OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460

August 28, 2014 

PC Code: 110902 

MEMORANDUM DP Barcode: 419903

SUBJECT: EFED Registration Review Problem Formulation for Diclofop-methyl 

FROM: N.E. Federoff, Wildlife Biologist 

 Greg Orrick, Environmental Scientist 

 Environmental Risk Branch 2 

 Environmental Fate and Effects Division (7507P) 

THRU: Brian Anderson, Chief 

 R. David Jones, PhD, Senior Agronomist 

 Christina Wendel, Biologist 

 Jean Holmes, DVM, MPH, RAPL 

 Environmental Risk Branch 2 

 Environmental Fate and Effects Division (7507P) 

TO: Marianne Mannix, Chemical Review Manager 

 Patricia Parrott, Branch Chief 

 Risk Management and Implementation Branch III 

 Pesticide Re-Evaluation Division (7508P) 

The Environmental Fate and Effects Division (EFED) has completed the preliminary problem 

formulation (attached) for the ecological risk, environmental fate, endangered species, and 

drinking water assessments to be conducted as part of the registration review of diclofop-methyl. 

The problem formulation describes the preliminary risk hypothesis and the processes that will be 

used during the completion of drinking water and ecological risk assessments in support of 

registration review. This document draws on information from both open literature and studies 

submitted by the registrants in response to data requirements in order to provide an overview of 

the environmental fate and ecological effects associated with the use of diclofop-methyl as well 

as to outline uncertainties regarding residues and taxa of concern. This document also identifies 

additional studies that would be beneficial to complete an ecological risk assessment. Major 

findings include: 

Studies Needed 

 Aerobic aquatic metabolism (835.4300; diclofop-methyl): two systems 

 Anaerobic aquatic metabolism (835.4400; diclofop-methyl): one system 
Page 2 of 50 

 Analytical method in water and associated independent laboratory validation (850.6100; 

diclofop-methyl and its acid): with an LOQ less than 7.5 μg/L (the lowest toxicological 

level of concern) for the ester and its acid. 

 Honeybee toxicity (850.3020 and non-guideline Adult Acute Oral and Larval Toxicity). 

In keeping with the Agency’s proposed new paradigm for determining potential adverse 

effects to insect pollinators from conventional pesticides (USEPA 2012), two additional 

studies are being requested in addition to the acute contact study. An adult acute oral 

toxicity study (following OECD 213) and a larval oral toxicity study (following OECD 

237) are necessary to evaluate the potential for diclofop-methyl to adversely affect bees 

and other pollinators. Also, several of the treated crop areas may be considered attractive 

to honey bees and this is a systemic chemical that is transported throughout the 

plant. Thus, residues may be available to pollinators via pollen and/or nectar. For 

assessment purposes, EFED will use the most current exposure assessment methodology 

to estimate exposures through pollen and nectar, thus EFED is not asking for pollen and 

nectar residue data at this time. 

 Aquatic Plant Toxicity (850.4500 & 850.4550). Aquatic plant testing is required for any 

herbicide that has outdoor non-residential terrestrial uses that may move off-site by 

runoff, by drift, or that is applied directly to water. Only one aquatic plant study has been 

submitted. A study using a non-vascular plant (algae) is needed. 

 Estuarine/Marine Fish and Invertebrate Acute Toxicity (850.1025, 850.1035 and 

850.1075). No data have been submitted regarding acute toxicity to estuarine/marine fish 

or invertebrates. Although applications are prohibited within 100 ft of any water bodies, 

diclofop-methyl is highly acutely toxic to freshwater fish and invertebrates. EFED will 

consider the effectiveness of the buffer in reducing risk to aquatic organisms in the 

preliminary risk assessment. In addition, use on golf courses can occur near estuarine 

areas. Acute studies with the sheepshead minnow, mysid and oyster (shell deposition) 

are needed. 

Major Uncertainties 

 The reapplication interval for uses on golf course turf is not stated on the label. In the 

absence of a stated interval, a 3-day interval will be assumed 

 Uncertainty exists for risk to terrestrial insects (honey bees) because no toxicity data have 

been submitted. Diclofop-methyl is a systemic herbicide and could pose risk to bees. 

 Also, only one aquatic plant toxicity study (growth inhibition using duckweed) has been 

submitted for diclofop-methyl or diclofop acid, as a systemic herbicide toxicity, risk to 

aquatic plants is presumed in the absence of data. 
Page 3 of 50 

Table	of	Contents	

1. Introduction ............................................................................................................................. 4

2. Use Characterization ............................................................................................................... 4

3. Conclusions from Previous Risk Assessments ....................................................................... 6

3.1. Ecological Risk Assessments ........................................................................................... 6

3.2. Drinking Water Exposure Assessments ........................................................................... 7

3.3. Clean Water Act Programs ............................................................................................... 7

3.3.1. Aquatic Life Criteria and Aquatic Life Benchmarks .................................................... 7

3.3.2. Impaired Water Bodies ................................................................................................. 7

4. Environmental Fate and Transport.......................................................................................... 8

4.1. Transformation Products ................................................................................................ 10

5. Receptors............................................................................................................................... 12

5.1. Effects to Aquatic Organisms ........................................................................................ 13

5.2. Effects to Terrestrial Organisms .................................................................................... 14

5.3. Ecological Incidents ....................................................................................................... 15

6. Exposure Pathways of Concern ............................................................................................ 16

7. Analysis Plan ........................................................................................................................ 16

7.1. Stressors of Concern....................................................................................................... 16

7.2. Measures of Exposure .................................................................................................... 17

7.3. Measures of Effect ......................................................................................................... 17

8. Endangered Species Assessments ......................................................................................... 17

9. Endocrine Disruptor Screening Program .............................................................................. 18

10. Preliminary Identification of Data Gaps ............................................................................ 19

10.1. Environmental Fate..................................................................................................... 19

10.2. Ecological Effects ....................................................................................................... 20

11. References .......................................................................................................................... 25

APPENDIX A: Eco and Fate Bibliography for Diclofop-methyl ................................................ 26

APPENDIX B: ECOLOGICAL TOXICITY DATA ................................................................... 39

APPENDIX C: Example of SIP INPUT and OUTPUT ............................................................... 47

APPENDIX D: STIR inputs and outputs ...................................................................................... 49
Page 4 of 50 

1. Introduction 

EFED evaluated the most recent ecological risk assessments for diclofop-methyl in association 

with the updated toxicity, exposure, and usage information to determine if sufficient data are 

available and if further updates are needed to support registration review. Recent risk 

assessments include a Reregistration Eligibility Decision (RED) in 2000. In addition, EFED 

considered the latest Agency science policies and risk assessment methodologies. The structure 

of diclofop-methyl, as well as the chemical names and other identifiers can be found in the 

environmental fate section. 

Diclofop-methyl is a restricted-use herbicide, first registered in 1982, for controlling annual 

grassy weeds in wheat and barley. Diclofop-methyl is a selective systemic herbicide but also has 

contact action. It is absorbed primarily by the leaves, with some absorption by the roots in moist 

soil. It undergoes rapid transformation to diclofop, which is translocated within the plant. It 

destroys the cell membrane, prevents the translocation of assimilates to the roots, reduces 

chlorophyll content and inhibits lipid/fatty acids by biosynthesis. 

Diclofop-methyl is an acetyl CoA carboxylase (ACCase) inhibitor in the aryloxyphenoxypropionate group that includes fenoxaprop-p-ethyl and nine “fop” herbicides (HRAC, 2012). In 

1990, target weeds resistant to diclofop and other ACCase inhibitors began to be observed in 

Oregon (USDA, 1996; Seefeldt et al., 1996). 

2. Use Characterization 

Diclofop-methyl is registered for use on wheat, barley, and closely mowed golf course turf 

(Table 1). Applications are prohibited within 100 feet of any water body. The reapplication 

interval for uses on golf course turf is not stated on the label. In the absence of a stated interval, 

a 3-day interval will be assumed. 

Table 1. Maximum use patterns for current uses of diclofop-methyl 

Product Label 

(EPA Reg. 

No.); 

Formulation 

Active 

Ingredient 

(%) 

Use Site 

Max. 

Single 

App. Rate

(lbs a.i./A)

Max. 

Annual 

App. Rate 

(lbs a.i./A)

App. 

Interval 

(d) 

Application 

Type 

Additional 

Application 

Directions 

Hoelon 3EC 

(264-641); 

Emulsifiable 

Concentrate 

Diclofopmethyl 

(34.7% by 

wt.) 

Winter wheat, spring 

wheat, barley 1.0 1.0 Not applicable

Aerial or 

ground 

Do not apply 

within 100 

feet of any 

water body. 

Illoxan 3 EC 

(432-1231); 

Emulsifiable 

Concentrate 

Diclofopmethyl 

(34.7% by 

wt.) 

Golf courses 

(includes greens, tees, 

fairways, and closely 

mowed roughs) 

1.02 1.53 Not stated

Broadcast 

or spot 

treatment 

Do not apply 

within 100 

feet of any 

water body. 

Figure 1 depicts a national-level summary of the estimated agricultural usage of diclofop-methyl 

in 2011 (USGS, 2014). National agricultural usage of diclofop-methyl peaked in 1996 and 

declined to relatively low levels over the next 12 years. Note that most of the crops listed in the 

figure are not currently registered uses of diclofop-methyl. 
Page 5 of 50 

Figure 1. Agricultural Usage of Diclofop-methyl in 2011 (USGS, 2014)
Page 6 of 50 

3. Conclusions from Previous Risk Assessments 

3.1. Ecological Risk Assessments 

The Agency has previously conducted ecological risk assessments on diclofop-methyl that serve 

as a basis for this scoping document, including the Reregistration Eligibility Decision (RED). 

The following are conclusions from the previous assessment. 

Diclofop-methyl is practically non-toxic to birds on an acute basis and poses minimal acute risk. 

Chronic toxicity to birds is uncertain because tests were not conducted at high enough 

concentrations, but based on the available information, chronic risk to birds is not likely to be a 

primary concern. Toxicity data indicate that diclofop-methyl is more toxic to mammals than to 

birds, both on an acute and chronic basis. Diclofop-methyl is moderately toxic to mammals on 

an acute basis. It does not pose a high acute risk to mammals except in the case of repeated spot 

applications to turf. Diclofop-methyl does pose a potential chronic risk to mammals. Risk 

quotients for chronic risk to mammals are as high as 8.0 for a single application at 1 lb ai/A, and 

up to 11.0 for repeated spot applications. Previous risk assessments resulted in RQs above 

established levels of concern (LOC) for threatened and endangered species of mammals. 

Diclofop-methyl is highly toxic on an acute basis to freshwater fish and invertebrates. The 

primary degradation product, diclofop acid, is only slightly toxic to freshwater fish. 

Supplemental information also suggests that diclofop-methyl is highly toxic to the eastern oyster. 

In a freshwater fish life-cycle test, diclofop-methyl affected larval growth at 15 ppb (NOAEC = 

7.5 ppb). In a waterflea life-cycle test, diclofop-methyl affected reproduction at 166 ppb 

(NOAEC = 64 ppb). However, because the environmental fate characteristics of diclofop-methyl 

do not favor transport to surface water, environmental concentrations are not expected to reach 

toxic levels. Thus, acute and chronic risk is minimal to freshwater fish and invertebrates. 

Like most herbicides, diclofop-methyl poses a risk to some terrestrial non-target plants, 

especially monocots (grasses and sedges). Spray drift and runoff poses a high risk to non-target 

terrestrial plants. The risk assessment for terrestrial plants indicated that risk is low from 

exposure of foliage to spray drift, but high from exposure of plant roots from a combination of 

runoff and spray drift. Risk quotients for soil exposure were 4.67 to 5.00 for plants in dry areas 

and 9.17 to 12.50 for semi-aquatic areas. Phytotoxicity data show that diclofop-methyl is 

selectively toxic to monocotyledonous plants (i.e., grasses and sedges), but not very toxic to 

dicotyledonous plants (i.e., broadleaf plants). This is expected since the target plants of this 

herbicide are grass weeds. If risk quotients were based on toxicity to dicotyledonous plants, they 

would not exceed the level of concern. The use of diclofop-methyl poses a high risk to nontarget 

grasses and sedges from exposure in the soil. 

Being an herbicide, diclofop-methyl and its acid were expected to be toxic to aquatic plants. 
Page 7 of 50 

3.2. Drinking Water Exposure Assessments 

In 1999, a drinking water exposure assessment for diclofop-methyl was conducted to support the 

Reregistration Eligibility Decision (RED) (USEPA, 1999). Upper bound exposure estimates 

were 1.47 μg/L (1-in-10-year peak) and 0.097 μg/L (10-year mean) for surface water and 0.067 

μg/L for ground water. Surface and ground water monitoring data were located in STORET 

for Minnesota and Idaho; all detections were <0.1 μg/L. A prospective ground water 

monitoring study also indicated concentrations were <0.1 μg/L, the limit of quantitation.

3.3. Clean Water Act Programs 

3.3.1. Aquatic Life Criteria and Aquatic Life Benchmarks 

The Clean Water Act requires the Agency to publish water quality criteria that accurately reflect 

the latest scientific knowledge on the kind and extent of all identifiable effects on health and 

welfare that might be expected from the presence of pollutants in any body of water, including 

ground water. While these recommended criteria do not, in themselves, impose any 

requirements, states and authorized tribes can use them to develop water quality standards. An 

Aquatic Life Ambient Water Quality Criteria document has not been published for diclofopmethyl (see url: http://www.epa.gov/waterscience/criteria/). 

The Office of Pesticide Programs (OPP) publishes aquatic life benchmarks for freshwater species 

based on toxicity values for the most sensitive species from the most recent risk assessments. 

However, aquatic life benchmarks have not been published for diclofop-methyl or its acid (see 

url: http://www.epa.gov/oppefed1/ecorisk_ders/aquatic_life_benchmark.htm#benchmarks). 

3.3.2. Impaired Water Bodies 

Diclofop-methyl is not identified as a cause of impairment for any water bodies listed as 

impaired under section 303(d) of the Clean Water Act, based on information provided at 

http://iaspub.epa.gov/tmdl_waters10/attains_nation_cy.cause_detail_303d?p_cause_group_id=88

5. 

No Total Maximum Daily Load (TMDL) criteria have been developed for diclofop-methyl, 

based on information provided at 

http://iaspub.epa.gov/tmdl_waters10/attains_nation.tmdl_pollutant_detail?p_pollutant_group_id

=885&p_pollutant_group_name=PESTICIDES. More information on impaired water bodies and 

TMDLs can be found at http://www.epa.gov/owow/tmdl/. The Agency invites submission of 

water quality data for this pesticide. To the extent possible, data should conform to the quality 

standards in Appendix A of the OPP Standard Operating Procedure: Inclusion of Impaired 

Water Body and Other Water Quality Data in OPP’s Registration Review Risk Assessment and 

Management Process (see: 

http://www.epa.gov/oppsrrd1/registration_review/water_quality_sop.htm), in order to ensure 

they can be used quantitatively or qualitatively in pesticide risk assessments. 
Page 8 of 50 

4. Environmental Fate and Transport 

Diclofop-methyl (CAS no. 51338-27-3; chemical structure in Table 3) is an ester that is rapidly 

hydrolyzed to its acid by microbial activity. Aerobic and anaerobic biodegradation half-lives 

range from <1 to 6 days depending on pH and other conditions. Diclofop-methyl is stable to 

abiotic hydrolysis at pH 5, but hydrolyzes to its acid in weeks in neutral conditions and within 

days in alkaline conditions. The compound is photolyzed relatively slowly with respect to 

biodegradation rates. 

Diclofop acid biodegrades with half-lives of weeks to months to HOE 30418 (up to 11% in 

aerobic conditions, 52% in anaerobic conditions), residues that are well sorbed to soil (11-69%), 

and carbon dioxide (1.4-29%). Unextracted residues in the laboratory studies are considered 

well sorbed to soil and not readily available because extraction solvents with a range of dielectric 

constants (from water to benzene) could not extract them under a range of conditions. 

Diclofop-methyl is non-volatile under field conditions (vapor pressure of 1.9 × 10-7 torr at 25°C). 

The compound is soluble in water at up to 0.39 mg/L (at 20°C) and lipophilic, with a logarithm 

of octanol-water partition coefficient (log KOW) of 4.77, indicating that bioaccumulation is a 

concern. A laboratory study shows that bioaccumulation in fish is moderate, with a whole fish 

BCF of 430-450. However, 65-73% of accumulated residues depurated within one day and the 

instability of the ester is expected to limit its aquatic exposure.

In soil, KOC values range from 11,000 to 25,000 L/kg, indicating that diclofop-methyl is “hardly 

mobile” in soil (FAO, 2014). However, diclofop acid is moderately mobile in soil (KOC values 

of 115 to 178 L/kg; MRID 42347801). Residues of diclofop-methyl and/or its acid leached to 

the 6-12” depth in a field study, indicating that diclofop residues may have increased mobility in 

some soils. However, diclofop-methyl and acid residues were not observed in soil pore water or 

ground water during a two-year prospective ground water (PGW) monitoring study, indicating 

that residues are not mobile in some soils that are vulnerable to leaching (MRID 44532501). 

Important means of transport off of agricultural fields following application will include spray 

drift and runoff of residues dissolved or sorbed to suspended solids. Field dissipation data 

indicate that diclofop-methyl does not persist on the field (dissipation half-life of 3.5 days) but its 

acid is moderately persistent (dissipation half-life of 28 days). Table 2 summarizes chemical 

properties and environmental fate parameters of diclofop-methyl (and not its acid, unless 

otherwise stated). 

Table 2. Chemical Properties and Environmental Fate Parameters of Diclofop-methyl 

Parameter Value Source

Selected Physical/Chemical Parameters

Molecular mass (molecular formula) 341.19 g/mol (C16H14Cl2O4) (Calculated)

Vapor pressure (25°C) 1.9 x 10-7 torr MRID 47973609

Aqueous solubility (20C) 0.39 mg/L MRID 47973608

Henry’s Law Constant (25°C) 2.2 x10-7 atm-m3/mol (Calculated)
Page 9 of 50 

Parameter Value Source

Log octanol-to-water partition 

coefficient (log KOW)

4.77 MRID 47973607 

Dissociation constant (pKa) None MRID 48100402

Persistence in Water

Hydrolysis half-life 21°C: 

2,650 d (pH 5), 21 d (pH 7), 1.9 d (pH 9) 

MRID 71389 

25°C: 

363 d (pH 5), 32 d (pH 7), 0.52 d (pH 9) 

MRID 41573309 

Aqueous photolysis half-life (25C) 22 d MRID 41573307 

Anaerobic aquatic metabolism halflife (24-25C) <1 d (pH 7.7-8.3) MRID 40806307 

Persistence in Soil

Aerobic soil metabolism half-life 

(20-22°C) 

2.1 d (IORE A; biphasic degradation; pH 6.8) 

6.4 d (IORE A; biphasic degradation; pH 5.2) 

MRID 38861 

<1 d (4 soils of pH 5.0-7.2) MRID 41573310 

Photolysis half-life in soil (25C) 100 d MRID 41573308 

Mobility

Organic carbon-normalized soilwater partition coefficients (KOC) 

11,000, 14,000, 15,000, 25,000 L/kgOC MRID 40806308 

Field Dissipation 

Terrestrial field dissipation half-life; 

leaching depth (ester plus acid) 

CA Hanford sandy loam soil; pH 6.3: 

2.6 d (barley crop), 3.5 d (bare soil) 

0-6” depth (barley), 6-12” depth (bare soil) 

MRID 42252101 

Prospective ground water 

monitoring results 

Diclofop-methyl and its acid were not 

detected (LOD=1 μg/L) in soil pore water or 

ground water up to 2 years after application 

MRID 44532501 

Activated sludge metabolism No effects were observed for activated sludge 

biota at concentrations 0.1-100 mg/L 

MRID 107473 

Fish Bioconcentration 

Fish bioconcentration factors 

(steady-state, total residues); 

depuration rate 

54-64 (edible), 930-1000 (inedible), 

430-450 (whole fish); 

65-73% depuration in 1 day 

[MRID 45878201] B

A IORE is the “indeterminate-order rate equation” kinetics model. 

B Studies with MRIDs in brackets are provisional until reviewed.
Page 10 of 50 

4.1. Transformation Products 

Diclofop acid has a pKa of 3.43, indicating that it is anionic in environmental conditions (MRID 42461501). The ac

at pH 5 and 0.70 at pH 7, indicating that bioaccumulation is not a concern (MRID 40806306). It is soluble in water 

7, 22°C (MRID 40806302). As stated above, it is moderately mobile in soil and biodegrades with half-lives of week

3 lists the degradates of diclofop-methyl, including their maximum and final concentrations. Major degradates incluHOE 30418, carbon dioxide, residues that are well sorbed to soil, and an unidentified compound similar to diclofop

Table 3. Diclofop-methyl and Its Environmental Transformation Products. A

Code Name/ Synonym Chemical Name Chemical Structure Study Guideline MRID System 

PARENT

Diclofop-methyl HOE 23408 

IUPAC: 2-(4-(2',4'-dichlorophenoxy)-phenoxy)-methylpropanoate CAS No.: 51338-27-3 Formula: C16H14Cl2O4

MW: 341.19 g/molSMILES: C1=C(C=C(C(=C1)OC2=CC=C(C=C2)OC(C(=O)OC)C)Cl)Cl 

MAJOR (>10%) TRANSFORMATION PRODUCTS 

Diclofop Diclofop acid HOE 21079 

IUPAC: 2-(4-(2',4'-dichlorophenoxy)-phenoxy)-propanoic acid Formula: C15H12Cl2O4

MW: 327.16 g/molSMILES: C1=C(C=C(C(=C1)OC2=CC=C(C=C2)OC(C(=O)O)C)Cl)Cl

835.2120 

71389 pH 7 

pH 9 

41573309

pH 5 

pH 7 pH 9 

835.4100 

38861 sand 

sandy clay 

41573310

sandy loam 

silt loam 

loamy sand sandy loam 

835.4400 40806307 pond system 
Page 11 of 50 

Code Name/ Synonym Chemical Name Chemical Structure Study Guideline MRID System HOE 30418 4-(2,4-dichlorophenoxy)-phenol 

Formula: C12H8Cl2O2

MW: 255.10 g/molSMILES:C1=C(C=C(C(=C1)OC2=CC=C(C=C2)O)Cl)Cl

835.4100 

38861 sand 

sandy clay 

41573310

sandy loam 

silt loam 

loamy sand sandy loam 

835.4400 40806307 pond system 

Unidentified compounds 

NA 

NA 835.2240 41573307 irradiated 

Carbon dioxide IUPAC: Carbon dioxide 

Formula: CO2

MW: 44 g/mol

SMILES: C(=O)=O 

835.2240 41573307 irradiated 835.2410 41573308 irradiated 835.4100 

38861 sand 

sandy clay 

41573310

sandy loam 

silt loam 

loamy sand sandy loam 

835.4400 40806307 pond system 

Unextracted residues 

NA NA 835.4100 

38861 sand 

sandy clay 

41573310

sandy loam 

silt loam 

loamy sand sandy loam 

835.4400 40806307 pond system 

A AR means “applied radioactivity”. MW means “molecular weight”. LOD means “limit of detection”. NA means “not applicable”. B Chemical is structurally similar to diclofop-methyl.
Page 12 of 50 

5. Receptors 

Consistent with EFED’s standard methodology, the risk assessment for diclofop-methyl will rely 

on a surrogate species approach. Toxicological data generated from surrogate test species, which 

are intended to be representative of broad taxonomic groups, are used to extrapolate to potential 

effects on a variety of species (receptors) included under these taxonomic groupings. 

The Agency evaluates the potential for adverse effects as a result of diclofop-methyl usage. The 

most sensitive endpoint for each taxon is used for RQ calculations. Assessment endpoints 

include direct toxic effects on the survival, reproduction, and growth of terrestrial and aquatic 

life, as well as indirect effects, such as reduction in prey base and/or modification of habitat. The 

evaluated taxa include freshwater fish, freshwater aquatic invertebrates, birds, small mammals, 

terrestrial invertebrates, algae, and terrestrial plants. 

Acute (short-term) and chronic (long-term) toxicity information is characterized based on 

registrant-submitted studies. Other sources of information, including use of the acute probit dose 

response relationship to establish the probability of an individual effect and reviews of the 

Ecological Incident Information System (EIIS), are conducted to further refine the 

characterization of potential ecological effects associated with exposure to diclofop-methyl. 

Diclofop-methyl is highly toxic on an acute basis to freshwater fish and invertebrates. 

Supplemental information suggests that diclofop-methyl may be highly toxic to the eastern 

oyster; however, there are no estuarine marine fish or invertebrate data available. In a chronic 

test, diclofop-methyl affected larval fish growth at 15 ppb (NOAEC=7.5 ppb). In a waterflea lifecycle test, diclofop-methyl affected reproduction at 166 ppb (NOAEC=64 ppb). 

The primary degradation product, diclofop acid, is only slightly toxic to freshwater fish. A study 

with the rainbow trout provides information on the free acid metabolite of diclofop-methyl. The 

96-hr LC50 was determined to be 21.9 ppm (19.3-24.9) with an NOAEC of 13.5 ppm. 

Diclofop-methyl is practically non-toxic to birds on an acute basis. There were no chronic effects 

to birds (NOAEL=200 ppm in both studies). Diclofop-methyl is moderately toxic to mammals 

on an acute basis. Diclofop-methyl is toxic to terrestrial plants, especially monocots (grasses and 

sedges). 

Uncertainty exists for risk to terrestrial invertebrates (honey bee) because no toxicity data are 

available. Diclofop-methyl is a systemic herbicide and could pose risk to bees. Also, only one

aquatic plant study (growth inhibition using duckweed) has been submitted for diclofop-methyl 

or diclofop acid. Results indicate no inhibition above 50% (LC50 for frond number was 1.3 

mg/L time-weighted average mean-measured concentrations) with an NOAEC of 1.0 mg/L timeweighted average mean-measured concentration. 

Table 4 and Table 5 provide a summary of the aquatic and terrestrial taxonomic groups, 

respectively, and most sensitive surrogate species tested to characterize the potential acute and 

chronic ecological effects of diclofop-methyl. 
Page 13 of 50 

5.1. Effects to Aquatic Organisms 

Table 4. Summary of the Most Sensitive Endpoints from Aquatic Toxicity Studies for 

Diclofop-methyl 

Taxonomic 

Group 

Study 

Type 

Surrogate Species Toxicity 

Value 

(μg ai/L) 

Acute 

Toxicity 

Classification 

+Source 

Freshwater fish 

Acute 

Bluegill sunfish 

(Lepomis 

macrochirus)

96 hr LC50 = 

150 ppb (0.15 

ppm) 

Highly toxic 

41606301 

Smith & 

Schweitzer, 

1990 

Chronic 

Fathead minnow 

(Pimephales 

promelas)

NOAEC= 7.5 

ppb (0.075 

ppm) 

(Based on wet 

weight) 

N/A 43284601 

Dionne, 1994 

Freshwater 

invertebrates 

Acute Water Flea 

(Daphnia magna) 

48 hr EC50 = 

370 ppb (0.37 

ppm) 

Highly toxic 

41606304 

Smith & 

Schweitzer, 

1990 

Chronic Water Flea 

NOAEC= 64 

ppb (0.064 

ppm) 

N/A 41737902 

Smith, 1990 

Estuarine/marine 

fish 

Acute 

Sheepshead Minnow 

(Cyprinodon 

variegatus) 

No data N/A N/A 

Chronic Sheepshead Minnow No data N/A NA 

Estuarine/marine 

invertebrates 

Acute 

Mysid Shrimp 

(Americamysis 

bahia) 

No data N/A N/A 

Chronic Mysid Shrimp No data N/A N/A 

Aquatic plants 

and algae 

Vascular Duckweed 

(Lemna gibba) 

No inhibition 

>50% 

(LC50 for 

frond number 

was 1.295 with 

an NOAEC of 

1.0 mg/L 

Time-weighted 

average 

(TWA) 

concentrations) 

Supplemental 45541703 

Nonvascular 

Green Algae 

(Pseudokirchneriella 

subcapitata) 

No data N/A N/A 

+ for study classifications see Appendix B
Page 14 of 50 

A toxicity study with the rainbow trout provides information on the free acid metabolite of 

diclofop-methyl. The 96-hr LC50 was determined to be 21.9 ppm (19.3-24.9) with an NOAEC of 

13.5 ppm, which is less toxic than the parent compound by two orders of magnitude. 

5.2. Effects to Terrestrial Organisms 

Table 5. Summary of the Most Sensitive Endpoints from Terrestrial Toxicity Studies for 

Diclofop-methyl 

Taxonomic 

Group 

Study 

Type 

Surrogate 

Species 

Toxicity Value 

(all units in terms 

of measured active 

ingredient) 

Acute 

Toxicity 

Classification 

+Source 

Birds 

Acute 

Northern 

Bobwhite 

(Colinus 

virginianus)

Acute Oral LD50 > 

2250 mg ai/kg-bw Practically 

non-toxic 

40072903 

Hinken et al., 

1986 

Sub-acute 

dietary 

Northern 

Bobwhite 

(Colinus 

virginianus)

Acute Dietary LC50 

>13,000 ppm 

Practically 

non-toxic 

Acc. No. 

097117 

Roberts,1977

Chronic 

Northern 

Bobwhite 

(Colinus 

virginianus)

NOAEL = 200 ppm 

No effects N/A 

Acc. No. 

098297 and 

243472 

Mallard duck 

(Anas 

platyrhynchos) 

NOAEL = 200 ppm 

No effects N/A

Acc. No. 

098297 and 

243472 

Mammals 

Acute Oral 

Laboratory rat 

(Rattus 

norvegicus) 

LD50 = 568 mg/kgbw Slightly toxic 097107 

Acute 

Inhalation 

Laboratory rat 

(Rattus 

norvegicus) 

LC50 >1.36 mg/L N/A *Footprint 

database 

Chronic 

Laboratory rat 

(Rattus 

norvegicus) 

NOAEL = 30 ppm N/A 097111 

Insects Acute 

contact 

Honey bee 

(Apis mellifera 

L.) 

48 hr LD50 

>100ug/bee 

Practically 

non-toxic *Footprint 

database 

Terrestrial Soil 

Invertebrate Acute 

Earthworm 

(Lumbricus 

terrestris) 

14 da LC50 >500 N.A *Footprint 

database 

Terrestrial 

plants nontarget 

Seedling 

Emergence 

Lettuce (Lactuca 

sativa) 

Dicot 

EC25 = 0.792 lb ai/A 

Plant dry weight N/A 

41606306 

Chetram, 

1990 

Ryegrass 

(Lolium sp. ) 

Monocot 

EC25 = 0.012 lb ai/A 

Plant height N/A 

41606306 

Chetram, 

1990 
Page 15 of 50 

Taxonomic 

Group 

Study 

Type 

Surrogate 

Species 

Toxicity Value 

(all units in terms 

of measured active 

ingredient) 

Acute 

Toxicity 

Classification 

+Source 

Vegetative 

Vigor 

Lettuce (Lactuca 

sativa) 

Dicot 

EC25 = 1.0 lb ai/A 

Plant dry weight N/A 

41606305 

Chetram, 

1990 

Ryegrass & 

Corn (Zea mays) 

Monocot 

EC25 = 0.10 lb ai/A 

Plant height N/A 

41606305 

Chetram, 

1990 

*http://www.eu-footprint.org/ppdb.html 

+ for study classifications see Appendix B

5.3. Ecological Incidents 

The ecological incident information system (EIIS) is an OPP database that houses ecological 

incidents that have been reported to the Agency. When available, EIIS includes date and 

location of an incident, type and magnitude of effects observed in various species, use(s) of 

pesticides known or suspected of contributing to the incident, and results of any chemical residue 

analysis or other analyses conducted during incident investigation. EIIS incidents are 

categorized according to the certainty that the incident resulted from pesticide exposure. The 

Avian Monitoring System (AIMS) is a database administered by the American Bird Conservancy 

that contains publicly available data on reported avian incidents involving pesticides. Many of 

the incidents listed in this database are also in the EIIS. 

Reported incidents from the EIIS database included damage to non-target terrestrial plants and 

mortality to fish. 

Table 6. EIIS Pesticide Summary Report for Diclopfop-methyl (110902) 

 Incident# Date County, 

State 

Certainty Legal. Appl. 

Method 

Species Response Rt. 

Exposure 

Magnitude 

AQUATIC 

 

Soybean 

I003826-

017 

8/15/1994 Rowan, NC 2 RU Unknown 

fish 

Mortality Runoff Unknown 

PLANTS 

 N/R I013636-

027 

2/4/2002 Washington, 

OR 

2 UN tulips Plant 

damage 

Treated 

directly 

6 acres 

Wheat, 

spring 

I013942-

001 

3/1/2003 San Diego, 

CA 

3 MA Spray Wheat, 

spring 

Plant 

damage 

Treated 

directly 

60 acres 

Wheat, 

winter 

I013103-

033 

4/19/2002 Monroe, AR 2 RU Broadcast Wheat Plant 

damage 

Treated 

directly 

All 50 acres 

 I013942-

005 

1/29/2003 Phillips, AR 2 RU Broadcast Wheat, 

winter 

Plant 

damage 

Treated 

directly 

1785 acres 

 I013942-

004 

2/18/2003 Lonoke, AR 2 RU Broadcast Wheat, 

winter 

Plant 

damage 

Treated 

directly 

105 acres 

 I013942-

003 

3/14/2003 Yolo, CA 2 RU Spray Wheat, 

winter 

Plant 

damage 

Treated 

directly 

78 acres 

 I013942-

002 

3/4/2003 Craighead, 

AR 

2 RU Spray Wheat, 

winter 

Plant 

damage 

Treated 

directly 

150 acres 

Certainty code: 0=Unrelated, 1=Unlikely, 2=Possible, 3 =Probably, 4=Highly Probable 

Legality Code: RU=Registered Use, M=Misuse, MA=Misuse (Accidental), MI=Misuse (Intentional), U=Unknown 
Page 16 of 50 

Terrestrial Plants 

Three possible incidents in Arkansas were reported in 2003, all involving plant damage to 2040 

acres of winter wheat and all from registered use applications (I013942-002, -004, -005). Also in 

2003, 78 acres of winter wheat was possibly damaged in Yolo CA (I013942-003). 

In another incident (I013942-001), also in 2003, 60 acres of spring wheat was damaged in San 

Diego CA. This incident was classified as “probable” but was likely an accidental misuse. 

In 2002, 6 acres of tulips were damaged in Washington OR under possible incident I013636-027. 

Fish 

One incident involving fish was reported. The incident (I003826-017) occurred in Rowan NC in 

1994 where an undetermined number of fish were killed after a runoff event after a registered use 

application to soybeans. The reported likelihood was “possible.” 

6. Exposure Pathways of Concern 

The conceptual model will consider the parent compound and its acid for the drinking water 

exposure assessment and ecological risk assessment. 

The environmental fate properties and use patterns of diclofop-methyl indicate that direct spray, 

spray drift, and runoff represent potential transport mechanisms of diclofop residues to aquatic 

and terrestrial organisms. 

Drinking water and inhalation exposure pathways were screened using the SIP (Screening 

Imbibition Program) and STIR (Screening Tool for Inhalation Risk) screening methods and were 

found not to be exposure pathways of concern (no LOC exceedances are expected). Appendix C 

and D contain details on the SIP and STIR analyses. SIP and STIR are described in detail at: 

http://www.epa.gov/oppefed1/models/terrestrial/index.htm. 

7. Analysis Plan 

7.1. Stressors of Concern 

Ecological Risk Assessment 

The stressor of ecological concern for terrestrial and aquatic organisms is diclofop-methyl only, 

with the exception that diclofop acid is of concern for terrestrial plants. Diclofop acid is two 

orders of magnitude less toxic to the Rainbow Trout than diclofop-methyl. Additional 

ecotoxicity data on diclofop acid are not available. Ecotoxicity data for cyhalofop-butyl, which 

is in the same chemical class (aryloxy-phenoxy-propionates), and cyhalofop acid indicate that 

the acid is two orders of magnitude less toxic than the parent compound to Bluegill Sunfish. 

However, the toxicity of the acid is similar to that of the parent for corn and barnyard grass. 

Therefore, the cyhalofop acid is a residue of concern for terrestrial plants, especially monocots. 

Also, ECOSAR (v.1.11) results indicate that diclofop acid is estimated to be much less toxic to 

aquatic organisms than diclofop-methyl. These lines of evidence indicate that the degradates of 

diclofop-methyl are likely to be much less toxic than the parent compound to aquatic and 
Page 17 of 50 

terrestrial organisms, with the possible exception of terrestrial plants, especially monocots. The 

diclofop-methyl residues of concern may be reevaluated pending receipt and review of additional 

environmental fate and toxicity data.

Drinking Water Exposure Assessment 

The drinking water exposure assessment conducted to support human health risk assessment of 

diclofop-methyl will incorporate model estimates of diclofop-methyl residues of concern, which 

are the parent compound and its acid (USEPA, 2000), in surface and ground waters. Exposure 

estimates reported for potential acute, chronic, and cancer assessment are the 1-in-10-year peak, 

1-in-10-year annual mean, and 30-year mean in a vulnerable reservoir with a drinking water 

intake. The diclofop-methyl residues of concern may be reevaluated pending receipt and review 

of additional environmental fate and toxicity data. 

7.2. Measures of Exposure 

EFED will use standard available models to evaluate potential exposures to aquatic and 

terrestrial organisms as described at http://www.epa.gov/pesticides/science/models_db.htm. For 

surface water, the measure of exposure for acute risks is the 1-in-10-year peak concentration at a 

site more vulnerable than 90% of sites where a pesticide use site occurs. For chronic risks, the 

measures of exposure are 1-in-10-year 21-day and 60-day means. For terrestrial risks the 

measure of exposure is the peak exposure on (and at the edge of) the field. 

7.3. Measures of Effect 

Toxicity data presented in Section 4 of this problem formulation will be used to calculate risk 

quotients. Any additional information submitted by the registrant or found in the open literature 

prior to conduct of the risk assessment will also be considered. The open literature studies are 

identified using EPA’s ECOTOXicology database (ECOTOX) (USEPA, 2007c), which employs 

a literature search engine for locating chemical toxicity data for aquatic life, terrestrial plants, 

and wildlife. The evaluation of both sources of data can also provide insight into the direct and 

indirect effects of pesticides on biotic communities from loss of species that are sensitive to the 

chemicals and from changes in structure and functional characteristics of the affected 

communities. 

8. Endangered Species Assessments 

Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), the 

Agency will evaluate risks to federally listed threatened and/or endangered (listed) species from 

registered uses of pesticides in registration review. The process for evaluating potential risks to 

listed species is further described at 

http://www.epa.gov/oppfead1/endanger/litstatus/riskasses.htm. 
Page 18 of 50 

9. Endocrine Disruptor Screening Program 

As required by FIFRA and FFDCA, EPA reviews numerous studies to assess potential adverse 

outcomes from exposure to chemicals. Collectively, these studies include acute, subchronic and 

chronic toxicity, including assessments of carcinogenicity, neurotoxicity, developmental, 

reproductive, and general or systemic toxicity. These studies include endpoints which may be 

susceptible to endocrine influence, including effects on endocrine target organ histopathology, 

organ weights, estrus cyclicity, sexual maturation, fertility, pregnancy rates, reproductive loss, 

and sex ratios in offspring. For ecological hazard assessments, EPA evaluates acute tests and 

chronic studies that assess growth, developmental and reproductive effects in different 

taxonomic groups. As part of its most recent registration decision, EPA reviewed these data and 

selected the most sensitive endpoints for relevant risk assessment scenarios from the existing 

hazard database. However, as required by FFDCA section 408(p), diclofop-methyl is subject to 

the endocrine screening part of the Endocrine Disruptor Screening Program (EDSP). 

EPA has developed the EDSP to determine whether certain substances (including pesticide 

active and other ingredients) may have an effect in humans or wildlife similar to an effect 

produced by a “naturally occurring estrogen, or other such endocrine effects as the Administrator 

may designate.” The EDSP employs a two-tiered approach to making the statutorily required 

determinations. Tier 1 consists of a battery of 11 screening assays to identify the potential of a 

chemical substance to interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal 

systems. Chemicals that go through Tier 1 screening and are found to have the potential to 

interact with E, A, or T hormonal systems will proceed to the next stage of the EDSP where EPA 

will determine which, if any, of the Tier 2 tests are necessary based on the available data. Tier 2 

testing is designed to identify any adverse endocrine-related effects caused by the substance, and 

establish a dose-response relationship between the dose and the E, A, or T effect. 

Under FFDCA section 408(p), the Agency must screen all pesticide chemicals. Between 

October 2009 and February 2010, EPA issued test orders/data call-ins for the first group of 67 

chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. A second list 

of chemicals identified for EDSP screening was published on June 14, 20131

 and includes some 

pesticides scheduled for registration review and chemicals found in water. Neither of these lists 

should be construed as a list of known or likely endocrine disruptors. 

Diclofop-methyl is on List 1 for which EPA has received all the required Tier 1 assay data. The 

Agency is currently reviewing all assay data received for the appropriate List 1 chemicals and 

planning to make the conclusions of those reviews available in early 2015. For further 

information on the status of the EDSP, the policies and procedures, the lists of chemicals, future 

lists, the test guidelines and the Tier 1 screening battery, please visit our website.2

 

 

1

 See http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0477-0074 for the final second list of 

chemicals. 2

 http://www.epa.gov/endo/ 
Page 19 of 50 

10. Preliminary Identification of Data Gaps 

10.1. Environmental Fate 

Table 7 and Table 8 identify environmental fate studies by their Master Record Identification 

(MRID) number that offer data for each guideline requirement, as well as study classifications 

and whether or not further data are needed in order to support risk assessment. 

Table 7. Submitted Environmental Fate Data for Diclofop-methyl 

OCSPP 

Guideline 

Data 

Requirement 

Submitted Studies 

(MRID) 

Study 

Classifications

Sufficient 

for 

EFED? 

Current Additional Data Need 

835.2120 Hydrolysis Acc. 97120 Unacceptable Yes -- 

71389 Acceptable 

41573309 Acceptable 

835.2240 Aqueous 

photolysis 

107471 Unacceptable Yes -- 

41573307 Acceptable 

835.2410 Soil photolysis 107470/87811 Unacceptable Yes -- 

41573308 Acceptable 

835.4100 Aerobic soil 

metabolism 

38861 Supplemental Yes -- 

87826 Unacceptable 

41573310 Supplemental 

835.4200 Anaerobic soil 

metabolism 

Acc. 97118 Non-guideline Yes -- 

835.4300 Aerobic aquatic 

metabolism 

(no studies) -- No A guideline-compliant study of two 

sediments and their associated waters

is needed. 

835.4400 Anaerobic 

aquatic 

metabolism 

87826 Unacceptable No A guideline-compliant study of one 

sediment and its associated water is 

needed. 40806307 Acceptable 

42734201 Unacceptable 

835.1230 

835.1240 

Adsorption/ 

desorption and 

leaching 

40520301 Supplemental Yes -- 

40806308 Acceptable 

42347801 Unacceptable 

835.6100 Terrestrial field 

dissipation 

87824/87825 Unacceptable Yes -- 

87828 Unacceptable 

156479/40520302/ 

40806309 

Unacceptable 

42252101 Supplemental 

835.6200 Aquatic field 

dissipation 

45695, 45696, 45697, 

84656, 87837, 87808, 

134716, 134717 

Pre-GLP * 

835.7100 Prospective 

ground water 

monitoring 

44532501 Acceptable Yes -- 

850.1730 Fish 

bioconcentration 

84654, 87812 Pre-GLP * Yes -- 

41996903 Unacceptable 

45878201 Supplemental 
Page 20 of 50 

OCSPP 

Guideline 

Data 

Requirement 

Submitted Studies 

(MRID) 

Study 

Classifications

Sufficient 

for 

EFED? 

Current Additional Data Need 

850.6100 Analytical 

method in water 

(no reports) -- No An initial and an independent 

laboratory validation report are 

needed for an analytical method in 

water for the ester and its acid with 

an LOQ less than 7.5 μg/L (the 

lowest toxicological level of 

concern). 

* “Pre-GLP” means that the study predates the 40 CFR Part 160 regulations and is not likely to be acceptable 

according to current guideline standards. 

Table 8. Submitted Environmental Fate Data for Diclofop Acid 

OCSPP 

Guideline 

Data 

Requirement 

Submitted Studies 

(MRID; Degradate)

Study 

Classifications

Sufficient 

for EFED? Current Additional Data Need 

835.2240 Aqueous 

photolysis 

Acc. 244465 Unacceptable Yes An aqueous photolysis study is not 

needed. 

835.2410 Soil photolysis Acc. 244465 Unacceptable Yes A soil photolysis study is not 

needed. 

835.1230 Adsorption/ 

desorption 

40806308 Acceptable Yes -- 

42347801 Supplemental 

Environmental fate data gaps for diclofop-methyl include an aerobic aquatic metabolism study 

(OCSPP 835.4300), an anaerobic aquatic metabolism study (835.4400) of one system, and an 

analytical method in water (OCSPP 850.6100) and associated independent laboratory validation. 

The aquatic metabolism data are needed to estimate aquatic exposure from residues that cross the 

100-foot buffer to reach water bodies. The amounts of diclofop-methyl and its degradates that 

may occur in aquatic systems are uncertain with only one anaerobic aquatic metabolism half-life 

and no aerobic aquatic metabolism half-lives. In the absence of additional data, conservative 

assumptions would be made regarding the degradation of diclofop-methyl in aquatic systems. 

The analytical method in water is needed to support potential monitoring. 

Additional aqueous photolysis and soil photolysis studies are not needed for diclofop acid mainly 

because the compound is not a residue of concern for aquatic organisms. 

10.2. Ecological Effects 

Table 9 and Table 10 identify ecological effects studies by MRID that offer data for each 

guideline requirement, as well as study classifications and whether or not further data are needed 

in order to support risk assessment. Rationale for the additional data requested is presented 

below the tables. 
Page 21 of 50 

Table 9. Submitted Aquatic Ecological Effects Data for Diclofop-methyl

OCSPP 

Guideline 

Data 

Requirement 

Submitted 

Studies 

(MRID) 

Study 

Classifications 

Are data 

needed to 

conduct risk 

assessment? 

Current Additional Data Need

 850.1010 Freshwater 

invertebrate 

acute toxicity 

41573303 Acceptable No 

850.1025 

850.1035 

850.1045 

850.1055 

Saltwater 

invertebrate 

acute toxicity 

None N/A Yes See explanation below 

None N/A 

None N/A 

 850.1075 Freshwater 

fish acute 

toxicity 

41573302 Acceptable No 

41606301 Acceptable 

 850.1075 Saltwater fish 

acute toxicity 

None N/A Yes See explanation below 

 850.1300 Freshwater 

invertebrate 

life cycle 

41737902 Acceptable No 

 850.1350 Saltwater 

invertebrates 

life cycle 

None N/A No 

850.1500 Freshwater 

fish life cycle 

43284601 Acceptable No 

 850.1400 Freshwater 

fish 

early-life stage 

246021 Acceptable No 

 850.1400 Saltwater fish 

early-life stage 

N/A N/A No 

850.4400 Aquatic plant 

growth: 

vascular plants 

45541703 

Duckweed 

Supplemental No 

850.4500 Aquatic Plant 

Growth: 

algae 

None N/A Yes See explanation below 

850.4550 Cyanobacteria 

(Anabaena 

flos-aquae)

None N/A Yes See explanation below 

Table 10. Submitted Terrestrial Ecological Effects Data for Diclofop-methyl

OCSPP 

Guideline 

Data 

Requirement 

Submitted 

Studies 

(MRID) 

Study 

Classifications 

Are data 

needed for 

risk 

assessment? 

Current Additional Data Need 

 850.2100 Avian oral 

toxicity 

097117 Supplemental No 

40072903 Acceptable 
Page 22 of 50 

OCSPP 

Guideline 

Data 

Requirement 

Submitted 

Studies 

(MRID) 

Study 

Classifications 

Are data 

needed for 

risk 

assessment? 

Current Additional Data Need 

 850.2200 Avian dietary 

toxicity 

40072901 Acceptable No 

40072902 Acceptable 

 850.2300 Avian 

reproduction 

098297 

243472 

Supplemental 

(waivers were 

granted) 

No 

 850.3020 Honey bee 

acute contact 

toxicity 

No data N/A Yes See explanation below 

850.3030 Honey bee 

residue on 

foliage 

N/A N/A No 

 850.3040 Field testing 

for pollinators

N/A N/A No 

850.4100 Terrestrial 

plant toxicity: 

seedling 

emergence 

41606306 Acceptable No 

850.4150 Terrestrial 

plant toxicity: 

vegetative 

vigor 

41606305 Acceptable No 

Nonguideline Honeybee 

acute oral 

larval 

N/A N/A Yes See explanation below 

Nonguideline Honeybee 

acute adult 

oral 

N/A N/A Yes See explanation below 

Nonguideline Earthworm 

acute 

N/A N/A No 

At the present time, all of the data requirements have been fulfilled except for acute 

estuarine/marine fish and invertebrate studies (850.1025, 850.1035 and 850.1075), aquatic plant 

growth studies (850.4500 & 850.4550), an acute contact bee study (850.3020), and acute adult 

oral and larval studies with the honeybee. Without these data, assumptions will be made which 

may be overly conservative. 

Guidelines 850.1025, 850.1035 & 850.1075 

No data have been submitted regarding acute toxicity to estuarine/marine fish or invertebrates. 

Although applications are prohibited within 100 ft of any water bodies, diclofop-methyl is highly 

acutely toxic to freshwater fish and invertebrates. In addition, use on golf courses can occur near 

estuarine areas. Acute studies with the sheepshead minnow, mysid and oyster (shell deposition) 

are needed. 

 
Page 23 of 50 

Guidelines 850.4500 & 850.4550 

Aquatic plant testing is required for any herbicide that has outdoor non-residential terrestrial uses 

that may move off-site by runoff, by drift, or that is applied directly to water. Only one aquatic 

plant study (Lemna gibba G3) has been submitted for diclofop-methyl or diclofop acid. The test 

guideline requirements have not been fulfilled. 

Guideline 850.3020 

No data have been submitted regarding toxicity to bees or other beneficial insects. A honeybee 

acute contact toxicity study is needed to assess risk to bees and other beneficial insects. 

Non-Guideline Adult Oral and Larval Studies 

In keeping with the Agency’s proposed new paradigm for determining potential adverse effects 

to insect pollinators from conventional pesticides (USEPA 2012), two additional studies are 

being requested in addition to the guideline acute contact study. An acute adult oral toxicity 

study (following OECD 213) and a larval oral toxicity study (following OECD 237) are 

necessary to evaluate the potential for diclofop-methyl to adversely affect bees and other 

pollinators. Several target crops are considered attractive to honey bees and this is a systemic 

chemical that is transported throughout the plant. Thus, residues may be available to pollinators 

via pollen and/or nectar. For assessment purposes, EFED will estimate exposures through pollen 

and nectar, thus EFED is not asking for pollen and nectar residue data at this time. 

 

Study Title: Pollinator Acute Oral Toxicity, Adult (single dose) 

Rationale for Requiring the Data 

Terrestrial invertebrates are likely to be impacted if exposed given diclofop-methyl’s use as an 

herbicide in various use settings. Diclofop-methyl may be transferred to pollen and/or nectar 

of treated plants and subsequently brought back to the hive. Therefore, potential effects to 

adult honeybees from oral exposure could exist. Currently available toxicity studies do not 

address possible effects of oral exposure on adult honeybee survival. Because of the potential 

for pollen and nectar to be contaminated and subsequently brought back to the hive, it is 

important to determine the toxicity of this compound to adult honeybees. Therefore, a nonguideline adult honeybee study is needed to measure acute oral toxicity.

The Office of Pesticide Programs has made available a guidance regarding ecological testing 

for invertebrates with the honeybee. These can be found at: http://www2.epa.gov/pollinatorprotection/pollinator-risk-assessment-guidance . 

Practical Utility of the Data 

How will the data be used? 

Data will be used to assess potential risk to non-target listed and non-listed terrestrial 

invertebrates, including pollinators, from acute exposures to diclofop-methyl. The data will be 

used to reduce uncertainties associated with the registration review risk assessment for 

terrestrial invertebrates and will improve EPA’s understanding of the potential effects on 

terrestrial species. If acute oral effects are not submitted, risks to terrestrial insects from acute 

exposure will be assumed.
Page 24 of 50 

How could the data impact the Agency’s future decision-making?

The data EPA intends to call in will inform the determination required under FIFRA or the 

ESA as to whether continued registration of a pesticide is likely to result in unreasonable 

adverse effects to non-target species or is not likely to jeopardize listed or endangered species 

or its critical habitat. The lack of these data will limit the flexibility that the Agency and 

registrants have in coming in to compliance with the ESA and could result in significant use 

restrictions. In addition, the lack of these data may result in assumed risk and potential 

mitigation of diclofop-methyl formulations under FIFRA. 

Study Title: Pollinator Acute Oral Toxicity, Larvae (single dose) 

Rationale for Requiring the Data 

Terrestrial invertebrates are likely to be impacted if exposed given diclofop-methyl’s use as an 

herbicide in various use settings. Diclofop-methyl may be transferred to pollen and/or nectar 

of treated plants and subsequently brought back to the hive where larvae and pupae may be 

exposed. Therefore, potential effects to developing bees could exist, as egg and larval stages of 

some of the pests are indicated to be the most sensitive stages, and developing bees may also 

be sensitive at these stages. Currently available toxicity studies do not address possible effects 

on brood (larvae and pupae) survival. Because of the potential for pollen and nectar to be 

contaminated and subsequently brought back to the hive, it is important to determine the 

toxicity of this compound to brood. Therefore, a non-guideline honeybee larval study is 

needed to measure acute oral toxicity. 

The Office of Pesticide Programs has made available a guidance regarding ecological testing 

for invertebrates with the honeybee. These can be found at: http://www2.epa.gov/pollinatorprotection/pollinator-risk-assessment-guidance . 

Practical Utility of the Data 

How will the data be used? 

Data will be used to assess risk to non-target listed and non-listed terrestrial invertebrate 

species. The data will reduce uncertainties associated with the registration review risk 

assessment for terrestrial invertebrates and will improve EPA’s understanding of the potential 

effects on terrestrial species. If acute oral effects are not submitted, risks to terrestrial insects 

from acute exposure will be assumed. 

How could the data impact the Agency’s future decision-making?

The data EPA intends to call-in will inform the determination required under FIFRA or the 

ESA as to whether continued registration of a pesticide is likely to result in unreasonable 

adverse effects to non-target species or is not likely to jeopardize listed or endangered species 

or its critical habitat. The lack of these data will limit the flexibility that the Agency and 

registrants have in coming into compliance with the ESA and could result in significant use 

restrictions. In addition, the lack of these data may result in assumed risk and potential 

mitigation of diclofop-methyl formulations under FIFRA. 
Page 25 of 50 

11. References 

Food and Agriculture Organization of the United Nations (FAO). 2014. Assessing soil 

contamination A reference manual; Parameters of pesticides that influence processes in 

the soil. Agriculture and Consumer Protection Department. 

http://www.fao.org/docrep/003/x2570e/x2570e06.htm 

HRAC. 2010. The World of Herbicides Poster. www.hracglobal.com (accessed Aug. 1, 2012) 

U.S. Department of Agriculture (USDA). 1996. Seefeldt, S., E. Fuerst, G. Irzyk, D. Gealy, A. 

Shukla, D. Hoffman, and B. Brewster. Diclofop-Resistant Avena Fatua from the 

Willamette Valley of Oregon. International Weed Control Congress Proceedings.

Accepted for publication: Jun. 24, 1996. Interpretive summary at: 

http://www.ncaur.usda.gov/research/publications/publications.htm?seq_no_115=66579

Seefeldt, S., E. Fuerst, D. Gealy, A. Shukla, G. Irzyk, and M. Devine. 1996. Mechanisms of 

Resistance to Diclofop of Two Wild Oat (Avena Fatua) Biotypes from the Willamette 

Valley of Oregon. Weed Science, 44: 776-781. 

U.S. Environmental Protection Agency (USEPA). 1999. Dutta, S. Drinking Water Memorandum 

for Diclofop-methyl for the Reregistration Eligibility Decision Document (RED). DP 

barcode 260166. Memorandum from the Environmental Fate and Effects Division to the 

Registration Division. Oct. 15, 1999. 

USEPA. 2000. Piper, S. Diclofop-Methyl: Outcome of HED Metabolism Assessment Review 

Committee Meeting on 4/4/00. DP Barcode 264794. Health Effects Division. Internal 

memorandum. Apr. 7, 2000. 

USEPA. 2009. Guidance for Selecting Input Parameters in Modeling the Environmental Fate 

and Transport of Pesticides. Version 2.1. U.S. Environmental Protection Agency, Office 

of Pesticide Programs, Environmental Fate and Effects Division, Oct. 22, 2009. 

www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm

USEPA. 2012. White Paper in Support of the Proposed Risk Assessment Process for 

Bees. Submitted to the FIFRA Scientific Advisory Panel for Review and Comment 

September 11-14, 2012. Office of Chemical Safety and Pollution Prevention Office of 

Pesticide Programs Environmental Fate and Effects Division, Environmental Protection 

Agency, Washington DC; Environmental Assessment Directorate, Pest Management 

Regulatory Agency, Health Canada, Ottawa, CN; California Department of Pesticide 

Regulation. www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2012-0543-0004

United States Geological Survey (USGS). 2014. National Water-Quality Assessment (NAWQA) 

Program, Pesticide National Synthesis Project, Pesticide Use Maps – Diclofop. 

http://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=2011&map=DICLO

FOP&hilo=L&disp=Diclofop (accessed Apr. 23, 2014) 
Page 26 of 50 

APPENDIX A: Eco and Fate Bibliography for Diclofop-methyl 

110902 Diclofop-methyl Eco Effects Bibliography 

71-1 Avian Single Dose Oral Toxicity

MRID Citation Reference 

38853 or 

133065 

 Kramer; Hollander (1974) Acute Oral Toxicity of ... (Hoe 23408 O H AT) in Male 

Quails (Carrier Substance: Starch Suspension): A02061. (Translation; unpublished 

study received 1974 under 6G1664; prepared by Hoechst, AG, W. Ger., submitted 

by American Hoechst Corp., Somerville, NJ; CDL:095400-A) or ACC 094682-B 

133066 or 

38854 

 Kramer; Hollander (1974) Acute Oral Toxicity of ... (Hoe 23408 O H AT) in Male 

Quails (Carrier Substance: Sesame Oil): A02055. (Translation; unpublished study 

received 1974 under 6G1664; prepared by Hoechst, AG, W. Ger., submitted by 

American Hoechst Corp., Somerville, NJ; CDL:095400-B) 

133067 or 

38855 

 Kramer; Hollander (1974) Acute Oral Toxicity of ... (Hoe 23408 O H AT) in Female 

Quails (Carrier Substance: Starch Suspension): A02059. (Translation; unpublished 

study received 1974 under 6G1664; prepared by Hoechst, AG, W. Ger., submitted 

by American Hoechst Corp., Somerville, NJ; CDL:095400-C) 

133068 or 

38856 

 Kramer; Hollander (1974) Acute Oral Toxicity of ... (Hoe 23408 O H AT) in Female 

Quails (Carrier Substance: Sesame Oil): A02060. (Translation; unpublished study 

received 1974 under 6G1664; prepared by Hoechst, AG, W. Ger., submitted by 

American Hoechst, Corp., Somerville, NJ; CDL:095400-D) 

107441 Roberts, S.; Parke, G.; Charles, S. (1977) Acute Oral Toxicity of HOE-23408 

Technical 95% in Bobwhite Quail: Laboratory No. 7E- 6135; A10868. (Unpublished 

study received May 26, 1978 under 8340-11; prepared by Cannon Laboratories, Inc., 

submitted by American Hoechst Corp., Somerville, NJ; CDL:097117-B) 

40072903 Hinken, C.; Grimes, J.; Jaber, M. (1986) Diclofop-Methyl Technical: (Code: HOE 

023408 OH ZD95 0003): An Acute Oral Toxicity Study with the Bobwhite: 

Laboratory Project ID No. 125-140. Unpublished study prepared by Wildlife 

International Ltd. 27 p. 

92036005 Dulak, L. (1990) Hoechst Celanese Corporation Phase 3 Summary of MRID 

40072903. Diclofop-methyl Technical (Code: HOE 023408 OH ZD95 0003): An 

Acute Oral Toxicity Study with the Bobwhite: Lab. Project ID. No. 125-140. 

Prepared by WILDLIFE INTERNATIONAL, LTD. 16 p. 

71-2 Avian Dietary Toxicity 

MRID Citation Reference 

38857 or 

107442 

 Terrell, Y.; Parke, G.S.E. (1975) Report--Eight Day Dietary LC50 Study of 

Technical HOE-23408--Coturnix Quail and Mallard Ducks: Laboratory Nos. 4E5200; 4E-5201. (Unpublished study received Aug 22, 1975 under 6G1664; prepared 

by Cannon Laboratories, Inc., submitted by American Hoechst Corp., Somerville, 

N.J.; CDL:094682-F) 

107454 Krize, J. (1978) Avian Dietary LC50 (5-day Dietary Exposure) of HOE-23408, 95% 

Pure to Mallard Duck: Laboratory No. 8E-1526. (Unpublished study received Aug 
Page 27 of 50 

17, 1978 under 8340-11; pre- pared by Cannon Laboratories, Inc., submitted by 

American Hoechst Corp., Somerville, NJ; CDL:097291-A) 

40072901 Hinken, C.; Grimes, J.; Jaber, M. (1986) Diclofop-Methyl Technical: (Code: HOE 

023408 OH ZD95 0003): A Dietary LC50 Study with the Bobwhite: Laboratory 

Project ID No. 125-138. Unpublished study prepared by Wildlife International Ltd. 

in cooperation with Ana- lytical Development Corp. 38 p. 

40072902 Hinken, C.; Grimes, J.; Jaber, M. (1986) Diclofop-Methyl Technical: (Code: HOE 

023408 OH ZD95 0003): A Dietary LC50 Study with the Mallard: Laboratory 

Project ID No. 125-139. Unpublished study prepared by Wildlife International Ltd. 

in cooperation with Analytical Development Corp. 36 p. 

92036006 Dulak, L. (1990) Hoechst Celanese Corporation Phase 3 Summary of MRID 

40072901. Diclofop-methyl Technical (Code: HOE 023408 OH ZD95 0003) A 

Dietary LC 50 Study with the Bobwhite: Lab. Project No. 125-138. Prepared by 

WILDLIFE INTERNATIONAL, LTD. 19 p. 

92036007 Dulak, L. (1990) Hoechst Celanese Corporation Phase 3 Summary of MRID 

40072902. Diclofop-methyl Technical (Code: HOE 023408 OH ZD95 0003) A 

Dietary LC 50 Study with the Mallard: Lab. Project No. 125-139. Prepared by 

WILDLIFE INTERNATIONAL, LTD. 19 p. 

107443 Roberts, S.; Parke, G.; Charles, S. (1977) Avian Dietary LC50 5-day Dietary 

Exposure with 3-day Observation Period of Bobwhite Quail to HOE-23408 

Technical 95%: Laboratory No. 7E-6136; A10867. (Unpublished study received 

May 26, 1978 under 8340-11; prepared by Cannon Laboratories, Inc., submitted by 

American Hoechst Corp., Somerville, NJ; CDL:097117-D) 

71-4 Avian Reproduction 

MRID Citation Reference 

94621 Lawatch, D.J. (1980) Letter sent to Richard F. Mountford dated Sep 30, 

1980: Hoelon^RI avian reproduction studies; Your letter of August 11, 

1980. (Unpublished study received Oct 7, 1980 under 8340-11; submitted 

by American Hoechst Corp., Somerville, N.J.; CDL:243473-A) 

107457 Terrell, Y. (1978) Reproduction Study of HOE 23408 (Batch 76-01) in 

Bobwhite Quail: Laboratory No. 7E-7620; A15554. (Unpublished study 

received May 21, 1979 under 8F2085; prepared by Cannon Laboratories, 

Inc., submitted by American Hoechst Corp., Somerville, NJ; CDL:098297-

C) 

107458 Terrell, Y. (1978) Reproduction Study of HOE 23408 (Batch 76-01) in 

Mallard Ducks: Laboratory No. 7E-7621; A15553. (Unpublished study 

received May 21, 1979 under 8F2085; prepared by Cannon Laboratories, 

Inc., submitted by American Hoechst Corp., Somerville, NJ; CDL:098297-

D) 

40440901 Beavers, J.; Frank, P.; Jaber, M. (1987) Diclofop-Methyl Technical 

Substance: (Code: HOE 023408 OH ZD95 0003): A One-generation Reproduction Study with the Bobwhite (Colinus virginianus): Labo ratory 

Project No.: 125-135. Unpublished study prepared by Wildlife International 

Ltd. 220 p. 

40440902 Beavers, J.; Frank, P.; Jaber, M. (1987) Diclofop-Methyl Technical 

Substance: (Code: HOE 023408 OH ZD95 0003): A One-generation Reproduction Study with the Mallard (Anas platyrhynchos): Labora- tory 
Page 28 of 50 

Project No.: 125-136. Unpublished study prepared by Wild- life 

International Ltd. 220 p. 

92036008 Dulak, L. (1990) Hoechst Celanese Corporation Phase 3 Summary of MRID 

40440901. Diclofop-methyl Technical (Code: HOE 023408 OH ZD95 

0003) A One-generation Reproduction Study with the Bob White (Colinus 

virginianus): Lab. Project ID. No. 125-135. Prepared by WILDLIFE 

INTERNATIONAL, LTD. 18 p. 

92036009 Dulak, L. (1990) Hoechst Celanese Corporation Phase 3 Summary of MRID 

40440902. Diclofop-methyl Technical (Code: HOE 023408 OH ZD95 

0003) A One-Generation Reproduction Study with the Mallard (Anas 

platyrhynchos): Lab. Project ID. No. 125-136. Prepared by WILDLIFE 

INTERNATIONAL, LTD. 18 p. 

130238 Eckert, J. (1979) Addendum to Report: Avian Reproduction study of HOE23408, 95% Pure, Batch #76-01-001 to Mallard Duck and Bob- white 

Quail: Laboratory No. 7E-7620 & 7E-7621. (Unpublished study received 

Oct 7, 1980 under 8340-11; prepared by Cannon Laboratories, Inc., 

submitted by American Hoechst Corp., Somerville, NJ; CDL:243473-B) 

72-1 Acute Toxicity to Freshwater Fish 

MRID Citation Reference 

76868 Knauf, W. (1978) The Acute Toxicity of HOE 21079 O H AT102 to the Rainbow 

Trout (Salmo gairdneri~Richardson): A16197. (Unpublished study received May 

21, 1981 under 8340-11; prepared by Hoechst AG, West Germany, submitted by 

American Hoechst Corp., Somerville, N.J.; CDL:245123-H) 

107445 Knauf, W.; Schulze, E. (1978) The Effect of HOE 23408 O H AT002 (Active 

Ingredient) on Salmo gairdneri (Rainbow Trout): A13481. (Translation of doc. no. 

A13472; unpublished study received May 26, 1978 under 8340-11; prepared by 

Hoechst Aktiengesellschaft, W. Ger., submitted by American Hoechst Corp., 

Somerville, NJ; CDL:097117-F) 

107446 or 

133070 or 

36860 

 Knauf, W. (19??) Toxicity of HOE 23408 3EC in Rainbow Trout (Salmo 

gairdneri): ?Submitter| AO 3692. (Translation; unpublished study received May 

26, 1978 under 8340-11; submitted by American Hoechst Corp., Somerville, NJ; 

CDL:097117-G) 

38859 or 

107444 

 Knauf, (1975) Toxicity of HOE 23408 OH (Active Ingredient) in Rainbow Trout 

(Salmo gairdneri): AO 3693. (Translation; un- published study received Aug 22, 

1975 under 6G1664; submitted by American Hoechst Corp., Somerville, N.J.; 

CDL:094682-H) 

107447 Knauf, W.; Schulze, E. (1978) Action of HOE 23408 O H AT002 (Active 

Ingredient) on Lepomis gibbosus (Pumpkinseed Sunfish): A13482. (Translation of 

document A13473; unpublished study received May 26, 1978 under 8340-11; 

prepared by Hoechst Aktiengesellschaft, W. Ger., submitted by American Hoechst 

Corp., Somerville, NJ; CDL:097117-H) 

107448 Knauf, W. (1976) HOE 23408 O H EH065 (Emulsifiable Conc.): Effect on 

Lepomis gibbosus: A09917. (Translation of document no. AO8544; unpublished 

study received May 26, 1978 under 8340- 11; prepared by Hoechst 

Aktiengesellschaft, W. Ger., submitted by American Hoechst Corp., Somerville, 

NJ; CDL:097117-I) 
Page 29 of 50 

107449 Knauf, W.; Schulze, E. (1976) HOE 23408 O H EH065 (Emulsifiable 

Concentrate): Effect on Cyprinus carpio (Carp): A08361. (Translation; 

unpublished study received May 26, 1978 under 8340-11; prepared by Hoechst 

AG, W. Ger., submitted by American Hoechst Corp., Somerville, NJ; 

CDL:097116-J) 

107462 Knauf, W.; Emmel (1975) Effect of HOE 30418 O F AT001 (Active Ingredient) 

on Salmo Gairdneri (Rainbow Trout): Bericht-Nr. 39/75; A16364. (Translation; 

unpublished study received May 21, 1979 under 8F2085; prepared by Hoechst 

AG, W. Ger., submitted by American Hoechst Corp., Somerville, NJ; 

CDL:098297-O) 

40746 Knauf, Schulze,; Ostmann, (1977) Hoe 23408 O H EF112 (Emulsifiable 

Concentrate 28) Effect on Salmo gairdneri~(Rainbow Trout): Report No. 37/77; 

A10230. (Translation from German; un- published study received Aug 11, 1977 

under 8340-EX-1; prepared by Hoechst, AG, submitted by American Hoechst 

Corp., Somerville, N.J.; CDL:096310-U) 

40747 Knauf, ; Schulze, ; Ostmann, (1977) Hoe 23408 O H EF112 (Emulsifiable 

Concentrate 28) Effect on Lepomis gibbosus (Blue Gill Sunfish): Report No. 

36/77; A10228. (Translation from German; unpublished study received Aug 11, 

1977 under 8340-EX-1; pre- pared by Hoechst, AG, submitted by American 

Hoechst Corp., Somerville, N.J.; CDL:096310-V) Pumpkinseed sunfish 

87813 Knauf, W.; Gorbach, S.; Kelbert, K.; et al. (1977) Continuous-flow Study with 

Hoe 23408 OH on Bluegill (Lepomis gibbosus): Bericht-NR. 101/77; A11582. 

(Unpublished study received Dec 30, 1981 under 8340-11; prepared by Hoechst 

AG, West Germany, sub- mitted by American Hoechst Corp., Somerville, N.J.; 

CDL: 246515-B) 

38858 Reinert, H.K. (1975) Report--Static TLM 96 Hour Toxicity Study of Technical 

HOE-23408 in Bluegill Sunfish and in Rainbow Trout: Cannon Nos. 4E5198; 

4E5199. (Unpublished study received Aug 22, 1975 under 6G1664; prepared by 

Cannon Laboratories, Inc., sub- mitted by American Hoechst Corp., Somerville, 

N.J.; CDL: 094682-G) 

107459 Calmbacher, C. (1978) The Acute Toxicity of HOE23408 Technical to the 

Rainbow Trout Salmo gairdneri Richardson: UCES Proj. No. 11506-88-01; 

A13840. (Unpublished study received May 21, 1979 under 8F2085; prepared by 

Union Carbide Corp., sub- mitted by American Hoechst Corp., Somerville, NJ; 

CDL:098297-F) 

107460 Calmbacher, C. (1978) The Acute Toxicity of HOE23408 Technical to the 

Bluegill Sunfish Lepomis macrochirus Rafinesque: UCES Proj. No. 11506-88-02; 

A13839. (Unpublished study received May 21, 1979 under 8F2085; prepared by 

Union Carbide Corp., submitted by American Hoechst Corp., Somerville, NJ; 

CDL:098297-H) 

111960 or 

76869 

 Fahmy, F. (1979) Toxicity Evaluation: T-3040; A16430. (Unpublished study 

received May 21, 1979 under 8F2085; prepared by Canadian Hoechst Ltd., 

submitted by American Hoechst Corp., Somerville, NJ; CDL:098297-N) 

111960 or 

76869 

 Fahmy, F. (1979) Toxicity Evaluation:HOE-21079 , Free acid metabolite of 

Hoelon (98%) with Rainbow trout. (Unpublished study received May 21, 1979 

under 8F2085; prepared by Canadian Hoechst Ltd., submitted by American 

Hoechst Corp., Somerville, NJ; CDL:098297 

133069 Reinert, H. (1975) Static TLM 96 Hour Toxicity Study of Technical Hoe-23403 in 

Bluegill Sunfish and in Rainbow Trout: Cannon # 4E-5198, 4E-5199. 

(Unpublished study received 1975 under 6G1664; prepared by Cannon 
Page 30 of 50 

Laboratories, Inc., submitted by American Hoechst Corp., Somerville, NJ; 

CDL:095400-F) 

40074009 Drottar, K. (1986) Acute Toxicity of HOE 023408 5H EC32 A101 to Bluegill 

Sunfish (Lepomis macrochirus): ESE No. 86-350-0300- 2130. Unpublished study 

prepared by Environmental Science & Engineering, Inc. 42 p. 

40074010 Ward, G. (1986) Acute Toxicity of HOE 203408 5H EC32 A101 to Rainbow 

Trout (Salmo gairdneri): ESE No. 86-350-0200-2130. Unpublished study prepared 

by Environmental Science & Engineering, Inc. 41 p. 

40213509 Fischer, R. (1986) The Effect of Diclofop-methyl--Oil in Water Emulsion 369 

(g/L)...to Salmo gairdneri (Rainbow Trout) in a Static-acute Toxicity Test...: Lab 

Project No. oek86-068e. Un- published study prepared by Hoechst AG. 21 p. 

40213511 Surprenant, D. (1986) Acute Toxicity of Hoelon 3EW (HOE-023408 OH EW34 

A204) to Bluegill (Lepomis macrochirus): Bionomics Report #BW-86=10-2163; 

Bionomics Study #1719.0986.6105.100. Unpublished study prepared by 

Springborn Bionomics, Inc. 20 p. 

41573302 Franks, T.; Smith, G.; Wilson, R. (1990) Static Acute 96-Hour Toxicity of 

Diclofop-methyl (HOE 023408 00 ZD93 0002) to Rainbow Trout: Lab Project 

Number: A 42731: 89-0162. Unpublished study prepared by Battelle Columbus 

Div. 57 p. 

41606301 Smith, G.; Schweitzer, M. (1990) Flow-through Acute 96-Hour Toxicity of 

Diclofop-methyl (...) to Bluegill Sunfish: Lab Project Number: SC900064. 

Unpublished study prepared by Battelle, Columbus Div. 61 p. 

41606302 Smith, G.; Schweitzer, M. (1990) Flow-through Acute 96-Hour Toxicity of 

Diclofop-methyl (...) Emulsifiable Concentrate (3 EC Formulation) to Bluegill 

Sunfish: Lab Project Number: SC900065. Unpublished study prepared by Battelle, 

Columbus Div. 63 p. 

41606303 Smith, G.; Schweitzer, M. (1990) Static Acute 96-Hour Toxicity of Diclofopmethyl (...) Emulsifiable Concentrate (3 EC Formula- tion) to Rainbow Trout: Lab 

Project Number: SC900066. Unpublished study prepared by Battelle, Columbus 

Div. 61 p. 

92036010 Mayasich, J. (1990) Hoechst Celanese Corporation Phase 3 Summary of MRID 

00107460. Diclofop-methyl Technical (Code: HOE 023408 OH ZD95 0003) 

Freshwater Acute Study: Bluegill Sunfish. Prepared by UNION CARBIDE CORP. 

13 p. 

116622 or 

40094602 

 Johnson, W.; Finley, M. (1980) Handbook of Acute Toxicity of Chemicals to Fish 

and Aquatic Invertebrates. By U.S. Fish and Wild- life Service, Columbia National 

Fisheries Research Laboratory. Washington, DC: USFWS. (Resource publication 

137, pages 59,60 only; published study; CDL:248614-Q) 

 McCann, J.A. 1979. Beltsville Animal Biology Laboratory study # 2402 with 

Bluegill sunfish and technical grade Diclofop 

 McCann, J.A. 1979. Beltsville Animal Biology Laboratory study # 2402 with 

Rainbow trout and technical grade Diclofop 

 McCann, J.A. 1979. Beltsville Animal Biology Laboratory study # 2439 with 

Bluegill sunfish Methyl 2- 4-(2,4-dich1orophenoxy)-phenoxy propanoate 

72-2 Acute Toxicity to Freshwater Invertebrates 

MRID Citation Reference 
Page 31 of 50 

107450 Knauf, W.; Schulze, E. (1977) HOE 23408 OH AT002 (Active Ingredient): Effect on 

Daphnia magna (Water Flea): A10637. (Translation of document no. A08777; 

unpublished study received May 26, 1978 under 8340-11; prepared by Hoechst 

Aktiengesellschaft, W. Ger., submitted by American Hoechst Corp., Somerville, NJ; 

CDL: 097116-K) 

107451 Knauf, W. (1976) HOE 23408 O H EH065 (Emulsifiable Conc.): Effect on Daphnia 

magna: AO9916. (Translation of document no. A07881; unpublished study received 

May 26, 1978 under 8340-11; prepared by Hoechst Aktiengesellschaft, W. Ger., 

submitted by American Hoechst Corp., Somerville, NJ; CDL:097116-L) 

107461 Knauf, W.; Schulze, E. (1979) Effect of HOE 23408 OH EH065 (Emulsifiable 

Concentrate) on Daphnia magna (Water Flea): Bericht- Nr. 21/79; A16955. 

(Unpublished study received May 21, 1979 under 8F2085; prepared by Hoechst AG, 

W. Ger., submitted by American Hoechst Corp., Somerville, NJ; CDL:098297-L) 

40074011 Ward, G. (1986) Acute Toxicity of HOE 023408 5H EC32 A101 to Water- fleas 

(Daphnia magna): ESE No. 86-350-0100-2130. Unpublished study prepared by 

Environmental Sciences & Engineering Inc. 36 p. 

40213510 Fischer, R. (1986) The Effect of Diclofop-methyl--Oil in Water Emulsion 369 

(g/L)...to Daphnia magna (Waterflea) in a Static- acute Toxicity Test...: Lab Project 

No.: oek86-069e. Unpublished study prepared by Hoechst AG. 22 p. 

41573303 Franks, T.; Smith, G.; Switzer, K.; et al. (1989) Static Acute 48- Hour Toxicity of 

Diclofop-methyl (HOE 023408 00 ZD93 0002) to Daphnia magna: Lab Project 

Number: A/42732: SC890024. Unpublished study prepared by Battelle Columbus Div. 

57 p. 

41606304 Smith, G.; Schweitzer, M. (1990) Static Acute 48-Hour Toxicity of Diclofop-methyl 

(...) Emulsifiable Concentrate (3 EC Formulation) to Daphnia magna: Lab Project 

Number: SC900067. Unpublished study prepared by Battelle, Columbus Div. 67 p. 

 McCann, J.A. 1979. Beltsville Animal Biology Laboratory study # 2404 with 

Daphnia magna and technical grade Diclofop 

72-3 Acute Toxicity to Estuarine/Marine Organisms 

MRID Citation Reference 

71388 or 

76865 

 Heitmuller, T.; Maziarz, T. (1981) Acute Toxicity of Hoelon(R)I (HOE-23408) to 

Eastern Oysters (Crassostrea virginica): Re- port No. BP-81-2-21. (Unpublished study 

received Mar 2, 1981 under 8340-11; prepared by EG & G, Bionomics, submitted by 

Amer- ican Hoechst Corp., Somerville, N.J.; CDL:244465-C) 

76863 Heitmuller, T.; Maziarz, T. (1981) Acute Toxicity of Hoelon(R)I (HOE-23408) to 

Eastern Oysters (Crassostrea virginica): Re- port No. BP-81-2-21-R. Rev. 

(Unpublished study received Nov 21, 1981 under 8340-11; prepared by EG & G 

Bionomics, submitted by American Hoechst Corp., Somerville, N.J.; CDL:245123-C) 

76864 Heitmuller, T.; Maziarz, T. (1981) Acute Toxicity of HOE-21079 to Eastern Oysters 

(Crassostrea virginica): Report No. BP-81-3- 22. (Unpublished study received May 21, 

1981 under 8340-11; prepared by EG & G Bionomics, submitted by American Hoechst 

Corp., Somerville, N.J.; CDL:245123-D) 

76865 Hollister, T.A.; Maziarz, T.P. (1981) Acute Toxicity of Hoelon (R)I (HOE-23408) to 

Embryos-larvae of Eastern Oysters (Crassostrea virginica): Report No. BP-81-4-51-R. 
Page 32 of 50 

Rev. (Unpublished study received May 21, 1981 under 8340-11; prepared by EG & G 

Bionomics, submitted by American Hoechst Corp., Somerville, N.J.; CDL:245123-E) 

76866 Hollister, T.A.; Maziarz, T.P. (1981) Acute Toxicity of Hoe-21079 to Embryos-larvae 

of Eastern Oysters (Crassostrea virginica): Report No. BP-81-5-71. (Unpublished study 

received May 21, 1981 under 8340-11; prepared by EG & G Bionomics, submitted by 

American Hoechst Corp., Somerville, N.J.; CDL:245123-F) 

72-4 Fish Early Life Stage/Aquatic Invertebrate Life Cycle Study 

MRID Citation Reference 

71386 EG & G, Bionomics (1978) Methods for Conducting Early Life Stage Toxicity Tests 

with Fathead Minnow (Pimephales promelas). (Unpublished study, including 

submitter summary, received Mar 2, 1981 under 8340-11; submitted by American 

Hoechst Corp., Somerville, N.J.; CDL:244464-H) 

97836 Wilson, Brenda. 1981. The toxicity of Hoelon to Rainbow Trout 

(Salmo gairdneri) Embryos and Lanrae. An unpublished report 

prepared by E. G. & G. Bionanics Aquatic Toxicology Laboratory for American 

Hoechst Corporation. ACC# 246021.

76867 LeBlanc, G.A.; Mastone, J.D.; Wilson, B.F. (1981) The Toxicity of Hoelon(R)I to 

Fathead Minnow (Pimephales promelas) Embryos and Larvae: Report #BW-81-4-

853. (Unpublished study received May 21, 1981 under 8340-11; prepared by EG & G 

Bionomics, sub- mitted by American Hoechst Corp., Somerville, N.J.; CDL: 245123-

G) 

41737902 Smith, G. (1990) Static-Renewal Chronic 21-Day Toxicity of Diclofop-methyl to 

Daphnia magna: Lab Project Number: SC900115: 90-0107. Unpublished study 

prepared by Battelle Columbus Div. 8 p. 

92036011 Mayasich, J. (1990) Hoechst Celanese Corporation Phase 3 Summary of MRID 

00076867. Diclofop-methyl Technical (Code: HOE 023408 OH ZD95 0003) Fish 

Early Life Cycle Study: Fathead Minnow. Prepared by EG & G, BIONOMICS. 14 p. 

71385 EG & G, Bionomics (1980) Methods for Conducting Early Life Stage Toxicity Tests 

with Rainbow Trout (Salmo gairdneri). (Un- published study, including submitter 

summary, received Mar 2, 1981 under 8340-11; submitted by American Hoechst 

Corp., Somer- ville, N.J.; CDL:244464-G) 

84653 Dorr, V.A. (1981) Summary: (Exposure of Rainbow Trout Embryos and Larvae to 

Hoelon). Summary of studies 246021-E and 246021-F. (Unpublished study received 

Oct 7, 1981 under 8340-11; submitted by American Hoechst Corp., Somerville, N.J.; 

CDL:246021-D) 

97836 LeBlanc, G.A.; Mastone, J.D.; Wilson, B.F. (1981) The Toxicity of Hoelon(R) to 

Rainbow Trout (Salmo gairdneri) Embryos and Larvae: Report #BW-81-6-929. 

(Unpublished study received Oct 7,1981 under 8340-11; prepared by EG & G 

Bionomics, submitted by American Hoechst Corp., Somerville, N.J.; CDL:246021-E) 

72-5 Life cycle fish 

MRID Citation Reference 

43284601 Dionne, E. (1994) Diclofop-methyl: The Chronic Toxicity to the Fathead Minnow 

(Pimephales promelas) During a Full Life-cycle Exposure: Lab Project Number: 
Page 33 of 50 

1719.0692.6199.122: 94-3-5180. Unpublished study prepared by Springborn Labs, Inc. 

705 p. 

72-6 Aquatic org. accumulation 

MRID Citation Reference 

41996903 Gildemeister, H. (1991) Hoe 023408-Carbon 14: Flow-Through Bioaccumulation and 

Metabolism Study with Bluegill Sunfish (Lepomis macrochirus). Unpublished study 

prepared by Hoechst Aktiengese- llschaft. 57 p. 

84654 Cubbedge, S.D. (1981) Analysis of HOE 23408 and HOE 35449 in Rainbow Trout: PL 

No. 81PL-624-1. (Unpublished study, including letter dated Jul 30, 1981 from S.D. 

Cubbedge to Hanson H. North, received Oct 7, 1981 under 8340-11; prepared by 

Biospherics, Inc., submitted by American Hoechst Corp., Somerville, N.J.; 

CDL:246021-F) 

72-7 Aquatic Field Study 

N.R. Mayland, P.G. 1979. Aquatic study conducted under Field Conditions in Minnesota 

(06-MN-79-019) 

45695 Kleis, M.M.; Spencer, W.T.; Mayland, P.G. (1980) Hoelon(R)I 3EC Herbicide Fish 

Monitoring Studies: North Dakota Test # 06-ND-79- 018; Montana Test # 13-MT-79-

100. (Unpublished study received Aug 21, 1980 under 8340-11; prepared in 

cooperation with Biospherics, Inc., submitted by American Hoechst Corp., Somerville, 

N.J.; CDL:243097-B) 

N.R. Grande, John A. 1980 Pond study in Virginia 

134716 American Hoechst Corp. (1979) North Dakota Fish Monitoring Study. (Unpublished 

study received Sep 25, 1979 under 8340-EX-1; CDL: 098988-B) 

134717 American Hoechst Corp. (1979) Montana Fish Monitoring Study. (Unpublished study 

received Sep 25, 1979 under 8340-Ex-1; CDL: 098988-C) 

N.R. The behaviour of the plant protection agent HOE 23408 Oil in an open-air pond

122-1 Seed Germination/Seedline Emergence and Vegetable Vigor 

MRID Citation Reference 

41606305 Chetram, R. (1990) Tier 2 Vegetative Vigor Nontarget Phytotoxicity Study using 

Technical Diclofop-methyl: Lab Project Number: LR89- 42A: 89-0148. Unpublished 

study prepared by Pan-Agricultural Laboratories, Inc. 138 p. 

41606306 Chetram, R. (1990) Tier 2 Seed Germination/Seedling Emergence Nontarget 

Phytotoxicity Study using Technical Diclofop-methyl: Project Number: LR89-42B; 

89-0147. Unpublished study prepared by Pan-Agricultural Laboratories, Inc. 183 p. 

123-2 Aquatic plant growth 

MRID Citation Reference 

45541703 Sowig, P. (2001) Duckweed (Lemna gibba G3) Growth Inhibition Test DiclofopMethyl Substance, Technical 94.4%: Lab Project Number: CE00/010: C008630. 

Unpublished study prepared by Aventis CropScience Gmbh. 60 p. 

Non Guideline Selections 
Page 34 of 50 

MRID Citation Reference

84656 Cubbedge, S.D. (1981) Analysis of HOE 23408 and HOE 35449 in Rainbow Trout, 

Mud Puppies, Buffer Plants and Pond Water: PL No. 81PL-487-2. (Unpublished 

study, including letter dated Jul 7, 1981 from G. Milad to Hanson H. North, prepared 

by Bio- spherics, Inc., submitted by American Hoechst Corp., Somerville, N.J.; 

CDL:246021-H) 

87812 Gorbach, S.; Kunzler, K.; Knauf, W.; et al. (1977) Uptake of Hoe 23408 OH Residues 

from a Water-soil System by Catfish (Ictalurus nebulosus) and Dissipation of the 

Taken Up Residues in Fresh Water: Bericht-Nr. Fo.Ber. 281/77; A11571. 

(Unpublished study received Dec 30, 1981 under 8340-11; prepared by Hoechst AG, 

West Germany, submitted by American Hoechst Corp., Somerville, N.J.; 

CDL:246515-A) 

40074008 Graney, R. (1986) Summary of Aquatic Toxicity of One Shot Herbicide. Unpublished 

summary prepared by American Hoechst Corp. 4 p. 

40213508 Graney, R. (1986) Aquatic Toxicology Testing of Hoelon 3EW: Sum- mary. 

Unpublished compilation prepared by Hoechst-Roussel Agri-Vet Co. 5 p. 

48033006 Jiao, B.; Yeung, E.; Chan, C.; et al. (2008) Establishment of a Transgenic Yeast 

Screening System for Estrogenicity and Identification of the Anti-Estrogenic Activity 

of Malachite Green. Journal of Cellular Biochemistry 105: 1399-1409. 

48033008 Kojima, H.; Katsura, E.; Takeuchi, S.; et al. (2004) Screening for Estrogen and 

Androgen Receptor Activities in 200 Pesticides by In Vitro Reporter Gene Assays 

Using Chinese Hamster Ovary Cells. Environmental Health Perspectives 112(5): 524-

531. 

41208201 Krebs, B.; Heinen, B. (1989) HOE 023408 (Diclofop-methyl): Calculation of the 

Expected Residue Concentration on wheat and Barley Plants at the Day of 

Application: Project ID OE 099/89. Unpublished study prepared by Hoechst 

Aktiengesellschaft. 

Fate/Chemistry Bibliography 

161-1 Hydrolysis 

MRID Citation Reference 

71389 Asshauer, J.; Klockner, C.; Thier, W. (1980) Abiotic Hydrolysis of HOE 23408: Fo. Ber. 310/80; 

A20914. (Unpublished study received Mar 2, 1981 under 8340-11; prepared by Hoechst, AG, W. 

Germany, submitted by American Hoechst Corp., Somerville, N.J.; CDL:244465-D) 

41573309 Gorlitz, G. (1990) HOE 023408, Diclofop-methyl Abiotic Hydrolysis as a Function of pH: Lab 

Project Number: A 42623: CP035/88. Un- published study prepared by Hoechst Ag. 37 p. 

ACC 

097120 

Hydrolysis of HOE-23408 Document Number A09903 Acc. No. I 

097120, Sect. J, Vol. 17, Part 3 5-44 

161-2 Photodegradation-water 

MRID Citation Reference 
Page 35 of 50 

41573307 Gildemeister, H. (1990) HOE 023408-carbon 14, Photodegradation in Water: Lab Project Number: A 

43058: CB89/160. Unpublished study prepared by Hoechst Ag. 61 p. 

107471 Thier, W.; Fischer, H. (1979) Photolytic Degradation of the Herbicide HOE 23408 in Aqueous 

Solution under Simulated Sunlight: A17429. (Unpublished study received Jun 27, 1979 under 

8F2085; prepared by Hoechst AG, W. Ger., submitted by American Hoechst Corp., Somerville, NJ; 

CDL:098356-H) 

161-3 Photodegradation-soil 

MRID Citation Reference 

87811 American Hoechst Corporation (1981)Residues of Hoe 23408, Hoe 21079 and Hoe 30418 in Soil|. 

(Compilation; unpublished study received Dec 30, 1981 under 8340-11; CDL:246516-D) 

107470 Thier, W.; Fischer, H. (1979) Photolytic Degradation of the Herbicide HOE 23408 on Soil Covered 

Thin-layer Slides under Simulated Sunlight: A17424. (Unpublished study received Jun 27, 1979 

under 8F2085; prepared by Hoechst AG, W. Ger., submitted by American Hoechst Corp., Somerville, 

NJ; CDL:098356-G) 

41573308 Gildemeister, H. (1990) HOE 023408-carbon 14: Photodegradation on Soil: Lab Project Number: 

CB89/161: A 42994. Unpublished study prepared by Hoechst Ag. 49 p. 

162-1 Aerobic soil metabolism 

MRID Citation Reference 

41573310 Speer, M. (1989) Diclofop-methyl: Aerobic Degradation and Metabolism in Four Soils at Two 

Temperatures and with two Different Moisture Contents: Lab Project Number: HOE/01/003: 

A/42498. Un- published study prepared by Fraunhofer-Institut Fur Umweltchemie und 

Okotoxikologie. 87 p. 

38861 Hoechst, Aktiengesellschaft (1975) Behaviour of the Plant Protective Active Ingredient in Soil: 

Report No. (B)40/75; AO 3687. (Translation; unpublished study received Aug 22, 1975 under 

6G1664; submitted by American Hoechst Corp., Somerville, N.J.; CDL:094682-J) 

87826 Martens, R. (1978) Degradation of the herbicide 14C-diclofop-methyl in soil under different 

conditions. Pesticide Science 9:127-134. (Also In unpublished submission received Dec 30, 1981 

under 8340-11; submitted by American Hoechst Corp., Somerville, N.J.; CDL:246514-E) 

162-2 Anaerobic soil metabolism 

MRID Citation Reference 

ACC 97118 Degradation of Herbicide HOE-23408 OH in the Soil under Anaerobic Conditions. Document A0-

63 16, Acc. No. 097118, Section J, part l of 3, Vol. 15 of 17 J-3. 

162-3 Anaerobic aquatic metabolism 

MRID Citation Reference 

40806307

 

Ellgehausen, H. (1986) Degradation of Diclofop-methyl (HOE 023408) in an Anaerobic Aquatic 

System: Project ID. 056654. Unpublished study prepared by Research Consulting Co. 43 p. 

42734201 Reynolds, J. (1993) Anaerobic Aquatic Metabolism of (carbon 14)-Diclofop-Methyl: Lab Project 

Number: RPT00120: XBL 91062. Unpublished study prepared by XenoBiotic Labs, Inc. 96 p. 
Page 36 of 50 

87826 Martens, R. (1978) Degradation of the herbicide 14C-diclofop-methyl in soil under different 

conditions. Pesticide Science 9:127-134. (Also In unpublished submission received Dec 30, 1981 

under 8340-11; submitted by American Hoechst Corp., Somerville, N.J.; CDL:246514-E) 

162-4 Aerobic Aquatic Metabolism 

MRID Citation Reference

(none) 

163-1 Leach/adsorp/desorption 

MRID Citation Reference 

40520301 Gildermeister, H. (1986) HOE 023408--(Carbon 14) (Diclofop-methyl-- (Carbon 14): Leaching Study: 

Laboratory Project ID CB016/85. Unpublished study prepared by Hoechst Celanese Corp. 27. p. 

40806308 Goerlitz, G.; Eyrich, U. (1987) Diclofop-methyl (HOE 023408) - Adsorption/Desorption in the System 

Soil/Water: Project ID. A37726. Unpublished study prepared by Hoechst AG. 72 p. 

42347801 Reynolds, J. (1992) Adsorption and Desorption of 14C-Diclofop-methyl in Four Soils: Lab Project 

Number: XBL 92021: RPT0092. Unpublished study prepared by XenoBiotic Laboratories, Inc. 116 p. 

164-1 Terrestrial field dissipation 

MRID Citation Reference 

40520302 Graney, R. (1988) Response to EPA's Review of the Hoelon Field Dissipation Study Conducted 

in Salisbury, MD 1985 ...: Laboratory Project ID EH-84-USA-40R. Unpublished study prepared 

by Hoechst Celanese Corporation. 45 p. 

40806309 Dorn (1988) Reanalyses of HOE 023408 and its Free Acid in Selected Soil Samples of the Field 

Dissipation Study EH USA 40R with an Improved Analytical Method: Project ID. A38541. 

Unpublished study prepared by Hoechst AG. 37 p. 

42252101 Hey, M.; Czarnecki, J.; Miller, M. (1992) Determination of the Combined Residues of Diclofopmethyl and its Metabolite Diclofop (Free Acid) in Soil: Lab Project Number: 1127: 1157. 

Unpublished study prepared by Colorado Analytical Research and Development Corp. and PanAgricultural Laboratories, Inc. 557 p. 

87824 Smith, A.E. (1979) Extraction of free and bound carboxylic acid residues from field soils treated 

with the herbicides benzoyl-prop-ethyl, diclofop-methyl, and flamprop-methyl. Journal of 

Agricultural and Food Chemistry 27(2):428-432. (Also In unpublished submission received Dec 

30, 1981 under 8340-11; submitted by American Hoechst Corp., Somerville, N.J.; CDL:246514-

C) 

87825 Smith, A.E. (1976) Use of acetonitrile for the extraction of herbicide residues from soils. Journal 

of Chromatography 129:309- 314. (Also in unpublished submission received Dec 30, 1981 under 

8340-11; submitted by American Hoechst Corp., Somerville, N.J.; CDL:246514-D) 

87828 Smith, A.E. (1979) Transformation of 14C-diclofop-methyl in small field plots. Journal of 

Agricultural and Food Chemistry 27(6):1145-1148. (Also In unpublished submission received 

Dec 30, 1981 under 8340-11; submitted by American Hoechst Corp., Somerville, N.J.; 

CDL:246514-G) 

156479 Johnson, J. (1985) Analytical Report: Analyses of Hoelon Residues in Soil from Salisbury, 

Maryland: Experiment No.: EH-84-USA-40R. Unpublished compilation prepared by American 

Hoechst Corp. 709 p. 
Page 37 of 50 

164-2 Aquatic Field Dissipation 

MRID Citation Reference 

45695 American Hoechst Corporation (1980) Hoelon® 3EC Pond Monitoring Studies in North Dakota, 

Minnesota, and Montana. Summary of studies 243097-A and 243097-B. (Unpublished study received 

Aug 21, 1980 under 8340-11; CDL:243097-D) 

45696 Grande, J.A.; Diaz, R.J. (1980) Pond Study in Virginia. (Unpublished study received Aug 21, 1980 

under 8340-11; submitted by American Hoechst Corp., Somerville, N.J.; CDL:243097-C) 

45697 American Hoechst Corporation (1980) Hoelon® 3EC Pond Monitoring Studies in North Dakota, 

Minnesota, and Montana. Summary of studies 243097-A and 243097-B. (Unpublished study received 

Aug 21, 1980 under 8340-11; CDL:243097-D) 

84656 Cubbedge, S.D. (1981) Analysis of HOE 23408 and HOE 35449 in Rainbow Trout, Mud Puppies, 

Buffer Plants and Pond Water: PL No. 81PL-487-2. (Unpublished study, including letter dated Jul 7, 

1981 from G. Milad to Hanson H. North, prepared by Biospherics, Inc., submitted by American 

Hoechst Corp., Somerville, N.J.; CDL:246021-H) 

87808 Cubbedge, S.D.; Grande, J. (1981) Analysis for Residues of HOE 23408 and HOE 35449 in Pond 

Samples: Virginia Pond Study: PL No. 80PL-1857-3-4. Rev. (Unpublished study received Dec 30, 

1981 under 8340-11; prepared by Biospherics, Inc., submitted by American Hoechst Corp., Somerville, 

N.J.; CDL:246516-A; 246515) 

87837 Ass|hauer, J.; Fischer, H.; Knauf, W.; et al. (1976) Behavior of the Plant Protection Agent Hoe 23408 

OH in an Open-air Pond: Bericht-Nr. Fo.Ber. 265/76; A07351. (Translation; unpublished study 

received Dec 30, 1981 under 8340-11; prepared by Hoechst AG, West Germany, submitted by 

American Hoechst Corp., Somerville, N.J.; CDL:246514-P) 

134716 American Hoechst Corp. (1979) North Dakota Fish Monitoring Study. (Unpublished study received 

Sep 25, 1979 under 8340-EX-1; CDL: 098988-B) 

134717 American Hoechst Corp. (1979) Montana Fish Monitoring Study. (Un- published study received Sep 

25, 1979 under 8340-Ex-1; CDL: 098988-C) 

165-4 Bioaccumulation in fish 

MRID Citation Reference 

41996903 Gildemeister, H. (1991) Hoe 023408-Carbon 14: Flow-Through Bioaccumulation and Metabolism 

Study with Bluegill Sunfish (Lepomis macrochirus). Unpublished study prepared by Hoechst 

Aktiengese-llschaft. 57 p. 

45878201 Madsen, T.; Leak, T.; Meyer, B. (2003) Bioconcentration and Metabolism of (Dichlorophenyl-U-

(Carbon 14))-Diclofop-Methyl in Bluegill, Lepomis macrochirus: Lab Project Number: 46910: 

601BL. Unpublished study prepared by ABC Laboratories, Inc. 139 p. 

84654 Cubbedge, S.D. (1981) Analysis of HOE 23408 and HOE 35449 in Rainbow Trout: PL No. 81PL624-1. (Unpublished study, including letter dated Jul 30, 1981 from S.D. Cubbedge to Hanson H. 

North, received Oct 7, 1981 under 8340-11; prepared by Biospherics, Inc., submitted by American 

Hoechst Corp., Somerville, N.J.; CDL:246021-F) 

87812 Gorbach, S.; Kunzler, K.; Knauf, W.; et al. (1977) Uptake of Hoe 23408 OH Residues from a 

Water-soil System by Catfish (Ictalurus nebulosus) and Dissipation of the Taken Up Residues in 

Fresh Water: Bericht-Nr. Fo.Ber. 281/77; A11571. (Unpublished study received Dec 30, 1981 under 

8340-11; prepared by Hoechst AG, West Germany, submitted by American Hoechst Corp., 

Somerville, N.J.; CDL:246515-A) 

166-1 Ground water-small prospective 

MRID Citation Reference 
Page 38 of 50 

41220701 

 

Chang, H. (1989) Phase I - Site Selection and Characterization Assessment of Diclofop-methyl 

Leaching Potential: Small Scale Prospective Groundwater Monitoring Study: Proj. ID 3/88-HRA.1. 

Unpublished study prepared by Twin City Testing Corp. 114 p. 

41367601 Chang, H. (1990) Phase I - Site Selection and Characterization Assessment of Diclofop-methyl 

Leaching Potential: Small Scale Prospective Groundwater Monitoring Study: Field Infiltration Test 

& Grain Size Analysis: Supplement to Phase I...: Lab Project 88-HRA-001-B; 88-0086; 3/88-

HRA.1. Unpublished study pre- pared by Twin City Testing Corp. 36 p. 

43860301 Bregger, T.; Holden, R.; Witkin, D. (1995) Small-Scale Prospective Groundwater Monitoring Study 

for Diclofop-Methyl (Hoelon 3EC): First Progress Report: Lab Project Number: BL-94R-01. 

Unpublished study prepared by Agvise Labs; Quanterra Environmental Services; and Waterborne 

Environmental, Inc. 25 p. 

43956801 Bregger, T.; Holden, P. (1996) Small-Scale Prospective Groundwater Monitoring Study for 

Diclofop-Methyl (Hoelon 3EC): (Second Progress Report): Lab Project Number: A 55773: 622.02: 

BL-94R-01. Unpublished study prepared by Waterborne Environmental, Inc.; Agvise Labs; and 

Quanterra Environmental Services. 20 p. 

44088301 Bregger, T.; Holden, P. (1996) Small-Scale Prospective Groundwater Monitoring Study for 

Diclofop-methyl (Hoelon 3EC): (Third Progress Report): Lab Project Number: A 55819: BL-94R01: 622.02. Unpublished study prepared by Waterborne Environmental, Inc.; AgrEvo USA Co.; and 

Agvise Labs. 81 p. 

44158301 Kelly, I. (1996) Prospective Groundwater Monitoring Study for Diclofop-methyl (Hoelon 3EC): 

Supplement: Lab Project Number: A 55819. Unpublished study prepared by Waterborne 

Environmental, Inc.; Agvise Labs; and Quanterra Environmental Services. 55 p. 

44247801 Kelly, I.; Kelley, K. (1997) Small-Scale Prospective Ground-Water Monitoring Study for DiclofopMethyl (Hoelon 3EC): Fourth Progress Report: Lab Project Number: A 57721: BL-94R-01: 622.02. 

Unpublished study prepared by AgrEvo USA Co.; Agvise Laboratories; and Quanterra 

Environmental Services. 102 p. 

44532501 Kelly, I.; Singer, S.; Johnson, L. et al. (1998) A Small-Scale Prospective Ground-Water Monitoring 

Study for Diclofop-Methyl (Hoelon 3EC): Final Report: Lab Project Number: BL-94R-01: A59908: 

622.02. Unpublished study prepared by Waterborne Environmental, Inc., Agvise Labs., Inc. and 

AgrEvo USA Co. 424 p. 

 
Page 39 of 50 

APPENDIX B: ECOLOGICAL TOXICITY DATA 

Toxicity to Terrestrial Animals 

Birds, Acute and Subacute 

The following are results for the acute oral toxicity testing with an upland game bird using 

technical grade diclofop-methyl. Since the LD50 obtained in both studies exceeds 2000 mg/kg, 

diclofop-methyl is categorized practically nontoxic to avian species on an acute oral basis. The 

guideline requirement for this test (71-1) is fulfilled by MRID 40072903. 

Acute Oral Toxicity to birds.

Species % ai LD50 (mg/kg) Toxicity Category 

MRID No. 

Author/Year 

Study 

Classification1

Northern bobwhite quail 

(Colinus virginianus)

94.5 >2250 Practically nontoxic 40072903 

Hinken et al., 

1986 

Core 

Northern bobwhite quail 

(Colinus virginianus)

95 4,400 Practically nontoxic Acc. No. 097117 

1977 

Supplemental 

1

 “Core” indicates the study satisfies the guideline; “supplemental” indicates the study is scientifically sound, but does not satisfy the guideline. 

 

The following are results of subacute dietary testing with an upland game bird (the northern 

bobwhite) and a waterfowl (the mallard) using technical grade diclofop-methyl. Since all of the 

LC50's exceed 5000 ppm, diclofop-methyl is categorized as practically nontoxic to birds on a 

subacute dietary basis. The test guideline requirement (71-2) is fulfilled by MRID 40072901 and 

40072902, and Acc. No. 097291. 

Subacute dietary toxicity to birds.

Species % ai 

5-Day LC50

(ppm)1 Toxicity Category 

MRID No. 

Author/Year 

Study 

Classification 

Northern bobwhite 

(Colinus virginianus)

95 13,000 Practically nontoxic Acc. No. 097117 

Roberts,1977 

Core 

Northern bobwhite 

(Colinus virginianus)

94.5 >5620 Practically nontoxic 40072901 

Hinken et al., 

1986 

Core 

Mallard 

(Anas platyrhynchos)

95 >20,000 Practically nontoxic Acc. No. 097291 Core 

Mallard 

(Anas platyrhynchos) 

94.5 >5620 Practically nontoxic 40072902 

Hinken et al., 

1986 

Core 

Coturnix quail 

(Coturnix coturnix japonica) 

95 >20,000 Practically nontoxic Acc. No. 094682 

Terrell & Parke, 

1975 

Supplemental 

 

1

 Test organisms observed an additional three days while on untreated feed. 
Page 40 of 50 

Birds, Chronic

The following are results of avian reproductive studies with technical grade active ingredient. 

The studies found no significant effect of reproduction or parental toxicity at dietary 

concentrations up to 200 ppm. The studies are supplemental because the test levels were not 

high enough to determine the NOAEL and LOAEL, and the highest test concentration was less 

than the maximum expected environmental concentration (EEC). With a maximum application 

rate of 1 lb AI/A, the maximum EEC is 240 ppm. Because the available data is sufficient to 

conclude a low risk of chronic effects to birds, a request to waiver new avian reproduction 

studies to fulfill this guideline has been approved by EFED (Bar Code #D261423). 

Avian reproduction toxicity 

Species/ 

Study Duration % ai 

NOAEL 

(ppm) 

LOAEL 

(ppm) 

LOAEL 

Endpoints 

MRID No. 

Author/Year 

Study Classification 

Northern bobwhite 

(Colinus virginianus)

94.5 200 Not 

determined 

None Acc. No. 098297 and 

243472 

Supplemental 

Mallard 

(Anas platyrhynchos)

94.5 200 Not 

determined 

None Acc. No. 098297 and 

243472 

Supplemental 

Mammals, Acute and Chronic

Wild mammal testing is not required for diclofop-methyl because rat toxicity test submitted to 

the Agency's Health Effects Division (HED) provide adequate information on toxicity to 

mammals. Table 4-eco gives acute rat toxicity values for technical diclofop-methyl and a 

formulated product. The geometric mean of the LD50 for male and female rats is 568 mg ai/kg. 

This indicates that diclofop-methyl is moderately toxic to small mammals on an acute oral basis. 

Acute Toxicity to Mammals

Species % ai Test type LD50 (mg/kg) MRID/Acc. No. 

Rat (Rattus norvegicus) “Technical” Acute oral 580 (male) 

557 (female) 

097107 

Rat (Rattus norvegicus) 36% Acute oral 2029 (male) 

(730 mg ai/kg) 

Rat (Rattus norvegicus) “Technical” Acute dermal > 5000 
Page 41 of 50 

A limited amount of information on the subchronic toxicity of diclofop acid, the primary 

degradation product of diclofop-methyl, is provided by a subchronic study with the rat (MRID 

not listed). This study found that a dietary concentration of 500 ppm of diclofop acid caused 

increased kidney weight in males. The NOAEL was 100 ppm. For comparison, a 30-day 

feeding study with the rat testing diclofop-methyl found increased organ weights in males at a 

dietary concentration of 80 ppm. This study did not determine the NOAEL. These results 

indicate that diclofop acid is less toxic to mammals than is the parent compound, diclofopmethyl. 

The following are the results of some chronic and subchronic mammalian studies that are 

pertinent to ecological effects. Based on these results, the NOAEL and LOAEL for ecologically 

significant effects in mammals are established at 30 ppm and 100 ppm, respectively, based on 

pup mortality observed in the 3-generation reproduction test. It is noteworthy that a short-term 

(15-week) developmental study showed fetotoxic effects with an oral dose of 32 mg/kg body 

weight, which is approximately equivalent to an dietary dose of 640 ppm. This indicates that 

short-term exposure to diclofop-methyl can impair reproduction of mammals, although 

somewhat higher doses are required than for long-term exposures. 

Subchronic and Chronic Toxicity to Mammals

Species % ai Test Type Toxicity Value 

Affected 

Endpoints MRID/Acc. No. 

Rat (Rattus 

norvegicus) 

98 3 generation 

reproduction 

NOAEL=30 ppm 

LOAEL=100 ppm 

Increased pup mortality 097111 

Rat (Rattus 

norvegicus) 

“Tech.” Developmental Teratogenicity: 

 NOAEL>100 mg/kg 

 (2000 ppm) 

Fetotoxic: 

 NOAEL=10 mg/kg 

 (200 ppm) 

 LOAEL=32 mg/kg 

 (640 ppm) 

Maternal: 

 NOAEL<10 mg/kg 

 (200 ppm) 

Teratogenic: 

 none 

Fetotoxic: 

reduced body weight gain, 

increased resorptions, 

dilation of renal pelvis, 

distention of uterus. 

Maternal: 

increased liver weight 

097108 

Insects

A honey bee acute toxicity study (Guideline No. 141-1) is required for diclofop-methyl because 

Diclofop-methyl is a systemic herbicide and could pose risk to bees. Its use sites (wheat, barley, 

and turf) and application methods may result in exposure to honey bees. 

Toxicity to Freshwater Aquatic Animals

Freshwater Fish, Acute

The following are the results of acute toxicity testing with freshwater fish using technical grade 

diclofop-methyl and a formulated product. The LC50 values for both a coldwater test species (the 

rainbow trout) and a warmwater test species (the bluegill sunfish) falls in the range of 0.1 to 1 
Page 42 of 50 

ppm, classifying diclofop-methyl as highly toxic to freshwater fish on an acute basis. The test 

guideline requirement (72-1) is fulfilled by MRIDs 41573302 and 41606301, and Acc. No. 

098297 for the TGAI (72-1(a) and 72-1(c)) and by MRIDs 41606302 and 41606303 for the 

formulated product. 

Acute toxicity to freshwater fish

Species, Study type % AI 

96-hour 

LC50 (ppm) Toxicity Category 

MRID No. 

Author/Year 

Study 

Classification 

Rainbow trout 

(Oncorhynchus mykiss)

static 

95.1 0.23 Highly toxic 41573302 

Frank et al., 1990 

Core 

Rainbow trout 

(Oncorhynchus mykiss)

“Technical” 0.54 Highly toxic USEPA, 1979 Core 

Rainbow trout 

(Oncorhynchus mykiss),

static 

95 0.25 Highly toxic USFWS, 1978 Core 

Rainbow trout 

(Oncorhynchus mykiss)

95 0.17 Highly toxic Acc. No. 094682 

Reinert & Roger, 

1975 

Supplemental 

Rainbow trout 

(Oncorhynchus mykiss)

“Technical” 0.32 Highly toxic Acc. No. 098297 Core 

Rainbow trout 

(Oncorhynchus mykiss),

static 

34.8 

(3 EC) 

0.65 (formulation) 

0.22 (AI) 

Highly toxic 41606303 

Smith & 

Schweitzer, 1990 

Core 

Bluegill sunfish 

(Lepomis macrochirus)

95.1 0.15 Highly toxic 41606301 

Smith & 

Schweitzer, 1990 

Core 

Bluegill sunfish 

(Lepomis macrochirus)

Technical 0.31 Highly toxic USEPA, 1979 Core 

Bluegill sunfish 

(Lepomis macrochirus)

95 0.54 Highly toxic USFWS, 1978 Core 

Bluegill sunfish 

(Lepomis macrochirus)

95 0.29 Highly toxic Acc. No. 094682 

Reinert & Roger, 

1975 

Supplemental 

Bluegill sunfish 

(Lepomis macrochirus)

Technical 0.24 Highly toxic 098297 Supplemental 

Bluegill sunfish 

(Lepomis macrochirus)

34.8 

(3 EC) 

0.36 (formulation) 

0.13 (AI) 

Highly toxic 41606302 

Smith & 

Schweitzer, 1990 

Core 

A study with the rainbow trout provides information on the free acid metabolite of diclofopmethyl. The 96-hr LC50 was determined to be 21.9 ppm (19.3-24.9) with an NOAEC of 13.5 

ppm. This indicates that the acid metabolite of diclofop-methyl is less toxic to fish than the 

parent by almost two orders of magnitude (Acc. No. 098297). 
Page 43 of 50 

Freshwater Fish, Chronic 

The following are the results of chronic toxicity testing with freshwater fish using technical 

grade diclofop-methyl. The results of two early life-stage toxicity tests indicate that 

concentrations of 46 ppb or greater are detrimental to the survival of immature fish. The lifecycle toxicity test indicates that exposure throughout a fish’s life-cycle will impairment of larval 

growth at concentrations of 15 ppb or greater. The NOAEC for the most sensitive chronic 

endpoint was established at 7.5 ppb. The test guideline requirement for early life-stage testing 

(72-4) has been fulfilled by MRID 00076867 and Acc. No. 246021, and that for life-cycle testing 

(72-5) has been fulfilled by MRID 43284601. 

 Chronic toxicity to freshwater fish

Species, 

Study duration % ai 

NOAEC 

(ppb) 

LOAEC 

(ppb) 

MATC1

(ppb) 

Endpoints 

Affected 

MRID No. 

Author/Year 

Study 

Classification 

Early Life-Stage Toxicity Test 

Fathead minnow 

(Pimephales 

promelas) 

93 39 86 58 Survival, percent 

hatch 

MRID 00076867 

Wilson, 1981 

Core 

Rainbow trout 

(Oncorhynchus 

mykiss), 30 days 

93 22 46 32 Survival Acc. No. 246021 

Wilson, 1981 

Core 

Life-Cycle Toxicity Test 

Fathead minnow 

(Pimephales 

promelas)

95.3 7.5 15 10.6 larval growth 43284601 

Dionne, 1994 

Core 

1

 defined as the geometric mean of the NOAEC and LOAEC. 

Freshwater Invertebrates, Acute

The following are the results of acute toxicity testing with freshwater invertebrates using 

technical grade diclofop-methyl and a formulated product. The mean LC50 value of the two core 

studies with the TGAI is 0.39 ppm. The LC50 obtained from a test with a formulated product 

was similar (0.37 ppm AI). Because the LC50's fall within the range of 0.1 to 1 ppm, diclofopmethyl is classified as highly toxic to freshwater fish on an acute basis. The test guideline 

requirement for the TGAI (72-2(a)) is fulfilled by 41573303 and USEPA (1979), and the test 

guideline requirement for a TEP (72-2(b)) is fulfilled by 4141606304. 

Acute toxicity to freshwater invertebrate

Species 

Static or Flow-through % AI 

48-hour LC50/ 

EC50 (ppm) Toxicity Category 

MRID No. 

Author/Year 

Study 

Classification 

Waterflea 

(Daphnia magna), 

static 

95.1 0.23 Highly toxic 41573303 

Frank et al., 1989 

Core 

Waterflea 

(Daphnia magna)

“Technical” 0.54 Highly toxic USEPA, 1979 Core 

Waterflea 34.8 1.06 (formulation) Moderately toxic 41606304 Core 
Page 44 of 50 

Acute toxicity to freshwater invertebrate

(Daphnia magna), 

static 

0.37 (a.i.) (formulation), highly 

toxic (a.i.) 

Smith & 

Schweitzer, 1990 

Waterflea 

(Daphnia magna)

34.8 1.9 (formulation) 

0.66 (a.i.) 

Moderately toxic 

(formulation), highly 

toxic (a.i.) 

ESVIIH, 1978 Supplemental 

Freshwater Invertebrate, Chronic

The following are the results from a freshwater aquatic invertebrate life-cycle test using technical 

diclofop-methyl. This test found that diclofop-methyl caused a reduction in number of eggs 

produced at a concentration of 166 ppb, whereas a concentration of 64 ppb caused no significant 

observed effect. The test guideline requirement (72-4) is fulfilled by MRID 41737902. 

Life-cycle toxicity with a freshwater aquatic invertebrate. 

Species, Study 

type % ai 

21-day 

NOAEC 

(ppb) 

LOAEC 

(ppb) 

MATC1

(ppb) 

Endpoints 

Affected 

MRID No. 

Author/Year 

Study 

Classification 

Waterflea 

(Daphnia magna), 

static renewal 

95.1 64 166 103 Number of 

young produced 

41737902 

Smith, 1990 

Core 

1

 defined as the geometric mean of the NOAEC and LOAEC. 

Toxicity to Estuarine and Marine Animals

Estuarine and Marine Fish 

Toxicity testing with estuarine/marine fish is required for current uses of diclofop-methyl (wheat, 

barley, and turf) because some of these uses can occur in coastal areas. Diclofop-methyl is highly 

acutely toxic to freshwater fish and invertebrates. 

The majority of use is on wheat and barley, which is grown mostly in inland areas. Use on turf is 

only as a Special Local Need registration for use on golf courses in 11 states and is a minor use 

of diclofop-methyl (2.6% of pounds sold). However, a small portion of the golf course use is 

expected to be adjacent to estuarine areas. Labels restrict use to within 100 feet of any water 

body. Chronic toxicity testing with a marine/estuarine fish is not required. 

Estuarine and Marine Invertebrates, Acute

Toxicity testing with estuarine/marine invertebrates is required for current uses of diclofopmethyl (wheat, barley, and turf) because some of these uses occur in coastal areas. Diclofopmethyl is highly acutely toxic to freshwater fish and invertebrates. Acute oyster toxicity studies 

have been conducted with diclofop-methyl and the diclofop-methyl metabolite 2-(4-(2,4-

dichlorophenoxy) phenoxy) propionic acid (Acc. No. 245123; however, the results of these 

studies are considered invalid because the percent active ingredient of the test material was not 

identified. Chronic toxicity testing with a marine/estuarine invertebrate is not required at this 

time. Labels restrict use to within 100 feet of any water body. 
Page 45 of 50 

Toxicity to Plants

Terrestrial 

Tier 2 terrestrial plant testing is required for diclofop-methyl because it is an herbicide that has 

terrestrial non-residential outdoor use patterns, could move off the application site via runoff and 

spray drift (for aerial applications), and might affect endangered or threatened plant species 

associated with the application sites. The required testing consists of seedling emergence and 

vegetative vigor tests with ten crop species. Six of the species must be dicotyledonous and 

represent at least four families. One of these species must be soybean (Glycine max) and a 

second must be a root crop. The remaining four species must be monocotyledonous and 

represent at least two families. One of these species must be corn (Zea mays). 

The following are the results of tier 2 seedling emergence testing. Ryegrass is the most sensitive 

monocotyledon and the most sensitive species overall, with an EC25 of 0.012 lb ai/A and an 

NOAEC of 0.0063 lb ai/A. Lettuce was the most sensitive dicotyledon. These data indicate that 

monocotyledons are much more sensitive to diclofop-methyl than are dicotyledons. The 

guideline for seedling emergence testing (123-1a) is fulfilled (MRID 41606306). 

Seedling emergence toxicity of nontarget terrestrial plant (Tier II)

Species % ai 

EC25

(lb ai/A) 

NOAEC 

(lb ai/A) Most Sensitive Endpoint 

MRID No. 

Author/Year 

Study 

Classification 

Corn (monocot) 95.1 0.083 0.100 Radical length 41606306 

Chetram, 1990 

Core 

Oat (monocot) 95.1 0.362 0.125 Plant height 41606306 

Chetram, 1990 

Core 

Onion (monocot) 95.1 0.394 0.500 Plant height 41606306 

Chetram, 1990 

Core 

Ryegrass (monocot) 95.1 0.012 0.0063 Plant height (based on 

the EC25) or radical 

length (based on the 

NOAEC) 

41606306 

Chetram, 1990 

Core 

Carrot (dicot, root crop) 95.1 >1.0 1.0 N/A 41606306 

Chetram, 1990 

Core 

Soybean (dicot) 95.1 > 1.0 1.0 N/A 41606306 

Chetram, 1990 

Core 

Cabbage (dicot) 95.1 1.25 0.5 Plant height 41606306 

Chetram, 1990 

Core 

Cucumber (dicot) 95.1 > 1.0 1.0 N/A 41606306 

Chetram, 1990 

Core 

Lettuce (dicot) 95.1 0.792 0.25 Plant dry weight 41606306 

Chetram, 1990 

Core 

Tomato (dicot) 95.1 > 1.0 1.0 N/A 41606306 

Chetram, 1990 

Core 
Page 46 of 50 

The following are results of Tier 2 vegetative vigor testing. Results were similar to the seedling 

emergence test in showing that monocotyledons are much more sensitive to diclofop-methyl than 

are dicotyledons. Ryegrass is the most sensitive monocotyledon and the most sensitive species 

overall, with an EC25 of 0.10 lb ai/A and an NOAEC of 0.0625 lb ai/A. Lettuce was the most 

sensitive dicotyledon. The guideline for vegetative vigor testing (123-1b) is fulfilled (MRID 

41606306). 

 Vegetative vigor toxicity to nontarget terrestrial plant (Tier II)

Species % ai 

EC25

(lb ai/A) 

NOAEC 

(lb ai/A) Most Sensitive Endpoint 

MRID No. 

Author/Year 

Study 

Classification 

Corn (monocot) 95.1 0.101 0.05 Plant height 41606305 

Chetram, 1990 

Core 

Oat (monocot) 95.1 > 0.5 0.5 N/A 41606305 

Chetram, 1990 

Core 

Onion (monocot) 95.1 > 1.0 1.0 N/A 41606305 

Chetram, 1990 

Core 

Ryegrass (monocot) 95.1 0.10 0.0625 Plant height 41606305 

Chetram, 1990 

Core 

Carrot (dicot, root crop) 95.1 > 1.0 1.0 N/A 41606305 

Chetram, 1990 

Core 

Soybean (dicot) 95.1 >1.0 1.0 N/A 41606305 

Chetram, 1990 

Core 

Cabbage (dicot) 95.1 4.69 0.500 Plant height 41606305 

Chetram, 1990 

Core 

Cucumber (dicot) 95.1 >1.0 1.0 N/A 41606305 

Chetram, 1990 

Core 

Lettuce (dicot) 95.1 1.00 0.50 Plant dry weight 41606305 

Chetram, 1990 

Core 

Tomato (dicot) 95.1 >1.0 1.0 N/A 41606305 

Chetram, 1990 

Core 

Data are not available on the phytotoxicity of diclofop acid, the major degradation product of 

diclofop-methyl. 

Aquatic Plants

Aquatic plant testing is required for any herbicide that has outdoor non-residential terrestrial uses 

that may move off-site by runoff, by drift, or that is applied directly to water. Only one aquatic 

plant study (growth inhibition using duck weed) has been submitted for diclofop-methyl or 

diclofop acid. Results indicate no inhibition above 50% (LC50 for frond number was 1.295 

Time-weighted average concentration with an NOAEC of 1.0 mg/L time-weighted average 

concentrations). 

 
Page 47 of 50 

APPENDIX C: Example of SIP INPUT and OUTPUT 

Drinking Water Exposure 

Drinking water for the purposes of terrestrial organism risk assessment is defined as that portion 

of an organism’s daily water intake that is not met by dietary or metabolic sources and must be 

consumed in liquid form. Typical drinking water sources for wildlife in pesticide use areas may 

include on-field puddles, irrigation equipment (e.g., drip irrigation in grape cultivation), dew 

deposited on treated plants, and off-field surface water exposures. 

The Screening Imbibition Program (SIP v.1.0, Released June 15, 2010) was used to calculate an 

upper bound estimate of exposure using diclofop-metyl’s solubility in water (0.8 mg/L at 25oC). 

Using TGAI data for the most sensitive acute (LD50 > 2250 mg a.i./kg-bw for the bobwhite 

quail, MRID 40072903) and chronic (NOAEC = 200 mg a.i./kg-diet, mallard duck, MRID 

243472) avian toxicity endpoints and the most sensitive acute (LD50 = 580 mg a.i./kg-bw, rat, 

MRID 097107) and chronic (reproduction NOAEC = 30 a.i./kg-diet, MRID 097111) mammalian 

toxicity endpoints. Drinking water exposure alone was determined not to be a potential pathway 

of concern for avian and mammalian species on an acute and chronic basis. Detailed information 

about the SIP v.1.0, as well as the tool, can be found on the EPA’s website at 

http://www.epa.gov/pesticides/science/models_pg.htm#terrestrial. 

 

 Table 1. Inputs 

 Parameter Value 

 Chemical name Diclofop-methyl 

 Solubility (in water at 25oC; mg/L) 0.8 

 

 Mammalian LD50 (mg/kg-bw) 580 

 Mammalian test species laboratory rat 

 

Body weight (g) of "other" mammalian 

species 

 

 Mammalian NOAEL (mg/kg-bw) 30 

 Mammalian test species laboratory rat 

 

Body weight (g) of "other" mammalian 

species 

 

 Avian LD50 (mg/kg-bw) >2250 

 Avian test species Quail 

 Mineau scaling factor 1.15 

 

 Mallard NOAEC (mg/kg-diet) 200 

 Bobwhite quail NOAEC (mg/kg-diet) 200 

 
Page 48 of 50 

 Table 2. Mammalian Results 

Parameter Acute Chronic 

Upper bound exposure (mg/kg-bw) 0.1376 0.1376 

Adjusted toxicity value (mg/kg-bw) 446.1131 23.0748 

Ratio of exposure to toxicity 0.0003 0.006 

Conclusion* Drinking water exposure alone is NOT a 

potential concern for mammals 

Drinking 

water 

exposure 

alone is 

NOT a 

potential 

concern 

for 

mammals

 

Table 3. Avian Results 

Parameter Acute Chronic 

Upper bound exposure (mg/kg-bw) 0.6480 0.648 

Adjusted toxicity value (mg/kg-bw) 1588.5471 9.9225 

Ratio of exposure to acute toxicity 0.0004 0.0653 

Conclusion* Drinking water exposure alone is NOT a 

potential concern for birds 

Drinking 

water 

exposure 

alone is 

NOT a 

potential 

concern 

for birds 

*Conclusion is for drinking water exposure alone. This does not combine all routes of exposure. 

Therefore, when aggregated with other routes (i.e., diet, inhalation, dermal), pesticide exposure through 

drinking water may contribute to a total exposure that has potential for effects to non-target animals. 

 
Page 49 of 50 

APPENDIX D: STIR inputs and outputs 

Inhalation Exposure 

The Screening Tool for Inhalation Risk (STIR v.1.0, November 19, 2010) was used to calculate 

an upper bound estimate of exposure using diclofop-methyl’s vapor pressure (1.9 x 10-7 mm Hg at 

25oC) and molecular weight (341.19 g/mol) for vapor phase exposure as well as the maximum 

application rate (1 lbs a.i./A, which is the maximum seasonal application rate to wheat and method 

of application (aerial spray) for spray drift. STIR incorporates results from several toxicity studies 

including acute oral and inhalation rat toxicity endpoints obtained from the “six-pack” of core 

studies, which are a series of six guideline studies that are submitted to the Registration Division 

of the Office of Pesticide Programs on laboratory rats for technical and formulated products of a 

pesticide (rat acute oral (TGAI): LD50 = 557 mg a.i./kg-bw; rat inhalation (TGAI): LC50 = >1.36 

mg/L (data from Footprint Database). In addition, the most sensitive acute oral avian toxicity 

endpoint (bobwhite quail, LD50 = 2250 mg a.i./kg-bw was used. Based on the results of the STIR 

model, inhalation exposure alone was not determined to be a potential pathway of concern for 

avian or mammalian species on an acute basis as a result of spray applications of diclofop-methyl. 

Inhalation exposure via spray drift and/or vapor-phase of the pesticide alone does not appear to be 

of concern. The analysis of the inhalation route in STIR does not consider that aggregation with 

other exposure pathways such as dietary, dermal, or drinking water may contribute to a total 

exposure that has a potential for effects to non-target animals. However, the Agency does consider 

the relative importance of other routes of exposure in situations where data indicate that pesticide 

exposures through other routes may be potentially significant contributors to wildlife risk (USEPA, 

2004). Detailed information about STIR v.1.0, as well as the tool, can be found on the EPA’s 

website at: http://www.epa.gov/pesticides/science/models_pg.htm#terrestrial. 

 

Input 

Application and Chemical Information 

Enter Chemical Name Diclofop-methyl 

Enter Chemical Use wheat 

Is the Application a Spray? (enter y or n) y 

If Spray What Type (enter ground or air) air 

Enter Chemical Molecular Weight (g/mole) 341.19 

Enter Chemical Vapor Pressure (mmHg) 1.90E-07 

Enter Application Rate (lb a.i./acre) 1 

 

Toxicity Properties 

Bird 

Enter Lowest Bird Oral LD50 (mg/kg bw) 2250 

Enter Mineau Scaling Factor 1.15 

Enter Tested Bird Weight (kg) 0.178 

Mammal 

Enter Lowest Rat Oral LD50 (mg/kg bw) 557 

Enter Lowest Rat Inhalation LC50 (mg/L) 1.36 
Page 50 of 50 

Duration of Rat Inhalation Study (hrs) 4 

Enter Rat Weight (kg) 0.35 

 

Output 

Results Avian (0.020 kg ) 

Maximum Vapor Concentration in Air at Saturation 

(mg/m3) 3.49E-03 

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 4.39E-04 

Adjusted Inhalation LD50 3.06E+01 

Ratio of Vapor Dose to Adjusted Inhalation LD50 1.43E-05 Exposure not Likely Significant 

Maximum Post-treatment Spray Inhalation Dose (mg/kg) 9.61E-02 

Ratio of Droplet Inhalation Dose to Adjusted Inhalation 

LD50 3.14E-03 Exposure not Likely Significant 

 

Results Mammalian (0.015 kg ) 

Maximum Vapor Concentration in Air at Saturation 

(mg/m3) 3.49E-03 

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 5.51E-04 

Adjusted Inhalation LD50 8.10E+01 

Ratio of Vapor Dose to Adjusted Inhalation LD50 6.81E-06 Exposure not Likely Significant 

Maximum Post-treatment Spray Inhalation Dose (mg/kg) 1.21E-01 

Ratio of Droplet Inhalation Dose to Adjusted Inhalation 

LD50 1.49E-03 Exposure not Likely Significant