UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

MEMORANDUM 

DAT E: 

SUBJECT: 

TO: 

FROM : 

June 9, 2015 

Response to Public Comments on the Pre liminary Environmental Fate and 

Ecological Risk Assessment for the Registration Review of Sulfentrazone 

(PC Code No. 129081; DP Barcode D409753) 

Christina Scheltema, Chemical Review Manager 

Patricia Parrott, Branch Chief 

Risk Management and Implementation Branch 3 

Pesticide Re-evaluation Division (7508P) 

Geoffrey 

Michael Barrett

Sinclair, 

, PhD

PhD

, Chemist 

, Biologist 

f.../V

~ 

t (' '-....../ ~U 

~ ~ 

Environmental Risk Branch V 

Environmental Fate and Effects Division (7507C) 

THROUGH: Mah T. Shamim, Ph.D., Chief 

Environmental Risk Branch V 

Environmental Fate and Effects Division (7507C) 

EPA received comments in response to the "Preliminary E11 viro11me11tal Fate and Ecological 

Risk Assessment f or tile Registration Review of S 11/fe11trazo11e" (Document ID EPA-HQ-OPP2009-0624-00 17 in www.regulations.Q.ov ) (DP Barcode: D409753. dated June 11, 2014) from 

FMC corporation during the public comment period. The purpose of this memorandum is to 

address those comments. The Environmental Fate and Effects Division (EFED) used an outlinetype of format to address the comments. The comments taken from the FMC submission are 

presented in italics and EFED responses to those comments follow in an indented paragraph. 

EFED·s purpose of the document is to respond to technical/science-related questions and 

comments. 

1 
2

FMC Comment 1: The conclusion of the second paragraph on page two infers that 

sulfentrazone is expected to move to surface water and groundwater but does not actually 

characterize the likelihood of potential movement. Characterization of potential movement 

should consider influential factors beyond Koc, such as: 1) sulfentrazone mobility and 

persistence under field conditions using the recommended and relevant rates and method of 

application and 2) spatial variations of soil characteristics that are linked to sulfentrazone 

behavior and maximum allowable application rates.

EFED agrees with the registrant’s comments regarding the factors that can be important 

in determining the ultimate fate of sulfentrazone from site to site. The available 

Prospective Ground Water (PGW) studies show that leaching of sulfentrazone residues 

occurs at all four different study sites with a variety of characteristics. Sulfentrazone is 

sufficiently persistent and mobile to leach at some measurable amount at a variety of 

locations but the actual amount of mass transport into subsurface horizons will be highly 

dependent on the amount and timing of precipitation or irrigation events after application 

as well as the site characteristics and specific fate properties of sulfentrazone observed at 

a site. The level of overall impact on groundwater will also be dependent on what the 

long-term use pattern for sulfentrazone is in areas that constitute the recharge area for the 

aquifer. Further delineation of areas where sulfentrazone may impact groundwater after 

its use is not practical with the available assessment information and tools.

FMC Comment 2: The conclusion of this paragraph indicates that screening-level non-target 

plant modeling results in potential risk to plants adjacent to use areas; however, potential risk 

should be evaluated using best-available data and refined risk assessment methods. The revised, 

final ecological assessment should include best available data and refinement and data before 

concluding potential for adverse effects to listed species.

EPA’s preliminary risk assessments are based on screening-level non-target plant 

modeling using studies submitted to the agency and agency reviewed literature. Based on 

this preliminary assessment, and refinements using the standard EFED AgDrift model the 

assessment identified risk to plants in adjacent use areas and attempted to characterize the 

effects distances needed to reduce risk. Refinements included changing boom height and 

median droplet sizes to assess impact of application methodology. Subsequent to the 

public comment period, the Agency incorporated additional refinements into the risk 

assessment. 

EPA is currently working with its federal counterparts and other stakeholders to 

implement an interim approach for assessing potential risk to listed species and their 

designated critical habitats. Once the scientific methodology for risk assessments for 

listed species and their designated critical habitats are finalized, the Agency will 

complete its endangered species assessment for sulfentrazone. 

FMC Comment 3: Marine/estuarine biota are not expected to be exposed to significant 

concentrations of sulfentrazone as once the herbicide enters the systems it is expected to be 

diluted well beyond the standard EPA ‘pond’ that is simulated (Table 23 of preliminary risk 
3

assessment). The standard EPA pond scenario does not physically represent marine/estuarine 

systems. FMC suggests that the RQ generated for marine/estuarine species, which is not derived 

from measured data, be revised to be reported in a format that reflects exposure uncertainty due 

to the considerable dilution potential difference between the standard EPA pond and 

marine/estuarine systems. Refer to additional FMC comments for further discussion and 

information regarding the aquatic risk assessment. The standardization of avian risk is a useful 

tool to indicate potential risk, but further revision to the draft assessment should be done to 

address the chemical-specific expected exposure estimate and conservative consumption 

assumptions that apply to sulfentrazone.

Risk Quotients are based on actual measured toxicity endpoint points or endpoints 

derived through acute-to-chronic ratios (ACRs) where data do not exist as is indicated in 

the preliminary risk assessment. Standard EPA models are used to generate estimated 

environmental concentrations that estuarine/marine organisms may be exposed to. Until 

other models are vetted and adopted, these models will be used in current and future risk 

assessments. The toxicity endpoints are compared to estimated environmental 

concentrations for both freshwater and estuarine/marine environments from modeling 

runs that are standard in all preliminary risk assessments. The chronic endpoint for the 

saltwater mysid was not available so an ACR was used in lieu of this endpoint, in 

accordance with EPA policy. Use of an ACR is accompanied by uncertainty, which 

characterized in the ecological risk assessment addendum for sulfentrazone. 

Additionally, the risk assessment addendum includes further description of avian risk and 

upper bound versus mean estimates of exposure through consumption of dietary items.

FMC Comment 4: EPA policy accounts for enhanced toxicity of LDPH chemicals to animals 

under UV radiation. In this case, habitat/water containing aquatic organisms is assumed to be 

clear or transparent so that the light could penetrate through the water and create a condition 

for enhanced toxicity. The EPA statement appears to indicate that worst-case UV conditions 

(light-penetrating aquatic systems) are the standard for assessing uncertainty in surface water 

toxicity. It follows that aquatic exposure estimation of sulfentrazone should also include this 

assumption of UV conditions, i.e. relatively clear water systems – as opposed to assuming turbid 

water environments, as is currently done. Modeling aquatic exposure as ‘turbid’ appears to be 

inconsistent with this policy.

Since photolysis was important to the degradation rate of sulfentrazone in aquatic 

systems, the best- and worse-case scenarios as dictated by turbidity (high and low light 

environments) were presented (Tables 23 and 24 in the preliminary risk assessment). In 

the case of fish (Table 23), incorporating the LDPH factor in both scenarios did not 

change the risk picture. It is noted that the majority of water bodies surrounding 

agricultural areas will, however, be turbid waters with low photolysis rates. Modeling 

only clear water columns where LDPH would be of greater concern would not be 

representative of most agricultural systems but was described to bound the risk to fish in 

different light environments in aquatic systems. 

FMC Comment 5: EPA’s use of the AgDrift model combined with the lowest observed 

ecological endpoint provides overly conservative estimates for typical sulfentrazone use 
4

environments. It is suggested that the EPA consider alternative drift models and revised endpoint 

selection.

The EPA acknowledges the utility for alternative drift models but does not currently 

employ those models as they are undergoing the QA/QC process and are not appropriate 

for risk assessment purposes. The current AgDrift model combined with observed 

ecological endpoint is the standard method for screening level risk assessments.

However, EPA has re-reviewed the vegetative vigor data and recalculated this endpoint 

using the CETIS software. The new endpoint is now 0.0016 lbs ai/A instead of the 

previous endpoint of 0.0005 lbs a.i./A. For more details, see the assessment addendum

and the revised data evaluation record associated with this study.

FMC Comment 6: Sulfentrazone is a pre-emergence herbicide that is typically applied to the 

soil before planting or prior to crop emergence. Over 99% of sulfentrazone is applied by low 

boom ground applications (GFK data software, 2013) to provide maximum soil coverage. 

Additional refinement to surface water and non-target plant modeling should consider aerial and 

high-boom applications independently from ground application because aerial/high-boom 

application scenarios are rare.

The role of the environmental and ecological assessment is to cover all possible uses. 

The preliminary risk assessment presents modeling results for low boom and coarse 

droplet applications as well as those for high boom and aerial application (see Tables 32

and 33). During risk description, it is possible to qualitatively describe that the majority 

of the applications are applied with low boom and coarse droplet applications. The risk 

assessment addendum describes in more detail the refinements that were performed using 

information provided by the Biological and Economic Analysis Division with an 

emphasis on low boom applications and coarse droplet sizes.

FMC Comment 7: This table considers spray drift alone and does not consider the refinement 

needed for runoff to dry and semi-aquatic areas in the TerrPlant model. Incorporating

mitigation from spray drift buffers to address a potential concern that includes spray drift and 

runoff combined does not represent a complete assessment and should be revised. As mentioned, 

more current spray drift data is available for use in identifying potential risk in tools such as 

RegDISP. Once exposure from drift has been characterized using more current tools/data, the 

exposure from runoff contribution to dry and semi-aquatic areas should also be revised.

TerrPlant and AgDrift are the current models being used by EPA to assess off-site 

transport of the active ingredient to adjacent plant populations. The Agency is not 

currently able to use alternative tools, such as RegDISP, in a direct fashion for risk 

assessments. Models such as AgDISP are currently undergoing internal Agency review 

and validation and may be incorporated into future assessments.

FMC Comment 8: Sulfentrazone is a pre-emergence herbicide that is typically applied to the 

soil prior to planting or before crop emergence. As sulfentrazone is predominantly used as a preemergent herbicide, efficacy depends on soil coverage rather than leaf contact. To maximize soil 

coverage, spray nozzles that provide medium/coarse droplet size are desirable, as indicated on 
5

the federal label. It is impractical and extremely unlikely for a grower to use a fine spray droplet 

size if the product is to be used in compliance with the label and current agronomic practices. 

Medium-very coarse droplets are desirable for growers for soil-applied herbicide control of preemergent weeds. All federal labels for sulfentrazone recommend nozzles that produce minimal 

amounts of fine spray droplets to avoid spray drift for both ground and aerial application. In 

addition, labels indicate that a fine spray should be avoided and that maximum soil/plant 

coverage should be targeted – avoiding spray drift beyond the area intended for treatment.

Fine to coarse droplet sizes were modeled to provide a range of impacts. Clearly coarse 

droplet sizes would decrease the extent of transport relative to fine droplet sizes. The 

assessment discusses the impact of each. We appreciate that it is impractical and 

extremely unlikely for a grower to use a fine spray droplet size if the product is to be used 

in compliance with the label and current agronomic practices. However, because not all 

labels were clear with regard to droplet size and because the current spray drift labeling 

is, in many cases, advisory rather than mandatory, EPA modeled all possible spray drift 

scenarios, including fine droplet size. For sulfentrazone as a pre-emergent application, 

EPA acknowledges that application through coarse droplet sizes is preferred to enhance 

soil delivery and minimize off-field drift.

FMC Comment 9: FMC understands that the Agencies (EPA, FWS, NMFS, and USDA) are 

coordinating efforts to further refine their approach to conducting ecological risk assessments in 

support of listed species effects determinations. FMC will provide any data needed to conduct 

refinements that include more detailed analyses of registered uses and specific use patterns. 

FMC is member of the FIFRA Endangered Species Task Force (FESTF) that has tools that can 

provide these refinements. Procedurally, for effects determination evaluation for individual listed 

species, FMC/ FESTF would work with the Agencies to provide additional details on spatial use 

patterns, sub-county spatial proximity data for co-occurrence of potential effects areas and listed 

species and designated critical habitat. FMC understands that the Agencies are coordinating 

efforts to further refine this screening level assessment to support listed species effects 

determinations.

EPA appreciates that FMC will work with Agencies to provide additional details on 

spatial use patterns, sub-county spatial proximity data for co-occurrence of potential 

effects areas and listed species and designated critical habitat.

FMC Comment 10: 

The Agencies’ characterization of ‘broad potential for direct adverse effects to listed and nonlisted species of aquatic and terrestrial plants’ has not been evaluated in the preliminary 

assessment. Further refinement of the preliminary risk assessment is necessary to accurately 

represent the risk to non-target organisms. 

The use of the word broad refers the sulfentrazone’s ability to adversely affect listed and 

nonlisted plants from all three of the modeled exposure scenarios (spray drift only, runoff 

and spray drift (dry areas) and runoff and spray drift (semi-aquatic areas). The capability 

of adversely affecting plants in these assessments constitutes a broad potential to 

adversely affect plants as would be expected from a herbicide. The assertion that “this 
6

preliminary assessment would not qualify as characterizing broad potential for adverse 

effects for the following reasons” lists reasons that pertain to how the EPA performs 

preliminary risk assessments. As stated earlier, the assessment utilized the models that 

are standard in preliminary risk assessments. The Agency agrees assumptions such as 

100% PCA are highly conservative for most ecological exposure scenarios but believes 

that, if the product is used at maximum label rates, the conclusions could apply to 

organisms living in or around water bodies with very small drainage areas. EPA 

performed additional analysis that are described in the addendum to consider additional 

exposure scenarios that increase droplet sizes and decrease boom heights.

This preliminary assessment would not qualify as characterizing broad potential for adverse 

effects for the following reasons: 

• Tier 1/Screening-level modeling for terrestrial plants: 

o Single-species effect endpoint exclusively used (monocot and dicot), i.e. no consideration of 

community-level effect or ecologic relevance of potential effect.

As part of the preliminary risk assessment process, EPA does not model community level 

effects. The single species endpoint is the standard way in which the Agency assesses 

risk to non-target plants. 

o Use of AgDRIFT provides inadequate and outdated spray drift exposure estimation 

techniques/modeling. More current and representative spray drift information is publically 

available (e.g. RegDISP) and should be utilized. 

AgDrift is currently the standard model used in the preliminary risk assessment process. 

Other models, such as RegDISP, are currently undergoing internal Agency review and 

validation and may be incorporated into future assessments.

o Aerial application method should be limited to appropriate crop/uses and small-scale 

geographies that represent 1% of all application methods. Ground application under a low boom 

application type should be the application method assessed broadly across the majority of crops 

and should consider rate restrictions around soil.

EPA appreciates that the predominant application method is ground application using 

coarse droplet size from a low boom. However, because some sulfentrazone labels list 

aerial application, Agency modeled all scenarios for completeness sake. The risk 

assessment addendum focused on applications with low boom height and coarser droplet 

sizes as well as specific application rates associated with aerial applications. It is 

understood that aerial applications generally only occur when fields are too wet to all 

access by ground equipment.

o No refinement of runoff contribution to terrestrial (dry and semi-aquatic) systems, 5% runoff 

assumed for all crop growing areas 

o No spatial co-occurrence analysis of semi-aquatic (wetland) habitat and adjacent use areas 
7

o Assumptions of application at the maximum application rate, % crop treated and registrations 

at the state level are not included in the assessment 

o Spatial and temporal co-occurrence, frequency, and likelihood of effects based on labeled 

rates and associated soil restrictions are not evaluated 

• Tier 1/Screening-level modeling of aquatic plants: o Aquatic exposure is based only on a highly 

conservative, single combination of soil and weather conditions per crop and region. A much 

broader range of soil and weather conditions are relevant for each crop and should be 

considered in a refined assessment before judgments on the extent of any potential effects can be 

determined 

o The assumption of 100% PCA for all crop scenarios is a highly conservative extreme case. 

Spatial analysis of small pond watersheds shows that PCAs are typically much less than 100%, 

with a case study of ponds in California showing median PCAs of approximately 12% (Winchell 

et al., 2014) 

The comments concerning more detailed spatial analysis associated with the assessment 

are noted. At this time, such an analysis is beyond the scope of a tier 1 preliminary 

assessment. There are spatial models such as a Spatial Aquatic Model (SAM) being 

developed that will help address these comments and help refine risk assessments and 

evaluate risk to endangered species in the future.

FMC Comment 11: 

FMC recommends the risk assessment to non-target plant toxicity follow the EPA’s proposal that 

provides the impetus for defining effect at the 25th percentile as outlined in an EPA SAP panel 

briefing (Davy, et. al. 2001). Michael Davy, et al. 2001. Scientific Advisory Panel Briefing. 

Proposal to update non-target plant toxicity testing under NAFTA. Joint EPA/PMRA document. 

http://www.epa.gov/oscpmont/sap/meetings/2001/june/sap14.pdf. FMC recommends the use of 

the EC50 value to be consistent with the other effect metrics for all other risk categories and as a 

more meaningful effect metric because: 

• The EC25 appears to be related to a cosmetic-level effect (protection goal) for high-value 

ornamentals and fruits and is not intended to cover terrestrial plants in natural ecosystems 

• Endpoints measured to determine risk corresponding to the EC25 (e.g. dry weight) are not 

linked to fundamental plant productivity metrics, such as flower formation, pollen or seed 

viability, etc 

• A tiered approach is recommended in which non-target terrestrial plants that are relevant to 

natural ecosystems would require a higher tier of assessment to determine adverse effects 

• Using the EC25 from surrogate plants with no correlation to natural plants does not 

characterize risk 

In addition to the issue of applying an appropriate effect endpoint from surrogate data, a 

correction should be made to the actual calculation of the EC25 for cucumber. The EC25 

calculation for cucumber (dry weight endpoint) was re-evaluated and upon confirming normality 

in the raw data, Probit Analysis was conducted using the original data (MRID 43345412) 

according to current standards. The resulting EC25 value was determined to be 0.00275 lb ai/A. 

Additionally, the EC50 value was also calculated as 0.00514 lb/ac (Standard error: 0.0003059). 
8

The corrected EC25 value of 0.00275 lb ai/A should be used in the risk assessment in lieu of the 

previously-calculated EC25 of 0.00052.

The EPA appreciates the value of alternate methods to risk assessment. EPA, however,

has an established protocol for assessment of risk to non-target plants. The vegetative 

vigor data for sulfentrazone (MRID 43345412) has been reevaluated using updated 

CETIS software. The EPA concurs that the previous endpoint for vegetative vigor in the 

cucumber was incorrectly calculated. The new EC25 endpoint, presented in more detail 

in the addendum, was determined to be 0.0016 lb ai/A. This endpoint was used to refine 

both TERRPLANT modeling to generate RQs as well as in AgDrift modeling to generate 

effects distances.

FMC Comment 12: Residue data for registered crops shows that plants do not uptake 

sulfentrazone residue from soil (pre-plant) and translocate (redistribute) it into the foliage and 

above-ground portion of the plant/crop. It is important to note the distinction between ‘systemic’ 

and the process of plant uptake of sulfentrazone through the root zone and via translocation. 

This distinction is important because it affects the potential sulfentrazone exposure to terrestrial 

organisms via plant tissue. Kenaga nomograms (page 46, Table 15) used within this preliminary 

risk assessment represent maximum dietary/plant residues and therefore overestimate risk to 

terrestrial organisms. FMC suggests that this information be considered and incorporated into 

the final risk assessment on a qualitative not quantitative basis.

 

EPA appreciates insight as to the difference between systemic uptake and translocation. 

The T-REX model is the standard model with which to assess risk to terrestrial animals in 

preliminary risk assessments. Further it is EPA policy to use the upper bound Kenega 

nomograms in risk characterization as they are the most protective, while the mean 

Kenaga nomograms may be used to describe risk in more detail. Additional analysis of 

avian risk was conducted by examining multiple application rates as well as comparing

upper bound and mean Kenaga values and the amount of time that residues are expected 

to be of concern. 

FMC Comment 13: The label restriction “Do not use on coarse soils classified as sand which 

have less than 1% organic matter.” is required on all sulfentrazone labels. The sizeable 

exclusion of soils that meets this criteria, as well as rate limitations corresponding to soil texture 

as outlined in Table 2, should be a significant element of characterizing potential risk to nontarget organisms and has not been applied in the preliminary assessment. The action area 

represented by conservative Tier I modeling used in the preliminary assessment likely represents 

a small and improbable use area, the exact spatial extent of which has not been quantified. 

Geospatial consideration of sulfentrazone rate limitations should be incorporated in the refined 

assessment. Mitigation or risk conclusions that ignore critical label language on the federal 

label disparages and undervalues past science and policy that were implemented to proactively 

and responsibly protect ecosystem integrity.

EPA believes that the label restriction regarding coarse low organic matter soils prevents 

usage on some of the most vulnerable sites for sulfentrazone leaching (we are assuming 

the registrant’s comments mostly have in mind potential for sulfentrazone residues to 
9

impact groundwater), but this restriction does not include large areas where there is a 

finite leaching potential for sulfentrazone. Therefore, this label restriction does not 

alleviate the need for mitigation measures in areas where sulfentrazone can still be used. 

EPA agrees that, should a more refined risk assessment become necessary in the future, 

consideration of spatial variability in soils, hydrogeology, weather, and agronomic 

practices and of the degree of alignment of the most vulnerable areas with existing or 

potential use areas for sulfentrazone products would be appropriate. 

FMC Comment 14: Page 18, row 3 & 4: Corn is listed twice. The correct corn minimum single 

application rate (column 2) is 0.09 lb ai/A and the correct maximum single application rate is 

0.25 lb ai/A. Page 19, row 2, column 2: The correct minimum single application rate for melons 

is 0.09 lb ai/A. Page 19, row 6/Page 20, row 9: Soybeans are listed twice. Soybeans should be 

removed from the reference on page 19 since row 6 is incorrect. Page 21, footnote: The 

maximum annual use rate is 0.375 lb ai/A for turf (sod production, lawns, golf fairways and 

roughs).

EPA will incorporate this information in a memorandum updating the assessment.

FMC Comment 15: FMC suggests that alfalfa, pumpkins, rice, winter wheat and spring wheat 

outside of the Pacific Northwest should not be included in the risk assessment. Neither a federal 

registration nor a tolerance are established for use on alfalfa, pumpkins or rice (rotational 

tolerance only). Wheat is limited to a regional registration/tolerance in the Pacific Northwest 

and only on the spring wheat variety. The qualitative implications related to the average and 

maximum percent crop treated data (ranges from <1% to 50%) suggest that sulfentrazone is 

being applied to a relatively small actual acreage for any given crop. This relatively small 

acreage has less likelihood of co-occurrence with sensitive species, compared to 100% percent 

crop treated. This information could be translated into the risk assessment, paired with the lack 

of incident reports since 2005. Together, this information is powerful weight of evidence toward 

the low likelihood of adverse effects on ecological integrity. This table also illustrates the 

importance of geospatial analysis to characterize probability (e.g. exposure frequency, spatial 

extent, co-occurrence with sensitive species and habitats) of risk to non-target organisms. It is 

inadequate to address potential risk and mitigation decisions using screening-level information 

(representing obscure and environmentally-irrelevant situations, in practice).

The Agency will consider improving the variety and representativeness of the modeled 

scenarios in future risk assessments. New, more spatially explicit methods have not yet 

been fully developed and approved for use in regulatory assessments. In addition, EPA is 

currently working with its federal counterparts to develop and implement an interim 

approach for assessing potential risk to listed species and their designated critical 

habitats. The Agency will not complete its endangered species assessment for 

sulfentrazone until the scientific methodology for risk assessment of listed species (and 

designated critical habitat) is finalized. 

The registrant’s points about the actual percent crop area treatments are important but 

difficult to implement in a screening risk assessment. It is beyond the scope of the current 

assessment to incorporate percent crop treated factors. We note that a more refined 
10

assessment incorporating such factors must be able to reliably forecast the upper bounds 

of future percent crop treated factors.

FMC Comment 16: 

The statement regarding photo-toxicity appears to infer the predominance of clear-water 

conditions. While the impact of clear-water conditions was assessed in the preliminary 

assessment, they are not reflected in the calculation of RQs for aquatic plants. Instead, a 

photolysis value of 98 days (from the soil photolysis study) was used in the aquatic exposure 

modeling to represent turbid conditions, which were then used to calculate RQs. Turbid water 

conditions are not consistent with the assumption of enhanced UV/photo-toxic effects 

(conceptually more representative of clear-water conditions). The guidance that is available 

from The Agency states that the direct photolysis value that is input into the EXAMS aquatic 

systems model is “... the minimum dark-control corrected environmental aqueous phototransformation rate constant (corresponding to the maximum half-life value).” 

(http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm#Przm). 

To determine potential for indirect effects due to effects on primary productivity and habitat, a 

quantitative characterization should be established and described instead of an assumed 

association. Indirect effects can be better addressed once adequate potential risk from direct 

effects is characterized. Given the significant corrections and screening-level nature of risk 

presented in the preliminary risk assessment, FMC suggests that statements of indirect effects be 

evaluated against considerable revisions and refinement that are needed to correctly 

characterize potential direct risk. A food web model may be a useful to begin quantifying 

relationships between direct and indirect effects and FMC supports the introduction, 

development and implementation of such tool.

Turbid waters would be more characteristic of water bodies associated with agricultural 

areas. Since sulfentrazone did not appear to degrade at rates approaching the aqueous 

photolysis study rate in some guideline ecological studies, it was appropriate to put an 

upper bound on exposure by using the longer soil photolysis rate. The intent of this 

methodology is to bracket the risk profiles under different degradation rates which are 

derived from laboratory studies. In both cases the RQ is near the LOC; this is indicative 

of potential risk. 

EPA currently does not use a food web model to quantify the relationships between direct 

and indirect effects. However, EPA is currently working with its federal counterparts and 

other stakeholders to implement an interim approach for assessing potential risk to listed 

species and their designated critical habitats. Once the scientific methods necessary to 

complete risk assessments for listed species and their designated critical habitats are 

finalized, the Agency will complete its endangered species assessment for sulfentrazone. 

FMC Comment 18: Because of major differences between ecological and human health drinking 

water assessments, this preliminary ecological assessment should not be used to support 

drinking water exposure in the future. While some information in the Tier II water modeling 

would be applicable (e.g. application rate, physical-chemical properties), major differences 
11

between ecological and human health water exposure estimation exists, including but not limited 

to: 

• Receiving water body for ecological assessment (farm pond) versus index reservoir for human 

health 

• Environmental fate input guidance is different between ecological and human health 

assessments 

• Application inputs for drift, application efficiency are different between ecological and human 

health assessments 

• Percent crop area is taken into account for human health drinking water assessments, whereas 

not for screening-level ecological assessments 

Drinking water exposure was estimated separately for surface waters using the Index 

Reservoir and for ground waters using the standard scenarios for PRZM-GW along with 

characterization provided by the four prospective groundwater monitoring studies for 

sulfentrazone. EPA acknowledges that the environmental fate inputs can be different for

various models depending on the requirements of each. The appropriate EPA guidance 

documents were followed for each model. For the surface water modeling of drinking 

water exposure, the default PCA for chemicals with both turf and multiple agricultural 

uses on major crops sites was used as noted in the drinking water assessment. The 

preliminary ecological assessment was not used to support drinking water exposure.

FMC Comment 19: Potential exposure through spray drift and runoff to non-target organism 

should take into account actual agronomic practices (application timing, rates according to soil 

characteristics, label restrictions including spray drift advisory language). Potential exposure to 

non-target plants and animals is not consistent with the low number of reported ecological 

incidents through EIIS over the past 12 years with wide-scale use of sulfentrazone and should be 

reevaluated.

The preliminary assessment uses the best available information and to the extent possible 

provides exposure estimates from established models and scenarios. Low reported 

ecological incidents in the EIIS database do not necessarily mean that incidents do not 

occur and so the assessment may not always closely reflect incidents that may or may not 

be reported.

Conceptually, while direct foliar exposure has the potential to occur to non-target plants 

adjacent to use areas, direct exposure to non-target plants from uptake of sulfentrazone from the 

roots in residue studies is not expected to be detected in the plant foliage that would lead to 

secondary exposure to terrestrial animals. In this case, the potential for terrestrial organisms via 

exposure from non-target plant feed items would only be expected to be exposed to non-target 

plants exposed to spray drift, not spray drift and uptake through the roots from sulfentrazone 

originating as off-field runoff. The conceptual model should be updated to consider this 

distinction, as it is important in the characterization of exposure and subsequent potential risk.
12

The Agency agrees that there is likely to be less sulfentrazone exposure potential for nontarget plants outside the treated area. Nonetheless, sulfentrazone could still be 

translocated from the soil to the roots and into the foliage as demonstrated in published 

literature (see, e.g., Thomas et al., 20051)

FMC Comment 20: This risk hypothesis is based on a screening-level effort and deterministic 

approaches to identify potential risk to the most sensitive plants under hypothetical conditions 

that are protective, but not representative. The final conclusion of risk should include thorough 

analysis of the following critical aspects that are not currently considered in the EPA draft risk 

assessment: 

1) Labeled instructions for use, such as application rate and timing, are not represented in the 

preliminary draft assessment results for potential risk to terrestrial or aquatic non-target plant 

systems. The federal label specifically limits or restricts the application rate of sulfentrazone 

based on soil texture and soil organic matter, which are spatially-dependent parameters and not 

currently addressed. 

2) Terrestrial and aquatic non-target plant effect endpoints used to calculate risk quotients do 

not represent community-level adverse effect. 

3) Spray drift exposure modeling (AgDRIFT) does not incorporate best-available data to 

evaluate the impact of potential mitigation of spray drift exposure to non-target plants adjacent 

to use areas. 

4) Spray drift mitigation does not address potential risk from runoff, which drives risk to the 

semi-aquatic terrestrial habitat. Geospatial co-occurrence of semi-aquatic habitat and use areas 

should be evaluated in parallel with temporal patterns of exposure to terrestrial organism. 

5) Edge-of-field runoff and possibly runoff connected with a vegetative buffer should be 

considered to revise the terrestrial exposure to dry and semi-aquatic habitats (and relevant 

plants in those areas). 

6) Sulfentrazone should be evaluated using all available field data (including more recent 

terrestrial field dissipation and aquatic dissipation data) to determine sensitive geographies and 

conditions. 

7) Probabilistic risk assessment approaches that characterize the potential frequency, duration, 

spatial extent, and magnitude of potential adverse effects should be incorporated to fully 

represent federal label directions, chemical-specific exposure, and spatial and temporal cooccurrence of use sites with sensitive plant ecosystems that could be impacted. 

Decisions to mitigate risk after a screening-level assessment of potential/theoretical risk would 

not effectively identify appropriate and meaningful mitigation to sensitive plant communities. 

Discussion of mitigation should only occur after a complete risk characterization is conducted so 

that appropriate measures are taken to proactively address concern around impact to sensitive 

ecosystems.

 1 Thomas, W.E., , S.C. Troxlera, W.D. Smith, L.R. Fisher, and J.W. Wilcut. 2005. Uptake, translocation, and 

metabolism of sulfentrazone in peanut, prickly sida (Sida spinosa), and pitted morningglory (Ipomoea lacunosa). 

Weed Science 53(4):446-450.
13

The EPA has established protocols and procedures to conduct a preliminary risk 

assessment. This assessment reflects the current models and practices used when 

conducting risk assessments and does not incorporate models or methods currently in 

development. Incorporation of the spatially explicit assessment procedures recommended 

by the registrant can be valuable when more highly refined risk assessments are required. 

FMC Comment 21: Molecular formula: The molecular formula should be C11H10Cl2F2N4O3S 

Aqueous Photolysis Half-life: Aqueous photolysis is one of the principal dissipation routes in the 

natural environment. The Agency has listed half-life values of 0.5, 0.05 and 0.05 days for 

aqueous photolysis at pH 5, 7, and 9 and it is important to evaluate and incorporate these values 

into the calculation of RQs. In nature, pH 7 is more representative for surface water modeling, 

therefore FMC recommends using the corresponding aqueous photolysis half-life value (0.05 

days). 

EFED could not find anywhere in the document where a different molecular formula was 

used for sulfentrazone. However, if FMC points out a specific place where this needs to 

be corrected, EFED will incorporate the updated molecular formula information in a 

memorandum updating the assessment. The recommendations regarding the 

incorporation of the aqueous photolysis half-life will be taken into consideration for 

future risk assessments, but see also our response to FMC Comment 16.

Additional data: Three terrestrial field dissipation studies are available and will be submitted by 

FMC to provide additional information on soil movement to surface and groundwater. Results 

from these three studies indicate actual field half-life values and should be considered rather 

than those previously observed in modeling. In addition, two aquatic dissipation studies have 

been conducted and will be provided to the Agency to help refine risk in surface water 

environments for sulfentrazone. The values found in these studies indicate that sulfentrazone is 

not persistent in the aquatic environment. The following aquatic and field dissipation studies 

will be submitted to the Agency: 

1. Dow, Karen. 2005. Sulfentrazone: Terrestrial Field Dissipation. FMC Study ID P-3778. FMC 

Corporation. Princeton, NJ. 

2. Boatwright, Megan. 2012. Terrestrial Field Dissipation of Sulfentrazone in California Soils. 

FMC Study ID PC-0750. Golden Pacific Laboratories, LLC. Fresno, CA. 

3. Culligan, John. 2008. Sulfentrazone: Terrestrial Field Dissipation in Canada. FMC Study ID 

P-3949. FMC Corporation. Princeton, NJ. 

4. Bertrand, Nicole. 2010. Sulfentrazone Aquatic Field Dissipation in Canada. FMC Study ID 

PC-0505. FMC Corporation. Ewing, NJ. 
14

5. Chen, Audrey. 2014. Greenhouse Aquatic Dissipation of Sulfentrazone and 3-carboxylic acid 

Sulfentrazone. FMC Study ID P-4028R. FMC Corporation. Princeton, NJ. 

EFED has received these studies. If these studies are deemed to provide information to 

meet specific environmental fate guidelines or provide significant supplemental data 

potentially useful in risk assessments, a full Data Evaluation Review will be conducted 

for each study. Following completion of the DERs, EPA will consider the appropriate use 

of these study results in future exposure assessments for sulfentrazone.

FMC Comment 22: Mobility and persistence data are available that suggest sulfentrazone is 

relatively persistent and mobile under the most vulnerable environmental conditions. The spatial 

extent of these conditions are not characterized or reported in this assessment, therefore the 

terms ‘under most’ should be revised to reflect actual field-level information related to mobility 

and persistence potential – or a quantification of the spatial extent of high-mobility conditions 

should be conducted. A generalized statement of expected movement does not take into account 

the impact of meteorological conditions and application timing that varies geographically 

and/or by crop type. Rainfall and evapotranspiration are two fundamental spatially- and 

temporally-dependent hydrologic processes that must be considered when evaluating potential 

movement. The Agency conducted numerical simulations that incorporated standardized crop 

scenarios, not all of which are representative of labeled use patterns that intend to be protective 

of certain geographies and use patterns. The output from these numerical simulations does not 

provide adequate characterization of movement to conclude ‘expected movement’ because that 

output is based on highly-conservative assumptions that may or may not be realistic or 

representative of environmental conditions associated with sulfentrazone use. Expected 

movement, in terms of standard EPA scenarios, is defined by the PRZM/EXAMS model, which 

implements many conservative assumptions.

In general, EPA agrees that these issues are valid and important when more refined risk 

assessments are mandated. EPA continues to work to make improvements in assessment 

methods that will provide more spatially explicit assessments and reduce 

conservativeness when it is defensible to do so. Incorporation of these procedures is, 

however, beyond the scope of the current risk assessment using currently accepted 

exposure assessment methods within EFED.

FMC Comment 23: FMC respectfully disagrees with EPA’s assessment that use of sulfentrazone 

is likely to result in contamination of groundwater and surface water. The studies referenced in 

the statement include groundwater leaching monitoring data from the upper 75th, 85th, and 95th 

percentile most vulnerable combinations of soil and weather conditions in the United States. The 

broad statement that those sites represent anything other than those most vulnerable conditions 

does not appear to consider that those soils actually represent a very small area of the US. 

Therefore, more clarity around the term ‘many soils’ appears warranted for revision in the final 

assessment. Use of the words ‘significant’ and ‘contamination’ are vague and should be revised 

to reflect the results of the screening-level risk assessment that suggest that potential for risk to 

freshwater systems is relatively low, even if further refinement may be prompted for listed 
15

species. There appears to be no clear metric for risk to aquatic systems from groundwater, so 

while sulfentrazone concentrations may be detectable in the most vulnerable groundwater 

conditions, the connection to surficial water systems is not evident. Trace level detection of 

sulfentrazone and SCA does not equal contamination. Therefore, the use of the term 

‘contamination’ in the context of an ecological risk assessment seems misplaced. Furthermore, 

neither sulfentrazone nor SCA metabolite has been reported in any ground water monitoring 

programs, as confirmed in EPA’s preliminary ecological risk assessment. In addition, 

sulfentrazone has low dietary risk based upon consumption of food and drinking water as 

outlined in the preliminary human health risk assessment (2014). Therefore, ‘contamination’ 

does not appear to apply to the human health risk assessment either and FMC suggests revising 

this language to eliminate vagueness. The preliminary risk assessment has not properly 

characterized groundwater exposure vulnerability. Modeling with appropriate Tier I or 

customized Tier II PRZM-GW scenarios (use of appropriate application rates based on texture 

and organic matter) would provide refinement in order to make assumptions concerning the 

potential for groundwater exposure. FMC is submitting three terrestrial field dissipation studies 

to provide additional information on sulfentrazone movement through the soil.

The 4 PGW study results show a potential for leaching in roughly 25% or more of row crop 

production areas of the Midwest and Atlantic coastal plain. EPA did not use the term 

contamination to imply whether or not the levels observed in groundwater should be associated 

with a measurable risk to organisms. The modeling approaches with PRZM-GW are consistent 

with current EPA guidelines. If the registrant disagrees with the way these have been

implemented they should provide a rationale for a change and present it to the Agency and 

request consideration of modifications of this policy.

FMC Comment 24: Within the context of the results from the groundwater vulnerability studies, 

groundwater monitoring data represent the upper 75th, 85th, and 95th percentile of the most 

vulnerable combinations of soil and weather conditions in the United States. In addition, the 

highest, single maximum detection/concentration was found in the >95th percentile site and 

corresponded to an application rate that is higher than that on the federal label. In that study it 

was more important to define the break-through, rather than the absolute, environmentallyrelevant groundwater concentration. Furthermore, there is no apparent relevance of single, 

maximum groundwater monitoring data in how ecological risk is characterized. FMC 

recommends removing groundwater from the ecological assessment unless there is a clear 

connection (quantifiable) to aquatic or terrestrial risk. The broad statement that those sites 

represent a ‘wide variety’ of sites in the US does not to consider that those most vulnerable soils 

actually represent a very small area of the US of highly-specific, vulnerable soil and weather 

combinations. Crop growing areas where sulfentrazone is used must also be considered in 

parallel, as most vulnerable conditions in the US should be limited to where sulfentrazone is 

actually registered for use, further narrowing the variety of soils that are representative of 

conditions in the groundwater vulnerability studies. Revision of the term ‘wide variety of sites’ is 

suggested for publication in the final ecological risk assessment. A conclusive statement should 

consider the results from available groundwater data with respect to vulnerability of soil and 

weather. Furthermore, neither sulfentrazone nor SCA has been reported in any ground water 

monitoring programs, as confirmed in EPA’s risk assessment.
16

The groundwater data are cited only for characterization purposes and have not directly 

been used to evaluate ecological risk. This information is cited in order to acknowledge 

the potential of herbicidal compounds found in groundwater affecting sensitive plants 

when, for example, impacted groundwater is used for irrigation purposes. EFED will 

consider revising the language of the risk assessment but we refer to our response to 

FMC Comment 23 and respectively ask the registrant to provide specific data to support

this request.

FMC Comment 25: Three corrections should be included in Table 11 of the refined assessment. 

The maximum shallow groundwater concentrations for parent sulfentrazone and SCA reported 

in the IN3 (75th site) should be corrected to: 0.09 ppb (1,149 d) and 0.07 ppb (753 d), 

respectively. The values reported by The Agency correspond to 9-ft pore water samples (soil 

water, not groundwater). The third value that should be corrected is the maximum SCA 

concentration at the 85th percentile site, which should be <0.1 ppb (0.1 ppb is the LOQ).

EFED will incorporate this information in a memorandum updating the assessment.

FMC Comment 26: FMC agrees the EECs are believed to be conservative overall for the 

ecological risk assessment. Table 12 should be updated to remove the 40-day post-emergence 

application pattern for all crops limited to pre-emergent uses. Sulfentrazone is typically applied 

as a soil application prior to crop planting or emergence, with typical application dates in 

agricultural settings from 40 days before planting until 3 days after emergence. EPA’s 

assumption that applications occur 40 days after emergence is incorrect for most agricultural 

uses. Foliar agricultural applications are only registered for use on sugarcane as a layby 

treatment, and dormant applications for strawberry, mint and rhubarb. Furthermore, application 

by air and the analysis presented in Table 12 should be updated to reflect that not all crops 

should be modeled using aerial application. Aerial application represents a very small use area 

(<1%) and should be assessed as minor contribution with respect to non-target effects in the risk 

assessment, compared to ground application that is the predominant application method. FMC 

recommends the Agency reconsider their use of a surrogate value for aqueous photolysis in 

turbid water systems in their revised assessment in Table 13. While there may be a conceptual 

difference in degradation potential between turbid and clear water systems, there is no 

quantitative metric to justify the use of a surrogate value for aqueous photolysis. Aqueous 

photolysis is one of the principal dissipation routes in the natural environment. The Agency has 

listed half-life values of 0.5, 0.05 and 0.05 days for aqueous photolysis at pH 5, 7, and 9 and it is 

important to evaluate and incorporate these values into the calculation of RQs. To be 

conservative, The Agency has assumed that all surface waters are at pH = 5, which lends the 

longest half-life value to the exposure modeling (0.5 days); however, in the calculation of RQs 

has used a surrogate half-life value of 98 days which was estimated from the soil photolysis 

guideline study. Selection of a surrogate value for an environmental fate parameter when a 

measured, acceptable value is available does not represent the environmental behavior and 

FMC suggests revising the aqueous photolysis input value. The justification The Agency uses to 

substitute surrogate data for measured data does not appear to be based on scientific data or 

experimental evidence (no references from the open literature were provided to support this 

substitution). In addition, if turbid water systems are assumed, as depicted by the preliminary 

assessment, the uncertainty factor associated with enhanced photo-toxicity should be 
17

reconsidered. If a distinction is made that two types of systems that are at risk (turbid and clear 

water), more context is needed to understand and characterize the implications and 

corresponding potential risk of each type of system in terms of: exposure spatial extent, 

frequency, duration, and relevant species effect endpoints. In addition to the selection of inputs 

to the aquatic exposure modeling, it is important to consider all of the conservative elements of 

the exposure estimation technique to add context to the values reported in the preliminary 

ecological assessment. Some important, conservative assumptions in the PRZM/EXAMS aquatic 

exposure estimation procedure include: 

• EPA’s determination of 1 in 10-year annual maximum concentrations as 90th percentile 

concentrations is inaccurate. Before estimating a “90th percentile”, the PRZM/EXAMS model 

first determines the highest daily pesticide concentration (or longer-term concentrations for nonacute exposures) for each year in a 30-year simulation. The model then calculates the 90th 

percentile from these 30 values. For a 30 year period, EPA’s “90th percentile” is actually a 

concentration that would only be exceeded on three days in 30-years (or a 1-in-10 year event). 

On a daily basis, this estimate would actually be a 99.97th percentile. In other words, the 

concentration estimated by EPA would be less for 99.97 percent of days in the pond, assuming 

that the other components of the modeling were accurate and unbiased (which they are not). 

• To derive valid probabilistic exposure estimates (e.g., a 90th percentile), all key input variables 

must be modeled as distributions that reflect the range of plausible values for each variable 

(particularly soils and topography). The only probabilistic variable in standard scenario 

PRZM/EXAMS modeling is the meteorology (most importantly, rainfall), and even the 

meteorology reflects only temporal variability, not spatial variability for a given crop. 

Conservative and sometimes implausible assumptions are made for almost all other key 

variables (e.g., 90th percentile estimates for rates of dissipation in the environment, high slope, 

zero interception by vegetative barriers). The compounding effect of these multiple, conservative 

assumptions is an implausibly high exposure estimate. 

• There is limited consideration of hydrology. The farm pond is assumed to be static, meaning 

that there are no inflows or outflows of water that would remove or dilute pesticide 

concentrations. In streams and rivers, any pesticide runoff would disperse downstream and be 

diluted. In flowing water bodies, pesticides would only be expected to occur during short pulses 

rather than over extended durations. In addition, the runoff water or sediment assumed to be 

carrying the pesticide to the water body has an associated volume that is not considered as an 

addition to the standard pond. In some scenarios used by EPA, the amount of soil assumed to 

enter the farm pond would be enough to fill it in well before the end of the 30-year simulation 

period. Ignoring the addition of sediment to the pond and the dynamics of suspended sediment 

within the water body leaves an important pesticide transport and dissipation process 

unaccounted for. 

• The wind is assumed to always be blowing in the direction from the application site to the 

pond, an unrealistic assumption given that wind direction is variable. From the standpoint of the 

probability of exposure due to spray drift, this assumption is overly conservative. 

• The Tier II results represent a situation with a farm pond immediately adjacent to an 

agricultural field without any distance or buffer between the field and the water body. In many 

geographic regions, this hypothetical scenario is unlikely to occur, with water bodies more often 

separated from the edge of a field by some distance. 

• The current PRZM3.12.2 crop standard scenarios do not include plant uptake as a potential 

source of pesticide removal from the treated field (EPA, 2009). 
18

• For foliar applications, the current EPA PRZM3.12.2 crop standard scenarios set foliar washoff from plant leaves to 50%, which for many products is quite high (EPA, 2009). 

• The current EPA PRZM3.12.2 crop scenarios ignore the fact that farmers are unlikely to apply 

pesticide during rainy conditions. 

• EPA uses an expert judgment procedure for identifying the soil series and geographical 

conditions that are supposed to represent 90th percentile worst-case scenarios in the Tier II 

exposure concentration estimation process. It is not possible to determine whether these 

scenarios actually represent a 90th percentile vulnerability. This expert judgment procedure is 

used in lieu of a quantitative process that would examine the entire set of available soil and 

geographical data and then rank vulnerability based upon predicted exposure. 

• The EPA standard scenario simulations ignore the likelihood that farmers are unlikely to apply 

pesticide during rainy conditions. Rainy conditions increase the quantity of off-field pesticide 

residues in run-off because the other loss functions (e.g., degradation in soil) have not yet had a 

chance to take place before the pesticide runs off. 

• The EPA standard scenarios have not been calibrated with hydrology-predicted results and 

have not been compared to actual “real-world” runoff and eroded sediment results. Rather, soil 

selection and input parameters are based upon recommendations from local crop experts. Thus, 

there is no way to assess whether off-field runoff and eroded sediment is over-estimated or 

under-estimated. Because off-field runoff and eroded sediment are primary mechanisms for offfield movement of pesticides (in addition to off-field drift), inaccurate estimates of runoff and offfield erosion will result in inaccurate estimates of off-field pesticide mass. 

• The assumption of a percent cropped area (PCA) of 100% in the standard farm pond scenario 

is overly conservative. A PCA of 100% is very rare, as has been shown in studies that have 

examined PCAs for small ponds in detail (Winchell et al., 2014). 

• The PRZM/EXAMS standard scenario modeling approach assumes that 100% of the standard 

pond watershed is treated with pesticide on the same date. In actuality, the area draining to or 

contributing spray drift to a receiving water body may be influenced by multiple fields treated on 

different days. Situations where applications occur over multiple days will result in lower 

exposure values in a receiving water body, making the standard EPA assumptions conservative. 

EFED conducted both application timing runs to see what effect the timing of the year 

had on exposure assessment. The change in application dates only modestly changes the 

predicted exposure level (for example, the highest peak EECs were 17.9 and 14.4 ppb for 

applications nominally stated to be 40 days after and 1 day before emergence, 

respectively. In fact though, in years in which planting was significantly the 40 day POE 

applications could actually be right around the time of emergence. The registrant’s 

request to eliminate the values for 40 days post planting for certain crops with only 

preemergence applications would generally be sensible. However, the standard scenarios 

used by EFED do not currently adjust the crop planting and maturity dates on an annual 

basis according to the changing weather patterns each year, including the fact that when 

soil moisture levels are high applications are less likely to occur (although in some cases, 

as the registrant notes, aerial applications will be made during such periods). Therefore 

EFED believes that the requested modifications and refinements should only occur when 

appropriate methods are approved to seamlessly vary agronomic practices and 

sulfentrazone applications according to environmental conditions (weather variations) on 

annual basis at each site that is modeled.
19

FMC Comment 27: Sulfentrazone is predominantly used as a soil-applied herbicide prior to 

crop emergence or planting. In pre-emergent residue studies, parent sulfentrazone has not been 

measured at detectable levels in plants and is not well represented by the assumptions used in 

the EPA T-REX model. A revision of expected plant residues should be conducted as most 

registered crops are not directly sprayed and residues on avian feed items due to spray drive 

should be considerably less than those derived from standard methods in the T-REX model. 

Post-emergent residue data may better represent expected residue in food items in the 

environment – especially chronic residues, as some PHIs may be relatively long to estimate 

maximum expected residue. Post-emergent applications are limited to only a few crops and 

parent residue values resulting from foliar application to mint (MRID 45393503), strawberry 

(MRID 47311408), rhubarb (MRID 48514802), and sugarcane (MRID 45077904, 45077905) 

are not detectable to the limit of detection or the limit of quantitation. This foliar residue data is 

on file with the Agency and could also provide a more reasonable residue values for the T-REX 

model. The crop residue data suggests lower potential maximum and chronic residue, compared 

to default T-REX assumptions. 

The screening-level approach of using maximum potential residue (acute) to describe chronic 

exposure does not consider best-available data and is overly-conservative for describing risk. 

Using acute exposure with a chronic effect endpoint is further compounded by inherent, 

conservative, simplistic assumptions by the consumption and exposure duration defined in the TREX model. The T-REX model calculates dietary exposure for any given bird species that 

consumes 100% of its diet from each food category (short grass, long grass, etc.) and that diet 

always contains the maximum chemical residue. The model further calculates dietary exposure 

based on a consumption rate that is not likely (e.g. a 20-g bird consumes 114% of its body 

weight daily). Finally, the model assumes that the maximum residue in feed items is present over 

an infinite period of time, essentially mismatching an acute exposure with a chronic effect. 

FMC understands that the standardization of avian risk is a useful tool to indicate potential risk, 

but further revision to the draft assessment should be done to address the chemical-specific 

expected exposure estimate and conservative consumption assumptions that apply to 

sulfentrazone. Birds have a varied diet that varies temporally and spatially and should be 

considered with the co-occurrence of chemical application areas (access to feed items that 

contain potential residues). For example, probabilistic techniques are available that can be 

easily employed to address crop- and chemical-specific risk evaluation (eg ECOFRAM, 1999, 

Moore et al., 2009; Brain et al., 2014, Moore et al., 2014).

It is difficult to preclude risk from vegetation or other food item residues on the field at 

the time of application. Sulfentrazone is used as a no-till herbicide in the spring and fall 

prior to plant or emergence. Residual weeds on the field will be exposed to sulfentrazone 

applications. While birds and mammals may not be exposed to sulfentrazone on the crop, 

they may be exposed through foraging on food items in the field such as weeds and 

insects. In the absence of conclusive proof that there are not sulfentrazone residues 
20

associated with dietary items left on the field, EPA will not revise EECs generated from 

the standard TREX model.

FMC Comment 28: There are two avian reproduction studies available for sulfentrazone and 

they are with bobwhite quail (MRID 43355901) and mallard duck (MRID 443355902). Taking 

both avian reproduction studies into consideration, a NOAEC of 100 ppm should be considered 

for risk assessment and both of the studies should be considered as core studies. 

In both studies the treatment groups were 0, 1, 10 and 100 ppm. Based on the initial evaluation 

of the study director for bobwhite quail, the LOAEC could not be determined, but the NOAEC 

was determined to be 100 ppm. However, per agency’s evaluation the LOAEC was concluded to 

be 100 ppm and, the NOAEC 10 ppm. This was based on reductions in 14-day old survivor 

weight with an 8% reduction at the LOAEC relative to the control. However, we believe a 

reduction in weight less than 10% in absence of any other significant physiological effects 

should not be considered as an adverse effect. Therefore, a NOAEC of 100 ppm should be used 

for risk assessment. 

In order to respond to the comments adequately we went back and more carefully 

considered the study. The previous assessment classified the study as supplemental 

because the test concentrations were too low to support the proposed uses on turf and 

lawn at that time (1995). Based on this criteria, we deemed the study acceptable for the 

current application rates and use patterns that fell within the range of the study. We feel 

that there is not enough evidence to discount the reduction of in body weight of 8% and 

consider this a significant effect. Based on the previous assessment using this endpoint is 

sufficient for the risk assessment and we cannot move away from it without further 

evidence. Our analysis revealed, however, that the high control mortality during the 

study reduced the statistical power of the study. Despite this lack of statistical power, the 

study was still able to detect the 8% decrease in female body weight. Statistical analysis 

was not able to detect differences in eggshell difference between the control and the 

highest treatment group even though there was a statistical difference between the lowest 

treatment group and highest treatment group. There also appears to be a reduction in the 

number of eggs between control group and the highest treatment group (100 ppm) 

although this difference was not statistically detected, likely due to the high control 

mortality. Current EFED guidance states that control mortality more than 10% in an 

avian reproduction study is reason to reject the study. The control mortality in this study 

was 12.5%. If the registrant finds that the current endpoint is unacceptable, the Agency 

could invalidate the study and require a new bobwhite reproduction study to confirm or 

refute the endpoints that are used.

For mallard duck (MRID 443355902), the NOAEC and LOAEC were determined to be 100 ppm 

and >100 ppm, respectively. In this study none of the measurement endpoints were adversely 

affected. However, the Agency classified this study as supplemental because no LOAEC was 

established. Potentially, the NOAEC could be higher than 100 ppm. However, conservatively 

100 ppm could be used in risk assessment as NOAEC and not the LOAEC. Therefore, the Agency 

should reclassify this study as a core not a supplemental study. 
21

EFED guidance states that studies with non-definitive endpoints be classified as 

supplemental but may be used in risk assessments. 

In its recent review and guidance document entitled: “Assessing Risks to Endangered and 

Threatened Species from Pesticides”, the National Academy of Sciences (NRC, 2013) outlines 

the use of best available data and quality of data to be used in environmental risk assessments. 

FMC is in agreement with the recommendation. 

In addition, several methods have recently been proposed to evaluate the relevance and quality 

of ecotoxicity studies. EPA should consider these methods when evaluating the relevance and 

quality of studies for risk assessment (Breton et al., 2009; Breton, 2014; Hall et al., 2010, 2012; 

Van Der Kraak et al., 2013; Solomon 2014). 

Breton, R. 2014. Data relevance and Data Quality for Ecological Risk Assessment. Presented at 

ACS/IUPAC San Francisco, August 2014. Intrinsik Environmental Sciences Inc. 

Breton, R. G. Gilron, R. Thompson, S. Rodney, and S. Teed. 2009. A New Quality Assurance 

System for Evaluation of Ecotoxicity Studies Submitted Under the New Substances Notification 

Regulations in Canada. Integrated Environmental Assessment and Management 5(1):127-137

EFED appreciates the input and additional methods that might be used.

FMC Comment 29: Exposure to marine/estuarine systems is expected to be diluted well beyond 

the standard EPA ‘pond’ that is simulated and reported in Table 23. The standard EPA pond is 1 

ha in surface area and 2 meters deep and does not represent marine/estuarine systems, but is 

considered protective of them. While no existing correlation in dilution and volume differences 

between the standard EPA pond and an actual marine/estuarine system has yet been available, 

without a policy around this dilution from The Agency, only a qualitative assessment can be 

assumed. RQs are deterministic and quantitative in nature and do not lend themselves to the 

concept of uncertainty in dilution or any other environmental metric. Therefore, FMC suggests 

that the RQ generated for marine/estuarine species, which is not derived from measured data, be 

revised to be reported in a more qualitative format that reflects exposure uncertainty due to the 

considerable dilution potential difference between the standard EPA pond and marine/estuarine 

systems. The EPA standard peppers scenario is not representative of all existing and proposed 

use of sulfentrazone. Tables 23 and 24 contain several errors when estimating risk such as: 

1. Sulfentrazone is not registered at the state level in Florida for agricultural uses. 

2. Assessment with aerial application is not representative and accounts for less than 1% of all 

applications in the United States on all registered crops. 

3. Environmental fate inputs are screening-level, according to guidance except aqueous

photolysis. 

An updated Table 23 would report the standard EPA PA, NC, and OR apple scenarios, ground 

application, and appropriate aqueous photolysis rate (0.05 days pH=7; all other environmental 

fate matching EPA’s screening-level input selections). FMC generated chronic exposure values 

using the EPA Surface Water Calculator (SWCC v 1.103 and corresponding .SCN scenario 

files), assuming the EPA Standard Pond and maximum application rate (0.375 lb/ac). Resulting 
22

chronic exposure values (21-day) for the standard EPA PA, NC, and OR apple scenarios were 

0.709, 0.68, and 0.621 ppb, respectively. Using the NOAEC of 0.003 ppm (3 ppb), updated RQ 

values for standard EPA PA, NC, and OR Apple scenarios can be calculated as: 0.24, 0.22, 0.21, 

respectively. Even though dilution would be very different for marine/estuarine systems (more 

dilute, lower exposure estimate), these RQs are below the Agency’s level of concern.

EFED will provide explicit representation of the lack of sulfentrazone registration in the 

entire state of Florida in a memorandum updating the assessment. We can note that the 

registrant believes that aerial applications represent less than 1% of all uses. EFED notes 

that, because, by all other transformation pathways conversion is much slower, the 

overall modeling results can be highly sensitive to the use of the 0.5 day aqueous 

photolysis have life. The available ecological studies (e.g., fish toxicity studies in waters 

subjected to sunlight or simulated sunlight) fail to confirm that photolysis is as relevant a 

transformation pathway in natural waters as the use of this half-life implies.

FMC Comment 30: Tables 30 and 31 report the output from the TerrPlant model and 

corresponding screening-level risk results for non-target plants but does not represent a 

characterization of the risk. The TerrPlant model contains the following assumptions and 

limitations that could be refined beyond the screening-level (Trask et al., 2010a,b): 

• The semi-aquatic non-target area is assumed to be one-tenth the size of the target application 

area. This assumption is based on observations of aquatic areas in Georgia. However, the size 

ratio is likely to be highly variable across agricultural areas in North America. 

• The spray drift component of TerrPlant only considers the application method and does not 

include additional factors such as wind speed, droplet size and height of pesticide release that 

may affect the quantity of pesticide moving off the field as spray drift. 

• TerrPlant assumes the maximum application rate which may not be representative (or 

allowable in specific environmental conditions according to the federal label) 

• The model conservatively assumes that runoff occurs at the time of application, an unlikely 

event given that farmers generally avoid applying pesticides on rainy days. 

• Both runoff and spray drift are assumed to be distributed uniformly throughout the non-target 

area. In reality, there is typically a decrease in the quantities of runoff and spray drift reaching 

areas of increasing distance from the application area. 

• TerrPlant assumes that runoff and spray drift reach the non-target area at the same time, and 

that non-target plants exposed to the pesticide residues are in the sensitive, early emergent life 

stages. Both of these assumptions are conservative. 

• Estimated Exposure Rates are calculated using only the solubility of a pesticide. The 

calculation of EERs does not consider other environmental fate parameters, such as the water 

and soil half-lives and Kd of the pesticide, which affect the amount of the pesticide that binds to 

soil and sediment and pesticide movement within these matrices. These parameters may 

considerably affect pesticide concentrations in runoff and spray drift in the non-treated area to 

which the terrestrial plants are exposed. 

• Calculation of the RQ for non-target plants exposed to runoff only considers seedling 

emergence and does not consider other life stages, which may be more or less sensitive. 

• TerrPlant uses effect metrics from tier II terrestrial plant studies to assess risk. It assumes that 

the effects observed in these studies of single species in pots would be equivalent for other 
23

species in the wild. Currently, there are no field data to evaluate the exposure estimates 

generated by TerrPlant. Thus, there is uncertainty concerning model performance in the real 

world. 

The binary trigger of RQ>LOC is a useful mechanism to determine whether or not a refined risk 

assessment should be conducted and for which exposure scenarios. For those exposure 

scenarios, refined techniques should be used to characterize the magnitude, direction, and 

uncertainty associated with potential for risk. Refined, community-level effects measures, which 

are more suitable for use in discerning risk to non-target plants off-field, should be developed 

and compared to the results of a refined exposure assessment. FMC recommends the use of

refined methods for exposure and community-level effects. For a recent review of refined 

methods, see Brain et al. (2014)

This is a screening level assessment conducted with approved models and methods. 

While the EPA evaluates alternative models such as AgDISP, they are not suitable for 

risk assessment purposes at this time. The EPA appreciates the points made in this 

comment and will consider these points in future assessments.

FMC Comment 31: The combination of conservative drift/runoff assumptions along with a 

broad label interpretation and worst case endpoint selection lead to the apparent need for large 

buffers at the screening level. Exclusive use of the AgDRIFT model should be avoided because of 

the known limitations and availability of more current data-sets (e.g. RegDISP http://www.stoneenv.com/agchem/agres.php#agdownload and recent research on AgDISP – primarily supported 

by the USDA). Beyond spray drift alone, a principal reason that terrestrial and semi-aquatic 

plant risk scenarios exceeded 1000-ft is because the runoff contribution is the “Tier 0” value of 

5%. The semi-aquatic scenario assumes that runoff contribution should be multiplied by a factor 

of 10, assuming that 10x the upland area contributes to runoff in a unit area of semi-aquatic 

habitat. Therefore, runoff is 10x more important than drift alone for the semi-aquatic scenario, 

yet no refinement of runoff exposure has been conducted by The Agency. This is an oversimplification that could be revised using a model such as PRZM to estimate edge-of-field values 

for acute and chronic exposure to plants. For example, the 99.7th upper-bound percentile 

exposure of daily values within a 30-year edge-of-field PRZM simulation, using the standard 

EPA soybean PRZM scenario, results in runoff fraction of 0.0024 (0.24% of the total 0.375 lb 

ai/A), compared to the 5% assumed by the EPA TerrPlant model. The screening-level 

assessment, summarized in Tables 32-35, do not characterize the spatial and temporal cooccurrence of plant species and use pattern by crop or geography. The federal label describes in 

detail the application rates corresponding to different soil conditions. While many uses on the 

label are up to 0.375 lb ai/A, the label carefully limits this rate by soil type and soil organic 

matter composition, protecting vulnerable areas. So, while some areas/crop geographies do 

allow the maximum application rate, the screening-level assessment conducted by the Agency 

does not characterize the extent to which these conditions occur and the corresponding cooccurrence of adjacent semi-aquatic and dry habitat. FMC suggests that this first effort by the 

Agency represents a screening-level effort that indicates the need for further, careful 

consideration of drift and runoff refinements and actual label practices before mitigation of 

spray drift is addressed. The most sensitive plant species endpoint was selected for establishing 

buffers (monocot and dicot). In cases where sensitive surrogate species endpoints indicate 

potential risk from off-target movement, it is important to relate those endpoints to the biological 
24

equivalent in the environment and its corresponding ecosystem function. One way to do this is by 

using a species sensitivity distribution to represent the ecosystem, instead of using the most 

sensitive single species. The protection goal of the assessment is at the plant community level, 

not the single species level. For example, if cucumber is the most sensitive dicot surrogate 

species then the biological equivalent of the cucumber in nature should be identified through 

expert opinion and open literature resources (e.g. USDA plant database 

http://plants.usda.gov/java/). Then, context for the ecosystem function of the natural equivalent 

of the cucumber would be more clear and relevant to address potential mitigation 

As sulfentrazone is predominantly used as a pre-emergent herbicide, efficacy depends on soil 

coverage rather than leaf contact. To maximize soil coverage, spray nozzles that provide 

medium/coarse droplet size are desirable. It is impractical and extremely unlikely for a grower 

to use a fine spray droplet size if the product is to be used in compliance with the label and 

current application practices. For ground applications, FMC recommends that spray drift data 

used in the assessment be derived from medium/coarse datasets under wind-speed conditions 

specified on the federal label. The draft ecological assessment should be revised to include more 

appropriate exposure estimates of runoff contribution within dry and semi-aquatic habitats. In 

parallel, best-available spray drift data should be included to adequately address potential risk 

from the ‘spray drift’, ‘dry’, and ‘semi-aquatic’ TerrPlant scenarios. The RegDISP model can be 

used to effectively identify data corresponding to the relevant application patterns needed for the 

risk assessment. FMC advocates for the inclusion of best-available spray drift data to evaluate 

potential risk to non-target plants.

The EPA periodically evaluates and tests new models (and the data used to inform such 

models) to be used in the risk assessment process to better refine the assessment. While 

the EPA appreciates the utility of alternative models and the additional data that may be 

available to support the models, the models and the methods for using them in this 

assessment represent the current methods approved for risk assessment purposes.

As part of the addendum, EPA evaluated spray drift using larger droplet sizes. However, 

since the size distribution of spray droplets delivered may be broad, the EPA used a range 

of droplet sizes to characterize risk. In general, the EPA must include the most 

conservative scenario in the ecological risk assessment and be inclusive of all 

sulfentrazone product labels.

FMC Comment 32: The lack of ecological incident reports over the last 9 years suggests that 

spray drift and off-site management associated with more current grower techniques and 

practices is an important consideration in the risk assessment. Furthermore, there are no 

reportable FIFRA 6(a)2 documentation for sulfentrazone causing adverse effects on crops due to 

spray drift, runoff or carryover harming neighboring fields and/or property. This lack of incident 

reports suggests that sulfentrazone is not likely to cause adverse effects to non-target plants. The 

conclusion of potential risk to non-target plants is not consistent with the lack of incidents over a 

significant period of time corresponding to wide-scale use and should be revised. 

FMC notes that Table D1 on page 134 contains errors or requires additional consideration by 

the Agency: 
25

1. Reported formulations (i.e granular, emulsifiable concentrate, water soluble packet) are not 

registered for agricultural use and indicate some degree of uncertainty in the reporting. 

2. The relevance of the ecological incidents defined with the “Certainty” values of “Possible” 

and “Probable” should be carefully considered when assessing risk of sulfentrazone. 

The lack of ecological incident reports does not necessarily indicate that incidents did not 

occur. The risk assessment considers both the risk incidents as well as the risk estimation 

and characterization when characterizing risk in an assessment. EPA will review Table 

D1 on page 134 of the preliminary risk assessment to determine if there are any errors. If 

corrections are required they will be incorporated into the update memorandum.

FMC Comment 33: FMC agrees that the screening-level dietary exposure using the T-REX 

model for small birds or small mammals is conservative and overestimates potential risks. The 

risk assessment should be revised to correct for the assumptions/inputs from the T-REX model: 

1. Any given bird species consumes 100% of its diet from each food category (short grass, long 

grass, etc.) 

2. Avian diet always contains the maximum chemical residue 

3. Dietary exposure calculated on a consumption rate that is unlikely (e.g. a 20-g bird consumes 

114% of its body weight daily) 

4. Maximum residue in feed items is present over an infinite period of time, not providing 

correlation from acute exposure to chronic effects. 

TREX is the standard model for on-field risk in preliminary risk assessments. While the 

EPA appreciates the comments, the TREX model is not being revised at this time. If and 

when new data are submitted and validated by the Agency, modeling procedures can be 

appropriately revised.