Open Literature Review Summary

Chemical Name: Atrazine

CAS No: 1912-24-9

ECOTOX Record Number and Citation:

Guasch, H. and S. Sabater. 1998. Light history influences the sensitivity to atrazine in periphytic

algae. Journal ofPhycology 34(2): 233-241. (MRID 48261116).

Purpose of Review:

Determine potential effects of atrazine on an aquatic community. Endpoints from this study

contribute to the weight-of-evidence regarding effects of atrazine on aquatic plant communities

and associated determination of a Level ofConcern (LOC).

Date of Review: 9/4/09

Purpose of Study:

This study examines the influence oflight history (light conditions during colonization) on the

sensitivity to atrazine of periphyton communities from stream and river sites with different water

chemistry and light regimes.

Summary of Study Findings:

Methods:

The study included seven sites located in five streams and rivers: Avenco (Avo, Avenco open;

Avs, Avenco closed/shaded); Castanyadell (Co, Castanyadell open; Cs, Castanyadell

closed/shaded); Gaia (G); Riera Major (RM); and Ter (T). In the Avenco and Castanyadell

systems, open canopy sites were located 100-200 m downstream from shaded sites. The

physiographical description ofthe streams and rivers are provided in Table 1.

Periphyton communities were allowed to colonize the surface of etched glass squares (1.4 cm2

)

throughout July 1996. The glass squares were glued to stream stones and placed in riffle areas at

each study site. Colonization time was short to avoid periphyton self-shading: 3 weeks in Avo,

Avs, Co, Cs and RM (sites with low nutrients and/or light availability) and 2 weeks in G and T

(open sites with high nutrients). Water and environmental conditions were measured at each

sampling date; values are reported in Table 2.

1 1II1IIIIII

2087864
After colonization, the glass substrates were removed from the sites and transported in coolboxes filled with site water. Ten to twenty liters ofsite water was also collected at each

sampling. Periphyton samples for atrazine testing (100-200 colonized glass substrates) were

stored in the refrigerator at 4°C until use after receipt at the laboratory.

The analysis ofthe photosynthetic pigments was performed by extracting the algal pigments in

90% acetone after sonication ofthe attached algae for 4 minutes. Total chlorophyll a was

measured via acidification corrections (Lorenzen 1967). The different pigment groups, such as

carotenoids, were identified and quantified via HPLC analysis using procedures described by

Mantoura and Llewellyn (1983) and detailed in Guasch and Sabater (1995). The

chromatographic results were used to estimate the percentage of chI a, other forms of chlorophyll

(including chI a' and b) and chlorophyll derivatives. Total carotenoids were calculated as the

sum of all carotenoid peaks.

The analysis ofthe algal taxonomic composition was performed by removing the cells from the

glass substrates via sonication. Cells post-sonication were monitored via scanning electron

microscope (SEM) in order to ensure that no viable damage was done during removal.

Successive short sonications (ca. 20 s) were performed until complete removal of algae. After

each sonication, the sonicated material was removed and 2 mL of distilled water was added. The

sonicated material was preserved in 4% formaldehyde. Light microscope (1000x) was used to

determine the algal taxonomic composition using permanent slides of diatom frustules;

nondiatom cells were identified and quantified via observation ofthe sonicated material. For

each sample, 250-300 cells were counted. Semiquantitative data on algal abundances was used

to calculate the proportions of different algal groups and cyanobacteria.

Photosynthesis-irradiance (P-I) curves were studied using natural light (neutral-density filters

were used to reduce incident light to desired levels). For Avo, Avs, G, Cs and T study sites, four

replicate glass substrates were incubated at each offour different light intensities (10-60, 70-200,

250-300 and 1200-1700 ~mol m-2 S-l). For Co study site, four replicate glass substrates were

incubated at each oftwo different light intensities (10-60 and 1200-1700 ~mol m-2 S·l). For RM

study site, four replicate glass substrates were incubated at one light intensity (10-60 ~mol m-2 s1). Intact colonized substrates were put in glass vials containing 4 mL offiltered stream water.

Incubations were performed outdoors in water bath (± 3°C, field temperature) with continuous

shaking. After pre-incubation (1 h), photosynthesis was measured by the addition of a 14C_

source (a diluted 14C-HC03- solution, specific activity 1 ~Ci per sample). After 1 h ofincubation

at the same conditions, the reaction was stopped by the addition of 0.4 mL of 37% formaldehyde

to each vial. P-I curves were fitted to the inhibition model ofPlatt et al. (1980). The fitted

curves were used to estimate a (the initial slope ofthe P-I curve) and p(the inhibition

parameter). The fitting was done via the GraFit program using nonlinear regression. The light

saturation and light inhibition parameters (Isat and Ib) were calculated as Pmax/a and Pmax/P,

respectively.

2
Atrazine concentration-response curves were studied using the same procedures, conditions, sites

and irradiances as described above for P-I curves. For each periphyton community and

irradiance, replicate glass substrates were incubated at five atrazine concentrations prepared from

a stock of "pure" atrazine (0, 10.78, 107.84,215.68, and 1078.40 /lg L·l

; all atrazine

concentrations converted from /lmol L-l to /lg L-l by reviewer). Diluted l4C-HC0 3' solution

(specific activity 1 /lCi per sample) was added after one hour pre-incubation with atrazine. An

hour later (two hours after atrazine exposure), the reaction was stopped by the addition of 0.4 mL

of 37% formaldehyde to each vial and photosynthesis was measured. ECso and EC10 values were

estimated using log-linear interpolation of photosynthetic activity in atrazine-treated samples,

expressed as the percentage ofthe mean activity ofthe controls.

Analysis for atrazine was performed on the test water after collection (for residual atrazine

contamination) and on the atrazine set ofstandards for toxicity testing. Identification and

quantification of atrazine was performed via HPLC equipped with a diode array following the

procedures described by Durand and Barcelo (1990). Prior to HPLC analysis, samples were

filtered and processed via solid extraction with 500 mg C18 cartridges. HPLC analysis was

performed using the following conditions: ODS 5-micron Hypersil column (250 mm length);

gradient mobile phase consisting of A) acetonitrile, B) methanol and C) distilled water; flow rate

1 mUmin.; and column pressure 1200-1300 psi. Atrazine was identified via spectra comparison

to reference standard atrazine. The detection limit was 0.1 /lg L-l

.

The study authors used Pearson correlation analysis to determine relationships between the

environmental data and biological variables and those concerning responses to atrazine. A threeway ANOVA was used to test for effects oflight regime during colonization (Leol), atrazine

exposure (A), and the irradiance of incubation (line) on photosynthesis. Photosynthesis was

expressed as the percentage ofthe maximum activity measured in each periphyton community.

The analysis included three factors: A, at the five concentrations; line, grouped into three levels

(50-80,250-300 and 1200-1700 /lmol photons m·

2 S·l); and light conditions during colonization,

Leo\' with two levels (high light, HL, and low light, LL; based on the photosynthetic behavior of

the corresponding periphyton communities).

Results:

Site characterization

Light extinction (Lext) measurements indicated that canopy covers (shaded sites) caused a

reduction ofirradiance, and stream sites which were open, undisturbed and had a low

concentration of nutrients had negligible reductions of irradiance.

3
Photosynthesis-irradiance (P-I) relationships

The P-l curves for periphyton from the three open sites (Avo, G and T) had similar initial slopes

and saturation irradiances around 50 /lmol m2 S-l. Additionally, a slight photoinhibition at high

intensity was observed. For Avs, the initial slope ofthe P-l curve was similar to the open

community, but photoinhibition occurred around 200 /lmol m-2 S-I. For Cs, the initial slope of

the P-l curve was the steepest ofthe test sites, and evidence for photoinhibition was observed

around 100 /lmol m2 s-l. For the five sites, the correlation ofthe irradiance of inhibition, lb, with

light conditions during colonization, Leo], resulted in the following values: r = 0.88, P < 0.05, n =

5. Two levels of Leol were established: high light, HL, where Leol were above 500 /lmol m-2 S-1 0r

Lext < 50% and low light, LL, where Leol were below 40 /lmol m-2 S-l or Lext > 95%. P-l

relationships in the presence and absence of atrazine are reported in Table 3 and illustrated in

Figure 1. For example, in the open-canopy sites, the respective mean ECso and ECIO values for

periphyton treated with atrazine were 295.5 and 97.06 /lg L-I for Avo, 291.2 and 127.3 /lg L-I for

Co, 327.8 and 60.39 /lg L-1for G, and 90.59 and 6.47 /lg L-1for T, respectively. For the closedcanopy sites, the mean ECso and EClO values, respectively, for periphyton treated with atrazine

were 552.1 and 155.3 Ilg L-1for Avs, 498.2 and 138.04 /lg L-I for Cs, and 521.9 and 157.5 /lg L-l

for RM, respectively.

Chlorophyll content and pigment composition

Algal communities on the glass substrates were generally thin biofilms due to the short amount

of colonization time. The periphyton from open sites had statistically significantly greater mean

chI a amounts than those of periphyton from closed sites; alternatively, the periphyton from open

sites had statistically significantly lower mean total carotenoids than those of periphyton from

closed sites. Pigment composition was correlated with Leol (% chI a: r = 0.821, P < 0.05, n = 6;

% TCar: r = -0.989, P < 0.05, n = 6). Therefore, differences in pigment composition coincided

with differences in the photosynthetic parameters of each algal community.

Community structure

Green algae (Chlorophyceae) and cyanobacteria were more prevalent than diatoms in periphyton

communities from open-canopy sites; and, alternatively, diatoms were the more dominant

taxonomic group for periphyton from closed-canopy sites. Cocconeis placentula was the

dominant group within the diatoms in all sites.

Atrazine toxicity

Periphyton from open-canopy sites was more sensitive to atrazine than periphyton from closed

canopy sites for incubations between 55 and 85 /lmol m2 S-I and for incubations at saturating

irradiances. At saturating irradiances (PS % sat = 100, see Table 6), periphyton from open4
canopy sites showed a slight increase in photosynthesis at 0 and 10.78 Jlg L-! atrazine

concentration and strong photosynthetic inhibition at atrazine concentrations above 21.57 Jlg/L.

For the periphyton from closed-canopy sites, the increase of photosynthesis was not observed;

however, the similar inhibition by atrazine at high atrazine concentrations was observed. The

effect of atrazine on the P-l relationships for open-canopy and closed-canopy sites is illustrated

in Figures 2 and 3; the tabulated forms ofthese graphs are provided in Tables 4 and 5,

respectively, where values for photosynthesis were estimated by the primary reviewer.

The mean ECso and ECIO values for periphyton treated with atrazine at open-canopy and closedcanopy sites at the various irradiances ofincubation are reported in Table 6.

A negative relationship between ECso values measured at saturating irradiance and Leo! was

determined (r2 = 0.56, P = < 0.005, n = 5). Results ofthis correlation are illustrated in Figure 3.

A negative relationship between mean ECso values for each site (mean data obtained at saturating

irradiances, see Table 3) and the percentage of chI a was determined (r = -0.857, P = < 0.05, n =

6).

Three-way ANOVA

The three-way ANOVA for the observed effects on photosynthesis, using Pearson correlation

analysis, determined the interdependence ofthe various treatment factors of light regime during

colonization (Leo], high light, HL, and low light, LL), algal sensitivity to atrazine (A, at the varied

concentrations), and the irradiance ofincubation (line, 50-80,250-300 and 1200-1700 Jlmol

photons m2 s-!). The Leo! x tne interaction was significant (df2; SS 32,254; F value 38.2; P

<0.001), suggesting a photosynthetic dependence. A dependence was also suggested for atrazine

and Leo], based on the significance ofthe Leo! x A interaction (df 4; SS 10,223; F value 6.06; P

<0.001). This explained the observed enhanced effect ofatrazine for open-canopy sites.

Additionally, the Leo! x line x A interaction was significant (df 8; SS 8375; F value 2.48; P

<0.05), suggesting that the magnitude of Leo1 and A was attenuated by line.

Overall, the study authors determined that the light conditions during colonization were shown to

be an important factor in the subsequent photosynthetic behavior of periphyton communities,

including the photosynthetic behavior in the presence of atrazine. The study authors also

concluded that the results ofthe study (light history of periphyton effecting the response to

atrazine) support the hypothesis that periphyton algal communities in low-light environments

have a certain degree of protection against this herbicide. The study authors also proposed that

the increased resistance to atrazine exhibited by low-light periphyton algal populations was due

to the higher chlorophyll content.

Regarding ecological implications, the study authors noted that field agricultural streams are

generally sites with little shading, high nutrient concentrations, and, consequently, periphyton

communities dominated by filamentous green algae. Based on the findings ofthis study, the

5
study authors conclude that the periphyton offield agricultural streams are likely to be more

sensitive to atrazine than other shaded, undisturbed sites.

Table 1. Physiographic description of streams and rivers (Guasch and Sabater 1998).

Water- Dominant shed Steam Stream Site Location order Lithology riparian Human use

area condition vegetation (km2

)

Avenc6 41°46'N 35 3 Calcareous Alnus Recreational, Undisturbed,

2°19'E glutinosa water supply closed

Castanyadell 41°55'N 16 3 Siliceous Alnus Recreational Undisturbed,

2°n'E glutinosa closed

Gaia 41°n'N Sewage Eutrophic, 240 3 Calcareous Populus alba inputs, I020'E agriculture open

41°56'N Alnus Recreational, Slightly Riera Major 2°25'E 194 4 Siliceous glutinosa sewage eutrophic,

inputs closed'

Agriculture, Eutrophic,

Ter 42°00'N 1380 5 Calcareous Arundo donax industry slightly

2°15'E sewage polluted,

inputs open

Table 2. Water quality and canopy cover ofsites sampled in July 1996 (based on Guasch and Sabater 1998).

Lcol Condo DOC Phosphate,

Light (Jimol Lex! Temp. pH (JiS (mg Alkalinity Nitrate,

conditions m-2 S-I)" (%)b ( DC) cm-1)C L-1)d (meq L-1

) Ammonium

Site (Jig L))"

Avenc6 Open 1700 ND 17.8 8.12 228 1.68 1.89 < 12,56, < 14

Avenc6 Closed 38 98 17.8 8.12 228 1.68 1.89 < 12, 56, < 14

Castanyadell Open 1100 ND 17.6 8.10 182 1.04 1.69 < 12,378, < 14

Castanyadell Closed 35 97 17.6 8.10 182 1.04 1.69 < 12, 378, < 14

Gaia Open 740 37 20.5 8.27 923 2.95 3.58 < 12,2002,28

Riera Major Closed 20 98 18.3 8.36 241 1.37 2.17 28,518,28

Ter Open 600 50 18.2 8.17 313 1.35 2.22 109, 1078, 154

ND = Not determmed.

a Irradiance at the substrate surfaces (Lco!)'

b extinction of light due to canopy cover and turbidity (Lext).

c Conductivity.

d Dissolved organic carbon.

e Phosphate, P04

3

-; Nitrate, N03- ; and Ammonium, NH4+ .

6
Table 3. Photosynthetic parameters and atrazine toxicity (from Guasch and Sabater 1998). The initial slope

(a) and inhibition parameter (P) are given in J,lgC cm-2 h-Ij J,lmol m-2 S-l (estimated parameter and standard

deviation). Units for irradiance ofsaturation (Is•t) and irradiance of inhibition (Ib) in J,lmol m-2 fl. Effective

atrazine concentration (ECso and EClO) means and standard deviations evaluated from concentrationresponse curve performed at light saturation and converted by reviewer to J,lg L-I.

Site Light a p Is•t Ib ECso (J,lg L-I

) ECIO

conditions' (J,lg L-I

)

Avenc6 (Avo) Open 1.89 ± 0.46 0.057 ± 50 1754 295.5 ± 144.51b 97.06 ± 1O.78b

0.024

Castanyadell Open ND ND ND ND 291.2 ± O.OOb 127.25 ± 114.31 b

(Co)

Gaia (G) Open 2.37 ± 0.57 0.048 ± 42 2083 327.8 ± O.OOb 60.39 ± O.OOb 0.016

Ter (T) Open 1.96 ± 0.50 0.058 ± 51 1724 90.59c 6.47c

0.031

Avenc6 (Avs) Closed 1.88 ± 0.68 0.54± 59 203 552.1 ± 153.13d 155.29 ± 107.84d

0.18

Castanyadell Closed 6.32 ± 0.66 1.12 ± 17 99 498.2c 138.04c

(Cs) 0.43

Riera Major Closed ND ND ND ND 521.9c 157.45c

(RM)

ND = Not detenmned.

a Open or closed with respect to canopy cover.

bn=2.

c n = 1.

dn = 3.

Av 0

1500

- --

1000

Av s

o 500

o

.'

100

75 "1'

i.

"I

50 ....f

25

-o

"#.

-

en

'(i,i

CD

..c

C

>..

C/)

o

-o

.r:.

Q..

-

e

-c

o

u

irradiance (I-lmo! . m'~'s')

Figure 1. P-I relationships for periphyton from open and shaded sites of the Avenc6 stram, Gaia stream,

shaded site of Castanyadell and Ter river (Guasch and Sabater 1998). Curves were fitted to the inhibition

model of Platt et ai. (1980).

7
-

e

"E.

o

(.)

-o

o

--

I

I

150 -;I

125 -i

Avenc6

(open)

....., 5€

-.. 192'

2iO

-IIf- 1sn

.....- 23

..... ' '2~

-4- 3(1.1:

--... 1703

___ 9

...... ;51

....- ~S-'

-y - j2.40

125 Ter

1_ (open)

100 -i .....

'~ "-

75 ...;I__ - ......--.. -<:"""---_"

:'fL--- ~', 50 1 ---~- ..... , <ii

l '--U\

25 -i -~

o !ie e ...~'- ;

...- 82

-II. ,375

.,. Castany.

(open)

75 -! i

50"': -\ . \

If-- -_

25 -i~ -------...

oj "i:

tf)

'u;

Q.l

.r::.

C

>- U)

o

'0

.r::.

0.

?ft. 100-::

-

"5-

.:: . c: 150-

8 j25-

o

10~ 10-3 10-2 1CT' 1()C 10~

atrazine concentration (log /lM)

10-01 10-3 10-2 10'1 100 10'

atrazine concentration (log ~M)

Figure 2 .The relationship between logarithm of atrazine concentration (,...M) and photosynthesis (% of

controls) for periphyton from sites with open canopy cover (Guasch and Sabater 1998). Four irradiance

levels for Avenco open, Gaia and Ter; two irradiance levels for Castanyadell open.

8
Table 4. Effect of atrazine exposure on the photosynthesis of periphyton communities using various irradiation intensity, from sites with open canopy

cover ECso and EClO

a from Guasch and Sabater (1998, Table 6).

Site Irradiation

ECso (/lg L-l

) ECIO (J-Lg L-l

) (J-Lmol m-2 S·l)

56 120.78 ± 30.20 10.568 ± 2.804

192 399.01 ± 79.80 104.820 ± 21.137 Avenc6 (open)

270 191.96±47.45 90.370 ± 2.588

1575 45.29 ± 21.57 0.431 ± 0.216

23 159.60 ± 25.88 11.647 ± 1.941

125 327.83 ± 88.43 61.037 ± 16.392 Gaia

304 327.83 ± 51.76 59.959 ± 8.627

1703 364.50 ± 196.27 86.49 ± 46.37

82 362.34± 88.43 207.484 ± 51.116 Castanyadell (open)

1375 222.15 ± 45.29 45.077 ± 8.627

9.3 NI NI

51 332.15 ± 69.02 64.06 ± 13.80

Ter

189 90.59 ± 21.57 7.117 ± 1.725

1241 131.56 ± 32.35 7.980 ± 1.941

NI = No inhibition by atrazine detected.

'Converted to Jlg L-l

by reviewer (see attached Worksheet).

9
,

•

50 .JI

.I

25 -!

o I

,

Riera Maior 125 .J 'J I (closed)

100 1~i>------.....a--••_~

7SJ

i

,

...... 56

..... Hl2

-4- 279

-y- 1sn

Avenc6

(closed)

-

e 150-' __ i

C :

8 125 _ '"l"

o 100 -"- __

7S ~. -----=---~i 'US : : - -~"-..~-.~~\ Q) 50 - -..L \ - \

25 - \\

o r

'0 0 - ..--------..... ~- ........-....,:

.:::

Q.

"0-

"-

'E

o

()

'0

c

--

100.4\ 1o·~ 10-2 10-1 10a 10'

atrazine concentration (log j..lM)

150 . Castany.

10": 10.3 10.2 ,o·~ 10: 10~

atrazine concentration (log J,.iM)

'iOo.4\ 10.3 10',2 10.1 100 10'

atrazine concentration- (log ~M)

Figure 3. The relationship between logarithm of atrazine concentration (JIM) and photosynthesis (% of

controls) for periphyton from sites with closed canopy cover (Guasch and Sabater 1998). Four irradiance

levels for Avenc6 closed and Castanyadell closed; one irradiance level for Riera Major.

10
Table 5. Effect of atrazine exposure on the photosynthesis of periphyton communities after varied irradiation, from sites with closed canopy cover, ECso

and EClO

a from Guasch and Sabater (1998, Table 6).

Site Irradiation

ECso (J.lg L-ll ECIO (J.lg L-l

) (J.lIDol m-2 S-l)

56 716.06 ± 183.33 270.247 ± 69.449

192 414.11 ± 99.21 55.430 ± 14.235 Avenc6 (closed)

270 526.26 ± 120.78 141.055 ± 33.352

1575 NI Nt

Riera Major 51 521.95 ± 120.78 158.309 ± 18.764

17 129.41 ± 30.20 47.665 ± 11.215

82 498.22 ± 10.78 138.251 ± 3.235 Castanyadell (closed)

258 601.75 ± 159.60 139.761 ± 36.881

1375 Nt Nt

Nt = No inhibition by atrazine detected.

aConverted to /lg L-l by reviewer.

11
1---.

I Ave

3 JI

-~I

I

I "'- -(l) RM~_ J c

ON

coIl-. 2 - -Ave, I

ro I Avo

-e-o - i .......- ...... ~TG

" 0 I

l,,": I

C) I

LJ..J

l , '"

1 I

'·.Co ·1 l '---Avo!

I

!

I l -I

I T I

0

10 100 1000

-2 .1) LCO! (.umol .m . 5

Figure 3. The relationship between light regime during colonization (J-lmol m·2 S·I) and ECso values (J-lmol L·1)

measured at saturating irradiance at the seven sites (Guasch and Sabater 1998). Regression line and

confidence limits.

12
Data Summary Table:

Time Weighted

Magnitude of Nominal Average

Atrazine Day ofStudy Atrazine Did Recovery

Effect Effect Concen- Effect Concentration Occur - ifso, Comments relative to

controls tration Occurred from Day Oto when?

(Ilg/L) When Effect

Occurred

Up to 62% Magnitude of effects

increase, 58% estimated from

decrease, or Not Figures 2 and 3.

no effect applicable Reasons for different

depending on 11 1 (2 hours) Not calculable (only one responses across test

experimental time point sites are uncertain, but

conditions measured) are likely influenced

(site and light by different

regime) environmental

Up to 42% conditions and

increase, 58% presence of different

decrease, or Not species. Atrazineno effect applicable related effects are

depending on 108 1 (2 hours) Not calculable (only one considered to have

experimental time point occurred at all

conditions measured) treatment

(site and light concentrations.

regime)

Change in Up to 200% Statistical test between

photosynthesis increase, 83% treatment and control

decrease, or Not not provided.

no effect applicable Treatment and control

depending on 216 1 (2 hours) Not calculable (only one responses with

experimental time point overlapping error bars

conditions measured) are not considered

(site and light effects (the study

regime) authors do not define

what the error bars

Up to 160% represent).

increase, 95% Magnitude of effects decreased, or Not

was calculated for

no effect applicable each site and light depending on 1078 1 (2 hours) Not calculable (only one regime combination as experimental time point photosynthesis (% of conditions measured) controls) in the (site and light atrazine control (0 regime) Ilg/L) compared to the

atrazine treatment.

Values not proVIded for madlances at less than lIght saturatIOn.

Reviewer Comments:

Atrazine was described as "pure," but no percentage was provided.

13
The use of a solvent was not reported.

The authors reported analyzing atrazine concentrations in the stream water and nominal

concentrations used in the toxicity test, however, no measurements were provided for the toxicity

tests (treatments or controls). Atrazine concentration was below the limit of detection «0.0005

~mol/L or <0.1 07 ~g/L) for all sampling sites. Samples were taken for atrazine measurement

after the periphyton colonization period.

For each light regime, photosynthesis in the atrazine treated and non-atrazine treated

communities (i.e. no atrazine controls) is expressed as a percentage ofthe controls. It is unclear

what constitutes a control for this purpose. It is assumed that these controls did not contain

atrazine. Because photosynthesis (as a % of controls) was 100% or lower for the non-atrazine

control communities (see figures 2 and 3), photosynthesis may have been normalized to

measurements taken at light saturation conditions (i.e., maximum photosynthesis) in samples

without atrazine. Not enough information was provided to be certain.

Saturation irradiance was not clearly presented. The study authors report that saturation

irradiance for all sites was around 50 ~mol m,2 S·1 (table 3) but for the toxicity tests, saturation

irradiance was higher for most ofthe sites (PS % sat as presented in tables 4 and 5). It is not

clear if atrazine exposure affected saturation irradiance or ifthe difference in reported saturation

irradiances for each site had a different meaning. Additionally, the "PS % sat" data for some

sites appears to be inconsistent with results plotted in figures 2 and 3. For instance, table 5 states

that the 56, 192, and 279 ~mol m·

2 S·1 irradiation regimes were saturating irradiances (100%) but

data plotted in figure 3 suggests that only the 279 ~mol m,2 S·1 irradiation regime was saturating

(100% of controls). Not enough information was provided to determine what this difference

indicates.

14
Description of Use in Document: Invalid for the purpose of setting an LOC for atrazine

Rationale for Use: Exposure durations were approximately 2 hours. The purpose ofthis

analysis is to estimate atrazine levels that produce community level effects. The ecological

relevance of a reduction in photosynthesis for a 2-hour duration is uncertain. Therefore, this

study was not used for the purpose <;>f setting a community level effect based LOC because the

time duration was insufficient to determine if community level effects could occur from

exposures used in this study.

Limitations of Study: Atrazine purity was not reported. The method of atrazine dissolution in

the treatments was not described (eg, solvent or no solvent). No measurements were reported for

atrazine concentrations in the toxicity tests (treatments or controls). Finally, the duration of

exposure was extremely short (2hrs).

Primary Reviewer: Lisa Muto, M.S., Staff Scientist, Cambridge Environmental Inc

Secondary Reviewer: Catherine Aubee, Biologist, Environmental Fate and Effects Division

U.S. Environmental Protection Agency

Tertiary Reviewer: Brian Anderson, Biologist, Environmental Fate and Effects Division

U.S. Environmental Protection Agency f,rq-

(/(51 / ~~ /

15