OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

Date: November 13, 2015

 PC Code: 129092

 DP Barcodes: D427655 

 

MEMORANDUM 

SUBJECT: Review of Comments on Addendum to the Ecological Risk Assessment for 

Fenoxaprop-p-ethyl 

TO: Miguel Zavala, Chemical Review Manager 

 Tracy Perry, Team Leader 

Kelly Sherman, Branch Chief 

Risk Management and Implementation Branch III 

Pesticide Re-evaluation Division (7505P) 

FROM: Thomas Steeger, Ph.D., Senior Science Advisor 

 Chuck Peck, Environmental Fate Scientist 

Environmental Risk Branch IV 

 Environmental Fate and Effects Division (7507P) 

 Office of Pesticide Programs 

THROUGH: Jean Holmes, D.V.M., Branch Chief 

 Katrina White, Ph.D., Risk Assessment Process Leader 

Environmental Risk Branch IV 

 Environmental Fate and Effects Division (7507P) 

 Office of Pesticide Programs 

The Environmental Fate and Effects Division (EFED) has reviewed comments from the technical 

registrant, Bayer CropScience, on the Addendum to the Ecological Risk Assessment written in 

support of the proposed Interim Registration Review decision for fenoxaprop-p-ethyl (FPE; PC 

Code 129092). Below is a brief summary of each comment followed by EFED’s response. 

 The registrant asserts that contrary to what is stated in the Addendum, Bayer did not 

recommend the use of root length or weight as an appropriate measure for effects in nontarget plant testing given the high variability of measures of root and/or radicle 

length/weight in such studies. 

EFED concurs with the registrant’s assertion that they did not recommend the use of root length 

or weight as an appropriate measure of effects in non-target terrestrial plant testing. Rather, the 
2 

registrant recommended the use of shoot length and weight, which is consistent with the 

measurement endpoints identified in the Office of Chemical Safety and Pollution Prevention 

Guideline 850.41001

 for examining the effects of pesticides on seedling emergence and seedling 

growth. The guideline specifies that shoot length and shoot biomass (dry weight) of surviving 

seedlings are measured for determining a no-observed-adverse effect concentration (NOAEC) and 

a lowest-observed-adverse effect concentration (LOAEC). 

 Bayer agreed with EFED’s use of a chronic dietary-based no-observed-adverse effect level 

(NOAEL) of 9 mg/kg/day based on the rat 2-generation study and concurred with the 

Agency’s characterization that the use of this endpoint is conservative and would likely 

overestimate any potential risk. 

EFED appreciates Bayer’s recognition that the chronic mammalian NOAEL is appropriate for use 

in risk assessment. 

 The registrant asserts that the minimum reapplication intervals (MRIs) of 159 days or 

longer used to estimate terrestrial risk using the T-REX were inappropriate to represent a 

chronic exposure scenario. According to the registrant, mammals exposed for 150+ days 

following initial application are in different life stages and treated crops have been 

harvested leading to turnover of plant material in-field. Bayer further noted though that 

specific to FPE, the foliar dissipation half-life (5.6 days) used in T-RED coupled with the 

long MRIs result in minimum residues by the time of the second application and that when 

the MRI is placed into context and when coupled with the conservative NOAEL of 9 

mg/kg/day, chronic risk is unlikely. 

As summarized in Table A1 of the Addendum, MRIs ranged from 14 days to a maximum of 285 

days. The long MRIs are intended to account for labels where the reapplication interval is either 

not specified or is vague. The long MRIs are also designed to account for applications that may 

occur to a field after the growing season, as allowed for on the label. The T-REX model (v 1.5.2) 

is intended as a screen and the uses modeled indicate that even with an MRI of 14 days, risk 

quotient (RQ) values exceed the level of concern (LOC) for chronic risk to mammals. The 

registrant is correct in noting that with the foliar dissipation half-life of 5.6 days used for modeling 

FPE in T-REX, residues by 150+ days would likely be low; however, based on multiple 

applications and the extended MRI, RQ values exceed chronic risk LOCs for mammals. The 

footnote to Table A1 indicates that when multiple reapplication intervals are used, the second 

interval represents an application that occurs outside the growing season, but still represents the 

potential for exposure. Therefore, while the registrant is correct in noting that treated crops would 

have likely been harvested leading to turnover of plant material in-field, the labels do not specify 

this practice and residues may remain on in-field plant materials which represent potential 

exposure route for mammals, particularly small mammals feeding on short grasses. 

 Bayer expressed appreciation for EPA’s willingness to review the non-target plant studies. 

However, Bayer disagreed with the non-definitive NOAEC (<0.081 lbs ai/A) identified for 

 

1

 USEPA. 2012. Ecological Effects Test Guidelines OCSPP 850.4100: Seedling Emergence and Seedling Growth. Office of Chemical Safety and 

Pollution Prevention. (7101). EPA 712-C-012. January 2012. 
3 

tomato based on shoot dry weight in a seedling emergence study (MRID 473334-232

) since 

the determination was based on empirical rather than statistical significance. 

The Agency’s determination regarding the biological relevancy of the magnitude of effect reported 

for tomatoes in the seedling emergence study was not based alone on the low variance surrounding 

the measurements in the treatment and control, but on the magnitude of effect, i.e., 16.9% decrease 

in biomass relative to controls. While the study was at Tier II for corn, other plants were tested 

using a limit treatment of 0.18 mg ai/kg. When the magnitude of an effect is uncertain with respect 

to its biological versus statistical significant, Agency reviewers would typically look at higher 

treatment levels to determine whether the effect appeared to be concentration dependent. 

However, in a limit test, no additional treatment levels available to put the single measurement 

endpoint into context; therefore, the non-definitive endpoint (<0.081 lbs ai/A) is still considered 

best available information. 

 With respect to a Tier II vegetative vigor study (MRID 412769-073

), Bayer agreed with 

the Agency’s inhibitory response level for 25% of the species tested (IR25) values for corn, 

oat and ryegrass; however, they disagreed with the NOAEC reported for each of these three 

species. According to Bayer, the endpoint used to establish the NOAEC appear to be 

generated from nonstandard data calculations. 

In Addendum Table A2, the NOAEC for corn and ryegrass are reported as <0.00480 and <0.0480 

lbs ai/A, respectively, while the value for oats is reported as non-applicable (NA). These results 

are consistent with what is reported in the data evaluation record (DER) except for corn where the 

DER reports a NOAEC of <0.0006 lbs ai/A based on plant height. Based on the limited information 

provided in the DER and after reviewing the actual study report, the measurement endpoint, i.e., 

plant height, is consistent with current guidelines. While the DER also presents the results of 

visual phytotoxicity ratings, these ratings and there statistical significance were not used to set the 

NOAEC. 

 With respect to a vegetative vigor study (MRID 473334-244

), Bayer disagreed with the 

NOAEC value reported in the Addendum for lettuce. According to the registrant, the 

percent inhibition of dry weight for lettuce was not found statistically significant up to the 

highest level tested (0.081 lbs ai/A). 

In Addendum Table A2, the NOAEC for lettuce from the Tier II vegetative vigor study is reported 

as 0.041 lbs ai/A. The registrant is correct in noting that according to the DER, the NOAEC for 

lettuce is 0.081 lbs ai/A; however, the NOAEC value for carrot reported in Addendum Table A2 

is 0.081 lbs ai/A, while that reported in the DER is 0.041 lbs ai/A based on reductions in root 

 

2

 Roshon, Roxana. 2001. Ecotoxicological Evaluation of Fenoxaprop-P-Ethyl + Mefenpyr-Diethyl Emulsifiable Concentrate (120 + 33 g/L) (Puma®

120 Super), Terrestrial Plant Seedling Emergence. Unpublished study performed by ESG International Inc., Ecotoxicity Laboratory, Specialty 

Chemicals Division, Guelph Ontario, Canada. Laboratory report number B003326. Study sponsored by Aventis CropScience Canada Co., Regina, 

Saskatchewan, Canada. Study completed May 31, 2001. (MRID 473334-23) 3

 Chetram, R.S. 1989. Tier II. Vegetative Vigor. Nontarget Phytotoxicity Study. HOE-04630 Study No. LR89-14A. Performed by PanAgricultural Labs., Inc., Madera, CA (MRID 412769-07). 

4

 Roshon, R. 2001. Ecotoxicological Evaluation of Fenoxaprop-P-Ethyl + Mefenpyr-Diethyl Emulsifiable Concentrate (120 + 33 g/l) (Puma® 120 

Super), Terrestrial Plant Vegetative Vigor. Unpublished study performed by ESG International Inc., Ecotoxicity Laboratory, Specialty Chemicals 

Division, Guelph Ontario, Canada. Laboratory report number B003327. Study sponsored by Aventis CropScience Canada Co., Regina, 

Saskatchewan, Canada. Study completed May 31, 200I. (MRID 473334-24) 
4 

length. Therefore, while the registrant is correct with respect to lettuce, the most sensitive NOAEC 

for dicots of 0.041 lbs ai/A used for risk assessment remains the same. 

EFED appreciates the comments provided by Bayer CropScience regarding the Addendum to the 

Ecological Risk Assessment written in support of the proposed Interim Registration Review 

decision for FPE. However, the comments do not affect the risk assessment conclusions.