time 50) is the time within which the concentration of the test substance is reduced by 50%; it is different from the half-life t 0.5 when transformation does not follow first-order kinetics.

DT 75 (Disappearance Time 75) is the time within which the concentration of the test substance is reduced by 75%.

DT 90 (Disappearance Time 90) is the time within which the concentration of the test substance is reduced by 90%.

The limit of detection (LOD) is the concentration of a substance below which the identity of the substance cannot be distinguished from analytical artefacts.

The limit of quantification (LOQ) is the concentration of a substance below which the concentration cannot be determined with an acceptable accuracy.

The definitions and units are taken from the Glossary of terms used in photochemistry (IUPAC Recommendations 1996) published in Pure and Applied Chemistry, 68 , 2223-2286, 1996. Commonly used and SI units are provided. Cited with permission from the International Union of Pure and Applied Chemistry

Absorbance (A), [Dimensionless] - The logarithm to the base 10 of the ratio of the spectral radiant power of incident, essentially monochromatic radiation (I= ∫ λ I λ d λ ) to the radiant power of transmitted radiation (P λ ):

A = log(P λ o /P λ ) = -log T

In practice, absorbance is the logarithm to the base 10 of the ratio of the special radiant power of light transmitted through the reference sample to that of the light transmitted through the solution, both observed in identical cells. T is the (internal) transmittance. The terms “absorbancy”, “extinction” and “optical density” should no longer be used.

Absorption Coefficient (a) , [m -1 or cm -1 ] - Absorbance divided by the optical pathlength, l. The term “absorptivity” is not recommended

Actinometer - A chemical system or physical device which determines the number of photons in a beam integrally or per unit time and it is commonly applied to devices used in the ultraviolet and visible wavelength ranges. Examples of a chemical actinometers are iron(III) oxalate solutions. Examples of physical devices are bolometers, thermopiles and phot odiodes. Actinometers give a reading that can be correlated to the number of photons detected.ENV/JM/TG/RD(2006)1/REV

118 Beer-Lambert Law - The absorbance of a beam of collimated monochromatic radiation in a homogeneous isotropic medium is proportional to the absorption pathlength, l , and to the concentration, c. This law holds only under the limitations of the Lambert Law and for absorbing species exhibiting no concentration dependent aggregation. The law can be expressed as,

A = log(P λ o /P λ ) = ε c l

or
P λ

= P λ o 10
- ε cl

where the proportionality constant, ε , is called the molar (decadic) absorption coefficient.

Units: For l in cm and c in mol dm 3 or M, ε will result in dm 3 mol -1 cm -1 or M -1 cm -1 . These are the commonly used units. The SI units for ε is m 2 mol -1

.

Chromophore - That part of a molecular entity consisting of an atom or group of atoms in which the electronic transition responsible for a given spectral band is approximately localized.

Depth of Penetration (of light), [m] - The inverse of the absorption coefficient . If the decadic absorption coefficient, a , is used, the depth of penetration (1/ a ) is the distance at which the spectral radiant power, P l decreases to one tenth of its incident value, P λ o

.

Einstein - One mole of photons . It is not an IUPAC-sanctioned unit. It is sometimes defined as the energy of one mole of photons.

Energy Transfer - From a phenomenological point of view, the term is used to describe d the process by which a molecular entity absorbs light and a phenomenon originates from the excited state of another molecule. In mechanistic photochemistry, the term has been reserved for the photophysical process in which an excited state of a molecular entity (the donor) is deactivated to a lower-lying state by transferring energy to a second molecular entity (the acceptor), which is thereby raised to a higher energy state. The excitation may be electronic, vibrational, rotational or translational. The donor and acceptor may be two parts of the same molecule, in which case the process is called intramolecular energy transfer

.

Excited State - A state of higher energy than the ground state of a chemical entity. In photochemistry an electronically excited state is usually meant.

Frequency (v or ω ), [sec -1 or rad*sec -1 ] - The number of waveperiods per unit time. The linear frequency, v, is the number of cycles per unit time. For the angular frequency, the symbol ω (= 2 π v) is used.

Ground State - The lowest energy state of a chemical entity. In photochemistry, ground electronic state is usually meant.

Half-width (of a band) - The full width of a spectral band at a height equal to half of the height at the band

maximum. Also known as full width at half maximum (FWHM). The dimensions of band width should be either inverse length ( wavenumbers, ) or inverse time ( frequencies ) so that the values give an indication of the energies. Note the hyphen in half-width. Half bandwidth has the meaning of half -width at half

maximum.

Hyperchromic Effect - Increase in the intensity of a band due to substituents or interactions with the molecular environment. Hypochromic effect is the opposite to hyperchromic effect.

Intensity - Traditional term for photon flux, irradiance or radiant power (radiant flux) . In terms of an objectENV/JM/TG/RD(2006)1/REV

119 exposed to radiation, the term should now be used only for qualitative descriptions.

Intensity (l) (of a light source)- Same as radiant intensity.

Intensity (of a spectral feature)- Describes the magnitude of the particular feature in the spectrum.

Irradiance (E) , [W m -2 ] - The radiant flux or radiant power, P, of all wavelengths incident on an infinitesimal element of surface containing the point under consideration divided by the area of the element (d P /d S, , simplified expression: E= P/S when the radiant power is constant over the surface area
considered). E = ∫ E

λ d λ , where E λ is the spectral irradiance at wavelength λ . For a parallel and perpendicular incident beam not scattered or reflected by the target or its surrounding fluence rate (E o ) is an equivalent term.

Lambert Law - The fraction of light absorbed by a system is independent of the spectral radiant power (

P λ o ). This law holds only if P λ o is small, scattering is negligible, and multiphoton processes, excited state populations, and photochemical reactions are negligible.

Lamp - A source of incoherent radiation.

Molar Absorption Coefficient, Molar Decadic Absorption Coefficient - [dm 3 mol -1 cm -1 , M -1 cm -1 or dm 3 mol -1 mol -1 ]

Absorbance divided by the absorption pathlength, l, and the concentration,

. ε = [1 / c l ] log(P λ o /P λ ) = A / c l : The term molar absorptivity for molar absorption coefficient should be avoided.

Photochemical Reaction - This term is generally used to describe a chemical reaction caused by absorption of ultraviolet, visible, or infrared radiation.

Photochemistry - The branch of chemistry concerned with the chemical effects of light (far UV to IR).

Photodegradation - The photochemical transformation of a molecule into lower molecular weight fragments, usually in an oxidation process. This term is widely used in the destruction (oxidation) of pollutants by UV-based processes.

Photolysis - A light-induced bond cleavage.

Photon - The quantum of electromagnetic energy at a given frequency . This energy, E = hv is the product of the Planck ( h) constant and the frequency of the radiation (v).

Photooxidation - Reactions induced by light. Common process are:

• The loss of one or more electrons from a chemical species as a result of photexcitation of that species;

• The reaction of a substance with oxygen under the influence of light. When oxygen remains in the product this latter process is also called photooxygenation. Reactions in which neither the substrate nor the oxygen are electronically excited are sometimes called “photoinitiated oxidations”.

Photoreductions - Reduction reactions induced by light. Common process are:

• Addition of one or more electrons to a photoexcited species;

• The photochemical hydrogenation of a substance. Reactions in which the substrate is not electronically excited are sometimes called “photinitiated reductions”.ENV/JM/TG/RD(2006)1/REV

120 Photosensitization - The process by which a photochemical or photophysical alteration occurs in one molecular entity as a result of initial absorption of radiation by another molecular entity called a photosensitizer . In mechanistic photochemistry the term is limited to cases in which the photosensitizer is

not consumed in the reaction.

Primary Photochemical Process (Primary Photoreaction) - Any elementary chemical process undergone by an electronically excited molecular entity yielding a primary photoproduct.

Primary (Photo)product - The first observable chemical entity which is produced in the primary photochemical process and which is chemically different from the reactant.

Quantum (of radiation) - An elementary particle of electromagnetic energy in the sense of the waveparticle duality.

Quantum Yield ( φ ) - The number of defined events which occur per photon absorbed by the system. The integral quantum yield is:

φ = number of events/ number of photons absorbed

For a photochemical reaction,

φ = amount of reactant consumed or produ ct formed/amount of photons absorbed

The differential quantum yield is Φ = d[x]/dt /n, where d[x]/dt is the rate of change of a measureable quantity, and n is the amount of photos (mol or its equivalent einstein) absorbed per unit time. Φ can be used for photophysical processes or photochemical reactions.

Radiant Energy ( Q), [J]

- The total energy emitted, transferred or received as radiation of all wavelengths in a defined period of time ( Q= ∫ Q λ d λ ). It is the product of radiant power, and time, t:Q= P t when the radiant power is constant over the time considered.

Radiant Exposure (H) , [J m -2 ] - The irradiance, E, integrated over time of irradiation ( ∫ E d t , simplified expression H= E t when the irradiance is constant over the time considered).

Radiant Intensity (I), [W sr -1 ] - Radiant (energy) flux or radiation power, P, at all wavelengths per unit solid angle, ω . The radiant power emitted in a given direction by a source or an element of the source in an infinitestimal cone containing the given direction divided by the solid angle of the cone (dP/d ω , simplified expression: I = P/S when the radiant power is constant over the surface area considered).

Radiant Power (P) , [J s -1 , or W] - Power emitted, transferred or received as radiation.

Singlet Molecular Oxygen - The oxygen molecule (dioxygen), O 2 , in an excited singlet state. The ground

state of oxygen is a triplet 3 Σ g - ). The two metastable singlet states derived from the ground state configuration are 1 ∆ g and 1 Σ g -

. The IUPAC discourages the use of the term “singl et oxygen” alone, without mentioning the oxygen species (in this case, dioxygen) to avoid confusion with 1S and 1D excited states of the oxygen atom.

Singlet State - A state having a total electron spin quantum number equal to 0.ENV/JM/TG/RD(2006)1/REV

121 Solvent Shift - A shift in the frequency of a spectral band of a chemical species arising from its interaction

with its solvent environment. Bathochromic shift , also known to as “red shift”, refers to the shift of a spectral band to lower frequencies (longer wavelenghts) as result of interaction with the solvent Hypsochromic shift , also known as “blue shift”, refers to the shift of a spectral band to higher frequencies (shorter wavelengths) as a result of interaction with the solvent..

Spectral Irradiance (E λ ) , [W m -3 , or W m -2 nm -1 ] - Irradiance, E, at wavelength λ per unit wavelength.

Triplet State - A state having a total soin quantum number of 1.

Wavelength ( λ ) - The distance, measured along the line of propagation, between two corresponding points on adjacent waves. The wavelength depends on the medium in which the wave propagates

Wavenumber ( σ
, υ ) , [m -1 or cm -1 ]- The reciprocal of the wavelength, λ , or the number of waves per unit length along the direction of propagation.

Xenon Lamp - An intense source of ultraviolet, visible a nd near-infrared light produced by electrical discharge in xenon under high pressure.ENV/JM/TG/RD(2006)1/REV

122 ANNEX 2

Symbols and Units Related to Photochemistry

Symbol Name SI Units Common Units

A Absorbance Dimensionless Dimensionless

a Decadic absorption

coefficient m -1 cm -1

D Attenuance Dimensionless Dimensionless

H

0 Fluence J m -2 Same

E

0 Fluence rate W m -2

E Irradiance W m -2

ε Molar (decadic) absorption coefficient m -2 mol -1 cm -1 dm 3 mol -1 or

cm 2 mmol -1

Sometimes L mol -1 cm -1

φ Quantum yield Dimensionless a Dimensionless a

Q Radiant energy J

H Radiant exposure J m -2

I Radiant intensity W sr -1

P W

I Spectral radiance intensity W sr -1 m -1 W sr -1 nm -1

λ Wavelength m nm

σ ; υ Wavenumber m -1 cm -1ENV/JM/TG/RD(2006)1/REV

123 ANNEX 3

Proposed test scheme for indirect photolysis

Tier 1: Experimental Screen Estimation of Indirect Photolysis Rate

in SNW and/or SNW-N and/or NWs

and PW

Decision Criteria: Photolysis Loss ≥ 20% in 30 Days Sunlight Exposure? no

yes

Tier 2 Kinetics Study Determination of Indirect Photolysis

Rate in SNW and/or SNW-N and/or

NWs and PW

Decision criteria: Photolysis Loss ≥ 20% in 30 Days Sunlight Exposure? no

yes

Tier 3: Isolation/Identification Of Major Phototransformation Products ( ≥ 10% of dose applied) No Further Photolysis WorkENV/JM/TG/RD(2006)1/REV

124 Figure 1: Proposed test scheme for direct photolysis

Tier 1

- Theoritical Screen

3. If the test chemical absorbs solar irridiation > 295 nm, estimate a maximum direct photoly sis rate

constant K d(max) in shallow natural water by assuming the quantum yield φ = 1; K d(max) = Σ ε λ L λ 4. Determine if the maximum direct photolysis rate constant would result in estimated direct photolysis

losses of ≥ 20% of an initial concentration over a 30

- day/night sunlight exposure period using the following equation: C/C 0 = exp [

- K d(max) (30

- days) ]

Yes ↓ → No → Quit or go to Tier 1 Indirect Photolysis

Tier 2

- Experimental Screen

4. Measure the de cline of the test chemical in sterilised buffer exposed to a xenon lamp or sunlight. If data fit a first order kinetics model, determine the apporximate direct photolysis rate.

5. Determine if approximate direct photolysis rate constant would result in estima ted direct photolysis losses

of ≥ 10% of an initial concentration from the following equation: C/C 0 = exp [

- K d(max) (30 days)] If yes, go to next step; if no, quit or go to Tier 1 Indirect Photolysis.

6. Is there interest in determining the quantum yield and i n estimating theoretical direct photolysis rate constant from the quantum yield?

Yes ↓ → No → Go to Tier 4 Direct Photolysis

Tier 3

- Quantum Yield and Estimation of Theoretical Rate constant

3. Determine the quantum y ield and use it to estimate theoretical direct photolysis rate constant for seasons, latitudes, elevations and types of water bodies of interest.

4. Is there interest in comparing experimental direct photolysis rate constants with theoretical ones and/or

iden tifying/quantifying major transformation products?

Yes ↓ → No → Quit or go to Tier 1 Indirect Photolysis

Tier 4

- Determine the Direct Photolysis Rate Constant

4. Measure the decline of the test chemical (a nd if of interest) the formation and decline of major transformation products in sterilised buff ers exposed to a xenon lamp or sunlight.

5. If data fit a first order kinetics model, determine the direct photolysis rate constants and corresponding

half

- life. O therwise, determine the DT 50 , DT 75 and DT 90 values from fitting data to a non

- first order model. If practical and of interest, determine the same parameters for major transformation products.

6. Is there interest in indirect photolysis? If yes, go to Tier 1 I ndirect Photolysis; if no, quit.ENV/JM/TG/RD(2006)1/REV

125 Figure 2: Proposed Test Scheme for Indirect Photolysis

Tier 1

- Screen

4. Measure the decline of the test chemical in synthetic water containing humics (and if applicable, nitrate)

in buffered distilled water and estima te indirect photolysis rate constant K i(approx). 5. Determine if the approximate indirect photolysis rate constant would result in estimated indirect photolysis losses of ≥ 10% of an initial concentration over a 30

- day/night sunlight exposure period using the following equation: C/C 0 = exp [

- K i(approx) (30 days)]

6. In some cases, it may be possible to supplement or even replace the experimental screen with a theoretical screen based on using structural activity relationships (SARs) to estimate second order rate constants and on information on the typical concentrations of photooxidation in surface water.

Yes ↓ → No → Quit

Tier 2

- Definitive Indirect Photolysis Test

4. Measure the decline of the test chemical (and if of interest) the formation and decline of majo r transformation products in synthetic and/or natural waters and in buffered distilled water exposure to a xenon lamp or sunlight.

5. If data fit a first order kinetics model, estimate net, indirect, and direct photolysis rate constants and corresponding half

- lives for the test chemical . Correct for photobleaching and attenuation effects.

6. If data fit a non

- first order model, determine the DT 50 , DT 75 and DT 90 values for fitting data to a non

first order model. If practical and of interest, determine the same pa rameters for major transformation products.ENV/JM/TG/RD(2006)1/REV

126 ANNEX 4

Derivations of Selected Equations

Background equations from Leifer (12):



# d C

dt j I jD IF F

sys 

# [ ]     



=− =−

λ λ λλ λ 

# φ φ

(abs by chem) (abs by sys) (abs by chem) 0

[eq. 3

- 1]



# d C

dt j I jD IF F

sys 

# [ ]

=− =− 

# ∑ ∑ φ φ

λ λλ λ

295 800

295 800

0 (abs by chem) (abs by sys) (abs by chem)

[eq. 3

- 2]

where:

φ = quantum yield j = conversion factor to make units consisten t with the L/mol • cm unit of the molar absorption

coefficient and the mol/L unit of concentration =

6.02 x 10 20 (L/cm 3 )(photons/mol)

I λ (abs by chem) = photon absorption rate by the chemical per unit volume over a 1 nm interval centered at wavelength λ ( photons/cm 3 • day)

D sys = depth of irradiated system (cm) = volume of irradiated system/incident area

I 0 λ = incident photon flux over a 1 nm interval centered at wavelength λ
(photons/cm 2 • day)

F λ (abs by sys) = fraction of incident photon flux abs orbed by the system

F λ (abs by chem) = fraction of incident photon flux absorbed by the chemical



# [ ]

F I I

I I

I t C l

C l
λ λ λ

λ λ α ε

λ α ε λ λ

λ λ (abs by sys) 

### = −

= −

= − − +

− + 0

0 0

0 

### 1 10 1 10 ( [ ])

( [ ])

[eq. 3

- 3]



# F C

C λ λ

λ λ 

# ε

α ε (abs by chem) 

# = + [ ]

[ ]

[eq. 3

- 4]

where:

α λ = attenuation coefficient of the system at wavelength λ (1/cm)ENV/JM/TG/RD(2006)1/REV

127 ε λ = molar absorption coefficient o f the chemical at wavelength λ (L/mol • cm)

l = light pathlength (cm)

Inserting equations 3

- 3 and 3

- 4 into equation 3

- 1 gives:



# [ ] d C

dt jD I C

C

sys C l 

## [ ] [ ]

[ ] ( [] 

##     

 =− − • + 
  


 − +

λ λ α ε λ

λ λ 

## φ ε

α ε λ λ 0 

## 1 10

[eq. 3

- 5]

Summing equation 3

- 5 over all wavelengths from 295 nm to 800 nm gives:



## [ ] d C

dt jD I C

C

sys C l [ ] [ ]

[ ] ( [] =− − • + 
  


 − +

= = 

## ∑ φ ε

α ε λ α ε λ

λ λ λ λ

λ λ 0

295 800 1 10

[eq. 3

- 6]

For sol ar irradiation on an aqueous system (12),



# I t It It solar d s 0 λ λλ ( ) 

# () () () = +

[eq. 3

- 7]



# lD t

d sys 

# ≅ sec ( ) θ

[eq. 3

- 8]



### l D

s sys 

### = 12

. [eq. 3

- 9]

where:

I 0 λ (solar) = total incident solar photon flux as a function of time

I d λ (solar) = direct incident solar photon flux as a function of tim e
I 0 λ (solar) = sky radiation incident solar photon flux as a function of time

l d = average light pathlength for direct irradiation

l

s = average light pathlength for sky irradiation



# [ ] [ ] 

# { } dC

dt jD I I C

C

sys d C D

s C D sys 

### =− − + − + 
  
  − + − +

= = 

# ∑ φ ε

α ε λ αε θ

λ α ε λ

λ λ λ λ

λ λ λ λ 

### 1 10 1 10 1 2

295 800 ( [ ]) sec ( [ ]) . 

### [ ]

[ ]

[eq. 3

- 10]

Derivation of equation 5 in the main text (12) :

10
- y = exp(

- 2.3y) [eq. 3

- 11]

Therefore,ENV/JM/TG/RD(2006)1/REV

128 

# { } 1 10 1 2 3 1

− =− − + =− − − +

( [ ]) 

# exp . ( [ ]) exp( )

α ε λ λ

λ λ 

# α ε C l 

# Cl x

[eq. 3

- 12]

where: 

# ( ) x Cl A =+ = 23 23

. [] . α ε λ λ

[eq. 3

- 13]

A = absorbance of the solution

A series expansion of the exponential in equation 3

- 12 gives:



### 1 2 3 4 5 2345



### − − = + − + − + ⋅⋅⋅⋅⋅

exp( ) ! ! ! ! x x xxxx

[eq. 3-14]

For an optically dilute soluti on of a test chemical in pure water or in shallow water or in the near surface of natural water such that the absorbance of the system is < 0.02, all of the higher terms in equation 3

- 14 are small compared to x such that equation 3

- 14 reduces to:



# 1 − −≅ exp( ) x x

[eq. 3

- 15]

Combining equations 3

- 13 and 3

- 15 with equation 3

- 12 gives for an optically dilute solution of a test
chemical in pure water or clear shallow water or in the near surface of natural water: 

# ( ) 1 10 2 3

− ≅+ − +

( [ ]) 

### . [] α ε λ λ

λ λ 

### α ε C l 

### C l

[eq. 3

- 16]

Substituting equation 3

- 16 into equation 3

- 6 and canceling out the resulting identical terms in the numerator and denominator gives for an optically dilute solution of a test chemical in pure water or in clear

shallow water or in the near surface of natural water:

d C

dt j l

D I C

sys [] . [ ] = − 

   

  

= = 

### ∑ 2 3

0

295 800 φ

ε λ λ
λ λ

[eq. 3

- 17]

By comparing equation 3

- 17 to equation 1 in the main text, it can be seen that for a test chemical in an optically dilute solution in pure water or in clear shallow water or in the near surface of natural water, the direct photolysis rate constant is given by:

k j l

D I d

sys

= 

### ∑

2 3

0

295 800

. φ ε λ λ
[eq. 3

- 18]

where equation 3

- 18 is identical to equation 5 of the main textENV/JM/TG/RD(2006)1/REV

129 Derivation of equation 6 in the main text (12)

By analogy to equation 3

- 16, it can be seen that for a solar irradiated, optically dilute solution of a test
chemical in pure water or in clear shallow water or in the near surface of natural water such that the absorbance of the system is < 0.02,

1 10 2 3

− ≅+ − + ( [ ]) sec . ( [ ]) sec αε θ

λ λ λ λ αε θ C D

sys sys C D [eq. 3

- 19]

1 10 2 3 12 1 2 − ≅+ − + ( [ ])( . ) . ( [ ])( . ) α ε
λ λ λ λ α ε C D

sys sys C D [eq. 3

- 20]

Substituting equations 3

- 19 and 3

- 20 into equation 3

- 10 and c anceling out the resulting identical terms in the numerator and denominator gives:

d C

dt j Zt C [] . ()[ ] = − 

  

  

### ∑ 2 3

φ

ε λ λ
[eq. 3

- 21]

where:

Zt I t I t d s λλ λ θ ( ) ( ) sec . ( ) = + 12 [eq. 3

- 22]

Equation 3

- 21 gives the direct photolysis rate as a function of time because the solar photon flux at any given wavelen gth varies over time as represented by Z(t) for an optically dilute solution.

Z Z t dt

hours λ λ

= 

### ∫ ( )

0 24

24 [eq. 3

- 23]

Mill et al (1985) defined 24 hour average solar irradience values as:

L j Z

λ λ

= 2 3

. [eq. 3

- 24]

Substituting equation 3

- 24 into 3

- 21 gives the average direct photolysis rate over a 24

- hour period:

d C

dt L C [ ] [ ]      

= − 

  

  

### ∑ φ ε λ λ
[eq. 3

- 25]

By comparing equation 3

- 25 to equation 1 in the main text, it can be seen that for an optically dilute

solution of a test chemical in pure water or clear shallow wat er or in the near surface of natural water exposed to sunlight, the 24 hour average direct photolysis rate constant is given by:

k L

d solar ( ) = 

### ∑ φ ε λ λ

295 800 [eq. 3

- 26]ENV/JM/TG/RD(2006)1/REV

130 where equation 3

- 26 is identical to equation 6 in the main text.

Derivation of equation 8 in the main text:

Rearranging equation 3

- 2 gives the total photon absorption rate per unit volume by the test chemical :

I I jdC

dt abs by chem abs by chem () () [ ]

= =−



### ∑

λ φ 295 800
[eq. 3

- 27]

where:

I λ (abs by chem) = photon absorption rate by the chemical per unit volume over a 1 nm interval centered at wavelength λ (photons/cm 3 • day)

I (abs by chem) = total photon absorption rate by the chemical per unit volume (photons/cm 3 • day)

Multiplying equations 3

- 18 and 3

- 25 by (

- j / .) gives the total photon absorption rate per unit volume by the

test chemical in an optical ly dilute solution exposed to xenon arc lamp or solar irradiation, respectively:

I l

D I C

sys xenon xenon ( xenon abs by chem)

=295 = 

   

   = 

### ∑ 2 3 0 800 . [] ( ) ε λ λ
λ λ

[eq. 3

- 28]

I j LC solar (solar abs by chem) = 

  

  

### ∑ ε λ λ [ ] [eq. 3

- 29]

The total number of photons absorbed per unit volume by a test chemical in a low optical density solution over x days of xenon arc lamp irradiation or over 30 day/nights of solar irradiation are given respectively by:



### ( ) Total # photons abs by chem / cm days xenon 3

= 

### ∑ X l

D I C

sys xenon xenon ( . )[ ] ( ) 2 3 0 ε λ λ [eq. 3

- 30]



### ( ) Total # photons abs by chem / cm days / nights solar 3

= 

  

  

### ∑ 30 j LC solar ε λ λ [ ] [eq. 3

- 31]

The number of days (X) of constant irradiation by a filtered xenon arc lamp that is equivalent to 30 days/nights of solar irradiation of a lo w absorbance water can be obtained by equating equations 3

- 30 and

3

- 31, assuming that the average concentration over 30 days/nights of solar irradiation is equal to the average concentration over X days of constant irradiation by a xenon arc lamp, and solv ing for X:

X days xenon = 
  
  

     

     = 
  
  

     

     

### ∑

∑ ∑

∑ 30

2 3 13

0 0 j D

l L

I j D

l L

I sys

xenon sys

xenon .
() () ε

ε ε

ε λ λ

λ λ λ λ

λ λ
[eq. 3

- 32]

where equation 3

- 32 is identical to equation 8 in the main text.ENV/JM/TG/RD(2006)1/REV

131 Derivation of equation 710 in the main text:

Substituting equation 3 4 -16 (see Part 1) for an optically dilute solution (applicable to a low optical density actinometer solution) into equation 3 4 -5 (see Part 1) , rearranging and incorporating subscripts to designate the use of monochromatic irradiation from a xenon arc lamp (obtained with a monochromator) gives:

d C

dt j l

D I C act

sys act xenon [ ]

. [ ] () ( )      

= −

λ λ λ φ

ε 2 3

0 [eq. 3 4

- 1 33 ]

By comparing equation 3 4

- 1 33 to equation 1 in the main text, it can be seen that the monochromatic pseudo first order rate direct photolysis rate constant of a low optical density actinometer exposed to monochromatic irradiation from a xenon arc lamp is given by:

k j l

D I d act

sys act act xenon λ λλ φ ε () () ( ) .

= − 2 3

0
[eq. 4-2 3

- 34 ]

Rearranging equation 4.2 34 to solve for I 0_(xenon) gives:

I j D

l k

xenon sys d act

act act 0 2 3 λ λ

λ φ ε ( ) ( )

( ) . =

[eq. 4- 3

- 3 5 ]

where equation 4 3 -3 5 is identical to equation 7 10 in the text.

Derivation of equation 811 in the main text

For a high optical density actinometer solution,

10 0

− + ≅ ( [ ]) α ε λ λ C l [eq. 4 3

- 4 36 ]

and

ε α λ λ

[ ] C > > [eq. 3 4

- 5 37 )]

such that

ε

α ε ε

ε λ

λ λ λ

λ [ ]

[ ] [ ]

[ ] C

C C

C + ≅ = 1 [eq. 3 4

- 6 38 ]

Substituting equations 3 4

- 4 36 and 3 4

- 6 38 for a high optical density actinometer solution into equation 3-6 (see Part 1) , summing only over the absorption spectrum of the actinometer above 295 290 nm, and using subscripts to designate the use of a filtered xenon arc lamp gives:

d C

dt jD I act

sys xenon initial final [ ]

( ) = −

= = 

### ∑ φ

λ
λ λ

0 [eq. 3 4

- 7 39 ]

Equation 3 4

- 7 39 is a zero order equation such that the zero order direct photolysis rate constant of the high optical density actinometer is given by:

k jD I d act zero order act

cell xenon initial final

( )( ) ( ) =

= = 

### ∑ φ

λ
λ λ

0 [eq. 3 4

- 8 40 )ENV/JM/TG/RD(2006)1/REV

132 Rearranging equation 3 4

- 8 40 gives:

I jD k

xenon cell

act d act

initial final

0 λ
λ λ

φ ( ) ( )( =

= = 

### ∑

zero order) [eq. 3 4

- 9 41 ]

where equation 4-9 3

- 41 is identical to equation 11 8 of the main text

Derivation of equation 14 in the main text:

Dividing equation 3

- 25 (for th e pseudo first order rate constant of a test chemical in an optically dilute solution exposed to sunlight) by equation 3

- 18 (for the pseudo first order rate constant of a test chemical in an optically dilute solution exposed to a filtered xenon arc lamp) a nd rearranging gives:

k j D

l k L

I d solar cell d xenon

xenon ( ) ( )

( ) . = 

### ∑

∑ 2 3 295 800

0 ε

ε λ λ

λ λ [eq. 3

- 42]

where equation 3

- 42 is identical to equation 14 in the main text

Derivation of equation 19 in the main text:

By analogy to equation 3

- 34 for a low optical density actinonmeter, the monochromatic pseudo first ord er direct photolysis rate constant of a test chemical in an optically dilute solution exposed to monochromatic irradiation from a xenon arc lamp is given by:

k j l

D I d chem

sys chem chem xenon λ λλ φ ε ( ) ( )( ) .

= − 2 3

0 [eq. 3

- 43]

Dividing equation 3

- 34 by equation 3

- 43, and rearranging gives:

φ φ ε

ε λ λ

λ λ chem act d chem act

d act chem k

k = ( )()

()( ) [e q. 3

- 44]

where equation 3

- 44 is identical to equation 19 of the main text

Derivation of equation 20 in the main text:

Substituting equations 3

- 36 and 3

- 38 (for a high optical density actinometer solution exposed to

monochromatic irradiation from a xenon arc lamp) into equation 3

- 5 gives:

d C

dt jD I act

cell xenon [ ]

( )      

= −

λ λ φ

0 [eq. 3

- 45]

Equation 3

- 45 is a zero order equation such that the monochromatic zero order direct photolysis rate constant of a high optical density actinometer is given by:

k jD I

act zero order act

cell xenon λ λ φ

( )( ) ( ) = 0 [eq. 3

- 46]ENV/JM/TG/RD(2006)1/REV

133 Dividing equati on 3

- 43 (for the monochromatic pseudo first order direct photolysis rate constant of a test
chemical in an optically dilute solution exposed to monochromatic irradiation from a xenon arc lamp) by equation 3

- 46 (for the monochromatic zero order direct photo lysis rate constant of a high optical density actinometer exposed to monochromatic irradiati on from a xenon arc lamp), and rearranging gives:

φ φ

ε λ λ

λ chem act

chem cell d chem

d act zero D k

k = 2 3

. ( ) ( )

( )( order) [eq. 3

- 47]

where 3

- 47 is identical to equation 20 in the main text

Derivation of equation 21 in the mai n text:

By analogy to equation 3

- 46 for a high optical density actinometer, the monochromatic zero order direct photolysis rate constant of a test chemical at high optical density in a solution exposed to monochromatic irradiation from a xenon arc lamp i s given by:

k jD I

chem zero order chem

cell xenon λ λ φ

( )( ) ( ) = 0 [eq. 3

- 48]

Dividing equation 3

- 48 by equation 3

- 46 and rearranging gives:

φ φ λ

λ chem act d chem zero

d act zero k

k = ( )( )

( )( ) [eq. 3

- 49]

where equation 3

- 49 is identical to equation 21 in the main text

Derivation of equation 22 in the main text:

Dividing equation 3

- 25 (fo r the pseudo first order rate constant of a test chemical in an optically dilute solution exposed to sunlight) by equation 3

- 25 (for the pseudo first order rate constant of a low optical density actinometer solution exposed to sunlight), and rearranging gi ves:

φ φ ε

ε λ λ

λ λ chem act d chem

d act act

chem k

k L

L = 

### ∑

∑ ( )

( ) ( )

( ) 295 800

295 800
[eq. 3

- 50]

where equation 3

- 50 is identical to equation 22 in the main text

Derivation of equation 23 in the main text:

Dividing equation 3

- 18 (for the pseudo first order rate constant of a test chemical in an optically dilute solution exp osed to a filtered xenon arc lamp) by equation 3

- 18 (for the pseudo first order rate constant of a low optical density actinometer solution exposed to a filtered xenon arc lamp), and rearranging gives:

φ φ ε

ε λ λ

λ λ chem act d chem

d act act xenon

chem xenon k

k I

I = 

### ∑

∑ ( )

( ) () ( )

( )( ) 0

295 800

0

295 800
[eq. 3

- 51]

where equation 3

- 51 is identical to equation 23 in the main textENV/JM/TG/RD(2006)1/REV

134 Derivation of equation 27 In the main text:

Dividing equation 3

- 25 (for the pseudo first order rate constant for a test chemical in an optically dilute solution in shallow or near to the surface water exposed to sunlight conditions 2 by equation 3

- 25 (for sunlight conditions 1), and rearranging gives:

k k L

L d shallow solar d shallow solar chem

chem ( )( ) ( )( ) ( )

( ) 2 1 2

295 800

1

295 800 = 

### ∑

∑ ε

ε λ λ

λ λ [eq. 3

- 52]

where equation 3

- 52 is identical to equation 27 in the main textENV/JM/TG/RD(2006)1/REV

135 ANNEX 5

Preparation of Direct Photolysis Test Media

Water meeting ASTM Type IIA st andards is recommended to prepare buffer solutions for direct photolysis

studies. This water is described in ASTM D 1193

- 99

- Standard Specification for Reagent Water. This document can be obtained from ASTM. In the USA, this document can be obtained from:

American Society for Testing and Materials (ASTM)

1961 Race Street Philadelphia, Pennsylvania 19103

For outside the USA, see http://www.astm.org/dist.htm

A recommended procedure for preparing buffers for direct photolysis studies is given in USEPA OP PTS 835.2210 Direct Photolysis Rate in Water by Sunlight (2). This guideline recommends:

Preparing all buffer solutions at 25 o C Using reagent grade chemicals free of impurities that could behave as photosensitizers For pHs in the range of 3 to 6, use NaH 2 PO 4 /HCl For pHs in the range of 6 to 8, use KH 2 PO 4 /NaOH Using procedures such as those described in the Handbook of Chemistry and Physics or by any

well establish method. Always checking the pH with a well calibrated pH meter Using the minimum concent ration of buffer

To prepare the test solutions for the direct photolysis studies, add the buffer solution to the test chemical to attain the desired pH. If necessary, adjust the pH with 1 M HCl or NaOH. It is highly recommended that the actual concentrat ion of the test chemical in the test solution be determined prior to starting the study.

Preparation of Indirect Photolysis Study Test Media

1. SNW (Simulated Natural Water):

(a) Prepare an initial stock solution of humic acid, followed by filtration, preaging and dilution. The stock solution should have about 60 ppm DOC of humic acid and absorbance of approximately 1.7 at 313 nm and 0.7 at 370 nm. Aging can be accomplished by exposing the stock humic acid solution in a 2-L flask for 3-4 days to direct su nlight (2). The absorbance of the solution is checked and used in estimating a dilution factor for preparing the test solution. (b) Buffer the SHW at pH 7 with 0.010 M phosphate solution. (c) The SNW test media should have an absorbance of 0.05 at 370 nm and a dissolved organic carbon concentration of about 5 mg/L or ppm. (d) The appropriate amount of the test chemical test substance is introduced to the test media immediately prior to irradiation.

2. SNW-N (Simulated Natural Water with Added Nitrate):

(a) Prepare test media as for SNW, Steps a through c ;ENV/JM/TG/RD(2006)1/REV

136 (b) Add nitrate as NaNO 3 or KNO 3 . In freshwater streams of the United States, average nitrate concentrations range from less than 0.1 mg/L to approximately 4 mg/L with the highest concentrations in agricultural followed by urban areas (USGS 1993). The mean nitrate concentration in some lakes may range up to 9 ppm ( 24 22 ). Nitrate concentrations in the agricultural and urban areas of Europe often exceed 9 mg/L (German personal communication). (c) The test chemical test substance is introduced immediately prior to irradiation.

3. NW (Natural Water):

Natural surface water may be taken from lakes, rivers, ponds, streams, creeks or coastal water

bodies where the test chemical test substance is expected to be present. Proper water sample collection and characterization is required. The geographical location (including longitude and latitude), site characteristics and date of collection should be recorded.

Collection and Sampling

(a) Sample containers such as polyethylene bottles should be soaked in 10% HNO 3 overnight, thoroughly washed, and then rinsed with distilled water at least three times. (b) Samples are collected from the surface (top few centimeters) of the selected water body. (c) Water samples that are not used shortly after collection should be stored at 4 o C.

Characterization

In the laboratory: The dissolved organic carbon (DOC), pH, and nitrate/nitrite need to be determined (6 2 1 ). As an option, additional factors that influence indirect photolysis can be determined including diisolved oxygen, redox potential, alkalinity, turbidity, other major major anions (HCO 3 - , Cl

- , SO 4 2- ), major cations (Na + , K + , Ca 2+ , Mg 2+ ) and other metal ions such as iron and manganese (6 2 1 ).

All waters (SNW, SNW-N, and NW) prepared for the i ndirect photolysis test should be filter-sterilized

with a 0.2 μ m filter. The absorptivity should be computed at 350 nm (absorptivity = 2.303 x absorbance/pathlength). Computing the absortivity at 350 nm in SHW, SHW-N, and NSW provides an estimate of CDOM. CDOM exhibits a much stronger correlation with indirect photolysis rates

than DOC.ENV/JM/TG/RD(2006)1/REV

137 ANNEX 6

Example for Measurement of the Intensity of Radiation

E.g. by a global sensor in the special sample platform during the measurement

Date/time Intensity of irradiation

mW/cm 2 Ws/cm 2

· min

Start of test

End of test Average during test e.g. 968

Calculation of Environmental Days based on Light Intensity of an Artificial Light Source (Example: Suntest unit used as artificial light source)

Light Intensity in the Suntest Unit

Light intensity of a Suntest unit measured at 300-800 nm (radiometer): 968 W/m 2

Light intensity of an artificial light source (calc. for 300-3000 nm): 58% of the light intensity 300-3000 nm falls in the range of 300-800 nm 3

(968 W

· m -2 /58%

· 100%) 1669 W/ m 3

Radiation (300-3000 nm) of a Suntest unit during 1 hour (1h = 3600 s): 6008276 Ws/m 2

(Ws = J) 6008276 J/m 2

(M = 1000000) 6.01 MJ/m 2

Examples for Global Radiation (300-3000 nm) 2 :

Location Latitude Month Global radiation 1 day (MJ/m 2 ) Phoenix, Arizona (USA) 33.26 N June 31 Athens, Greece (EU) 38.03 June 20 Edmonton, Alberta (CAN) 53.33 June 22 Tokyo, Japan 35.11 April 15

Irradiation Time (Suntest Unit) Transferred to Environmental Days

Location Suntest (hours) Environment (days) Suntest (hours) Suntest (days) Environment (days)
Phoenix, Arizona, USA 5.16 1 154.8 6.45 30 Athens, Greece, (EU) 3.33 1 99.9 4.16 30 Edmonton, Alberta (CAN) 3.66 1 109.8 4.58 30 Tokyo,Japan 2.50 1 74.9 3.12 30

3 Solar radiation data: Handbook of Material Weathering; 2 nd edition, Chemtec Publishing, Ontario, Canada (1995).ENV/JM/TG/RD(2006)1/REV138ANNEX 3November 2004Compilation of comments on the proposal for a new Guideline onPhototransformation of Chemicals in Water – Direct and IndirectPhotolysisand Secretariat’s responses.The following document comprises all comments received from Member Countries and industry on the proposal (August 2000) for a new OECDTest Guideline: Phototransformation of Chemicalsin Water – Directand Indirect Photolysis. This proposal was circulated for comments to OECDMember Countries in September 2000. Comments were received fromseven countries (Canada, France, Germany, Japan, Switzerland, UK andUSA), the European Commission (EU) and industry (CropLifeInternational/ECPA).In this annotated guideline document, the comments are identifiedby their origin (see above). Responses from the Secretariat are provided for allMember Countries comments explaining (i) which points were adoptedand how the subsequent changes were made, and (ii) which points could notbe adopted.CountryCommentSecretariat’s ResponseGeneral CommentsCanada In general, the current guideline is well presented and has detailed information on thesubject.Agreed.France In a general point of view, French experts welcome the draft proposal. They think that thedocument is complete, useful and the most important points are mentioned. Theyunderline, in particular, the recommendations made for the choice of the labelled carbon.Agreed.Germany The document as a whole would profit a lot from a better structuring and substantiallyshortening some chapters (table of content). The actual information for the user of theguideline on what to do and how to do it is embedded in a lot of background informationwhich can also be found in the abundant list of references. Alternatively, the “practicalpart” should be more clearly separated from the theoretical background.The restriction of the test results should be noted at a very prominent place; just to saywhat the whole exercise is good for: to get a rough estimateof something like an overallphototransformation rate for natural water bodies, while accepting a considerable degreeof “scientific fuzziness”.The draft document is split into two separate guidelines fordirect and indirect photolysis, respectively. It is alsorestructured and shortened and thus should cover thesepoints.Scope and approach are sufficiently described in paragraph 9.Germany To be scientifically correct one would have to study the transformation process(es) muchmore in detail even for pure water systems (e.g. wavelength dependence, side reactionwith dissolved oxygen, etc.). Using “natural” water as a solvent, things get even morecomplicated under kinetic aspects since several reactions may proceed in parallel or inThe main purpose of this guideline is to estimate rates ofphotolysis and environmental life-times for compounds inpure and natural water. It is not a guidance how “scientificresearch” should be conducted.ENV/JM/TG/RD(2006)1/REV139CountryCommentSecretariat’s ResponseGeneral Commentscompetition to each other (2ndorder rate constants for singlet oxygen, peroxy-radicals,OH-radicals, H2O2).Japan First of all, Japan highly appreciates theSecretariat’s effort for developing this draft newtest guideline. Although the main parts ofthe proposed draft TG would be acceptable, wewould herewith send our comments. Furthermore, the test guideline of “PhotolysisStudies” and “Fate of Photolysis Studies” of MAFF would be sent in the near future forthe Secretariat’s reference and we would be grateful that the Secretariat would take intoaccount our guidelines as well.We are looking forward to receive the MAFF guidelines totake these into account.Switzerland Our experts have reviewed the draft document “Phototransformation of Chemicals inWater – Direct and Indirect Photolysis (August 2000). We feel that the publication of sucha guideline is timely and welcome. Below we give you general remarks followed by morespecific comments and recommendations. They are structured in the order of theparagraphs, as they appear in the document.Agree.Switzerland According to our experience, the directand indirect photolysis is important for theassessment of the fate of chemicals and pesticides. The tier-wise approach is useful forboth direct and indirect phototransformation processes. We have, however, realised thattrivial equations (such as first order degradation) are presented in the text whereas morecomplex equations which are needed are just referenced. In many cases, the reproductionof the equation is desirable, especially in cases where the reference is not in the openliterature (see below).Agree. With regard to the reproduction of more complexequations, please indicate which equations should bereproduced in the text.Switzerland The subject of photochemistry is quitea complex one, especially where photosensitisersand radical quenchers are involved. Reading through the draft, we see that especially inthe field of indirect photolysis the experimenter is confronted with a wide choice ofconditions to be applied with respect to nature and concentration of sensitizer andquencher. A more precise guidance how to select appropriate conditions would bedesirable. Furthermore, the document does not provide sufficient information how toextrapolate the results found under the various conditions to natural environmentalconditions. At least, this should be a major goal of the guideline. We therefore feel that thepresent draft needs a careful revision beforeit can be considered for adoption as an OECDtest guideline.Photochemical reactions in the presence of photosensitisersand radical quenchers are certainly more complex than directphotolysis reactions in pure water. Some choice of conditionsis needed to evaluate the influence of sensitisers andquenchers.The document provides the information which is availablebased on the present state of the art.UK We commend the efforts of the authors of this very complex guideline. Keeping themathematical derivations out of the main body text makes the document much morereadable, whilst not loosing the detail. In order to make these studies easier to perform wewould like to suggest the inclusion of worked examples (in a new Annex). Also a diagramof typical experimental systems would aid the reader not familiar with these types ofstudy.Worked examples are available for Tier 1, 2 and 3 inreferences (2) and (12) as “Illustrative Examples”. Typicalexperimental set-ups will be included in an Annex to theguideline.ENV/JM/TG/RD(2006)1/REV140CountryCommentSecretariat’s ResponseGeneral CommentsUSA(1) Direct and indirect photolysis studies should be addressed in separate guidelines.US position:Agree. Separation of the two types of studies would result in much simpler,clearer guidance for each type. Separate documents or chapters are needed.The draft guideline will be split in two separate guidelineparts as proposed.USA(1) The proposed guidance does not make efficient use of laboratory resources. The tieredapproach to direct photolysis studies may require the same experiment to be set up and runfour times for different purposes. This will increase the cost of the study beyond the valueof the added information obtained.US position:Agree. The number of tiers for direct photolysis should be reduced to two: ascreening step to determine if a laboratory studyis needed (like tier 1) and full study (liketier 4). Tier 2 should be eliminated. Tier3 (determination of quantum yield) should beoptional.This point should be covered by the changes made.USA(1) The proposed guideline gives the laboratory the discretion to run a full study, or notdepending on intermediate results from the tiered decision tree. The laboratory should nothave this discretion.US position:Agree. The instructions on when to proceed to the next tier must be explicit.It is exactly the goal of the tiered system to have thediscretion to conduct only those studies which are triggeredby the decision criteria / trigger values given in the text andin Annex 3.USA (1) The proposed guideline requires the laboratory to use computer models (GCSOLAR orABIWAS) to determine estimated photolysis rate constants, as part of the decision tree todetermine the need for a full study.We disagree with this requirement.US position:Agree. Modelling studies to estimate rate constants should not be part of thelaboratory protocol. The result of the study should be a measured rate constant.Computer models such as GCSOLAR and ABIWAS may beused as additional possibility to estimate environmentallyrelevant photolysis rate constants. Their results do not triggera full kinetic study in the revised tiered system.USA(1) The proposed guidance is overly vague in many places. For example, the choice ofsimulated or natural water in paragraph 26, “fairly substantial volatilisation” in paragraph31, the choice of natural or commercial humic and fulvic substances in paragraph 55,“substantial decline” in paragraph 57, “somewhat comparable to that of sunlight” inparagraph 74 and the choice of actinometers and radiometers in paragraphs 80-85.US position:Agree. See also commenter 2, paragraph 31, for proposed benchmark for“fairly substantial volatilisation”. The vagueness of the guideline on the points will makeit difficult to write a study protocol and to interpret the study results.A test guideline always also needs some flexibility in thedescription of the procedures. It is not possible to exactlydefine every single detail like in cook-book.USA(2) In general, the document could be improved by reformatting all of the equations to asimilar size and font, and using a font size that is easily read. It is difficult to readequations in paragraph 27-30 (pp. 26 and 28) due to the small font size.US position:Agree.Agree. Equations will be re-formatted to the same readablefont size.USA(2) A review of the OPPTS 835.2210 guidelines for direct photolysis in water and the currentdraft of the OECD guidelines reveals that there are a few points on which the twoThis draft guideline was written under consideration of avariety of national and international guidelines and theENV/JM/TG/RD(2006)1/REV141CountryCommentSecretariat’s ResponseGeneral Commentsdocuments are not in agreement. While these are minor points (such as the acceptability ofthe use of the term molar absorptivity or the range of wavelengths that should be takeninto account), it is a shame that the two documents, which represent the state- of- the- artguidance on the conduct of aqueous photolysis studies, are not in agreement.US position:Agree.recommendations of the experts attending the Rome meetingin September 1998. So, it is not surprising that it is not inagreement with OPPTS 835.2210 in every aspect.USA(2) The text contains multiple references to a “30 days / nights” test period. It would behelpful to clarify the intended length of irradiation exposure per day (such as 12 hourslight / 12 hours dark) unless multiple calculations (for different seasons and locations) areintended. Additionally, it would be helpful to discuss at some point whether the use ofcontinuous irradiation (24 hours per day for 15 days) is preferable or whether a dark“recovery” period should be used in most cases. While this is more applicable tophotodegradation in soil, it should at least be mentioned in this guideline. A suitable placemight be paragraph 73 on page 14.US position:Agree. The proposed mechanism for selecting the irradiation period is toocomplex. Either 15 days continuous, or 30 days with 12 hours light / 12 hours dark shouldbe required. This will help to ensure the comparability of studies on different chemicals.The irradiation of the samples should be done at theminimum until 75% transformation of the test substance orfor a period equivalent to 30 days sunlight exposurewhichever comes first. Whether continuous 15 days or 30days with light and dark cycles are used, seems mainly aquestion of which light source is used (Xenon lamp orsunlight).USA(3) The proposed guideline incorporates many of the developments in environmentalphotochemistry of the past 20 years. The principle of the test guideline is straightforwardand clear, but the guideline is very complicates and lacks regulatory tightness. We wouldsuggest that at least 2 or 3 documents need to be produced:APhotolysis Guidance Documentwould incorporate the principles, experiments, etc.from the draft guideline document. SeparateDirect and Indirect Photolysis Guidelineswould spell out the regulatory requirements in an ambiguous fashion, including theproposed tiered approach to decision making which we see as useful. It might be possibleto combine some of the processes within the tiers and satisfy requirements of multipletiers. ThePhotolysis Guidance Documenthas been greatly improved by moving many ofthe equations to Annex 4, but there is still a lot of background information woven into themain body of the guideline. Unfortunately, that features makes it difficult to understandhow to conduct the required experiments. We suggest further separation of theexperimental procedures from the supporting information.US position:Agree. However, such an OECD Guidance Document already exists (seeRef. 10). The proposed new document would supersede that 1997 reference.The number of tiers for direct photolysis should be reduced to two: a screening step todetermine if a laboratory study is needed (like tier 1) and a full study (like tier 4). Tier 2should be eliminated. Tier 3 (determination of quamtum yield) should be optional.The draft document will be split into two separate guidelinesfor direct and indirect photolysis. An OECD GuidanceDocument (No. 7) already exists, at least for DirectPhototransformation. Also, the draft was shortened andrestructured based on the numerous comments and thus therevised version should be clearer and less complicated.USA(3) The primary goal of aqueous photolysis guidelines should be to produce a photolysis rate These points should be coveredby the changes made in theENV/JM/TG/RD(2006)1/REV142CountryCommentSecretariat’s ResponseGeneral Commentsthat can be used in risk assessments (i.e. Tier 1 model inputs) and to define the significantphotolysis products (10% of initial dose) that may be important to analyze for indissipation studies. It is important that the data generated be as real world as possible. Aswritten, this guideline would generate a variety of direct and indirect photolysis rateconstants (under buffered systems, with artificial or natural humic substances and withnitrate, also theoretical rates determined by models based on quantum yields and tables ofsunlight irradiance). A study conducted in accordance with the guideline would generatemany more rate constants than are needed for risk assessment.US position:Agree. The rational for collection of eachtype of rate constant needs to bebetter explained.tiered testing schemes for direct (part 1) and indirectphotolysis (part 2), respectively.USA(3) Currently, when Pesticide Concentrationsin Drinking Water are estimated with EXAMSthe aqueous photolysis input is set at1/124thof the aquatic photolysis rate constant.Thus all the nuances of the photolytic rate constant determined in this guideline arecompletely swamped by the 1/124thfactor and will not affect the risk assessment.Therefore, this guideline should examine the photolytic behaviour of test compoundsunder the most important scenarios. These important scenarios are probably buffered purewater (PW) and representative natural water (NW) from the proposed usage area.Expansion of the requirements to additional scenarios (simulated natural water (SNW)),nitrate (SNW-N), multiple pH’s, etc. is academically interesting, but it may be argued thatat times other situations could be just as important (algae blooms, oxidants such assuperoxide, hydrogen peroxide or singlet oxygen). Given the current regulatory use ofaqueous photolysis outputs, these studies should be limited to buffered pure water (PW)and representative natural water (NW).US position:Agree in part. The comment regarding EXAMS is EPA program-specific,and should have no effect on the guideline.The option of using synthetic natural water should be preserved, but better guidance on theformulation of SNW is needed. Data will be more comparable between chemicals if SNWis used.As the draft document is written it seems to give enoughflexibility to the Study Director to use SNW and/or SNW-Nand /or natural water (NW) for indirect photolysis studies.The formulation/composition of SNW seems to besufficiently well described in Annex 5.USA(3) Recent work, such as that of Scott Mabury suggests that photolysis data generated with atypical sterile buffer, containing no photosensitisers, is not relevant to the real world.Thus, the use of natural waters for photolysis should be elevated in importance when theresults are to be used in risk assessment. This approach would effectively cover thesituation most relevant to indirect photolysis, photolysis in shallow water bodies such asrice paddies.US position:Disagree in part. The option of using natural water should be preserved, butbetter guidance on the formulation of SNW is needed. Data will be more comparableIt may well be that the use of natural water for photolysisstudies seems to better reflect real environmental situationsand thus be more important. However, the principles laiddown in this draft document were agreed upon at the experts’meeting in Rome in September 1998.ENV/JM/TG/RD(2006)1/REV143CountryCommentSecretariat’s ResponseGeneral Commentsbetween chemicals if SNW is used.USA(3) Regarding calculation of rate constants, we believe that pseudo-first order kinetics areacceptable, but second order should also beexpected. Equations and compartment kineticsprovided for that option should be included in the guideline. It would be good to specifywhat output is wanted, half-life, DT50 or dissipation (if volatilization occurs).US position:Agree.This point should be covered by the changes made.USA(3) There is some confusion over the duration of the study. Photolysis studies usingcontinuous irradiation with simulated light should be acceptable since the objective of theguideline is the determination of the photolytic fate of the test chemical. The study shouldbe conducted for a sufficient time to allow determination of the DT75 of the test chemical.US position:Agree. The proposed mechanism for selecting the irradiation period is toocomplex. Either 15 days continuous, or 30 days with 12 hours light/12 hours dark shouldbe required. This will help to ensure the comparability of studies on different chemicals.As we understand the text in paragraph 72, the irradiation ofthe samples should be done at minimum until 75%transformation of the test substance or for a period equivalentto 30 days sunlight exposure whichever comes first. Whethercontinuous 15 days or 30 days with light and dark cycles areused, seems mainly a question of which light source is used(Xenon lamp or natural sunlight).EU This guideline is a very comprehensive document on photochemical methods. Indeed, ourimpression is that it might be difficult to use, because of its complexity.The separation in one version for direct photolysis andanother one for indirect photolysis and the other changesshould make this guideline simpler and easier to use.CropLife/ECPA We greatly appreciate the efforts of the authors for preparing this very complex testguideline. It is a comprehensive document covering many important aspects ofphototransformation in aqueous medium and is certainly a good start for developing acorresponding OECD Test Guideline. Transferring most of the mathematical equationsfrom the main body text to an Appendix makes the document much more readable, whilstnot loosing the detail. Nevertheless, there are still many equations left in paragraphs whichdescribe experimental procedures; these equations should be transferred to a separatechapter “Treatment of results and calculations”.The paragraphs containing these equations are often alsogiving explanations needed for the understanding of theexperimental procedures. Thus, this point is not adopted.CropLife/ECPA However, the guideline is not straightforward, is still rather bulky and contains too muchtextbook knowledge. Due to its bulky structure and its voluminous contents the documentis rather difficult to read, even for readers familiar with these types of photolysis studies.In order to increase readability, the guideline should be more structured (titles andsubtitles) and a table of contents should be given. We would like to suggest the inclusionof worked examples (in a new Annex) to make these studies easier to perform. Anotherproposal for improving readability and applicability of this guideline is to split it intoseparate guidelines for direct and indirect photolysis, respectively. In this case, the directphotolysis guideline could include a statement on when an indirect photolysis study shouldbe conducted.These points should be covered by the changes made.With regard to the inclusion of worked examples, seeprevious response on UK comment.CropLife/ECPA The test schemes for direct and indirect photolysis shown in Annex 3 are not in agreementwith those proposed by the photolysis experts attending the Rome meeting in SeptemberAnnex 3 is revised accordingly and should now be in linewith the text in the corresponding paragraphs.ENV/JM/TG/RD(2006)1/REV144CountryCommentSecretariat’s ResponseGeneral Comments1998. As experimental steps and decision steps were mixed together the schemes havealso lost their transparency. These flowchartsfor decision-making should be simplified tocontain critical information only, because detailed reasoning is already given in the maintext. There are also differences between the text and the schemes with regard to the triggerpercentages. In addition, the percentage triggers given in the text in paragraphs 17-19, 26,90-92, 100-102, 128 and 150-152 differ from those agreed upon by the experts attendingthe Rome meeting (i.e. 10% transformation in5 days); we would greatly appreciate if theauthors of this guideline could explain their reasons for these changes.In the text explaining the schemes, sentences like “if required, proceed to next tier” (e.g.paragraphs 91 and 102 are found) but nothing is said under which circumstances tests atthese Tiers are required. Also double work is often recommended (e.g. Tier 2 and 4 indirect photolysis, Tier 1 and 2 in indirect photolysis). The reporting requirements for thepre-tests should be specified and the possibility to omit lower Tiers and to directly to ahigher Tier should be given.CropLife/ECPA As this is a guideline which describes how to conduct aqueous photolysis experiments thereader can expect some illustrations of useful experimental set-ups. Therefore, examplesof appropriate photolysis apparatus must be given in additional Figures. Otherwise, suchan experimental guideline is of limited value.Examples of useful experimental set-ups are included inAnnex 6.CropLife/ECPA Different letter sizes are used in the various equations given in the main text and also inAnnex 4. Some letters are so small that they can hardly be read without a magnifyingglass. The same letter size should be used in all equations through the whole document.This point is adopted.CropLife/ECPA When comparing this guideline with other OECD E-Fate Test Guidelines it is obvious thatadditional definitions, such as test substance, transformation products, DT50, DT75, halflife, etc. have to be included inthe chapter DEFINITIONS AND UNITS.This point is adopted.ECPA membercompanyMaybe the guideline contains too much details about different methods or possibilities forcalculating half-lives, quantum yields, etc. Many of those details could be deleted becausethey can be found in the high quality list of references.Readers may prefer to find these details in the guidelineinstead of looking for it in a various references.ECPA membercompanyThe major issue I would like to address here is a statement on Section 9 (PRINCIPLE OFTHE STUDY, Scope and approach). This is my personal experience and that of all mycolleagues I have talked to:At the moment (and even much more when following this new tiered draft), we waste a lotof resources for investigating the direct photolysis kinetics and product formation in purewater or buffer because that studies are required for the registration data packages. In mostcases, the outcome of those studies is totally irrelevant for the environment. I have oftenperformed those studies and I have got scientifically interesting results, but they can onlybe used for storage in a library. Thus, the direct photolysis in pure water or buffer shouldThe principles of this guideline were established by theexperts attending the Rome meeting in September 1998based on the available national and international guidelines.ENV/JM/TG/RD(2006)1/REV145CountryCommentSecretariat’s ResponseGeneral Commentsonly be further investigated, if it is definitely a very fast reaction (e.g. in case of an E-fateDT50 <1 day). Indeed, we will get that information by Tier 1 (theoretical screen,section17) and then, when relevant, by Tier 3 (determination of the quantum yield and itsuse to estimate direct photolysis rate constants, section 19). The outcome of both Tiersresults in kinetic data, which clearly belong to the physical-chemical data of a testchemical and, therefore, that data should be a basic information in the physical-chemicaldata packages of a chemical. Further, they can be used for calculating maximum E-fatehalf-lives via modelling, then.ECPA membercompanyHowever, corresponding requests on what amounts and kind of metabolites are formedunder natural sunlight conditions in highly pure water or buffer (i.e. during e.g. 30 solardays) make not any sense , because there is not any highly pure water present in anyenvironmental aqueous solution!However, then performing a well-designed photolysis study in natural water we will getall the information together: the net (combined direct and indirect) photolysis kinetics aswell as the degradation products relevant for environmental assessment and effects testing.Even in highly pure water (or buffer) the indirect processes can hardly be excluded totally.This is the more the fact the longer the irradiation must be performed, namely in that caseswhere the direct photodegradation is a comparatively slow process (i.e. for most of thepesticides we have to investigate).I would like to suggest changing the title of theGuideline to “Pure and Natural Water Photolysis”. From the scientific point of view, theearlier title is more accurate, but in practice we can hardly differentiate the individualprocesses. The “pure and natural water photolysis” of a chemical is what we actuallyinvestigate in the tests for getting data on environmental assessment. Comparing thesituation to e.g. an aerobic soil metabolism study, nobody would have any interest to setup a guideline for creating detailed data, what individual processes (either bioticdegradation by fungi, bacteria, algae, etc., orby different abiotic catalysed reactions in soilsolution) are responsible for the observed degradation. Thus, we always determine the sumof processes leading to the respective degradation kinetics and pathway in a simulatedecosystem. The same should consequently be followed with the phototransformation inwater, too.To perform a well-designed photolysis study in naturalwaters only could certainly be an interesting alternative to theproposed draft document. This might be a topic fordiscussion for the National Coordinators.ECPA membercompanyThere is not any doubt that the draft guideline is an excellent review and guide through thecomplex issue of phototransformation in water. However, it should be clearly highlightedin Section 9 (page 2), what data and / or information are definitely needed forenvironmental risk assessment purposes in order to create a complete data package, e.g.for registration of a pesticide.The major needs are:We think that paragraph 9 clearly highlights what data andinformation are provided bythe draft test guideline.ENV/JM/TG/RD(2006)1/REV146CountryCommentSecretariat’s ResponseGeneral Comments- The quantum yield of direct photodegradation in pure water or buffer (as a basicphysical-chemical parameter), and resulting theoretical direct photolysis rate constants forthe chemical for various types of water bodies, seasons, and latitudes of interest.- The combined (direct and indirect) photolysisrate constant of the test chemical and thetransformation pathway, identities and rates of formation and decline of majorphototransformation products in two selected natural surface waters (e.g. pond, reservoir,river, etc) probably (intended use area) or in fact contaminated by the test chemical in theenvironment (indicated by monitoring data). The selected natural waters should differ intheir characteristics, i.e. in pH, CDOM and nitrate content.Paragraph 1Switzerland The role and relative importance of photosensitisers NO3 ̄, NO2 ̄, Fe-III-complexes) is notclearly described. Nitrite is a strong sensitiser but also readily oxidised in water, thereforea fast decrease in concentration is expected. Comments on choice of sensitisers,concentrations are required.The role of sensitisers is mentioned, for example, inparagraphs 4 to 6.CropLife/ECPA Typing error in last line: environment should read “environmental”. This point is adopted.Paragraph 6Germany CDOM in first line; this abbreviation is used without definition throughout the text. CDOM is explained in the last line of paragraph 4 on page 1.Paragraph 8USA(3) This section is too general. It should specifically state the desired endpoints of the studyand briefly explain how these results may be used in a risk or environmental fateassessment. For example, it is mentioned that the results from an aqueous photolysisexperiment are used as inputs for environmental fate computer models. Clarification maybe necessary to specify if these values are net photolysis, direct photolysis, indirectphotolysis, etc. As mentioned in the general comments, a photolysis rate constant, thesignificant metabolites formed at >10% of the initial dose, and quantum yields forestimating rate constants under various scenarios are the desired endpoints of the study.The section should document the need to generate multiple rate constants. A balance mustbe struck between practicality and the desire to develop theoretical information. Theopening sections in general are well written but need to discuss the environmentalsignificance of aqueous photolysis as it relates to regulatory decisions.US position:Agree. The rationale for the collection of data should be better explained.The right to request generation of more data must be reserved, if the situation warrants it.This draft is a guideline which should instruct a user how toconduct photolysis experiments; it is not the goal of anexperimental guideline to explain how the results can be usedin a risk assessment. The desired endpoints are listed inparagraph 9 and are further explained in paragraphs 17-20 fordirect photolysis and in paragraphs 26-27 for indirectphotolysis.Paragraph 9USA(3) There is a great amount of potential information to be generated in this guideline. Thedata requests must satisfy the requirements of the regulatory community. How crucial tothe risk assessment are photolysis determinations in the presence of nitrate or at multipleAs this draft is based on existing national and internationalguidelines, it should satisfy also the requirements of theregulatory community. The revised version asks in case ofENV/JM/TG/RD(2006)1/REV147CountryCommentSecretariat’s ResponseGeneral CommentspHs? Also, the guideline seems to be asking for quantum yield determination (todetermine estimated direct photolysis rate constants) and also asks for laboratorydetermined rate constants. Are both needed in the regulatory assessment?US position:Agree in part. The rationale and advantages for collection of each type ofrate constant needs to be better explained.direct photolysis for quantum yield determination (Tier 3)which allows the calculation of half-lives and environmentallife-times of chemicals for a variety of conditions.Laboratory determined rate constants in Tier 2 are optional.Tier 4 only asks for the isolation, quantification andidentification of phototransformation products asrecommended by the experts attending the Rome meeting inSeptember 1998.CropLife/ECPA In point 2, the short wave cut-off value is given here and in many other sections of thisguideline as 295 nm. It should be noted that in section 2.9.1 of the EU CommissionDirective 94/37/EC, in the OECD Guidance Document No. 7 on DirectPhototransformation of Chemicals in Water (reference 10) and also in the SETACguidelines (reference 7) 290 nmis stipulated as a cut-off value. This comment also refersto paragraphs 12, 17, 43, 50, 52, 53, 56,60, 83, 85, 87, 88, 122, 170, Annex 3 andAnnex 4.This point is adopted.Canada Delete “major” before phototransformation products. This change is needed because ofthe following reasons:- it is necessary to analyse all the possible phototransformationproducts at differenttime intervals, to identify the major and minor phototransformation products- information on major and minor phototransformation products is needed to determinethe phototransformation pathway- information on minor phototransformation products is important, particularly if theyare highly toxic- other OECD Guidelines on chemical transformation do not specify the analysis ofonly the major transformation products (e.g. Aerobic and anaerobic transformation inaquatic sediment systems – Guideline No. 308). Therefore, the above change isnecessary to have consistency between the OECD Guidelines on chemicaltransformation.This point is adopted.Paragraph 10UK The triggers in Annex 3 are not consistent with the body text. This Annex requirescorrection.This point should be covered by the changes made in Annex3.CropLife/ECPA The triggers in Annex 3 are not consistent with the body text (in paragraphs 17-19 and26) and thus this Annex requires correction.This point should be covered by the changes made in Annex3.Paragraph 11Canada Insert “at time t” before “(mol/L)”. This change is necessary to specify that, c = testchemical concentration at time t (mol/L).This point is adopted.ENV/JM/TG/RD(2006)1/REV148CountryCommentSecretariat’s ResponseGeneral CommentsGermany The recommended symbol of the amount of substance concentration is c not C. Thesubstance itself can be specified in brackets or as a subscript, e.g. c(HCl) = 0.1 mol/L orcHCl = 0.1 mol/L.This point is adopted.UK Half-life does not appear in eq. 1-3. Move to eq. 4. This point is adopted.USA(3) The guideline should allow for kinetics other than pseudo first order. Section 16mentions that pseudo first order assumptions are valid for studies conducted for one toseveral weeks or for 2-4 hours mid-day, but it may not be valid for studies lasting fourhours to several days or for those conducted beyond 30 days. This is confusing and needsfurther clarification.US position:Agree. Further clarification is needed.This point should be covered by inclusion of a correspondingsentence at the end of this paragraph.CropLife/ECPA This paragraph should be rather part of a chapter “Treatment of results and calculations”.This comment also applies to paragraphs 14, 15, 25, 73, 78, 81, 83, 88, 98, 107, 112-118,123, 135, 139, 149, 161, 163 and 164. Also half-life does not appear in equations 1-3 andshould thus be moved to equation 4.In principle we agree with this comment but adopting thefirst point would require major restructuring of the guidelineand may make it more difficult to understand. The secondpoint is adopted.Paragraph 12Germany Delete “of light” at the end of sentence 1. This point is adopted..USA(3) This section specifies wave lengths 295-800 nm. The Suntest instrument is supposed togenerate energy within the distribution but we are aware of instruments that onlymeasure up to 700 nm. We are not sure what the availability is for an instrument in thisrange.US position: Disagree. The guideline provides references for the 295 to 800 nm range..To be in line with OECD Guidance Document No. 7 thewavelength range is changed in 290-800 nm.Paragraph 13UK In line 6 „e.g.“ should read “i.e.”. This point is adopted.CropLife/ECPA In sentence 4 e.g. should read i.e.This point is adopted.Paragraph 14UK It is not clear if A < 0.02 refers to a single wave length or 295-800 nm. Suggest the textfrom para 69 is used or reference is made to this para.A < 0.02 refers to the absorption maximum of a chemical andthus to a single wavelength.USA(3) The symbol defining light path length in eq. 5 and in the definition and everywhere elseshould be consistent.US position:Agree.Agree.CropLife/ECPA It is not clear if A<0.02 refers to a single wave length or to the whole range of 290-800nm. Suggest the text from paragraph 69 is used or reference is made to this paragraph.A < 0.02 refers to the absorption maximum of a chemical andthus to a single wavelength.Paragraph 17Germany The expression “near surface” means actually not any attenuation due to ingredients inwater. In fact one can expect that absorbance of light by the test chemical is much lessParagraph 17 describes the theoretical screen proposed asTier 1 test for direct photolysis reactions and thus attenuationENV/JM/TG/RD(2006)1/REV149CountryCommentSecretariat’s ResponseGeneral Commentsthan attenuation caused by e.g. humics. This is just a poor trigger for higher tierinvestigations. To get a more realistic idea about what goes on in natural waters weshould take into account this effect (ref. to document of R. Frank /equ. 9). Besideattenuation from cloud cover the ABIWAS programme allows to calculate rate constantsfor any depths and attenuation from natural water ingredients. We would prefer to use atrigger based on a more realistic surface water body; e.g. 100 cm depth, standardisedoptical properties of the natural water and test chemical concentration (e.g. 10-6– 10-10mol /L).due to water ingredients is not of interest at this stage.Japan In this guideline, the general situation for evaluation is “in summer at lat. 40 ̊ or 50 ̊. Butthe general situation is different among countries, therefore, the description of thesituation should be as examples. For your information, Japan is located at lat. 20 ̊ ~ 40 ̊N., and the situation for evaluation is determination to lat. 35 ̊ N. and in April to June,taking into account our general application pattern of pesticides.This paragraphs describes the estimation of a maximumphotolysis rate assuming a quantum yield of one, so therelevance of the latitude is rather lowUK These tabular data should be included in the guideline, along with a worked example. Inaddition, Annex 3 does not reflect the text.Agree. Worked examples are available in refs. (2) and (12).Annex 3 is revised accordingly.USA(3) Triggers for proceeding to higher tiers are not consistent throughout the document. Forexample, compare Section 17 and Annex 3. Also, it is not clear what regulation thestatement “if required” would refer to. This type of wording needs clarification in orderto understand whether indirect photolysisis required. The wording “if required” alsoappears in Section 18 & 20 and maybe other places.US position: Agree. If the tiered approach is kept the triggers should be made consistent.The words “if required” should be deleted if a higher-tiered study is meant to betriggered automatically.Annex 3 is revised to be in line with the text in this and alsoin the other related paragraphs. The words “if required” inTier system are meaningless and are thus generally deleted.USA(3) Tables of daily sunlight irradiance should be included. For instance, Section 17 indicatesthat tabular irradiance data should be used to determine a maximum direct photolysisrate.US position:Disagree. The needed references are provided.Agree with US position.CropLIfe/ECPA The tabular solar irradiance data should be included in the guideline, along with aworked example. The triggers given here are different from those given in Annex 3 (thisalso refers to paragraphs 18, 19, 26, 90, 100 and 150).The needed references are provided. Annex 3 will be revisedto reflect the text in this and other related paragraphs.ECPA membercompanyChange last sentence in: If the maximum possible losses are≥50, proceed to PurePhotolysis Tier 3 (determination of the quantum yield).All the other options are nice to have, but not needed. However, the quantum yielddetermination should be obligatory in that cases, in order to get this physical-chemicalparameter of the test chemical. Compare section 90-92, too.The wording in this paragraph leaves enough flexibility forthe Study Director; he may go to Tier 2 or directly to Tier 3as an option.Paragraph 18ENV/JM/TG/RD(2006)1/REV150CountryCommentSecretariat’s ResponseGeneral CommentsUK With regard to the triggers, Annex 3 does not reflect the text. Guidance on when Directphotolysis Tier 4 is required should be added.Annex 3 will be revised accordingly. The choice to go alsodirectly to Tier 4 from Tier 2 is not in line with therecommendations of the experts attending the Rome meetingin September 1998 and thus is removed here.USA(3) It is difficult to understand when one would go to higher tiers or conduct additionalexperiments. Statements such as “...proceed too Indirect Photolysis Tier 1, if required”leave open the question of when the indirect photolysis tier 1 is required.US position: Agree. If the tiered approach is kept, the triggers should be made consistentThe words “if required” should be deleted if a higher-tiered study is meant to betriggered automatically.This point should be covered by the changes made.CropLife/ECPA With regard to 30 days/nights, does this mean the number of 24-hour days or theequivalent days of summer sunlight received?Also, guidance should be given when to proceed directly to Tier 4. However, a kineticstudy at Tier 4 was not proposed by the experts attending the Rome meeting inSeptember 1998; Tier 4 was only recommended for Identification of Photoproducts(>10% of degraded parent chemical). Thiscomment also applies to paragraph 20.The first point should be covered by the changes made. Thechoice to also go directly to Tier 4 is removed as this was notrecommended at the Rome meeting.Paragraph 19Germany Same comment as for paragraph 17. See response on comment for paragraph 17.UK These programs (GCSOLAR or ABIWAS) do not easily run on modern PCs without agreat deal of work by computer experts. These programs are difficult to use. Also, havethe programs been GLP validated?These programs should be updated / improved before being recommended for generaluse.With regard to the triggers, Annex 3 does not reflect the text.The first point should be covered by the changes made.Annex 3 will be revised accordingly.USA(3) For some reason GCSOLAR does not run well on a PC. A revised version should beprepared if the program will be used to meet data requirements.US position:Agree. Appropriate modifications to any required computer programshould be made.This point should be covered by the changes made.Croplife/ECPA These programs do not easily run on modern PCs without a great deal of work bycomputer experts. Therefore, these programs are difficult to use. It is also not clearwhether these programs have been validated. The programs should be updated /improved before being recommended for general use. This comment also applies toparagraphs 89, 124, 125, 155, 163, 163 and 170.This point should be covered by the changes made.ECPA membercompanyDelete the sentences after Ref. (2) and add:Further work on Pure Water Photolysis (i.e. the Tier 4) is only required, if the estimatedlosses are greater than 50% during one day under relevant environmental irradiationThis point should be covered by the changes made.ENV/JM/TG/RD(2006)1/REV151CountryCommentSecretariat’s ResponseGeneral Commentsconditions. Otherwise proceed to Natural Water Photolysis (Tier 1 or 2). Comparesection 126.128, too.Paragraph 20UK Guidance is needed how to do this, since in some circumstances the transformationproduct may also be susceptible to photodegradation.The triggers in Tier 3 define when to conduct Tier 4 studies.USA(2) In this paragraph, under the Section “Summary of the proposed Tiered Approach forDirect Photolysis”, and in paragraph 129 (page 25), it would be appropriate to expandthe definition of major transformation products by indicating that the 10% guidelinevalue applies to individual replicate data rather than mean data, particularly when apattern of increase with time is evident from a review of the replicate data. In numerousfate studies submitted for registration / re-registration, I have observed registrants’claims that certain compounds were not major degradates because they were not presentat greater than or equal to 10% of the applied; however, a review of replicate data oftenshowed that the compounds were present as major degradates in many of the replicates,but the mean values were lowered by the inclusion of outlier data points.US position:Agree.This point should be covered by the changes made.USA(3) When would it be necessary to estimate the half-life of a transformation product? Whatis the best method for doing so? Log-transformed data with a best-fit line through all theformation and declining concentration points is not adequate modelling. Appropriatekinetic modelling should be conducted to determine the rate constants for decline ofphotolysis products, if possible.US position: Agree. Clear instructions for measuring the kinetics of transformationproducts should be given.Some explanations / instructions are given in theexperimental section (paragraph 144).Croplife/ECPA Change title before paragraph 20 in “Identification of Major Transformation Products”;for reasons see comments on paragraph 18.This point is adopted.Paragraph 21-25USA(3) Sections 21-25 are good examples of background information that could be separatedfrom the experimental procedure.US position: Agree.Paragraphs 21-25 are not part of the TESTMETHODOLOGY. They belong to main chapterPRINCIPLE OF THE STUDY and thus are separated fromthe experimental procedure.Paragraph 26UK It should be made clear that this tier is not required if comparable direct photolysis datais available, as mentioned in paragraph 160 (this paragraph should be moved closer tothe start of the indirect photolysis section to highlight this information). The text shouldbe referred to at each mention of PW, or mention of PW should be removed or moved toan appropriate section.Indirect photolysis studies are only carried out when directphotolysis of a chemical is not a relevant process (see revisedAnnex 3). Therefore, the inclusion of a test in buffered purewater is not reasonable.ENV/JM/TG/RD(2006)1/REV152CountryCommentSecretariat’s ResponseGeneral CommentsThe statement that “the use of a xenon lamp light source for indirect photolysis studies isnot recommended at this time” should be explained further as it is not obvious why thisshould be the case. Annex 3 Figure 2 states a xenon lamp may be used.With regard to the triggers, Annex 3 does not reflect the text.We agree that a Xenon lamp should be allowed as alternativeto natural sunlight.Annex 3 is revised accordingly.USA(3) A xenon arc lamp should be allowed for indirect photolysis. In an indirect photolysisscreen, we can expect to determine whether the chemical can be degraded by an indirectprocess and whether the process will be significant in natural systems. Since indirectphotolysis is a second order process, the rate constant will be dependent on theconcentration of radicals (and their precursors) more than on the intensity and wavelength distribution of the light source. Hence, a light source simulating sunlight shouldbe acceptable as long as the source’s emission spectrum overlaps the action spectrum forradical production. Is it possible to extrapolate results from the use of simulated sunlightto evaluate indirect photolysis? Most registrants have xenon-arc lamp equipment and theinvestigation of indirect photolysis will require them to have natural sunlight equipmentunder this guidance.US position:Agree. The rationale for exclusion of xenon-arc lamps from indirectphotolysis studies should be provided.The use of a Xenon arc lamp will be included as alternativeto natural sunlight.USA(3) This section does not clearly define the criteria for when SNW, SNW-N or NW is thepreferred experimental conditions. Without clear guidance, registrants could do a SNWtest and only find out years later that the regulatory agency desired SNW-N. It wouldappear that there is an intent to discern photooxidative mechanisms, which goes beyondwhat is useful for a regulatory decision. The indirect photolysis study should beconducted with natural water (NW).US position:Agree in part. The option of using synthetic natural water should bepreserved, but better guidance on the formulation of SNW is needed. Data will be morecomparable between chemicals if SNW is used.As the draft document is written it seems to give enoughflexibility to the Study Director to use SNW and/or SNW-Nand /or natural water (NW) for indirect photolysis studies.The formulation/composition of SNW seems to besufficiently well described in Annex 5.CropLife/ECPA It should be made clear that this is not required when comparable direct photolysis dataare available as mentioned in paragraph 160; perhaps this paragraph should be movedcloser to the start of the indirect photolysis section to highlight this information. Asindirect photolysis studies are only conducted when direct photolysis does not occur to asignificant extent under the conditions of this model experiment it does not make senseto include tests in buffered pure water.Why should a Xenon lamp not be used for indirect photolysis studies? Annex 3 states inFig. 2 that a Xenon lamp may be used.Also the tiered approach for indirect photolysis consists of only 2 Tiers although at theRome meeting the experts agreed upon 3 Tiers; we would appreciate if the authors of thisIndirect photolysis studies are only carried out when directphotolysis of a chemical is not a relevant process (see revisedAnnex 3). Therefore, the inclusion of a test in buffered purewater is not reasonable.We agree that a Xenon lamp should be allowed as alternativeto natural sunlight.The last point is adopted (see revised Annex 3).ENV/JM/TG/RD(2006)1/REV153CountryCommentSecretariat’s ResponseGeneral Commentsguideline could explain their reasons for this.ECPA membercompanyParagraphs 26 and 27 are nice to have but not needed. Thus,directly proceed to Tier 2. This point is not adopted.Paragraph 27USA(3) Criteria for substitution of SAR to estimate rate constants is not clear – examples areneeded.US position:Agree. SAR studies may be beyond the capabilities of some laboratories,and may not be properly included in a guidance for a laboratory protocol. Betterguidance is needed.Agree with US position. This paragraph is deleted.Paragraph 28UK Annex 3 Figure 2 states a xenon lamp may be used. This point is adopted.CropLife/ECPA Change title in “Identification of Major transformation Products” because kineticinformation was not recommended for Tier 3 at the Rome meeting. With regard to lightsource see comment on paragraph 26.This point should be covered by the changes made.ECPA membercompanyChange text as follows: Determine the rate of decline in a realistic environmentalconcentration of the test chemical and its combined (direct and indirect) degradation rateconstants in at least two NWs irradiated with sunlight or simulated sunlight. Identify /quantify the major transformation products (set up the degradation pathway) anddetermine their rates of formation and decline. The selected NWs should represent asurface water (e.g. pond, reservoir, river, etc.) and originate from an area probably (or infact) contaminated with the chemical. They should differ in their characteristics, i.e. pH,CDOM and nitrate content. Compare section 154.160, too.This point is not adopted.Paragraph 30Japan The pHs of the test solution (pH 5, 7, 9) are not consistent to those in OECD TG 111(pH 4, 7, 9). So the pHs should be consistent to those in OECD TG 111.This point is adopted.UK Reference to environmental pH values (as elsewhere) should be added, i.e. pH 5 - 9. This point is adopted.USA(3) EU data requirements specify pH 4-9. Harmonisation would be desirable. The testshould always be conducted at environmentally relevant pHs. Section 30 contains thestatement that if the half-life of the parent molecule is < 1 day in the hydrolysis studythen photolysis should be conducted on each major hydrolytic product (defined as allcompounds seen at > 10% in hydrolysis study). We have a problem with this because itclearly introduces a new or change in the data requirements. This study is concernedwith photoproducts, not the photolysis of hydrolysis products. If the photolysis ofsignificant hydrolysis products is proposed it must be done based on a weight of theevidence approach to determine what is significant. As written, this guideline could haveReference will be made to OECD TG 111 whichrecommends pH range 4-9 as environmentally relevant. If atest substance is readily hydrolysed at a relevantenvironmental pH at 20-25 ̊C, it seems reasonable to us toconduct a photolysis study with the major hydrolysisproduct(s).ENV/JM/TG/RD(2006)1/REV154CountryCommentSecretariat’s ResponseGeneral Commentsphotolysis studies conducted on environmentally insignificant compounds. This changein data requirements would require further discussion. At this time we believe that thephotolysis of transformation products from parent study should be sufficient.US position:Disagree as to pH range. It is well recognised that pH 5, 7, and 9 representenvironmentally relevant pH.The comment on new or changed data requirements is EPA program-specific. Flexibilityin the design of the experiment must be retained, on a case-by-case basis.CropLife/ECPA Reference to environmental pH values (as elsewhere) should be added to sentence one(i.e. pH 5-9). With regard to additional photolysis studies with all relevant hydrolysisproducts, it should be rather recommended to conduct the photolysis studies with theparent test substance and see if hydrolytic transformation products are built up there.The first point is adopted. With regard to the second point,see response above on USA(3) comment.ECPA membercompanyChange 2ndsentence in: However, pure water photolysis tests should be conducted at apH ff.This point is not adopted.Paragraph 31UK Further guidance when photolysis studies are not required would be welcome, e.g.trigger values.We propose not to include trigger values here to avoid longdiscussions on what values are appropriate.USA(2) In this paragraph it would be helpful to give a reference value to help define or clarifywhat is meant by the term “fairly substantial volatilisation”. I suggest adding 10-3atm-cum/mole as a benchmark order of magnitude for Henry’s Law constant, above which youwould expect sufficient volatilisation from water as to make the test non-applicable orindicate the need for the precautions noted in the text. Also in that paragraph, I wouldlike to indicate the need for confirmatory sterility checks if an aliquot sampling methodis utilised.US position:Agree that better guidance is needed. The decision to run a study or notshould be made on a case-by-case basis.With regard to a reference value for volatilisation seeprevious response on UK comment. An appropriate place forsterility checks is in the experimental sections.USA(3) There seems to be a contradiction in this section. If a compound has a Henry’s LawConstant or VP that indicates substantial volatilisation will occur then an aqueousphotolysis study may not be appropriate. The physical properties of the compound (highescaping tendency, low water solubility) may indicate that the compound will neverreach a significant concentration in water.US position:Agree (Note that commenter 2 provided a potential benchmark for thisfactor). The decision to run a study or not should be made on a case-by-case basis.This paragraph mentions possible problems with volatilecompounds and recommends some precautions how tominimise volatility losses but the decision to run a study ornot has to be made by the Study Director on a case-by-casebasis.Croplife/ECPA Further guidance when photolysis studies would not be required for volatile chemicalswould be welcome (e.g. by inclusion of appropriate trigger values).See above responses on related comments.Paragraph 32Germany Supplement list by: The UV-vis spectrum is measured in Tier 1 for directENV/JM/TG/RD(2006)1/REV155CountryCommentSecretariat’s ResponseGeneral Comments(m)UV-vis spectrum(n)Information about biodegradability.photolysis. The other point seems of little relevance foraqueous photolysis experiments.CropLife/ECPAThe draft guideline contains two chapters dealing with information on the test substance(paragraphs 32-34 and 44-48, respectively). These should be combined in a similar wayas in other OECD E-Fate Test Guidelines (e.g. 307 and 308).This point is adopted.Croplife/ECPA The information in points (g) to (l) is normally required for the test substance in section“Test report” and should be deleted here.The test temperatures required for the determination of physical-chemical properties inthe corresponding OECD Guidelines (i.e. 104, 105, 107, 111 and 112) are different fromthe range given in the “Note”. Therefore, change this “Note” as follows: Thetemperatures at which the physical-chemical properties listed above were determinedshould be reported.This point is adopted.Paragraph 33CropLife(ECPA “Solubility in organic solvents” should be added to the items in paragraph 32 and deletedhere. The other two points of information are of little relevance for aqueous photolysisstudies and should be deleted here.These points are adopted.Paragraph 35-42CropLifeECPA This chapter contains too much unnecessary detail. Paragraphs 36 and 37 overlap withparagraph 62 and thus can be deleted here. We propose to create separate chapters forREFERENCE SUSTANCES and for QUALITY CRITERIA with a similar wording asin other OECD E-Fate test Guidelines (e.g. 307 and 308). The analytical methods shouldbe included as additional paragraph in the chapter INFORMATION ON THE TESTSUBSTANCE.These points are adopted.Paragraph 36Switzerland This paragraph does not contain information; delete.. This point is adopted.CropLife/ECPA TLC should be included as standard analytical technique because the concerns raised canalso be applied to the other analytical techniques quoted.?This point is adopted.Paragraph 38Switzerland This paragraph does not contain information, delete. This point is adopted.CropLife/ECPA The use of radio-labelled reference standards is not necessary; unlabelled material issuitable fort his purpose.This point is covered by the changes made.Paragraph 40Croplife/ECPA The statement “if samples are stored prior to analysis, storage stability test should beperformed” is too rigid. The necessity to conduct stability tests depends on:- the time period of storing the samples under usual storage conditions (-20 ̊C in theThis point is adopted.ENV/JM/TG/RD(2006)1/REV156CountryCommentSecretariat’s ResponseGeneral Commentsdark) and- the formation of photoproducts susceptible to hydrolysis.But if samples are deep-frozen, hydrolysis isvery unlikely to happen. Therefore, suchsamples should then be stable for several weeks, even in the presence of photosensitisersand this paragraph should be deleted.Paragraph 43Japan The dry heat sterilising method should be added to sterilising method. This method isusual and there is no problem to date.This point should be covered by the changes made.USA(3) Test Materials: should provide more specification as to type of material and shape here.It is buried in other parts of the document, but this is an obvious place for it.US position:Agree. Paragraphs 43-64 are about the Test Materials (vessels, media, testsubstances, et.). Paragraph 43 is only about test vessels. Thus this comment appearsunclear.Agree with US position.ECPA membercompanyIn case of pure water photolysis tests all glassware ff. This point is not adopted.Paragraph 44-48CropLifeECPA See previous comment for chapter INFORMATION ON THE TEST SUBSTANCE(page 8). The whole chapter should be shortened by using a similar wording as otherOECD E-Fate Test Guidelines (e.g. 307 and 308). Unlabelled test substance should alsobe allowed for all kinetic measurements.Considering this and previous comments on paragraphs 35-42, these paragraphs are renamed “Test substanceapplication” (new paragraphs 34-36). They now contain thecontents of paragraph 53 and 68-71.Paragraph 44Switzerland Chemicals possessing more complex structures are often difficult to judge where the“stable portion” is. Stability may also be dependent on actual conditions. Be moreprecise.This point should be covered by the changes made.CropLife/ECPA The position of the radiolabels should allow the identification of transformation productsand the elucidation of the transformation pathway. The use of other isotopes (other than14C) should be limited to those which would aid the analysis. Typing error in line 5“pathways”.This point should be covered by the changes made.ECPA membercompanyIf radio-labelling is used, test chemicals (i.e. that used for transformation pathwaystudies) should be labelled at one or more atoms within a stable or a relatively stableportion of the molecule (usually in rings). Experiments with more than one radiolabelshould be performed, if the pattern of decline cannot be evaluated with one label (e.g. forchemicals containing more rings or if the molecule is thought to be readily susceptible tocleavage to two parts). ffThis point should be covered by the changes made.Paragraph 47ENV/JM/TG/RD(2006)1/REV157CountryCommentSecretariat’s ResponseGeneral CommentsUSA(2) It would be helpful to state some of the special criteria that may apply if a formulatedproduct is used in place of the active ingredient. For example, will it be a requirementthat the carriers in the formulated product be tested separately to determine if they arephotosensitisers? Or, will separate photolysis data be needed for each formulation type ifthis option is taken? It may be helpful to address these issues as well as to give anexample.of when it may be preferable to use the formulated product.US position:Agree. If formulations contain photosensitisers, testing should be done onthe pure test compound also, to separatedirect and indirect photolysis effects.Aqueous photolysis studies are normally conducted with thepure test substance; therefore, the use of formulated productsis not recommended and this paragraph is deleted.Paragraph 49UK Annex 5 does not recommend pH 9 buffer details – these should be added. This point is adopted.Paragraph 50Switzerland The inclusion of a list of suitable buffer systems which are adequate would be desirable. A reference is made to OECD TG 111 in which suitablebuffer systems are extensively described.CropLife/ECPA It may be helpful to specify the sterilisation method for the buffer solutions /autoclavingor 0.2μm filtration?).Sterilisation methods are mentioned in paragraph 33. Areference to this paragraph is included.Paragraph 51CropLife/ECPA For non-ionisable compounds, the test should be conducted at a pH at which the testsubstance is hydrolytically most stable. The recommendation to use buffers of pH 5,7,and 9 as in the SETAC guidelines, however, is in contradiction to section 2.9.1 of theEU Commission Directive 94/37/EC in which pH 4, 7 and 9 are recommended.These points are adopted.Paragraph 52USA(3) EU data requirements specify pH 4-9. Harmonisation would be desirable. This sectionseems to indicate that photolysis experiments at up to 3 pHs could be required. The guidelines should recommend that photolysis be conducted at the single pH exhibiting thehighest UV/VIS absorbance. Could rate constants for the other pHs be calculated basedon extrapolation from the UV/VIS absorbance data? For an ionic compound where 3radiolabels are used, one would normally do3 experiments at the most stable pH (6experiments if corresponding SNW or NW experiments are done). Practical limits on thenumber of experiments to be conducted need to be set, balancing the use of the data inrisk assessments against the cost. Given the significance of photolysis in risk assessment(see general comment), the large number of possible separate experiments does notappear warranted.US position:Disagree as to pH range (also see US position on section 300 above). It iswell recognised that pH 5, 7, and 9 represent environmentally relevant pH.Flexibility in the design of the experiment must be retained, on a case-by-case basis.This point is adopted.Paragraph 53ENV/JM/TG/RD(2006)1/REV158CountryCommentSecretariat’s ResponseGeneral CommentsUSA(3) There are cases where low water solubility and the desire to have enough material insolution for reliable analysis, requires the use of 10% co-solvent.US position:Disagree. Co-solvent should be used only when absolutely necessary andlimited to 1% in order to reduce potential buffer effects.The use of up to 10% co-solvent is not excluded in paragraph53.Croplife/ECPA Lists of permissible co-solvents and of known sensitisers would be helpful. Acetonitrile is recommended as appropriate solvent.Paragraph 54USA(2) In this paragraph, there are several references listed. I suggest also adding as a referencethe chapter “Phototransformation of Pesticides in Aqueous Solution” by P. Méallier, pp.240-260 in The Handbook of Environmental Chemistry (1999), eds. C. Richard and G.Grabner. This chapter is an excellent source of information on indirect photolysis inaqueous solution. It also includes a discussion of direct photolysis, quantum yield, andtypical reaction types, for which examples (with initial and modified chemical structures)are given.US position:Agree.This point is adopted.USA(3) The triggers for SNW-N experiments are not clear. A clear criteria to trigger SNW-Nstudies needs to be set if this requirement is decided to be significant for risk assessmentpurposes. As mentioned previously, there are a variety of water conditions wherephotosensitisers, suspended sediments, algae may play a significant role in effectingphotolysis rates in NW systems. The natural water systems that the pesticide will beexposed to can be highly complex and understanding all the effects of one of thesefactors (SNW-N production of OH radicals) may not be possible. An indirect photolysisin NW representative of the proposed use pattern seems more useful. The guidelinesshould specify taking UV/VIS of test media for the indirect photolysis without testsubstances in it, as well as when the test substance is in it.US position:Agree in part. The option of using synthetic natural water should bepreserved, but better guidance on the formulation of SNW-N is needed. Data will bemore comparable between chemicals if SNW-N is used.A Study Director may first conduct studies in SNW and lateralso in SNW-N and NW to confirm that indirect photolysis isa relevant process for the chemical tested.The requirement for measuring UV-Vis spectra of the testmedia is mentioned in paragraph 55. The UV-Vis spectrumof the test substance will be available from Direct Photolysistier 1.Paragraph 55US(3) If the use of SNW is to be required, specific guidance on the humic acid concentrationneeds to be stated.US position:Agree.In formation on humic acid concentration in SNW is given inAnnex 5.Paragraph 56UK Should both methods be required since they serve the same function? Suggest“actinometers or a spectral analyser” would be sufficient.This point is adopted.USA(2) The UV-Visible wavelength of interest is stated as “295-800 nm”. As the visible lightregion of the spectrum ends at 750 nm, this statement (which appears in multiple placesSeveral references in this document mention the wavelengthrange of 290-800 nm, for example references (2)(3)(8)(10)ENV/JM/TG/RD(2006)1/REV159CountryCommentSecretariat’s ResponseGeneral Commentsthroughout the document) should be amended to improve its accuracy. Additionally, thechoice of 295 nm as the initial value in the range is interesting; often it is presented as290 nm in the literature, perhaps because of the different indirect photolysis reactionsthat occur at on either side of the 290 nm cut-off. I suggest considering the use of 290nm as the initial value in the range for that reason.US position:Disagree. The guideline provides references for the 295 to 800 nm range.etc. Therefore, this range will be used in the revised version.USA(3) The statement that xenon lamps are not recommended needs to be supported. Need tore-examine the recommendation that sunlight is the only option at this time. Naturalsunlight is not necessarily the best choice. It limits locations and times of the year forfacilities that are not located in “sunny” climates to conduct studies, and the naturalsunlight in Madison, Wisconsin, is not a model for use of the pesticide in San Diego, orHouston. In particular these studies are meant to be guidance for field expectations at anumber of different locations within the USor across Europe / around the world (if aglobal registration data package is being developed). There are going to be too manyvariables between these simulated waters and even natural waters selected for thesestudies to be more than guidance.US position:Agree in part. The rationale for exclusion of xenon-arc lamps from indirectphotolysis studies should be provided.The option of using synthetic natural water should be preserved, but better guidance onthe formulation of SNW is needed. Data will be more comparable between chemicals ifSNW is used.In the revised versions, Xenon lamps are allowed for bothdirect and indirect photolysis studies.CropLife/ECPA Irradiation with the xenon arc lamp should be continuous and should also be allowed forindirect photolysis studies. With regard to sentence 3, should both methods be requiredsince they serve the same function. We suggest that “actinometers ora spectral analyser”would be sufficient. Because comparative measurements with a new and used Xenonlamp (1600 operating hours) have shown the long-term stability of the lamp spectrum ofa Suntest apparatus, it should be sufficient to measure the integralphotoflux at thebeginning and at the end of an irradiation experiment.These comments should be covered by the changes made.ECPA membercompanyChange 2ndsentence in: For natural water photolysis studies, the recommended lightsource is sunlight or filtered xenon arc lamp light.This point is not adopted.Paragraph 58Switzerland For pesticides, the application season may not be equal to highest concentration in theaquatic compartment. Give more information on possible time lags.We do not see a need to go beyond these very generalrecommendations.UK More guidance is needed for chemicals with wide dispersive use, on season, latitude, etc.May not be known or may vary significantly. It is suggested that conditions under whichthe study was conducted are reported.Agree that these general recommendations may not be veryhelpful and that the conditions under which the study wasconducted should be reported.ENV/JM/TG/RD(2006)1/REV160CountryCommentSecretariat’s ResponseGeneral CommentsParagraph 60France In the first line, (generally quatz) has to be removed by (generally quartz). This point is adopted.CropLife/ECPA If it can be demonstrated that no significant differences in the light intensity spectrumtransmitted is detected between quartz and borosilicate, the latter material should also beallowed.The “merry-go-round” equipment is good for static systems when no trapping ofvolatiles is needed but is not suitable to trap volatiles in flow-through systems. As thissupposed to be an experimental guideline, illustrations of appropriate apparatus have tobe included as examples in corresponding Figures (see also General Comment).It may be simpler to use optical cells made of quartz glass toavoid long discussions about the acceptability of borosilicateglass.Illustrations of appropriate experimental set-ups will beincluded in an Annex.Paragraph 61UK Phosphate buffers will not cover the full pH range 5-9. The text here and in Annex 5 arenot consistent. Either use the same buffers as for hydrolysis (pH 5, 7 and 9) or phosphatebuffer and test pH 5-8.These points should be covered by the changes made.USA(3) A cautionary note on the use of phosphate buffers in cases where they might promote acatalytic effect could be included (see current EPA guidelines).US position:Agree.This point is adopted.Croplife/ECPA Phosphate buffers will not cover the full pH-range 5 to 9. The text here and in Annex 5are not consistent; either use the same buffers as for hydrolysis (pH 5, 7 and 9)orphosphate buffer and test at pH 5-8.These points should be covered by the changes made.Paragraph 65Canada Replace this section with the following: The study should be conducted at a temperaturechosen for other laboratory transformation studies, and should be maintained within ±2 ̊C. The temperature should be monitored periodically.As rates of photolytic reactions are almost independent of thetemperature, this temperature range was proposed by theexperts attending the Rome meeting.Agree that temperature should be monitored periodically.USA(2) Under “Test Methodology –Test Conditions” (paragraphs 65 and 67) I suggest adding acomment which notes that the dark controls should be kept at the same temperature asthe irradiated samples. A 10 degree temperature variation allowance seems a bit wide inrange, so, at the very least, it should be specified that the dark controls are to besubjected to a similar temperature pattern (inclusive of range of temperatures andduration of exposure to various temperatures within that range).US position:Agree. A temperature of 25 ± 1 ̊C should be maintained to minimisevolatilisation losses and to allow for better comparison to other studies.The first point is adopted by adding a corresponding sentenceto paragraph 67. With regard to the second point, see aboveresponse on Canadian comment.Paragraph 66Canada Replace “± 0.5” before pH with “± 0.1”. This point is adopted.Paragraph 67ENV/JM/TG/RD(2006)1/REV161CountryCommentSecretariat’s ResponseGeneral CommentsUSA(2) See comment on paragraph 65. This point is adopted.Paragraph 68CropLife/ECPA Paragraphs 68-71 are related to the test substance application and should be combinedwith paragraph 53 in a separate chapter Test substance application.This point is adopted (see paragraphs 34-36).Paragraph 70USA(3) Guidance should be given on the appropriate concentration of SNW and SNW-N to usein these studies. If NW systems are to be used some general parameters that fit theproposed use pattern of the pesticide should be outlined.US position:Agree.Information on these aspects is given in Annex 5.Paragraph 71USA(3) There should be more discussion of the requirement to maintain oxygen content prior tocompletion of the guideline. It is not clear that changes in oxygen content during anaqueous experiment will significantly change the photolysis of most chemicals.Requiring air-saturated solutions may result in a de-facto requirement for aliquotsampling from large systems in which a continuous flow of air can be maintained. If thisrequirement is retained, then we suggest making it very clear that the solution should besaturated with air only at the beginning of the experiment. Also, “saturated” is imprecisein its use here.US position:Agree in part. Because sacrificial sampling is preferred, oxygenation willbe difficult.It seems that the authors of this guideline were fully aware ofthe significant influence of oxygen on the rate of photolysisin water. They also made it very clear that the aqueoussolutions should be saturated with air at the beginning of thestudy. We also think that “saturated” is precise enough forthe purpose of the studies.CropLife/ECPA The guideline stipulates that the water should be fully oxygenated. Could the authors ofthis guideline please recommend a method of saturation which would maintain thesterility of the aqueous solution?Saturation can be achieved, for example, by bubbling filtersterilised air/oxygen through the aqueous solutions.Paragraph 73Switzerland Equation 8 contains a factor j which is not commented in the caption. This point is adopted.UK Note. This is true for any “box” cell, it is not only true of rectangular cells. Disagree.USA(1) It is not clear what irradiation period is required (15 days continuous, or 30 days dark /light). The proposed guideline calls for the laboratory to calculate an irradiation periodfrom equation8, based on “equating photons absorbed by the test chemical per unitvolume...”US position:Agree. The proposed mechanism for selecting the irradiation period is toocomplex. Either 15 days continuous, or 30 days with 12 hours light / 12hours darkshould be required. This will help to ensure the comparability of studies on differentchemicals.The guideline calls for a duration equivalent to 30 dayssunlight exposure which corresponds to approx. 15 days ofcontinuous exposure to a Xenon arc lamp.USA(3) If the study should be performed for the length of time necessary to simulate 30 days of The only place where this pointmight be a problem is in TierENV/JM/TG/RD(2006)1/REV162CountryCommentSecretariat’s ResponseGeneral Commentsexposure to sunlight, then of course the question is – What is the intensity of sunlight?The US industry has more or less standardised on irradiance of summer sunlight at noonat 40 N latitude, and we recommend that this standard should be adopted. The only wayto avoid arguments over sunlight irradiance is to require determination of the quantumefficiency and calculation of rates at different latitudes and times of the year usingGCSOLAR, ABIWAS or EXAMS. The identity of photoproducts would be requiredunder controlled conditions simulating the fastest rate of photolysis in the geographicalregion where the parent chemical is likely to be found.US position:Agree. The adjustment for season or latitude should be done after thelaboratory work in most cases. Flexibility in experimental design should be preservedfor special cases.2 which is an optional step. With the inclusion of thedetermination of the quantum yield such arguments can beavoided.CropLife/ECPA Note. This is true for any “box” cell, not only for rectangular cells. Disagree.Paragraph 74USA(2) This paragraph should be re-written for clarity and accuracy. In general, the documentcontains numerous and repetitive errors in grammar, syntax and punctuation. In somecases, these interfere with sentence meanings. I find that the OPPTS 835.2210 guidelinesare more easily understood.US position:Agree.We would highly appreciate if the commenter could supply aclearer and more accurate version of this paragraph and alsodetailed information on the numerous and repetitive errors ingrammar, syntax and punctuation.USA(3) Section 74 introduces a new data requirement to the US and EU, namely thedetermination of the photolytic fate of hydrolysis products. The existing guidance in theUS specifies conduct of the photolysis study at the pH where the parent is most stable.Rather than complicate the photolysis study guideline, we suggest a change in the datarequirements if photolysis of hydrolysis products is important for environmental fate. Inmost regulatory assessment schemes, photolysis is not considered an important factor fordetermination of Predicted or Estimated Environmental Concentrations. We suggest thatexpanding the data requirements is inappropriate when the current data requirementshave minimal value in risk assessments.US position:Disagree. This is a proposed test method and not a new or changed datarequirement. Data requirements are determined by the appropriate regulatory authority.Flexibility in the design of the experiment must be retained, on a case-by-case basis.The right to request generation of more data must be reserved, if the situation warrantsit.Agree with US position.Paragraph 75Switzerland If the analytical methodology produces data with a precision of ± 15%, the number ofdata points suggested in the text (less than five) is not sufficient to establish a reliableregression function.The number of sampling points also depends on otherfactors, such as the rate of photolysis, duration of theexperiment, etc. It is finally in the competence of the StudyENV/JM/TG/RD(2006)1/REV163CountryCommentSecretariat’s ResponseGeneral CommentsDirector to establish the appropriate number of samples.Paragraph 76USA(3) Agitation is most common in natural systems. What about allowing for stirring insamples? This would be particularly useful in situations where larger “bulk” samples aresub-sampled.US position:Disagree. Agitation should not be allowed, as it may cause volatilisation ofthe test substance.Agree with US position.Paragraph 77USA(3) The requirement for three replicates is not warranted. Generally, two replicates havebeen found to be adequate when 5-6 samples are taken over the course of theexperiment.US position:Disagree. At least three replicates should be required for a statisticallyrobust experiment.This point should be covered by the changes made.CropLife/ECPA A minimum of 3 replicates is excessive, in particular for all experiments conductedunder controlled laboratory conditions. It should be sufficient to use duplicates.This point should be covered by the changes made.Paragraph 79UK More guidance should be given. When are they required and if so, how should they beconducted?As these calculations are optional, the given guidance seemsto be sufficient.CropLife/ECPA More guidance should be given when this is required and if so, how this should becarried out.See above response.Paragraph 82USA(3) Sections 82, 83, 84 (missing) and 85 offer guidance rather than requirements for conductof the experiments. This is the kind of information that should be included in aPhotolysis guidance Document. The use of a single actinometer solution should beproposed to give a reasonable estimate of the photon flux. Again, the use of a singlestandard actinometer solution should be adequate since the current data requirementshave minimal value in risk assessments.US position:Agree as to sections 82-85. Better guidance on the appropriate use ofactinometer solutions is needed.This guidance how to determine the photon flux of a Xenonarc lamp is certainly needed as an important aspect of theTEST METHODOLOGY. Guidance on the use ofactinometers is given later in the experimental sections ofTier 3.Paragraph 83GermanyAn explanation would be desirable on why for an optically dense solution a zero-orderkinetics is employed instead of a pseudo-first-order one.Agree. Please supply explanation.Paragraph 86USA(3) Compare recommendation for pH to section 74.US position:See response to section 74 comment.Agree with US position.ENV/JM/TG/RD(2006)1/REV164CountryCommentSecretariat’s ResponseGeneral CommentsParagraph 87USA(3) Ordinarily, one would not use the UV spectrum obtained in a neat organic solvent unlessthere was no other way to obtain the UV spectrum of the test chemical. We suggestomitting this recommendation unless there is a clear use of the information.US position:Disagree. For example, this is useful for ionisable chemicals.Agree with US position.CropLife/ECPA A trigger value for the molar extinction coefficient should be set (e.g. >10). In lastsentence, change “neat” in pure.This trigger is not needed here. The second point is adopted.Paragraph 89Switzerland Include Table 2 of Ref. 12 in the text. This point is not adopted.UK With regard to GCSOLAR and ABIWAS, see previous comments on paragraph 19 These programs are mentioned here only as alternativemethods.Paragraph 90UK Annex 3 does not reflect the text. Annex 3 will be revised accordingly.USA(3) In the guidance section, the rationale behind the selection of the cut-off of 50%photolysis might be explained. We are accustomed to waiving the study if the molarabsorptivity is less than 10. The criterion in section 90 makes sense, but needs greaterexplanation.US position:Agree. Better explanation of rationale is needed.The trigger of 50 % is a rather conservative value whenconsidering that the maximum photolysis rate is estimatedfor a quantum yield of one.Paragraph 91USA(3) The statement “if required” needs to beclarified. The criteria for going to IndirectPhotolysis Tier I is unclear.US position:Agree. The words “if required” should be deleted if a higher-tiered study ismeant to be triggered automatically.The words “if required” are generally deleted.Paragraph 93Canada It should be noted that the test chemical and some of the transformation products formedduring the study may be volatile. Therefore, it is necessary to detect and quantify theformation of organic volatiles and CO2. Consequently, both the direct and indirectphotolysis test should be carried out in test vessels attached to suitable traps for thecollection of organic volatiles and CO2. This is also necessary to establish the massbalance in the study and to maintain consistency among the OECD Guidelines onchemical transformation. Sections 146 and 156 should also be modified based on thiscomment.This point should be covered by the changes made.USA(3) Sections 93-97: If Tier 1 says photolysis is possible, then a logical next step is adetermination of the quantum efficiency. Tier 2, in effect, is a rough determination ofq.e., and one might as well go straight to Tier 3 and do a reasonably good determination.According to the recommendations of the experts attendingthe Rome meeting in September 1998, the tiered system isrevised in the text and also in Annex 3. As Tier 2 is optional,ENV/JM/TG/RD(2006)1/REV165CountryCommentSecretariat’s ResponseGeneral CommentsWhat is the uncertainty associated with screening data? If using “screening” data alwaysresults in unacceptable uncertainty, then registrants might always have to go to the nexttier. Would a preliminary screening test on the test compound be needed to estimate arough half-life? Or is the half-life estimated from the theoretical screen sufficient todetermine the appropriate composition of the actinometer.US position:Agree in part. The rationale and advantages for collection of each type ofrate constant needs to be better explained.The number of tiers should be reduced to two: a screening step to determine if alaboratory study is needed (like Tier 1) anda full study (like Tier 4). Tier 2 should beeliminated. Tier 3 (determination ofquantum yield) should be optional.it practically consists of three Tiers:• Tier 1 – Theoretical Screen• Tier 2 - Quantum Yield determination• Tier 3 - Identification of Photolysis Products.Paragraph 95USA(3) A significant number of dark samples should be required to calculate a “net” rateconstant. The registrant should choose the appropriate number of dark controls.US position:Disagree. A dark control sample foreach sampling interval is needed toaccount for other loss processes.This paragraph leaves sufficient flexibility to the StudyDirector to select the appropriate number of dark controlsamples.Paragraph 98Switzerland Equation 14 describing the attenuation of natural sunlight (seasonal variation, clouds...)has to be included.Equation 14 is already included in this paragraph.UK L_ should be Lλ. This point is adopted.CropLife/ECPA It was not proposed at the Rome meeting to determine a direct photolysis rate constantfor the test substance in near surface clear natural water; therefore, delete this and thefollowing paragraph. Typing error: L_ should be Lλ.The first point is not adopted; this Tier 2 is optional. Thesecond point is adopted.Paragraph 99UK Should both methods be required since they serve the same function? Suggest“actinometers ora spectral analyser” would be sufficient.This point is adopted.CropLife/ECPA Same comment as for paragraph 56 (page 11). Same response as for paragraph 56.Paragraph 100UK Annex 3 does not reflect the text. Annex 3 is revised accordingly.Paragraph 102CropLife/ECPA The experts attending the Rome meeting in September 1998 agreed upon that at Tier 4identification of major phototransformation products (>10% of applied dose) should becarried out; There is also no need to do additional kinetic measurement when quantumyield is already determined at Tier 3. Therefore, delete “and/or 4” in the first sentenceand also in title of this sub-chapter and also delete the last sentence.These points are adopted.Paragraph 104-109ENV/JM/TG/RD(2006)1/REV166CountryCommentSecretariat’s ResponseGeneral CommentsUSA(3) These sections contain good discussions but do not provide experimental procedures.Also, the length of time it takes to do the q.e. experiment will depend on the intensity ofthe light source more than the number of wavelengths in the emission spectrum.US position:Agree. Sections 104-109 should be moved to the background document, orto an appendix.Clarification of the quantum efficiency experiment issue is needed.Paragraphs 104-109 are transferred to Annex 7.Paragraph 108Germany The azobenzene actinometer should be included. This is a very convenient actinometeras it affords no exact initial concentrations, is insensitive to oxygen, solutions can behandled at daylight, it affords no additional analytical procedures, it has been calibratedat various wavelengths and it affords no sophisticated data analysis (Reference: G.Gauglitz and S. Hubig, Photokinetische Grundlagen moderner Aktinometer, Z. Phys.Chem. N. F. 139 (1984) 237-246. // G. Gauglitz and S. Hubig, Chemical actinometry inthe UV by azobezene in concentrated solutions: A convenient method, J. Photochem. 30(1985) 12-125.This point is adopted by adding the azobenzene actinometerand the references to the Table in Annex 7.CropLife/ECPA The suggested actinometers do not include the oxalic acid which appeared in theECETOC report No. 12 (reference 12).This point is adopted.Paragraph 111CropLife/ECPA Typing error; paragraph number should be 111. This point is adopted.Paragraph 116France On our paper version, equation 21 could not be read clearly (web transmissiondistortion?).This point is adopted.Paragraph 121-123USA(3) Sections 121-123 introduce the possible, but unlikely, need to determine q.e. in differentabsorption bands for a general guideline, it should be adequate to specify how thedeterminations should be made for most cases. Exceptional cases will always requirespecialised knowledge and expert judgement to determine the need for additionalexperiments.US position:Agree. Special cases can be handled individually.This point is adopted by deleting these paragraphs.Paragraph 122CropLife/ECPA In second line, insert atbetween yield and at least. This paragraph is deleted.Paragraph 126CropLife/ECPA As a consequence of comments on paragraph 102, change first sentence in :A direct photolysis Tier 4 study should be performed if the direct photolysis rateconstant(s) for the parent test substance (estimated from its quantum yield) indicate(s)This point is adopted.ENV/JM/TG/RD(2006)1/REV167CountryCommentSecretariat’s ResponseGeneral Commentsthat direct photolysis is a significant process.Paragraph 128CropLife/ECPA Delete last point/sentence of this paragraph. For reasons see previous comments onparagraphs 102 and 126.This point is adopted.Title Tier 4CropLife/ECPA AS a consequence of previous comments on paragraphs 102, 126 and 128, the titleshould be changed in: Identification and quantification of major phototransformationproducts.Also, the two subtitles should consequently be deleted and the paragraphs 129-144 should be re-phrased accordingly.This point is adopted.Paragraph 129USA(2) With the exception of the three-word phrase in parentheses, paragraphs 129 and 137 areidentical. Likewise, paragraph 138 is a repeat of paragraph 130.US position:Agree. Paragraphs 137 and 138 should be deleted.This point is adopted.Paragraph 130Canada Delete “/or their major” before transformation. All transformation products includingorganic volatiles and co2should be measured.This point is adopted.UK No recommended methods are stated. Suggest this text is deleted as it is very difficult toprove the solutions were sterile.This point is adopted.CropLife/ECPA No methods for checking sterility are stated here. We suggest to delete this text as it israther difficult to prove the solutions were sterile.This point is adopted.Paragraph 134Japan “f the date...” should be changed to “If the data...” This paragraph is deleted.UK “f” should read “If”. This paragraph is deleted.CropLife/ECPA Typing error: f should be if. This paragraph is deleted.Paragraph 137UK More guidance should be given. When are they required and if so, how should they beconducted?This paragraph is deleted.Paragraph 138Switzerland 138 duplicates 130, omit. This point is adopted.Paragraph 139France All equations up to number 25 are written with “big” character size and the size isreduced for the following. It would be better to harmonise all equation sizes.This paragraph is deleted.UK Text should refer to Annex 4. This paragraph is deleted.Performance of indirect photolysis tiersCropLife/ECPA A 3-Tier system was proposed by the experts attending the Rome meeting, we would Annex is revised to be in line with the recommendations ofENV/JM/TG/RD(2006)1/REV168CountryCommentSecretariat’s ResponseGeneral Commentsgreatly appreciate if the authors of this guideline could explain the reasons for deletingone of these Tiers.the Rome meeting.Paragraph 146CropLife/ECPA Should the guideline specify that the water be sterilised in this paragraph? Sterilisation may be problematic assome sterilisationmethods might alter the properties of the water ingredients.Paragraph 147USA(3) The recommendation to use sunlight for indirect photolysis experiments needselaboration and discussion. As long as the intensity of the source and the emissionspectrum overlap the action spectrum of the photosensitiser or radical precursorsimilarly to sunlight, the source should beacceptable. Is this recommendation consistentwith the comments in section 160?US position:Agree. The rationale for exclusion of xenon-arc lamps from indirectphotolysis studies should be provided.The Xenon lamp is included as alternative irradiation sourcefor indirect photolysis studies.CropLife/ECPA The use of a Xenon lamp should also be allowed for indirect photolysis studies. Thiscomment also applies to paragraphs 154 and 156.The Xenon lamp is included as alternative irradiation sourcefor indirect photolysis studies.Paragraph 150UK Annex three does not reflect the text. Annex 3 is revised accordingly.Paragraph 153USA(1) The proposed guideline calls in paragraph 153 for the laboratory to conduct StructureActivity Relationship 8SAR) studies to determine the second-order rate constants for thedisappearance of degradates. We disagree with this requirement.US position:Agree. SAR studies may be beyond the capabilities of some laboratories,and may not be properly included in a guidance for a laboratory protocol. Betterguidance is needed.Agree with US position. The paragraph is deleted.Tier 2(page 29)CropLife/ECPA Identification/quantification of major phototransformation products should be treated asa separate Tier (see previous comment on performance of indirect photolysis study onpage 27).This point should be covered by the changes made.Paragraph 154CropLife/ECPA Experiments in buffered pure water (PW) should be deleted; for reasons see comment onparagraph 26 (page 7). This comment also applies to paragraphs 156-159.This point is adopted.Paragraph 155UK Should the recommended method be detailed in this guideline, along with guidance onwhen this effect should be accounted for?We think that some guidance is given in paragraphs 166-168.CropLife/ECPA Last point. Should the recommended method be detailed in this guideline, along with We think that some guidance is given in paragraphs 166-168.ENV/JM/TG/RD(2006)1/REV169CountryCommentSecretariat’s ResponseGeneral Commentssome guidance on when this effect should be accounted for?Paragraph 160UK This text should be moved further forward in the guideline.Due to the changes made, thisparagraph is not needed andthus deleted.CropLife/ECPA This paragraph should be deleted (see comments on paragraphs 26 and 154). This point is adopted.Paragraph 161-165CropLife/ECPA Direct photolysis rates are determined in direct photolysis studies and should be deletedhere; for reasons see comments on paragraph 26.This point is adopted.Paragraph 162UK As these programs are difficult to use, worked examples would be helpful. Worked examples can be found in reference 12.Paragraph 166-168USA(3) Is the decrease in the determined rate constant due to photobleaching significant enoughto warrant this level of refinement in the experimental test given the significance ofphotolysis in risk assessment?US position:Disagree. The guideline directs the laboratory to end the study ifphotobleaching occurs, or to continue thestudy and then correct for photobleaching.Agree with US position.Paragraph 169USA(3) Yes. Consequently, restricting indirect photolysis experiments to irradiation withsunlight reflects an unrealistic expectation for use of the data. At most, the experimentindicates the possibility for degradation of the test chemical by indirect photolysis.Using rate constants from such an experiment may be justified if the field experimentsclearly demonstrate that direct photolysis alone cannot account for the observeddegradation rates or products. Using the rate constants from the laboratory experimentsto determine an environmental concentration requires assumptions not only about thelight source, but also about the concentrations of photosensitisers, suspended sediments,radical precursors and radical scavengers. Those assumptions may be valid andconclusions about the significance of indirect photolysis may be valid, but we mustaccept that our ability to model degradation by indirect photolysis is at a very earlystage.US position:Agree. The rationale for exclusion of xenon-arc lamps from indirectphotolysis studies should be provided.The xenon lamp is included as alternative irradiation sourcefor indirect photolysis studies.CropLife/ECPA In line 3, insert space between is and that. This point is adopted.Paragraph 170Germany Under computational methods for, on page 36: “Quantum yield calculations (...fractionsand not as a percent)”. What is the difference? The following symbols have the sameThis point is adopted.ENV/JM/TG/RD(2006)1/REV170CountryCommentSecretariat’s ResponseGeneral Commentsmeaning: 5 = 10-2= 0.01. So the sentence can be deleted.Japan Second point under Tier 1 on page 33: According to this paragraph, the site of collectionand the preservation method are also important factors. So, they should be describedwell.The full term of “DOC” (Dissolved organic Carbon) is described in only Annex 5: Itshould be described in the text of this draft.Instructions on collection and sampling of NW are given inAnnex 5.The second point is adopted.CropLife/ECPA The reporting requirements seem to be unnecessarily detailed and should be shortened.A corresponding title for reporting test substance data should be added.This point should be covered by the changes made.Paragraph 171-177CropLife/ECPA Discussion greatly depends on the individual results obtained in each study and thus isnormally done in each test report. We have some doubts whether these paragraphs 171-177 are o great help for the reporting study directors and therefore propose to justinclude it as a separate point Interpretation and discussion of results.This point is adopted.LiteratureEU Typing errors in the following references:- 26, 27 and 28: Hoigné instead of Hoigne or Hoigne’-...41: Sulzberger instead of Suizberger- 50: Lemaire instead of Lemarie.These points are adopted.EU It would be useful to consider adding some of the following references:Paragraph 4, Direct photolysis:Boule P., Guyon C. and Lemaire J. 1982. Photochemistry and Environment IV :photochemical behaviour of monochlorophenols in aqueous dilute solution.Chemosphere 11, 1179-1188.Boule P., Guyon C., Tissot A. and Lemaire J. 1987. Specific phototransformation ofxenobiotic compounds : chlorobenzene and chlorophenols. Photochemistry ofEnvironmental Aquatic Systems, R.G. Zit and W.J. Cooper (eds) Miami, 10-26.Influence of Humic Substances:Aguer J.P., Richard C. and Andreux F. (1997). Comparison of the photoinductiveproperties of commercial, synthetic and soil extracted humic substances. J. Photochem.Photobiol. A 103, 163-168.Vialaton D., Richard C., Baglio D. and Paya-Perez A. 1998. Phototransformation of 4-chloro-2-methylphenol in water; influence of humic substances on the reaction. J.Photochem. Photobiol. A 119, 39-45.Nitrate ions:Niessen R., Lenoir D. and Boule P. 1988. Phototransformation of phenol induced byexcitation of nitrate ions. Chemosphere 17, 1977-1984.These references are included.ENV/JM/TG/RD(2006)1/REV171CountryCommentSecretariat’s ResponseGeneral CommentsHydroxyl radicals:Mailhot G., Astruc M. and Bolte M. 1999. Degradation of tributyltin chloride in waterphotoinduced by iron(III). Applied Organometallic Chem. 13, 53-61.Annex 1France Page 45: For the wavelength and wave number definitions, it seems that some symbolsare forgotten in the brackets.All definitions are in line with those given in the IUPACreference on page 42.Germany Page 43: Energy transfer: The first sentence is a single statement without any relation tothe rest of the text. It is interesting but it can be cancelled.Page 44: Photodegradation:Replace “molecular weight” by molar mass.Photolysis:In the text of the guideline “photolysis” is often used. In most cases this doesnot fit to the definition of photolysis given in Annex 1. So, either “photoreaction orPhotochemical reaction or phototransformation or a similar word” should be usedinstead of “photolysis” or the definition of photolysis in Annex should be altered. Thelatter surely would cause a lot of additional misunderstandings.These points are not adopted. These definitions are takenfrom the IUPAC document mentioned on page 42.Germany Photon flux: This quantity is frequently used in the text but is not given in Annex 1.Obviously, it is used in the sense of irradiance or spectral irradiance. If photon flux orirradiance is defined as the amount of photons incident on a given surface per time, itsunit becomes mol m-2s-1or (more usual in photochemistry) mol cm-2s-1.Thus the “units”photons cm-2s-1or photons cm-2d-1frequently used in the text as the unit of the photonflux are not correct. In some cases, “mol photons” or “Einstein” is used, this also has tobe replaced by “mol”. Expressions like these obviously stem from those times before theSI quantity “amount of substance” with the unit of mol was introduced. To clarify whatis meant: Photon is another word for expressions like “quantum of light” or “lightparticle” but it is no unit. We should clearly distinguish quantities, units and numbersand not mix them up to entities like “number of meters per second” when we arespeaking about the velocity. The still wide spread “number of mols” is another exampleof such an obscure mixture of numbers and units.Quantum yield: The quantity “quantum yield (Φ) should carefully be defined. A straightforward definition could be:Φ= amount of transformed chemical / amount of photons absorbed by chemicalThe rest of the text in this paragraph is unclear, in part this is due to missing text andsymbols.Spectral irradiance:The quantity power and the corresponding units W m-3orW m-2nm-1are without use in photokinetics. In photokinetics we need to know theWe assume that all the definitions in the IUPAC paper werediscussed and agreed upon by photochemistry experts. It istherefore surprising and disturbing that they should not beapplicable to this photolysis test guideline.ENV/JM/TG/RD(2006)1/REV172CountryCommentSecretariat’s ResponseGeneral Commentsincident amount of photons per time and irradiated area, so the corresponding unitbecomes mol m-2s-1or mol cm-2s-1nm-1. The analogue holds for all other quantitieswhich are related to the irradiance.Irradiation:Irradiation is not defined in Annex 1.So irradiation should be replaced byirradiance throughout the text.Solar photon flux spectrum:This quantity is not defined in Annex 1. It should bereplaced by spectral solar irradiance.Annex 3, Figure 1Japan In figure 1, the trigger from tier 1 to Tier 2/3 and from Tier 2 to Tier 3/4 are differentfrom the text of this draft TG. They should be the same.Annex 3 is revised accordingly.USA(2) The term “Kd” is used in reference to the rate of direct photolysis. This term (with acapitalised K) is generally used in reference to a coefficient of adsorption in soil, andthe use of it here seems inappropriate. Elsewhere in the document (and as generallydone in scientific documents), a small “k” is used to represent the rate constant. Figure1 should be amended to conform with the standard usages of scientific parameternotation. Similar corrections should be applied to Figure 2 in Annex 3, as the sametype of mistake occurs under Tier 1.US position.Agree.This point should be covered by the changes made.USA(2) Figure 1 is incomplete with regard to the decision criteria/items listed under Tier 3. Thetrigger value and other decision criteria information provided on page 6 of the maintext should be added so that the figure more completely describes the decision process.US position:Agree. If the tiered approach is kept, the triggers should be madeconsistent.This point should be covered by the changes made.CropLife/ECPA Typing error in Tier 2 box, line 2: approximate. This point is covered by the changes made.Annex 3, Figure 2Japan In Figure 2, the trigger from Tier 1 to Tier 2 is different from the text of this draft TG.They should be the same.This Figure will be revised accordingly.USA(2) Figure 2 in Annex 3 is incomplete with regard to decision criteria/items listed under Tier1. A definitive question that may be answered with either “yes” or “no” is needed so thatthe reader is guided to proceed to tier 2 or to quit.US position:Agree. If the tiered approach is kept, the triggers should be madeconsistent.This Figure will be revised accordingly.Annex 5Japan Under point 3 NW (Natural Water): Add “paddy fields” in the collection places. This point is adopted.UK These buffers do not cover the full range of environmental pH values (i.e. 5-9); see This point is adopted.ENV/JM/TG/RD(2006)1/REV173CountryCommentSecretariat’s ResponseGeneral Commentsearlier comment on pH.USA(2) In the discussion of the preparation of test media in Annex 5, it states that the test watershould be “filter-sterilised with a 0.2μm filter”. The unit appears to be incorrect as given,and should likely be a smaller unit such as “_m”.US position: Agree.The proposed unit is not readable.CropLife/ECPA The buffers recommended do not cover the full range of environmental pH values (i.e.5-9); see earlier comments on paragraph 61 (page 12).Is filtration through 0.2μm filters the only acceptable sterilisation method or canautoclaving and gamma-irradiation be used instead?The first point is adopted.We would not recommend autoclaving because this mightchange the nature of the water ingredients.The comments from the USA came from the following three sources:-(1) U.S. Environmental Protection Agency, Office of Pesticide Programs, Environmental Fate and Effects Division, Environmental FateTech Team, Washington, D.C. 20460-(2) Syracuse Research Corporation, 1215 Jefferson Davis Highway, Arlington, VA 22202-(3) American Crop Protection Association, 1156 15thSt, NW, Washington, DC20005ENV/JM/TG/RD(2006)1/REV

174 

### ANNEX 4

DRAFT DOCUMENT February 2004



## OECD GUIDELINES FOR THE TESTING OF CHEMICALS

PROPOSAL FOR A NEW GUIDELINE

Phototransformation of Chemicals on Soil Surfaces

INTRODUCTION

1. 1. Man-made chemicals may reach soil directly via deliberate application ( e.g. agrochemicals) and/ or via indirect routes (e.g. via waste water → sewage sludge → soil or air → wet/dry deposition). For risk assessment of these chemicals, it is important to estimate their potential for transformation in soil and for distribution in and between the various environmental compartments (soil, water, air).

2. 2

. Chemicals can be transformed in soil by microbial, chemical and/or photochemical processes. The method described in this Test Gu ideline deals with the photochemical transformation (rate and route) of chemical substances on soil surfaces. It is based on existing guidelines (1) (2) (3) (4) (5).



### SCOPE AND RELEVANCE

3. When irradiating a test substance on a soil surface under the experimental conditions described in this Test Guideline, besides photochemical transformations (direct and indirect photolysis) also chemical (hydrolysis, oxidation) and microbial transformations can occur, the latter in particular when “viable” (microbially active) soils are used. To assess the relevance of the latter two processes, non-irradiated dark

controls are included in this test. The difference in transformation rates and routes observed between irradiated samples and dark controls can then be attributed to phototransformation processes on the soil surface. The methodology is neither designed to determine the quantum yield of a test substance on a solid surface nor to distinguish between direct and indirect photolytic reactions, but should allow to estimate photolysis half-lives likely to occur on soil surfaces under outdoor conditions and also to isolate and identify phototransformation products.



### PRINCIPLE OF THE TEST

3. 4. Thin-layers of soil are treated with the test substance and irradiated by simulated sunlight (Xenon lamp) under controlled laboratory conditions or, as an option in sunny climatic regions, by natural sunlight

. Simultaneously, not-irradiated dark controls are ke pt under identical conditions to distinguish between photochemical and other reactions. After appropriate time intervals, the soil thin-layers are extracted and analysed for the parent test substance and/or for major phototransformation products. Volatile products are collected by appropriate absorption devices and are also analysed for at time intervals. Using 14 C-labelled material, phototransformation products can be identified and a mass balance, including the formation of soil bound (non-extractable) residues, can be established.ENV/JM/TG/RD(2006)1/REV

175 

### APPLICABILITY OF THE TEST

4. 5. The method is applicable to all test substances (unlabelled and radiolabelled) for which an analytical method with sufficient accuracy and sensitivity is available. It is applicable to slightly volatile or non-volatile, water-soluble or water-insoluble compounds. The test should not be applied to chemicals which are highly volatile from soil (e.g. fumigants, organic solvents) and thus cannot be kept in soil under the experimental conditions of this test.



### INFORMATION ON THE TEST SUBSTANCE

6. Unlabelled or labelled test substances can be used to measure the rate of phototransformation. Labelled material is required for studying the pathway of phototransformation and for establishing a mass

balance. 14 C-labelling is recommended but other isotopes, such as 13 C, 15 N, 3 H, 32 P, may also be useful. As far as possible, the label should be positioned in the most stable part(s) of the molecule 4

. The chemical and

radiochemical purity of the test substance should be at least 95 %.

7. 6. Before carrying out a phototransformation test on soil surfaces, the following information

on the test substance should be available:

(a) UV

- VIS Absorption Spectra [ OECD Guideline 105 ] (6);
(a) (a ) solubility in water [ OECD Guideline 105 ] (6); (b) solubility in organic solvents; (c) vapour pressure [ OECD Guideline 104 ] (6) and Henry’s Law constant; (d) n-octanol/water partition coefficient [ OECD Guidelines 107 and/or 117 ] (6); (e) adsorption coefficient (k d , k f or K OC ) [OECD Guideline 106 and/or Guideline 121] (6); (f) chemical stability in the dark (hydro lysis) [OECD Guideline 111] (6); (g) aerobic and anaerobic transformation in soil [OECD Guideline 307] (6); (h) phototransformation in water [OECD Guideline, in preparation](7). (i) dissociation constant (pK

a ) [OECD Guideline 112] (6).

The temperature at which these measurements were made should be reported.

7. 8. An appropriate analytical method of known accuracy, precision and sensitivity for the quantification and identification of the test substance and its phototransformation products in soil should be

available. The analytical detection limit for the test substance and its phototransformation products ( > 10 % of the applied dose) should also be known (see paragraph 13 12 ).

REFERENCE SUBSTANCES

8. 9. Reference substances should be used for the characterisation and/or identification of phototransformation products by spectroscopic and chromatographic methods.

4 For example, if the test substance contains one ring, labelling on this ring is required; if the test substance contains two or more rings, separate studies may be needed to eval uate the fate of each labelled ring and to obtain suitable information on formation of phototransformation products.ENV/JM/TG/RD(2006)1/REV

176 DEFINITIONS AND UNITS

10. 9. See Annex 1.

QUALITY CRITERIA

Recovery

10. 11. Extraction and analysis of, at least, duplicate soil samples immediately after the addition of the test substance gives a first indication of the repeatability of the analytical method and of the initial

recoveries uniformity of the application procedure for the test substance. Recoveries for later stages of the experiments are given by the respective mass balances obtained with labelled material . Recoveries should range from 90 % to 110 % for labelled chemicals (5) and from 70 % to 110 % for non-labelled chemicals (3).

Repeatability and sensitivity of analytical method

11. 12. Repeatability of the analytical method (excluding the initial extraction efficiency) to quantify test substance and phototransformation products can be checked by duplicate analysis of the same extract of the soil, incubated long enough for formation of phototransformation products.

13. 12. The limit of detection (LOD) of the analytical method for the test substance and for the phototransformation products should be at least 0.01 mg

· kg -1 soil (as test substance) or 5 1 % of the applied dose which ever is lower. The limit of quantification (LOQ) should also be specified equal or less than 10% of the applied concentration

.

Accuracy of transformation data

14. 13. Regression analysis of the concentrations of the test substance as a function of time gives the appropriate information on the reliability of the phototransformation curve and allows the calculation of the confidence limits for half-lives (in case of pseudo first order kinetics) or DT 50 values and, if appropriate, DT 90 values.



### DESCRIPTION OF THE TEST METHOD

Light source

15. 1 4. Natural sunlight or Simulation of artificial sunlight simulated with solar simulators under well-controlled laboratory conditions are is considered the optimal light source s . A characteristic of spectral power distribution for sunlight is shown in Annex 2 given elsewhere (8) ; it can also be obtained from ISO 10977 (8) or from GCSOLAR (9) as function of latitude and season . The cut-off of radiation of the light source used has to be 290 295 nm (10) . Xenon lamps equipped with appropriate filters, such as the Hanau Suntest apparatus (see Annex 2) are recommended as irradiation source (5) (7) (8) because they simulate very closely natural sunlight in the 29 0 5 -800 nm region

. (see Annex 2). Whereas mercury-metal halide arc lamps or equivalents can be used for other tests requiring lower level s of energy than xenon lamps, such lamps are less appropriate not suitable to evaluate the pho to transformation of chemicals because they have less power than xenon lamps. For the assessment of phototransformation of chemicals,ENV/JM/TG/RD(2006)1/REV

177 generally higher level of irradiation power is required which can only be provided by xenon lamps for the time being.

16. Since light in the wavelength range of 29 0 5 to 400 nm is most relevant for phototransformation

of chemicals in the environment (11)(13) , the spectral energy distribution of the Xenon light source (i.e. the incident light available at the soil surf ace level) in this range is recorded using , for example, a portable spectroradiometer 5 , consisting of a holographic grating monochr omator and a Teflon cosine diffuser in combination with glass fibre optics. Alternatively, the light intensity during a study performed with a Xenon lamp/filter system (e.g. Hanau Suntest) can be measured by a calibrated radiometer with sufficient accuracy or can be obtained from the manufacturers data. Typical light intensities (irradiance) between 300 and 400 nm at different exposure positions are given in Annex 3.

Conversion of laboratory irradiation time into days of natural summer sunlight

17. 16

. In order to relate the rate of phototransformation caused by the Xenon light to the rate likely to occur in sunlight, it is necessary to comp are the irradiance of the Xenon lamp with sunlight (13). (9). For this purpose, the integral of light intensity between 29 0 5 to 400 nm is either measured at the various positions of the soil thin-layers in the test system s described in paragraph s 21-24 16

- 18 before

and after the test or can be obtained from the data supplied by the manufacturer of the lamp . These values are compared to energy values of natural summer sunlight (midday) at latitude 30 to 50° N 6 which can be

obtained from reference (12) (10) or which can also be measured with the spectroradiometer (see Annex 3).

18. 17. Furthermore, it is assumed that the average daily sun radiation intensity is approx. 75 % of the maximum intensity over a 12-hour period (13) (10) , whereas irradiation intensity of the Xenon lamp is constant over time. The equivalent days d of natural summer sunlight can be calculated by the following equation:



### 12 75

. 0 r h d

⋅ ⋅

=

where d = days of summer sunlight h = hours of irradiation by the Xenon lamp r = ratio of intensity (irradiance) of the Xenon radiation to that of summer sunlight 0.75 = correction for diurnal variation of natural sunlight 12 = conversion factor of hours to days.

The above calculations are just one possible way for transferring the experimental light intensity to environmental irradiation conditions. Light intensity can also be calculated based on the following equations:

Light intensity (300-400 nm) (W/m 2 )

· 6.07% / 100% = global light intensity (300-3000 nm) (W/m 2 )

Global light intensity (300-3000 nm) (W/m 2 )

· 3600 sec = global light intensity in one hour experiment (300-3000 nm) (MJ/m 2 ).

5 For example, Model LI

- 1800, LICOR Ltd., Lincoln, NE 68504, USA can be used. This information is given for the convenience of readers. Equivalent instruments may be used if they can be shown to lead to the same result.

6 2 Intensities of sunlight depend on the geographical latitude in spring, autumn and winter, but vary little by latitude during the are practically not influenced in summer.ENV/JM/TG/RD(2006)1/REV

178 This experimental light intensity can then be relate d to environmental light intensity per day which are available for different locations and seasons, e.g. in reference (14).

Another way is to compare the intensity of the Xenon lamp with tables of GCSO LAR instead of measured intensity. In this way, the days of irradiation are calculated to a “standard” and the results obtained at different times and locations can be compared. The tables of GCSOLAR give average daily irradiancies L( λ ) in millieinstein per day per cm 2 which can be compared to irradiance by using the following formula:

L( λ )[millieinstein/cm 2

· day]

· 10 -3

· 6.023

· 10 23 [photons/einstein]

· 1/86400 [day/sec]

· 10 4 [cm 2 /m 2 ]

· h

·

c/ λ

· 10 -9 [Watt/m 2 ]

where h = Planck’s constant (6.63

· 10 -34 J/Hz) and c = velocity of light (3.00

· 10 8 m/sec).

This calculation should be performed for each wavelength λ (in nm). After that, the values obtained can be summated over the region 300 - 400 nm and the result compared to the measured value of the Xenon light source.

Incubation Test system

19. 18. The treated soil thin-layers (for preparation see paragraphs 27 – 28) are incubated and irradiated under temperature-controlled conditions in static or a flow-through system s which allow to trap any volatile products formed during the experiments. An example of a useful flow-through system is

shown in Annex 4 A (13). (9). Other test systems are described in references (15)(16)(17). (11) (12) (13).

20. 19. This test system consists of a stainless steel cooling tank containing the soil plates. This tank is sealed with a quartz lid, using teflon tape between and bound around the lid/tank interface, and placed beneath the Xenon lamp or exposed to sunlight . Cooling water at a pre-set temperature is pumped through the base of the tank to control the temperature of the irradiated soil-coated plates. The temperature is monitored in the soil during the experiments using an electronic thermologger 7

.

21. 2 0. In order to trap any volatile products formed during irradiation, air is drawn sucked through the tank at a certain flow rate (e.g. 10 – 12 ml/min) using a peristaltic pump. The incoming air is bubbled through traps containing 2 M potassium hydroxide solution and then through traps containing water to ensure that moist, carbon dioxide free air enters the system. The effluent air is bubbled through a series of traps containing, for example, 1 M sulphuric acid solution (to trap volatile basic compounds), methoxyethanol (to trap volatile organosoluble compounds) and ethanolamine (to trap 14 CO 2 or other acidic volatile compounds).

22. Alternatively, static systems consisting, for example, of individual quartz vessels (e.g. inner surface approx 10-12 cm 2 ) equipped with traps containing soda lime and polyurethane foam may be used (see Annex 4B).

7 For example, Grant Instruments Cambridg e Ltd., Barrington, Cambridge, UK. This information is given for the convenience of readers. Equivalent instruments may be us ed if they can be shown to lead to the same result.ENV/JM/TG/RD(2006)1/REV

179 Laboratory equipment and chemicals

21. 23. Standard laboratory equipment is required, in particular the following:

- analytical instruments such as GLC, HPLC and TLC equipment, including the appropriate detection systems for analysing labelled or unlabelled substances or inverse isotop e dilution method;

- instruments for identification purposes (e.g. MS, GC-MS, HPLC-MS, NMR, etc.);

- liquid scintillation counter for radiolabelled test substance;

- oxidiser for combustion of labelled material;

- extraction apparatus (for example, centrifuge tubes for cold extraction and Soxhlet apparatus for continuous extraction under reflux);

- instrumentation for concentrating solutions and extracts (e.g. rotating evaporator)

- water bath

24. 2 2. Chemicals used include: organic solvents, analytical grade such as acetone, methanol, etc.; scintillation liquid; various absorption solutions (see paragraph 2 3 0 ).

Soil

Soil selection

25. 23. For phototransformation studies on soil surfaces, the use of one two soil types is

recommended. sufficient. One soil should be the same type as used in the aerobic soil transformation study. As these experiments require glass or metal plates to be covered with thin-layers of soil, only those soils can be used which can form thin and solid layers on a glass or metal surface. Generally, a silty loam or clay loam soil rather than a sandy soil should be selected (5).

26. 24. The selected soil should be characterised , at least, for texture [according to FAO and USDA classification systems (18) (14 )], pH, organic carbon content and water holding capacity. For

determination of soil characteristics the methods recommended in references (19)(20)(21)(22)(23)(24) (15) (16) (17) (18) (19) can be used.

Collection and storage of soil

1. 25. The soil should be taken from the top layer (A-horizon) to a maximum depth of 20 cm. Remains of vegetation, macrofauna and stones should be removed. The soils are air-dried at room temperature (preferably between 20 - 25°C). Desaggregation should be performed with minimal force, so that the original texture of the soil will be changed as little as possible. The soils are sieved through a < 2 mm sieve. Before use the soils can be stored at ambient temperature and kept air-dried as microbial activity is of little relevance when studying physico-chemical processes on the soil surface. No limit on storage time is recommended but soils stored for more than 3 years should be re-analysed prior to use with respect to their organic carbon content and pH.

2. When “viable” (microbially active) soils are required for conducting the experiments, the soils should be collected freshly from the field and should be handled cautiously as outlined in the OECD Test Guideline 307 (6) and also in references (25)(26)(27).

27. 26. Detailed information on the history of the field sites from where the test soil is collected should be available. Details include exact location [exactly defined by UTM (Universal Transversal Mercator-Projection/European Horizontal Datum) or geographical co-ordinates], vegetation cover,ENV/JM/TG/RD(2006)1/REV

180 treatments with crop protection chemicals, treatments with organic and inorganic fertilisers, additions of biological materials or accidental contaminations (25). (20).

Preparation of soil thin-layer plates

28. 27. Soil thin-layers are prepared by applying an aqueous slurry of soil to a glass or metal plate 3

8 in such a way that a soil layer of about 2 mm thickne ss is formed. Thereafter, the soil layers are allowed to air-dry to reach a soil moisture corresponding to a pF of 2.0 to 2.5. This is the same moisture level as also required in the aerobic soil transformation study. of about 75 % of field capacity (about 24 hours).

24.

29. 28. An additional set of soil thin-layers is allowed to completely dry-out before test substance application. Theses samples are used to measure phototransformation on irradiated dry soil surfaces.

Test substance application

30. 29. To apply the test substance to the soil thin-layers it should be dissolved in water (deionised or distilled) or in a suitable organic solvent. Each soil thin-layer is then evenly treated with the test substance by distributing small droplets (e.g. 2-3 μ l) of the test substance solution (e.g. 40-50 μ l total volume) over the whole soil surface by means of an appropriate syringe (e.g. Hamilton microliter syringe or by a Hamilton dispenser unit) . In case an organic solvent is used, it should not be a photosensitiser and

should be evaporated from the soil thin-layers prior to the start of the irradiation process. As light penetration in soils is generally lower than 200 μ m (28) it is important to apply the test substance in a very low volume of solvent to minimise its penetration into deeper soil layers.

31. 30. The amount of test substance applied to the soil thin-layers should correspond, for general chemicals, to the estimated amount normally reaching the soil, or for crop protection chemicals, to the maximum recommended use rate, and should be related to the surface area of the soil thin-layers used 4 9

.

Test conditions

Test temperature

32. 31. During the test, the treated soil thin-layers are kept in the incubation test system described in paragraphs 21-24 18

- 20 at a constant temperature of 20 ± 2°C. The temperature is monitored during the test by a thermocouple which is inserted in the slu rry of one soil thin-layer before the slurry dries out. Adequate temperature control is necessary to help ma intain also soil moisture and comparable microbial activities within the light-exposed and dark controls.

3 8 An appropriate plate size is 5.5 cm × 3.5 cm. Parts of the soil thin-layers are scraped off at the edges of the plate,

so that a soil area of 5 cm × 2.5 cm is left which corresponds to approx. 12.5 cm 2

. 4 9 The amount to be applied to the soil thin-layers can be calculated by the following formula:



## [ ] [ ][ ] 

# [ ] [ ] ha / cm 10 cm F kg / g 10 ha / kg A g M

2 8 2 9



### ⋅

μ

⋅

= μ

where: M = amount applied on soil thin-layer [μg] A = rate of application [kg · ha -1 ] F = surface area of soil thin-layer [cm 2 ]ENV/JM/TG/RD(2006)1/REV

181 Moisture content

33. 32. Soil thin-layers are kept either moist ( at a pF of 2.0-2.5, see paragraph 32 5 ) 75 % of the field capacity 10 ) or air-dried during the irradiation period. Soil moisture is adjusted in the moist samples each time when samples are removed for analysis or at least every 48 hours by adding water to the soil thin-layers when necessary. Soil moisture should be measured and recorded.

.

Dark controls

34. 33. Additional moist and air-dried soil thin-layers are kept under identical conditions in the

dark but not irradiated to distinguish between photochemical and other reactions (5).

Test duration

35. 34. Duration of exposure to sunlight (natural or artificial) should not exceed 30 environmental solar days or two half-lives of the test substance wh ichever is shorter. The soil layers should be incubated in appropriate static or flow-through systems for time periods corresponding to the above limits. For example, All soil thin

- layers are continuously incubated in the described test system for a period of 240 hours (=10 days) which corresponds to approx. 30 days of natural midsummer sunlight (calculated by the equation given in paragraph 1 8 7 using intensity values of Annex 3).

Performance of the test

36. After treatment with the test substance, the soil thin-layers are placed in an incubation system such as the ones illustrated in Annex 4 the stainless steel cooling tank illustrated in Figure 3. The

system tank is then sealed with the quartz lid as described in paragraph 17 and placed beneath the Xenon light source or exposed outside to natural sunlight . The soil thin-layers are then irradiated for appropriate time intervals under the test conditions described above (see paragraphs 36-39). 31

– 34). Irradiation in the laboratory may be carried out continuously or discontinuously simulating day and night cycles (e.g. 12 hours each). The latter procedure would allow for compensation of soil moisture during the dark period and thus would not interfere with the irradiation process.

36. 37. At least, D d uplicate soil thin-layers are removed at appropriate time intervals and the soil samples are extracted with appropriate solvents of different polarity and analysed for the test substance and/or phototransformation products. Also, absorption solutions are removed at the same time intervals and analysed for volatile products. Besides a soil sample taken directly after application (0-hour sample) at

least 6 5 additional sampling points should be included. Time intervals should be chosen in such a way that pattern of decline of the test substance and patterns of formation and decline of phototransformation products can be established (e.g. 0, 17, 24, 41, 65, 137 and 240 hours).

37. 38. When using 14C-labelled test substance, non-extractable residues will be quantified by combustion and a mass balance will be calculated for each sampling interval.

5 10 For determination of water holding capacities, see OECD Guideline 307.ENV/JM/TG/RD(2006)1/REV

182 DATA AND REPORTING

Treatment of results

38. 39. The amounts of test substance, phototransformation products, volatile products and nonextractables should be given as % of applied initial dose for each sampling interval. Also a mass balance should be given in percentage of the applied initial dose for each sampling interval. A graphical presentation of the test substance percentages against time will allow an estimation of its phototransformation half-life or DT 50 . Major phototransformation products should be identified and their percentages should also be plotted against time to show their rates of formation and decline. A major phototransformation product is any product representing > 10 % of the applied dose at any time during the study.

40. More accurate determinations of half-lives or DT 50 values and, if appropriate, DT 90 values should be obtained by applying appropriate kinetic model calculations. The half-life and DT 50 values should be reported together with the description of the mode l used, the order of kinetics and the correlation coefficient (r 2 ). If appropriate, the calculations should also be applied to the major phototransformation products. Examples of appropriate models are described in references (29) (21) to (34). (24).

34.

35.

Test report

40. 41. The test report must include:

Test substance:

- common name, chemical name, CAS number, chem ical structure (indicating position of label when radiolabelled material is used) and relevant physical-chemical properties (see paragraph

7 6 ); - purity (impurities) of test substance; - radiochemical purity of labelled chemical and specific activity (where appropriate).

Test soil:

- details of collection site;

- date and procedure of soil sampling; - properties of soil, such as pH, organic carbon content, texture and water retention characteristics;

- length of soil storage and storage conditions

Xenon light source:

- manufacturer and model;

- filters and their purpose;

- measured spectrum of the light source between 29 0 5 and 800 nm given by the manufacturer

or measured at the beginning and the end of the test; of the test;

- comparison of the spectrum of the light with that of natural sunlight;

- intensity at sample level (Watt • m -2 ) and area irradiated.ENV/JM/TG/RD(2006)1/REV

183 Test conditions:

- dates of the performance of the studies; - amount of test substance applied; - solvents used and method of application for the test substance;

- area of soil thin-layers treated;

- description of the incubation system used;

- air flow rates (if applicable) ;

- temperature of experimental set-up;

- soil moisture content during incubation;

- method(s) of extraction;

- methods for quantification and identification of the test substance and major phototransformation products in soil and absorption solutions including LOD and LOQ ;

- number of replicates.

Test results:

- tables of results expressed as % of applied dose for the soil thin-layers;

- mass balance during and at the end of the studies;

- quantification characterisation of non-extractable (bound) radioactivity or residues in soil;

- quantification of volatile products;

- plots of percentages in soil versus time for the test substance and, where appropriate, for the major phototransformation products;

- half-life or DT 50 and DT 90 for the test substance and, where appropriate, for major phototransformation products including confidence limits;

- an assessment of phototransformation kinetics for the test substance and, where appropriate, for major phototransformation products;

- proposed pathway of phototransformation, where appropriate;

- discussion and interpretation of results.

LITERATURE

(1) US-Environmental Protection Agency (1982). Pesticide Assessment Guidelines, Subdivision N. Chemistry: Environmental Fate.

(2) Agriculture Canada (1987). Environmental Chemistry and Fate. Guidelines for registration of pesticides in Canada.

(3) European Union (EU) (1995). Comission Dire ctive 95/36/EC amending Council Directive 91/414/EEC concerning the placing of plant protection products on the market. Annex I: Fate and

Behaviour in the Environment.

(4) Dutch Commission for Registration of Pesticides (1995). Application for registration of a pesticide. Section G: Behaviour of the product and its metabolites in soil, water and air.

(5) SETAC (1995). Procedures for Assessing the Environmental Fate and Ecotoxicity of Pesticides. Mark R. Lynch, Ed.

(6) OECD (1993). Guidelines for the Testing of Ch emicals. Paris. OECD (1994 – 2000): Addenda 6-11 to Guidelines for the Testing of Chemicals.ENV/JM/TG/RD(2006)1/REV

184 (7) OECD (2000). Draft Guideline “Phototransfor mation of Chemicals in Water” – Direct and Indirect Photolysis.

(8) ISO 10977 (1993). Photography – Processed phot ographic colour films and paper prints – Methods for measuring image stability.

(9) Zepp, R.G. and Cline, D.M. (1977). Rates of direct photolysis in aquatic environment. Environm.Science and Technology, 11, 359-366.

(10) OECD (1997). Gu idance Document on Direct Phototransformation of Chemicals in Water. Series on Testing and Assessment No. 7.

(11) Miller, G.C. and Zepp, R.G. (1983). Extrapolating photolysis rates from the laboratory to the environment. Residue Reviews, 85, 89-110.

( 12 9 ) Mill,T., Mabey, W.R., Bomberger, D.C., Chou, T.-W., Hendry, D.G. and Smith, J.H. (1982).Laboratory Protocols for Evaluation of the Fate of Organic Chemicals in Air and Water. U.S. Environmental Protection Agency; EPA 600/3-82-002.

(1 3 0 ) Parker, S. and Leahey, J.P. (1988): Development of a method to investigate the photodegradation of pesticides. Brighton Crop Protection C onference – Pests and Diseases – 1988, 663 – 668.

(14) Wypych, G. (19..?). Handbook of Ma terial Weathering. Second Edition, Chapter 4, 61-94.

(1 5 1 ) Burkhard, N. and Guth, J.A. (1979). Photolysis of organophosphorus insecticides on soil surfaces. Pestic. Sci. 10, 313 – 319.

(1 6 2 ) Guth, J.A. (1980). The study of transformations. In Interactions between Herbicides and the Soil. R.J. Hance, Ed., Academic Press, 123 – 157.

(1 7 3 ) Guth, J.A. (1981). Experimental approaches to studying the fate of pesticides in soil. Progress in Pesticide Biochemistry. D.H. Hutson, T.R. Roberts, Eds. J. Wiley & Sons. Vol. 1, 85 – 114.

(1 8 4 ) Soil Texture Classification (US and FAO systems). Weed Science, 33, Suppl. I (1985) and Soil Sci. Soc. Amer. Proc. 26, 305 (1962).

(1 9 5 ) Methods of Soil Analysis (1986). Part I, Physical and Mineralogical Methods (A. Klute, Ed.). Agronomy Series No. 9, 2 nd Edition.

( 20 16 ) Methods of Soil Analysis (1982). Part 2, Chemical and Microbiological Properties (A.L. Page, R.H. Miller and D.R. Kelney, Eds.). Agronomy Series No. 9, 2 nd Edition.

( 21 17 ) ISO Standard Compendium Environment (1994). Soil Quality – General aspects; chemical and physical methods of analysis; biological methods of analysis. First Edition.

( 22 18 ) Mückenhausen, E. (1975). Die Bodenkunde und ihre geologischen, geomorphologischen, mineralogischen und petrologischen Grundlagen. DLG-Verlag, Frankfurt/Main.ENV/JM/TG/RD(2006)1/REV

185 ( 23 19 ) Scheffer, F. and Schachtschabel, P. (1998). Lehrbuch der Bodenkunde. F. Enke Verlag, Stuttgart.

(24) Schlichting, E., Blume, H.-P. and Stahr, K. (1995). Bodenkundliches Praktikum: eine Einführung in pedologisches Arbeiten für Oekologen. 2nd Edition. Blackwell, Berlin-Oxford.

(2 5 0 ) OECD (1995). Final Report of the OECD Workshop on Selection of Soils/Sediments. Belgirate, Italy, 18-20 January 1995.

(26) ISO 10381-6 (1993). Soil Quality – Sampling – Part 6: Guidance on the collection, handling and storage of soil for the assessment of aerobic microbial processes in the laboratory.

(27) Anderson, J.P.E. (1987). Handling and storage of soils for pesticide experiments. In Pesticide Effects on Soil Microflora. L. Somerville, M.P. Greaves, Eds. Taylor & Francis, 45-60.

(28) Ciani, A. (2003). Photolysis processes in soils and other porous media. Diss. ETH No. 15306.

(2 9 1 ) Hamaker, J.W. (1976), The application of mathematical modelling to the soil persistence and accumulation of pesticides. Proc. BCPC Symposium: Persistence of Insecticides and Herbicides,

181 – 199.

( 30 22 ) Goring, C.A.I., Laskowski, D.A., Hamaker, J.W. and Meikle, R.W. (1975). Principles of pesticide degradation in soil. In Environmental Dynamics of Pesticides. R. Haque and V.H. Freed, Eds., 135 – 172.

( 31 23 ) Timme, G. and Frehse, M. (1980). Statistical interpretation and graphic representation of the degradational behaviour of pesticide residues. I. Pflanzenschutz – Nachrichten Bayer 33, 47 –

60.

( 32 24 ) Timme, G., Frehse, H. and Laska, V. (1986). Statistical interpretation and graphic representation of the degradational behaviour of pesticide residues. II. Pflanzenschutz – Nachrichten Bayer 39,

188 – 204.

(33) Hill, B.D. and Schaalje, G.B. (1985). A tw o compartment model for the dissipation of deltamethrin on soil. J. Agri. Food Chem., 33,1001-1006.

(34) Gustafson, D.I. and Holden, R.L. (1990). Nonlinear pesticide dissipation in soil: A new model based on spatial variability. Environm. Science and Technology, 24, 1032-1038.ENV/JM/TG/RD(2006)1/REV

186 ANNEX 1

DEFINITIONS AND UNITS

Test substance : any substance, whether the parent compound or relevant transformation products.

Transformation products : all substances resulting from biotic or abiotic transformation reactions of the test substance including CO 2 and products that are in bound residues.

Bound residues : “Bound residues” represent compounds in soil, plant or animal, which persist in the matrix in the form of the parent substance or its metabolite(s)/transformation product(s) after extraction. The extraction method must not substantially change the compounds themselves or the structure of the matrix. The nature of the bond can be clarified in part by matrix-altering extraction methods and sophisticated analytical techniques. To date, for example, covalent ionic and sorptive bonds, as well as entrapments, have been identified in this way. In general, the formation of bound residues reduces the bioaccessibility and the bioavailability significantly (1) [modified from IUPAC 1984 (2)].

Phototransformation : reactions occurring on soil thin-layers under the influence of light (> 290 nm).

Soil is a mixture of mineral and organic chemical constituents, the latter containing compounds of high carbon and nitrogen content and of high molecular weig hts, animated by small (mostly micro-) organisms. Soil may be handled in two states: (a) undisturbed, as it has developed with time, in characteristic layers of a variety of soil types; (b) disturbed, as it is usually found in arable fields or as occurs when samples are taken by digging and used in this guideline (3).

Xenon lamp : An intensive source of ultraviolet, visible and near-infrared light produced by electrical discharge in Xenon under high pressure.

Intensity : Traditional term for photo n flux, irradiance or radiant power (radiant flux). In terms of an object exposed to radiation. The term should now be used only for qualitative descriptions.

Irradiance (E) [W • m -2 ]: The radiant flux or radiant power P of a all wavelengths incident on an infinitesimal element of surface containing the point under consideration divided by the area of the element (dP/dS; simplified expression: E = P/S when the radiant power is constant over the surface area considered).

Radiant Power (P), [J • s -1 or W]: Power emitted, transferred or received as radiation.

Half-Lif e, t 0.5 is the time taken for 50 % transformation of a test substance when the transformation can be described by first-order kinetics; it is independent of the concentration.

DT 50 (Disappearance Time 50) is the time within which the concentration of the test substance is reduced by 50 %; it is different from the half-life t 0.5 when transformation does not follow first order kinetics.

DT 90 (Disappearance Time 90) is the time within which the concentration of the test substance is reduced by 90 %.ENV/JM/TG/RD(2006)1/REV

187 The limit of detection (LOD) is the concentration of a substance below which the identity of the substance cannot be distinguished from analytical artefacts.

The limit of quantification (LOQ) is the concentrati on of a substance below which the concentration cannot be determined with an acceptable accuracy.

LITERATURE REFFERRED IN THE ANNEX 1

(1) DFG: Pesticide Bound Residues in Soil. Wiley – VCH (1998).

(2) T.R. Roberts: Non-extractable pesticide residue s in soils and plants. Pure Appl. Chem. 56, 945 – 956 (IUPAC 1984).

(3) OECD Test Guideline 304 A: Inherent Biodegradability in Soil (adopted 12 May 1981).ENV/JM/TG/RD(2006)1/REV

188 ANNEX 2

LIGHT SOURCE

A. SCHEME OF THE HANAU SUNTEST APPARATUS ( 15 9 )ENV/JM/TG/RD(2006)1/REV

189 ANNEX 2 (continued)

B. SPECTRUM OF UNFILTERED XENON ARC COMPARED TO SUNLIGHTENV/JM/TG/RD(2006)1/REV

190 ANNEX 3

LIGHT INTENSITIES OF A XENON LAMP AND OF NATURAL SUMMER SUNLIGHT

A. XENON LAMP 1

Position

No. Irradiance E (300 – 400 nm)

[W/m 2 ] r*

Start End Mean

1 + 69.2 69.7 69.4 1.036

2 78.0 78.9 78.4 1.171

3 79.6 80.7 80.1 1.196

4 ++ 79.2 80.8 80.0 1.194

5 78.5 79.9 79.2 1.182

6 75.3 76.4 75.9 1.132

7 + 63.3 65.0 64.1 0.957

Mean 74.7 ± 6.2 75.9 ±6.2 75.3 1.124 ± 0.09

75.3 ± 6.0

(1) U. Morgenroth, personal communication.

+ edge positions

++ central position

* r = ratio between artificial and natural light

B. NATURAL SUMMER SUNLIGHT

[Values taken from references ( 12 7 ) and ( 13 8 )]

Region latitude Irradiance E (300 – 400 nm)

[W/m 2 ]

Florida, USA 30°N 66.98

Greensboro, NC, USA 40°N 68.98

Basel, Switzerland 50°N 65.32

Mean 30 – 50°N 67 ±3 %ENV/JM/TG/RD(2006)1/REV

191 ANNEX 4 A

EXAMPLE OF A TEST SYSTEM FOR PHOTOTRANSFORMATION EXPERIMENTS ON SOIL SURFACES ( 138 )

A. INCUBATION AND COOLING TANK

B. SOIL PHOTOLYSIS PLATEENV/JM/TG/RD(2006)1/REV

192 ANNEX 4BENV/JM/TG/RD(2006)1/REV193ANNEX 5February 2004Compilation of comments on the proposal for a new Guideline on Phototransformation of Chemicals on Soil Surfacesand Secretariat’s responses.The following document comprises all comments received from Member Countries and industry on the proposal (January 2002) for anew OECDTest Guideline: Phototransformation of Chemicals on Soil Surfaces.This proposal was circulated for comments to OECD Member Countries until26thApril 2002. Comments were received from eight countries (Australia, Austria, France, Germany, Japan, The Netherlands, Switzerland andUSA) and industry (CropLifeInternational/ECPA).In this annotated guideline document, the comments are identifiedby their origin (see above). Responses from the Secretariat are provided for allMember Countries comments explaining (i) which points were adoptedand how the subsequent changes were made, and (ii) which points could notbe adopted.CountryCommentSecretariat’s ResponseGeneral CommentsAustralia Only suggestion is that there may be more recent degradation model references that couldbe added (pursuant to para 39/refs 21-24), eg.:"Gustafson DI and Holden LR (1990). Nonlinear pesticide dissipation in soil: a new modelbased on spatial variability. Environmental Science and Technology 24(7): 1032-1038.""Hill BD and Schaalje GB (1985). A two-compartment model for the dissipation ofdeltamethrin on soil. Journal of Agricultural and Food Chemistry 33(5): 1001-1006."I note that the refs given on this are the classical ones - but there may be a preference tolook for more real world models than the Timme ones (eg I think Hamaker/Goring &Hill/Schaalje are two compartment ones ... but I also note the latter seems to have an errorin the presentation of the model [missing ( )'s] ). Maybe there is a better more recentreview or book? Just as a thought, if not, maybe there is room for a review article with amathematician?This point is adopted by including the proposed references.France In a general point of view, this proposal is very close to the SETAC guideline currentlyused for registration of Plant Protection Product according to theEuropean directive71/414/EC. However, it gives rise to a few remarks (see specific comments).Agreed.The Netherlands In general, the documents of phototransformation of chemicals on soil surfaces andphototransformation in water should be uniform in the way of measuring light irradiancesin a lab test and comparing the values obtained with “actual sunlight”.Agreed.Germany The German position reflects the view of several involved experts, expressing We certainly understand these concerns. We may notENV/JM/TG/RD(2006)1/REV194CountryCommentSecretariat’s ResponseGeneral Commentsconsiderable concern with regard to e.g.- lacking scientific understanding of underlying processes;- excessive influence of soil composition;- transferability to “real” out-door conditions;- degree of validation.At the present state, the guideline gives just a rough estimate of phototransformationpotential at optimal conditions.completely understand all the processes occurring on/in soilunder the influence of sunlight. On the other hand, suchexperiments required since many years for the registration ofcrop protection products can give useful information whether achemical can be transformed on soil surfaces and whichproducts can be formed under the influence of sunlight.Germany It has to be recognized that the processes on soil causing “phototransformation” arescientifically not very well understood, yet. When irradiating a test substance adsorbed tosoil surface several processes occur in parallel: (I) direct photolysis, (ii) photosensitisation of the soil matrix and (iii) light induced radical formation (OH, NO3, O, Cl,etc.). The relative contribution to an overall breakdown of a test substance depends to alarge extent on the chosen type(s) of soil(s). Given the broad variety of soil compositions,it is worthwhile to deliberate the idea of an artificial well-defined standard soil in order toenhance comparability.The measured degradation rates from this test are just relative values, depending not onlyon chosen type of soil but also on temperature, geometry of test system, etc. It is muchdoubted by some experts that different laboratories would yield rather identical results (i.e.within an acceptable range). For more confidentiality in the outcome of such test alaboratory inter-comparison exercise should be performed. It should also be considered toinclude a substance of well known photochemical behaviour as an internal standard forsome sort of calibration.The method also suffers from another severe shortcoming: that of transferability to “real”outdoor conditions. From this aspect it would be much more desirable to determinequantum efficiencies (as for phototransformation in water and air). Clearly, such anapproach is more difficult in the adsorbed state, e.g. requiring remission (diffusereflectance-) spectroscopy instead of simpleabsorption spectroscopy for measuring theoptical density and, hence, the number of photons adsorbed. However, it allows forcalculation of transformation rates at any season or geographical latitude. The presentguideline is suitable for summer only. The reason for this deficiency is that manychemicals absorb only weakly at wavelengths greater than 295 nm (often just a “tailing”from a maximum at shorter wavelengths). But it is just for that region around 300 nm thatthere are great differences in irradiance between winter and summer [Frank, R.; Klöpffer,W.:Spectral solar photon irradiance in Central Europe and the adjacent North Sea.Chemosphere 17 (1988) 985-994]. Calculations based on summer-time irradiance,including a relatively strong fraction of UV near 300 nm substantially overestimateWe agree that the processes occurring on soil surfaces underthe influence of light are scientifically not well understood.This is the reason why a group of specialists at the SwissFederal Institute for Environmental Science and Technology(EAWAG) in Dübendorf has started a corresponding researchprogram; their basic findings might be appropriate forinclusion in the present or later versions of this guideline orlead to the development of additional OECD Test Guidelines.For the time being we have to accept some lack of knowledgein this area. Nevertheless, experiments such as the onedescribed in this draft guideline are carried out in a variety oflaboratories since many years for registra-tion purposes andhave given reproducible results.The requirement to use “viable” soils does not allow to workwith an artificial well-defined standard soil.In addition, it is not the purpose of this guideline to measurequantum yields in the adsorbed state or to distinguish betweendirect and indirect photolysis reactions. The above mentionedresearch group has developed a procedure to determinequantum yields for chemicals on solid surfaces which couldbecome the basis for a corresponding OECD Test Guideline inthe future.We will include an additional paragraph explaining theSCOPE AND RELEVANCE of the test procedure.ENV/JM/TG/RD(2006)1/REV195CountryCommentSecretariat’s ResponseGeneral Commentsphototransformation rates.As it is now, the guideline gives just a rough estimate of phototransformation potential atoptimal conditions. This should be stated, e.g. in a chapter on scope and relevance.Switzerland One goal of the test is to determine the rate of phototransformation on soil surfaces undercontrolled conditions so that it can be related to environmental conditions.We believe that this goal cannot be achieved because:- many factors that will have a crucial impact on the outcome of the experiments are notsufficiently controlled- in many cases the measured rate will be influenced or even dominated by diffusionkinetics and will not represent the pure phototransformation kinetic.It may well be that not all the factors which have a crucialimpact on the outcome of this studies are sufficientlycontrolled but past experience over many years has shown thatthe procedure described can give useful and satisfactoryresults.Diffusion may be a relevant factor depending on thechemical’s properties but it is also a process occurring underout-door conditions.SwitzerlandSpectrum and intensity of the lightThe document contains detailed information about the light source that should be used sothat the light spectrum and intensity can be compared to natural sun light. However, thereis no discussion about how light penetrates into a soil and how this process is affected bythe soil properties.The light intensity in the soil depends on the absorption and scattering coefficients (k ands, both are wavelength dependent) of the soil and can vary largely as a function of particlesize, type of mineral, humidity and organic carbon content. Results of a specificphototransformation experiment are only comparable to others or to natural conditions ifthe k and s values of the used soil are reported. (Application of Kubelka-Munk equationwill be required!). Up to now, k and s values for soils in the range 300 – 400 nm cannot befound in the literature so that the range of values that must be expected for natural soils isunknown. We plan to measure these values in our lab for a set of standard soils in the nearfuture.As described in this draft guideline the test substance is notincorporated into the whole soil layers but is applied directlyto the surface of the soil thin-layers in a very small volume ofsolvent to avoid significant penetration of the chemical intodeeper zones of the layers by which light penetration couldbecome a factor influencing the results.According to your results with 19 different soils, lightpenetration seems not to be significantly affected by the soiltype in the most relevant wavelength range o 300-400 nm.SwitzerlandSorption in organic materialAccording to the guidelines the organic carboncontent of the soil needs to be reported butthere is no statement about the preferableorganic carbon content and there is also noadvice on how organic carbon content could affect the results and how this should beconsidered in the evaluation of the results.It seems likely that chemicals absorbed inorganic matter are not susceptible to directphototransformationbecause light probablycannot enter into the organic matter to a significant degree (apparently, experimentalresults concerning this topic do not yet exist.)There is certainly some experimental evidence that it is thedissolved (non-adsorbed) portion of a chemical in a soil whichis susceptible for transformation. On the other hand, we knowfrom experience with crop protection chemicals that stronglysorbed, not-extractable materialcan also be degraded in soil.This may also occur in a phototransformation experiment.SwitzerlandThickness of the soil layer and diffusion kineticsThe penetration depth of light in soils is in the order of 0.1 – 0.5 mm(1, 2). Hence, most ofthe 2 mm soil layer that is used as test system remains in the dark. Obviously, directAs already outlined above, the test substance is directlyapplied to the surface of the soil thin-layers to minimiseproblems with light penetration and with other interferingENV/JM/TG/RD(2006)1/REV196CountryCommentSecretariat’s ResponseGeneral Commentsphototransformation can only occur to the small fraction of the chemical that resides in theirradiated part of the soil. Most of the chemical applied to the soil must first diffuse fromthe deeper, dark parts of the soil to the upper, irradiated part of the soil before it can bedegraded. This has to effects:1)if diffusive transport of the compound from the dark to the irradiated part of thesoil is fast compared to the photolytic transformation then the dark part of the soilacts as an instantaneous reservoir. As a consequence the observed transformationrate for the compound in the complete soil layer is directly proportional to thethickness of the soil layer (3).2)If the diffusion kinetic that is responsible for the transport of the compound fromthe dark parts of the soil into the irradiated parts of the soil cannot supply thecompound faster than it is transformed then the experimentally determined rate ofphototransformation truly is a combination of both kinetics: diffusion andphototransformation. In many cases the overall kinetic can even be dominated bythe diffusion process. The type of transformation curve that results from adiffusion controlled process under the given boundary conditions does notdeviate significantly from a first order kinetic as it is expected forphototransformation. Hence, the form of the degradation curve will not allow todecide whether the observed process was diffusion controlled or not (3).The diffusion kinetics strongly depend on parameters that are not (or not sufficiently)standardized in the experimental procedure: surface area of the soil, type of minerals,organic carbon content and humidity. The kinetics also depends on the thickness of thesoil layer. The guidelines do not suggest any method on how to gain a soil layer thatwould exactly match the desired 2 mm. This is not a trivial task and it must be expectedthat the true thickness of the used soil layer would rather range from 1 to 3 mm or more.All these factors have nothing to do with phototransfomation itself but can have asignificant effect on the observed ‘transformation rate’ as we have shown in a detailedpaper by experiments and theoretical considerations (3).processes such as diffusion which could influence the results.Considering this, the true thickness of the complete layer maynot be so relevant.SwitzerlandHumidity of the soil layerSoil humidity may exhibit a considerable influence on the results. However, this influenceis not recognised in the document and the suggested control of soil humidity isinsufficient. Humidity exhibits the following effects which have a direct or indirect impacton the observed experimental results:-Light penetration is very different in soils at field capacity or in air-dry condition.(Everybody knows that moist soils look darker than the same soils in air-drycondition).It is one of the goals of this test guideline to determine theinfluence of soil moisture on the transformation rates in theirradiated samples and dark controls.But it is certainly not a trivial task to maintain a constant soilmoisture during the study. The procedure described in thisdraft guideline tries to minimise moisture losses from the soilthin-layers in two ways:-by ventilation of the incubation system by moistenedENV/JM/TG/RD(2006)1/REV197CountryCommentSecretariat’s ResponseGeneral Comments-At field-capacity the chemical will mostly be sorbed inside the organic matter(and therefore not susceptible to the light). At air-dry conditions the chemicalwill partly or mostly be adsorbed to the mineral surfaces where it is susceptible tolight (4).-The diffusion kinetic (which is part of the observed degradation rate, see above)of a chemical in the soil is inversely proportional to its sorbed fraction andtherefore also depends on humidity. Diffusion also depends on whether the porespace is filled with water or air.air and-by adding water to the layers, whenever necessary.Switzerland Control of Soil Humidity.Concerning the humidity of the soil the guideline suggests that the experiments areconducted at “about 75 % of field capacity”. It is further suggested that this condition isreached if the 2 mm soil layer are allowed to air-dry for about 24 hours. 75 % of fieldcapacity correspond to a soil that is in equilibrium with 99% relative humidity in air.However, a soil layer of 2 mm that is allowed to air-dry for 24 hours will usually reach anequilibrium with the laboratory air which most likely is in the range of 30 – 80% rh. Thisdifference has a huge impact on the sorbed state of the chemical and on its diffusionkinetics as well as on light penetration (see above).In point 32. One reads: “Soil moisture is adjusted in the moist samples each time whensamples are removed for analysis.” However, there is no advice given how this can beperformed so that the desired75% of field capacity will be reached. From our experiencewe conclude that this goal is impossible to reach. Large variations in the experimentalconditions during the course of the experiment and between different laboratories will bethe consequence. Most importantly, rewetting of the soil can often lead to an instantaneousloss of major amounts of the chemical becausemolecules that are adsorbed on the mineralsurface in the air-dry soil are quantitatively displaced by water when the soil layerbecomes wetted. We have observed complete loss of compound in our experiments withkaolinite layers (3). Similar effects have been observed in the field:No suggestions are supplied in the guidelines about how to handle the air-dry soil layers.However, adsorption of all organic compounds to air dry minerals depends exponentiallyon relative humidity (6) (see Fig.2). Hence, it matters whether these air-dry soil layers arekept at 40 or at 80 % rh.The guideline suggests that the soil moisture content during the incubation is to bereported in the test report. However, it will not be possible to correctly record the soilIt is common practice in many laboratories to prepare soilsamples with a certain level of soil moisture, either as pFvalue, as % of field capacity or as a percentage of themaximum water holding capacity, for conducting aerobictransformation studies. For details how to determine thesemoisture the guideline refers to OECD Test Guideline 307.See also previous response.ENV/JM/TG/RD(2006)1/REV198CountryCommentSecretariat’s ResponseGeneral Commentsmoisture content during the course of the experiment. Even if this could be done it wouldbe of little value for the evaluation of the results because the possible ways of howhumidity can affect the results are much too complex to be easily understood.SwitzerlandCONCLUSIONWithin the wide limits given by the guideline the possible experimental conditions canvary so much that one can find degradation rates for a given chemical that might varylargely. Such results are impossible to evaluate and therefore must no be taken as a basisfor a risk assessment.See previous responses on the above German comments.Figures provided by the Swiss expertTime (h)Evaporative flux from the soil surfaceENV/JM/TG/RD(2006)1/REV1990 1002 10-54 10-56 10-58 10-51 10-41.2 10-40 20 40 60 80 100% relative humidity

K ads = (m 3 /m 2 )quartzFe2O3CaCO3Al2O3

adsorbed concentration concentration in the gas phaseFig. 2: Air/surface-adsorption constants of 1,2-dichlorobenzene on various minerals as a function of relative humidity (6).References referred to the Swiss comments1. Miller, G.C., et al.Chemosphere1989,18,1265-1274.2. Helmig, D., J. Müller, and W. KleinChemosphere1989,19,1399-1412.3. Balmer, M., K.-U. Goss, and R.P. SchwarzenbachEnviron. Sci. Technol.2000,34,1240-1245.4. Goss, K.-U. and R.P. SchwarzenbachEnviron. Sci. Technol.1999,33,4073-4078.5. Majewski, M., et al.Environ. Sci. Technol.1993,27,121-128.6. Goss, K.-U. and S.J. EisenreichEnviron. Sci. Technol.1996,30,2135-2142.ENV/JM/TG/RD(2006)1/REV200CountryCommentsSecretariat’s ResponseGeneral CommentsCroplife/ECPA In general, we support the guideline as proposed with the additions of the commentslisted below. We would greatly appreciate if these comments could be introduced andsupported in future discussions of this draft guideline.Croplife/ECPA The methodology described in this draft guideline is typical of what is currently viewedas standard procedure for conducting phototransformation tests on soil surfaces as itconsiders all available national and international test guidelines.Agreed.ECPA membercompanyLaboratories may have different technical equipment. Therefore it is necessary, thatcommon guidelines should be more general in points, where different technicalequipment can be used. This should be considered especially according to requirements,which do not have any influence on the essential outcomes of the study (examples: flowthrough versus biometer flask test systems, measurement of light intensity, etc.).Guidelines should not introduce further requirements which do not provide newinformation needed for risk assessment of fate and behaviour of a test substance in theenvironment, and which are not pointed out in the valid existing guidelines (example:data on photolysis on a dry soil surface may be nice to have, but there the reactions aremuch more slowly and, therefore, are not at all further relevant for the environment).This point should be covered by the changes made inparagraphs 15 and 18.As the surface of a field soil quickly becomes dry duringsunny periods, the rate on a dry soil surface certainly hassome environmental relevance. Together with the ratesobtained on moist soil, it gives to some extent the range forthe photolysis rate of a particular chemical on the soil surface.Austria “...may reach soil directlyvia deliberate application (e.g.agrochemicals) and/or viaindirect routes...” Man-made chemicals (agrochemicals as well as biocides) may reachsoil by direct application. However, in addition indirect routes can also contribute to theoverall exposure.This point is adopted.Germany Paragraph 1 is from introduction to adsorption on soil. It should be replaced by a morespecific justification on why it is useful to do such a test and what kind of informationone can yield beyond from tests in aquatic solution. (photocatalytic effects,semiconductors in soil)This point should be covered in the new paragraph SCOPEAND RELEVANCE.Paragraph 2Germany Emphasis should be laid not just on the rate of degradation but also on the route ofdegradation. Products may be different from those of bio-degradation.This point is adopted.Paragraph 3GermanyInsert:As far as possible, the label should be positioned eitherin the most stable part(s)of the molecule or in the effective functional moiety(es), e.g. for bioactive substances.The purity of the test substance.This point is sufficiently covered in paragraph 5 and footnote1.US(1) Agree to the use of Xenon lamps to replace natural sunlight.Spectrum and intensity Natural sunlight is included as an optional irradiation sourceENV/JM/TG/RD(2006)1/REV201CountryCommentsSecretariat’s Responsesource should be submitted before and after experiment at least. This will allowassessment of difference from natural sunlight. Spectrum of chemical should also besubmitted to determine what wavelengths it absorbs.US position: The U.S. partially agrees. If a Xenon lamp is used, the irradiation intensityto which the soil thin layers are exposed should be measured at least before and after thestudy. However, this comment is unnecessary because the determination of theirradiation intensity of the Xenon lamp is adequately addressed later in paragraphs 15and 16 of the guideline. The U.S. does not agree that the use of a xenon lamp (instead ofsunlight) be mandated. At the very least, the use of sunlight should remain as an option.(See reviewer #2: para 14 comment on Xenon lamp versus sunlight.)for certain climatic regions.Paragraph 4Paragraph 5US(1) (EFED noted that3H was among isotopes identified in the guideline as potentially usefulfor radiolabeling.) Use of tritium should not be allowed for radiolabeling because ofpotential proton exchange with media.US position: The U.S. agrees.This point is adopted.US(2) There should be a distinction made between chemical and radiochemical purity. Forlabeled compounds, indicate the minimal acceptable chemical and radiochemical purity.For unlabeled compounds, indicate the minimal acceptable chemical purity.US position: The U.S. agrees. There is a major difference between chemical andradiochemical purity.This point is adopted.Croplife/ECPA This paragraph states that “as far aspossible, the label should be positioned in the moststable part(s) of the molecule. For example, if the test substance contains one ring,labelling on this ring is required; if the test substance contains two or more rings,separate studies may be needed to evaluate the fate of each labelled ring and to obtainsuitable information on formation of phototransformation products.”We think that the location of the label should be left to the discretion of the studydirector. While a ring is often the choice location in most cases, there may be occasionswhen equally valuable data can be generated by the use of labels in locations other thanrings. Of course, the degradation of the molecule would need to demonstrate that thelocation of the label has indeed provided allpotential degradates of concern. Therefore,the wording “labelling on this ring is required” should be changed and the choice of thelabel location should not be restricted to rings only.It is always left to the discretion of the study director and/orthe synthesis chemist to decide where the label can bepositioned in a particular molecule by the available synthesismethods. It is considered as recommendation to position thelabel, whenever possible, in the most stable part(s) of amolecule. The text in footnote 1 is given as additionalexplanation and just mentions ring-labelling as example butnot as a mandatory requirement.Paragraph 6Austria Addition suggested: “(I) pKa if a molecule is liable ionisation (e.g. protonation) [OECDGuideline 112]”This point is adopted.ENV/JM/TG/RD(2006)1/REV202CountryCommentsSecretariat’s ResponseReason: Degradation in moist samples is also investigated.Germany Replace: Before carrying out a phototransformation test on soil surfaces, the followinginformation on thetest substance should be availablemay be helpful.Insert a foodnote for (a): Note: absorption behaviour of test substances inaqueous solution (homogenous phase) may differ from adsorption behaviour on surfaces(heterogenous phase)The formulation used in the first sentence of this paragraph isin agreement with that used in other environmental fate testguidelines (e.g. 307, 308, 309). The proposed footnote is notneeded because Point (a) is deleted based on a comment fromthe Netherlands.The Netherlands (h) already required UV VIS absorbence spectra. Extra UV VIS spectra therefore do notprovide extra information. Anyway, the use of UV-VIS spectra can be disputed forphototransformation of chemicals on soil surfaces, since indirect photolytic degradationcannot be excluded.This point is adopted.US(2) Indicating that the temperatures at which each study was conducted should be reportedimplies that the results of each study should be reported. Therefore in the first sentence,change “should be available” to “should be availableand reported”.US position: The U.S. agrees.The information listed in paragraph 6 may be available anduseful before being finally reported. This point is thereforenot adopted.US(3) This seems like a long list of physical/fate properties that “should” (I assume that meansmust be) available before the test can be run. If this is followed, the soilphototransformation test could only be run after all of these other tests. Some of the listmake sense (e.g., phototransformation in water) but others don’t (e.g., anaerobictransformation in soil). Also, most of the physical properties could be estimatedaccurately enough to run the test. I don’t see why this test has to be run as the last in asequence of tests. Many of these could be run concurrently.US position: The U.S. agrees.All this information may be helpful before starting a test onphototransformation on soil surfaces but it is not required thatall this must be available at that time. None of these tests hasto be conducted in a certain sequence; they all can be carriedout concurrently as far as possible. The physical-chemicaldata (a-d and i) will certainly be available first.Croplife/ECPA Only the solubility in water and solvents and the vapour pressure are truly needed toconduct this test. Soil metabolism information may be nice additional information, butthis study can be conducted concurrently with the soil metabolism study. Requiring allthis other information prior to initiation of the soil photolysis study can delay theinitiation of the soil photolysis study while this other information is being generated.See response above.ECPA membercompanythe following information on thetest substance should be available:this sentence should be “The following information may be helpful (but is not essentialand may be not available before commencement of the study):”See response above.Paragraph 7Austria Insertion: “The analytical detection limit for the test substance and itsphototransformation products (≥10 % of the applied dose or lower where relevant) ...”In the current discussion of the risk assessment of metabolites in connection withDirective 91/414/EEC the 10 % trigger for characterisation and identification ofdegradation products is not applied automatically. Degradation products, which fallwithin the definition of “relevant metabolites” have to be evaluated as the activeThis point should be covered by the changes made.ENV/JM/TG/RD(2006)1/REV203CountryCommentsSecretariat’s Responsesubstance and therefore all relevant endpoints have to be obtained, even if theirconcentration in degradation studies is below 10%.GermanyReplace and Delete: The analytical detectiondeterminationlimit for the test substanceand its phototransformation products (>10 % of the applied dose)should also be knownComment: This is no information on the test substance itself (cf. heading). This item isalso mentioned in paragraph 11 and 12.This information is required under the same heading also inother environmental fate test guidelines (e.g. 307, 308).US(2) As currently written, the last sentence of paragraph 7 could be misinterpreted to meanthat the detection limit for the test substance and for its phototransformation products is>10% of the applied dose. Therefore, thelast sentence should be replaced by “Theanalytical detection limit(s) for the parentand any phototransformation products thatcould possibly represent greater than 10% of applied at any time during the study shouldbe known (see paragraph 12).”US position: The U.S. agrees.This point should be covered by the changes made.ECPA membercompanyThis paragraph provides no information on the test substance itself. This item is alsomentioned in paragraph 11 and 12.See response above on German comment.Paragraph 8Paragraph 9Paragraph 10Japan(1) When the amount of the test substance applied to soil is small, in general, it is difficult tomeasure the transformation rate of the test substance accurately and the mass balance islow because the recovery of the test substance from soil is difficult. Therefore, therecovery should be taken into account when the amount of the application is nominated.It may be difficult to always recover the test substance whensmall amounts are applied to soil. However, the recoveryranges given here agree with those defined also in otherguidelines for similar low rates (e.g. 307, 308).US(2) A clearer distinction should be made between recovery (accuracy) of the soil analyticalmethod for the parent and degradates, and total recovery of radiolabeled material (massbalance). That can be done by deleting the 2ndsentence (which refers to mass balance)and inserting an additional paragraph (with a new #) that separately addresses the totalrecovery of radiolabeled material (mass balance).US position: The U.S. agrees.This point should be covered by the changes made.Paragraph 11Germany Duplicate analysis is not sufficient for repeatability of an analytical method. Thisinvolves also accuracy and sensitivity of the method.Duplicate analysis was found sufficient for other fate testguidelines (e.g. 307, 308).US(2) Give an example of a quantitative measure of repeatability (precision) of the soilanalytical method such as the relative percent deviation.US position: The U.S. agrees.As this strongly depends on the analysis method available fora chemical it seems rather difficult to define a generallyacceptable relative deviation.ENV/JM/TG/RD(2006)1/REV204CountryCommentsSecretariat’s ResponseParagraph 12Germany Replace: The limit of detectiondetermination(LOD) of the analytical method for thetest substance and for the phototransformation products should be at least 0.01 mg·kg-1soil (as test substance) or 1 % of the applied dose which ever is lower. The limit ofdetection quantificationshould also be specified.This point should be covered by the changes made.The Netherlands LOD<0.01 mg/kg soil. How to specify the limit of quantification (LOQ)? Please givedefinitions of LOD and LOQ, since different definitions are used.This point is adopted by including the definitions used inguideline 309.Croplife/ECPA Why is a LOD of 1% required? 5% of applied would be more reasonable. This point is adopted.Paragraph 13Austria Deletion of the bracket term or correction suggested:1stalternative: “... the confidence limits for half-lives (in case of pseudo-first-orderkinetics)”2ndalternative: “...(in case of first-order andpseudo-first-order kinetics) ...”In Annex I of the Guideline the term half-life is defined as time taken for 50 %transformation of a test substance when the transformation can be described by firstorder kinetics. Therefore the definition should be precise and consistent throughout thedocument. So either “pseudo” or add “first-order” should be deleted in the text andupdated with the definition of half-life in the Annex.Another possibility would be to delete the bracket term, which refers to ourunderstanding to the definition of half-life.This point is adopted.Germany linear regression of log concentration versus time => R2 is the common term. It may also be non-linear regression.US (EFED noted that the guideline “allows for” the determination of confidence levels.)Require calculation of confidence limits on half-life, to determine the statistical validityof the results.US position:The U.S. agrees. Although this is a somewhat subtle point, the currentstatement in the guideline does (to some degree) imply that the determination ofconfidence limits is optional. The statement should be strengthened to indicate that thedetermination of confidence limits should be performed.Confidence limits are mentioned in paragraph 40 under testresults and thus are clearly required.US Replace “Accuracy of transformation data”with “Confidence limits for regressionderived parameters”.US position: The U.S. agrees that the latter title more accurately reflects the contents ofthe paragraph than the former.We would like to keep the present sub-title because it coversmore than just” confidence limits”.Croplife/ECPA While fitting half-lives, confidence intervals are not generally calculated. The goodnessof fit is described by r2. There are some EUguidance documents where it is stated thatr2 should be >0.7 for an acceptable DT50. As our current tools which we use for fittingdo not deliver confidence intervals, this requirement should not be obligatory orremoved from the guideline.This requirement for confidence limits is in line with otherfate test guidelines (e.g. 307, 308).ENV/JM/TG/RD(2006)1/REV205CountryCommentsSecretariat’s ResponseECPA membercompanyLinear regression of log concentration versus time => R2 is the common term Non-linear regression may also be used.Paragraph 14France Paragraphs 14, 15 & 16. The lower cut-off value for light wavelength is proposed to be295 nm but a value of 290 nm is stated in the scheme of the Hanau Suntest apparatus(Annex 2). The SETAC guideline requires a filter removing wavelengths below 290 nm.We support this last recommandation because it takes account of presence of UVB evenif they are in low proportion.This point is adopted.GermanyDelete:...(5)(8) because they simulate verycloselynatural sunlight in the 295-800 nmregion (see Annex 2). Comment: Annex 2 (B) shows that the spectra are not identical isthe sensitive region around 290 nm. It may be that the Xenon-arc spectrum in B ismeasured without filter, but in that case this should be mentioned or, better, the Xespectrum with filter should be presented. If the spectrum in Annex 2, B is correct, i.e.measured with filter, the method is bound to produce much too high degradation rates.Replace: Whereas mercury-metal halide arc lamps or equivalents can be usedfor other tests requiring lower level of energy than xenon lamps, such lamps are lessappropriate not suitableto evaluate the phototransformation of chemicals because theyhave less power than xenon lamps. Comment: This type of source should not be strictlyexcluded just for reasons of power.Comment: Reference (5) is deemed not helpful here.These points should be covered by the changes made.Japan(2) The cut-off wavelength of a light source should be harmonized between Para14 andANNEX2.This point is adopted.The Netherlands ISO 10977 (1993) is used as characteristic of spectral power distribution for sunlight. Inthe OECD and US EPA guidelines for phototransformation in water, tables generated bya computer program (GC SOLAR) are used as characteristic of spectra powers (asfunction of latitude and season). Why not use these tables? They give a daily average ofthe irradiance reaching the surface of the earth.This point is adopted.US(2) The option of using sunlight (or some rationale for not using sunlight) should beprovided. In fact, arguments have also beenmade for preferring the use of sunlight incases (such as phototransformations on soil) where indirect photolysis generallypredominates. The argument is based on the difficulty in accurately converting artificialirradiation durations to sunlight irradiation duration equivalents for indirect photolysisprocesses. For indirect photolysis, the conversion has to be based (as in this proposedguideline) on equating total photon/energy flux across some wavelengths that may noteven be involved in the process. The conversion is more accurate for direct photolysisbecause it can be based on equating total photons/energy absorbed by the test substance.This point is adopted.ENV/JM/TG/RD(2006)1/REV206CountryCommentsSecretariat’s ResponseUS position: The U.S. partially agrees. Although the use of sunlight should be providedas an option, its use should not be mandated over the use of the xenon lamp (as possiblyimplied by the comment). There are pros and cons for both light sources.US(3) “Whereas mercury-metal halide arc lamps or equivalent can be used for other testsrequiring lower level of energy than xenon lamps [shouldn’t this be lower wavelength–mercury arc lamps are at 254 nm which is higher energy not lower], such lamps are notsuitable to evaluate the photransformation[should bephototransformation] of chemicalsbecause they have less power [same as above – lower wavelength or higher energy] thanxenon lamps.”US position: The U.S. agrees. The guideline should refer to a mercury lamp as a lowerwavelength/higher energy lamp than a xenon lamp. In addition, the wording should bechanged to more explicitly emphasize that while a xenon lamp with appropriate filterscan simulate multiple wavelength solar irradiation above the 295 nm solar irradiationcutoff at the earth’s surface, the 254 nm mercury lamp cannot.This paragraph is discussing the use of lamps equipped withappropriate filters to exclude short-wave UV light below 290nm. Thus this point seems to be of little relevance.Paragraph 15Austria Footnote: Deletion of footnote 2 is strongly suggested for the following reason: Thecitation of a distinct spectroradiometer model of a company should be avoided since thisGuideline should not contribute to the advertisement of a specific instrument.Nevertheless a description of such an instrument as the current standard which has to bemet when following this test procedure should be given without referring to a specificinstrument model including the producer company.Addition of a reference suggested:“Since light in the wavelength range of 295 to 400 nm is most relevant forphototransformation of chemicals in the environment, ...”We would appreciate, if this statement is connected to one or more references.These points are adopted.Germany Light intensities for a too broad wavelength range are not appropriate.For most testsubstances and organic matter of soil the region around 300 nm is of particularimportance (cf. General Comments). For typical Xenon light sources this narrow sectionis just a small portion of intensity and relative variations in this region are not adequatelyreflected by total intensity. At least an optical filter of measured absorptioncharacteristics should be employed. So,complement text:In case of Xenon lamp and filter (system®Suntest, Hanau) acharacteristic spectrum is available by the manufacturer. Additionally, it is generallyaccepted that the quantum yield of phototransformation is not dependent on thewavelength within one electronic band. Therefore, it is not necessary to measure theenergy distribution by a monochromator within this study. The light intensity during astudy performed in a Xenon lamp/filter system (e.g.®Suntest, Hanau) can be measuredThis point should be covered by the changes made.ENV/JM/TG/RD(2006)1/REV207CountryCommentsSecretariat’s Responseby a calibrated radiometer with sufficient accuracy.Japan(2) “using ... glass fiber optics.” Should bedeleted, because it is not necessary to limit anoptical spectrum distribution measurementequipment to the specific equipment.This point should be covered by the changes made.ECPA membercompanyIn case of Xenon lamp and filter (system®Suntest, Hanau) a characteristic spectrum isavailable by the manufacturer. Additionally, it is generally accepted that the quantumyield of phototransformation is not depended on the wavelength within one electronicband. Therefore, it is not necessary to measure the energy distribution by amonochromator within this study. The light intensity during a study performed in aXenon lamp/filter system (e.g.®Suntest, Hanau) can be measured by a calibratedradiometer with sufficient accuracy.See above response on German comment.Paragraph 16GermanyReplacein 4thline: ... described in paragraph 16–1818 – 20before and after ... .Comment:the calculations given here apply to summer midday conditions. This is nota worst case or even an annual average!!The first point is adopted. With regard to the second point,such calculations can be done also for other periods of theyear (e. g. spring, autmn,etc.).The Netherlands The tables mentioned under (3) can be used to compare the irradiance of the Xenon lampwith sunlight. It can be done by simply summating the values given in these tables (atappropriate latitude and season) over 300 (or 295 nm?) until 400 nm. In this way, it isnot necessary to have a spectroradiometer measuring the irradiance. The irradiancemeasured by the Xenocal 300-400 nm light irradiance meter should be sufficient, underthe constraints that the Xenon radiant power as function of wavelength is given by themanufacturer.These points should be covered by the changes made.US(3) footnote #3:“Intensities of sunlight depend on the geographical latitude in spring,autumn and winter, but are practically not influenced in summer.” Suggest differentwording – “, butthe intensities vary little by latitude during the summer.”US position: The U.S. agrees with the suggested change in wording.This point is adopted.Paragraph 17Germany The given calculations given here are just one way for transferring the experimental lightintensity to environmental irradiation conditions. There are others, too. Light intensitycan also be calculated based on the following equation:Light intensity (W/m2) (300-400 nm) * 6.07% /100% = Global light intensity (300- 3000nm) (W/m2)Global light intensity (300- 3000 nm) (W/m2) 3600 sec = Global light intensity in onehour in experiment (300- 3000 nm) (MJ/m2)This experimental light intensity can then be related to environmental light intensitiesper day, which are available for different locations and different seasons e.g. inGeorge Wypych, 2ndedition of HANDBOOK of MATERIAL WEATHERING, ChapterThis point is adopted in an additional paragraph 19. For theinclusion of the reference, we would greatly appreciate if thecommenter could supply number and year of the edition.ENV/JM/TG/RD(2006)1/REV208CountryCommentsSecretariat’s Response4, Pages 61 –94ISBN 1-895198-12-7ChemTech Publishing / CanadaThe Netherlands It is better to compare the intensity of the Xenon lamp with tables of GC SOLAR insteadof a measured intensity. In this way, the days of irradiation are calculated to “a standard”and the results obtained at different times or from other labs can be compared. In a “selfmeasured” intensity is used, it is more difficult to compare the results of differentstudies.Further, the formula gives other results than the tables of GC SOLAR. Maybe this is dueto the assumption that 75 % of the daily maximum intensity gives the average intensityover a 12-hour period. The formula of 17 underestimates the incubation period,compared to tabulated values of GC SOLAR. The tables of GC SOLAR give averagedaily irradiances (m Einstein per day per cm2), which can be compared to irradiance inWatt/m2by using of the following formula:×××××××−−29222332mWatt10*mcm10000secday864001einsteinphotons10*023.610daycmmEinsteins)( λ

λchLh = constant of Planck (6.63*10-34J/Hz)c = speed of light (3.00*108m/s). (Values of constants are rounded; non-rounded valuesshould be used)This calculation should be performed for each wavelength (λ, in nm). After that, thevalues obtained can be summated over the region 300 – 400 nm and the result obtainedcompared to the measured value of Xenon light source. A spreadsheet is very useful toperform these calculations and the comparison with the irradiance of the Xenon lightsource.This point is adopted in an additional paragraph 20.US(2) The equation needs to be slightly modifiedin one of two alternate ways to be moreaccurate. To keep 12 (hrs/day) in the denominator, the r in the numerator needs to reflectthe ratio of the Xenon lamp to early Spring (rather than mid-Summer) solar irradiation.Alternately, to keep r as the ratio of the Xenon lamp to mid-Summer solar irradiation,the 12 in the denominator needs to be increased to reflect longer than 12 hours ofsunlight/day in mid-Summer.In addition to modifying the equation as recommended in the previous comment, itThe equation (including the various factors) given in thisparagraph is just an example how such estimations can becarried out. They can always be adapted to otherenvironmental conditions.Also the equation can always be rearranged to cover otherneeds.ENV/JM/TG/RD(2006)1/REV209CountryCommentsSecretariat’s Responseshould be rearranged to give what the equation is being used to calculate (the number ofhours a sample needs to be continuously irradiated with a xenon lamp to give a totalirradiation approximately equivalent to what the sample would receive if it was exposedto the sun by being placed outside for 30 days)US position: The U.S. agrees.ECPA membercompanyThe given calculations are just one example how to transfer the experimental lightintensity to environmental irradiation conditions. Light intensity can also be calculatedbased on the following equation:Light intensity (W/m2) (300-400 nm) * 6.07% /100% = Global light intensity (300- 3000nm) (W/m2)Global light intensity (300- 3000 nm) (W/m2) 3600 sec =Global light intensity in one hour in experiment (300- 3000 nm) (MJ/m2)This experimental light intensity can then be related to environmental light intensitiesper day, which are available for different locations and different seasons e.g. inWYPYCH, HANDBOOK of MATERIAL WEATHERING.See response above on German comment.Paragraph 18Japan(2) Paragraph 18,19,20 and 31. It is appropriate that a title and an applicable term of “TestSystem” should be replaced with “Incubation System” etc., because the word “Testsystem” is used to define incubation tank and examination equipment in this documentand it would lead to misunderstanding.This point is adopted.The Netherlands Annex is not optimal for comparison of irradiated soil with soil under dark treatment:the temperatures in the exposed soil may be different from the covered soil as the coverabsorbs the light and converts it into heat. The set-up of Annex 4 is much better, in thisrespect.Agree. Therefore, the system shown in Annex 4 is given as auseful test system. Annex 2 is referenced in paragraph 14 onlyto show and explain the Hanau Sun Test apparatus.ECPA membercompany(paragraphs 18 to 20) As alternative a static system consistent of individual quartz glassvessels (e.g. inner surface about 10-12 cm2) equipped with trap attachments with sodalime and PU foam may be used (biometer flask systems)This point should be covered by the addition of a newparagraph 24.Paragraph 19Austria Deletion of footnote 4 strongly suggested. See comment above. This point is adopted.Croplife/ECPA The description of the test system is nice, but it should be stated that this is an example,not a requirement. There is no reason that the cooling tank has to be made of stainlesssteel and sealed with Teflon tape. It could justas easily be made of another material witha gasket system to seal it. The test guideline should allow some flexibility in studydesign.Paragraph 18 clearly says that the described system is shownas a useful example and thus does not exclude other studydesigns and materials. Static systems will be included in aseparate paragraph.Paragraph 20ENV/JM/TG/RD(2006)1/REV210CountryCommentsSecretariat’s ResponseGermanyLaboratories may have different technical equipment. Therefore guidelines should bemore general, where different technical equipment can be used. This should beconsidered especiallyaccording to requirements which do not have any influence on theessential outcomes of the study (examples: flow-through versus biometer flask testsystems, measurement of light intensity, etc.) soAdd: As alternative static systems consistent of individual quartz glass vessels (e.g.inner surface about 10-12 cm2) equipped with trap attachments with soda lime and PUfoam may be used (e.g. biometer flask systems)This point should be covered by the addition of a newparagraph 24.US(2) 1stsentence:Replace “air is sucked through” with “air is drawn through”US position: The U.S. agrees.This point is adopted.Croplife/ECPA Although this is a guideline, we thinkthat this paragraph is excessively detailed. We seeno reason to ensure a CO2 free air inlet asonly radiolabelled CO2 is detectable. Also, nosuggestion other than a peristaltic pump for the flow-through system.The system described here is just given as an example. Staticsystems will be included as alternative. The use of CO2-freeair prevents rapid saturation of the sodium hydroxide traps.Paragraph 21Japan(1) “isotop” should be corrected to “isotope”. This point is adopted.The Netherlands (also includes the comment of paragraph 18). Temperature registration (and control) See response above.Paragraph 22Paragraph 23Austria One of the experts is of the opinion that it might be advisable to use 2 soil types for thedetermination of the rate of phototransformation because the matrix is of relevance forphotochemical processes. Soils of different organic composition absorb differently,which has an influence on the reaction kinetics.This point is adopted.Germany The use of one soil is not believed to be sufficient. Is type of soil of minor importance?Is there any evidence behind?Two soil types are recommended in the revised version.US(1) (EFED noted that the guideline indicates “the use of one soil is sufficient”.) At least onesoil must be the same type as used in an acceptable aerobic soil metabolism studysubmission. This facilitates the modelling of combined routes of dissipation.US position: The U.S. partially agrees. The U.S. agrees whenever it is experimentallypractical. However, in cases where only one or more sandy soils were used in the aerobicsoil metabolism, it may not always be practical to successfully generate and/or maintainsoil thin layers for such sandy soils as indicated in paragraph 23.This point is adopted.Paragraph 24Austria Insertion: "...The selectedsoil should be characterised at leastfor texture [according toFAO, USDA or DINclassification systems (14)]..."The first point is adopted. With regard to the second point wethink that in an international OECD Test Guideline we shouldENV/JM/TG/RD(2006)1/REV211CountryCommentsSecretariat’s ResponseProposal for the reference: "German Standardisation: DIN 4220, Standard Committee;Berlin, Köln (Beuthrather refer to international than to national ClassificationSystems when those are available.Germany Replace content of reference 19 with Schlichting E., Blume H.-P., Stahr K. (1995)Bodenkundliches Praktikum: eine Einführung in pedologisches Arbeiten für Oekologen,2ndedition, Blackwell Berlin-Oford.This reference is added to the literature list.Paragraph 25Austria Reference to the ISO Guideline 10381-6 Soil Quality - Sampling "Guidance on thecollection, handling and storage of soil for the assessment of aerobic microbial processesin the laboratory" should be made in the relevant place of this paragraph.This point is adopted by adding an additional paragraphoutlining how soils should be handled when “viable”(microbially active) soils are required for conducting thesestudies.Germany Conditions during experiment (temperature, moisture, 30-d-period) favour bioactivity.Biodegradation may cause formation of other metabolite, altering CO2 balance orpartition equilibria in soil, etc.So add text: In case of test substances susceptible to biodegradation, soil samples (orwhole test system) should be pretreated prior to starting the test, e. g. by irradiation withshort wavelength UV light, in order to minimise such impact.This pre-treatment cannot be recommended because someguidelines (e.g. SETAC, USEPA) require the use of “viable”soil at the start of the study. However, due to the irradiationduring the study (in some cases up 30 day equivalents)microbial activity of the test soils may decrease.Croplife/ECPA The sentence “Desaggregation should be performed at minimal force ...” claims not tochange the original texture of the soil. The relevance of this statement is not clear. Thesieving process should not change the particle size distribution of the soil, but later on aslurry will be made of the soil, so the original “texture” is heavily affected.Suspended slurries of soil are used for the determination ofthe particle size of soils and thus slurry preparation should notaffect the texture of a soil.Paragraph 26Paragraph 27Austria Please add a reference where the assumption, that 24 hours after the application of thesoil slurry to a plate the field capacity is about 75 % is based on.This value of approx. 24 hours is based on experience withsuch experiments and was thought as help for peopleconducting such experiments. But as this value may vary fromsoil to soil it is deleted.Germany Moisture of the soil should be in the range used in soil degradation studies (75% of 1/3bar moisture or 40-60 % of max. water holding capacity). A moisture of 75% of fieldcapacity is regarded as too wet and not representative for usual outdoor conditions.Footnote 5 refers to a very specific test device.We agree that soil moisture should be in the same range asused in the degradation studies. Thus to harmonise withOECD guideline 307 this paragraph is revised accordingly.The footnote is thought as help for experimenters to give themsome idea of the dimensions of plates and soil thin-layerswhich can be used together with the experimental set-upshown as example in Annex 4.France (Paragraphs 27 and 28) Photodegradation is proposed to be investigated with both wet Perhaps the SETAC guideline is notvery clear in this respect.ENV/JM/TG/RD(2006)1/REV212CountryCommentsSecretariat’s Response(75% FC) and air-dried soil. Because it is difficult to maintain constant soil moistureunder light conditions and thus differences in soil moisture content may occur betweenlight and dark conditions, we believe that photodegradation should be preferablydetermined on air-dried soil as stated in the SETAC guideline.We think that both experiments should be conducted to showthe different rates in dry and moist soil as quasi 2 extremesituations. We agree that it may be different to maintain soilmoisture during irradiation but know from practice that thiscan be done by regularly controlling total weights of the soilplates.Japan(2) Paragraph 27 and 28. Although the studies under two conditions (using moist soil ofabout 75% of field capacity and completely dry-out soil) are mentioned in thisdocument, the study using dry-out soil should be treated as a supplementary or optionalstudy. And it is necessary to be defined specific test conditions for the study using dryout soil. (i.e, soil thin layer or ventilation conditions, etc.) in this document.See responses above on French comment.The Netherlands Could you explain the necessity studying both moist soil layers and dry soil surfaces? Isparagraph 28 an extra requirement? It is hardly possible to keep the 2 mm soil layersmoist under high radiant power source.As the surface of a field soil can become quickly dry duringsunny periods, the rate on a dry soil surface has certainlysome environmental relevance. Together with the ratesobtained on moist soil, it gives to some extent the range ofphotolysis rates which can be expected for a particularchemical on soil surfaces.US(3) Paragraph[s] 27 [& 32]:"Therefore, the soil layers are allowed to air-dry to reach a soilmoisture of about 75% of field capacity (about 24 hours).” This implies that at 24 hoursafter coating, the soil moisture will be 75% of field capacity.US position:The U.S. agrees. Guidance on how to maintain soil moisture should beincluded.See response above on Austrian comment.Guidance on how soil moisture is maintained is described inparagraph “Moisture content”.Croplife/ECPA (Paragraph 27 & 32 including footnote 7) OECD guideline 307 describes determinationof the water holding capacity. In these paragraphs, the test guideline refers to fieldcapacity. This is not the same. To avoid confusion, we suggest to use the term ”waterholding capacity” instead of field capacity.This point should be covered by the changes made.ECPA membercompanyMoisture of the soil should be in the range used in soil degradation studies ( 75% of 1/3bar moisture or 40 – 60 % of max. water holding capacity). A moisture of 75 % of fieldcapacity is regarded as too wet and not representative for usual outdoor conditions.This point should be covered by the changes made.Paragraph 28Germany Only in special cases it may be interesting to investigate phototransformation on dry soilsurface. In general, no additional information with respect to the above mentionedexperiment (paragraph 27) is to be expected.See above response on Netherlands comment on paragraph27.US(2) Because soil moisture may substantially affect phototransformation rates and/ortransformation pathways on soil, the use of dry as well as moist soil in the study cancertainly be justified from a scientific standpoint. However, from a resource as well asscientific standpoint, it could also be argued that the additional resources could be betterAgree with US position. See also above response onNetherlands comment on paragraph 27.ENV/JM/TG/RD(2006)1/REV213CountryCommentsSecretariat’s Responsespent on replicate experiments and/or additional sampling intervals using moist soil. Thatis particularly true of agricultural soils in the environment for which some moisture willpresumably be maintained to some degree.US position: The U.S. agrees. However, the reviewer should also have indicated that inparagraph 32, an option is given to use either moist or dry soil. While it is OK to use dryas well as moist soil in separate experiments, the use of dry soil should never replace theuse of moist soil.Croplife/ECPA It is not clear if the conduct of an additional test on dry soil is obligatory. Werecommend that such tests are only required in special cases.See responses on this point made above on paragraph 27 andon this paragraph.ECPA membercompanyOnly in special cases it may be interesting to investigate phototransformation on dry soilsurface. In general, no additional information with respect to the above mentionedexperiment (paragraph 27) is to be expected. In addition, this is a new requirement withrespect to the valid guidelines.See responses on this point made above on paragraph 27 andon this paragraph.Paragraph 29France Suitable organic solvent is proposed to be used for application of the test compound. Itshould be specified that solvent should not be a photosensitiser.This point is adopted.Germany Ad text. “by means of an appropriate syringe, e.g. Hamilton microlitre syringe.Other techniques of application should also be allowed, e.g. spray application. Suchtechniques can help to reduce non-uniform penetration depths of droplets in 2mm layerthus reducing uneven shelter from irradiation.The first point is adopted. We would not recommend sprayapplications for reasons of substance losses and crosscontamination.Japan(1) A method to estimate the amount of the test substance distributed to soil in theenvironment should be shown. In addition, the standard amount of the application of thetest substance should be shown.As amounts reaching the soil differ from chemical tochemical, a standard amount cannot be given.Japan(2) It would be appropriate to mention clearly that photosensitized solvents (acetone etc)should not used in this study.This point is adopted.US(1) (EFED noted that the guideline only recommends test chemical application via syringe tosoil thin layers.) EFED recommends that both methods of test material application,mixing test substance with soil before plating, and application with syringe to preparedthin layer, be allowed. A single method may not be applicable to all chemicals.US position: The U.S. partially agrees. Mixing the test substance with soil before platingshould also be included as an option, but only for chemicals that remain stable(degradation and/or volatilization are negligible) during the pre-test drying period (up to24 hours).We should not recommend incorporation because the goal ofthis test is to measure phototransformation on the soil surfacewhere the chemical is available for the irradiation.Paragraph 30Japan(1) A method to estimate the amount of the test substance distributed to soil in theenvironment should be shown. In addition, the standard amount of the application of thetest substance should be shown.See response above for paragraph 29.ENV/JM/TG/RD(2006)1/REV214CountryCommentsSecretariat’s ResponseThe Netherlands In combination with paragraph 12: Is it not better to relate the LOD and LOQ to themaximum recommended use rate instead of fixing the LOD at a value of 0.01 mg/kg(orat 10% of activity applied whichever is lowest?The limits given in paragraph 12 of the revised version are inagreement with those of other fate test guidelines (e.g.307).US(1) (EFED noted that the guideline calls for a pesticide test substance application rateequivalent to the maximum recommended use rate.) EFED recommends that exaggeratedapplication rates (be used) to increase the amount of degradates formed to concentrationsabove the analytical method limit of quantification, be allowed.US position: The U.S. partially agrees. The use of exaggerated application rates may benecessary as a supplemental study to adequately characterize degradates. However,unless phototransformation is following pseudo-first order kinetics, such exaggeratedapplication rates should only be used in a study that is supplemental to a study on thephototransformation rate of the parent. The reason is that unless the phototransformationrate of the parent is following pseudo-first order kinetics, its DT50 will depend (in part)upon its initial concentration in the soil.Agree with US position.US(2) Footnote equation:The equation is correct.US position: The U.S. agrees.Agreed.Paragraph 31Japan(1)The test temperature should be in the range from 20 to 25°C, kept a constant±2°C.A temperature of 20°C is recommended, for example, by theSETAC guideline. See also US position below.Japan(2) Considering the Japanese weather condition, the test temperature defined in thisdocument (20±2 °C) is too low, therefore it is desirable that the test temperature include25°C or description such as "although 20°C is recommended as test temperature, it canalso be set up, taking into account the weather conditions of each country" be added tothe text.Also it seems to be difficult to keep the temperature within the limit of ±2 °C in the halfseal container under irradiation, “2°C” should be defined as a recommended margin asthe accuracy of soil temperature.As photochemical rates are relatively insensitive totemperature changes within the environmental range (see USposition below), it seems not relevant whether theseexperiments are carried out at 20 or 25°C. However,whenever possible the lower temperature is recommendedbecause substance losses and particularly soil moisture lossesshould be lower.US(1)Temperature range should be between 18-30 +1°C (rather than 20 +2°C) as thisreflects the range of growing season temperature for most crops.US position: The U.S. partially agrees in that the proposed temperature range is morereflective of temperature differences among the member countries of the OECD.However, the use of 20°CC is also acceptable. The reason is that photochemical kineticsare relatively insensitive to temperature changes within the environmental range.Temperature control is needed in a phototransformation on soil study more to ensurecomparable temperatures between irradiatedand dark control samples (because of thesensitivity of non-photochemical kinetics such as hydrolysis and biotransformation totemperature) than to ensure that the photochemical kinetics occurs at any particularAgree with US position.ENV/JM/TG/RD(2006)1/REV215CountryCommentsSecretariat’s Responsetemperature. Also, although maintaining a +1°C tolerance is desirable, it is not criticalfor photochemical kinetics for the reasons stated above. In addition, maintaining a +1°C tolerance may not be as practical in a photochemical on soil study as maintaining a+2°C tolerance.US(2) It should be pointed out that whiledirect temperature effects on photochemicalprocesses are generally small, adequate temperature control is necessary to helpmaintain soil moisture and comparable microbiological activities within the lightexposed and dark controls.US position: The U.S. agrees.This point is adopted.Paragraph 32Germany Moisture content affects extractability of test substances from soil, thus apparentdegradation. Intervals and methods to determine and adjust the soil moisture depend onthe study design and should not be committed in detail; just a maximum interval forcorrection of moisture should be prescribed.So add text: ...are removed for analysis or at least every 48 hours. Soil moisture shouldbe determined and recorded.It is unclear why air-dried soils should be tested. Phototransformation will be at leastless effective. For reasons of comparability of results this option should not be allowedfor.The first point is adopted. With regard to the second point seeresponse made above on French comment on paragraph 27.US(1) Paragraph 32 and 33: (EFED noted that the guideline allows for the use of either moistor dry soil thin-layers, and the use of additional moist soil thin layers for dark controls).EFED recommends that moisture conditions beidentical for both irradiated and controltest samples. This facilitates comparison of control to irradiated samples for “darkcorrection”.US position: The U.S. agrees that “moistureconditions be identicalfor both irradiatedand control test samples.” [Although the U.S. thinks that it is OK to conduct a study ondry soil in addition to conducting one on moist soil, a study on dry soil should notbeused to replace a study on moist soil.]This point is adopted by including “dry soil thin-layers” inparagraph 33.US(3) "Soil thin-layers are kept either moist (75% of field capacity) or air-dried during theirradiation period." [But the] Protocol does not indicate how to maintain the moisturecontent and the irradiation apparatus does not have any provisions for maintainingmoisture content.US position:The U.S. agrees. Guidance on how to maintain soil moisture should beincluded.As described in paragraph 20, moist air is pumped through thesystem to saturate the tank atmosphere with water and thusminimise moisture losses from soil thin-layers. In addition,moisture losses of individual soil thin-layers are measured andwater is added to the “moist” samples, when necessary, at thetime intervals given in paragraph 32.US(4) It will be extremely hard to maintain a constant moist soil (i.e. 75% of field capacity)during the study period. The air flow and heat generated by the Xenon lamps will drythe soil. It would be impractical to add water to soil thin layers during the test.It is certainly not easy to maintain a constant moist soil duringthe study period. The procedure described in this draftdocument tries to minimise moisture losses from soil thin-ENV/JM/TG/RD(2006)1/REV216CountryCommentsSecretariat’s ResponseUS position: The U.S. partially agrees. It is difficult to maintain a constant soil moistureof 75% field capacity because of air flow and heat generation by the lamps. Thedocument should include guidance on how to maintain soil moisture. However, itshould be practical to approximately maintain at least some soil moisture throughvarious methods such as the use of cooling tanks for temperature control and moist airflow as discussed in the guidance document.layers in two ways:-by ventilation of the incubation system with moist airand-by adding water to the layers at the time intervalsmentioned in paragraph 32, when necessary.ECPA membercompanyIntervals and methods to determine and adjust the soil moisture depend on the studydesign and should not be committed in detail.Nevertheless, some guidance has to be given in a testguideline on how to adjust soil moisture during such a test.Paragraph 33Austria Following change suggested:"Additional moist and air-driedsoil thin layers are kept under identical conditions..."In order to distinguish between photochemical and other reactions irradiated and darksoil thin-layers should be kept under identical conditions. Therefore also air-dried soilthin layer plates treated with test substance should be treated as dark controls.This point is adopted.Germany Replace...but not irradiated by “in the dark”. This point is adopted.US(2) If dry as well as moist soil is used, dry as well as moist soil dark controls need to beused. Therefore change “Additional moist soil” to “Additional moistand drysoil”.US position: The U.S. agrees.This point is adopted.Paragraph 34Germany Add. Duration of exposure to light shouldnot exceed 30 environmental solar days or twohalf-lives of the test substance, whatever is longer.The sentence is included but modified by the phrase“whichever is shorter”. If substances are susceptible tophotolysis they react rather quickly and certainly within 30days; thus it seems not reasonable to prolong the test beyondthis period.Japan(1) The incubation period should depend on the irradiance energy used because theirradiance energy is not necessarily the same as ANNEX 3.This point should be covered by the changes made.Croplife/ECPA (Paragraph 34 & 35) It also not clear whether irradiation is required continuously or inday and night cycles. Both options should be allowed and discussed.The first point is adopted. The second point should be coveredby the changes made in paragraph 35.ECPA membercompanyDuration of exposure to light should not exceed30 environmental solar days or two halflives of the test substance, whatever is longer.See above response on German comment.Paragraph 35Germany Replace Figure 3 by “Annex 4” and solvents of different polarity by “appropriateextraction solvents”.This point is adopted.Japan(1) “Figure 3” should be correctedto “ANNEX4”. This point is adopted.Japan(2) 1) "Cooling tank illustrated in Figure 3" should be corrected to "cooling tank illustratedin ANNEX 4."The first point is adopted. The second point should be coveredby the changes made.ENV/JM/TG/RD(2006)1/REV217CountryCommentsSecretariat’s Response2) Cooling tank does not have to be limited to those which are made of stainless steel.ECPA membercompanyDetails of “stainless steel cooling tank”and “the quartz lid”will depend on the specifictest design.This point should be covered by the changes made.Paragraph 36US(2) 3rdsentence: Change “at least 5" to “at least 6".US position: The U.S. agrees, particularly if the kinetics does not follow pseudo-firstorder and/or the rates of formation and decline of major degradates needs to bedetermined. Note that the example given in para 36 of the guidance includes6 ratherthan 5 non-zero hour sampling points.This point is adopted.US(2) Some clarification is needed with respectto the purpose of removing duplicate soil thinlayers at each sampling interval for extraction and analysis. Such a protocol falls short offully duplicating the experiment, but is somewhat of an overkill for determining theprecision of the analytical method.Replicate experiments (preferably a minimumof 3) are recommended (when practical) todetermine variability and reduce uncertainty in the determination of kinetic parameters.However, the uncertainty in the determination of kinetic parameters can also besomewhat reduced by increasing the number of sampling intervals within eachexperiment. That is particularly true when rates of transformation are not first orderand/or when the rates of formation and decline of major transformation products arebeing determined. Therefore, with generally limited resources, the researcher should begiven the flexibility of weighing the pros and cons of increased experimental replicationversus increased numbers of sampling times per experiment in designing the study.US position: The U.S. agrees that some additional clarification is needed. The U.S. alsoagrees that in a kinetics study, some flexibility and practical balance needs to bemaintained in allocating resources between additional experimental replication andadditional sampling intervals.This point should be covered by the changes made.Croplife/ECPA This paragraph states that “Duplicate soil thin-layers are removed at appropriate timeintervals and ...”. Can the duplicate sampling requirement be met when two differentlabelled versions of the test substance are used and a single sample from each label issampled and analysed? The guideline should clarify if in such a case duplicate samplingfor each label is still required.We think that when two different labels of a test substance areused, two separate experiments should be conductedECPA membercompany“solvents of different polarity”should be replace by: ... with appropriate extractionsolvents and .....This point is not adopted.Paragraph 37Germany Replace sentence by: “When using 14C-labelled test substances, mineralization, volatile,extractable and non-extractable residues are determined as to set up detailed massbalances for each sampling interval.Analysis of extractable and volatile materials is alreadymentioned in paragraph 36 and thus there is no need to repeatthis in this paragraph.ENV/JM/TG/RD(2006)1/REV218CountryCommentsSecretariat’s ResponseThe Netherlands Should a mass balance also include duplo non-extractable residues or is the soil of oneplate per sample time enough (under the requirement that the mass balance is between 90and 110%)? It does not provide extra information if non-extractables are analyzed induplo if the mass balance is between 90 and 110% for the soil of one plate.The amounts of soil per plate are normally rather small inthese experiments; in the order of a few grams depending onthe dimensions of the plates. So duplicate analysis may notalways be possible and thus single analysis should besufficient.US(2) Paragraphs 37 and/or 38: Mention again (as earlier in paragraph 13) that confidencelimits should be computed and provided for rate constants, half-lives, DT50s, DT90s,etc.US position: The U.S. agrees.This point should be covered by the changes made inparagraph 39.Paragraph 38Austria see comments to p.2, para. 7, Addition:“... during the study or a phototransformation product below 10%, where relevant.”The proposed changes were adopted in paragraph 7 withregard to the analytical method. This paragraph deals with theidentification of major phototransformation products and theirplots against time. It is notconsidered necessary to producesuch plots also for minor products.Germany We suggest to add: ...10% of the applied dose at any time during the study “or > 5%toward the end of the test without trend to further decline in concentration.This definition of major phototransformation products is inagreement with that used in other OECD fate test guidelines(e.g. 307, 308, 312).Japan(1) When the amount of the test substance applied to soil is small, in general, it is difficult tomeasure the transformation rate of the test substance accurately and the mass balance islow because the recovery of the test substance from soil is difficult. Therefore, therecovery should be taken into account when the amount of the application is nominated.A prerequisite to conduct such studies is the availability of asufficiently sensitive and reproducible analytical method toanalyse the small concentrations applied to the soil thinlayers. If the available analysis method is not sensitiveenough, higher application rates may be used.The Netherlands Why should the results be graphically plotted? A tabular representation is sufficient. This requirement for graphical plots is in line with that inother OECD fate test guidelines (e.g. 307,308).Paragraph 39Austria “If appropriate, the calculations should also be applied to the majorall relevantphototransformation products."The term “major phototransformation products” is used inagreement with other OECD fate test guidelines (e.g. 307,308, 309, 312) and thus should not be exchanged by anotherterm.Austria For the calculations of half-lives and DTx values more updated references should begiven. If the degradation behaviour of a chemical is complex and influenced by a numberof processes, then simulation tools should be used. E.g.- TOPFIT, Pharmacokinetic and Pharmacodynamic Data Analysis System, Heinzel, G.,Woloszczak, R. and Thomann, P. Gustav Fischer, Stuttgart, Jena, New York.- ModelMaker, Cherwell Scientific Publishing Limited, Oxford, UK.These references will be included in the literature list. Butplease supply additional information such as year ofpublication, authors (for ModelMaker), etc.France First order kinetic should be recommended because it can beeasily handled. However, Always that model should be used which best fits the data.ENV/JM/TG/RD(2006)1/REV219CountryCommentsSecretariat’s Responseother models might be used if data do not fit first order. Therefore, first order kinetics cannot be generallyrecommended.Germany References given here are not up-to-date. Models currently in use for such purposes areMODELMAKER (Heinzel, G. Woloszczak, R. Thomann, P. (1993): TopFit 2.0:Pharmacokinetic and PharmacodynamicData Analysis System for PC; VCH PublishersInc., NY),TOPFIT (ModelMaker version 4.0, FamilyGenetics Ltd, The Magden Centre, Oxford,GB) orACSL (ACSL Optimize version 1.2 (Oct. 1996) MGA software, Concord,Massachusetts, USA).These references will be added to the literature list. But pleasesupply additional information such as authors, year ofpublication, meaning of abbreviation (ACSL), etc. From theabove Austrian comment it seems that TOPFIT andMODELMAKER are two different models. In your commentyou use both names for the same model; this is confusing.Could you please clarify this?The Netherlands r2is not the correlation coefficient but the determination coefficient. The determinationcoefficient compares the actual Y-values with estimated y-values (from the model used).the correlation coefficient (ρXY) gives the relation between (an array of) x and y values.This point is adopted.Paragraph 40Austria Test results:"- plots of percentages in soil versus time for the test substance and, where appropriate,for the majorall relevantphototransformation products.- half life DT50and DT90for the test substance and, where appropriate, for the majorallrelevantphototransformation products.- ... kinetics for the test substance and, where appropriate, for the majorall relevantphototransformation products."See previous comment to p.2, para. 7. As the recommendation for identification ofdegradation products in environmental compartments is under discussion in theframework of 91/414/EWG the wording of the Test Guideline should take into accountthis discussion by lowering the trigger value of 10% for phototransformation productsfor cases, where relevant.The term “major transformation product” was used in OECDfate test guidelines so far (e.g. 307, 308, 309, 312). Thus itseems not appropriate to introduce another term because thismay be confusing for the users of these guidelines.Germany Please add under:-properties of soil: “type and rates of clay minerals (if available),-xenon light source: measured spectrum ... “or radiometer results andspectrometer of the manufacturer”,-Test conditions: “air flow rates (if applicable)” and “limit of detection, limit ofdetermination, data on method validation” under methods for quantification andidentification.As active sites of clay minerals are, in general, covered byorganic matter in natural soils, their potential influence onreactivity of a chemical can be neglected and thus this point isnot adopted.The second point is adopted.The third point is partially adopted; data on method validationare not part of this test.Japan(2)Light source intensity should be described together with wavelength-range(e.g.OOW/m2(OO-OOnm)).The required wavelength range is already given. Lightintensity at sample level depends not only on the light sourcebut also on the experimental set-up used and thus cannot bespecified.ENV/JM/TG/RD(2006)1/REV220CountryCommentsSecretariat’s ResponseThe Netherlands A spectrum given by the manufacture from which the values are calculated to the actualvalues seems sufficient, especially since in the light calculations the spectral informationis not used.This point is adopted.Croplife/ECPA With regard to “test soils”, different people may understand different things under“water retention characteristics”. For the scope of this test guideline, the water holdingcapacity according to OECD Test Guideline 307should be sufficient and consistent (wethink it is not appropriate to be asked to measure pF-curves for this test).This general term is used also in other OECD fate testguidelines (e.g. 307, 312).Croplife/ECPA With regard to “test results”, why ischaracterisation of bound residues required? If weare asked here for fractionation of the bound residue, this information does not reallyadd anything to the study. We think what is really meant here is quantification of thebound residues.The requirement for the confidence limits should be removed (see also comment onparagraph 13).This point is adopted.ECPA membercompany- measured spectrum of the light source between 295 and 800 nm at the beginning andthe end of the test (or radiometer results and spectrum of the manufacturer);- air flow rates (if applicable);These points are adopted.Annex 1Germany Please correct under Phototransformation:reactions occurring under the influence oflight. Delete “on soil thin-layers” and “(>290 nm).Comment on DT5o: DT50 is identical with t1/2 in the case of 1st- order kinetics. Theshape of the curve may be different, not the time at which 50% reduction is observed.Please correct under intensity: Photonflux.The definition refers to this test and therefore “soil thinlayers” are included. 290 nm is the cut-off valuerecommended by many references and is in agreement withthat of paragraph 15 of the revised version.Agree with your comment.The last point is adopted.Annex 2Germany Please put in line: the cut-off of 290 nm here is not inline with the cut-off in paragraph14 which is 295 nm.The cut-off is in line with that of the revised version.Croplife/ECPA We would like to propose to change the title of the Figure as follows: “Spectrum ofXenon Arc (without Cut-off Filter) compared to Sunlight”.This point is adopted.Annex 3Germany A reference is missing for Table A.Integral light intensities (300-400nm) are only relevant for substances which stronglyabsorb in the whole range and provided that quantum yield is not dependent onwavelength (different absorption bands may occur in this broad range!)cf. comments onpara 15.Even for summertime it is surprising that Basel has the same irradiance as Florida.Typical values for Central Europe are 20-30 W/sqm at 300-400 nm (=0.2-0.3 mol/sqm/hA reference will be included in the revised version.Agree with your comment which describes the situation inaqueous medium. In this test, we do not distinguish betweendirect and indirect photolysis and also cannot measure thequantum yield.The irradiance values listed in Table B are those reported byMill et al. (1982). Other sources may show differentENV/JM/TG/RD(2006)1/REV221CountryCommentsSecretariat’s Responsephotons). And again, such irradiance is not representative for many regions, e.g. CentralEurope (cf.reference Frank/Klöpffer given in General Comments).irradiance values (e.g. A. Leifer, Zepp & Cline, Frank andKlöpffer).Croplife/ECPA One would expect a higher irradiancein Florida (30°N) than in Greensboro (40°N), butwe would like to propose to delete the names of regions and just mention the latitudes.The names of the regions can give the reader someinformation for which geographical regions these values maybe applied.The comments from Japan came from the following two sources:-(1)Yamaguchi-Takashi@meti.go.jp- (2) Takemoto Akio (takemoto@deljp-ocde.fr)The comments from the USA came from the following four sources:-(1) U.S. Environmental Protection Agency, Office of Prevention, Pesticides, and Toxic Substances, Office of Pesticide Programs,Environmental Fate and Effects Division, 1200Pennsylvania Ave., N.W., Washington, D.C. 20460-(2) U.S. EPA, Office of Prevention, Pesticides, and Toxic Substances, Office of Science Coordination and Policy, Exposure Division,1200 Pennsylvania Ave., N.W., Washington, D.C. 20460-(3) Syracuse Research Corporation, Environmental Science Center, 301 Plainfield Rd., Syracuse, NY 13212-(4) Rohm & Haas Company, 727 Norristown Road, P.O. Box 904, Spring House, PA 19477ENV/JM/TG/RD(2006)1/REV

222 

### ANNEX 6

DRAFT DOCUMENT July 2005



## OECD GUIDELINES FOR THE TESTING OF CHEMICALS

PROPOSAL FOR A NEW GUIDELINE

Phototransformation of Chemicals on Soil Surfaces

INTRODUCTION

1. 42. Man-made chemicals may reach soil directly via deliberate application (e.g. agrochemicals) and/or via indirect routes (e.g. via waste water → sewage sludge → soil or air → wet/dry deposition). For risk assessment of these chemicals, it is important to estimate their potential for transformation in soil and for distribution in and between the various environmental compartments (soil, water, air).

2. 43. Chemicals can be transformed in soil by microbia l, chemical and/or photochemical processes. The method described in this Test Guideline deals with the photochemical transformation (rate and route) of chemical substances on soil surfaces. It is based on existing guidelines (1) (2) (3) (4) (5).



### SCOPE AND RELEVANCE

3. 44. When irradiating a test item on a soil surface under the experimental conditions described in this Test Guideline, besides photochemical transformations (direct and indirect photolysis) also chemical (hydrolysis, oxidation) and microbial transformations can occur, the latter in particular when “viable” (microbial active) soils are used. To assess the relevance of the latter two processes, non-irradiated dark

controls are included in this test. The difference in transformation rates and routes observed between irradiated samples and dark controls can then be attributed to phototransformation processes on the soil surface. The methodology is neither designed to determine the quantum yield of a test item on a solid surface nor to distinguish between direct and indirect photolytic reactions. However, it should allow estimating minimum photolysis half-lives under optimum outdoor irradiation conditions and showing maximum of phototransformation products of test item likely to occur on soil surfaces, which have to be isolated and identified in order to get a complete ri sk assessment for the environment, then. Simulating a higher degree of translocation or diffusion of test item into dark zones of soil and/or a stronger binding of test item to soil matter (i.e. whenever the soil is rather dry) would not lead to a risk assessment differing from that under exclusion of sunlight as a degradation process relevant for the environment.



### PRINCIPLE OF THE TEST

4. 45. Thin-layers of soil are treated with the test item and irradiated by simulated sunlight (xenon lamp) under controlled laboratory conditions or, as an option in sunny climatic regions, by natural sunlight. Simultaneously, not-irradiated dark controls are ke pt under identical conditions to distinguish between photochemical and other reactions. After appropriate time intervals, the soil thin-layers are extracted andENV/JM/TG/RD(2006)1/REV

223 analyzed for the parent test item and/or for major phototransformation products. Volatile products are collected by appropriate absorption devices and are also analyzed for at time intervals. Using 14 C-labeled material, phototransformation products can be identified and a mass balance, including the formation of soil bound (non-extractable) residues, can be established.



### APPLICABILITY OF THE TEST

5. 46. The method is applicable to all test items (unlabeled and radiolabel) for which an analyticalmethod with sufficient accuracy and sensitivity is available. It is applicable to slightly volatile or nonvolatile, water-soluble or water-insoluble compounds. The test should not be applied to chemicals which are highly volatile from soil (e.g. fumigants, organic solvents) and thus cannot be kept in soil under the experimental conditions of this test.



### INFORMATION ON THE TEST ITEM

6. 47. Unlabeled or labeled test items can be used to measure the rate of phototransformation. Labeled material is required for studying the pathway of phototransformation and for establishing a mass balance.

14 C-labeling is recommended but other isotopes, such as 13 C, 15 N, 32 P, may also be useful. As far as possible, the label should be positioned in the most stable part(s) of the molecule 11 . The chemical and radiochemical purity of the test item should be at least 95 %.

7. 48. Before carrying out a phototransformation test on soil surfaces, the following information on the test item may be helpful in order to optimize test design and procedures of treatment and processing:



### (a) (j) solubility in water [ OECD TG 105 ] (6); (b) (k) solubility in organic solvents;
(c) (l) vapor pressure [ OECD TG 104 ] (6) and Henry’s Law constant; (d) (m) dissociation constant (pKa) [OECD TG 112] (6). (e) (n) chemical stability in the dark (hydrolysis) [OECD TG 111] (6); (f) (o) aerobic and anaerobic transformation in soil [OECD TG 307] (6); (g) (p) phototransformation in water [O ECD TG in preparation](7).

8. 49. An appropriate analytical method of known accuracy, precision and sensitivity for the quantification and identification of the test item and its phototransformation products in soil should be available. The analytical detection limit for the test item and its phototransformation products should also be known (see paragraph 13).

REFERENCE SUBSTANCES

9. 50. Reference substances should be used for the characterization and/or identification of phototransformation products by spectroscopic and chromatographic methods.

11 For example, if the test item contains one ring, labeling on this ring is required; if the test item contains two or more rings, separate studies may be needed to evaluate the fate of each labeled ring and to obtain suitable information on formation of phototransformation products.ENV/JM/TG/RD(2006)1/REV

224 

### DEFINITIONS AND UNITS

10. 51. See Annex 1.



### QUALITY CRITERIA

Recovery

11. 52. Extraction and analysis of, at least, duplicate soil samples immediately after the addition of the test item gives a first indication of the repeatability of the analytical method and of the initial recoveries for the test item. Recoveries for later stages of the experiments are given by the respective mass balances obtained with labeled material. Recoveries should range from 90 % to 110 % for labeled chemicals (5) and from 70 % to 110 % for non-labeled chemicals (3).

Repeatability and sensitivity of analytical method

12. 53. Repeatability of the analytical method (excluding the initial extraction efficiency) to quantify test item and phototransformation products can be checked by duplicate analysis of the same extract of the soil, incubated long enough for formation of phototransformation products.

13. 54. The limit of detection (LOD) of the analytical method for the test item and for the phototransformation products should be at least 0.01 mg kg -1 soil (as test item) or 1 % of the applied dose whichever is lower. The limit of quantification (LOQ) should also be specified.

Accuracy of transformation data

14. 55. Regression analysis of the concentrations of the test item as a function of time gives the appropriate information on the reliability of the photo transformation curve and allows the calculation of the confidence limits for half-lives (in case of pseudo first order kinetics) or DT 50 values and, if appropriate, DT 75 and DT 90 values.



### DESCRIPTION OF THE TEST METHOD

Light source

15. 56. Natural sunlight or artificial sunlight simulated with solar simulators under well-controlled laboratory conditions is considered the optimal light sources. A characteristic of spectral power distribution for sunlight is shown in Annex 2; it can also be obtained from ISO 10977 (8) or from GCSOLAR (9) as function of latitude and season. The cut-off of radiation of the light source used has to be 290 nm (10). Xenon lamps equipped with appropriate filters, such as that of Suntest 12 apparatus (see Annex 2) are recommended as irradiation source (5)(7)(8) because they simulate very closely natural sunlight in the 290- 800 nm region. Whereas mercury-metal halide arc lamps or equivalents can be used for other tests requiring lower levels of energy than xenon lamps, such lamps are less appropriate to evaluate the phototransformation of chemicals because they have less power than xenon lamps. For the assessment of phototransformation of chemicals, generally higher leve l of irradiation power is required which can only be provided by xenon lamps for the time being.

12 Atlas MTT GmbH, GermanyENV/JM/TG/RD(2006)1/REV

225 16. 57. Since light in the wavelength range of 290 to 400 nm is most relevant for phototransformation of chemicals in the environment (11)(13), the spectral energy distribution of the xenon light source (i.e. the incident light available at the soil surface level) in this range is recorded using, for example, a portable spectroradiometer, consisting of a holographic gra ting monochromator and a Teflon cosine diffuser in combination with glass fiber optics. Alternatively, the light intensity during a study performed with a xenon lamp/filter system (e.g. Suntest) can be measured by a calibrated radiometer with sufficient accuracy (e.g. irradiance monitor XenoCal WB 300-800 nm) 2 or obtained from the manufacturer’s data. Typical light intensity (irradiance) between 300 and 400 nm at different exposure positions is given in Annex 3.

Conversion of laboratory irradiation time into days of natural summer sunlight

17. 58. In order to relate the rate of phototransformation caused by the xenon light to the rate likely to occur in sunlight, it is necessary to compare the irra diance of the xenon lamp with sunlight (13). For this purpose, the integral of light intensity between 290 to 400 nm or between 290-800 nm (dependent on the irradiance monitor used) is either measured at the various positions of the soil thin-layers in the test systems described in paragraphs 21-24 before and after the test or can be obtained from the data supplied by the manufacturer of the apparatus. These values are compared to energy values of natural summer sunlight (midday) at latitude 30 to 50° N 13 which can be obtained from reference (12) or which can also be measured with the spectroradiometer (see Annex 3) or the irradiance monitor used.

18. 59. Furthermore, it is assumed that the average daily sun radiation intensity is approx. 75 % of the maximum intensity over a 12-hour period (13), whereas irradiation intensity of the Xenon lamp is constant over time. The equivalent days d of natural summer su nlight can be calculated by the following equation:



### 12 75

. 0 r h d

⋅ ⋅

=

where d = days of summer sunlight h = hours of irradiation by the xenon lamp r = ratio of intensity (irradiance) of the xenon radiation to that of summer sunlight 0.75 = correction for diurnal variation of natural sunlight 12 = conversion factor of hours to days.

19. 60. The above calculations are just one possible way for transferring the experimental light intensity to environmental irradiation conditions. Light intensity can also be calculated based on the following equations (compare table in Annex 2):

Measured light intensity at 300-400 nm (W/m 2 ) / (6.07 x 100) = global light intensity at 300-3000 nm (W/m 2 )

or

Measured light intensity at 300-800 nm (W/m 2 ) / (57.9 x 100) = global light intensity (300-3000 nm) (W/m 2 )

The calculated global light intensity (W/m 2 ) x 3600 sec = global light intensity in one hour experiment at 300-3000 nm (MJ/m 2 ).

3 Intensities of sunlight depend on the geographical latitude in spring, autumn and winter, but vary little by latitude during th e summer.ENV/JM/TG/RD(2006)1/REV

226 This experimental global light intensity per one hour experiment can then be related to environmental light intensity per day (expressed as MJ/m2) which are available for different locations and seasons, e.g. in reference (14).

20. 61. Another way is to compare the intensity of the xenon lamp with tables of GCSOLAR instead of measured intensity. In this way, the days of irradiation are calculated to a “standard” and the results obtained at different times and locations can be compared. The tables of GCSOLAR give average daily irradiancies L( λ ) in millieinstein per day per cm 2 which can be compared to irradiance. The calculation should be performed for each wavelength λ (in nm). After that, the values obtained can be summated over the region 300 - 400 nm and the result compared to the measured value of the xenon light source.

Incubation system

21. 62. The treated soil thin-layers (for preparation see paragraphs 27–33) are incubated and irradiated under temperature-controlled conditions in static or fl ow-through systems which allow to trap any volatile products formed during the experiments. An example of a useful flow-through system is shown in Annex 4B (13). Other test systems are described in references (15)(16)(17).

22. 63. This test system consists of a stainless steel cooling tank containing the soil plates. This tank is sealed with a quartz lid, using Teflon tape between and bound around the lid/tank interface, and placed beneath the Xenon lamp or exposed to sunlight. Cooling water at a pre-set temperature is pumped through the base of the tank to control the temperature of the irradiated soil-coated plates. The temperature is monitored in the soil during the experiments using a thermocouple connected to a data logger.

23. 64. In order to trap any volatile products formed during irradiation, air is drawn through the tank at a certain flow rate (e.g. 10 – 12 ml/min) using a peristaltic pump. The incoming air is bubbled through traps containing 2 M potassium hydroxide solution and then through traps containing water to ensure that moist, carbon dioxide free air enters the system. The effluent air is bubbled through a series of traps containing, for example, 1 M sulphuric acid solution (to trap volatile basic compounds), methoxyethanol (to trap volatile organosoluble compounds) and ethanolamine (to trap 14 CO 2 or other acidic volatile compounds).

24. 65. Alternatively, static systems consisting, for example, of individual quartz vessels (e.g. inner surface approx 10-12 cm 2 ) equipped with traps containing soda lime and polyurethane foam may be used (see Annex 4C). In such a case para. 32 is not applicable since the thin soil layer is prepared and handled cautiously as outlined for larger portions of soil in the OECD Test Guideline 307 (6).

Laboratory equipment and chemicals

25. 66. Standard laboratory equipment is required, in particular the following:

- Analytical instruments such as GLC, HPLC and TLC equipment, including the appropriate detection systems for analyzing labeled or unlabeled substances or inverse isotope dilution method;

- instruments for identification purposes (e.g. MS, GC-MS, HPLC-MS, NMR, etc.);

- liquid scintillation counter for radiolabel led test item;

- oxidizer for combustion of labeled material;

- extraction apparatus (for example, centrifuge tubes for cold extraction and Soxhlet apparatus for continuous extraction under reflux);ENV/JM/TG/RD(2006)1/REV

227 - instrumentation for concentrating solutions and extracts (e.g. rotating evaporator)

- water bath.

26. 67. Chemicals used include: organic solvents, analytical grade such as acetone, methanol, etc.; scintillation liquid; various absorption solutions (see paragraph 23).



### Soil

Soil selection

27. 68. For phototransformation studies on soil surfaces, the use of two soil types is recommended. One soil should be the same type as used in the aerobic soil transformation study. As these experiments require glass or metal plates to be covered with thin-layers of soil, only those soils can be used which can form thin and solid layers on a glass or metal surface.

28. 69. The selected soil should be characterized, at least, for texture [according to FAO and USDA classification systems (18))], pH, organic carbon content and water holding capacity. For determination of soil characteristics the methods recommended in references (19)(20)(21)(22)(23)(24) can be used.

Collection and storage of soil

29. 70. The soil should be taken from the top layer (A-horizon) to a maximum depth of 20 cm. Remains of vegetation, macro fauna and stones should be removed. The soils are air-dried at room temperature (preferably between 20 - 25°C). Crushing of aggregates should be performed with minimal force, so that the original texture of the soil will be changed as li ttle as possible. The soils are sieved through a < 2 mm sieve. Before use the soils can be stored at ambient temperature and kept air-dried as microbial activity is of little relevance when studying physico-chemical processes on the soil surface. No limit on storage time is recommended but soils stored for more than 3 years should be re-analyzed prior to use with respect to their organic carbon content and pH.

30. 71. When “viable” (microbial active) soils are required for conducting experiments closely simulating field conditions, the soils should be collected freshly from the field and should be handled cautiously as outlined in the OECD Test Guidelin e 307 (6) and also in references (25)(26)(27).

31. 72. Detailed information on the history of the field sites from where the test soil is collected shouldbe available. Details include exact location [exactly defined by UTM (Universal Transversal MercatorProjection/European Horizontal Datum) or geographical co-ordinates], vegetation cover, treatments with crop protection chemicals, with organic and inorganic fe rtilizers, and additions of biological materials or accidental contaminations (25).

Preparation of soil thin-layer plates

32. 73. Soil thin-layers are prepared by applying aqueous slurry of soil to a glass or metal plate 14 in such a way that a soil layer of about 2 mm thickness is formed. Thereafter, the soil layers are allowed to air-dry to reach soil moisture corresponding to a pF of 2.0 to 2.5. This is the same moisture level as also required in the aerobic soil transformation study.

14 An appropriate plate size is 5.5 cm x 3.5 cm. Parts of the so il thin layers are scrapped off the edges of the plate, so that a soil area of 5 cm x 2.5 cm is left which corresponds to approx. 12.5 cm2.ENV/JM/TG/RD(2006)1/REV

228 33. 74. If further information is needed, an additional se t of soil thin-layers is allowed to completely dryout before test item application. Theses samples may be used to measure phototransformation on dry soil surfaces for determination of minimum phototransformation rates.

Test item application

34. 75. To apply the test item to the soil thin-layer s it should be dissolved in water (deionized or distilled) or in a suitable organic solvent. Each soil th in-layer is then evenly treated with the test item by distributing small droplets (e.g. 2-3 μ l) of the test item solution (e.g. 40-50 μ l total volume) over the whole soil surface by means of an appropriate syringe (e.g. Hamilton micro liter syringe or by a Hamilton dispenser unit). In case an organic solvent has to be used, it should not be a photosensitizer and should be allowed to evaporate from the soil thin-layers prior to the start of the irradiation process. As light penetration in soils is generally lower than 200 μ m (28) it is important to apply the test item in a very low volume of solvent to minimize its penetration into deeper soil layers.

35. 76. The amount of test item applied to the soil thin-layers should correspond, for general chemicals, to the estimated amount normally reaching the soil, or for crop protection chemicals, to the maximum recommended single use rate, and should be related to the surface area of the soil thin-layers used. An example for calculating the application rate is shown in the following for a single maximum field use rate of 288 g/ha calculated for the top 1-cm soil layer based on a bulk density of 1.5 g/cm 3 . Then it corresponds to a dose of approx. 5.8 μg if 3 g soil is used for each test system.

288 g test item ha 1 x 10 6 μ g test item 1 cm 3 1.92 μ g test item

ha x 1 x 10 8 cm 2 x g test item x
cm x 1.5 g soil = g soil

1.92 μ g test item 3.0 g soil 5.8 μ g test item g soil x test system = test system

In case the dose rate together with the available analytical method is borderline, it might be reasonable to reduce the depth of soil layer to <1 cm (finally to 0.1 cm.) for calculation or to exclude the terms on soil depth and bulk density (cursive typed above), i.e. just calculating a dose rate per surface area, then ignoring the depth of soil.

Test conditions

Test temperature

36. 77. During the test, the treated soil thin-layers are kept in the incubation system described in paragraphs 21-24 at a constant temperature of 20 ± 2°C. The temperature is monitored during the test by a thermocouple which is inserted in one soil thin-layer. Adequate temperature control is necessary to help

maintain also soil moisture within the light-exposed and dark controls.

Moisture content

37. 78. Soil moisture should be measured and recorded. The soil thin-layers (see paragraphs 21, 24 and 32) are adjusted to moisture of a pF of 2.0-2.5 15 , corresponding to a water holding capacity of 40 to-60 %. For sure it is inevitable that the very top soil surface is getting dried during each irradiation interval. However, soil moisture is re-adjusted in the remaining samples each time when samples are

15 For determination of water holding capacity (WHC) or field capacity (pF) see OECD TG 307.ENV/JM/TG/RD(2006)1/REV

229 removed for analysis or at least every 48 hours by adding lost portion of water to the soil thin-layers when necessary. This procedure (thus including to some extent drying and re-wetting) is regarded as best simulation of outdoor irradiation conditions of contaminated top soil.

Dark controls

38. 79. Additional soil thin-layers are kept under identical conditions in the dark to distinguish between photochemical and other reactions (5). Experience shows that it might happen that the dark controls show a faster transformation of test item than the irradiated samples. On the one hand this finding clearly indicates that light has no greater degradation potential for the test item. On the other hand it shows that a kind of sterilization occurs under the influence of intense light then lowering the degree of biodegradation.

Test duration

39. 80. For rate and pathway studies duration of exposure to sunlight (natural or artificial) should normally not exceed 30 environmental solar days. The soil layers should be incubated in appropriate static or flow-through systems for time periods corresponding to the above limits. For example, a period of 240 hours (= 10 days) corresponds to approx. 30 days of natural midsummer sunlight (calculated by information given in paragraphs 17-20 or using intensity values of Annex 3).

Performance of the test

40. 81. After treatment with the test item, the soil thin-lay ers are placed in an incubation system such as the ones illustrated in Annex 4. The system is then sealed and placed beneath the xenon light source or exposed outside to natural sunlight. The soil thin-layers are then irradiated for appropriate time intervals under the test conditions described above (see paragraphs 36-39). Irradiation in the laboratory may be carried out continuously or discontinuously simulating day and night cycles (e.g. 12 hours each).

41. 82. At least, duplicate soil thin-layers are removed at appropriate time intervals and the soil samples are extracted with appropriate solvents and analyzed for test item and/or phototransformation products. If applicable, absorption solutions are removed at the same time intervals and analyzed for volatile products. Besides a soil sample taken directly after application (0-hour sample) at least 6 sampling points should be included. Time intervals should be chosen in such a way that pattern of decline of the test item and patterns of formation and decline of phototransformation products can be established (e.g. 0, 17, 24, 41, 65, 137 and 240 hours).

42. 83. When using 14 C-labeled test item, non-extractable residues will be quantified by combustion and a mass balance will be calculated for each sampling interval.

DATA AND REPORTING

Treatment of results

43. 84. The amounts of test item, phototransformation products, volatile products and non-extractable should be given as % of applied initial dose for each sampling interval. Also a mass balance should be given in percentage of the applied initial dose for each sampling interval. A graphical presentation of the test item percentages against time will allow an estimation of its phototransformation half-life or DT50ENV/JM/TG/RD(2006)1/REV

230 under the experimental test conditions. Major phototransformation products should be identified and their percentages should also be plotted against time to show their rates of formation and decline.

44. 85. More accurate determinations of half-lives or DT 50 values and, if appropriate, DT 90 values should be obtained by applying appropriate kinetic model calculations and their conversion to environmental sunlight conditions (see paragraphs. 17-20). The half-life and DT 50 values should be reported together with the description of the model used, the order of kinetics and the correlation coefficient (r). If appropriate, the calculations should also be applied to the major ph ototransformation products. Examples of appropriate models are described in references (29) to (34).

Test report

45. 86. The test report must include:

Test item: - Common name, chemical name, CAS number, chemical structure (indicating position of label when radiolabeled material is used) and relevant physical-chemical properties (see para. 7) - Purity (impurities) - Radiochemical purity of labeled chemical and specific activity (where appropriate).

Test soil:

- Details of collection site - Date and procedure of soil sampling - Properties of soil, such as pH, organic carbon content, texture and water retention

characteristics

- Length of soil storage and storage conditions.

Xenon light source:

- Manufacturer and model

- Filters and their purpose Spectrum of the light source between 290 and 800 nm given by the manufacturer or measured at the beginning and the end of the test

- Comparison of the spectrum of the light with that of natural sunlight

- Light intensity measured at sample level (Watt • m -2 ) and area irradiated.

Test conditions: - Dates of the performance of the studies - Amount of test item applied - Solvents used and method of application for the test item

- Area of soil thin-layers treated

- Description of the incubation system used

- Air flow rates (if applicable)

- Temperature of experimental set-up

- Soil moisture content during incubation

- Method(s) of extraction

- Methods for quantification and identification of the test item and major phototransformation products in soil and absorption solutions or traps including LOD and LOQ

- Number of replicates.

Test results:

- Tables of results expressed as % of applied dose for the soil thin-layersENV/JM/TG/RD(2006)1/REV

231 - Mass balance during and at the end of the studies

- Quantification of non-extractable (bound) radioactivity or residues in soil

- Quantification of volatile products

- Plots of percentages in soil versus time for the test item and, where appropriate, for the major phototransformation products

- Assessment of phototransformation kinetics and half-life or DT 50 for the test item and, where appropriate, for major phototransformation products including confidence limits

- Proposed pathway of phototransformation, where appropriate

- Discussion and interpretation of results, i.e. significance of results to environmental behavior

of test item.

LITERATURE

(1) US-Environmental Protection Agency (1982). Pest icide Assessment Guidelines, Subdivision N. Chemistry: Environmental Fate.

(2) Agriculture Canada (1987). Environmental Chemistry and Fate. Guidelines for registration of pesticides in Canada.

(3) European Union (EU) (19 95). Commission Directive 95/36/EC amending Council Directive 91/414/EEC concerning the placing of plant protection products on the market. Annex I: Fate and

Behaviour in the Environment.

(4) Dutch Commission for Registration of Pestic ides (1995). Application for registration of a pesticide. Section G: Behaviour of the product and its metabolites in soil, water and air.

(5) SETAC (1995). Procedures for Assessing the Environmental Fate and Ecotoxicity of Pesticides. Mark R. Lynch, Ed.

(6) (7) OECD (1993). Guidelines for the Testing of Chemicals. Paris. OECD (1994 – 2000):

Addenda 6-11 to Guidelines for the Testing of Chemicals.

(7) OECD (2000). Draft Guideline “Phototransfor mation of Chemicals in Water” – Direct and Indirect Photolysis.

(8) ISO 10977 (1993). Photography – Processed phot ographic colour films and paper prints – Methods for measuring image stability.

(9) Zepp, R.G. and Cline, D.M. (1977). Rates of dire ct photolysis in aquatic environment. Environm. Science and Technology, 11, 359-366.

(10) OECD (1997). Guidance Document on Direct Phototransformation of Chemicals in Water Series on Testing and Assessment No. 7.

(11) Miller, G.C. and Zepp, R.G. (1983). Extrapolating photolysis rates from the laboratory to the environment. Residue Reviews, 85, 89-110.ENV/JM/TG/RD(2006)1/REV

232 (12) Mill,T., Mabey, W.R., Bomberger, D.C., Chou, T.-W., Hendry, D.G. and Smith, J.H. (1982).Laboratory Protocols for Evaluation of the Fate of Organic Chemicals in Air and Water. U.S. Environmental Protection Agency; EPA 600/3-82-002.

(13) Parker, S. and Leahey, J.P. (1988): Developm ent of a method to investigate the photodegradation of pesticides. Brighton Crop Protection C onference – Pests and Diseases – 1988, 663 – 668.

(14) Wypych, G. (19..?). Handbook of Material Weathering. Second Edition, Chapter 4, 61-94.

(15) Burkhard, N. and Guth, J.A. (1979). Phot olysis of organophosphorus insecticides on soil surfaces. Pestic. Sci. 10, 313 – 319.

(16) Guth, J.A. (1980). The study of transformations. In Interactions between Herbicides and the Soil. R.J. Hance, Ed., Academic Press, 123 – 157.

(17) Guth, J.A. (1981). Experimental approaches to studying the fate of pesticides in soil. Progress in Pesticide Biochemistry. D.H. Hutson, T.R. Roberts, Eds. J. Wiley & Sons. Vol. 1, 85 – 114.

(18) Soil Texture Classification (US and FAO systems). Weed Science, 33, Suppl. I (1985) and Soil Sci. Soc. Amer. Proc. 26, 305 (1962).

(19) Methods of Soil Analysis (1986). Part I, Physical and Mineralogical Methods (A. Klute, Ed.). Agronomy Series No. 9, 2 nd Edition.

(20) Methods of Soil Analysis (1982). Part 2, Chemical and Microbiological Properties (A.L. Page, R.H. Miller and D.R. Kelney, Eds.). Agronomy Series No. 9, 2 nd Edition.

(21) ISO Standard Compendium Environment (1994). Soil Quality – General aspects; chemical and physical methods of analysis; biological methods of analysis. First Edition.

(22) Mückenhausen, E. (1975). Die Bodenkunde und ihre geologischen, geomorphologischen, mineralogischen und petrologischen Gr undlagen. DLG-Verlag, Frankfurt/Main.

(23) Scheffer, F. and Schachtschabel, P. (1998). Lehrbuch der Bodenkunde. F. Enke Verlag, Stuttgart.

(24) Schlichting, E., Blume, H.-P. and Stahr, K. (1995). Bodenkundliches Praktikum: eine Einführung in pedologisches Arbeiten für Oekologen. 2 nd Edition. Blackwell, Berlin-Oxford.

(25) OECD (1995). Final Report of the OECD Workshop on Selection of Soils/Sediments. Belgirate, Italy, 18-20 January 1995.

(26) ISO 10381-6 (1993). Soil Quality – Sampling – Part 6: Guidance on the collection, handling and storage of soil for the assessment of aerobic microbial processes in the laboratory.

(27) Anderson, J.P.E. (1987). Handling and storage of soils for pesticide experiments. In Pesticide Effects on Soil Microflora. L. Somerville, M.P. Greaves, Eds. Taylor & Francis, 45-60.

(28) Ciani, A. (2003). Photol ysis processes in soils and other porous media. Diss. ETH No. 15306.ENV/JM/TG/RD(2006)1/REV

233 (29) Hamaker, J.W. (1976), The application of mathematical modelling to the soil persistence and accumulation of pesticides. Proc. BCPC Symposium: Persistence of Insecticides and Herbicides,

181 – 199.

(30) Goring, C.A.I., Laskowski, D.A., Hamaker, J.W. and Meikle, R.W. (1975). Principles of pesticide degradation in soil. In Environmental Dynamics of Pesticides. R. Haque and V.H. Freed, Eds., 135 – 172.

(31) Timme, G. and Frehse, M. (1980). Statistical interpretation and graphic representation of the degradational behaviour of pesticide residues. I. Pflanzenschutz – Nachrichten Bayer 33, 47 – 60.

(32) Timme, G., Frehse, H. and Laska, V. (1986). Statistical interpretation and graphic representation of the degradational behaviour of pesticide residues. II. Pflanzenschutz – Nachrichten Bayer 39,

188 – 204.

(33) (35) Hill, B.D. and Schaalje, G.B. (1985). A two compartment model for the dissipation of deltamethrin on soil. J. Agri. Food Chem., 33,1001-1006.

(34) (36) Gustafson, D.I. and Holden, R.L. (1990). Nonlinear pesticide dissipation in soil: A new model based on spatial variability. Environm. Science and Technology, 24, 1032-1038.ENV/JM/TG/RD(2006)1/REV

234 ANNEX 1: DEFINITIONS AND UNITS

Test item : any substance, whether the parent compound or relevant transformation products.

Transformation products : all substances resulting from biotic or abiotic transformation reactions of the test item including CO 2 and products that are in bound residues.

Bound residues : “Bound residues” represent compounds in soil, plant or animal, which persist in the matrix in the form of the parent substance or its metabolite(s)/transformation product(s) after extraction. The extraction method must not substantially change the compounds themselves or the structure of the matrix. The nature of the bond can be clarified in part by matrix-altering extraction methods and sophisticated analytical techniques. To date, for example, covalent ionic and sorptive bonds, as well as entrapments, have been identified in this way. In general, the formation of bound residues reduces the bioaccessibility and the bioavailability significantly (1) [modified from IUPAC 1984 (2)].

Phototransformation : reactions occurring on soil thin-layers under the influence of light (> 290 nm).

Soil is a mixture of mineral and organic chemical constituents, the latter containing compounds of high carbon and nitrogen content and of high molecular weig hts, animated by small (mostly micro-) organisms. Soil may be handled in two states: (a) (c) undisturbed, as it has developed with time, in characteristic layers of a variety of soil types; (b) (d) disturbed, as it is usually found in arable fields or as occurs when samples are taken by digging and used in this guideline (3).

Xenon lamp : An intensive source of ultraviolet, visible and near-infrared light produced by electrical discharge in Xenon under high pressure.

Intensity : Traditional term for photon flux, irradiance or radiant power (radiant flux). In terms of an object exposed to radiation. The term should now be used only for qualitative descriptions.

Irradiance (E) [W • m -2 ]: The radiant flux or radiant power P of a all wavelengths incident on an infinitesimal element of surface containing the point under consideration divided by the area of the element (dP/dS; simplified expression: E = P/S when the radiant power is constant over the surface area considered).

Radiant Power (P), [J • s -1 or W]: Power emitted, transferred or received as radiation.

Half-Lif e, t 0.5 is the time taken for 50 % transformation of a test item when the transformation can be described by first-order kinetics; it is independent of the concentration.

DT 50 (Disappearance Time 50) is the time within which the concentration of the test item is reduced by 50 %; it is different from the half-life t 0.5 when transformation does not follow first order kinetics.

DT 90 (Disappearance Time 90) is the time within which the concentration of the test item is reduced by

90 %.

The limit of detection (LOD) is the concentration of a substance below which the identity of the substance cannot be distinguished from analytical artifacts.

The limit of quantification (LOQ) is the concentration of a substance below which the concentration cannot be determined with an acceptable accuracy.ENV/JM/TG/RD(2006)1/REV

235 LITERATURE REFFERRED IN THE ANNEX 1

(1) (4) DFG: Pesticide Bound Residues in Soil. Wiley – VCH (1998).

(2) (5) T.R. Roberts: Non-extractable pesticide residues in soils and plants. Pure Appl. Chem. 56, 945 – 956 (IUPAC 1984).

(3) (6) OECD Test Guideline 304 A: Inherent Biodegradability in Soil (adopted 12 May 1981).ENV/JM/TG/RD(2006)1/REV

236 ANNEX 2: SPECIMEN LIGHT SOURCE AND APPARATUS (if artificial light is used)

A. C. Suntest ® CPS+ Irradiation Unit

1: Refrigerated circulating chiller connected to cooling platform, etc.

2. SUNTEST unit with irradiation

chamber inside (not visible here), usually equipped with xenon lamp

NXE 1500 B

3. Cooling platform.

4. Data logger connected to a

thermocoupleENV/JM/TG/RD(2006)1/REV

237 ANNEX 2 (continued)

B. D. Spectrum Of Unfiltered Xenon Arc Compared To Sunlight

C. E. GLOBAL RADIATION

Global radiation (data from CIE Publication No. 20, 1972)

Wavelength Irradiance Percentage of total radiation in each range (nm) (W*m-2) (%)

280-400 68 6.1

400-800 580 51.8

800-1400 329 29.4

1400-3000 143 12.7

Total 1120 100 Sum (280-800): 57.9

Compiled data taken from J. Boxhammer (Original Hanau Heraeus GmbH, Hanau) : XenonBestrahlungseinheiten und Ultratest Bestrahlungseinheiten – Basiselemente zur Projektierung von Expositions- und Prüfanlagen.ENV/JM/TG/RD(2006)1/REV

238 ANNEX 3

LIGHT INTENSITIES OF A XENON LAMP AND OF NATURAL SUMMER SUNLIGHT

A. XENON LAMP 1

Position

No. Irradiance E (300 – 400 nm)

[W/m 2 ] r*

Start End Mean

1 + 69.2 69.7 69.4 1.036

2 78.0 78.9 78.4 1.171

3 79.6 80.7 80.1 1.196

4 ++ 79.2 80.8 80.0 1.194

5 78.5 79.9 79.2 1.182

6 75.3 76.4 75.9 1.132

7 + 63.3 65.0 64.1 0.957

Mean 74.7 ± 6.2 75.9 ±6.2 75.3 1.124 ± 0.09

75.3 ± 6.0

(1) U. Morgenroth, personal communication.

+ edge positions

++ central position

* r = ratio between artificial and natural light

B. NATURAL SUMMER SUNLIGHT

[Values taken from references (12) and (13)]

Region latitude Irradiance E (300 – 400 nm)

[W/m 2 ]

Florida, USA 30°N 66.98

Greensboro, NC, USA 40°N 68.98

Basel, Switzerland 50°N 65.32

Mean 30 – 50°N 67 ±3 %ENV/JM/TG/RD(2006)1/REV

239 ANNEX 4A

EXAMPLE OF A TEST SYSTEM FOR PHOTOTRANSFORMATION EXPERIMENTS ON SOIL SURFACE (15)ENV/JM/TG/RD(2006)1/REV

240 ANNEX 4B

EXAMPLE OF A TEST SYSTEM FOR PHOTOTRANSFORMATION EXPERIMENTS ON SOIL SURFACE (13)

A. INCUBATION AND COOLING TANK

B. SOIL PHOTOLYSIS PLATEENV/JM/TG/RD(2006)1/REV

241 ANNEX 4C

EXAMPLE OF A TEST SYSTEM FOR PHOTOTRANSFORMATION EXPERIMENTS ON SOIL SURFACE (Static system)

A. Test Vessel for Soil Photolysis Studies

trap for CO 2 and volatile organic compounds

Quartz wool

Soda lime (for adsorption of atmospheric CO 2 ): 0.5g

Quartz wool

Soda lime (for adsorption of CO 2 emanating from soil): 2g

Quartz wool

Polyurethane plug for adsorption of volatile organic compounds

quartz glass cover

soil layer E.g. the test systems consist of glass vessels (36-mm inner diameter, 35-mm height, base

area 10.2 cm 2 ) each containing 3 g soil (dry weight), which provide an about 3-mm soil depth. A glass neck with ground joint (NS 10) is attached to the side of the wall. There, the flask is closed with a solid trap attachment, a small glass tube of 90 mm length and 12 mm inner diameter, in which volatile compounds are bound to soda lime and polyurethane foam. The trap is packed in the sequence: PU-foam plug → quartz wool → 2 g soda lime → quartz
wool → 0.5 g soda lime → quartz wool (see Figure). The quartz glass cover (thickness 3- mm) is sealed with metallic clips and the ground glass joint was covered with a rubber

septum.

B. Test Vessels Position in the Suntest ® CPS+ Irradiation Unit

Light source

Measuring cell Irradiation vessel 

## d a b c

Sample platform

Distance of light source ..from the cooling ..from the measuring ..from the soil ..from the quartz lid (top) of the a: approx. 230 b: approx. 230 c: approx. 226 d: approx. 195

Measuring cell: e.g. XenoCal WB 300-800 nm (Atlas MTT GmbH, Germany)