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OFFICE OF CHEMICAL SAFETY 

ANDPOLLUTION PREVENTION

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

PC Code: 035201

DP Barcodes: 424259, 426211, and 427439

MEMORANDUM

DATE: September 10, 2015

SUBJECT: Response to Comments Submitted to the Dicrotophos Registration Review 

Docket (Docket ID: EPA-HQ-OPP-2008-0440) and Addendum to the 

Dicrotophos Preliminary Ecological Risk Assessment

TO: Khue Nguyen, Chemical Review Manager

Neil Anderson, Branch Chief

Risk Management and Implementation Branch I

Pesticide Re-Evaluation Division (7508P)

FROM: Nathan Miller, Biologist

Andrew Shelby, Physical scientist

Environmental Risk Branch VI

Environmental Fate and Effects Division (7507P)

Through: Mark Corbin, Branch Chief

Monica Wait, Risk Assessment Process Leader

Environmental Risk Branch VI

Environmental Fate and Effects Division (7507P)

In response to the “Transmittal of the Preliminary Environmental Fate and Ecological Risk 

Assessment for the Registration of Dicrotophos” (Document ID EPA-HQ-OPP-2008-0440-0022

in www.regulations.gov, DP 393746, 7/10/2014), AMVAC Chemical Company (“AMVAC”)

provided comments during the public comment period. The purpose of this memorandum is to 

address those comments and respond to technical/science-related questions and comments as 

they pertain to the preliminary risk assessment document. 

Additionally, the Environmental Fate and Effects Division (EFED) explored the impact of 

typical application rates — as described in a memorandum from the Biological and Economic 

Analysis Division (Mallampalli and Becker, 2014) — on risk conclusions. Assuming typical 

application rates and retreatment intervals, estimated environmental concentrations (EECs) are 

reduced by approximately 50%; however, risk quotients (RQs) still exceed the level of concern 

(LOC) for all taxa identified as having RQs exceeding the LOC in the preliminary risk 

assessment, albeit at a lesser magnitude (see Appendix A).
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AMVAC Comment: Section 3.2.1. Selection of Screening-level Effects Metrics, Birds and 

Mammals; PDF Pages 55 & 56- Avian acute oral study selection: A closer review of the 

selected acute effect metric for domestic goose used in the assessment suggests that there are 

many deficiencies in the study (Doyle and Elsea (1963)) [MRID 00013439]... As a result, this 

study is insufficient in terms of data reporting in accordance with OPP's evaluation guidelines 

(EPA, 2011a)... Further, a more recent literature study on starlings provides a better basis for 

calculating dose-based dietary risk (Grue and Shipley, 1984).

EFED Response: EFED concurs with AMVAC that MRID 00013439 is insufficient in 

terms of data reporting to be used quantitatively in risk assessment. A table of the avian 

acute oral toxicity studies available for dicrotophos can be found on page 15 (PDF page 17) 

of the October 28, 1998 EFED RED Chapter for Dicrotophos (Document ID EPA-HQ-OPP2008-0440-0009). The 1984 Grue and Shipley study referenced in the AMVAC comment is 

cited on page 16 (PDF page 18) in Table 4 of the EFED RED chapter. California quail were 

the most sensitive avian species in acute oral toxicity studies and the LD50 of 1.51 mg/kg-bw 

from this study, classified acceptable, is now used for risk estimation (Table 1). The T-REX 

acute avian dose-based risk quotients using the California quail LD50 (bodyweight treated as 

northern bobwhite) are presented in Table 1. These tabulated RQs were derived using the 

dicrotophos-specific Mineau scaling factor of 1.118 (a default scaling factor of 1.15 was 

inadvertently used in the T-REX calculations for the preliminary risk assessment). RQs 

presented in Table 1 are approximately half as large as the RQs that were presented in Table 

4.9 (Page 52) of the dicrotophos preliminary risk assessment for registration review (DP 

393746, 7/10/2014).

Table 1. Upper Bound Kenaga, Acute Avian Dose-Based Risk Quotients

Size 

Class

(grams)

Adjusted

LD50

EECs and RQs

Short Grass Tall Grass Broadleaf 

Plants Fruits/Pods/Seeds Arthropods Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

20 1.17 240.24 205.92 110.11 94.38 135.14 115.83 15.02 12.87 94.10 80.65 3.34 2.86

100 1.41 137.00 97.11 62.79 44.51 77.06 54.63 8.56 6.07 53.66 38.04 1.90 1.35

1000 1.85 61.34 33.13 28.11 15.19 34.50 18.64 3.83 2.07 24.02 12.98 0.85 0.46
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AMVAC Comment: Section 3.2.1. Selection of Screening-level Effects Metrics, Birds and 

Mammals; PDF Page 56- Avian subacute dietary study selection: EPA (2014) also 

presented risk results based on dietary exposures. Typical guideline acute dietary studies have a 

five day exposure period followed by three days of observation. However, the toxicity study 

selected by EPA (2014) was actually 28 days in length.

EFED Response: EFED concurs with AMVAC that the exposure duration of MRID

00013707 limits the utility of this study for quantitative use in risk assessment. A table of the 

avian subacute dietary toxicity studies available for dicrotophos can be found on page 17 

(PDF page 19) of the October 28, 1998 EFED RED Chapter for Dicrotophos (Document ID 

EPA-HQ-OPP-2008-0440-0009). Japanese quail were the most sensitive avian species in 

subacute dietary toxicity studies and the LC50 of 32 mg/kg-diet from this study, classified 

supplemental, is now used for risk estimation (Table 2). The 2014 EFED PRA (DP 393746, 

7/10/2014) found RQs to range from 1.01 (dietary items: fruits/pods/seeds) to 16.23 (short 

grass). Using the LC50 of 32 mg/kg-diet results in slightly lower RQs ranging from 0.41

(dietary items: fruits/pods/seeds) to 6.59 (short grass). 

Table 2. Upper Bound Kenaga, Subacute Avian Dietary Based Risk Quotients

LC50

EECs and RQs

Short Grass Tall Grass Broadleaf 

Plants Fruits/Pods/Seeds Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

32 210.94 6.59 96.68 3.02 118.66 3.71 13.18 0.41 82.62 2.58

AMVAC Comment: Section 3.2.1. Selection of Screening-level Effects Metrics, Birds and 

Mammals; PDF Page 56- Avian chronic study endpoints: For chronic exposure, EPA (2014) 

used the NOEC (1 ppm) from a mallard duck reproduction study. The NOEC was based on an 

8% reduction in female body weight at the next highest treatment level (3 ppm). However, an 8% 

reduction in female body weight should not be considered ecologically relevant as such small 

changes would reflect natural variability. Certainly, minor reductions in body weight in the 

laboratory are unlikely to be realized in the field as birds are mobile and will spatially average 

their daily exposure. These minor effects on body weight are unlikely to result in population level 

effects particularly as dicrotophos is applied only twice a year within 14 days for crop 

protection, and recovery from acetylcholinesterase (AChE) inhibition tends to be rapid (Fleming 

et al. 1981; Fleming and Grue, 1981).

EFED Response: The selection of the NOAEC in the mallard reproduction study was based 

on a statistically significant reduction in bodyweight. EFED reviews ecotoxicological studies 

for effects to the apical endpoints of survival, growth, and reproduction. A weight effect is a 

growth effect that could adversely affect survival in the wild.

AMVAC Comment: Section 3.2.1. T-REX; PDF Page 63: The dislodgeable foliar residue 

data that are available to the Agency demonstrates that residues decline with a half-life 
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established at two different field sites of less than 2.33 days (Prochaska, 1978) [MRID 

44728501]. It is recognized that these data do not account for the possibility of a different 

decline profile for residues that are not dislodged. Therefore, relative abundance of surface 

based residues versus residues within the target plant system is not clearly understood. In spite 

of a lack of certain information, EPA's designation of a 35-day foliar half-life for modeling 

purposes is likely to be highly exaggerated.

EFED Response: EFED will consider any data on foliar half-life that AMVAC makes 

available to support an alternative to the 35-day default foliar half-life used to parameterize 

the T-REX model. EFED concurs with AMVAC’s evaluation of the limitation of the 

available dislodgeable foliar residue study for half-life estimation.

AMVAC Transmittal Memo Comment #1, PDF Page 72: While EPA has identified possible 

chronic risks of concerns, they are based on a screening level assessment and AMVAC has 

herein provided a more refined analysis.

EFED Response: EFED will consider AMVAC’s comments in future refinements to the 

dicrotophos ecological risk assessment.

AMVAC Transmittal Memo Comment #2, PDF Page 72: The study that we believe EPA is 

referring to is titled, "Dicrotophos and Monocrotophos in Dislodgeable Foliar Residues on 

Cotton Leaves" and is indexed under MRID 44731002. Our interpretation of this study is that it 

validates our view that monocrotophos is only a very low level foliar metabolite that is rapidly 

degraded in the environment and therefore has a very negligible effect on any risk assessments. 

This study was composed of two field sites and at the site located in Washington County, 

Mississippi. Detectable levels of monocrotophos were only measured at two sampling intervals. 

The first finding was on the day of the 2nd application for which the arithmetic mean 

monocrotophos residue level was less than the limit of quantification. The second finding was 4 

days after the 3rd application for which the arithmetic mean monocrotophos residue level was 

0.0145 ppm, less than 2X the limit of quantitation. Because the highest total residues occurred 

immediately following each application, the contribution of monocrotophos during these periods 

is negligible. Also, the labile nature of the monocrotophos residues would not support a 

contention that the enhanced activity of monocrotophos residues relative to dicrotophos residues 

would extend the time of acute risk LOC exceedances in a meaningful way, given the significant 

differences in concentration between parent and metabolite.

EFED Response: It is agreed that monocrotophos is likely a minor foliar degradation 

product based on the cited study but two samples in one study do not represent a robust 

dataset and cannot provide conclusive characterization on the magnitude of monocrotophos 

as a degradate of dicrotophos
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AMVAC Transmittal Memo Comment #3, PDF Page 73: As the ecological risk assessments 

are envisioned to be refined over time, it would be clearer to indicate when a risk table was 

developed using screening-level modeling and when a refined approach is used. On this basis, 

we propose that the title be changed to, "Screening-Level Risk Resulting from Dicrotophos 

Exposure Presented by Taxon".

EFED Response: It is agreed that the title proposed by AMVAC is more accurate and clear.

AMVAC Comment #1, PDF Page 73: Although the butanamide degradates SD 6167 or SD 

11733 may pose some undetermined level of risk to certain aquatic species, these chemicals 

belong to a class of compounds that is distinct from the organophosphates. On this basis, these 

two metabolites should not be included in the aquatic risk assessment for dicrotophos.

EFED Response: It is agreed that these degradates may represent different modes of action 

than parent dicrotophos. However, toxicity may be similar for taxa where AChE inhibition is 

not the toxicity pathway of concern (e.g., plants). Differences between parent-only and total 

toxic residues (TTR) estimated environmental concentrations (EECs) were demonstrated to 

be too small to impact risk conclusions on any taxa. For the purposes of risk assessment, it is 

useful to demonstrate the impact of uncertainties that do not impact risk conclusions so that 

efforts can be concentrated on uncertainties that weigh more heavily on risk conclusions.

AMVAC Comment #2, PDF Page 73: When discussing the metabolism or degradation of 

dicrotophos in the context of SD 6167 and SD 11733 formation, it should be clarified that these 

compounds are not organophosphates. One suggestion is to describe the metabolites as the oxobutanamide SD 6167 and the hydroxy-butanamide SD 11733.

EFED Response: Chemical structures are provided in the risk assessment that show the 

differences between dicrotophos and degradates.

AMVAC Comment #3, PDF Page 74: The concentration of bifenthrin in product mixes is 

generally low and its contribution to the overall toxicity to aquatic invertebrates is uncertain. 

Generally, pesticide mixtures act in an additive fashion (NAS, 2013; Rodney et al. 2013) thus 

there is little reason to believe toxicity would be enhanced beyond what would be expected by an 

additive response.

EFED Response: EFED agrees that the overall toxicity of these product mixtures are

uncertain.

AMVAC Comment #4, PDF Page 74: For a screening level assessment, this approach may be

appropriate; however, for a refined assessment, a more accurate assessment would consider the 

oxo-butanamide SD 6167 and the hydroxy-butanamide SD 11733, separately. For that reason, it 
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would be appropriate to add an additional statement such as, "Because the oxo-butanamide SD 

6167 and the hydroxy-butanamide SD 11733 are butanamides and not organophosphates, and 

should not be included in the dicrotophos risk assessment.

EFED Response: It is agreed that these degradates may represent different modes of action 

than parent dicrotophos. However, toxicity may be similar for taxa where AChE inhibition is 

not the toxicity pathway of concern (e.g., plants). Differences between parent-only and TTR 

EECs were demonstrated to be too small to impact risk conclusions on any taxa. For the 

purposes of risk assessment, it is useful to demonstrate the impact of uncertainties that do not 

impact risk conclusions so that efforts can be concentrated on uncertainties that weigh more 

heavily on risk conclusions.

AMVAC Comment #5, PDF Page 74: In the absence of toxicity data for terrestrial-phase 

amphibians and reptiles, it is standard practice to use endpoints for avian species as a surrogate 

(EPA, 2008a). This extrapolation has little, if any, empirical support. That is, the extrapolation is 

made out of necessity due to a paucity of herptile toxicity data, not because of scientific 

justification. Birds and herptiles belong to different taxonomic classes, and therefore, have 

different metabolic rates, diets, respiratory and reproductive systems and ecology in general. 

Many of these factors can be addressed using a more appropriate exposure model (T-HERPS) 

that can account for the lower metabolic rates and thus lower food and residue ingestion 

experienced by a herptile in the field.

EFED Response: Acute dose-based RQs for three size classes of herptile were calculated 

using T-HERPS to explore the magnitude of reduction in EECs and RQs for three size 

classes of herptiles compared to the RQs determined for avian species using T-REX (Tables 

3 & 4). Whereas the T-REX calculated RQs for a 20 gram bird range from 0.46 to 205.92, 

T-HERPS parameterized with the same avian LD50 and application information used in TREX calculated a range of RQs from 0.37 to 120.98 for a 20 gram amphibian.

Table 3. Upper Bound Kenaga, Acute Herptile Dose-Based EECs

Dose-based EECs 

(mg/kg-bw)

Herpetofaunal Size Classes and Body Weights

small (g) mid (g) large (g)

2 20 200

Short Grass 11.72 6.95 4.12

Tall Grass 5.37 3.18 1.89

Broadleaf plants/sm Insects 6.59 3.91 2.32

Fruits/pods/seeds/lg insects 0.73 0.43 0.26

Herbivore mammals 385.18 141.14 51.72

Insectivore mammals 24.07 8.82 3.23

Reptile/Terrestrial phase amphibian 4.82 2.86 1.69
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Table 4. Upper Bound Kenaga, Acute Herptile Dose-Based Risk Quotients

Dose-based RQs

(Dose-based EEC/adjusted LD50)*

Amphibian/Reptile Acute RQs for Small, 

Medium, and Large Species (grams)

2 20 200

Short Grass 13.18 5.95 2.69

Tall Grass 6.04 2.73 1.23

Broadleaf plants/sm insects 7.41 3.35 1.51

Fruits/pods/seeds/lg insects 0.82 0.37 0.17

Herbivore mammals 433.22 120.98 33.78

Insectivore mammals 27.08 7.56 2.11

Terrestrial phase amphibian 5.42 2.45 1.11

*LD50 of 1.51 mg/kg-bw from California quail

AMVAC Comment #6, PDF Page 74: As discussed in Section 2.3.4 of this report, the SIP 

model is extremely conservative and does not consider dissipation kinetics, application rates, 

chronic exposure durations, application timing (on days without precipitation events), 

mammalian and avian mobility, and other factors that would result in a significantly more 

realistic exposure scenario. AMVAC recommends that the Agency re-evaluate the use of

SIP even at the screening level, and conduct a more reasonable, realistic drinking water 

assessment for all pesticide products.

EFED Response: SIP is not a risk assessment tool. EFED uses the SIP model as a screen at 

the problem formulation stage to determine whether additional consideration should be given 

to the drinking water exposure route.

AMVAC Comment #7, PDF Page 75: It is recognized that there is very limited background 

data concerning the cause of the peak detection in water of 6.83 ppb. As this value is 

significantly out of range of other reported values, it remains a distinct possibility that the 

finding represents some aberration as opposed to a true value. A more thorough assessment of 

the NAWQA data set is contained within AMVAC's response to EPA's assessment of water 

exposure and aggregate risk.

EFED Response: The peak detection of 6.83 ppb for dicrotophos is not an aberration when 

considered in the context of organophosphates with similar environmental fate properties 

(i.e., short metabolic half-lives) but more NAWQA monitoring data. Of more than 62,000 

samples for malathion, six samples had detections between 6 ppb and 22.5 ppb. Much like 

dicrotophos, it was found that detections were below one part per billion on days 

immediately following peak detections of malathion. NAWQA currently contains 8,831 

samples for dicrotophos. Given that there is one detection above 6 ppb for every 10,000 

malathion samples, it is not unreasonable that there is only one dicrotophos detection at this 

concentration. Single maximum application rates for agricultural uses of malathion range 
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from 0.5 to 7.5 lbs a.i./A as compared to the dicrotophos rate of 0.5 lb a.i./A on cotton. 

Malathion is used as an example because it has a similar short half-life and also has a large 

non-targeted monitoring dataset. Additionally, areas of high dicrotophos usage, such as 

northwest Texas, have no reported NAWQA surface water monitoring samples for 

dicrotophos. 

AMVAC Comment #8, PDF Page 75: Soil dissipation studies do not provide evidence of 

residues occurring at lower soil depths. Also, the EPA has demonstrated through PRZM-GW 

modeling that there is little exposure potential for dicrotophos within groundwater.

EFED Response: It is concluded that the terrestrial field dissipation study (MRID 

41114301) does not address the formation and decline of degradates. However, PRZM-GW 

estimates provided in the revised DWA indicate groundwater is not a substantial exposure 

pathway.

AMVAC Comment #9, PDF Page 75: Information concerning the identity of the compounds 

should be provided in the text. As previously stated, SD 6167 is better described as the 

oxobutanamide SD 6167 and SD 11733 as the hydroxy-butanamide.

EFED Response: AMVAC’s naming preferences will be incorporated in future risk 

assessments.

AMVAC Comment #10, PDF Page 76: AMVAC Chemical Corporation has labeling provisions 

that prescribes certain drift reduction technology (DRT) measures and would seek that the effect 

of such mitigation be incorporated into the risk assessment. For example, on this basis, the 

default ASAE Fine to Medium droplet size distribution should be modified to a coarser droplet 

size.

EFED Response: Incorporation of DRT measures on dicrotophos labels is good; however, 

these labels do not appear to have the specificity to support modifying the risk assessment 

assumptions as claimed by this AMVAC comment.

AMVAC Comment #11, PDF Page 76: Information concerning the low potential for 

monocrotophos to be formed on foliage surface is evident based on the foliar residue study titled, 

"Dicrotophos and Monocrotophos in Dislodgeable Foliar Residues on Cotton Leaves" and filed 

under MRID 44731002. The study demonstrates that residues of monocrotophos on cotton 

foliage at two distinct sites remained at very low levels over a 35 day period after 3 applications. 

On this basis, the words, "in and/or on foliage" should be modified to "in foliage".

EFED Response: The language change could be made but does not substantially change the 

meaning of the statement.
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AMVAC Comment #12, PDF Page 76: EPA's Preliminary Environmental Fate and Ecological 

Risk Assessment for the Registration of Dicrotophos (Case #145), is not an Endangered

Species Assessment, but rather an ERA to evaluate the registration of dicrotophos under

FIFRA.

EFED Response: In November 2013, the EPA, along with the U.S. Fish & Wildlife Service 

(USFWS), the National Marine Fisheries Service (NMFS) (collectively, the Services), and 

the U.S. Department of Agriculture (USDA) released a summary of their joint Interim 

Approaches for assessing risks to listed species from pesticides. The Interim Approaches 

were developed jointly by the agencies in response to the National Academy of Sciences’ 

(NAS) recommendations and reflect a common approach to risk assessment shared by the 

agencies as a way of addressing scientific differences between the EPA and the 

Services. The NAS report outlines recommendations on specific scientific and technical 

issues related to the development of pesticide risk assessments that EPA and the Services 

must conduct in connection with their obligations under the Endangered Species Act (ESA) 

and FIFRA. The joint Interim Approaches were released prior to a stakeholder workshop 

held on November 15, 2013. In addition, the EPA presented the joint Interim Approaches at 

the December 2013 Pesticide Program Dialogue Committee (PPDC) and State-FIFRA Issues 

Research and Evaluation Group (SFIREG) meetings, and held a stakeholder workshop in 

April 2014, allowing additional opportunities for stakeholders to comment on the Interim 

Approaches. As part of a phased, iterative process for developing the Interim Approaches, 

the agencies will also consider public comments on the Interim Approaches in connection 

with the development of upcoming Registration Review decisions. The details of the joint 

Interim Approaches are contained in the white paper “Interim Approaches for NationalLevel Pesticide Endangered Species Act Assessments Based on the Recommendations of the 

National Academy of Sciences April 2013 Report,” dated November 1, 2013. 

Given that the agencies are continuing to develop and work toward implementation of the 

Interim Approaches to assess the potential risks of pesticides to listed species and their 

designated critical habitat, this preliminary risk assessment for dicrotophos does not contain a 

complete ESA analysis. While the agencies continue to develop a common method for ESA 

analysis, this preliminary, screening-level risk assessment indicates potential risks of direct 

effects to listed freshwater and estuarine/marine invertebrates, mammals, birds, and 

terrestrial invertebrates from the use of dicrotophos on some of its registered use sites. Listed 

species of freshwater and estuarine/marine invertebrates, mammals, birds, and terrestrial 

invertebrates may also be affected through indirect effects because of the potential direct 

effects on listed and non-listed species. Potential direct effects on listed freshwater and 

estuarine/marine invertebrates, mammals, birds, and terrestrial invertebrates from the use of 

dicrotophos may be associated with modification of Primary Constituent Elements (PCEs) of 

designated critical habitats, where such designations have been made. Once the agencies 

have fully vetted the scientific methods necessary to complete risk assessments for 

endangered and threatened (listed) species and their designated critical habitats, these 

methods will be applied to subsequent analyses for dicrotophos as part of completing this 

registration review. 
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To conduct full ESA analysis for individual listed species, useful refinements may include, 

but are not limited to, analyses of: 1) more detailed, species-specific ecological and 

biological data; 2) more detailed and accurate information on cotton and tree injection use 

patterns; and 3) sub-county level spatial proximity data on the co-occurrence of potential 

effects areas and listed species and any designated critical habitat. 

AMVAC Comment #13, PDF Page 76: It is not clear whether EPA intended to list the NOEAC 

and LOEAC for reproductive effects, which are 0.0028 and 0.0044 mg ai/L, respectively. With 

respect to length measurements, the NOAEC and LOAEC are 0.00099 and 0.0017 mg ai/L, 

respectively. However, the length data do not indicate any trend in effect versus concentration; 

thus we would conclude are not appropriate endpoints for consideration.

EFED Response: In an addendum dated August 27, 2014, EFED upgraded the classification 

of the data evaluation record (DER) for MRID 44956501 from supplemental to acceptable. In 

order to review the study data supplement submitted by the contract laboratory, EFED 

analyzed the data for all study endpoints (e.g., length, weight, parental survival, offspring per 

parent, time to first brood) using the Division’s current statistical analysis software

(CETISTM) and Divisional policy (e.g., treatment response was compared to the negative 

control instead of the solvent or pooled control). It was determined that dry weight and total 

length were the most sensitive study parameters, with NOAEC and LOAEC values of 1.7 and 

2.8 μg a.i./L, respectively. 

AMVAC Comment #14, PDF Page 77: We propose that the reproduction-based NOAEC and 

LOAEC be utilized for risk assessment purposes.

EFED Response: EFED policy is to use the most sensitive endpoint from among the apical 

response endpoints of survival, growth, or reproduction. It was determined that dry weight 

and total length were the most sensitive endpoints in the study, with NOAEC and LOAEC 

values of 1.7 and 2.8 μg a.i./L, respectively. 

AMVAC Comment #15, PDF Page 77: Even for the individual avian species of highest 

residues, the measured internal dose level did not exceed the laboratory-based LD50 of 3 

mg/kg/bw associated with the House sparrow (Passer domesticus), another passerine species. 

There is no data to suggest that an external dose of this magnitude would have a detrimental

effect on avian species. This data indicates that this exposure level would not place this avian 

species at undue risk. Sample identification is contained within Table 7 of the report and 

indicates that the sample consisted of skin and feathers. The efficiency of transfer of residues 

associated with the feathers onto the skin is likely not high and the range of concentration 

associated with samples having measured internal residues is consistent with that view. In the

sample in question that had external residues of 17 ppm, the concentration of residues in the 

associated carcass was only 0.09 ppm. Therefore, there is no evidence that dicrotophos residues 

having toxicological implications occur at high levels.
Page 11 of 25

EFED Response: The fact that the measured internal dose level did not exceed the LD50 is 

no basis for disputing the toxicological relevance of the detected dicrotophos residue 

concentration to an individual bird since the very definition of the LD50 is the dose required 

to kill 50 percent of a population of test animals; mortalities are typically recorded at doses 

lower than the LD50. External carcass residue concentrations further help to substantiate TREX modeled field residues. Beyond the toxicological relevance and bioavailability of 

external residues uncertainty, a separate uncertainty is whether internal residue 

concentrations may underestimate maximum internal dicrotophos concentrations in the 

sampled bird since metabolism of dicrotophos may have preceded the mortality event.

AMVAC Comment #16, PDF Page 77: We agree with the statement [“While neither study 

design is sufficiently robust for quantitative use in risk estimation, anecdotal information 

contained within the study reports is useful for risk characterization”] only in that the avian 

effects due to the different individual insecticides, including dicrotophos, should be no worse 

than that observed in this study. On this basis, one can conclude that the overall effects seen in

both studies are limited.

EFED Response: EFED does not agree that either field study is necessarily representative 

of a worst case scenario. These studies were not designed robustly enough or adequately 

executed so as to conclude that effects should be no worse than effects observed in the 

studies. 

AMVAC Comment #17, PDF Page 78: Although we do not dispute the EPA's [avian toxicity] 

classification on the basis of the laboratory studies, the extent of exposure as evident in the two 

field studies even in view of the complications previously discussed, demonstrate that the 

chemical is not highly toxic in the field where there were only limited mortalities noted.

EFED Response: While EFED risk assessments do rely on multiple lines of evidence, it is 

important to note the limitations of the carcass search employed by the study authors which 

may have resulted in an underestimate of avian mortalities in the field; namely that fields 

were not searched for carcasses until 48 hours after application (in accordance with the 

reentry restriction) and carcass search efficiency trial failures.

AMVAC Comment #18, PDF Page 78: AMVAC believes that the chronic risk to aquatic 

organisms is best assessed by considering the extensive NAWQA monitoring data set, which 

substantiates that actual exposure levels would be far lower than that determined from modeling

efforts. Therefore, although chronic risk as calculated using baseline PRZM/EXAMS modeling 

implies that there is some risk to aquatic organisms, realistic exposures in surface waters 

associated with agricultural areas as evident by monitoring data is very low and would not pose 

a risk of concern to aquatic organisms.

EFED Response: Use of PRZM/EXAMS modeled EECs to calculate RQs is consistent with 

EFED policy. In the case of dicrotophos, monitoring data from Bogue Phalia is of the same 
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magnitude as the modeled EECs for 1-in-10-year peak exposure. However, direct 

comparison of NAWQA monitoring data from waterbodies with variable flow and variable 

watershed sizes to EECs from the PRZM/EXAMS farm pond should not be made. 

Dicrotophos monitoring indicates that concentrations may attenuate quickly in flowing 

waterbodies but it cannot be assumed this attenuation will occur in all environmental, 

watershed, and usage conditions. The PRZM/EXAMS farm pond is intended conservatively 

represent these conditions and is therefore the best tool for quantitatively assessing chronic 

risk to aquatic organisms.

AMVAC Comment #19, PDF Page 78: Context should be provided on the 23X exceedance 

factor as this maximum is as a result of an exposure scenario that is unlikely to occur in nature 

(i.e. a 20 g mammal consuming exclusively short grass). This information has been further

refined within this document.

AMVAC Comment #20, PDF Page 78: [Chronic dose-based LOC exceedances for mammals 

have] been further refined within this document.

AMVAC Comment #21, PDF Page 78: [Acute dose-based LOC exceedances for birds have]

been further refined within this document.

AMVAC Comment #22, PDF Page 79: [Sub-acute dietary-based LOC exceedances for birds 

have] been further refined within this document.

AMVAC Comment #23, PDF Page 79: [Chronic LOC exceedances for birds have] been 

further refined within this document.

EFED Response to AMVAC comments 19-23: EFED will consider AMVAC’s comments

in future refinements to the dicrotophos ecological risk assessment.

AMVAC Comment #24, PDF Page 79: No comment

EFED Response: EFED will correct the typographical error in spelling in future 

dicrotophos ecological risk assessments.

AMVAC Comment #25, PDF Page 79: EPA has cited incidents as late as 1976 and has 

suggested that the weight of the evidence forms a basis for assessing direct ecological effects 

from the current registered use. However, the current registered use differs from previous labels

and agricultural practices in many ways. These exposure mitigation changes, some prescribed 

by EPA, have had a significant impact on reducing environmental concerns related to product 

use. Further and most importantly, there is no evidence of avian incidents associated with the 

current registered use on cotton.
Page 13 of 25

EFED Response: EFED concurs that there are no incidents recorded in either the Avian 

Incident Monitoring System or the Ecological Incident Information System associated with the 

current registered use of dicrotophos on cotton. The absence of incident data cannot be 

construed as an absence of incidents resulting from use on cotton, but EFED will consider 

AMVAC’s comment in future refinements to the dicrotophos ecological risk assessment.

AMVAC Comment #26, PDF Page 79: Our understanding is that EPA did not utilize the 90th 

percentile mean of metabolism half-life estimates as stated, but instead added conservatism to 

the assessment by incorporating a 3X multiplier to the single aerobic and anaerobic metabolism 

half-lives on file and a 6X factor to the aerobic aquatic metabolism half-life.

EFED Response: When there is one study, the half-life is multiplied by 3, i.e., half-life 

x 3 = input parameter. This is viewed as an estimate of the upper bound on the mean that 

is calculated under the following assumptions: (a) The experimental half-life is the mean 

value from a normally distributed population. (b) The standard deviation is equal to the 

mean (i.e., coefficient of variation= 100%). (3) The "mean" value times 3 (equivalent to 

mean plus 2 standard deviations) represents the 90% upper bound. This is almost 

equivalent to using the value of 3.078 for one degree of freedom (df=l). Some 

experimental justification for this approximation is provided by Howard and Howard1

who extensively studied soil respiration (carbon evolution) rates in diverse soils with 

different microbiological activities and about 75% of water holding capacity, the current 

EFED soil moisture norm. Inspection of their data shows that the temperatureindependent ratio of carbon dioxide evolution of the most active soil to that of the least 

active soil was approximately 2.7, or close to 3. In addition, a preliminary data evaluation 

for several pesticides suggests that soil metabolism half-lives vary by about a factor of 3.

AMVAC Comment #27, PDF Page 80: We do not dispute the factual nature of the comment; 

however, the implications of the finding need to be more thoroughly examined. It is important to 

consider that this single value is not representative of the entire very large NAWQA dataset 

where residues are more than an order of magnitude lower for all other samples. A more 

thorough assessment of the NAWQA data set is contained within AMVAC's response to EPA's 

assessment of water exposure and aggregate risk.

EFED Response: It is agreed that the single value is not representative of the entire dataset 

but the dataset is not targeted monitoring data. Non-targeted monitoring data may provide 

characterization of pesticide concentrations but lacks sufficient context and sampling timing 

to capture peaks associated with pesticide usage, especially for a pesticide like dicrotophos 

that is demonstrated to differ in concentration by more than an order of magnitude from one 

day to the next. The use of targeted monitoring bias factors presented at Scientific Advisory 

Panels (6/12-15/2012; 7/26-28/2011, and 4-26-29/2010) were considered but are not 

appropriate for dicrotophos’ non-targeted monitored data. Due to dicrotophos’ short aerobic 

metabolism half-life, malathion chemographs are expected to behave similarly to the “flashy” 

 

1 Howard, D. M., and P. J. A. Howard. "Relationships between CO~ 2 evolution, moisture content and temperature 

for a range of soil types." Soil Biology and Biochemistry 25 (1993): 1537-1537.
Page 14 of 25

runoff events with sharp peaks and rapid recessions described in the bias factors SAPs. 

These events do not allow for robust estimates of bias factors for peak concentrations with 

sparse, systematic sampling. 

AMVAC Comment #28, PDF Page 80: The spray drift assessment using AgDrift v 2.01 is 

accurate for use practices that underlie the model when it was developed. Since the time when 

this data was developed, there have been important advances in reducing drift through 

implementation of more modem, good agricultural practices. For example, changes in nozzle 

specifications have led to coarser droplets that are less prone to drift. On AMVAC's Bidrin 

labels are significant instructions to reduce drift and we believe these have dramatically reduced 

drift. Therefore, the results of AgDrift overestimate exposure and risk.

EFED Response: The spray drift language on Bidrin labels have been reviewed and the 

instructions therein are not inconsistent with AgDRIFT parameterizations made in the risk 

assessment for dicrotophos.

AMVAC Comment #29, PDF Page 82: The exposure of aquatic organisms is best reflected by 

the very large NAWQA dataset, which indicates that exposure levels in surface water should not 

be detrimental to aquatic species. The EPA's PRZM/GW modeling assessment is sufficient to 

demonstrate that exposure associated with groundwater sources would not pose a risk to aquatic 

organisms.

EFED Response: Non-targeted monitoring is used only for risk characterization and not for 

risk estimation. Surface water modeling through PRZM/EXAMS or SWCC is principally 

relied upon for assessing exposure to aquatic taxa.

AMVAC Comment #30, PDF Page 82: AMVAC proposes that the Agency's statement be 

further clarified by adding information that explains that the AgDrift model is based on a dataset 

that reflects application practices that have since been refined and are included on current 

product labels; therefore the modeling outputs likely exaggerate actual drift concerns; but 

provide a useful screening level assessment.

EFED Response: Current product labels do not make reference to Drift Reduction 

Technology (DRT) nor have studies been submitted to support DRT for dicrotophos uses. 

For more information on EPA’s DRT program, please visit the following website: 

http://www2.epa.gov/reducing-pesticide-drift/about-drift-reduction-technology-program

AMVAC Comment #31, PDF Page 82: [Acute LOC exceedances for mammals have] been 

further refined within this document.

EFED Response: EFED will consider AMVAC’s comment in future refinements to the 

dicrotophos ecological risk assessment.
Page 15 of 25

AMVAC Comment #32, PDF Pages 82-83: [Dose and dietary-based chronic LOC 

exceedances for mammals have] been further refined within this document. As this assessment 

addresses reproductive issues that are indicative of population-based effects, it is worthier 

noting that the baseline risk assessment itself is derived from the risk to the most sensitive 

individual of a group of animals. The use of the NOAEC is not population-based as the impact of 

a small portion of animals is unlikely to cause a detrimental effect to the population as a whole. 

Therefore, we find that EPA's statement that it believes that there is a high level of confidence in 

their prediction of adverse chronic effects is overstated. A more appropriate statement would 

have been that based on the Agency's risk assessment, it finds that chronic RQs exceed the 

regulatory standards.

EFED Response: EFED concurs with AMVAC that mammalian chronic RQs exceed the 

EFED’s established level of concern. EFED will consider AMVAC’s comment in future 

refinements to the dicrotophos ecological risk assessment.

AMVAC Comment #33, PDF Page 83: [Acute LOC exceedances for mammals have] been 

further refined within this document.

EFED Response: EFED will consider AMVAC’s comment in future refinements to the 

dicrotophos ecological risk assessment.

AMVAC Comment #34, PDF Page 83: As previously stated, the spray drift assessment using 

AgDrift v 2.01 is accurate for use practices that underlie the model. Since the time when this 

data was developed, there have been important advances in reducing drift through 

implementation of more modem, good agricultural practices. For example, changes in nozzle 

specifications have led to coarser droplets that are less prone to drift. On AMVAC's Bidrin 

labels, these practices are provided to the user and ensure that previous concerns relating to 

chemical drift have been properly mitigated.

EFED Response: Current product labels do not make reference to Drift Reduction 

Technology (DRT) nor have studies been submitted to support DRT for dicrotophos uses. 

For more information on EPA’s DRT program, please visit the following website: 

http://www2.epa.gov/reducing-pesticide-drift/about-drift-reduction-technology-program

AMVAC Comment #35, PDF Page 84: [Acute dose-based, sub-acute dietary, and chronic 

dietary LOC exceedances for birds have] been further refined within this document. Also, it is 

not clear what the Agency means when it states that there is a high degree of certainty that avian 

species will be adversely impacted by dicrotophos. As stated earlier, the chronic risk assessment 

is more geared towards assessing the impact on individual birds, rather than on the species due 

to the use of the NOAEC as the toxicological endpoint. Also, we believe that the Agency is 

overstating its conclusion based on a deterministic, screening level assessment without fully 

examining the supporting evidence (incident reports and field studies).
Page 16 of 25

EFED Response: EFED will consider AMVAC’s comment in future refinements to the 

dicrotophos ecological risk assessment. The risk assessment’s statement about a high degree 

of certainty in the prediction of avian risk stems from the magnitude of the RQs which are 

directly related to the estimated exposure concentrations. 

AMVAC Comment #36, PDF Pages 84-85: [Acute and chronic LOC exceedances for birds 

have] been further refined within this document. Also, it is important to place into perspective 

the timing calculated for achieving an acceptable LOC as the shape and slope of the curves have 

a significant basis on how far the acceptable values extend and relatively small overages in the 

RQ values may occur well before the calculated times associated with these values. This is 

evident for assessing the effect of time on achieving an acceptable chronic LOC in EPA's Figure 

4.2 Avian LOCs Superimposed on Residue Decline Curve. It is also important to note that the 

residue decline curves represent generic upper bound estimates that likely underestimate the rate 

of residue degradation on food items. It is also worth noting that to properly assess a 

sophisticated approach for evaluating the meaning of the time periods associated with RQ 

exceedances, it is important to consider the likely exposure periods of different species of birds.

EFED Response: EFED will consider AMVAC’s comment in future refinements to the 

dicrotophos ecological risk assessment.

AMVAC Comment #37, PDF Page 86: As previously stated, the use of AgDRIFT is 

appropriate for a screening level assessment; however, with the implementation of more modem 

good agricultural practices, appropriate labeling provisions have been developed for 

dicrotophos products that address these previous concerns relating to drift associated with 

outdated application procedures. AMVAC believes that current labeling practices relating to 

drift fully address environmental exposure issues.

EFED Response: Current product labels do not make reference to Drift Reduction 

Technology (DRT) nor have studies been submitted to support DRT for dicrotophos uses. 

For more information on EPA’s DRT program, please visit the following website: 

http://www2.epa.gov/reducing-pesticide-drift/about-drift-reduction-technology-program

AMVAC Comment #38, PDF Page 86: AMVAC agrees with the EPA's statement that 

inhalation should not be regarded as a primary route of exposure. We also believe that in 

consideration of all of the information associated with inhalation exposure, especially the 

changes in application to minimize any fine aerosol spray droplets, that it is appropriate to

characterize inhalation exposure as an unlikely route of exposure concern.

EFED Response: EFED will consider AMVAC’s comment in future refinements to the 

dicrotophos ecological risk assessment, but any changes to the inhalation exposure 

component of the conceptual model will need to be based on explicit nozzle and droplet size

restrictions specified on the label.
Page 17 of 25

AMVAC Comment #39, PDF Page 86: AMVAC believes that although there is always some 

value for developing additional information, there is already sufficient evidence that dicrotophos 

use on cotton does not yield environmental incidents on honey bees nor is there data to indicate 

any exposure. The Bidrin label also calls for care in terms of not utilizing the product when bees 

are detected in the fields designated for treatment. Also, consideration of dislodgeable foliar 

residue data on cotton as previously described in this document provides evidence to support the 

contention that dicrotophos residues are not persistent on foliage.

EFED Response: The Agency has issued guidance for the data needed to assess pesticide 

risk to bees (USEPA et al., 2014). This guidance document indicates that if exposure of bees 

to a pesticide is expected2, a Tier I screening-level risk assessment is conducted. The Tier I 

assessment is intended to be sufficiently conservative that chemicals that pass the screen are 

considered to represent a relatively low risk of adverse effects to bees. Tier I toxicity data 

that are generally needed to complete screening-level risk assessments include:

 acute contact toxicity data to adult honey bees (honey bees serving as a surrogate for all 

bee species)

 acute and chronic oral toxicity to adult honey bees

 acute and chronic oral toxicity to juvenile (i.e. larval) honey bees. 

If risk concerns are identified in the screening-level assessment, it may be refined using data 

that further define exposure or through additional data including Tier II semi-field or Tier III 

full-field toxicity tests.

The use of dicrotophos on cotton include ground and aerial applications where spray drift 

may land on blooming non-target plants and could result in residues in pollen and nectar 

(which could then be transported to the hive). Residues can in turn be brought back to bee 

colonies where in-hive bees including young adult and developing brood (i.e., eggs, larvae 

and pupae) may be exposed. Therefore, exposure at all bee life stages would be expected. 

Since exposure of bees to dicrotophos residues is expected, Tier I honey bee laboratory 

toxicity data are needed to conduct a screening-level risk assessment. Acute contact toxicity 

data is available that indicates dicrotophos residues are highly toxic to honey bees on an 

acute contact basis. However, no data are available that evaluate dicrotophos’ toxicity from 

the oral exposure route to adult bees on a chronic basis and larval bees on an acute or chronic 

basis. 

Therefore, the Agency is requesting Tier I laboratory toxicity data for acute and chronic oral 

toxicity for larval honey bees and chronic oral toxicity to adult honey bees in order to 

complete the screening-level risk assessment for bees. Should the screening level risk 

assessment identify that there are risk concerns to bees, mitigation measures may need to be 

 

2 Exposure is expected for the cotton use because bees are required for crop pollination 

(Delaplane and Mayer, Crop Pollination by Bees) and exposure is presumed for the tree injection 

use on pollinator-attractive trees
Page 18 of 25

considered and/or the registrant may need to conduct Tier II or III effects studies that reduce 

uncertainty by characterizing dicrotophos’ effects at the whole-colony level.

AMVAC Comment #40, PDF Page 86: As EPA has determined that the acute risk to 

freshwater and estuarine/marine fish is not of concern and that the chronic risk quotients for 

freshwater fish are all less than 0.001, the development of additional chronic data for the 

refinement of risk to estuarine/marine species is not warranted.

EFED Response: The chronic toxicity of dicrotophos to estuarine/marine fish is a risk 

assessment uncertainty that can only be resolved through the submission of additional data.

AMVAC Comment #41, PDF Pages 86-87: AMVAC recognizes the current variability in the 

approach and proposed methods for the conduct of National Endangered Species Assessments 

for pesticide products. In 2012, the Services and EPA asked the National Academy of Sciences 

(NAS) to address several areas of concern with regard to how pesticide risk assessments are 

conducted by EPA and the Services. In the 2013 report entitled "Assessing Risks to Endangered 

and Threatened Species from Pesticides" (NAS, 2013), NAS provided a proposed framework for 

conducting generic endangered species assessments under FIFRA with direct consideration of 

the ESA Section 7 requirement (Figure 1). In addition, the NAS panel recommended the use of 

refined approaches (e.g., probabilistic methods, population modeling) when conducting risk 

assessments for endangered species. The EPA, Services and USDA are currently evaluating the 

NAS panel report and are providing fairly regular updates on progress (e.g. Federal Family,

2013; EPA, 2013; EPA, 2014a; EPA, 2014b).

One comment on the Agency's description of the process relates to the use of endangered species 

LOCs (Section 6.2- 3rd pp). The NAS report recommended strongly against the use of LOCs, 

favoring probabilistic approaches (NAS, 2013). The Agency and Services initially responded 

with a recommendation of use of a one-in-a-million analysis as described in the Interim 

Approach. Thus, use of endangered species LOCs is unlikely in the process at this time.

Recognizing the on-going uncertainty in the ESA process for pesticides, Intrinsik and AMVAC 

will monitor progress in this area and will provide appropriate input as required to support 

dicrotophos.

EFED Response: EFED’s methodology for listed threatened and endangered species risk 

assessment continues to evolve in collaboration with various stakeholders. EFED encourages 

AMVAC and Intrinsik to participate in the comment period for the three NAS pilot chemical 

risk assessments, particularly since the three pilot chemicals (chlorpyrifos, diazinon, and 

malathion) are organophosphate insecticides.

AMVAC Comment #42, PDF Page 87: The Agency was not consistent in the application of the 

Mineau scaling factor for dicrotophos of 1.118 for birds in this analysis, but used the default 

1.15 for birds in the T-REX analysis (Appendix C-Table C-2). It is recommended that no scaling 

factor be applied for birds and dicrotophos.
Page 19 of 25

EFED Response: The Mineau scaling factor of 1.15 was inadvertently not modified to 

reflect the chemical specific factor of 1.118 available for dicrotophos in the T-REX model. 

RQs associated with the 1.118 scaling factor are slightly lower than the RQs associated with 

the 1.15 scaling factor.

AMVAC Appendix 4

ABC Laboratories Comment, PDF Page 111: The reviewer classified [MRID 48482901] as

SUPPLEMENTAL. However, the inadvertent mingling of fish from two closely linked control 

replicates early in the study did not result in any trend or effect on sensitive test endpoints 

determined at study termination. The EPA reviewer determined that this inadvertent mingling of 

fish from two control replicates early in the study did not impact study integrity. The few 

edematous fish observed on or before day 0 of the post-hatch period were not observed at any 

later time points, and specifically, no edematous fish were observed at test termination, so no 

edematous fish affected the body weight measurements taken at test termination. Therefore, ABC 

Laboratories, based on the information provided, believe that the study classification should be 

upgraded to a CORE classification.

EFED Response: EFED has considered ABC laboratories’ comment requesting a change to 

the study classification for MRID 48482901 but maintains that the supplemental 

classification is appropriate. While noting that MRID 48482901 does provide information 

useful for risk assessment and a new study is not requested, EFED concluded in the 

transmittal memo dated March 20, 2014 that the redistribution of fry in control replicates is a 

violation of independence of replicates and calls the integrity of the study conduct into 

question. EPA concurs that edema effects observed no later than study day five would not be 

expected to affect the weights recorded at study termination; however, dry weight 

measurement is still preferable to wet weight (blotted dry) measurement as stated in the Draft 

OPPTS 850.1400 guideline.

Response to study classification rebuttal, DP 426211, MRID: 49527901

EFED has reviewed AMVAC’s response to the study classification assigned to a Tier I seedling 

emergence DER for dicrotophos (MRID 48482902) but maintains that dicrotophos’ mobility, in 

conjunction with the study’s top-watering regimen, makes the true dicrotophos exposure level 

uncertain for the plants tested in the study. EFED therefore considers the previously assigned 

supplemental study classification appropriate. As stated in the transmittal memo for MRID 

48482902, this study is classified supplemental but a new seedling emergence study is not 

requested since MRID 48482902 contains useful information for the purposes of risk assessment. 

The nominal concentrations of dicrotophos applied in the available study (MRID 48482902) are 
Page 20 of 25

treated as estimates of exposure for the purposes of risk assessment; however, the distribution 

and availability of dicrotophos within the soil of the treated pots after the pots were top-watered 

remains uncertain.

References:

Delaplane and Mayer, 2000. Crop Pollination by Bees. CABI Publishing, New York.

Mallampalli, Nikhil and Jonathan Becker, 2014. Information to Support Registration Review of 

Dicrotophos: Cotton Crop Phenology in the Southern U.S., Recent Dicrotophos Use Patterns, 

and Potential Alternative Insecticides. Memorandum from the Biological and Economic 

Analysis Division, Office of Pesticide Programs. September 15, 2014.

USEPA, PMRA and CDPR, 2014. Guidance for Assessing Pesticide Risks to Bees. Office of 

Pesticide Programs, USEPA, Washington D.C. Health Canada Pest Management Regulatory 

Agency, Ottawa, ON, Canada. California Department of Pesticide Regulation, Sacramento, CA. 

June 23, 2014.
Page 21 of 25

Appendix A

Aquatic risk:

Aquatic estimated environmental concentrations (EECs) are reduced by approximately 50% 

when the typical application rates, dates, and intervals are modeled. However, all freshwater and 

estuarine/marine invertebrate acute and chronic RQs still exceed the Agency’s LOCs under the 

alternative application assumptions.

Terrestrial risk:

Terrestrial EECs are similarly reduced by approximately 50% when the typical application rates, 

dates, and intervals are modeled. However, all avian and mammalian acute and chronic RQs 

(with the exception of acute dose-based mammalian granivores) still exceed the Agency’s LOCs 

under the alternative application assumptions. A 50% reduction in EECs does not alter the risk 

conclusions for terrestrial invertebrates.

Figure 1. TREX parameterization for typical dicrotophos application to cotton, as defined by BEAD’s September 

2014 memo
Page 22 of 25

Figure 2. Dicrotophos ecotoxicity endpoints used to parameterize TREX model
Page 23 of 25

Summary of Risk Quotient Calculations Based on Upper Bound Kenaga EECs

Table A-1. Upper Bound Kenaga, Acute Avian Dose-Based Risk Quotients

Size 

Class

(grams)

Adjusted

LD50

EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/Seeds Arthropods Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

20 1.09 118.78 109.19 54.44 50.05 66.82 61.42 7.42 6.82 46.52 42.77 1.65 1.52

100 1.38 67.74 48.91 31.05 22.42 38.10 27.51 4.23 3.06 26.53 19.16 0.94 0.68

1000 1.96 30.33 15.50 13.90 7.11 17.06 8.72 1.90 0.97 11.88 6.07 0.42 0.22

Table A-2. Upper Bound Kenaga, Subacute Avian Dietary Based Risk Quotients

LC50

EECs and RQs

Short Grass Tall Grass Broadleaf 

Plants Fruits/Pods/Seeds Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

32 104.30 3.26 47.80 1.49 58.67 1.83 6.52 0.20 40.85 1.28

Size class not used for dietary risk quotients 
Page 24 of 25

Table A-3. Upper Bound Kenaga, Chronic Avian Dietary Based Risk Quotients

NOAEC 

(ppm)

EECs and RQs

Short Grass Tall Grass Broadleaf 

Plants Fruits/Pods/Seeds Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

1 104.30 208.59 47.80 95.61 58.67 117.33 6.52 13.04 40.85 81.70

Size class not used for dietary risk quotients

Table A-4. Upper Bound Kenaga, Acute Mammalian Dose-Based Risk Quotients 

Size 

Class

(grams)

Adjusted

LD50

EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/Seeds Arthropods Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

15 17.58 99.44 5.66 45.58 2.59 55.93 3.18 6.21 0.35 38.9472 2.2151 1.3811 0.0785

35 14.23 68.73 4.83 31.50 2.21 38.66 2.72 4.30 0.30 26.9177 1.8921 0.9545 0.0671

1000 6.15 15.93 2.59 7.30 1.19 8.96 1.46 1.00 0.16 6.24096 1.0142 0.2213 0.036
Page 25 of 25

Table A-5. Upper Bound Kenaga, Chronic Mammalian Dietary Based Risk Quotients

NOAEC 

(ppm)

EECs and RQs

Short Grass Tall Grass Broadleaf 

Plants

Fruits/Pods/Seeds/Large 

Insects Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

2 104.30 52.15 47.80 23.90 58.67 29.33 6.52 3.26 40.85 20.42

Size class not used for dietary risk quotients 

Table A-6. Upper Bound Kenaga, Chronic Mammalian Dose-Based Risk Quotients

Size 

Class

(grams)

Adjusted 

NOAEL

EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/Seeds Arthropods Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

15 0.22 99.44 452.44 45.58 207.4 55.93 254.50 6.21 28.28 38.95 177.2 1.38 6.28

35 0.18 68.73 386.48 31.50 177.1 38.66 217.39 4.30 24.15 26.92 151.3 0.95 5.37

1000 0.08 15.93 207.17 7.30 94.95 8.96 116.53 1.00 12.95 6.24 81.14 0.22 2.88