Ecological Risk Assessment for Use of 

S-Metolachlor (PC 108800) 

On 

Pumpkins and Winter Squash (DP324973, DP327861) 

May 2006 

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Table of Contents 

1. Executive Summary.................................................................................................... 5 

1.1 Nature of Stressor ............................................................................................... 5 

1.2 Potential Risk...................................................................................................... 5 

1.3 Endangered Species Assessment ........................................................................ 7 

2. Problem Formulation ................................................................................................ 11 

2.1 Stressor Description.......................................................................................... 11 

2.2 Environmental Fate Summary .......................................................................... 12 

2.3 Mode of Action................................................................................................. 13 

2.4 Use Characterization......................................................................................... 14 

2.5.1 Ecosystems Potentially at Risk ................................................................. 15 

2.5.2 Ecological Effects ..................................................................................... 16 

2.7 Risk Hypotheses................................................................................................ 18 

2.8 Key Uncertainties and Information Gaps ......................................................... 18 

3. Exposure Assessment................................................................................................ 19 

3.1 Label Application Rates and Intervals.............................................................. 19 

3.2 Aquatic Exposure.............................................................................................. 19 

3.2.1 PRZM-EXAMS Modeling Inputs and Scenario Selection ....................... 19 

3.2.2 PRZM-EXAMS Modeling Output............................................................ 20 

3.2.3 GENEEC Modeling for Degradates.............................................................. 21 

3.3 National Surface Water Monitoring Data Assessment ..................................... 22 

3.5 Bird and Mammal Exposure (TREX)............................................................... 23 

3.6 Terrestrial Plant Exposure (TerrPlant & AgDrift)............................................ 24 

3.6.1 TerrPlant ................................................................................................... 24 

3.6.2 AgDrift...................................................................................................... 25 

4. Effects Assessment ................................................................................................... 26 

4.1 Aquatic Hazard Summary................................................................................. 26 

4.3 Avian and Small Mammal Guideline Data....................................................... 33 

4.4 Terrestrial Insect Data....................................................................................... 34 

4.5 Terrestrial Animal Data from ECOTOX .......................................................... 34 

4.7 Incident Database Review................................................................................. 34 

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5. Risk Estimation......................................................................................................... 34 

5.1 Aquatic RQ Summary....................................................................................... 35 

5.2 Terrestrial RQ Summary................................................................................... 36 

5.2.1 Terrestrial Plants ....................................................................................... 36 

5.2.1.1 TerrPlant ................................................................................................... 36 

5.2.1.2 AgDrift...................................................................................................... 38 

5.2.2 Avian RQ Summary.................................................................................. 38 

5.2.3 Small Mammal RQ Summary................................................................... 39 

5.2.4. Terrestrial Insects...................................................................................... 39 

6. Risk Description........................................................................................................ 40 

6.1 Aquatic Risk...................................................................................................... 40 

6.1.2 Aquatic Animals ....................................................................................... 40 

6.2 Terrestrial Risk.................................................................................................. 41 

6.2.1 Plants......................................................................................................... 41 

6.2.2 Animals (Birds, Mammals, Insects).......................................................... 41 

6.3 Endangered Species .......................................................................................... 42 

6.3.1 Aquatic Endangered Species..................................................................... 42 

6.3.2 Plants......................................................................................................... 43 

6.3.3 Birds, Reptiles & Amphibians .................................................................. 45 

6.3.4 Mammals................................................................................................... 48 

6.3.5 Probability of Individual Effects............................................................... 49 

References......................................................................................................................... 50 

ECOTOX References....................................................................................................... 51 

Appendix A Aquatic Exposure PRZM-EXAMS Output ........................................... 52 

Appendix B Terrestrial Animals Exposure TREX Output........................................ 53 

Appendix C Terrestrial Plant Exposure Output (TerrPlant, AgDrift) .................... 54 

Appendix D Aquatic RQ Calculations......................................................................... 55 

Appendix E Incident Database Report EIIS Output.................................................. 56 

Appendix F Risk Quotient Method and Levels of Concern....................................... 57 

Appendix G Threatened and Endangered Species LOCATES Output.................... 58 

 

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List of Tables 

Table 1 Endangered Species Occurring in the Same County as Proposed Crops .............. 7 

Table 2 Summary of Direct and Indirect Effects............................................................. 10 

Table 3 Label Application Rates....................................................................................... 19 

Table 4 Input Parameters for PRZM-EXAMS Modeling................................................. 20 

Table 5 PRZM-EXAMS EECs ........................................................................................ 21 

Table 6 GENEEC Input Parameters for Degradates........................................................ 21 

Table 7 EECs for Degradates........................................................................................... 22 

Table 8 Bird Dose Estimates............................................................................................. 23 

Table 9 Mammal Dose Estimates ..................................................................................... 24 

Table 10 Terrestrial Plant Exposure (TerrPlant)............................................................... 25 

Table 11 Terrestrial Plant Exposure (AgDrift, Ground spray) ......................................... 25 

Table 12 Acute Aquatic Data from Registrant-submitted Studies.................................... 28 

Table 13 Chronic Aquatic Data from Registrant-submitted Studies ................................ 28 

Table 14 Acute Aquatic Degradate Data from Registrant-submitted Studies .................. 29 

Table 15 Aquatic Data from ECOTOX ............................................................................ 30 

Table 16 Terrestrial Plant Guideline Data ........................................................................ 32 

Table 17 Terrestrial Plant Data from ECOTOX............................................................... 32 

Table 18 Avian and Small Mammal Guideline Data from Acute Studies........................ 33 

Table 19 Avian and Small Mammal Guideline Data from Chronic Studies .................... 33 

Table 20 Summary of Aquatic RQs for S-metolachlor .................................................... 35 

Table 21 Summary of Aquatic RQs for Degradates ......................................................... 36 

Table 22 Terrestrial Plant Risk Quotients Based on TerrPlant......................................... 37 

Table 23 Required Distance from Application to Fall Below LOC ................................. 38 

Table 24 Avian RQ Summary........................................................................................... 38 

Table 25 Small Mammal RQ Summary............................................................................ 39 

Table 26 Endangered Plants by State and Crop................................................................ 44 

Table 27 Endangered birds potentially at risk from s-metolachlor................................... 46 

Table 28 Endangered reptiles and amphibians potentially at risk from S-metolachlor.... 47 

Table 29 Endangered mammals potentially at risk from S-metolachlor .......................... 48 

Table of Figures 

Figure 1 Chemical structure of metolachlor and all possible stereochemical 

conformations ........................................................................................................... 11 

Figure 2 Chemical structures for S-metolachlor degradates............................................ 12 

Figure 3 Conceptual model for S-metolachlor effects..................................................... 17 

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1. Executive Summary 

This ecological risk assessment evaluates the use of the herbicide S-metolachlor 

(PC108800) on the minor crops of pumpkins and winter squash. Based on the proposed 

label addition, the existing label (Dual II Magnum®, EPA Reg. #100-818), and 

communications with the registrant (Syngenta), the model parameters included a yearly 

maximum rate of 1.33 pt/A/year of formulated product (1.27 lb ai/A/year), and 

application via ground spray. A 400 ft buffer from sensitive plants is noted in the label. 

Application rates vary dependent on soil organic matter. A higher rate (1.33 pt/A 

formulated product, equivalent to 1.27 lb ai/A) is used on soils containing >3% organic 

matter, and a lower rate of 1.0 pt/A formulated product (equivalent to 0.95 ai/A) for soils 

with less organic matter. Throughout the assessment, both rates are evaluated for all 

endpoints. 

1.1 Nature of Stressor 

S-metolachlor is a chloroactanilide herbicide, classified as a seedling shoot growth 

inhibitor. It inhibits biosynthesis in plants, although the specific biochemical target has 

not been identified. It is slightly toxic to practically nontoxic to birds, and moderately 

toxic to fish. Two degradates, the ethane sulfonic acid (ESA) and the oxanilic acid (OA) 

have been identified as potentially of toxicological concern. OA is slightly toxic to both 

fish and aquatic invertebrates. ESA is slightly toxic to fish, and practically nontoxic to 

aquatic invertebrates. Neither is as active against aquatic or terrestrial plants as the 

parent. S-metolachlor is persistent and highly mobile in soil. S-metolachlor and the 

major degradates OA and ESA have been detected in surface and groundwater, especially 

in the Midwest, where it is used extensively for corn. 

1.2 Potential Risk 

Terrestrial Plants 

Non-target organisms most at risk from S-metolachlor use are terrestrial plants near the 

use site(s), especially herbaceous plants that are newly emerging. Plants are less likely to 

be affected when they are mature or actively growing, and are exposed to S-metolachlor 

via foliar contact. Non-endangered plant and endangered plant LOCs are exceeded by at 

least an order of magnitude and sometimes up to three orders of magnitude in any areas 

receiving runoff from treated fields. Based on spray drift alone, risk quotients (RQs) for 

plants fall below the non-endangered species level of concern (LOC) beyond a downwind 

distance from the treated field of 250-300 ft (based on the more sensitive seedling 

emergence endpoint). This potential zone of impact is within the required 400-ft buffer 

established on the label for application distances from sensitive plants. However, the 

endangered species acute risk LOC is still exceeded at 600 ft away from the application 

point, based on AgDrift modeling. Clearance distances for mature plants (based on

vegetative vigor endpoints) are considerably less, ranging from 10-60 ft for the nonendangered plants LOC and at approximately 100 ft for the endangered plants. These 

clearance distances do not apply if the area receives runoff from the field. 

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Plant toxicity data was available for the metolachlor degradates OA and ESA. No 

significant effects are expected from the degradates, based on the toxicity data and 

estimated environmental concentrations (EECs). 

Disruption of plant communities near the use site could have effects on the diversity and 

abundance of wildlife inhabiting these areas. The composition and health of plant 

communities determine quantity and type of wildlife present. Plant communities serve 

both as shelter and food. 

Terrestrial Animals 

There were no acute risk or chronic risk concerns for direct effects to non-endangered 

birds. However, acute endangered species LOCs for small insectivorous and herbivorous 

birds were exceeded at the higher application rate (1.27 lb ai/A) and for small 

herbivorous birds at the lower application rate (0.95 lb ai/A). Acute RQs for birds ranged 

from <0.01 (frugivores and granivores) to 0.19 (small herbivorous birds, 1.27 lb ai/A 

application rate). 

There were no acute non-endangered or endangered species acute risk concerns for small 

mammals based on the conditions modeled. The chronic dose-based RQs ranged from 

1.70 to 8.81, which exceed the chronic risk LOC of 1). Chronic dietary-based RQs for 

these organisms ranged from 0.05 to 1.02. The RQ for small mammals consuming short 

grass exceeded the LOC at the higher application rate. Chronic effects noted in guideline 

studies were reduced weights of offspring in the F1 and F2 generations. These were the 

only effects noted, and occurred at the highest treatment level. Reduced offspring 

weight, especially for organisms in a natural environment, is often correlated with 

reduced survivability of individuals. 

Aquatic Plants and Animals 

In the aquatic environment, the primary productivity of the ecosystem is most likely to be 

affected. Acute risk and endangered species acute risk RQs exceeded the LOCs for the 

most sensitive freshwater non-vascular plant (a green alga, Selenastrum capricornutum) 

in all scenarios evaluated. Freshwater vascular plants appear to be less sensitive to the 

effects of S-metolachlor. Endangered species acute risk RQs exceeded the LOCs for the 

freshwater vascular plant (Lemna gibba) in all scenarios evaluated and RQs for nonendangered plants exceeded the LOC in scenarios where there is low organic matter 

(<3%) in the soil. The saltwater non-vascular plant (a diatom, Skeletonema costatum) 

was less sensitive than the green alga and there were no exceedences of the acute risk 

LOC, although aquatic concentrations from the uses in California and Florida were high 

enough that the endangered species acute risk LOC for saltwater aquatic plants was 

exceeded. 

In aquatic systems, the importance of primary productivity occurring within a given 

ecosystem varies widely. However, differential selection pressure for algal species could 

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have cascading effects up the food chain. Reduction in the numbers of green algae, 

which are generally considered a good food source for herbivorous aquatic invertebrates 

(such as Daphnia), with a concurrent increase in less palatable algal genera, such as bluegreen algae, could cause shifts in aquatic community composition, and/or result in overall 

reduction in biomass in the system. Assessing the likelihood or magnitude of such an 

effect on specific systems is beyond the scope of this document. Additionally, the 

presence and/or effectiveness of compensatory mechanisms within certain environments 

is unknown. 

There were no risk concerns for acute direct effects to endangered or non-endangered 

aquatic animals in freshwater or saltwater environments. The highest aquatic 

concentrations of S-metolachlo (1-in-10 year peak 35.1 ppb) were associated with the 

California scenario, although it was the lower application rate. For this scenario, the acute 

risk RQs for the aquatic animals were ranged from <0.01 to 0.02. Chronic RQs for 

aquatic invertebrates and fish ranged from 0.01 to 0.97. The chronic RQ for freshwater 

fish (0.97) approached, but did not exceed the LOC. The other chronic RQs were 

significantly lower (0.01-0.03). 

1.3 Endangered Species Assessment 

As an initial screening to determine what endangered species may be affected by 

proposed uses of S-metolachlor, EFED used LOCATES (Ver 2.10.0) to determine what 

species are known to occur in counties where the proposed crops are grown. All taxa 

were searched and a total of 1175 species are present in counties where pumpkins and 

squash are grown. Of all species identified, 56% are plants. A total of 830 (71%) could 

be directly affected, and 345 (29%) could be indirectly affected via habitat modification 

or food chain effects. Table 1 shows the number of unique species (i.e., species are 

counted only once, even if they are affected in multiple counties) which may be directly 

affected by use of S-metolachlor, based on exceedences of the endangered species LOCs. 

Aquatic organisms, which may be indirectly affected, are not included in the table but are 

listed in Appendix G. 

Table 1 Endangered Species Occurring in the Same County as Proposed Crops 

Taxa Pumpkins Winter Squash All Uses 

Monocots 58 61 61 

Dicots 520 568 576 

Other Plants1 19 21 22 

Amphibians 12 16 16 

Birds 70 71 71 

Reptiles 26 29 29 

Mammals 51 55 55 

1 Consists of conifers and cycads, ferns and allies, and lichens

Table 2 presents a summary of potential direct and indirect effects of S-metolachlor on 

endangered species. 

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Direct Effects -Plants 

S-metolachlor is primarily a germination inhibitor, thus the endangered plants most likely 

to be affected are ones in the process of germinating. Drift deposition of the herbicide on 

mature or actively growing plants appears unlikely to cause much effect. The TerrPlant 

model, which estimates exposure based on both runoff and drift, indicates that plants 

(both monocots and dicots) in areas receiving runoff from the treated field are likely to be 

affected. Total loading endangered species RQs (runoff plus drift) ranged from 57 to 

2328. 

A significant number of endangered plants occur in counties where pumpkins and squash 

are grown, especially the states of Hawaii, California, and Florida. An important aspect 

of determining the risk to these plants is their proximity to the use site(s). 

Direct Effects – Animals 

EFED evaluates risk to terrestrial organisms based on ingestion of contaminated food 

items. The amount of pesticide deposited on the food item varies dependent on its size 

and surface area. The dose the organism ingests is calculated using allometric equations. 

By sorting the animals identified by LOCATES into diet and size classes that correlate 

with the output from the TREX model, a refined list of animals potentially at risk can be 

created. Diet and size information was obtained from NatureServe database. 

Using this method, a total of 26 endangered birds were identified as potentially at risk. 

All were small insectivorous birds, and 13 of them occur only in Hawaii. Species 

information is shown in Table 27. Potential risk to reptiles and terrestrial phase 

amphibians is determined based on bird data. Reptiles and amphibians are not sorted by 

size class, as allometric equations derived for warm-blooded organisms are not expected 

to be applicable. A total of 26 herbivorous and insectivorous reptiles and amphibians 

were identified as potentially at risk (

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Table 28). Herbivorous and insectivorous mammals of all size classes exceeded chronic 

risk LOCs. A total of 12 species (Table 29) were identified as potentially at risk. 

Indirect Effects – Plants 

Pesticide-mediated indirect effects to plants are usually the loss of an important pollinator 

or dispersal species. Given the relatively low toxicity of s-metolachlor to animals in 

general, the likelihood of these types of effects appears to be low. Some endangered 

plant species may require the presence of other non-endangered plant species to create a 

suitable habitat. The effects of s-metolachlor on plant habitat could constitute an indirect 

effect, but without detailed information on the plant’s life history and distribution, EFED 

is unable to even qualitatively evaluate this type of effect. 

Indirect Effects - Animals 

The most likely indirect effect on animals is modification of habitat as a result of damage 

to plants. The habitat modification could include reduced food supply, reduced locations 

for nesting or burrowing, and/or reduced cover for predator avoidance. EFED is 

currently unable to evaluate the likelihood or magnitude of such an effect. 

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Table 2 Summary of Direct and Indirect Effects 

Evaluation 

Organism 

LOCATES 

Category Direct Effects Indirect Effects 

Monocots Monocots Other1

Dicots Dicots 

Yes 

Effects at both 

proposed application 

rates of 1.33 and 1.0 

pt/A 2

Possible 

Effects on birds or 

mammals could affect 

pollinator or dispersal 

species 

Birds 

Reptiles 

Birds Terrestrial 

Phase 

Amphibians 

Yes 

Acute effects, 

herbivores and 

insectivores, small size 

class, at 1.33 and 1.0 

pt/A 2

Mammals Mammals 

Yes 

Chronic effects, 

herbivores and 

invertivores, all size 

classes, at 1.33 and 1.0 

pt/A 2

Possible 

Modification of plant 

community could affect 

food and shelter 

FW Aquatic 

Plants 

FW Aquatic 

Plants 

Yes 

LOC exceedences for 

both algae and vascular 

plants 

SW Aquatic 

Plants 

SW Aquatic 

Plants 

Yes 

LOC exceedences

FW Crustacea No 

FW Bivalves No FW Aquatic 

Invertebrates FW Gastropods No 

FW Fish No 

FW Fish Aquatic Phase 

Amphibians No 

SW Crustacea No 

SW Bivalves No SW Aquatic 

Invertebrates SW Gastropods No 

SW Fish SW Fish No 

Possible 

Modification of primary 

productivity in the 

system could affect 

survival or fecundity of 

individuals. 

Modification of riparian 

vegetation could affect 

water temperature, 

allochthonous input, 

sedimentation, or bank 

stability 

1 Cycads, Conifers, Fern Allies. These genera have no direct corollary test organism, and have 

been evaluated based on the most sensitive plant endpoint. 

2 formulated product

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2. Problem Formulation 

Problem formulation provides a strategic framework for the risk assessment. By 

identifying the important components of the problem, it focuses the assessment on the 

most relevant chemical properties, exposure routes, and endpoints. 

2.1 Stressor Description 

S-metolachlor is a chloroactanilide herbicide, classified as a seedling shoot growth 

inhibitor. Metolachlor has four stable stereoisomers (Figure 1), because there is one 

chiral center (producing S- and R- enantiomers) and a chiral axis (U.S. PTO 1991). The 

product registered as S-metolachlor (PC108800) consists of 88% S-enantiomer and 12% 

R-enantiomer. It is a separate registration than the product known as metolachlor or 

racemic metolachlor (PC 108801), which consists of 50% S-enantiomer and 50% Renantiomer. The S-enantiomer is more herbicidally active. The Agency has determined 

that both environmental fate (D23688) and ecotoxicity (D233184) data submitted for 

racemic metolachlor and S-metolachlor to be comparable. For the purposes of this 

assessment, data for S-metolachlor are used if available. Gaps in the S-metolachlor data 

set are filled with data for racemic metolachlor if they are available. 

Figure 1 Chemical structure of metolachlor and all possible stereochemical conformations 

Empirical formula: C15H22NO2Cl 

Molecular weight: 283.8 

CAS Registry Nos.: 51218-45-2 and 87392-12-9 

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Metolachlor is a pale yellow to light brown liquid with a boiling point of 334 degrees C; 

density of 1.117 g/cm3

 at 20 degrees C; log Pow of 3.05 at 25 degrees C; and vapor 

pressure of 2.8 x 10-5 mm Hg at 25 degrees C. Metolachlor is completely miscible in nhexane, methanol, acetone, toluene, and n-octanol at 25 degrees C. 

No impurities of toxicological concern have been identified for metolachlor or Smetolachlor. 

Two degradates have been identified as potentially of toxicological concern. Each of 

these two degradates, the ethane sulfonic acid (ESA) and the oxanilic acid (OA) of 

metolachlor are considered as part of this assessment. The degradation products also 

have chiral centers and are stereoisomers. Structures are shown in Figure 2. 

Figure 2 Chemical structures for S-metolachlor degradates 

2.2 Environmental Fate Summary

The environmental fate data for S-metolachlor are based on bridged environmental fate 

data for S-metolachlor and racemic metolachlor. The bridging strategy relies on the fact 

that the type and quantities of transformation products between racemic metolachlor and 

S-metolachlor are similar. 

The information from all acceptable environmental fate data indicate that parent 

metolachlor appears to be moderately persistent to persistent in soil. It also ranges from 

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mobile to highly mobile in different soils and it has been detected extensively in surface 

water and groundwater. Metolachlor degradation appears to be dependent on both 

microbially mediated (aerobic soil metabolism t1/2 = 66 days, 37.8 days, 37.8 days, 14.9 

days, 13.9 days, and 50.3 days, anaerobic soil metabolism t1/2 =81 days) and abiotic 

processes (photodegradation in water t1/2 = 70 days under natural sunlight and 

photodegradation on soil t1/2 = 8 days under natural sunlight). 

The major degradates of metolachlor were initially identified as CGA-51202 

(metolachlor OA), CGA-50720, CGA-41638, CGA-37735, and CGA-13656. Subsequent 

studies also identified CGA-354743 (metolachlor ESA). Of these major degradates, 

metolachlor ESA and metolachlor OA have been identified in both groundwater and 

surface water. Depending on the soil (i.e., organic matter content), metolachlor has the 

potential to range from a moderately mobile to a highly mobile compound with Kd values 

ranging from 0.11 to 44.8, and Koc values ranging from 21.6 to 367. 

EFED concluded there is no significant difference in soil sorption affinity between 

metolachlor and S-metolachlor. There was no statistical difference between Koc values in 

non-paired batch equilibrium studies; similar Koc coefficients for metolachlor (mean 

Koc=249.250) and S-metolachlor (mean Koc=265.875) were observed in paired batch 

equilibrium studies. These data suggest that metolachlor and S-metolachlor are both 

expected to be highly mobile to mobile in soil and water environments. 

Field dissipation studies indicate that metolachlor is persistent in surface soil, with half 

lives ranging from 7 to 292 days in the upper six inch soil layer, depending on geographic 

location. Metolachlor was reportedly detected as deep as the 36 to 48 inch soil layer in 

some studies. Metolachlor OA (CGA-51202), was detected (0.11 ppm) as deep as the 

30-36 inch soil depth (MRID 41335701); CGA-40172 was detected as deep as the 36-48 

inch depth (MRID 41309802); CGA-40919 was detected in the 36-48 inch depth (0.21 

ppm in MRID 41309802); and CGA-50720 was not detected (LOD = 0.07 ppm) in any 

soil segment at any interval. 

2.3 Mode of Action 

S-metolachlor is a biosysnthesis inhibitor, absorbed by the roots and shoots 

(www.syngentacropprotection-us.com/prod/herbicide/dualiimagnum). It translocates in 

the plant. S-metolachlor may be active in the soil for several months following 

application. Germinating monocots primarily absorb metolachlor through the shoot just 

above the seed, and germinating diots absorb at the shoot and the roots (Zimdahl 1993). 

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A single specific biochemical target of metolachlor and other chloroacetamide herbicides 

has not been defined and it appears the chemicals may act via multiple pathways. 

Alkylation appears to be important in phytotoxicity (Jablonkai 2003) and lipophilicity has 

been correlated with algal reproduction effects (Junghans et al. 2003). Covalent 

inhibition of coenzyme A elongation (Schmalfuss et al. 2000) and covalent inhibition of 

very-long-chain fatty acid synthesis via chalcone synthase have been proposed as 

mechanisms of action in terrestrial plants (Eckermann et al. 2003). Inhibition of protein 

biosynthesis has also been proposed as a mechanism of action in plants (Pillai et al.

1979). Several proposed mechanisms of action in plants involve irreversible, covalent 

binding to cysteine residues. Consistent with cysteine reactivity, glutathione Stranserfase has been shown to be important in detoxifying chloroacetanilide herbicides in 

tolerant plants (Rossini et al. 1998). 

2.4 Use Characterization 

The proposed label addition includes an application rate of 1.0-1.33 pints of formulated 

product per acre (equivalent to 0.95-1.27 lb ai/A) for pumpkins and winter squash. 

Unless otherwise specified, EFED has assumed that general use directions on the current 

label (EPA Reg. #100-818, Trade Name Dual II Magnum®) apply to both pumpkins and 

winter squash. The label specifies the herbicide be applied no closer than 400 ft to 

sensitive plants. This specification was incorporated into the terrestrial plant evaluation. 

For pumpkins and squash it is proposed for pre-emergence, post-plant use, as a 

groundspray. Specific use rate is dependent on soil texture and percent organic matter, 

with the lower rate applied to sandier, lower organic content soils. Based on 

communications with IR-4 personnel and the registrant, the maximum yearly application 

rate for these crops is 1.33 pt/A/year. 

For the purpose of aquatic and terrestrial modeling EFED has interpreted the available 

application information as follows: 

• Application method: ground spray 

• Frequency: 1 application 

• Timing: 1 June 

• Maximum yearly rate: 1.33 pt/A/year (1.27 lb ai/A/year) 

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Pumpkins 

Pumpkins are a minor crop, with approximately 67,000 acres under cultivation 

(AgCensus 1997). They are grown in nearly every state including Alaska and Hawaii, 

although the most intense cultivation is in the Northeast (New Jersey, eastern 

Pennsylvania, southeastern New York, Connecticut, and Massachusetts), Pacific Coast 

(California, Washington, and western Oregon), and upper Midwest (Michigan, Ohio, 

Wisconsin, Indiana, and Illinois). They have a long growing period, and are generally 

planted in late May or early June, and harvested in mid-October to November. 

Winter Squash 

Winter squash is also a minor crop, and total acreage statistics are included in a more 

general “squash” group. Cultivation patterns are similar to pumpkins, with the most 

intense cultivation in the Northeast (New Jersey, eastern Pennsylvania, southeastern New 

York, Connecticut, and Massachusetts) and Pacific Coast (California, Washington, and 

western Oregon). Squash are also grown in the Southeastern Coastal Plain, Florida, and 

Texas. 

2.5 Assessment Endpoints 

Assessment endpoints are selected based on ecosystems typically at risk from agricultural 

pesticide applications. Specific ecological effects are evaluated based on toxicity 

information from guideline tests and open literature data, and focus on the general 

categories of survival, growth, and reproduction. Information regarding sub-lethal 

effects, if available, is discussed in the risk characterization. EFED assesses behavioral 

or biochemical endpoints if they are quantitatively linked to effects on survival or 

fecundity. 

2.5.1 Ecosystems Potentially at Risk 

For typical crop applications, the ecosystem at risk is the field itself, in terms of 

organisms that might be sprayed during application, organisms affected by accumulation 

of s-metolachlor in the soil; and the adjacent aquatic and terrestrial environments affected 

due to runoff, spray drift, or groundwater contamination. In water bodies receiving 

runoff from agricultural fields, pelagic and benthic elements are considered. Terrestrial 

organisms assessed include non-target plants, insects, amphibians, reptiles, birds, and 

mammals. Because s-metolachlor is an herbicide, potential affects on non-target plants 

have been addressed at length. The conceptual model for s-metolachlor (Figure 3) is 

located on the following page. 

15
16

2.5.2 Ecological Effects 

Evaluation of ecological effects focuses initially on direct effects to the groups of 

organisms residing in the ecosystems at risk, based on ratios (risk quotients) of the 

estimated environmental concentration (EEC) to a designated toxicity endpoint for a 

surrogate test organism. If pre-established levels of concern (LOCs) are exceeded for 

direct effects, indirect effects to endangered species (e.g., food chain, decrease in 

community diversity) are evaluated based on the group of organisms exceeding the LOC. 

Details on the RQ method and LOCs are in Appendix G. 

Direct 

Direct effects evaluated are the survival, growth, and reproduction of various taxa of 

organisms potentially exposed to s-metolachlor. Taxonomic groups evaluated include 

aquatic plants (algae and vascular), aquatic invertebrates, aquatic vertebrates, terrestrial 

plants, terrestrial invertebrates, birds, and mammals. There are currently no guideline 

tests for reptiles or amphibians, so these taxa are evaluated using bird data as a surrogate 

for reptiles and terrestrial phase amphibians, and fish as a surrogate for aquatic phase 

amphibians. Both acute and chronic effects are considered. 

Indirect 

When herbicides are applied, indirect effects may include a decline in primary 

productivity, or change in composition of plant communities proximate to the treated area 

or systems (wetlands and water bodies) receiving runoff from the site. If LOCs are 

exceeded for any taxa, potential indirect effects to endangered species are assessed. 
Stressor 

Source 

s-Metolachlor applied to crop 

Figure 3 Conceptual model for S-metolachlor effects

Runoff Spray drift Direct application 

Receptors 

Terrestrial Birds Mammals insects 

Soil ac

leachin

Individual organisms Reduced survival Reduced growth Reduced reproduction 

Aquatic plants invertebrates vertebrates 

Terrestrial plants 

Food chain Reduction in primary productivity Reduction in prey Shift in community composition 

HaReCo

Attribute Change 

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2.7 Risk Hypotheses 

• S-Metolachlor, OA, or ESA in runoff from treated areas may kill aquatic plants, 

aquatic invertebrates, or fish. 

• S-Metolachlor may be toxic to non-target plants. 

• S-Metolachlor residues in plant and animal dietary sources may affect growth, 

survival, or fecundity of birds and/or small mammals ingesting these materials. 

2.8 Key Uncertainties and Information Gaps 

• Bioavailability of S-metolachlor to non-target organisms is influenced by site 

characteristics. An effort has been made to examine a variety of sites typical of areas 

where it might be used. Scenarios and input parameters have been selected to represent 

conditions where S-metolachlor is most bioavailable. Overall, conditions have been 

selected to develop a conservative, screening level estimate. In some locations and under 

some conditions, risk may be overestimated. 

• Natural genetic variability in wild organisms may affect their response to Smetolachlor, and the distribution of species sensitivity is not well understood. Risk may 

be under- or over-estimated for any given species by available toxicity data and use of 

surrogate taxa. 

• The locations of sensitive and/or valuable plant communities are not available, 

thus effects on these communities can only be assessed in a general, qualitative sense. 

• The enantioselectivity of toxicity and environmental fate for metolachlor ESA and 

metolachlor OA were not considered in the assessment. 

• Aerobic and anaerobic aquatic metabolism half-lives for metolachlor ESA and 

metolachlor OA were assumed to be stable due to the lack of data. 

18
3. Exposure Assessment 

EFED conducted the exposure assessment using standardized exposure modeling. 

3.1 Label Application Rates and Intervals 

The application rates, application frequency, and other information used in the exposure 

assessment are listed in Table 3. These conditions are based on information contained in 

the currently existing label as well as the language for the proposed new use. 

Table 3 Label Application Rates 

Application 

Rate Soil Texture First Application Date Frequency Interval 

0.95 lb ai/A Light, 

Low organic matter June 1 1 N/A 

1.27 lb ai/A Moderate-heavy, 

Organic matter >3% June 1 1 N/A 

3.2 Aquatic Exposure 

Tier II EFED aquatic exposure modeling use the linked Pesticide Root Zone Model and 

Exposure Analysis Model System (PRZM-EXAMS). PRZM uses the chemical’s 

physical and environmental fate properties and the site characteristics to predict the 

concentration of pesticide in runoff and entrained sediment from the field. EXAMS 

estimates the concentration of pesticide in an edge-of-field small water-body receiving 

runoff from the field. The water-body has no outflow with a constant volume (20 million 

liters), and is intended to represent an upper-end occurrence concentration. 

A complete fate data set was not available for the degradates metolachlor ESA and 

metolachlor OA, thus EFED opted to use GENEEC (Tier I) to model aquatic 

concentrations of these compounds. 

3.2.1 PRZM-EXAMS Modeling Inputs and Scenario Selection 

The aquatic exposure assessment for S-metolachlor was conducted to assess use on 

pumpkins and winter squash. EFED currently has no standard scenarios for these crops. 

Standard row crop scenarios were selected to assess runoff potential from vulnerable use 

sites in several of the more common growing areas. Application rates for the various 

scenarios were selected based on the percent of organic matter in soil horizon 1 in the 

scenario. Other input parameters were selected according to EFED Input Parameter 

Guidance for PRZM/EXAMS1

. Input parameters are shown in Table 4. 

 

1

 Guidance for Selecting Input Parameters in Modeling the Environmental Fate and Transport of Pesticides. 

Version II, 2/28/02. 

19
Table 4 Input Parameters for PRZM-EXAMS Modeling 

Parameter Value Comments Source 

Application Rate (kg a.i./ha)1-ground spray 1.064 OM<3% label 

Application Rate (kg a.i./ha) 1 - ground spray 1.42 OM>3% label 

Molecular Weight (grams/mole) 283.8 

Solubility (mg/L) 4800 10X reported value 

Vapor Pressure (torr) 2.8E-5

Henry’s Constant (atm m3/mol) 3.75E-5

product 

chemistry 

Kd (L/kg) 181 Average Koc

2 MRID00078291 

MRID43928935 

MRID40430203 

MRID40476404 

MRID43928937 

MRID40495602 

MRID40495603 

MRID40495604 

Aerobic Soil Metabolism Half-life (days) 48.9 Estimated upper3

90th percentile 

MRID41309801 

MRID43928936 

MRID45499606 

Aerobic Aquatic Metabolism Half-life (days) 141 Based on 3X single 

aerobic aquatic 

metabolism linear 

first order half-life 

MRID41185701 

Anaerobic Aquatic Metabolism Half-life 

(days) 

234 Based on 2X single 

anaerobic aquatic 

metabolism linear 

first order half-life 

MRID41185701 

Photodegradation in Water (days) 70 MRID40430202 

Hydrolysis Half-life (days) Stable MRID40430201 

1

 - Application rate given in input units for PRZM-EXAMS. Conversion is kg/ha x 1.12 = lb/A 2 - Average Koc using values 118.5, 303.0, 151.4, 241.4, 66.8, 21.6, 110.4, 74.4, 175.0, 333.3, 

230.0, 244.7, 226.3, 367.2, 176.5, 120.7, 111.1 as per “Guidance for Chemistry and Management 

Practice Input Parameters for Use in Modeling the Environmental Fate and Transport of 

Pesticides” dated February 28, 2002. 3 - Upper 90th Percentile based on acceptable aerobic metabolism half-lives of 66, 37.8, 37.8, 

14.9, 13.9, and 50.3 days. 

3.2.2 PRZM-EXAMS Modeling Output 

The 1-in-10-year peak concentrations of S-metolachlor ranged from 9.65 ppb (PA corn) 

to 35.11 ppb (CA lettuce). Water concentrations did not necessarily correlate with 

application rate, as the higher aquatic concentrations occurred in the low soil organic 

matter, lower application rate scenarios. The 1-in-10-year 60-day concentrations of Smetolachlor ranged from 6.22 ppb (FL peppers) to 29.07 ppb (CA lettuce). 

20
Table 5 PRZM-EXAMS EECs 

Peak 4 days 21 days 60 days Crop Scenario Application 

Method μg/L (ppb) 

Application Rate 1.064 kg/ha (OM <3.0%) 

CA lettuce Ground 35.11 34.81 33.31 29.07 

FL peppers Ground 24.32 21.65 14.04 6.22 

Application Rate 1.42 kg/ha (OM >3.0%)

IL corn Ground 9.87 9.77 9.41 5.33 

PA corn Ground 9.65 9.56 9.20 8.15 

3.2.3 GENEEC Modeling for Degradates 

Limited data were available for modeling the degradates metolachlor ESA and 

metolachlor OA. These data included the soil adsorption/desorption studies for both ESA 

(MRID 44931722) and OA (MRID 40494605), as well as the conversion efficiency of 

metolachlor to the two degradates (MRIDs 43928936, 41309801). Application rates for 

the two degradates were determined by multiplying the maximum S-metolachlor 

application rate (1.27 lb ai/A) by the fraction of the relevant degradate. Half-lives for the 

two compounds were estimated using the decline portion of the formation and decline 

data contained in the Comparative Aerobic Soil Metabolism Study (MRID 43928936). 

For other parameters where data was not available, the compounds were conservatively 

assumed to be stable. GENEEC input parameters are shown below (Table 6). A 400-ft 

buffer was assumed. 

Table 6 GENEEC Input Parameters for Degradates 

Parameter Value Comments Source 

Application Rate ESA (lb a.i./ha) 0.15 1.27 lb ai/A X 0.12 MRID43928936 

Application Rate OA (lb a.i./ha 0.36 1.27 lb ai/A X 0.28 MRID41309801 

Kd ESA (L/kg) 0.041 MRID44931722 

Kd OA (L/kg) 0.079 

Lowest non-sandy 

soil, Maryland clay MRID40494605 

Solubility (mg/L) 4800 10X reported value product 

chemistry 

Aerobic Soil Metabolism Half-life ESA (days) 162.5 MRID4392836 

Aerobic Soil Metabolism Half-life OA (days) 127.5 

Based on decline 

portion of formation 

and decline data 

Aerobic Aquatic Metabolism Half-life (days) 0 

Anaerobic Aquatic Metabolism Half-life(days) 0 

Photodegradation in Water (days) 0 MRID40430202 

Hydrolysis Half-life (days) 0 

Assumed stable 

MRID40430201 

21
EECs for the degradates were 8.25 ppb for metolachlor ESA and 19.63-19.65 ppb for 

metolachlor OA. 

Table 7 EECs for Degradates 

Peak 4 days 21 days 60 days Degradate Application 

Method μg/L (ppb) 

Metolachlor ESA Ground 8.25 8.25 8.25 8.25 

Metolachlor OA Ground 19.65 19.65 19.65 19.63 

 

3.3 National Surface Water Monitoring Data Assessment 

In the 2002 TRED for S-metolachlor, EFED evaluated data from several sources of 

monitoring studies (including several sources with treated drinking water with detections 

of metolachlor/S-metolachlor1) for use in acute and chronic exposure estimates. 

Extensive monitoring data exists for metolachlor/S-metolachlor, allowing distributions of 

concentrations to be estimated. Acute exposure estimates presented in this assessment 

are the maximum measured from the distributions of annual maximum concentrations. 

Chronic exposure estimates are the maximum measured concentrations from the 

distribution of time weighted annual mean concentrations. 

At the national scale, the frequency of detection of metolachlor/S-metolachlor from the 

entirety of the monitoring data evaluated (NAWQA, ARP, STORET, and USGS 

Reservoir studies) suggests that metolachlor/S-metolachlor contamination in both surface 

water and groundwater is widespread. In addition, the data suggest that the two primary 

degradates (metolachlor ESA and metolachlor OA), are detected in surface and 

groundwater resources in Iowa and Illinois at frequencies (99% for ESA and 92% for 

OA) and at concentrations exceeding the parent compound. It is likely that where 

metolachlor/S-metolachlor is detected in surface and groundwater the degradates are 

present as well, although many monitoring studies do not measure them. 

From the available national-scale data, the highest annual maximum concentration of 

metolachlor/S-metolachlor in surface water is 77.6 μg/l (NAWQA surface water 

monitoring data). The maximum value detected from all data evaluated was 138.8 μg/l 

(STORET data). From the available data, the maximum time-weighted mean 

concentration of metolachlor/S-metolachlor in surface water is 4.3 μg/l from the 

NAWQA surface water monitoring data. These concentrations were primarily detected 

in the Midwestern corn belt, a high use area 

From the available national-scale data, the maximum peak concentration of metolachlor 

ESA is 12.40 μg/l and the maximum time-weighted mean concentration of metolachlor 

ESA is 7.30 μg/l (Iowa NAWQA surface water monitoring data). The maximum peak 

concentration of metolachlor OA is 6.75 μg/l and the maximum time-weighted mean 

concentration of metolachlor OA is 2.27 μg/l from the Iowa NAWQA surface water 

 

1

 These studies do not discriminate between racemic metolachlor and S-metolachlor. 

22
monitoring data. More details on the results of the evaluation of surface water 

monitoring data may be found in the TRED drinking water assessment dated May 22, 

2002. 

3.5 Bird and Mammal Exposure (TREX) 

EFED estimates exposure of birds and mammals using the Terrestrial Exposure Model 

(TREX). TREX uses the Kenaga nomagram, as modified by Fletcher et al. (1994) to 

determine pesticide residues on several categories of food items, then calculates the 

potential dose an organism might receive from ingesting contaminated items using 

allometric equations. Dose estimates in Table 8 and Table 9 are based on the upper 

bound dose and the assumptions that the organism exclusively eats one type of food item 

and forages only in the treated and/or overspray areas. S-metolachlor translocates in 

plant tissue and the residence time of the parent compound or any degradates is unknown. 

For pumpkins and winter squash, only a single application is proposed, thus residues in 

the plant are not expected to exceed residues on the plant. 

At the lower application rate (0.95 lb ai/A) avian doses ranged from 4.1 to 260 mg/kgbw/day. Doses ranged from 5.5 to 347 mg/kg-bw/day at the higher application rate (1.27 

lb ai/A). 

Table 8 Bird Dose Estimates 

Dose-based EECs (mg/kg-bw) 

Feeding Category 

Dietary-based 

EECs (mg/kgfood item) 

Small 

(20 g)

Medium 

(100 g) 

Large 

(1000 g) 

Application Rate 0.95 lb ai/A 

Short grass 228.00 259.67 148.07 66.29 

Tall grass 104.50 119.02 67.87 30.39 

Broadleaf plants/small insects 128.25 146.06 83.29 37.29 

Fruits/pods/seeds/large insects 14.25 16.23 9.25 4.14 

Application Rate 1.27 lb ai/A 

Short grass 304.80 347.14 197.95 88.63 

Tall grass 139.70 159.10 90.73 40.62 

Broadleaf plants/small insects 171.45 195.26 111.35 49.85 

Fruits/pods/seeds/large insects 19.05 21.70 12.37 5.54 

23
At the lower application rate (0.95 lb ai/A) mammal doses ranged from 0.48 to 217 

mg/kg bwt/day. Doses ranged from 0.65 to 291 mg/kg bwt/day at the higher application 

rate (1.27 lb ai/A). 

Table 9 Mammal Dose Estimates 

Dose-based EECs (mg/kg-bw) 

Feeding Category 

Dietary-based 

EECs (mg/kgfood item) 

Small 

(15 g)

Medium 

(35 g) 

Large 

(1000 g) 

Application Rate 0.95 lb ai/A 

Herbivores and Insectivores 

Short grass 228.00 217.38 150.24 34.83 

Tall grass 104.50 99.63 68.86 15.97 

Broadleaf plants/small insects 128.25 122.28 84.51 19.59 

Fruits/pods/seeds/large insects 14.25 13.59 9.39 2.18 

Granivores 

Fruits/pods/seeds/large insects 14.25 3.02 2.09 0.48 

Application Rate 1.27 lb ai/A 

Herbivores and Insectivores 

Short grass 304.80 290.60 200.85 46.57 

Tall grass 139.70 133.19 92.05 21.34 

Broadleaf plants/small insects 171.45 163.46 112.98 26.19 

Fruits/pods/seeds/large insects 19.05 18.16 12.55 2.91 

Granivores 

Fruits/pods/seeds/large insects 19.05 4.04 2.79 0.65 

3.6 Terrestrial Plant Exposure (TerrPlant & AgDrift) 

Currently, EFED uses the TerrPlant Model (Version 1.2.1) to evaluate exposure of 

terrestrial plants to pesticides applied on agricultural fields. In cases where spray drift 

may be of concern in the risk assessment EFED also uses the AgDrift model. 

3.6.1 TerrPlant 

TerrPlant has two basic exposure scenarios. The first is an adjacent upland area, which is 

exposed to the pesticide via drift and dissolved concentrations in sheet runoff. The 

second is an adjacent semi-aquatic (wetland) area, which is exposed to the pesticide via 

drift and to dissolved concentrations in channelized runoff. Drift is calculated as a 

percentage of the application rate (1% for ground, and 5% for aerial, airblast, or spray 

chemigation) and is not adjusted for distance from the application site. The amount of 

dissolved pesticide in the runoff component is estimated based on solubility of the active 

ingredient. TerrPlant estimates are shown in Table 10. Total loading (runoff plus drift) 

for S-metolachlor ranged from 0.08-0.65 lb ai/A, depending on application rate, and 

environment. Drift estimates were approximately 0.01 lb ai/A. TerrPlant was also used 

to calculate EECs for the two major degradates, ESA and OA. Application rates for the 

degradates were estimated by multiplying the highest application rate of the parent by the 

highest single day conversion efficiency to the degradate, based on the aerobic soil 

24
metabolism study (12% for ESA, 28% for OA). Total loading ranged from 0.01-0.08 lbs 

ai/A for ESA, and from 0.02-0.19 lbs ai/A for OA. 

Table 10 Terrestrial Plant Exposure (TerrPlant) 

Total Loading (Runoff +Drift) (lb ai/A) Drift EEC (lb ai/A) Application Rate Upland areas Wetland areas All areas 

0.95 lb ai/A 0.0570 0.4845 0.0095 

1.27 lb ai/A 0.0762 0.6477 0.0127 

Degradate ESA 0.15 lb ai/A 0.0090 0.0765 0.0015 

Degradate OA 0.36 lb ai/A 0.0216 0.1836 0.0036 

3.6.2 AgDrift 

Because of concerns about effects on non-target plants located in overspray or spray drift 

areas, EFED elected to perform an analysis of potential deposition of s-metolachlor using 

AgDrift modeling software. AgDrift was developed using extensive field-measured data 

sets, and provides a method of estimating deposition of the compound of concern at a 

specified distance away from the application source. Deposition is heavily dependent on 

the method of application and droplet size. A Tier I analysis, which is driven primarily 

by these two variables, was conducted for both ground and aerial applications. AgDrift 

was run in the Tier I, Terrestrial Assessment, Point Deposition mode. Droplet size 

evaluated was ASAE very fine-fine, and values shown represent the 90th percentile 

estimate. Deposition was estimated for ground application, with a low boom (Table 11). 

For this set of application conditions, the 1% drift assumed in TerrPlant is equivalent to 

approximately 100 ft away from the application site. EFED notes label directions specify 

that S-metolachlor not be sprayed closer than 400 ft to sensitive plants. 

Table 11 Terrestrial Plant Exposure (AgDrift, Ground spray) 

Distance from Point Deposition (lb ai/A) 

Application 

Source (ft) 

Fraction 

of 

Applied 

Proposed Rate 

(1.27 lb ai/A) 

Proposed Rate 

(0.95 lb ai/A) 

10 0.0923 0.1172 0.0877 

20 0.0437 0.0555 0.0415 

30 0.0291 0.0370 0.0276 

40 0.0218 0.0277 0.0207 

50 0.0177 0.0225 0.0168 

60 0.0149 0.0189 0.0142 

70 0.0130 0.0165 0.0124 

80 0.0115 0.0146 0.0109 

90 0.0104 0.0132 0.0099 

100 0.0095 0.0121 0.0090 

150 0.0066 0.0084 0.0063 

200 0.0051 0.0065 0.0048 

250 0.0042 0.0053 0.0040 

300 0.0035 0.0044 0.0033 

350 0.0030 0.0038 0.0029 

500 0.0021 0.0027 0.0020 

550 0.0019 0.0024 0.0018 

600 0.0017 0.0022 0.0016 

25
4. Effects Assessment 

Toxicity endpoints are established based on data generated from guideline studies 

submitted by the registrant, and from open literature studies that meet the criteria for 

inclusion into the ECOTOX database maintained by EPA/ORD. EFED policy is to use 

the effects endpoint from the most sensitive tested species for each taxa evaluated. In 

aquatic systems, taxa evaluated include aquatic plants, invertebrates, and fish. Fish serve 

as a surrogate for aquatic-phase amphibians. Where data are available, separate 

endpoints are used for freshwater and estuarine/marine organisms. In terrestrial systems, 

taxa evaluated include birds and mammals. Bird endpoints are generally derived from 

guideline studies on bobwhite quail and/or mallard duck. Bird data are used as a 

surrogate for reptiles and terrestrial-phase amphibians. Mammal data are derived from 

guideline studies conducted on laboratory rats, mice, or rabbits. 

4.1 Aquatic Hazard Summary 

S-metolachlor is classified as slightly to moderately toxic to both fish and aquatic 

invertebrates, based on both registrant-submitted guideline studies (Table 12-Table 14) 

and data from the open literature (Table 15). Acute LC50s for fish range from 3.2 mg/L 

(bluegill sunfish, MRID 43928910) to 8.4 mg/L (fathead minnow, ECOTOX 6797). Data 

available for an estuarine fish (sheepshead minnow, MRID 43487101, racemic) indicate 

toxicity to fish in a brackish water environment is similar to freshwater. Acute LC50s for 

invertebrates range from 3.8 mg/L (midge fly, ECOTOX 6797) to 26 mg/L (water flea, 

MRID 43928912). Values used to calculate RQs (3.2 mg/L for fish, 3.8 mg/L for aquatic 

invertebrates) are marked in the tables with an asterix (*). ECOTOX data included 

results for two amphibian species, the African clawed frog (LC50 13.6 mg/L) and the 

American bullfrog (LC50 17.4 mg/L). Based on this limited data set, it appears 

amphibian sensitivity to metolachlor and S-metolachlor is similar to that of aquatic 

invertebrates and fish. How sensitive these species are relative to other amphibians is 

unknown, thus EFED elected to use the more sensitive fish endpoint to assess potential 

effects on amphibians. 

Effects on aquatic plants occur at lower concentrations than for aquatic animals. LC50s 

range from 0.008 mg/L (green alga, MRID 43928929) to >3.00 mg/L (water milfoil, 

ECOTOX 19461). Based on the available data, green algae and some vascular plants 

appear to be most sensitive to the effects of metolachlor and S-metolachlor. Diatoms 

seem to be less sensitive, and blue-green algae, along with some other species of vascular 

plants are the least sensitive of the aquatic plants. 

Data for the two major degradates of metolachlor, ESA and OA were available. Of the 

two, OA was most toxic to the aquatic invertebrate tested (water flea, LC50 15.4 mg/L). 

OA effects on aquatic invertebrates occur in approximately the same concentration range 

as the parent compound. Other than this instance, both degradates are generally less toxic 

to all organisms than the parent. LC50s for the other organisms tested (green algae, 

vascular plants, fish) were all >50 mg/L. The degradate ESA was most toxic to vascular 

plants (LC50 43 mg/L) and fish (LC50 43 mg/L). For both green algae and aquatic 

26
invertebrates, the LC50 was greater than 99 mg/L. No open literature data was available 

for the degradates. 

Sublethal effects were noted in some of the guideline tests, usually in test concentrations 

in which mortality occurred. Effects noted in fish tests included lethargy, distended 

abdomen, swimming at the surface, and loss of equilibrium. Sublethal effects noted in 

invertebrate tests include lethargy (oyster, mysid, water flea), reduced feeding (oyster), 

and dark pigmentation (water flea). 

Chronic effects (reduced growth) in fish were noted at concentrations of 0.056 mg/L 

(fathead minnow, MRID 44995903) to 2.2 mg/L (sheepshead minnow, MRID 

43044602). Effects in aquatic invertebrates were similar, but occurred at slightly higher 

concentrations, ranging from 4.0 mg/L (mysid MRID 43487103) to 9.4 mg/L (water flea 

MRID 46322101). 

Two studies in the open literature reported behavioral and/or biochemical endpoints. One 

study (ECOTOX 20274) reported cellular damage in American bullfrog tadpoles at 0.27 

mg/L. Another study, performed on the rusty crayfish (ECOTOX 68515), showed a 

reduced response to predator and food source olfactory cues at metolachlor 

concentrations of 0.025 mg/L. 

27
 

Table 12 Acute Aquatic Data from Registrant-submitted Studies 

Species LC50 (mg/L) 95% C.I. (mg/L) NOAEC 

(mg/L) 

Classification 

(MRID) 

Freshwater Organisms 

Green alga 

(Selenastrum 

capricornutum)

0.008* 0.0026-0.025 0.0015 

Core 

(43928929) 

S-metolachlor 

Duckweed 

(Lemna gibba) 0.021* 0.019-0.023 0.0076* 

Core 

(43928931) 

S-metolachlor 

Water flea 

(Daphnia magna) 

26* 

slightly toxic 23-30 4.8 

Core 

(43928912) 

S-metolachlor 

Bluegill Sunfish 

(Lepomis 

macrochirus) 

3.2*

moderately 

toxic 

2.8-4.6 1.5 

Core 

(43928910) 

S-metolachlor 

Estuarine/Marine organisms 

Marine diatom 

(Skeletonema 

costatum)

0.11* 0.091-0.128 0.021 

Core 

(43928930) 

S-metolachlor 

Mysid shrimp 

(Mysidopsis bahia) 

4.9 

moderately 

toxic 

4.2-5.9 2.3 

Core 

(4387103) 

Racemic 

Eastern oyster 

(Crassostrea 

virginica) 

1.6*

moderately 

toxic 

1.4-1.9 0.7 

Core 

(43487102) 

Racemic 

Sheepshead minnow 

(Cyprinodon 

varigetus) 

9.8*

moderately 

toxic 

8.5-11.4 3.6 

Core 

(43487101) 

Racemic 

* denotes values used to calculate RQs 

Table 13 Chronic Aquatic Data from Registrant-submitted Studies 

Species NOAEC 

(mg/L) 

LOAEC

 (mg/L) Endpoints Affected Classification (MRID) 

Freshwater Organisms 

Water flea 

(Daphnia magna) 4.9* 9.4 Length 

Core 

(46322101) 

Racemic 

Fathead minnow 

(Pimephales 

promelas) 

0.030* 0.056 Dry weight 

Core 

(44995903) 

S-metolachlor 

Estuarine/Marine organisms 

Mysid shrimp 

(Mysidopsis bahia) 2.3* 4.0 Lethargy, dark 

pigmentation 

Core 

(43487103) 

Racemic 

Sheepshead minnow 

(Cyprinodon varigetus) 1.0* 2.2 Length 

Supplemental 

(43044602) 

Racemic 

* denotes values used to calculate RQs 

28
Table 14 Acute Aquatic Degradate Data from Registrant-submitted Studies 

Species LC50 /EC50

(mg/L) 95% C.I. (mg/L) NOAEC (mg/L) 

Classification 

(MRID) 

Degradate-ESA (CGA-354743) 

Green algae 

(Selenastrum 

capricornutum) 

>99.5 ND 99.5 Supplemental 

(44931720) 

Duckweed 

(Lemna gibba) 43* 30-61 4 Core 

(44931720) 

Water flea 

(Daphnia magna) 

>108* 

practically 

nontoxic 

ND 108 Core 

(44931703) 

Rainbow Trout 

(Onchorynchus 

mykiss) 

43* 

slightly toxic 36-64 36 Supplemental (44931702) 

Degradate-OA (CGA-51202) 

Green algae 

(Scenedesmus 

subspicatus) 

57.1* 29.3-infinity 29.3 Supplemental 

(44929515) 

Duckweed 

(Lemna gibba) >95.4 ND 95.4 Core 

(4492514) 

Water flea 

(Daphnia magna) 

15.4* 

slightly toxic 13.0-18.4 5.2 Supplemental (44929503) 

Rainbow Trout 

(Onchorynchus 

mykiss) 

>96.3* 

slightly toxic ND >96.3 Supplemental (44929501) 

ND – Not determined, * denotes values used to calculate RQs 

29
Table 15 Aquatic Data from ECOTOX 

Species LC50 /EC50

(mg/L) 

LOAEC 

(mg/L) 

NOAEC 

(mg/L) 

Endpoints 

Measured 

(Lifestage) 

ECOTOX 

Reference # 

Freshwater plants–Survival, reproduction, and growth endpoints 

Green algae 

(Selenastrum 

capricornutum) 

0.04 NG NG Population 

(N/A) 19186 

Green algae 

(Chlamydomonas 

reinhardtii) 

1.14 NG NG Population 

(N/A) 19461 

Bluegreen algae 

(Anabeana flos-aquae) 3.00 NG NG Population 

(N/A) 19186 

Vascular – Coontail 

(Ceratophyllum 

demersum) 

0.07 NG NG Biomass 

(N/A) 19461 

Vascular - Water milfoil 

(Myriophyllum 

heterophyllum) 

>3.00 NG NG Biomass 

(N/A) 19461 

Freshwater animals –Survival, reproduction, and growth endpoints

Fathead minnow 

(Pimephales promelas) 8 to 8.4 NG NG Mortality (adult) 6797 

(technical) 

African clawed frog 

(Xenopus laevis) 13.6 NG NG Mortality (embryo) 66376 

(technical) 

American Bullfrog 

(Rana catebeiana) 17.4 NG NG Mortality (tadpoles) 20274 

(formulation) 

Water flea 

(Daphnia magna) 4.3* NG NG Mortality (Neonates) 

67700 

(unknown) 

Water flea 

(Daphnia magna) 23.5 NG NG Mortality 

(not stated) 

6797 

(technical) 

Water flea 

(Daphnia magna) 26.0 NG NG Mortality 

(not stated) 

6797 

(Emulsifiable 

concentrate) 

Midge fly 

(Chironomus 

plumulosus) 

3.8* NG NG Mortality 

(not stated) 

6797 

(technical) 

Midge fly 

(Chironomus 

plumulosus)

4.4 NG NG Mortality 

(not stated) 

6797 

(Emulsifiable 

concentrate) 

Hydra 

(Hydra attenuata) >45 NG NG Mortality 

(not stated) 

67700 

(technical) 

Freshwater organisms – Behavioral and biochemical endpoints 

American Bullfrog 

(Rana catebeiana) ND 0.27 NG Cellular damage 

(tadpoles) 

20274 

(formulation) 

Rusty crayfish 

(Oronectes rusticus) NG 0.025 <0.025 Behavioral 

modifications 

68515 

(technical) 

NG-not given in reference 

* Used in RQ calculation for aquatic invertebrates 

30
4.2 Terrestrial Plant Hazard Summary 

Vegetative vigor and seedling emergence guideline tests were available for S-metolachlor 

(Table 16). Both monocots and dicots were more sensitive in the seedling emergence 

tests, which was not unexpected given S-metolachlor’s mode of action. The seedling 

emergenceEC25 for the most sensitive monocot (ryegrass) was 0.0048 lb ai/A, and the 

EC25 for the most sensitive dicot (lettuce) was 0.0057 lb ai/A. In terms of vegetative 

vigor, monocots appeared significantly more sensitive than dicots, with a monocot 

(ryegrass) EC25 of 0.021 lb ai/A, and dicot (cucumber) EC25 of 0.27 lb ai/A. The seedling 

emergence NOAEC for the most sensitive monocot (ryegrass) was 0.001 lb ai/A, and the 

NOAEC for the most sensitive dicot (lettuce) was 0.0003 lb ai/A. Vegetative vigor 

NOAEC endpoints for monocots (ryegrass, 0.011 lb ai/A) and dicots (cucmber, 0.01 lb 

ai/A) were essentially the same. 

Three plant studies evaluating effects of metolachlor and S-metolachlor on non-crop 

plant species were available in ECOTOX. Generally, these studies were conducted on 

mature and/or growing plants, rather than pre-emergence, thus they are more comparable 

to the vegetative vigor endpoints than the seedling emergence endpoints from the 

guideline studies. Open literature studies on crop species produced less sensitive 

endpoints than the registrant-submitted studies. Ecological effects data is located in 

Appendix D. Table 17 shows select ECOTOX data for non-crop species. Plants have 

been grouped into two classes: herbaceous (grasses and forbs) and woody (trees and 

shrubs). This classification is intended to reflect both a difference in ecological function, 

and expected differences in sensitivity to the herbicide. In order to establish upper and 

lower bounds, the most sensitive and the least sensitive endpoints for each group are 

included in the table. For the grasses and forbs, a test concentration of 0.11 lb ai/A was 

applied (ECOTOX 73233). At this concentration, results ranged from no observed effect 

(broomcorn) to a 90% reduction in height (barnyard grass). The most sensitive species 

tested in the trees and shrubs class was the Tatarian maple, which exhibited reduced 

growth at an application of 3.0 lb ai/A (ECOTOX 73251). The least sensitive species 

tested was the European white birch, which had no observable effects at an application 

rate of 9.1 lb ai/A. 

In a natural landscape, plants most at risk from use of S-metolachlor would be newly 

emerging plants located near the use site The effect of the herbicide on plants some of 

which reproduce from cut stumps and/or root propagation is unknown, as no data were 

located evaluating these situations. Drift or runoff of S-metolachlor into primarily 

herbaceous natural areas near the use site (grasslands, marshes) when mature plants are 

present may create a selection pressure for dicots. 

Vegetative vigor and seedling mergence guideline tests were also available for both the 

ESA degradate and the OA degradates. Both are less toxic than the parent compound. 

The Tier I studies submitted (MRIDs 44931718, 44929513) evaluated the effects of the 

degradates at an application rate of 0.5 lb ai/A. With the exception of the monocot 

seedling emergence endpoint for ESA, the EC25s for all endpoints were greater than the 

31
amount applied. No definitive endpoint was established for monocot seedling emergence 

and ESA, as the NOAEC was below the concentration tested. 

Table 16 Terrestrial Plant Guideline Data

Species Common 

name 

Class EC25 

(lb ai/A) 

NOAEC 

(lb ai/A)) 

Classification 

(MRID) 

Vegetative Vigor (S-metolachlor) 

Lolium perenne Ryegrass M 0.021 0.011 

Cucumis sativus Cucumber D 0.27 0.01 

Supplemental 

(43928933) 

Seedling emergence (S-metolachlor) 

Lolium perenne Ryegrass M 0.0048 0.001 

Lactuca sativa Lettuce D 0.0057 0.0003 

Supplemental 

(43928932) 

Vegetative Vigor (Degradate ESA) 

Lolium perenne Ryegrass M >0.5 0.5 

Lycopersicon 

esculentum 

Tomato D >0.5 0.5 

Core 

(44931718) 

Seedling emergence (Degradate ESA)

Lolium perenne Ryegrass M <0.5 <0.5 

Lycopersicon 

esculentum 

Tomato D >0.5 <0.5 

Core 

(44931718) 

Vegetative Vigor (Degradate OA)

Allium cepa Onion M >0.5 <0.5 

Lycopersicon 

esculentum 

Tomato D >0.5 <0.5 

Core 

(44929513) 

Seedling emergence (Degradate OA)

All monocots tested M >0.5 <0.5 

All dicots tested D >0.5 <0.5 

Core 

(44929513) 

Table 17 Terrestrial Plant Data from ECOTOX

Species ECxx

(lb ai/A) 

LOAEC 

(lb ai/A) 

NOAEC 

(lb ai/A) 

Endpoints 

Measured 

ECOTOX 

Reference # 

Grasses and Forbs

Barnyard grass 

(Echnochloa crus-galli) 0.11 NG NG 90% reduction 

 in height 73233 

Millet 

(Panicum millaceum) 0.11 NG NG 50% reduction 

 in height 73233 

Broomcorn 

(Sorghum bicolor) NG NG 0.11 0% reduction 

 in height 73233 

Trees and Shrubs 

Tatarian maple 

(Acer tatarium) NG 3.0 NG Growth (over 2 

growing seasons) 73251 

Pin oak 

Quercus palustris NG 8.0 4.0 Growth and mortality 

(549 day) 73249 

NG – Not given in reference 

32
4.3 Avian and Small Mammal Guideline Data 

Registrant-submitted data was available for both birds and mammals (Table 18 and Table 

19). No treatment-related mortality was reported in any of the bird studies. On an acute 

effects basis, S-metolachlor is practically non-toxic to birds (MRIDs 43928907, 

43928906). No data for S-metolachlor were available for mammals, but testing of 

racemic metolachlor on rats (MRID 00015523) classifies it as practically non-toxic. 

Treatment-related mortality occurred in rats at all doses tested 1670-4640 mg/kg). 

Table 18 Avian and Small Mammal Guideline Data from Acute Studies 

Species LD50 / LC50

(mg/kg-bw) 95% C.I. (mg/L) NOAEC (mg/kg-bw) 

Classification 

(MRID) 

Acute dose 

Bobwhite quail 

>2510 

practically 

nontoxic 

ND 1000 

Core 

(43928907) 

S-metolachlor

Mallard 

>2510 

practically 

nontoxic 

ND 2510 

Core 

(43928906) 

S-metolachlor 

Rat 

2780 

practically 

nontoxic 

2180-3545 <1670 

Acceptable 

(00015523) 

Racemic 

Acute dietary 

Bobwhite quail >4912 

slightly toxic ND 2762 

Core 

(43928908) 

S-metolachlor

Mallard duck >4912 

slightly toxic ND 1556 

Core 

(43928909) 

S-metolachlor

ND-no data 

Registrant submitted studies indicate metolachlor has chronic reproductive effects on 

birds (MRID 46508901) and mammals (MRID 000808097) at the highest tested dose. 

These effects, noted for both groups of organisms at approximately 1000 mg/kg diet, 

include a reduction in egg quality (birds) and reduced weight of pups (rats). No 

treatment-related mortality or other effects were noted in the studies. 

Table 19 Avian and Small Mammal Guideline Data from Chronic Studies 

Species 

NOAEC 

(mg/kgdiet) 

LOAEC 

(mg/kgdiet) 

Endpoint Affected Classification 

(MRID) 

Bobwhite quail 403* 1010 Egg quality (Eggs cracked, 

percentage of eggs laid) 

Acceptable 

(46508901) 

Racemic 

Bobwhite quail 1000 >1000 No effects noted 

Core 

(44995901) 

S-metolachlor 

Rat 300* 1000 Reduced pup weights in F1

and F2 litters 

Acceptable 

(000808097) 

Racemic 

33
4.4 Terrestrial Insect Data 

The only guideline insect tests are for honeybees. Registrant submitted studies include 

acute contact and acute oral toxicity studies for s-metolachlor (MRID 44718402, Core). 

The acute contact LD50 is >200 μg a.i./bee and the oral LD50 is >85 μg a.i./bee. 

NOAELS are 200 μg a.i./bee for acute contact and 85 μg a.i./bee for oral dose. 

4.5 Terrestrial Animal Data from ECOTOX 

No data regarding S-metolachlor or metolachlor effects on terrestrial animals are 

currently available in ECOTOX. 

4.7 Incident Database Review 

The incident database contains a total of 117 reported incidents for S-metolachlor. Of 

these, only two reports are for organisms other than plants. In one case, there is a report 

of three birds dying as a result of S-metolachlor use. The certainty of this incident was 

unrated, and legality designated as unknown. The second case was a reported fish kill, of 

an unspecified magnitude. The legality of the use was designated unknown, and the 

incident was designated unlikely to be the result of the pesticide. The remainder of the 

incidents was damage to agricultural crops. Based on the data, it appears that most of the 

reports are for the crop at the treatment site applied in accordance with registered use. 

The most commonly reported crops damaged were corn, cotton, and soybean. The 

certainty was generally rated as possible. 

Incidents are reported separately for metolachlor, but the number and type of reports are 

similar. A total of 171 reports are in the database. Of the reports, 150 are of plant 

damage, again to agricultural crops under registered use conditions. The most commonly 

reported crop damage was to corn, peanuts, and soybeans. There was one reported bird

kill that was rated as unlikely to be associated with the metolachlor use. There are 19 

reported incidents of effects on aquatic animals, primarily fish. Generally, these occurred 

under registered use conditions, and were rated as possibly or unlikely to be associated 

with the application of metolachlor. One incident, a fish kill in Minnesota, has a certainty 

rating of highly probable, but was also listed as accidental misuse. 

5. Risk Estimation 

Risk is estimated by calculating the ratio of the expected environmental concentration 

and the appropriate toxicity endpoint. This value is the risk quotient (RQ), which is then 

compared to pre-established levels of concern (LOC) for each category evaluated. The 

RQ methodology, LOCs , and specific details of calculation are contained in Appendix 

G. The highest EECs and most sensitive endpoints are used to determine the screening 

level RQ. Using these two values theoretically results in a conservative estimate of risk. 

34
5.1 Aquatic RQ Summary 

A summary of RQs for the parent S-metolachlor (Table 20) and the degradates ESA and 

OA (Table 21) is presented below. No LOCs for any of the aquatic animals were 

exceeded in either freshwater or saltwater. Acute RQs for animals ranged from <0.01 to 

0.02. Chronic RQs for the animals ranged from <0.01 to 0.97. For all scenarios, both the 

acute and endangered species LOCs were exceeded for freshwater algae. For two uses 

(FL peppers and IL corn) the endangered species acute risk was exceeded for saltwater 

algae. Endangered species LOCs were exceeded for vascular aquatic plants (RQ 1.27-

4.62) in all scenarios, and non-endangered LOCs for vascular aquatic plants (RQ 1.67-

11.58) were exceeded in scenarios with low organic content in the soil (CA lettuce and 

FL peppers). RQs for the scenarios with higher organic content (>3%) approached but 

did not exceed the non-endangered plant LOC. 

Table 20 Summary of Aquatic RQs for S-metolachlor 

Taxa Acute RQ Chronic RQ Endangered 

Species RQ1

Use on CA lettuce

FW Algae 4.39a 23.41b

FW Vascular Plants 1.67 a 4.62 b

FW Aquatic Invertebrates <0.01 0.01 

FW Fish 0.01 0.97 

SW Algae 0.32 1.67 b

SW Aquatic Invertebrates 0.02 0.01 

SW Fish <0.01 0.03 

Use on FL peppers 

FW Algae 3.04 a 16.21 b

FW Vascular Plants 1.16 a 3.20 b

FW Aquatic Invertebrates <0.01 <0.01 

FW Fish <0.01 0.21 

SW Algae 0.22 1.16 b

SW Aquatic Invertebrates 0.02 0.01 

SW Fish <0.01 0.01 

Use on IL corn 

FW Algae 1.23 a 6.58 b

FW Vascular Plants 0.47 1.30 b

FW Aquatic Invertebrates <0.01 <0.01 

FW Fish <0.01 0.18 

SW Algae 0.09 0.47 

SW Aquatic Invertebrates <0.01 <0.01 

SW Fish <0.01 0.01 

Use on PA corn

FW Algae 1.21 a 6.43 b

FW Vascular Plants 0.46 1.27 b

FW Aquatic Invertebrates <0.01 <0.01 

FW Fish <0.01 0.27 

SW Aquatic Plants 0.09 0.46 

SW Aquatic Invertebrates <0.01 <0.01 

SW Fish <0.01 <0.01 

1 for plants, calculated based on NOAEC 

a

 equals or exceeds aquatic plant acute risk LOC (1) 

b equals or exceeds endangered species plant acute risk LOC (1) 

35
RQs were calculated for S-metolchlor degradates ESA and OA, based on the exposure 

concentrations estimated using GENEEC. No LOCs were exceeded, and all RQs were 

<0.01. 

Table 21 Summary of Aquatic RQs for Degradates 

Taxa Acute RQ Endangered 

Species RQ 

Degradate-ESA Application Rate 0.15

FW Algae <0.01 <0.01 

FW Vascular Plants <0.01 <0.01 

FW Aquatic Invertebrates <0.01 

FW Fish <0.01 

Degradate-OA Application Rate 0.36

FW Algae <0.01 <0.01 

FW Vascular Plants <0.01 <0.01 

FW Aquatic Invertebrates <0.01 

FW Fish <0.01 

5.2 Terrestrial RQ Summary 

Risk quotients for terrestrial plants were calculated using the most sensitive plant and 

most sensitive endpoint. Because of the concern for herbicide impacts on non-target 

plants RQs were calculated using both EFED’s standard method, TerrPlant, and also 

based on an AgDrift estimate of point deposition. 

Terrestrial RQs for birds and mammals were calculated using EFED’s TREX program, 

version 1.1. TREX uses the Kenaga nomagram, as modified by Fletcher et al. (1994) to 

estimate potential chemical residue on food items, calculates exposure by estimating food 

consumption via allometric equations (assuming the organism exclusively consumes 

contaminated items), and then calculates RQs based on a weight-adjusted LC50. 

5.2.1 Terrestrial Plants 

Risk quotients were calculated based on the exposures estimated by both TerrPlant and 

AgDrift. Calculations were made using data from both types of guideline studies 

(vegetative vigor and seedling emergence). Evaluations were done for both monocots 

and dicots 

5.2.1.1 TerrPlant 

Based on TerrPlant calculations for total loading (runoff plus drift), acute risk LOCs and 

endangered species LOCs are exceeded for both monocots and dicots in both uplands and 

wetlands for all application rates and methods (Table 22). Acute risk total loading RQs 

ranged from 10 to 101 for the 0.95 lb ai/A application rate, and from 13 to 135 for the 

1.27 lb ai/a application rate. Based on spray drift alone, no acute risk RQs were 

36
exceeded. Acute endangered species RQs based on drift exceeded the LOC both 

monocots and dicots at the 1.27 lb ai/A application rate. 

TerrPlant was also used to calculate acute risk RQs for the degradates ESA and OA, 

using the expected conversion efficiency to estimate application rates. Because only one 

application rate was tested for the degradates, and the NOAECs were not determined, 

only the acute risk RQs were evaluated. No LOCs were exceeded. Acute risk RQs for 

ESA ranged from <0.01-0.17. Acute risk RQs for ESA ranged from 0.01-0.40. RQs for 

ESA are higher than the calculated value, because the test only established that the 

NOAEC for ESA was >0.5 lb ai/A. 

Table 22 Terrestrial Plant Risk Quotients Based on TerrPlant 

Total Loading RQ 

(Seedling emergence) 

Total Loading RQ 

(Seedling Emergence) 

Drift RQ 

(Vegetative vigor) 

Upland areas Wetland areas All areas Application Rate 

Monocot Dicot Monocot Dicot Monocot Dicot 

Acute risk 

Use at 0.95 lb ai/A 11.88 a 10.00 a 100.9 a 85.00 a 0.45 0.04 

Use at 1.27 lb ai/A 15.88 a 13.37 a 134.94 a 113.63 a 0.60 0.05 

Endangered species acute risk 

Use at 0.95 lb ai/A 57.00 a 190.0 a 484.6 a 1615 a 0.86 0.95 

Use at 1.27 lb ai/A 76.20 a 254.0 a 647.7 a 2159 a 1.15 a 1.27 a

Acute risk degradates 

ESA 0.15 lb ai/A 0.02 0.02 0.15 0.15 <0.01 <0.01 

OA 0.36 lb ai/A 0.04 0.04 0.37 0.37 0.01 0.01 a Equals or exceeds LOC of 1

37
5.2.1.2 AgDrift 

AgDrift was used to estimate clearance distances based on spray drift alone2

. Using 

estimated point deposition of S-metolachlor from the AgDrift Tier I analysis, plant RQs 

were calculated using both seedling emergence and vegetative vigor endpoints (Table 

23). For the seedling emergence endpoint, ground applications of S-metolachlor at both 

rates clear the acute risk LOC at < 300 ft, but do not fall below the endangered species 

LOC until >600 ft. For ground applications, both endangered species RQs and acute risk 

RQs are below the LOC at 100 ft using the vegetative vigor endpoint. 

Table 23 Required Distance from Application to Fall Below LOC 

Clearance Distance (ft) 

Application Method Application Rate 

(lb ai/A) Acute LOC Endangered 

Species LOC 

Based on seedling emergence (monocot, guideline data) 

Ground 0.95 250 > 600 

(low boom) 1.27 300 > 600 

Based on vegetative vigor (monocot guideline data) 

Ground 0.95 10 100 

(low boom) 1.27 60 100 

5.2.2 Avian RQ Summary 

No acute or chronic risk LOCs are exceeded for birds, at any application rate (Table 24). 

Acute endangered species risk LOCs are exceeded for small birds (20g) eating short grass 

at the 0.95 lb ai/A application rate (RQ 0.14). At the higher application rate, endangered 

species acute risk LOCs are exceeded for herbivorous and insectivorous small birds (20g, 

RQ 0.11-0.14). 

Table 24 Avian RQ Summary 

Acute dose-based RQs1 Acute dietarybased RQs1Chronic 

RQs Risk quotients based on 

Kenaga upper bound EECs 20g 100g 1000g All birds All birds 

Application Rate 0.95 lb ai/A

Short grass <0.14b <0.06 <0.02 <0.05 0.57 

Tall grass <0.07 <0.03 <0.01 <0.02 0.26 

Broadleaf plants/small insects <0.08 <0.04 <0.01 <0.03 0.32 

Fruits/pods/seeds/lg insects <0.01 <0.01 <0.01 <0.01 0.04 

Application Rate 1.27 lb ai/A 

Short grass <0.19 b <0.09 <0.03 <0.06 0.76 

Tall grass <0.09 <0.04 <0.01 <0.03 0.35 

Broadleaf plants/small insects <0.11 b <0.05 <0.02 <0.03 0.43 

Fruits/pods/seeds/lg insects <0.01 <0.01 <0.01 <0.01 0.05 

1 LD50/LC50 values only established as greater than(>) a particular concentration, so RQs are 

reported as less than (<) values 

a

 Equals or exceeds acute risk LOC (0.5) 

b Equals or exceeds endangered species acute risk LOC (0.1) c

 Equals or exceeds chronic risk LOC (1.0) 

 

2

 Locations near the use site that receive runoff should be evaluated on the basis of total loading (runoff 

plus spray drift). 

38
5.2.3 Small Mammal RQ Summary 

No acute risk or endangered species acute risk LOCs are exceeded at any application rate 

(Table 25). Chronic risk LOCs are exceeded for all size classes of herbivores at both 

application rates, using the dose-based estimations. Chronic risk LOCs are also exceeded 

for small (15g) and medium (35g) insectivores. Chronic LOCs are exceeded at the 1.27 

lb ai/A application rate for mammals eating short grass using the dietary-based RQs. 

Table 25 Small Mammal RQ Summary 

Acute 

dose-based RQs 

Chronic 

dose-based RQs 

Chronic 

dietary-based 

RQs 

Risk Quotients based 

on Kenaga 

upper bound EEC 15 g 35 g 1000 g 15 g 35 g 1000 g All mammals 

Application Rate 0.95 lb ai/A

Short grass 0.04 0.03 0.02 6.59c 5.63 c 3.02 c 0.76 

Tall grass 0.02 0.01 0.01 3.02c 2.58 c 1.38 c 0.35 

Broadleaf plants/ 

small insects 0.02 0.02 0.01 3.71c 3.17 c 1.70 c 0.43 

Fruits/pods/seeds/ 

lg insects <0.01 <0.01 <0.01 0.41 0.35 0.19 0.05 

Seeds (granivores) <0.01 <0.01 <0.01 0.09 0.08 0.04 

Application Rate 1.27 lb ai/A

Short grass 0.05 0.04 0.02 8.81c 7.53 c 4.04 c 1.02 c

Tall grass 0.02 0.02 0.01 4.04 c 3.45 c 1.85 c 0.47 

Broadleaf plants/ 

small insects 0.03 0.02 0.01 4.96 c 4.24 c 2.27 c 0.57 

Fruits/pods/seeds/ 

lg insects <0.01 <0.01 <0.01 0.55 0.47 0.25 0.06 

Seeds (granivores) <0.01 <0.01 <0.01 0.12 0.10 0.06 a

 Equals or exceeds acute risk LOC (0.5) 

b Equals or exceeds endangered species acute risk LOC (0.1) 

c

 Equals or exceeds chronic risk LOC (1.0) 

5.2.4. Terrestrial Insects 

EFED currently has no standard procedure for calculating RQs for terrestrial insects. 

However, guideline data are available for honeybee toxicity, and the Kenaga residue (as 

modified by Fletcher, et al. (1994) estimates can be used as a rough approximation of 

exposure. The honeybee acute contact NOAEL is 200 μg/bee. If the mass of a honeybee 

is assumed to be approximately 0.08g, this would correlate to approximately 2,500 μg/g. 

Residue estimates for the higher (1.27 lb ai/A) application rate range from 25 μg/g (large 

insects) to 224 μg/g (small insects). Thus, it appears that terrestrial insects that react to 

acute contact with S-metolachlor in a fashion similar to honeybees are unlikely to be at 

risk. Given currently available data and models, EFED is unable to evaluate the potential 

effects of an oral dose. 

39
6. Risk Description 

The risk description is presented in terms of the type of ecosystem assessed (aquatic or 

terrestrial). Where appropriate, the description is further subdivided into taxa and 

application rate. A separate section is included to summarize potential effects on 

endangered species. 

6.1 Aquatic Risk 

Aquatic risk was evaluated based on EECs for the S-metolachlor, and the two major 

degradates. Several different scenarios were run in PRZM-EXAMS to determine how 

concentrations of S-metolachlor in the receiving water body might vary based on 

application rates, and site soil and meteorological conditions. Soil organic matter in the 

scenario was used to determine application rate, in accordance with label directions 

6.1.1 Aquatic Plants 

Aquatic plants, both algal and vascular are at risk based on all scenarios evaluated. Acute 

risk RQs for algae ranged from 1.21-4.39. Algae are important as a primary producer in 

many aquatic systems. The specific effect S-metolachlor may have on the alga is 

difficult to predict, and may vary widely, dependent on the type of receiving waters. The 

EXAMS water body is static, with no downstream dilution effects. The 21-day and in 

some cases the 60-day EECs exceed the acute risk LC50 of the most sensitive algal 

species. Thus, there could be effects such as a 1-2 month depression of algal growth in 

ponds and other still water bodies such as vernal pools receiving S-metolachlor input. 

Alternatively, there may instead be a shift to more resistant algal species. The effect an 

algal community shift would have on higher organisms is difficult to predict. However, 

if the selection pressure leads to greater concentrations of algal species that are less 

palatable, such as blue-green algae, it could result in reduced survival and/or growth in 

aquatic organisms dependent on the algal food chain. 

In some use scenarios (CA lettuce and FL peppers), the non-endangered aquatic plant 

LOC is exceeded for vascular aquatic plants, and in all scenarios the endangered species 

LOC is exceeded. In aquatic systems, vascular plants generally serve a structural 

function, providing cover for various organisms rather than serving as a food source. In 

certain aquatic systems, vegetated zones contain the greatest diversity of organisms and 

the greatest biomass per unit area. Loss of these vegetated areas, and/or conversion to an 

alternative dominant plant could change the overall biotic community. 

6.1.2 Aquatic Animals 

On an acute basis, S-metolachlor is slightly to moderately toxic to fish and aquatic 

invertebrates. Based on all scenarios evaluated, no acute LOCs were exceeded or 

approached for these organisms, and use of S-metolachlor at the proposed rate appears 

unlikely to cause any direct effects on growth, reproduction, or survival. While EFED 

does not have a procedure for evaluating behavioral or biochemical endpoints, 

40
concentrations at which effects are noted can be compared to EECs. All peak EECs were 

an order of magnitude lower than the cellular damage endpoint for the American bullfrog. 

In two scenarios (CA lettuce 0.035 mg/L, FL peppers 0.024 mg/L), the 1-in-10 year peak 

concentration of S-metolachlor was close to or exceeded the concentration at which 

behavioral modifications were noted in the rusty crayfish (0.027 mg/L). Whether the 

same effects might occur in a natural setting is unknown, as is whether the effects would 

have an impact on the survival of the organism. 

6.2 Terrestrial Risk 

The terrestrial risk description is divided into two sections: plants and animals. Risk to 

plants is evaluated based on RQs generated from guideline test toxicity data and exposure 

estimates from TerrPlant and AgDrift. Risk to animals is evaluated based on guideline 

toxicity test data and exposure estimates from TREX. 

6.2.1 Plants 

As is expected with an herbicide, non-target plants are the organisms with the greatest 

potential for effects. All total loading (runoff plus drift) acute risk RQs calculated using 

TerrPlant exceeded the LOC by 1-2 orders of magnitude at both use rates. Exceedences 

of the endangered species acute risk LOCs were generally in the range of 1-3 orders of 

magnitude. In some cases, endangered species LOCs were exceeded on the basis of 

spray drift alone. 

Ecologically, terrestrial plants are important to wildlife both as a food source and a 

structural habitat component. Removal and/or modification of the terrestrial plant 

community could change both the number and type of organisms it can support. 

The AgDrift model was used to estimate the distance required for expected spray drift 

concentrations to fall below the LOC. Estimates are based on Tier I modeling, which is 

non-site-specific. Deposition of the pesticide is dependent mainly on application rate, 

application method, droplet size, and distance from the source. Clearance distances were 

estimated based on both seedling emergence data, and vegetative vigor data. Currently, 

the S-metolachlor label (Dual II Magnum®, EPA Reg # 100-818, Syngenta) contains a 

400-ft buffer requirement for sensitive plants. Based on the most sensitive endpoint, the 

seedling emergence, clearance distances for the non-endangered plants are 250-300 ft, 

but clearance distances for endangered plants are >600 ft. 

6.2.2 Animals (Birds, Mammals, Insects) 

Generally, use of S-metolachlor at the proposed rates appears to pose relatively low risk 

to terrestrial animals on an acute basis. No acute risk LOCs were exceeded for either 

birds or mammals, although there were exceedences of the endangered species acute risk 

LOC for herbivorous and insectivorous small birds (20g) and herbivorous medium-sized 

birds (100g). However, the guideline tests did not establish a definitive LC50, instead

41
only determining a “greater than” value, so there is some uncertainty regarding the 

potential risk to birds, which could be over-estimated by existing data. 

Chronic risk exceedances for several size classes and guilds of mammals using the dosebased RQs indicates the potential for effects similar to these noted in the guideline 

studies. Chronic dietary-based RQs exceed the LOC only for mammals eating short 

grass. Chronic effects appear to be mostly reduced quantity and viability of offspring. 

Based on acute contact tests for honey bees, S-metolachlor does not appear to pose a 

threat to terrestrial insects. 

6.3 Endangered Species 

For a screening level risk assessment, EFED determines what endangered species may be 

affected by using the LOCATES database to search for organisms which are present in 

the same county as the crop being assessed. Potential direct effects are evaluated based 

on taxa which have RQs that exceed the LOC. For terrestrial organisms, evaluation of 

potential effects is also based on the organism’s size and diet. Organisms at risk for 

indirect effects include ones whose: 

1) habitat may have been altered by the action, or 

2) primary food source may have been affected. 

6.3.1 Aquatic Endangered Species 

Direct Effects 

No aquatic LOCs for animals were exceeded. Endangered species LOCs were exceeded 

for aquatic vascular plants. Table 26 show the number of endangered or threatened 

plants located in the same counties where pumpkins and squash are grown. A species list 

is included in Appendix G. 

Indirect Effects 

Indirect effects could include modification of the food chain due to changes in the 

quantity and/or composition of the algal community. Based on available data, green 

algae appear to be more sensitive to the effects of S-metolachlor than blue-green algae or 

diatoms. The magnitude and potential impact of such a shift is difficult to predict on a 

non-site specific basis. However, certain ecosystems characterized by relatively low 

volume to surface area and still waters (e.g., vernal pools) may be more susceptible to 

these types of effects. These locations provide important habitat for amphibians. 

Vascular aquatic plants also may be affected by runoff of S-metolachlor into waters 

adjacent to the use site. In aquatic systems, vascular plants generally serve a structural 

function, providing a refuge for small fish and habitat for some types of crustaceans and

42
gastropods. Reduction of the vegetated areas and/or shifts to an alternative dominant 

species could affect the viability of other organisms in the waterbody. 

6.3.2 Plants 

Direct Effects 

S-metolachlor has the potential to directly affect endangered plants located near the use 

site. The most vulnerable plants are those that are germinating, especially if they are 

exposed to S-metolachlor in both runoff and drift. Proximity to the use site will affect 

risk. Table 26 shows the number of endangered or threatened plants are located in the 

same counties where pumpkins and squash are grown. A species list is included in 

Appendix G. 

43
Table 26 Endangered Plants by State and Crop 

Pumpkin Squash State Monocot Dicot Other Monocot Dicot Other 

Alabama 2 9 2 2 9 2 

Arizona 3 11 0 3 16 0 

Arkansas 0 3 0 0 3 0 

California 15 153 2 15 153 2 

Colorado 1 3 0 1 5 0 

Connecticut 1 1 0 1 1 0 

Delaware 2 0 0 2 0 0 

Florida 1 10 1 2 43 2 

Georgia 5 6 0 4 8 3 

Hawaii 22 233 12 22 233 12 

Idaho 0 3 0 0 3 0 

Illinois 1 7 0 1 7 0 

Indiana 1 4 0 0 3 0 

Iowa 2 3 1 2 3 1 

Kansas 1 1 0 1 1 0 

Kentucky 0 9 0 0 6 0 

Lousiana 0 1 1 0 1 0 

Maine 2 1 0 2 1 0 

Maryland 2 4 0 2 4 0 

Massachusetts 2 1 0 2 1 0 

Michigan 3 4 1 3 4 1 

Minnesota 2 2 0 2 2 0 

Mississippi 0 1 0 0 1 1 

Missouri 1 7 0 1 6 0 

Montana 0 2 0 0 2 0 

Nebraska 1 1 0 1 1 0 

Nevada 0 1 0 0 8 0 

New Hampshire 1 1 0 1 1 0 

New Jersey 3 2 0 3 2 0 

New Mexico 0 11 0 0 12 0 

New York 1 4 1 1 4 1 

North Carolina 5 19 1 5 19 1 

North Dakota 1 0 0 1 0 0 

Ohio 2 4 0 2 4 0 

Oklahoma 0 0 0 1 0 0 

Oregon 1 9 0 2 9 0 

Pennsylvania 2 0 0 2 0 0 

Rhode Island 1 1 0 1 1 0 

South Carolina 5 11 1 6 12 2 

South Dakota 1 0 0 1 0 0 

Tennessee 1 16 2 1 13 1 

Texas 0 13 0 2 20 0 

Utah 1 15 0 1 16 0 

Vermont 1 1 0 1 1 0 

Virginia 4 12 0 4 11 0 

Washington 0 5 0 0 7 0 

West Virgina 1 4 0 1 4 0 

Wisconsin 2 4 0 2 4 0 

Wyoming 0 1 0 0 0 0 

44
Indirect Effects 

Pesticide-mediated indirect effects to plants are usually the loss of an important pollinator 

or dispersal species. Some endangered plant species may require the presence of other 

non-endangered plant species to create a suitable habitat. S-metolachlor effects on the 

habitat plants could constitute an indirect effect, but without detailed information on the 

plant’s life history and distribution, EFED is unable to even qualitatively evaluate this 

type of effect, although they could occur. 

6.3.3 Birds, Reptiles & Amphibians 

Direct effects (Birds) 

A search was conducted on LOCATES to determine what endangered birds are reported 

to occur in the same counties in which pumpkins and squash are grown. A total of 71 

bird species were reported. These organisms were sorted by dietary habits and size 

classes to determine which were in categories with exceedences of the LOCs. A full list 

of specific organisms and reasons why they were not retained as a species of concern is 

included in Appendix G. A total of 26 species (Table 27) remained in categories 

potentially at direct risk from S-metolachlor. 

45
Table 27 Endangered birds potentially at risk from s-metolachlor 

Species Size 

class 

1.27 

lb ai/A 

0.95 

lb ai/A 

Common name Latin name A C A C 

Invertivores

‘Akepa, Hawaii Loxops coccineus coccineus S * * 

‘Akepa, Maui Loxops coccineus ochraceus S * * 

‘Akia Pola’au Hemignathus munroi S * * 

Creeper, Hawaii Oreomystis mana S * * 

Creeper, Molokai Paroreomyza flammea S * * 

Creeper, Oahu Paroreomyza maculata S * * 

Elepaio, Oahu Chasiempis 

sandwichensis ibidis S * * 

Finch, Laysan Telespyza cantans S * * 

Finch, Nihoa Telespyza ultima S * * 

Flycatcher, 

Southwestern Willow 

Empidonax traillii extimus S * * 

Gnatcatcher, Coastal 

California 

Polioptila 

californica californica S * * 

Millerbird, Nihoa Acrocephalus familiaris kingi S * * 

Nuku Pu’u Hemignathus lucidus S * * 

Parrotbill, Maui Psuedonestor xanthophrys S * * 

Plover, Piping Charadrius melodus S * * 

Plover, Western Snowy Charadrius alexandrinus 

nivosus S * * 

Po’ouli Melamprosops phaeosoma S * * 

Scrub-jay, Florida Aphelocoma coerulescens S * * 

Starling, 

Ponape Mountain 

Aplonis pelzelni S * * 

Tern, California Least Sterna antillarum browni S * * 

Tern, Interior Least Sterna antillarum S * * 

Vireo, Least Bell’s Vireo belli pusillus S * * 

Warbler, 

Golden-cheeked 

Dendroica chrysoparia S * * 

Warbler, Kirtland’s Dendroica kirtlandii S * * 

Warbler, Bachman’s Vermivora bachmanii S * * 

Woodpecker, 

Red-cockaded 

Picoides borealis S * * 

A- Acute, C-Chronic, * - risk

Direct effects (Reptiles and Amphibians) 

A search was conducted on LOCATES to determine what endangered reptiles and 

amphibians are reported to occur in the same counties in which pumpkins and squash are 

grown. A total of 29 reptiles and 16 amphibians were reported. These organisms were 

sorted by dietary habits to determine which were in categories with exceedences of the 

LOCs. Amphibians with no terrestrial phase were excluded. A full list of specific 

organisms and reasons why they were not retained as a species of concern are listed in 

Appendix G. A total of 26 species (Table 28) remained in categories potentially at direct 

risk from S-metolachlor. 

46
Table 28 Endangered reptiles and amphibians potentially at risk from S-metolachlor 

Species Size 

class

1.27 

lb ai/A 

0.95 

lb ai/A 

Common name Latin name A C A C 

Herbivores 

Tortoise, Desert Gopherus agassizii N/A * * 

Tortoise, Gopher Gopherus polyphemus N/A * * 

Turtle, Alabama 

Red-belllied 

Pseudemys 

alabamensis N/A * * 

Invertivores 

Frog, California 

Red-legged 

Rana aurora draytonii N/A * * 

Frog, Chriricahua 

Leopard 

Rana ciricahuensis N/A * * 

Frog, Mountain 

Yellow-legged 

Rana muscosa N/A * * 

Lizard, Blunt-nosed 

Leopard 

Gambelia silus N/A * * 

Lizard, Coachella Valley 

Fringe-toed 

Uma inornata N/A * * 

Lizard, Island Night Xantusia riversiana 

Salamander, California 

Tiger 

Ambystoma 

californiense N/A * * 

Salamander, Cheat 

Mountain 

Plethodon nettingi N/A * * 

Salamander, Desert 

Slender 

Batrachoseps aridus N/A * * 

Salamander, Flatwoods Ambystoma cingulatum N/A * * 

Salamander, Red Hills Phaeognathus hubrichti N/A * * 

Salamander, Santa 

Cruz Long-toed 

Ambystoma 

macrodactylum 

croceum 

N/A * * 

Salamander, 

Shenandoah 

Plethodon shenandoah N/A * * 

Salamander, Sonora 

Tiger 

Ambystoma tigrinum 

stebbinsi N/A * * 

Skink, Blue-tailed Mole Eumeces egregious 

lividus N/A * * 

Skink, Sand Neoseps reynoldsi N/A * * 

Toad, Arroyo 

Southwestern 

Bufo californicus 

(=microscaphus) N/A * * 

Toad, Houston Bufo houstonensis N/A * * 

Turtle, Northern Bog Clemmys muhlenbergii N/A * * 

Turtle, Flattened Musk Sternotherus depressus N/A * * 

Turtle, Plymouth Redbellied 

Pseudemys rubriventris 

bangsi N/A * * 

Turtle, Ringed Sawback Graptemys oculifera N/A * * 

Turtle, 

Yellow-blotched Map 

Graptemys 

flavimaculata N/A * * 

A- Acute, C-Chronic, * - risk, NA – Not applicable (allometric equations used for birds 

 are not expected to be applicable to reptiles) 

47
Indirect Effects (Birds, Reptiles and Amphibians) 

The most likely indirect effect on birds, reptiles, and amphibians is modification of 

habitat as a result of damage to plants. The habitat modification could include reduced 

food supply, locations for nesting or burrowing, and/or reduced cover for predator 

avoidance. EFED is currently unable to evaluate the likelihood or magnitude of such an 

effect.

6.3.4 Mammals 

Direct effects 

A search was conducted on LOCATES to determine what endangered mammals are 

reported to occur in the same counties in which pumpkins and winter squash are grown. 

A total of 55 mammals were reported. These organisms were sorted by dietary habits and 

size classes to determine which were in categories with exceedences of the LOCs. A full 

list of specific organisms and reasons why they were not retained as a species of concern 

are listed in Appendix G. A total of 12 species (Table 29) remained in categories 

potentially at direct risk from S-metolachlor. 

Table 29 Endangered mammals potentially at risk from S-metolachlor 

Species Size 

class 

1.27 

lb ai/A 

0.95 

lb ai/A 

Common name Latin name A C A C 

Herbivores

Mountain Beaver, 

Point Arena 

Aplodontia rufa nigra L * * 

Mouse, Salt Marsh 

Harvest 

Reithrodontomys 

raviventris M * * 

Prairie Dog, Utah Cynomys parvidens L * * 

Rabbit, Pygmy Brachylagus idahoensis M * * 

Rabbit, Riparian 

Brush 

Sylvilagus bachmani 

riparius L * * 

Vole, Florida Salt 

Marsh 

Microtus 

pennsylvanicus 

dukecampbelli 

M * * 

Vole, Hualapai 

Mexican 

Microtus mexicanus 

hualpaiensis M * * 

Invertivores 

Bat, Gray Myotis grisescens S * * 

Bat,Hawaiian Hoary Lasiurus cinerus 

semotus S * * 

Bat, Indiana Myotis sodalis S * * 

Bat, Ozark Big-eared Corynorhinus 

(=Plecotus) townsendii 

ingens 

S * * 

Shrew, Buena Vista 

Lake Ornate 

Sorex ornatus relictus S * * 

A- Acute, C-Chronic, * - risk 

48
Indirect Effects (Mammals) 

The most likely indirect effect on mammal is modification of habitat as a result of 

damage to plants. The habitat modification could include reduced food supply, locations 

for nesting or burrowing, and/or reduced cover for predator avoidance. EFED is 

currently unable to evaluate the likelihood or magnitude of such an effect. 

6.3.5 Probability of Individual Effects 

Toxicity data available for birds and mammals does not support evaluation of potential 

individual mortality based on a probit dose-response relationship. 

49
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51
Appendix A Aquatic Exposure PRZM-EXAMS Output 

52
Appendix B Terrestrial Animals Exposure TREX Output 

53
Appendix C Terrestrial Plant Exposure Output (TerrPlant, AgDrift) 

54
Appendix D Aquatic RQ Calculations 

55
Appendix E Incident Database Report EIIS Output 

56
Appendix F Risk Quotient Method and Levels of Concern 

57
58

Appendix G Threatened and Endangered Species LOCATES Output