Page 2 of 49 

the Actellic® and Execute® labels to further minimize the potential for exposure in the 

environment. 

For cattle eartag uses, risks of concern leading to adverse impacts are not identified for any 

aquatic or terrestrial taxa considering its usage limited to pasture use sites. The number of 

treated cattle anticipated at a pasture site, does not result in any risk within the terrestrial 

environment about the treatment site or within nearby water bodies. Pirimiphos-methyl is not 

widely used at feedlots since infestations of its targeted pests, horn flies (Haematobia irritans) 

and face flies (Musca autumnalis) are not anticipated at these use sites. 
Page 3 of 49 

 

Preliminary Environmental Fate and Ecological Risk 

Assessment for the Registration Review of Pirimiphosmethyl 

O-(2-Diethylamino-6-methylpyrimidin-4-yl) O,O-dimethyl phosphorothioate 

(Pirimiphos-methyl, CAS 029232-93-7) 

Prepared by:

Justin Housenger, Biologist 

Gabe Rothman., Environmental Scientist 

U. S. Environmental Protection Agency 

Office of Pesticide Programs 

Environmental Fate and Effects Division

Environmental Risk Branch IV 

1200 Pennsylvania Ave., NW 

Mail Code 7507P 

Washington, DC 20460

Reviewed by: 

Geoffrey Sinclair, Biologist 

José L. Meléndez, Chemist 

Mah Shamim, Branch Chief
Page 4 of 49 

Table of Contents 

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

2. Use Characterization ............................................................................................................... 7

3. Exposure Characterization ...................................................................................................... 8

3.1 Transport and Dissipation Pathways .............................................................................. 11

3.2 Degradation .................................................................................................................... 11

3.3 Bioaccumulation ............................................................................................................. 12

3.4 Exposure Pathways ........................................................................................................ 12

3.5 Aquatic Exposure Analysis ............................................................................................ 15

3.6 Terrestrial Exposure Analysis ........................................................................................ 18

4. Ecological Effects Characterization ...................................................................................... 19

4.1 Aquatic Effects Summary .............................................................................................. 19

4.2 Terrestrial Effects Summary .......................................................................................... 20

4.3 Degradate toxicity ......................................................................................................... 22

4.4 ECOTOX Open Literature .............................................................................................. 23

4.5 Review of Incident Data ................................................................................................. 23

5. Risk Characterization ............................................................................................................ 24

5.1. Risk Estimation .............................................................................................................. 24

5.2. Risk Description ............................................................................................................. 26

6. Endocrine Disruptor Screening Program .............................................................................. 32

7. Federally Threatened and Endangered (Listed) Species of Concern .................................... 33

7.1 Action Area .................................................................................................................... 34

7.2 Listed Species Occurrence Associated with Registered Uses ........................................ 35

8. Conclusions ........................................................................................................................... 35

9. References ............................................................................................................................. 36

Appendix A. Environmental Fate and Ecological Effects Data for Pirimiphos-methyl .............. 38

Appendix B. Aquatic Exposure Modeling Summary .................................................................. 42

Appendix C. Inhalation Exposure Screening Evaluation ............................................................ 44

Appendix D. Drinking Water Exposure Screening Evaluation ................................................... 47

Appendix E. Degradates Summary for Pirimiphos-Methyl ......................................................... 48

 
Page 5 of 49 

1. Executive Summary 

This document contains the environmental fate and ecological risk assessments for the registered 

uses of the organophosphate chemical pirimiphos-methyl [O-(2-Diethylamino-6-

methylpyrimidin-4-yl) O,O-dimethyl phosphorothioate]. 

Pirimiphos-methyl was originally introduced in the United States in 19841. There are a number of 

active Section 3 products containing pirimiphos-methyl that include post-harvest treatment of corn 

or sorghum seeds and grain for immediate storage as well as treated ear tag products applied to 

beef and non-lactating dairy cattle or calves. Pirimiphos-methyl ear tags ultimately result in 

residues being absorbed by the hide of cattle. There are also two special local needs Section 24(c) 

labels. The Washington State label is for indoor fogger treatment on iris bulbs. Michigan labeled 

uses include dip and drench treatment to gladiola bulbs and indoor fogger treatment for gladiola 

bulbs. According to Office of Pesticide Programs Information Network (OPPIN), cancellation is 

pending for the Michigan label. 

Post harvest Stored Grain Uses 

For pirimiphos-methyl post harvest stored grain uses, it was previously concluded in the Problem 

Formulation (DP Barcode 362650, dated March 9, 2009) and reaffirmed in this assessment, that 

aquatic and terrestrial exposure resulting from the treated seed storage is limited considering the 

small application rate made to grain as well as the long interval between time of treatment and 

planting of the treated seeds. Therefore, risks of concern are not expected for the post-harvest 

stored grain uses of pirimiphos-methyl. However, while the exposure scenario associated with 

replanting treated seed is expected to be most prevalent, EFED recommends to address potential 

pirimiphos-methyl treatments to corn and sorghum grain stored at locations other than indoor 

storage bins, such as outdoor bunkers, on the Actellic® and Execute® labels to further minimize 

the potential for exposure in the environment. 

Eartag Uses 

The conceptual model in this risk assessment identifies the main potential for exposure to aquatic 

organisms associated with pirimiphos-methyl eartags uses resulting from wash off of residues and 

subsequent runoff to aquatic environments from cattle eartag applications. These applications are 

mainly expected to occur at pastureland use sites and not at feedlots (refer to the Use 

Characterization Section in Section 2 for a further description). The main uncertainties that exist 

for this scenario are the amount of cattle simultaneously treated with eartags at a given use site and 

the washoff fraction from cattle hide resulting from rainfall occurring concurrent with pirimiphosmethyl treatment. As a result of these uncertainties, risk quotients (RQs) were not estimated in 

this assessment as they would be in a deterministic fashion for conventional uses (i.e. foliar spray). 

Instead, this risk assessment addresses these uncertainties by utilizing a bracketing approach 

exploring numbers of cattle treated that would indicate a risk concern to aquatic organisms over a 

range of washoff fractions to determine the level pirimiphos-methyl treatment causing a concern. 

 

1

 http://pmep.cce.cornell.edu/profiles/insect-mite/mevinphos-propargite/pirimiphos-methyl/insect-prof-actellic.html 
Page 6 of 49 

The screening aquatic exposure model, the GENeric Estimated Exposure Concentration model 

(GENEEC) is used as the basis of the bracketing analysis described above, to assess runoff from a 

generic 10-hectare treated use site to a 1-hectare pond. The Pesticide in Water Calculator (PWC), 

which is normally used to assess runoff of pesticide residues for cropped fields, is not employed 

in this assessment given unique eartag treatment. The adverse impacts analysis initially 

incorporates the GENEEC estimated exposure concentration (EEC) in surface water normalized 

to one head of treated cattle. Then, available acute toxicity data for freshwater fish and freshwater 

invertebrates are incorporated to determine the number of head of treated cattle meeting and 

exceeding the levels of concern (LOCs) threshold for aquatic species. Additionally, the level of 

washoff or washoff fraction to result in adverse impacts to aquatic taxa is determined. As is 

discussed and justified in Section 4.3, the combined residues of parent pirimiphos-methyl along 

with the residues of O-2 diethylamino-6-methylpyrimidin-4-yl o-methyl-phosphorothioate 

(hereafter referred to as degradate No.2) will be considered the stressor of concern for ecological 

risk assessment purposes. The final results with the bracketing analysis are presented in Table 9. 

The results with the number of heads of cattle causing concern at certain levels of washoff fractions 

of residues presented in Table 9 are put into perspective with the density of cattle at expected at 

potential pastureland use sites in Risk Description Section (Section 5.2). In general, adverse 

impacts to aquatic organisms from washoff of residues from pirimiphos-methyl eartags are 

not expected considering that much of its use occurs at sites with small cattle inventories. 

While adverse impacts to listed aquatic invertebrates may occur with 5 percent of residues from 

eartags washing off into water bodies at feedlot sites keeping 40 head of cattle or less, it is not 

expected that this level of washoff would occur considering the expected reduction in 

environmental loading from factors such as its semi-volatile nature and propensity for delayed 

rainfall events during treatments not captured in this assessment. These uncertainties, discussed 

further in Section 6, provides further insights that a small portion of residues (less than 5 percent) 

are likely to washoff and end up in water bodies nearby pirimiphos-methyl eartag use sites, and 

therefore not result in risks of concern for aquatic orgnaisms. 

It is worth noting that only acute freshwater fish and invertebrate toxicity data is available. 

However, given the toxicity that is established with organophosphate (OP) insecticides to aquatic 

taxa, similar effects and thresholds will be assumed for estuarine/marine fish and invertebrates 

when used in proximity to these environments. No data are available to characterize the chronic 

toxicity of pirimiphos-methyl to aquatic species. It is an uncertainty as to what level of washoff 

would be needed to yield effects to growth or reproduction on fish or aquatic invertebrates. 

Additionally, no data are available to characterize the subchronic and chronic toxicity of 

pirimiphos-methyl to sediment dwelling invertebrates. Environmental fate data indicate 

pirimiphos-methyl has a propensity to partition to the sediment based on its range of Kd values 

(15.6 – 161.9 mL/g) and moderately high log KOW value of 4.2. 

Additionally, no data are available for vascular or non-vascular aquatic plants or terrestrial plants. 

Pirimiphos-methyl is highly toxic to adult honey bees on an acute contact and acute oral basis as 

would be anticipated from an organophosphorus (OP) insecticide. There are no data to 

characterize the acute and chronic oral toxicity to honey bee larvae. Available data indicate 

pirimiphos-methyl is highly toxic to birds on an acute oral and subacute dietary basis, however, as 
Page 7 of 49 

indicated previously, the extent as to the magnitude of residues this taxa as well as mammals would 

be exposed to is an uncertainty. 

There are also more general uncertainties as to the extent that terrestrial organisms would be 

exposed as a result of the cattle eartag use. Pirimiphos-methyl does show high levels of toxicity 

to birds on an acute oral and subacute dietary basis although toxicity is lower for mammals on an 

acute oral basis as compared to birds. The literature shows that some species of birds and mammals 

are not only present in feedlots2, but also may be responsible for the spread of certain diseases in 

cattle feedlots such as E. coli and Salmonella3. Because there are toxic effects to taxa confirmed 

to be present in pastureland use sites the estimation of a dose or concentration that would be 

available to these taxa is necessary but difficult with standard approaches. As pirimiphos-methyl 

does not have spray or granular uses, simulating exposure estimation with the Terrestrial Exposure 

Model (T-REX) is not feasible. Additionally, any exposure of pirimiphos-methyl to these taxa 

would likely originate from the eartags falling off of the cattle, a scenario that this assessment 

assumes is not frequent. 

2. Use Characterization 

In this document, only the most pertinent details regarding the Use Characterization are briefly 

summarized below. Section 3.3 of the original problem formulation document can be referred to 

for further details. 

Pirimiphos-methyl uses encompass six active registrations. The labels by FIFRA classification 

are summarized below: 

 Four Section 3 labels, and 

 Two Special Local Needs (Section 24c) labels 

Uses for the Section 3 pirimiphos-methyl registrations include cattle eartag uses (for lactating and 

beef cattle) and post-harvest stored grain seed treatments for corn and sorghum seeds. Eartags 

contain up to 3.84 grams a.i. per animal (or 1.92 grams a.i. per eartag). For post-harvest seed 

treatments, up to 0.12 lbs a.i. per 1,000 square feet of grain may be applied. There are no 

restrictions for where pirimiphos-methyl can be used nationwide. 

 

2

 Palmer, Thomas K. 1976. “Pest Bird Damage Control in Cattle Feedlots: The Integrated Systems Approach.” 

Proceeedings of the 7th Pest Vertebrate Conference,. Available online at: 

http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=1035&context=vpc7&seiredir=1&referer=http%3A%2F%2Fscholar.google.com%2Fscholar%3Fhl%3Den%26as_sdt%3D0%2C9%26q%3D

birds%2Band%2Bmammals%2Bin%2Bcattle%2Bfeedlots#search=%22birds%20mammals%20cattle%20feedlots%

22 3

 Gaukler, Shannon M et al. (2009). “Escherichia coli, Salmonella, and Mycobacterium avium subsp. 

Paratuberculosis in Wild European Starlings at a Kansas Cattle Feedlot.” Avian Diseases, 53(4):544-551. Available 

online: http://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1040&context=vmpm_pubs&seiredir=1&referer=http%3A%2F%2Fscholar.google.com%2Fscholar%3Fq%3Dbirds%2Band%2Bmammals%2Bin%

2Bcattle%2Bfeedlots%2Band%2Be%2Bcoli%26btnG%3D%26hl%3Den%26as_sdt%3D0%252C9#search=%22bir

ds%20mammals%20cattle%20feedlots%20e%20coli%22 
Page 8 of 49 

Special Local Needs uses include indoor fogger treatments using pirimiphos-methyl for 

ornamental bulbs in Washington State and Michigan. Up to 0.224 lbs. a.i. per 1,000 cubic feet of 

space may be applied for these uses. 

There are no restrictions related to the use sites where pirimiphos-methyl can be used. In addition, 

for pirimiphos-methyl eartag uses, the maximum quantity of cattle treated or the maximum 

frequency of application per use site is not specified on product labels. 

Discussion of Eartag Use Sites 

Potential pirimiphos-methyl use sites for cattle eartags, based alone on areas where cattle reside 

associated with commercial livestock production operations, may include pasture sites, rangeland, 

and feedlots. Out of all of these use sites, the feedlot use site is expected to possess the highest 

concentration of cattle by far. According to USDA’s Feedlot Report from 20114, small feedlots 

equal to or less than 1,000 head of cattle accounted for the vast majority of sites accounting for 

97.1 percent of feedlots nationwide, while larger feedlots only accounted for 2.8 percent of total 

sites. While widely variable, pasture and rangeland sites are expected to possess concentrations 

of cattle at far less head per acre than at feedlots, most of which contain no more than 1,000 head 

of cattle. 

However, while feedlots may appear to be a vulnerable use site related to insecticidal eartag use 

based on cattle density as described above, there is evidence to suggest that feedlots are not areas 

where eartags are used frequently, if at all, considering that pirimiphos-methyl eartags are used to 

control infestations of horn fly and face fly pests. Feedlots are generally not recognized as suitable 

habitats to maintain sustainable populations of horn flies and face flies since these insects require 

stagnant soils and fresh manure for their reproduction cycles with incubation of fly larvae. To this 

point, the dense presence of cattle is known to generate large and constant turnover of soil and 

manure matter at feedlots. Therefore, horn fly and face fly infestations and related pirimiphosmethyl eartag usage are expected to be most common at pasture and rangeland sites as opposed to 

feedlot sites. This information is conveyed by multiple state agricultural extension services (e.g., 

Alabama, Mississippi, Kentucky, and Nebraska) where eartag usage is common or where feedlots 

are present (refer to Section 9 for complete citations). 

3. Exposure Characterization 

Registrant-submitted data defining the physical, chemical, fate and transport characteristics 

associated with pirimiphos-methyl are summarized in Table 1. As part of registration review, 

available environmental fate studies for pirimiphos-methyl have been reevaluated. The fate and 

transport of pirimiphos-methyl in the environment is discussed below. 

 

4

 Full Citation:.U.S. Department of Agriculture (USDA). 2011. Feedlot 2011 Report, Part I: Management Practices 

on US Feedlots with a Capacity of 1,000 or More Head. United States Department of Agriculture. Available online 

at:. http://www.aphis.usda.gov/animal_health/nahms/feedlot/downloads/feedlot2011/Feed11_dr_PartI.pdf. Accesed 

December 2015. 
Page 9 of 49 

Table 1. General physical-chemical and environmental fate properties of pirimiphosmethyl.

Chemical/Fate parameter Value Source (MRID) Study Acceptability 

Physical Chemical Properties 

Chemical Structure and SMILES 

Code 

CCN(CC)c1nc(C)cc(OP(=S) 

(OC)OC)n1 

Product 

Chemistry 

(MRID 

00129333 

N/A 

Molecular Weight (g/mol) 305 Product 

Chemistry 

(MRID 

00129333) 

N/A 

Vapor Pressure (torr at 30°C) 1.1 x 10-4 Product 

Chemistry 

(MRID 

00129333) 

N/A 

Octanol-water Partition Coefficient 

(Log KOW at 20°C) 

4.2 Product 

Chemistry 

(MRID 

92147003) 

N/A 

Octanol-air Partition Coefficient 

(Log KOA) 

8.743 EPI Suite 

(KOAWIN v. 1.1 

estimate) 

N/A 

Water Solubility (mg/L; at 20°C) 9.9 mg/L at pH 5.2 

8.6 mg/L at pH 7.3 

9.3 mg/L at pH 9.3 

Product 

Chemistry 

(MRID 

92147003) 

N/A 

Henry's Law Constant (atm-m3

mol-1) 

5.105 x 10-6 EPI Suite 

(HENRYWIN v. 

3.10) 

N/A 
Page 10 of 49 

Chemical/Fate parameter Value Source (MRID) Study Acceptability 

Soil-water partition coefficients 

(Kd) 

England Soils5: 

LS1: 15.6 mL/g (OC = 1.60%) 

LS2: 27.4 mL/g (OC = 1.69%) 

LS3: 32.7 mL/g (OC = 2.97%) 

S: 11.6 mL/g (OC = 0.29%) 

SiCL: 161.9 mL/g (OC = 

1.63%) 

SL: 45 mL/g (OC = 1.92%) 

MRID 48355601 Supplemental: 

 Significant 

degradation was 

observed in low pH 

soils (S, SiCL, SL) 

Abiotic Degradation1

Hydrolysis half=lives (days) 7.3 days at pH 5 

79 days at pH 7 

54 – 62 days at pH 92

MRID 42982401

MRID 43177601

Acceptable 

Aqueous photolysis half-life (days 

at 20°C) 3

0.2 days 

IUPAC Pesticide 

Properties 

Database6

N/A 

Photolysis in air half-life (hours at 

25°C) 

2.4 hours 

0.802 hours 

SRC Database 

EPI Suite 

(AopWIN v. 

1.92) 

N/A 

Soil Photolysis half-life (days) No Data Available - N/A 

Biotic Degradation1

Aerobic Soil Metabolism half-life 

(t1/2 in days) 

England Soils5: 

SL1: 33.6 days (OC = 3.70%,

 pH7.1) 

SL2: 28.7 days (OC = 1.00%, 

pH6.6) 

L: 42.7 days (OC = 6.0%, 

 pH7.5) 

P: 31.5 days (OC = 36.2%, 

 pH6.0) 

MRID 135358 Supplemental: 

Potential degradation 

associated with the 

extraction procedures 

not addressed.

Pertinent test 

conditions (e.g., 

temperature and 

moisture content) 

throughout the studies 

not reported.

Anaerobic Soil Metabolism halflife (days) 4

England Soils5

: 

SL1: 36.4 days 

(OC = 3.7%, pH7.1) 

L: 31.5 days 

(OC = 6.0%, pH7.5) 

Aerobic Aquatic Metabolism halflife (days) No Data Available - N/A 

Anaerobic Aquatic Metabolism 

half-life (days) 

No Data Available - N/A 

Field Studies
Page 11 of 49 

Chemical/Fate parameter Value Source (MRID) Study Acceptability 

Terrestrial Field Dissipation No Data Available - N/A 

Bioaccumulation

BCF Fish 274X SRC Database 

EPI Suite 

(WSKOW v. 

1.42) 

N/A 

1

 Half-lives based on first order rate constant, k (t1/2 = ln2/k) derived from Time – Ln(Concentration) regression. 2

 Half-life range at pH9 among multiple replicates reported. 

3

 Estimated based on DT-50 value. 

4

 Half-life ranges based on replicates with flooded water soil atmosphere reported. 

5

 Soil texture identifiers: SLn: Sandy loam replicate, LSn: Loamy sand replicate, L: Loam, P: Peat, SiCL: Silty 

Clay Loam

6

 Available on-line: http://sitem.herts.ac.uk/aeru/iupac/

3.1 Transport and Dissipation Pathways 

The measured soil-water partition coefficients (Kd) for pirimiphos-methyl residues range between 

11.6 mL/g to 161.9 mL/g. These measured partition coefficients in soil are poorly correlated to 

organic carbon content (r2 = 0.012). The water solubility limit of pirimiphos-methyl ranges 

between 8.6 to 9.9 mg/L. Both pirimiphos-methyl’s values of solubility and sorption coefficients 

indicate that pirimiphos-methyl residues will partition both to the sorbed phase and dissolved phase 

in soil and aquatic sediment. Therefore, pirimiphos-methyl can be transported to offsite water 

bodies via runoff and erosion processes. 

The vapor pressure of 1.1 x 10-4 torr suggests that pirimiphos-methyl can exist in the vapor-phase. 

However, the photolysis in air half-life of between 0.802 and 2.4 hours suggests that the residence 

time of pirimiphos-methyl vapors in air will be limited. Furthermore, no VOCs (including vaporphase pirimiphos-methyl) were detected in any volatile trap in the aerobic and anaerobic soil 

metabolism studies summarized above in Table 1. The screening analysis presented in Section 

3.4 verifies that pirimiphos-methyl exposure via the air and inhalation exposure pathway is not of 

concern. 

3.2 Degradation 

The major degradation pathway for pirimiphos-methyl O-(2-Diethylamino-6-methylpyrimidin-4-

yl) O,O-dimethyl phosphorothioate) is hydrolysis, especially in acidic environments. Hydrolysis 

half-lives from laboratory studies ranged from 7.3 days at pH 5, to 79 days at pH 7 with a half-life 

of 54 – 62 days at pH 9. In acidic environments, the major degradate was 2(diethylamino)-4-

hydroxy-6-methyl pyrimidine (hereafter referred to as degradate no. 1). In the pH 5 solution, 

degradate no. 1 reached maximum levels up to 87.3 days post treatment of the overall material 

balance. In neutral and alkaline environments, degradate no. 1 was also found at major levels 

along with the degradate no. 2 (exact chemical name defined in the executive summary of this 

document). In the pH 7 solution, degradate nos. 1 and 2 reached maximum levels of 22.5 % and 
Page 12 of 49 

26.5% of the overall material balance at 90 days post-treatment, respectively. In the pH 9 solution, 

degradate no. 1 and 2 reached levels of 21.0 and 18.2%, respectively of the overall material 

balance. Degradate no. 1 did not retain the organophosphate (P=S bond) linkage, whereas 

degradate no. 2 did. 

Aqueous photolysis is also expected to be a significant degradation process for pirimiphos-methyl 

with an experimentally-determined DT50 of 0.2 days. Pirimiphos-methyl is also expected to be 

photolabile in air, with experimentally determined half-lives ranging between 0.802 – 2.4 hours 

(see Table 1 above). 

Pirimiphos-methyl degradation in soil occurs at similar rates and appears to be mediated by 

hydrolysis, with half-lives ranging between 28.7 – 42.7 days in four soils. The major metabolite 

from aerobic and anaerobic soil metabolism is degradate no. 1 (defined above) which formed at 

levels up to between 37 – 66% of applied. Major levels of unextractable residues consistently 

occurred throughout all tested soils, in the range of up to 28.2 – 66.3% of the applied material, and 

a nonpolar extraction solvent was not used to extract residues partitioned to soil. However, given 

pirimiphos-methyl’s high sorption to soil (see Section 3.1 above) and partially thorough extraction 

method utilizing acetone followed by methanol extraction solvents, residues appear to be bound 

to sediment. No Agency guideline studies have been conducted to determine the biodegradation 

of pirimiphos-methyl in water or its dissipation in the field. 

Degradate no. 1 did not maintain the organophosphate moiety (P=S bond) and is not expected to 

possess toxicity exceeding that of parent pirimiphos-methyl. However the organophosphate 

moiety was maintained with degradate no. 2. Therefore, the potential for toxicity exists with 

degradate no.2. Please refer to Appendix E for further information on the formation of degradates, 

and Table 8 of Section 4.3 supporting the findings on the toxicity of the degradates relative to 

parent-pirimiphos-methyl. 

3.3 Bioaccumulation

A log Kow of 4.2 indicates that pirimiphos-methyl is sufficiently hydrophobic for binding to fatty 

tissue for aquatic organisms as well as available sediment. While there are no BCF in fish studies 

available, a regression Kow –based model suggests that the BCF value for pirimiphos-methyl is 

approximately 274X in aquatic organisms. This BCF further indicates the high potential for 

pirimiphos-methyl residues to build up in the tissues of aquatic biota. 

3.4 Exposure Pathways 

Pirimiphos-methyl and its organophosphate demethylated degradate [degradate No. 2] are 

considered to be the primary stressors in this risk assessment. The degradate formed at major 

levels of up to 26.5% of applied due to hydrolysis (at pH7). For further information on the 

formation of degradates please refer to Appendix E. Furthermore, the degradate’s toxicity is 

likely similar to the parent compound given its similar organophosphate moiety. Please refer to 

Table 8 of Section 4.3 supporting the findings on the toxicity of the degradates relative to parent-
Page 13 of 49 

pirimiphos-methyl. Given the similar moieties between parent pirimiphos-methyl and the 

degradate, this risk assessment will use a total toxic residues approach in exposure estimates 

assuming equal toxicity for both constituents. 

Potential exposure to aquatic and terrestrial organisms with pirimiphos-methyl exists only with 

cattle eartag and post-harvest grain seed treatment uses. There is no ecological risk associated 

with the indoor fogger treatment to iris included in the Washington State Section 24(c) label and 

the indoor fogger, dip, and drench treatments to gladiola bulbs in the Michigan Section 24(c) label. 

The identification of relevant environmental exposure pathways to pirimiphos-methyl applications 

for this risk assessment evaluating impact to non-target organisms are discussed below: 

 Aquatic Exposure: Pirimiphos-methyl may impact aquatic environments after off-site 

movement mainly from pasture use sites associated with cattle ear tag uses for lactating and 

beef cattle. Pirimiphos-methyl residues from treated cattle with eartags may washoff from 

treated cattle and become embedded within runoff in an accumulated form from pastures. 

Freshwater and estuarine marine fish and invertebrates as well as aquatic plants in the water 

column may be impacted. In addition, benthic organisms residing in the bottoms of water 

bodies may also be impacted given pirimiphos-methyl’s tendency to partition to sediment. 

Refer to Section 3.5 of this document for the aquatic exposure assessment. Section 3.5

describes the use of GENEEC to evaluate pirimiphos-methyl cattle treatments at pasture use 

sites. 

Given pirimiphos-methyl’s low application rates with post-harvest stored grain seed

treatments, there is a smaller potential for exposure resulting from runoff of pirimiphosmethyl residues to nearby water bodies associated with this use pattern. Nonetheless, this 

exposure pathway was evaluated in Attachment A in the original problem formulation 

document (DP Barcode No. 362650, dated March 9, 2009). Please refer to this document 

for further details. 

 Dietary Exposure: Birds and mammals can potentially be impacted through dietary routes 

resulting mainly from pirimiphos-methyl post-harvest stored grain seed treatment residues. 

Pirimiphos-methyl residues may be bioavailable on harvested corn and sorghum seeds 

which are harvested, treated during storage, and then re-planted the next season. The dietary 

exposure analysis for pirimiphos-methyl was completed in a memo responding to a waiver 

request for an avian reproduction study (DP Barcode 357626, dated February 18, 2011). 

The analysis using the T-REX model (version 1.4.1, 12/07/2006) showed that there were no 

adverse impacts associated with post-harvest seed treatment uses for pirimiphos-methyl and 

therefore this pathway will not be further addressed in this assessment. This model has since 

been updated to version 1.5.2 (06/11/2013) but the conclusions remain the same. Please see 

the data waiver response memo for details. T-REX is publically available at the following 

website: 

http://www.epa.gov/oppefed1/models/terrestrial/trex/t_rex_user_guide.htm

Furthermore, piscivorous birds and mammals feeding on contaminated fish may potentially 

be exposed with pirimiphos-methyl residues bioavailable from exposed aquatic organisms 
Page 14 of 49 

primarily due to washoff and subsequent runoff associated with eartag uses. 

Bioaccumulation of pirimiphos-methyl residues is possible in fish given pirimiphos-methyl’s 

Log Kow value of 4.2. There is no quantitative method available to evaluate this route of 

exposure for the eartag use. The KOW-based Aquatic BioAccumulation (KABAM, v.1.0) 

model is available but without all necessary inputs available. Please see the Risk Description 

section for an analysis with KABAM using conservative assumptions. Fixed equivalent 

maximum application rates cannot be defined with eartag uses given the nature of this use 

pattern and information available on labels. The application rate is a key factor for 

determining the amount of pirimiphos-methyl residues bioavailable to piscivorous birds 

since it largely impacts the water body concentrations which can be expected. Please refer 

to the Risk Description Section (Section 5.2) for further discussion regarding risks which 

may occur resulting from this exposure pathway as well as a description of the uncertainties 

which exist related to this exposure pathway for pirimiphos-methyl. 

 Terrestrial plants and Terrestrial Invertebrates: Sporadic and low density of pirimiphosmethyl residues are expected on pasurelands with cattle treated are expected. As eartag uses 

are not associated with a foliar spray, there would be no drift expected from these uses of 

pirimiphos-methyl. Therefore, exposure to terrestrial plants and terrestrial invertebrates 

which forage on and around plants will be limited. 

 Drinking water exposure: An analysis using the Screening Imbibition Program (SIP 

version 1.0, 6/15/2010) indicated that drinking water exposure alone is not a potential 

concern for mammals on an acute basis. Conversely, exposure though drinking water alone 

is a potential concern for mammals on a chronic basis as well as for birds on an acute basis. 

As an avian reproduction study is not available for pirimiphos-methyl, risk could not be 

precluded from the model. There is currently no refinement in the risk assessment process 

to further characterize the likelihood of this exposure pathway being complete or the relative 

risk associated with this pathway. It is an uncertainty whether significant residues of 

pirimiphos-methyl would exist in puddles present in feed lots as well as the frequency to 

which birds and other mammals visit these feed lots to potentially be exposed through 

drinking water. SIP is available publically at: 

http://www.epa.gov/oppefed1/models/terrestrial/sip/sip_user_guide.html

 Inhalation exposure to terrestrial animals: The potential for pirimiphos-methyl inhalation 

exposure only exists via the vapor-phase. Inhalation to spray droplets would not exist for 

pirimiphos-methyl since it is not applied in a spray form for eartag and seed treatment uses. 

The STIR model is used to initially evaluate this exposure pathway. The Screening Tool for 

Inhalation Risk (STIR, version 1.0; 11/23/2010)model relies on user-inputs of vapor pressure 

as well as mammal inhalation, mammal oral, and inhalation oral toxicity data to determine 

need to address the inhalation exposure pathway in the risk assessment. The results of STIR, 

indicate the need to proceed to further refinements only for birds, as indicated by the ratio of 

vapor dose to adjusted inhalation LD50 is a value that indicates the need to proceed to 

refinements. STIR may be accessed on-line at:

http://www.epa.gov/oppefed1/models/terrestrial/stir/stir_user_guide.html

 The likelihood of exposure via inhalation for birds can be explored further using the Health 
Page 15 of 49 

Effects Division (HED) Tier 1 Air Exposure Model (Tool Developed by Chuck Peck, version 

1, dated 7/22/13). However, it should be noted that this model accounts for vapor-phase 

release from soil surfaces, and can depict the potential release of pirimiphos-methyl from the 

grounds of pasturelands after it washes off from eartags. Since no off-gasing data are 

available for pirimiphos-methyl from eartags, exposure resulting from pirimiphos-methyl’s 

release from soil can only be assessed. As such, this exploration will conservatively assume 

that 100 percent of pirimiphos-methyl are available to off-gas from the grounds of pastures 

after washoff from the eartags. The HED Tier 1 Air Exposure Model contains additional 

physical chemical properties such as vapor pressure, solubility, and soil-water partition 

coefficients to determine the upper-bound volatile flux rate of pirimiphos-methyl from soil. 

This flux rate is carried over to EPA’s AERSCREEN dispersion model to determine the 

resulting vapor-phase estimated exposure concentration (EEC) in air. Given the equivalent 

avian LC50 value of 930.75 g/m3 in air estimated from STIR5 for birds and air EEC 43.48 

g/m3 (equivalent to a risk quotient of 0.05), a more refined analysis for inhalation exposure 

of pirimiphos-methyl released from soil in the vapor-phase is not needed. 

The analyses using the STIR model and HED Tier 1 Air Exposure model is presented in 

detail in Appendix C. 

3.5 Aquatic Exposure Analysis 

Post-Harvest Stored Grain Seed Treatment Uses

Please refer to Attachment A of the original problem formulation document (DP Barcode No. 

362650, dated March 9, 2009) for the evaluation of aquatic exposure resulting from post-harvest 

seed treatment uses of pirimiphos-methyl. Upper-bound estimated exposure concentrations 

(EECs) in surface water were calculated using the pe5 shell for the PRZM/EXAMS model, ranging 

up to 0.002 μg/L.6

Cattle Ear Tag Uses

Attachment B of the original problem formulation document also presented a preliminary analysis 

of aquatic exposure occurring from ear tags. However, the exposure analysis is updated in this 

risk assessment. The exposure analysis presents an evaluation of the number of heads of treated 

cattle leading to adverse impacts (i.e., LOC exceedances) rather than deterministic risk quotients 

 

5 The equivalent avian inhalation endpoint of 930.75 g/m3

 is calculated from the dose-based adjusted avian 

inhalation LD50 of 0.468 mg/kg-bw determined from STIR (see Table C.1, Appendix C). The conversion is 

shown as follows, based on equation 9 within the STIR User’s Manual: 

LC50 = LD50 adjusted / (Abs x CF x D x A)] x 1,000 L/m3

 x 1,000 g/mg= 930.75 g/m3 

where LD50 adjusted = 0.468 mg/kg-bw, Abs (chemical absorption into tissue) = 1.0, D (exposure duration) = 4 

hours, A (animal activity factor at rest) = 1.0, CF {conversion factor = [avian inhalation rate (2,514.1 cm3

/hr) x 

0.001 L/cm3]/body weight (0.02kg)} = 502.82 L/hr 

6

It should be noted that Kd/Koc and aerobic soil metabolism half-lives inputs used in the exposure analysis for postharvest seed treatments in the problem formulation were different from the analysis with eartag uses presented in 

this document considering the preliminary review status of environmental fate studies at that time. However, all 

inputs utilized in the problem formulation result in a conservative assessment of exposure. 
Page 16 of 49 

based on an exposure scenario for which ecotoxicological data are available (freshwater fish and 

invertebrates). This approach captures of range of outcomes possible associated with potential 

aquatic exposure with pirimiphos-methyl eartag usage while considering two major uncertainties: 

1.) The amount of cattle that is simultaneously treated with pirimiphos-methyl, and 2.) The 

amount washoff or washoff fraction from the treated cattle to the feedlot, which is then available 

for runoff to nearby water bodies. 

Since runoff of pirimiphos-methyl is being evaluated, aquatic exposure models can be used to 

evaluate the amount of pirimiphos-methyl eartgas that would be required to runoff in sufficient 

quantities to trigger adverse impacts to listed and non-listed aquatic species. The screening aquatic 

exposure model GENEEC (latest version dated 10/10/14, developed by Ron Parker) is used for 

this evaluation given that it uses a runoff scenario (modified to exclude spray drift) from a generic 

10-hectare treated area to a 1-hectare pond. The Surface Water Concentration Calculator (SWCC), 

which is normally used to assess runoff of pesticide residues for cropped fields, is not employed 

in this case given the unique use pattern for eartags. The adverse impacts analysis incorporates 

the GENEEC estimated exposure concentration (EEC) in surface water normalized to one head of 

treated cattle and available acute toxicity data for freshwater fish and freshwater invertebrates to 

determine the number of head of treated cattle meeting and exceeding the acute listed and nonlisted levels of concern (LOCs) for aquatic species. This analysis is presented in Section 5.1. 

The exposure analysis for pirimiphos-methyl use at pastureland use sites will evaluate the potential 

exposure which occurs from heads of cattle treated simultaneously. It will be assumed that each 

head of cattle possesses two eartags containing 1.92 grams a.i. each for a total of 3.84 grams (8.47 

x 10-3 lbs.) total of pirimiphos-methyl as permitted by the label. From this scenario, an application 

rate can be calculated with the initial assumption that the total amount of pirimiphos-methyl 

washes off from the treated cattle, is available for runoff, and that the resulting residue will be 

evenly distributed with the 10-hectare treated pasture. From these assumptions, an equivalent 

application rate normalized to one head of treated cattle can be calculated considering the 3.84 

grams (8.47 x 10-3 lbs.) of pirimiphos load with each head of cattle and the 10-ha treated area. The 

resulting equivalent application rate is 3.43 x 10-4 lbs./A per head of cattle [8.47 x 10-3 lbs. ÷ (10 

ha x 2.47 A/ha)]. Use sites larger than 10 hectares are not evaluated since the amount of treated 

cattle is expected to be proportional to the pasture site size impacted by runoff. Therefore, the 

total pirimiphos-methyl runoff mass per unit area is expected to be conserved over all pasture land 

use site sizes and thus the effective application rate should not be impacted. 

However, the major uncertainty is the fraction of pirimiphos-methyl that could potentially wash 

off from treated cattle. The 3.43 x 10-4 lbs./A value is a high-end application rate assuming 100% 

of pirimiphos-methyl residues washes off. Therefore, this aquatic exposure analysis will use a 

bracketing technique, where the equivalent application rate is linearly proportional to the amount 

that washes off. Accordingly, the application rates for each of the washoff fractions (evaluated for 

100%, 20%, 10%, 5%, and 1%) from treated cattle are shown in Table 3.

The remaining parameterization for GENEEC is composed of the physical chemical and fate 

properties of pirimiphos-methyl utilizing EFED Model Input Parameter Guidance7

. All input 

parameter values for the aquatic exposure assessment for pirimiphos-methyl cattle eartags are 

 

7

 Available on-line: http://www.epa.gov/oppefed1/models/water/input_parameter_guidance.htm
Page 17 of 49 

shown in Table 2. 

Table 2. Input parameter values used in GENEEC for pirimiphos-methyl adverse impacts 

analysis for cattle ear tag uses at pasture use sites. 

GENEEC Input Parameter Input Value and 

Unit Comment Source 

Application Rate 

(lbs. a.i./A per head of treated cattle) 

See Table 3 Based on 3.84 grams 

of pirimiphosmethyl per head of 

treated cattle and 10-

hectare use site size 

for specified 

washoff fraction 

Product label and 

standard runoff 

exposure scenario 

evaluated 

Application Method Broadcast1 No Spray Drift, 

Incorporated to 

Surface Only 

Consistent with washoff 

scenario for eartag use 

Hydrolysis (t1/2) 198 days Total Toxic Residue 

half-life including 

parent pirimiphosmethyl and its OP 

demethylated 

degradate (see 

Section 3.2 and 

Appendix E for 

chemical name and 

identification) at pH 

7 

MRID Nos. 42982401 

& 43177601 

Aerobic soil metabolism (t1/2) 39.1 days Parent only, OP 

demethylated 

degradate not 

detected in study 

90th percentile on the 

upper confidence 

bound half-life from 

n=4 soils (refer to 

Table 1) 

MRID 135358 

EFED Model Input 

Parameter Guidance 

Aerobic aquatic metabolism (t1/2) Stable Conservative 

assumption 

- 

Solubility in Water at 20oC 8.6 mg/L Product Chemistry Product Chemistry 

(MRID 92147003) 

Soil-Water Partition Coefficient (Kd) 49.03 mL/g Average value from 

n=6 soils (refer to 

Table 1) 

MRID 48355601 

EFED Model Input 

Parameter Guidance 

Aqueous Photolysis (t1/2) 0.2 days DT-50 value IUPAC Pesticide 

Properties Database2

1

 Broadcast application method consistent with chemical distribution associated with granular application as defined 

in GENEEC. 

2

 Available on-line: http://sitem.herts.ac.uk/aeru/iupac/

The resulting EEC normalized to one head of treated cattle for each washoff fraction evaluated is 
Page 18 of 49 

provided in Table 3 (see Appendix B for the sample GENEEC file). The EECs normalized to 

one head of treated cattle along with endpoints available from freshwater fish and freshwater 

invertebrate toxicological studies will be used to compute the number of treated cattle leading to 

adverse impacts resulting from eartag use. This analysis is possible since the EECs are directly 

proportional to the amount of cattle treated, assuming all cattle possess the same number of eartags. 

In this assessment, all cattle are assumed to contain two eartags, one on each ear. The normalized 

EECs to one head of cattle shown in Table 3 is used to determine the amount of treated cattle 

leading to adverse impact. This evaluation is presented in Section 5.1. 

Table 3. GENEEC pirimiphos-methyl surface water EECs at equivalent application rates 

normalized to one head of treated cattle for certain washoff fractions.

Input/Output Variable Washoff Fraction 

100% 20% 10% 5% 1% 

Equivalent Application Rate 

(lbs. a.i./A per head of treated 

cattle)a,b

3.43 x 10-4 6.85 x 10-5 3.43 x 10-5 1.71 x 10-5 3.43 x 10-6

Surface Water EECs 

(μg/L per head of treated 

cattle)b

2.49 x 10-3 4.98 x 10-4 2.49 x 10-4 1.25 x 10-4 2.49 x 10-5

a For calculation of the equivalent application rate, please refer to the discussion above Table 2. b

 Based on 10-hectare size use site. 

Water Quality Monitoring Data 

According to a recent search of existing monitoring databases, there are no surface water or ground 

water data monitoring data available for pirimiphos-methyl. However, this does not indicate that 

detections of pirimiphos-methyl are not possible, especially in the vicinity of pasture lands where 

pirimiphos-methyl is used. Rather, EFED is not aware of any attempts to measure pirimiphosmethyl in the environment. Therefore, this risk assessments relies solely on upper-bound exposure 

estimates provided by environmental fate and transport models such as GENEEC. 

3.6 Terrestrial Exposure Analysis 

Please refer to the memo that was completed in response to a waiver request related to the Avian 

Reproduction study (DP Barcode 357626, dated February 18, 2011) for the terrestrial exposure 

assessment for pirimiphos-methyl uses. This memo contains the dietary exposure analysis for 

pirimiphos-methyl resulting from post-harvest stored grain steed treatment use. The analysis used 

label information to calculate upper-bound exposure concentrations bioavailable to birds and 

mammals using the TREX model (version 1.3.1, 12/07/2006). This model has since been updated 

to version 1.5.2 (06/11/2013) but the conclusions remain the same. 

As stated in Section 3.4., there is limited exposure to non-target terrestrial organisms associated 

with the cattle eartag uses of pirimiphos-methyl. It cannot be stated with certainty that non-target 

terrestrial organisms would not be present at a pasture use site but it is not expected that terrestrial 

organisms would be exposed to pirimiphos-methyl residues to a large extent. Therefore, no further 

analysis addressing exposure to non-target terrestrial organisms resulting from pirimiphos-methyl 

cattle eartag uses is presented in this risk assessment. 
Page 19 of 49 

4. Ecological Effects Characterization 

The ecological effects characterization for pirimiphos-methyl is based upon registrant-submitted 

toxicity data for the TGAI (parent pirimiphos-methyl) and for specified formulations. 

4.1 Aquatic Effects Summary 

Pirimiphos-methyl exposure effects on aquatic organisms were determined by assessing 

freshwater fish and freshwater invertebrates. For these two taxa, only acute exposure studies were 

available. There were no acute or chronic studies available for estuarine/marine fish and 

invertebrates nor for any aquatic plant species. Additionally, there were no data available to 

evaluate the subchronic and chronic toxicity of pirimiphos-methyl to sediment dwelling 

invertebrates. Each study’s species tested, endpoint, and MRID number are tabulated below 

separated by taxa. 

Toxicity to Freshwater Fish

There are two acute freshwater fish toxicity studies available for pirimiphos-methyl. In an acute 

study conducted with the rainbow trout (Oncorhynchus mykiss, MRID 00103924), fish were 

exposed to pirimiphos-methyl concentrations (88.9% purity) ranging from 0.18 to 0.75 mg a.i/L 

in a continuous flow-through system. Total (100%) mortality occurred at the highest treatment 

concentration. Clinical signs of toxicity included darkening of skin and gill inflammation but these 

effects were not quantified in the individual treatment concentrations. The 96-hour LC50 was 

determined to be 0.40 mg a.i/L (95% CI: 0.34 – 0.45) and this study is classified as acceptable. 

In an acute toxicity study conducted with both rainbow trout and bluegill sunfish (Lepomis 

macrochirus, MRID 00103925), fish were exposed at concentrations ranging from 0.33 – 2.2 mg 

a.i/L and 1.0 – 4.7 mg a.i/L, respectively. There were no clinical signs of toxicity observed in the 

rainbow trout study but in the bluegill sunfish study, signs of toxicity included rapid jaw 

movements, disorientation, keeling, and gill inflammation (concentrations at which the signs were 

observed were not reported). The 96-hour LC50 values for rainbow trout and bluegill sunfish were 

determined to be 1.18 (0.98 – 1.47) and 2.80 (2.46 – 3.10) mg a.i/L, respectively. This study is 

classified as acceptable. 

Table 4. Summary of Acute Toxicity Data for Freshwater Fish Exposed to Pirimiphosmethyl 

Species Study Duration 

(Exposure System) 

Purity of Test 

Substance (as %) 

LC50 (mg 

a.i/L)1,2,3 

(95% CI; 

slope) 

Toxicity 

Classification 

(MRID) 

Rainbow trout 

(Oncorhynchus mykiss) 

96-hour (flowthrough) 88.9 0.40 (0.34 – 

0.45; 8.04) 

Highly toxic 

(00103924) 
Page 20 of 49 

Species Study Duration 

(Exposure System) 

Purity of Test 

Substance (as %) 

LC50 (mg 

a.i/L)1,2,3 

(95% CI; 

slope) 

Toxicity 

Classification 

(MRID) 

Rainbow trout 96-hour (flowthrough) 84 

1.18 (0.98 – 

1.47; N/A) Moderately toxic 

Bluegill sunfish (Lepomis (00103925) 

macrochirus) 

2.80 (2.46 – 

3.10; 10.5) 

CI: Confidence interval. LC50: Lethal concentration to 50% of the population. N/A = not applicable 1

Bolded values represent the most sensitive toxicity endpoints for freshwater fish exposed to parent pirimiphosmethyl 

2

Based on mean measured concentrations. 

There is one acute freshwater invertebrate toxicity study available for pirimiphos-methyl. In a 

study with Daphnia magna (MRID 00103926), organisms were exposed to both TGAI (99.5% 

purity) and formulated pirimiphos-methyl (50% purity) at varying concentrations. TGAI and 

formulated product exposures ranged from 0.01 – 50 μg a.i/L. There was no mention of any 

clinical signs of toxicity being observed throughout the study. The 48-hour EC50 was determined 

to be 0.21 μg a.i/L (0.15 – 0.31) and 0.11 μg a.i/L (0.08 – 0.15) for TGAI and formulated 

pirimiphos-methyl, respectively. This study was classified as acceptable for the TGAI component 

and supplemental for the formulated product component. The rationale for supplemental status 

for the formulated product component was that there was no need to cite a formulation study at 

the time of the review. It was further stated this classification could be upgraded to acceptable if 

that status changed. 

Table 5. Summary of Acute Toxicity Data for Freshwater Invertebrates Exposed to 

Pirimiphos-methyl 

Species Study Duration 

(Exposure System) 

Purity of Test 

Substance (as %) 

LC50 (μg 

a.i/L)1 

(95% CI; 

slope) 

Toxicity 

Classification 

(MRID) 

Water flea 

(Daphnia magna) 48-hour (flow-through) 

99.5 0.21 (0.15 – 

0.31; N/A) Very highly toxic 

(00103926) 50 0.11 (0.08 – 

N/A) 

CI: Confidence interval. LC50: Lethal concentration to 50% of the population. N/A = not applicable 1

Based on mean measured concentrations. 

4.2 Terrestrial Effects Summary 

There is one avian acute oral and three avian subacute dietary studies available for pirimiphosmethyl. In an acute oral study with the northern bobwhite quail, birds were exposed to control or 

nominal treatment doses of 19.4, 32.4, 54, 90, 150, and 250 mg a.i/kg bw. There was total (100%) 

mortality in the three highest doses and 80% mortality in the 54 mg a.i./kg bw group. Clinical 

signs of toxicity were observed at all but the lowest treatment group (19.4 mg a.i/kg bw) that 

included ruffled appearance, depression, reduced reaction to external stimuli, loss of coordination, 

wing droop, lower limb weakness, walking stiffly, prostrate posture, shallow and rapid breathing, 

salivation, loss of righting reflex, minor muscle fasciculations, and muscle spasms. A marked 

weight loss was also observed at these treatment doses. The 14-day LD50 was determined to be 
Page 21 of 49 

40 mg a.i/kg (32 – 50). This study was classified as acceptable (Table 6). 

In a subacute dietary study with the mallard duck, birds were exposed to control or concentrations 

in the diet of 215, 464, 1000, 2150, and 4640 ppm. Total (100%) mortality was observed in the 

two highest treatment concentrations and 80% at the middle treatment concentration (1000 ppm). 

Clinical signs of toxicity included lethargy, labored respiration, and loss of coordination. The 8-

day LC50 was determined to be 633 ppm (453 – 883). This study is classified as acceptable (MRID 

00107422). 

In a subacute dietary study with the northern bobwhite quail, birds were exposed to control or 

concentrations in the diet of 21, 46, 100, 215, and 464 ppm. Total (100%) morality was observed 

in the highest treatment concentration. Clinical signs of toxicity included wing droop, depression, 

loss of coordination, and loss of righting reflex. This study is classified as acceptable (MRID 

00107423). In a second dietary study conducted with the mallard duck, birds were exposed to 

control or concentrations of 163, 325, 650, 1300, 2600, and 5200 ppm. Total (100%) mortality 

was observed at the four highest treatment concentrations and 60% was observed at the 325 ppm 

treatment concentration. Clinical signs of toxicity were observed at the five highest treatment 

concentrations and included subdued behavior, huddling together, unsteadiness of gait, drooped 

wings, and stumbling/lying on the pen floor. The 8-day LC50 was determined to be 284 ppm (164 

– 643). This study (MRID 42037001) is classified as supplemental since there was no 

confirmatory analysis of concentrations in the feed was conducted. 

Table 6. Summary of Acute Oral and Subacute Dietary Toxicity for Birds Exposed to 

Pirimiphos-methyl 

Species Study Type Purity of Test 

Substance (as %) 

LD50 (mg a.i/kg bw) 

or LC50 (mg a.i/kg 

diet)1,2 

(95% CI; slope) 

Toxicity 

Classification 

(MRID) 

Northern Bobwhite quail 

(Colinus virginianus) 

Avian 

Acute Oral 89.8 40 (32 - 50; 7.3) Highly toxic (43442101) 

Mallard duck (Anas 

platyrhynchos) 

Subacute 

Dietary 

Not specified (study 

report did indicate 

TGAI) 

633 (453 – 883; N/A) Moderately toxic 

(00107422) 

Northern Bobwhite quail 

(Colinus virginianus) 

Subacute 

dietary 

Not specified (study 

report did indicate 

TGAI) 

207 (106 – 407; N/A) Highly toxic 

(00107423) 

Northern Bobwhite quail 

(Colinus virginianus) 

Subacute 

dietary 89.3 284 (164 – 643; N/A) Highly toxic 

(42037001) 

CI: Confidence interval. LD50: Lethal dose to 50% of the population. N/A = not applicable 1

Bolded values represent the most sensitive toxicity endpoints for birds exposed to pirimiphos-methyl 2

Based on mean measured concentrations. 

Mammals 

In an acute oral study available for pirimiphos-methyl, formulated (75.4% purity) product was 

administered to rats (MRID 00126257). There are no acute oral studies available for rats with 

technical pirimiphos-methyl. The actual treatment levels the rats were exposed to was not 

available in the DER and the study report was difficult to interpret. The LD50 was determined to 

be >2400 mg/kg, which classifies pirimiphos-methyl as practically non-toxic to mammals on an 
Page 22 of 49 

acute oral basis. Clinical signs of toxicity included diarrhea, lethargy, decreased respiratory rate, 

and body tremors at the lowest treatment dose. There was no mortality in the lowest treatment 

dose and 75 and 100% mortality in the middle and highest treatment doses, respectively. This 

study was classified as acceptable. 

In a two generation reproduction study, rats were fed diets containing technical pirimiphos-methyl 

(86.7% purity) at dose levels of control, 10, 40, and 160 ppm. There were no treatment related 

effects observed on any reproductive parameters. There was a reduction in body weight (percent 

effect or statistical significance not indicated in DER or study report) at the highest treatment 

concentration. There were sporadic findings of clinical signs of toxicity that were not associated 

with any one generation nor were they observed in a dose responsive manner. These included hair 

loss, swollen forepaw, protruding eyes, piloerection, and trembling. The most sensitive endpoint 

was significant (p<0.05) plasma cholinesterase inhibition that occurred at all treatment 

concentrations and therefore a definitive NOAEL could not be established. 

Table 7. Summary of Acute Oral and Chronic Toxicity for Mammals Exposed to 

Pirimiphos-methyl 

Species Study Type Purity of Test 

Substance (as %) 

LD50 (mg a.i/kg bw) or 

NOAEL (effects)1 

(95% CI; slope) 

Toxicity 

Classification 

(MRID) 

Norway rat (Rattus 

norvegicus) 

Acute oral 

toxicity 75.4 >2400 (N/A; N/A)

Practically nontoxic 

(00126257) 

2-generation 

reproduction 86.7 <10 ppm (cholinesterase inhibition) 

-- 

 (43726801) 

CI: Confidence interval. LD50: Lethal dose to 50% of the population. N/A = not applicable 1

Bolded values represent the most sensitive toxicity endpoints for mammals exposed to pirimiphos-methyl 

Terrestrial Invertebrates 

There is one study available to characterize the acute contact and oral toxicity to adult honey bees. 

The study (MRID 05001991) tests several other chemicals and only provides the acute contact and 

oral LD50 determinations with no accompanying information on sublethal effects, confidence 

intervals, or any other narrative pertaining to study design and test methods. The acute contact 

and acute oral LD50 were determined to be 0.13 and 0.39 μg a.i/bee, respectively which classifies 

pirimiphos-methyl as very highly toxic to honey bees. 

4.3 Degradate toxicity 

As described in Section 3.2, pirimiphos-methyl is subject to degradation to various products via 

multiple pathways. There are no available toxicity studies to characterize the toxicity of the 

degradation products of pirimiphos-methyl. Therefore, the ECOSAR (v.1.1) module of EPISUITE 

(v.4.1) was employed to estimate the toxicity of these degradates as compared to the registrant 

submitted studies available for parent pirimiphos-methyl. ECOSAR uses structure activity 

relationships (SAR) to predict the toxicity of compounds that share similar structural moieties. For 

each degradate of pirimiphos-methyl, the most sensitive (i.e. lowest) estimate of toxicity for a 

given taxa was tabulated below in Table 8. Also shown are the ECOSAR estimates for parent 
Page 23 of 49 

pirimiphos-methyl which corroborate the registrant submitted toxicity study for freshwater fish 

but under predict the toxicity to freshwater invertebrates by approximately one order of magnitude. 

Environmental fate data indicate that two major (i.e >10% of the applied residues) degradates form 

in the available hydrolysis study. One degradate (degradate No.2), forming as a result of 

demethylated pirimiphos-methyl, preserves the organophosphate moiety of the parent compound. 

Accordingly, ECOSAR results shown in Table 8 below estimates similar toxicity of this degradate 

to that of parent pirimiphos-methyl. A second degradate, 2(diethylamino)-4-hydroxy-6-methyl 

pyrmidine (degradate No. 1), which loses the organophosphate moiety, is estimated by ECOSAR 

to be at least three orders of magnitude less toxic to freshwater fish and invertebrates on an acute 

and chronic exposure basis. Please refer to Section 3.3 and Appendix E on the formation of this 

degradate. Based on this analysis, the stressor of concern for ecotoxicological risk will be the 

combined residues of parent pirimiphos-methyl and its demethylated organophosphate degradate 

(i.e. degradate no. 2). 

Table 8. ECOSAR predicted toxicity (mg a.i/L) of the degradates of pirimiphos-methyl 

Stressor (Endpoint Source) 

Endpoint (in mg a.i/L) 

Freshwater 

Fish LC50 

Freshwater 

Invertebrate 

EC50

Chronic 

Freshwater Fish 

NOAEC 

Chronic 

Freshwater 

Invertebrate 

NOAEC 

Pirimiphos-methyl (registrant 

submitted studies) 0.4 0.00021 

Pirimiphos-methyl (ECOSAR 

estimates) 0.23 0.002 0.033 0.00000007 

2(diethylamino)-4-hydroxy-6-

methyl pyrimidine(degradate 

no. 1) (ECOSAR estimates) 

396 39.1 40.7 2.68 

O-2 diethylamino-6-

methylpyrimidin-4-yl omethyl-phosphorothioate 

(degradate no.2) (ECOSAR 

estimates) 

0.24 0.001 0.035 0.00007 

4.4 ECOTOX Open Literature 

Open literature studies are identified using EPA’s ECOTOXicology database (ECOTOX) 

(USEPA, 2007c), which employs a literature search engine for locating chemical toxicity data for 

aquatic life, terrestrial plants, and wildlife. The evaluation of both sources of data can also provide 

insight into the direct and indirect effects of pesticides on biotic communities from loss of species 

that are sensitive to the chemicals and from changes in structure and functional characteristics of 

the affected communities. A search of ECOTOX in October, 2014 yielded no endpoints more 

sensitive than those already available. 

4.5 Review of Incident Data 

The ecological incident information system (EIIS) is an EFED-maintained database that houses 

ecological incidents that have been reported to the Agency. When available, EIIS includes date 
Page 24 of 49 

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

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

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

according to the certainty that the incident resulted from pesticide exposure. The OPP-maintained 

Incident Database System (IDS) and the Aggregate Incident Database provide incident counts at 

the chemical and product level but do not provide the narrative information contained in EIIS. The 

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

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

Many of the incidents listed in this database are also in the EIIS. Searches of the incident databases 

were conducted in November, 2014. 

A search of EIIS, the IDS, Aggregate Incident Database, and AIMS returned no reported wildlife 

incidents involving pirimiphos-methyl. 

5. Risk Characterization 

5.1. Risk Estimation 

Aquatic Exposure: Post-Harvest Stored Grain Seed Treatment Uses

PRZM/EXAMS runs (via pe5 shell) using the Georgia Farm Pond scenario, presented in the 

original problem formulation document do not indicate a concern for exposure to aquatic 

organisms in surface water with acute (one-in-ten year peak) pirimiphos methyl surface water 

EECs < 0.0018 ppb and chronic (one-in-ten year 60-day average) pirimiphos-methyl EECs < 

0.0007 ppb8. The EECs result in risk quotients (RQs) for acute freshwater fish of <<0.01 and 

<0.01 for acute freshwater invertebrates9

. Despite pirimiphos-methyl’s potential for off-site 

movement, the most likely reason for low EECs is the very low application rate on treated seed. 

It is noted that the EECs are conservative since the amount of pirimiphos-methyl available for offsite transport was based on a standard seed treatment use whereby degradation during storage time 

as well as release of residues from treated seeds were not taken into account. Since this analysis 

presented in the problem formulation did not reveal risk quotients above the level of concern, 

aquatic risks are not expected and therefore, are not further evaluated in this assessment. 

Environmental exposure from pirimiphos-methyl grain treatments are not expected during its 

application since the labels instruct pirimiphos-methyl to be applied as grain is stored. The Actellic 

label is especially explicit restricting use-sites off of farms. EFED recommends similar explicit 

language for the Execute label, which is the only other product used for post harvest grain storage 

treatments. Furthermore, for both labels, EFED recommends restricting pirimiphos-methyl use to 

corn and sorghum grain that is contained indoors or otherwise in storage containers, and 

 

8

 It should be noted that Kd/Koc and aerobic soil metabolism half-lives inputs used in the exposure analysis for postharvest seed treatments in the problem formulation were different from the analysis with eartag uses presented in 

this document considering the preliminary review status of fate studies at that time. However, all inputs utilized in 

the problem formulation result in a more conservative assessment of exposure. 

9

 Based on surface water EEC and freshwater fish LC50 = 404 ppb (MRID No. 00103924) and freshwater 

invertebrate EC50 = 21 ppb (MRID No. 00103926). 
Page 25 of 49 

prohibiting its use in outdoor bunkers to more explicitly ensure the intentional use of pirimiphosmethyl while minimizing exposure in the environment. 

Aquatic Exposure: Cattle Ear Tag Uses

As mentioned in Section 3.5, this risk estimation presents an evaluation of the number of heads of 

treated cattle leading to adverse impacts (i.e., LOC exceedances) rather than deterministic risk 

quotients based on an exposure scenario with a fixed assumption on the number of simultaneous 

treated cattle at the use site. The EECs normalized to one head of treated cattle for each washoff 

fraction, shown in Table 3, are used along with endpoints available from freshwater fish and 

freshwater invertebrate toxicological studies to compute the number of treated cattle leading to 

adverse impacts resulting from eartag use. This analysis is possible since the EECs are directly 

proportional to the amount of cattle treated, assuming all cattle possess two eartags. The number 

of treated cattle leading to adverse impacts for acute freshwater fish and acute freshwater 

invertebrates is presented in Table 9. The results presented in Table 9 are discussed further in 

context with the cultural practices of cattle and pasture operations in the Risk Description section 

(Section 5.2) below. 

Table 9. Summary of pirimiphos-methyl treated heads of cattle to trigger adverse impacts 

for listed and non-listed species on an acute basis.

a

 Acute concentration of concern for freshwater fish based on the following calculation: Rainbow Trout acute 

endpoint (LC50 = 404 g/L) x 0.05 or 0.5 (LOCs for listed and non-listed species). Rainbow Trout acute endpoint 

from MRID No. 00103924. 

b

 Acute concentration of concern for freshwater invertebrates based on the following calculation: Daphnid acute 

endpoint (EC50 = 0.11 g/L) x 0.05 or 0.1 (LOCs for listed and non-listed species). Daphnid acute endpoint from 

MRID No. 00103926. 

c

 Heads of Cattle Causing Concern = Concentration of Concern (g/L) ÷ GENEEC peak EEC (g/L) for each 

washoff fraction shown in Table 3. 

Aquatic 

Species and 

Adverse 

Impacts 

Thresholds 

PirimiphosMethyl Water 

Body 

Concentration 

of Concern 

(g/L) 

Head of Treated Cattle Causing Concern Given Washoff Fractions 

(number of cattle)c

100% 20% 10% 5% 1% 

Freshwater Fish

Acute Listed 

Species 

(LOC = 0.05) 

20.2 a 8,038 40,188 80,376 160,751 803,757 

Acute NonListed 

Species 

(LOC = 0.5) 

202a

 80,038 400,188 800,376 1,607,510 8,037,570 

Freshwater Invertebrates

Acute Listed 

Species 

(LOC = 0.05) 

0.0055b

 2 10 20 40 200 

Acute NonListed 

Species 

(LOC = 0.5) 

0.055b

 20 100 200 400 2,000 
Page 26 of 49 

Terrestrial Exposure: Post-Harvest Stored Grain Seed Treatment Uses

The registrant provided an argument on why there would be negligible exposure for terrestrial 

organisms resulting from the stored grain seed treatment uses of pirimiphos-methyl. These lines 

of evidence were originally captured in a waiver request submitted by the registrant for an avian 

reproduction study, contending that there would be insufficient exposure to necessitate such a test 

(“EFED Response to Avian Reproduction Study - OCSPP 850.2300 – Waiver Request for 

Pirimiphos-methyl,” D357626, February 18, 2011). The main arguments were made from an 

absence of exposure basis (as described below), and unnecessary use of animals for toxicity testing 

when compared to overall value to the risk assessment. 

Estimated environmental concentrations (EECs) were calculated from the highest rates on current 

labeled seed treatment uses for sorghum and corn (0.48 lbs a.i per 30 tons of grain, Acetallic® 5E 

Insecticide). The registrant provided an example where it was assumed that only 1% of the 

pesticide will remain on the soil surface due to spillage (Imazilil Reregistration Eligibility 

Decision; US EPA, 2005). However, because the application rate is so low, either 1% or 100% 

assumptions for seed consumption do not result in high exposure levels. The maximum exposure 

concentration is 2.03 mg a.i/kg-bw/day based on the assumption of 100% bioavailability following 

seed treatment. Therefore, maximum potential exposure levels of pirimiphos-methyl from seeds 

treated in the field appears to be very low. 

The determination made previously at the time of the problem formulation regarding risk resulting 

from this pathway remains unchanged and therefore risk to terrestrial organisms resulting from the 

storage of treated seed is expected to be below Agency levels of concern. 

Terrestrial Exposure: Cattle Ear Tag Uses

Given the limited exposure to non-target terrestrial organisms associated with the spotty nature of 

cattle eartag uses of pirimiphos-methyl at pastureland use sites, risk quotients are not expected to 

exceed the LOCs for any non-target terrestrial organism. 

5.2. Risk Description 

This section discusses the potential for risks occurring to non-target aquatic organisms as a result 

of the washoff associated with pirimiphos-methyl eartag uses. As discussed in Section 5.1., a 

qualitative evaluation of the amount of heads of cattle resulting in a risk of concern to aquatic 

organisms is conducted (Table 9) as opposed to deterministic risk quotients given the uncertainty 

associated with the amount of simultaneous head of cattle treated. However, this section will place 

these estimates into context with what is known regarding the density of cattle only at pasture use 

sites. As discussed in Section 2, feedlots would not be use sites where pirimiphos-methyl eartags 

are used. Risks to other non-target organisms associated with eartag use or general ecological 

risks associated with other use patterns are not elaborated in this section since no risks of concern 

are expected as discussed in Section 5.1.

- 
Page 27 of 49 

Aquatic Exposure: Cattle Ear Tag Uses

As explained above, the amount of treated cattle resulting in a risk of concern to aquatic organisms 

is conducted (Table 9), and these results can be placed into context with information regarding 

cattle populations at pasture sites where pirimiphos-methyl eartags are potentially used. This 

information on cattle populations can inform and discern the potential number simultaneous heads 

of cattle treated with the eartags per use site. Cattle population data from USDA’s AgCensus 

(citation: http://www.agcensus.usda.gov/Publications/2012/Online_Resources/Ag_Atlas_Maps/ 

Livestock_and_Animals/Livestock,_Poultry_and_Other_Animals/12-M136-RGBDot1-

largetext.pdf) can be used for a preliminary estimate for cattle populations at use sites. Figure 1

shows that up to 200 head of cattle or more are common over a high density of farms nationwide. 

While some sites may possess over 200 head of cattle, it is not anticipated that many of such sites 

would possess more than 300 head of cattle, as these numbers of cattle are more likely associated 

with major regulated feedlots under EPA’s NPDES program, which as discussed in Section 2, 

feedlots would not be use sites where pirimiphos-methyl eartags are used. Furthermore, it is 

expected there would be many more sites less than 200 head of cattle, which would be the use sites 

where pirimiphos-methyl eartag treatments would be more likely. Sites that possess hundreds of 

heads of cattle would likely not possess the degree of horn fly and face fly infestations for the same 

reasons that eartags would not be used at feedlots as discussed in Section 2. 

Figure 1. Dot density map showing approximate localities of farms keeping 200 or more head of 

cattle (Source: USDA AgCensus, 2012). 

For non-listed and listed freshwater fish, Table 9 shows that much more head of cattle than 

numbers of cattle at farms which possess less than 300 head of cattle (not associated with feedlots) 

would be required to result in adverse impacts on an acute basis. This is even the case if 100 
Page 28 of 49 

percent of residues washoff from eartags. Therefore, no adverse impacts would be expected with 

eartag use associated with freshwater fish.

For non-listed freshwater invertebrates, Table 9 also shows that more head of cattle than the 

number of cattle at non-feedlot farms would be required to result in acute adverse impacts with 10 

percent or less of residues washing off from feedlots. In many cases, it would not be expected that 

less than 10 percent of pirimiphos-methyl residues would washoff and end up in water bodies for 

resosons further discussed in Uncertainties Section below. Therefore, adverse impacts would also 

not be expected with eartag use associated with non-listed freshwater invertebrates.

For listed freshwater invertebrate species, Table 9 conveys that between 40 – 200 cattle can 

potentially result in acute adverse impacts with between 5 percent down to 1 percent, respectively, 

of residues washing off into a water body. However, as explained above, while some non-feedlot 

farms may keep in excess of 200 head of cattle, pirimiphos-methyl eartag use sites are not expected 

to be used at use sites keeping hundreds of head of cattle for reasons discussed in Section 2, and 

is therefore expected that pirimiphos-methyl would be most commonly used at sites keeping less 

than 40 head of cattle. According to the results presented in Table 9, greater than 5 percent of 

residues being washed off from eartags treating 40 head of cattle would lead to adverse impacts. 

However, it is expected that less than 5 percent of pirimiphos-methyl residues would wash off and 

end up in nearby water bodies for reasons discussed in the Uncertainties Section below. Therefore, 

in summary, no risks are anticipated for listed aquatic invertebrate species with pirimiphos-methyl 

eartag use which is expected to be used mainly at use sites keeping small inventories of cattle. 

Uncertainties and Limitations 

 Acute Exposure of Pirimiphos-methyl and Washoff Fractions from Treated Cattle with 

Eartags 

While the results presented in Table 9 provides a preliminary indication of the potential for risk 

associated pirimiphos-methyl eartags, the discussion below identifies uncertainties which exist 

regarding the fate and behavior of pirimiphos-methyl which are not explicitly captured in the 

analysis. The uncertainties in the analysis discussed below collectively provides insights that a 

small portion of residues (less than 5 percent) are likely to washoff and end up in water bodies 

nearby use sites with pirimiphos-methyl eartags. 

1. The number of cattle and respective washoff fractions threshold for concern presented in 

Table 9 is based on the assumption built into the GENEEC model that pirimiphos-methyl 

residues on the ear tag washes off within two days of the treatment off and runs off into a 

static water body. While possible, the washoff fraction would be even less in reality when 

rainfall events are delayed from the onset of eartag treatments given the potential for 

pirimiphos-methyl to degrade once it diffuses onto the skin of cattle. 

2. Pirimiphos-methyl washoff and loadings in the underlying environment about the use site 

is likely to be reduced by a number of factors not captured in the analysis presented here. 

First, pirimiphos-methyl is semi-volatile with a vapor pressure 1.1 x 10-4 torr (Table 1), 

but the analysis did not account for any loss of residues due to volatilization. Second, this 
Page 29 of 49 

assessment assumes that pirimiphos-methyl residues are not bound to the hide of treated 

cattle while rainfall occurs. In reality, there is the possibility that residues bound to treated 

cattle would further reduce the loadings of pirimiphos-methyl in the environment as 

compared to the washoff scenario presented in the analysis. It should be noted, however, 

that no data exists regarding the fate properties of pirimiphos-methyl on cattle skin and 

tissue. 

Aside from washoff fractions potentially ending up in water bodies, the main underlying 

uncertainty in this assessment is related to the amount of cattle that are treated simultaneously with 

pirimiphos-methyl by use site. Labels do not specify limits for the amount of cattle that are treated 

with pirimiphos-methyl by use site. This uncertainty is addressed in the analysis by that it presents 

an evaluation of the number of heads of treated cattle leading to adverse impacts (i.e., LOC 

exceedances) rather than deterministic risk quotients based on a rigid exposure scenario based on 

a fixed number of cattle treated with eartags. As explained in Section 5.2, given the density of 

cattle at pasture use sites and that only a percentage of those cattle would be treated, and that 

infestations of horn flies and face flies are not likely to occur at large industrial-scale farms, the 

amount of simultaneous heads of cattle treated with ceartags are expected to be less than 40 head 

over many cases. 

 Chronic Exposure with Pirimiphos-methyl Eartags and Associated Data Gaps 

As mentioned previously, there are no chronic data available for freshwater fish and 

estuarine/marine fish and invertebrates as well as to sediment dwelling organisms. Environmental 

fate data are only available to show abiotic routes of degradation of parent pirimiphos-methyl when 

in water bodies. The available hydrolysis study shows that at pH 7, parent pirimiphos-methyl has 

a half-life of 79 days. The rate of photodegradation in water is much faster with a half-life of 0.2 

days. However, light penetration through water may not be significant in many cases. No 

information is available to indicate how parent pirimiphos-methyl would break down in a biotic 

aquatic system. Therefore, pirimiphos-methyl was only assumed to degrade abiotically (via 

hydrolysis and photolysis) and not biotically in the aquatic exposure analysis discussed in Section 

3.5. Furthermore, consistent with other insect control type of applications, there are uncertainties 

related to frequency of applications. Therefore, these uncertainties related to the rate of 

degradation in water and pirimiphos-methyl application frequencies result in further uncertainties 

related to the duration of pirimiphos-methyl exposures persisting in aquatic environments. 

While chronic toxicity studies are longer duration studies than acute studies, the intent of chronic 

studies is to expose organisms at different life stages than those of acute studies and below levels 

known to be lethal in order to elicit effects on growth and reproduction. It is anticipated due to the 

toxic nature of OP insecticides that chronic risk cannot be precluded to all aquatic taxa. 

The suite of submitted studies for pirimiphos-methyl reveals that there was a submitted chronic 

daphnia life cycle study submitted in 1991. This study (MRID 48411701) is not associated with 

a data evaluation record (DER) and therefore its results are described here as they are not fully 

verified. Chronic daphnia were exposed to nominal concentrations of control, solvent control, 

0.025, 0.05, 0.1, 0.2, and 0.4 μg a.i/L. There was total (100%) mortality in the two highest 

treatment concentrations, and 70% mortality in the 0.1 μg a.i/L treatment concentration. There 
Page 30 of 49 

were no significant (p<0.05) reductions in length at all treatment concentrations (excluding the 

ones with 100% mortality for which no data were available). Additionally, there was a significant 

reduction in the total number of live young as compared to the control in the three highest treatment 

concentrations. The NOAEC for this study (based on live number of young and mortality) was 

therefore set at 0.05 μg a.i/L. As stated previously, these results are not statistically verified and 

therefore cannot be considered final but can be used qualitatively to indicate pirimiphos-methyl 

exposure appears to be an order of magnitude more toxic on a chronic basis as compared to an 

acute basis. 

In extending the analysis for chronic data as it was presented for acute impacts in Table 9 for all 

percent washoff scenarios assessed (1, 5, 10, 20, and 100%), the number of heads of cattle within 

a typical use site would result in similar amounts of treated cattle triggering risks of concern for 

aquatic invertebrates. Furthermore, similar washoff fractions for cattle densities presented in 

Table 11 would result in risk of concerns for aquatic invertebrates considering the available 

chronic toxicity data. Therefore, given these similar outcomes, the above justification discounting 

risks of concern for acute aquatic invertebrates would also apply to chronic impacts. 

 Bioaccumulation of Pirimiphos-methyl 

As indicated by available environmental fate data, pirimiphos-methyl has the potential to 

bioaccumulate in the tissues of organisms based on its Log KOW of 4.2. This is further corroborated 

by the bioconcentration factor (BCF) being estimated as 274X (SRC and EpiSuite, WSKOW 

v.1.42). While this potential exists, it is unclear, due to a lack of a registrant submitted fish BCF 

study, how quickly and to what extent pirimiphos-methyl residues are depurated from living 

tissues. Therefore, given the potential for pirimiphos-methyl’s offsite transport to water bodies 

and its hydrophobic properties, pirimiphos-methyl has the potential to bioaccumulate in aquatic 

organisms like fish. The extent to which the consumption of those contaminated fish by birds will 

pose a risk is uncertain as a propensity to bioaccumulate does not necessarily indicate that those 

residues will be available in the tissues for days or weeks later. 

Although GENEEC does not provide pore water EEC estimates, a run of the KABAM model using 

water column values provided by GENEEC is used to evaluate piscivorous birds including 

sandpipers, rails, and small osprey consuming pirimiphos-methyl contaminated fish. When 

assuming 20% washoff and subsequent runoff from 300 head of cattle getting treated at the same 

time, the highest RQ, occurring with dose-based risk to sandpipers eating pirimiphos-methyl 

contaminated fish remains, is below the listed species LOC (RQ < 0.006). Furthermore, there 

were no risk findings above the LOC for dose or dietary-based risk to mammals. 

 Terrestrial Exposure 

The exposure pathway for terrestrial organisms was determined to be minimal for the seed 

treatment stored grain use in the problem formulation of pirimiphos-methyl. Exposure to 

terrestrial organisms via the ear tag use was also determined to be minimal. Although acute and 

subacute dietary studies for birds indicate that pirimiphos-methyl is moderately to highly toxic to 

birds on both an acute oral and subacute dietary basis, and available data determined what doses 

and what concentrations would elicit lethal effects as well as clinical signs of toxicity, it is 
Page 31 of 49 

unknown as to the extent of pirimiphos-methyl that would be available to terrestrial organisms. 

As mentioned previously the scenario of ear tags falling off heads of cattle was determined to not 

be likely and will therefore not be further discussed. That leaves few plausible scenarios as to how 

birds and other mammals would be exposed to pirimiphos-methyl resulting from this ear tag use. 

The lack of reported wildlife incidents to birds and other mammals for pirimiphos-methyl further 

suggest this pathway is potentially incomplete although the literature indicates birds and mammals 

may be an important vector for diseases transmission in cattle feed lots. 

Pirimiphos-methyl is highly toxic to adult honey bees on an acute contact and oral basis as would 

be anticipated from an OP insecticide, although there are no data to characterize the toxicity to 

honey bee larvae. Additionally, there is an uncertainty as to what extent honey bees would be 

exposed to pirimiphos-methyl residues as cattle feedlots would likely not serve as attractive areas 

for forage. 

 Ecological Effects Data Gaps 

There are only three studies available to characterize the acute toxicity of pirimiphos-methyl to 

freshwater fish and invertebrates. The analysis presented above indicates that there is a plausible 

exposure pathway that can exist with at worst a 0.03% washoff threshold that is needed to cause 

impacts to listed freshwater invertebrates. While data are not available for estuarine/marine 

invertebrates, risk to this taxa cannot be precluded as washoff fractions could reach these 

environments, and as pirimiphos-methyl is an organophosphate insecticide, lethality to this taxa 

can be expected based on the extensive data set of other active ingredients. 

There are also no data present to characterize the toxicity of pirimiphos-methyl to sediment 

dwelling aquatic invertebrates. Environmental fate data indicate pirimiphos-methyl has some 

propensity to bind to sediment as evidenced by its hydrophobic nature as evidenced by a Log KOW

of 4.2. Although no data are present, the case for the presence of risk to freshwater and 

estuarine/marine sediment dwelling invertebrates can be made based on the likelihood of some 

washoff of pirimiphos-methyl residues into aquatic systems and its propensity to bind to organic 

carbon. Furthermore, water column freshwater invertebrates were observed to be very sensitive 

to pirimiphos-methyl exposure as expected from an OP insecticide and so similar toxicity can be 

presumed to benthic invertebrates given that this exposure pathway cannot be precluded. 

It was previously stated that no chronic toxicity data are available for birds. In a review of the 

submitted studies for pirimiphos-methyl, a study entitled “Egg Production and Hatchability 

Following Inclusion of Pirimiphos-methyl at Various Levels in the Diet of the Laying Hen,” was 

found but was not associated with any DER. Therefore, the results of this study will be discussed 

here in the uncertainties section as they are not verified and therefore cannot be considered final 

at this time. This study (MRID 48361701) was conducted in 1978, which was prior to the 

availability of the current OCSPP 850.2300 avian reproduction study guideline. In the study, birds 

(species not identified) were exposed to pirimiphos-methyl concentrations in the diet of control, 4, 

12, and 40 ppm. There were no treatment related mortalities that were observed nor were there 

any clinical signs of toxicity. There was no significant (p<0.05) reduction in food consumption 

that was observed in the treatment groups as compared to control although food consumption in 

the treatment groups were generally less than that of control. During the recovery period, food 
Page 32 of 49 

consumption between the control and treatment groups was similar. There were no significant 

(p<0.05) reductions in egg production, fertility, and hatchability in the treatment groups as 

compared to control. The NOAEC for this study was therefore determined to be 40 ppm. As 

stated previously, it is not expected that birds would be subjected to exposure of pirimiphos-methyl 

resulting from the cattle eartag use. 

 Risk to Aquatic and Terrestrial Plants 

There is no data available to characterize the toxicity of pirimiphos-methyl to terrestrial and aquatic 

vascular and non-vascular plants. For terrestrial plants, exposure to this taxa would be limited for 

both stored grain seed treatment as well as for the ear tag use. As there are no spray uses for 

pirimiphos-methyl, non-target terrestrial plants would only be exposed via runoff from a feedlot. 

Given the mode of action of this chemical is the inhibition of cholinesterase, toxic effects to plants 

are not anticipated but there is uncertainty in toxicity to plants being mediated by some other mode 

of action. Furthermore, there are no reported ecological incidents with terrestrial plants and 

pirimiphos-methyl that provide some suggestion that this exposure pathway is potentially 

complete. 

Risk to aquatic plants is a bigger uncertainty given that this exposure pathway would be complete 

via washoff from ear tags and the fact that there is no data available to characterize the toxicity to 

aquatic vascular and non-vascular plants. 

6. Endocrine Disruptor Screening Program 

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

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

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

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

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

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

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

studies that assess growth, developmental and reproductive effects in different taxonomic groups. 

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

and other ingredients) may have an effect in humans or wildlife similar to an effect produced by a 

“naturally occurring estrogen, or other such endocrine effects as the Administrator may designate.” 

The EDSP employs a two-tiered approach to making the statutorily required determinations. Tier 

1 consists of a battery of 11 screening assays to identify the potential of a chemical substance to 

interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal systems. Chemicals that go 

through Tier 1 screening and are found to have the potential to interact with E, A, or T hormonal 

systems will proceed to the next stage of the EDSP where EPA will determine which, if any, of 

the Tier 2 tests are necessary based on the available data. Tier 2 testing is designed to identify any 

adverse endocrine-related effects caused by the substance, and establish a dose-response 

relationship between the dose and the E, A, or T effect. 
Page 33 of 49 

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

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

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

identified for EDSP screening was published on June 14, 201310 and includes some pesticides 

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

construed as a list of known or likely endocrine disruptors. 

Pirimiphos-methyl is not among the group of 58 pesticide active ingredients receiving EDSP test 

orders. For information on the status of the orders issued under the EDSP for each chemical, 

please visit our website at http://www.epa.gov/endo/ and click on the "Status of EDSP 

Orders/DCIs" in the Highlights Box. Additional information on the EDSP, including the policies 

and procedures, the list of 67 chemicals, the test guidelines and the Tier 1 screening battery, can 

also be found at this website. 

7. Federally Threatened and Endangered (Listed) Species of 

Concern 

Based on this screening-level assessment, there are potential risks of direct effects to listed birds, 

mammals, freshwater and estuarine/marine fish, invertebrates, and sediment dwelling 

invertebrates, aquatic vascular plants, and terrestrial dicot plant species from the use of pirimiphosmethyl on some of its registered use sites. Listed species of birds, mammals, freshwater and 

estuarine/marine fish and invertebrate taxa may also be affected through indirect effects because 

of the potential direct effects on listed and non-listed species. Potential direct effects on listed 

birds, mammals, freshwater and estuarine/marine fish, invertebrates, and sediment dwelling 

invertebrates from the use of pirimiphos-methyl may be associated with modification of Primary 

Constituent Elements (PCEs) of designated critical habitats, where such designations have been 

made. However, at this current stage of the Registration Review process, it is premature to make 

effects determinations for listed species until further scientific analysis and refinements are 

conducted, based on recommendations received from the National Academy of Sciences’ (NAS) 

National Research Council (NRC) April 2013 report, available at 

http://www.nap.edu/catalog.php?record_id=18344. The NAS report outlines recommendations 

on specific scientific and technical issues related to the development of pesticide risk 

assessments that are compliant with the Endangered Species Act (ESA) and the Federal 

Insecticide, Fungicide, and Rodenticide Act (FIFRA). 

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 implementation plan for assessing risks of pesticides to listed species 

ahead of the stakeholder workshop held on November 15, 2013. This plan was developed in 

response to the NAS’ recommendations, including a common approach to risk assessment as a 

way of addressing scientific differences between EPA and the Services. During the workshop, the 

agencies received feedback from the public on the interim scientific approaches that were 

 

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

chemicals. 
Page 34 of 49 

developed as part of the initial implementation of the NAS recommendations. These approaches 

will be jointly implemented and vetted as part of a phased iterative process. Once fully vetted, 

EPA will further refine the listed species effects determination portion of this risk assessment. 

To make effects determinations 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 pirimiphos-methyl use patterns; and 3) sub-county level 

spatial proximity data for the co-occurrence of potential effects areas and listed species and any 

designated critical habitat. Examples of such refinements are described below. 

EFED is currently developing tools that are expected to further refine the assessment and are 

designed to support effects determinations for individual federally listed species and their 

designated critical habitats (where applicable). Scientific information obtained from the 

Services, and other reliable sources is being collated by EFED to address all currently listed 

species. This information is being stored in an Office of Pesticide Programs (OPP) Pesticide 

Registration Information SysteM (PRISM) listed species knowledgebase. The listed species 

knowledgebase consists of an information repository that houses biological and behavioral 

information relevant to individual species (e.g., habitat, diet, and life history, including specific 

temporal and spatial associations) and a document repository that contains supporting documents 

(e.g., USFWS recovery plans) and electronic information (e.g., GIS data files). For terrestrial 

taxa, biological information relevant to the assessment (e.g., diet and body weight) will be used 

to parameterize exposure estimates using a method consistent with currently used methods in the 

T-REX and T-HERPS models. 

Refinements will also include more detailed analyses of the registered uses and specific use 

patterns that result in either “Likely to Adversely Affect” (LAA) or “Not Likely to Adversely 

Affect” (NLAA) determinations for federally listed species. The analyses may include more 

information on where, when, and how pirimiphos-methyl is used on all use sites. Actual usage 

data (when available) and national land-cover datasets that indicate potential use sites [e.g., 

National Land Cover Dataset (NLCD), Cropland Data Layer (CDL)] may be used to support a 

more refined analysis of where pirimiphos-methyl is reasonably expected to be used. Similarly, 

refinements on the timing of applications and a more in-depth exploration of agronomic practices 

for pirimiphos-methyl may be included as part of the refinement. 

The refinements based on individual species data; additional, detailed usage information, when 

available; and recommendations from the NRC report are expected to help to more accurately 

identify potential areas of effect and to better inform effects and habitat determinations for listed 

species and any designated critical habitats. 

7.1 Action Area 

For listed species assessment purposes, the action area is considered to be the area affected directly 

or indirectly by pirimiphos-methyl use and not merely the immediate area where pirimiphosmethyl is applied. At the initial screening-level, the risk assessment considers broadly described 

taxonomic groups and conservatively estimates exposure for organisms that are co-located with 

the pesticide treatment area. This means that terrestrial plants and wildlife are assumed to be 
Page 35 of 49 

located on or adjacent to the treated site and aquatic organisms are assumed to be located in a 

surface water body adjacent to the treated site, except in the case of direct application to aquatic 

habitat. 

3

No data are available on terrestrial and aquatic plants which may serve as food items for all terrestrial and aquatic 

taxa. It is unclear of the toxicity of pirimiphos-methyl to these taxa and in the case of terrestrial plants, as to 

whether a complete exposure pathway would exist given the absence of spray uses of pirimiphos-methyl. 

4

Although no toxicity data are available, the acute and chronic toxicity to these taxa to OP insecticides is well 

established as well as the fact that pirimiphos-methyl is stable to aerobic aquatic metabolism. 

7.2 Listed Species Occurrence Associated with Registered 

Uses 

The screening-level risk assessment for pirimiphos-methyl assumes that it may be applied 

nationwide, including U.S. territories and possessions. Therefore, no federally listed species are 

excluded from the screening level analyses, unless otherwise indicated (e.g., if only listed due to 

Similarity of Appearance to another listed species). A spatial co-occurrence analysis that 

compares the best available data regarding pirimiphos-methyl potential and documented use areas 

and listed species occurrence is needed to more explicitly address potential risk to listed species 

of concern. The Agency has requested data to support this analysis from the Federal Endangered 

Species Task Force (FESTF). 

8. Conclusions 

There are many uncertainties related to pirimiphos-methyl, several of which were detailed in the 

Risk Description Section of this assessment. These uncertainties mainly relate to environmental 

fate and ecological effects data gaps, as well as the unconventional nature of the uses associated 

with pirimiphos-methyl where exposure cannot be estimated in a conventional manner using 

standard EFED models. However, given the highly conservative nature of the assumptions for 

environmental loading as provided in this assessment, and that small cattle operations are where 

pirimiphos-methyl eartags are only used, exposure is not expected to occur at levels exceeding 

levels of concern to aquatic or terrestrial organisms. 
Page 36 of 49 

9. References 

Alabama (State of), Alabama A & M and Auburn Universities. Fly Control for Alabama Cattle 

Opearions. Available online at http://www.ag.auburn.edu/ 

enpl/directory/faculty/hu/documents/ANR-2083-VetFlyControl-20140211.pdf Accessed 

December 2015 

CFR 40. 2007. Code of Federal Regulations 40 Parts 150 to 189. Protection of the 

Environment. U.S. Government Printing Office. 

Charizopoulos E. and Papadopoulou-Mourkidou, E. 1999. Environ Sci. Technol., 33: 2363-

2368. 

Close M.E. 1999. New Zealand J Marine Freshwater Res., 27: 267-273. 

Cremlyn, R.J. 1991. Agrochemicals: Preparation and Mode of Action. p. 121 - 124. John Wiley 

and Sons. New York, NY. 

European Food Safety Authority. 2005. Conclusion regarding the peer review of the pesticide 

risk assessment of the active substance pirimiphos-methyl. 44, 1-53. Available online at 

http://www.efsa.europa.eu/cs/BlobServer/PRAPER_Conclusion/praper_concl_sr44_piri

miphos-methyl_en1.pdf?ssbinary=true Accessed November 2014. 

Fletcher, J.S., J.E. Nellessen, and T.G. Pfleeger. 1994. Literature review and evaluation of the 

EPA food-chain (Kenaga) nomogram, an instrument for estimating pesticide residues on 

plants. Environ. Tox. Chem. 13:1383-1391. 

Hoerger, F. and E. E. Kenaga, 1972. Pesticide Residues on Plants: Correlation of Representative 

Data as a Basis for Estimation of their Magnitude in the Environment. In F. Coulston and 

F. Korte, eds., Environmental Quality and Safety: Chemistry, Toxicology, and 

Technology, Georg Thieme Publ., Stuttgart, West Germany, pp. 9-28. 

Kentucky (State of), University of Kentucky. Horn Flies and Cattle. Available online at 

http://www2.ca.uky.edu/entomology/entfacts/ef509.asp Accessed December 2015. 

Kizil, U. and Lindley J., 2002. Feedlot Runoff and Manure Management Modeling. United 

States Department of Agriculture State Water Resources Research Institute, 2002 State 

Water Projects. Available online at http://water.usgs.gov/wrri/02grants/prog-complreports/2002ND7B.pdf. Accessed November 2014. 

Mayer, F.; Ellersieck, M. 1986. Manual of Acute Toxicity: Interpretation and Data Base 410 

Chemicals and 66 Species of Fresh-Water Animals. US Fish & Wildlife Service; 

Resource Publication (160): 579 p. 
Page 37 of 49 

Mississippi (State of), Mississippi State University. Horn Flies on Cattle: Biology and 

Management. Available on-line at 

http://store.msuextension.org/publications/AgandNaturalResources/MT200912AG.pdf

Accessed December 2015. 

Nebraska (State of), University of Nebraska. Controlling Flies on Pastured Cattle in Nebraska. 

Available on-line: http://newsroom.unl.edu/announce/beef/3199/18423 Accessed 2015. 

Syngenta. Actellic 50EC Environmental Information. Cambridge, UK. Available online at 

http://www.syngentacrop.co.uk/pdfs/products/Actellic50EC_uk_environmental_information.pdf. 

Accessed November 2014. 

Syngenta. Actellic 50EC Safety Data. Cambridge, UK. Available online at 

http://www.syngenta-crop.co.uk/pdfs/products/Actellic50EC_uk_safety_data.pdf. 

Accessed November 2014. 

U.S. Department of Agriculture (USDA). 2011. Feedlot 2011 Report, Part I: Management 

Practices on US Feedlots with a Capacity of 1,000 or More Head. United States 

Department of Agriculture. Available online at: . 

http://www.aphis.usda.gov/animal_health/nahms/feedlot/downloads/feedlot2011/Feed11

_dr_PartI.pdfAccessed Accesed Novermber 2014. 

USDA, Economic Research Service Briefing Room. 2014. United States Department of 

Agriculture. Available online at: http://www.ars.usda.gov/IS/pr/2005/051216.htm. 

Accessed November 2014. 

USDA. 2000. National Agricultural Census – Agricultural Chemical Usage – 1999 Cattle and 

Cattle Facilities. United States Department of Agriculture National Agricultural Statistics 

Service, Washington, DC. 

U.S. Environmental Protection Agency (USEPA). 1998. Guidelines for Ecological Risk 

Assessment. Risk Assessment Forum, Office of Research and Development, 

Washington, D.C. EPA/630/R-95/002F. April 1998. 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=30759. Accessed November 2014. 

USEPA. 2002. Guidance for Selecting Input Parameters in Modeling the Environmental Fate and 

Transport of Pesticides, Version II. US Environmental Protection Agency, Washington 

DC. Online at: http://www.epa.gov/oppefed1/models water/input_guidance2_28_02.htm. 

Accessed November 2014. 

USEPA. 2004. Overview of the Ecological Risk Assessment Process in the Office of Pesticide 

Programs. U.S. Environmental Protection Agency, Office of Prevention, Pesticides and 

Toxic Substances, Office of Pesticide Programs, Washington DC. January 23, 2004. 
Page 38 of 49 

USEPA. 2006. Reregistration Eligibility Decision (IRED): Pirimiphos Methyl. U.S. 

Environmental Protection Agency, Office of Pesticide Programs, Washington, DC. July, 

2006. 

USEPA. 2007a. Ecological Incident Information System. 

http://www.epa.gov/espp/consultation/ecorisk-overview.pdf. Accessed November 2014. 

USEPA. 2007b. 40 CFR Part 158. Pesticides; Data Requirements for Conventional Chemicals: 

Final Rule. 72 FR 60934. October 26, 2007. 

USEPA. 2007c. ECOTOXicology Database. Office of Research and Development National 

Health and Environmental Effects Research Laboratory’s (NHEERL’s) Mid-Continent 

Ecology Division (MED). http://cfpub.epa.gov/ecotox/. Accessed November 2014. 

U.S. Fish and Wildlife Service (USFWS) and National Marine Fisheries Service (NMFS). 1998. 

Endangered Species Consultation Handbook: Procedures for Conducting Consultation 

and Conference Activities Under Section 7 of the Endangered Species Act. Final Draft. 

March 1998. 

Appendix A. Environmental Fate and Ecological Effects Data 

for Pirimiphos-methyl 

161-1 Hydrolysis 

MRID Citation Reference 

135353 ICI Americas, Inc. (1977) Actellic 7E Insecticide: ?Product Chem- istry|. 

(Compilation; unpublished study received Dec 1, 1978 under 10182-EX15; CDL:097668-A) 

135356 Easton, C.; Seaman, D. (1970) Pyrimidines: Effect of pH on the Hydrolysis 

of PP 211 and PP 511: Ref. No. AR 2175 A. (Unpub- lished study received 

Dec 1, 1978 under 10182-EX-15; prepared by Plant Protection Ltd., Eng., 

submitted by ICI Americas, Inc., Wilmington, DE; CDL:097680-A) 

135357 Bowker, D.; Hughes, H. (1974) Pirimiphos-methyl: Fate in Water: AR 

2516A. (Unpublished study received Dec 1, 1978 under 10182-EX- 15; 

prepared by Plant Protection Ltd., Eng., submitted by ICI Americas, Inc., 

Wilmington, DE; CDL:097680-B) 

42982401 Hall, B. (1993) The Determination of the Hydrolytic Stability of (carbon 14)-

Pirimiphos-Methyl: Lab Project Number: 9545: 382403. Unpublished study 

prepared by Inveresk Research International. 112 p. 

43177601 Hall, B.; Williams, S. (1994) Report Amendment to Study Report (MRID 

# 42982401): The Determination of the Hydrolytic Stability of (carbon 14)-
Page 39 of 49 

Pirimiphos-Methyl: Lab Project Number: 382403: WECO-9206: 9545 

ADDENDUM. Unpublished study prepared by Inveresk Research 

International. 37 p. 

 

162-1 Aerobic soil metabolism 

MRID Citation Reference 

135358 Arnold, D.; Hill, I.; Harvey, B.; et al. (1976) Pirimiphos-methyl: Degradation 

of the Pesticide in Soil under Laboratory Condi- tions: AR 2656 A. 

(Unpublished study received Dec 1, 1978 under 10182-EX-15; prepared by 

Imperial Chemical Industries, Ltd., Eng., submitted by ICI Americas, Inc., 

Wilmington, DE; CDL: 097680-D) 

163-1 Leach/adsorption/desorption 

MRID Citation Reference 

68104 Riley, D.; Stevens, J.E. (1975) Pirimiphos-ethyl: Leaching in Soil: AR 

2592A. (Unpublished study received Dec 17, 1976 under 10182-9; 

prepared by Plant Protection Ltd., submitted by ICI Americas, Inc., 

Wilmington, Del.; CDL:227314-W) 

48355602 Schocken, M. (2010) Acceptability of Foreign Soils Used in a PirimiphosMethyl Batch Equilibrium Study. Project Number: 2010/P/3. Unpublished 

study prepared by Schocken Consulting, LLC. 23 p. 

48355601 Hartfree, Y.; Muller, K.; Lane, M. (2011) Pirimiphos-Methyl: Adsorption 

and Desorption in Soil. Project Number: RJ1461B. Unpublished study 

prepared by Jealott's Hill Res. Station. 70 p. 

164-1 Terrestrial field dissipation 

MRID Citation Reference 

154033 Heuer, B.; Birk, Y.; Yaron, B. (1976) Effect of phosphatases on the 

persistence of organophosphorus insecticides in soil and water. Journal of 

Agric. Food Chem. 24(3):611-614. 

Non-Guideline Studies 

MRID Citation Reference 

44053301 Hathorn, S. (1996) Nu-Gro Insecticide S.P...: Response to EPA Chemistry Branch Review of 
Page 40 of 49 

Data Requirements to Defend the Use on Corn Seed and Sorghum Seed for Controlling 

Storage Pests: Lab Project Number: DEFENSE OF BULK/BAGGED SEED USE 

RESPONSE. Unpublished study prepared by Compliance Services International. 129 p. 

44584702 Sielaty, R. (1998) Pirimiphos-Methyl in vitro Absorption from a 500g/l EC Formulation through 

Rat Epidermis: Lab Project Number: WECO-9802: JV1483: CTL/P/5239. Unpublished study 

prepared by Compliance Services International. 27 p. 

45932601 Wo, C. (2003) UV/Visible Absorption: Pirimiphos-methyl Technical: Lab Project Number: 

13425: P805. Unpublished study prepared by Product Safety Labs. 13 p. {OPPTS 830.7050} 

46173801 Lake, R. (2004) Product Chemistry: Storage Stability and Corrosion Characteristics: 

Dominator Insecticide Ear Tags. Project Number: 071/006, EXP/071/006, EXM/071/004. 

Unpublished study prepared by Exygen Research. 56 p 

71-1 Avian Single Dose Oral Toxicity 

MRID Citation Reference 

41311001 Ross, D.; Roberts, N.; Fairley, C. (1979) The Acute Oral Toxicity (LD50) of 

Pirimiphos Methyl to the Mallard Duck: Lab Project Number: CTL/C/726. 

Unpublished study prepared by Imperial Chemical Industries Ltd., 

Huntingdon Research Centre. 18 p. 

43442101 Campbell, S.; Beavers, J. (1994) Pirimiphos-Methyl: An Acute Oral Toxicity 

Study With the Northern Bobwhite: Lab Project Number: 94041-WECO: 

134-103. Unpublished study prepared by Wildlife International Ltd. 59 p. 

80742 Gage, 1971. Oral with Green finch, Pigeon, and Japanese quail. 

Accession 097679. 

71-2 Avian Dietary Toxicity 

MRID Citation Reference 

42037001 Hakin, B.; Johnson, A.; Anderson, A.; et al. (1990) Pirimiphos- Methyl 

Dietary Toxicity (LD50) to the Bobwhite Quail: Lab Proj- ect Number: JAN 

244/90755. Unpublished study prepared by Hunt- ingdon Research 

Centre, Ltd. 30 p. 

103923 Parkinson, G.; Banham, P. (1971) Pirimiphos-methyl (PP 511): Avian 

Toxicity: Report No. HO/1H/R/329. (Unpublished study received Dec 1, 

1978 under 10182-EX-15; prepared by Imperial Chemical Industries, Ltd., 

Eng., submitted by ICI Americas, Inc., Wilmington, DE; CDL:097679-B) 

107422 Fink, R. (1974) Final Report: Eight-day Dietary LC50--Mallard Ducks: 

?Technical Pirimiphos Methyl|: Project No. 123-102. (Unpublished study 

received Dec 1, 1978 under 10182-EX-15; prepared by Truslow Farms, 

Inc., submitted by ICI Americas, Inc., Wilmington, DE; CDL:097679-D) 

107423 Fink, R. (1974) Final Report: Eight-day Dietary LC50--Bobwhite Quail: 
Page 41 of 49 

?Technical Pirimiphos Methyl|: Project No. 123-101. (Unpublished study 

received Dec 1, 1978 under 10182-EX-15; prepared by Truslow Farms, 

Inc., submitted by ICI Americas, Inc., Wilmington, DE; CDL:097679-E) 

72-1 Acute Toxicity to Freshwater Fish 

MRID Citation Reference 

92147004 Smyth, D.; Hill, R. (1990) ICI Americas Inc. Phase 3 Summary of MRID 

00103924. Pirimiphos-methyl (PP511): Determination of the Acute Toxicity 

to Rainbow Trout (Salmo gairdneri): Report No. BL/B/1868; Study No. 

D608/A. Prepared by ICI BRIXHAM LABORATORY. 12 p. 

103925 Bluegill Acute Brixham Laboratories, 1975 

103925 Rainbow Acute Brixham Laboratories, 1975 

103924 Hill, R. (1978) Determination of the Acute Toxicity of Pirimiphos- methyl to 

Rainbow Trout ...: BL/B/1868. (Unpublished study received Dec 1, 1978 

under 10182-EX-15; prepared by Imperial Chemical Industries, Ltd., Eng., 

submitted by ICI Americas, Inc., Wilmington, DE; CDL:097679-F) 

108078 Hill, R. (1978) Determination of the Acute Toxicity of Pirimiphos- methyl to 

Fathead Minnow ...: BL/B/1873. (Unpublished study received Dec 1, 1978 

under 10182-EX-15; prepared by Imperial Chemical Industries, Ltd., Eng., 

submitted by ICI Americas, Inc., Wilmington, DE; CDL:097679-G) 

72-2 Acute Toxicity to Freshwater Invertebrates 

MRID Citation Reference 

92147005 Hamer, M. (1990) ICI Americas Inc. Phase 3 Summary of MRID 00103926. 

Pirimiphos-methyl: Toxicity to First Instar Daphnia magna: Report No. 

TMJ1411B. Prepared by ICI AGROCHEMICALS. 13 p. 

103926 Pirimiphos-methyl: Toxicity to First Instar Daphnia magna: Report No. 

TMJ1411B. Prepared by ICI AGROCHEMICALS. 13 p. Test includes 

technical and formulation testing 

850.1300 Chronic Toxicity Freshwater Invertebrates 

MRID Citation 

48417101 Rapley, J.; Hamer, M. (1991) Pirimiphos-Methyl: Chronic Toxicity to Daphnia 

magna. Project Number: RJ0940B. Unpublished study prepared by ICI 

Agrochemicals. 29 p. 

141-1 Honeybee Acute Toxicity Testing 

MRID Citation Reference 
Page 42 of 49 

05001991 Stevenson, 1978. Bee studies conducted at Univ. of California 

142-3 Simulated or Actual Field Testing 

MRID Citation Reference 

43717 Smith, F.D. (1976) PP557: Effects on Predatory and Parasitic Arthropods: 

Report Series TMJ 1283 B. (Unpublished study received Dec 2, 1976 under 

10182-EX-3; prepared by Imperial Chemi- cal Industries, Ltd., submitted by 

ICI Americas, Inc., Wilmington, Del.; CDL:095996-G) 

50011991 Stevenson, J.H. (1976). The acute toxicity of unformulated pesticides to 

worker honey bees (Apis mellifera L.). Plant Pathol. 27(1): 38-40. 

Non-Guideline Study 

MRID Citation Reference 

46364315 

 Brealey, C.; Walker, C.; Baldwin, B. (1980) A-Esterase Activities in 

Relation to the Differential Toxicity of Pirimiphos-Methyl to Birds and 

Mammals. Pestic. Sci. 11: 546-554. 

Appendix B. Aquatic Exposure Modeling Summary 

Figure B-1. GENEEC model run for pirimiphos-methyl eartag uses. 

RUN No. 1 FOR Pirimiphos-methy ON eartags * INPUT VALUES * 

 -------------------------------------------------------------------- 

 RATE (#/AC) No.APPS & SOIL SOLUBIL APPL TYPE NO-SPRAY INCORP 

 ONE(MULT) INTERVAL Kd (PPM ) (%DRIFT) ZONE(FT) (IN) 

 -------------------------------------------------------------------- 

 1.000( 1.000) 1 1 49.0 8.6 GRANUL( 0.0) 0.0 0.0 

 FIELD AND STANDARD POND HALFLIFE VALUES (DAYS) 

 -------------------------------------------------------------------- 

 METABOLIC DAYS UNTIL HYDROLYSIS PHOTOLYSIS METABOLIC COMBINED 
Page 43 of 49 

 (FIELD) RAIN/RUNOFF (POND) (POND-EFF) (POND) (POND) 

 -------------------------------------------------------------------- 

 39.10 2 198.00 0.20- 24.80 0.00 22.04 

 GENERIC EECs (IN MICROGRAMS/LITER (PPB)) Version 2.0 Aug 1, 2001 

 -------------------------------------------------------------------- 

 PEAK MAX 4 DAY MAX 21 DAY MAX 60 DAY MAX 90 DAY 

 GEEC AVG GEEC AVG GEEC AVG GEEC AVG GEEC 

 -------------------------------------------------------------------- 

 7.26 6.97 5.60 3.62 2.75 

Notes: 

1. Please refer to Table 2 for explanation and rationale for input parameter values. 

2. Modeling conducted normalized to an application rate of 1 lb. a.i./A. Results shown in Tables 8 and 9 are 

derived from linearly scaling the peak EEC shown in this figure to the application rates per head of cattle 

shown in Table 8 for each washoff fraction.
Page 44 of 49 

Appendix C. Inhalation Exposure Screening Evaluation 

Figure C-1. STIR run for pirimiphos-methyl eartag and seed treatment uses. 

This tool is designed to provide the risk assessor with a rapid method for determining the potential 

significance of the inhalation exposure route to birds and mammals in a risk assessment. 

Input 

Application and Chemical Information 

Enter Chemical Name Pirimiphos-methyl 

Enter Chemical Use Eartag 

Is the Application a Spray? (enter y or n) n 

If Spray What Type (enter ground or air) ground 

Enter Chemical Molecular Weight (g/mole) 305 

Enter Chemical Vapor Pressure (mmHg) 1.10E-04 

Enter Application Rate (lb a.i./acre) 

 

Toxicity Properties 

Bird 

Enter Lowest Bird Oral LD50 (mg/kg bw) 40 

Enter Mineau Scaling Factor 1.15 

Enter Tested Bird Weight (kg) 0.178 

Mammal 

Enter Lowest Rat Oral LD50 (mg/kg bw) 2400 

Enter Lowest Rat Inhalation LC50 (mg/L) 5.04 

Duration of Rat Inhalation Study (hrs) 4 

Enter Rat Weight (kg) 0.35 

Output 

Results Avian (0.020 kg ) 

Maximum Vapor Concentration in Air at Saturation (mg/m3) 1.81E+00 

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 2.27E-01 

Adjusted Inhalation LD50 4.68E-01 

Ratio of Vapor Dose to Adjusted Inhalation LD50 4.85E-01 Proceed to Refinements 

Maximum Post-treatment Spray Inhalation Dose (mg/kg) not applicable 

Ratio of Droplet Inhalation Dose to Adjusted Inhalation LD50 not applicable not applicable 

 

Results Mammalian (0.015 kg ) 

Maximum Vapor Concentration in Air at Saturation (mg/m3) 1.81E+00 

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 2.85E-01 

Adjusted Inhalation LD50 3.00E+02 

Ratio of Vapor Dose to Adjusted Inhalation LD50 9.51E-04 Exposure not Likely Significant 

Maximum Post-treatment Spray Inhalation Dose (mg/kg) not applicable 

Ratio of Droplet Inhalation Dose to Adjusted Inhalation LD50 not applicable not applicable 
Page 45 of 49 

Figure C-2. HED Tier 1 Air Exposure Model run for pirimiphos-methyl eartag and seed treatment uses. * Equivalent application rate calculated assuming 8,000 head of cattle present on 10 ha feedlot. 

Pirimiphos‐MethylVapor Pressure (Pa) 1.10E‐04 10 20 40 

Solubility (mg/L) 8.6 Bare soil 0 0 0 

Koc (ml/g) 3329 Cole crop 0 0 0 

Bare soil Foliar apps to crops Row crop 0 0 0 

Application rate (lbs ai/A) 2.744 NA Orchard1 0 0 0 

Hourly Flux Rate (μg/m2‐s) 8.10E‐02 2.61E‐02

Application timing Worst case

Averaging time for concentration (hours) 1 1

Inhalation POD (μg/m3) 930.75

UF (unitless) 10Concentration of concern (μg/m3) 93

Notes:1. Air flow through an orchard is complex and AERSCREEN does not take this complexity into account.

Orchard values should be characterized appropriately.

2. Areas shaded in green are for user input. The user should not enter information in the areas shaded in red.3. "Duration of maximum emission" should be less than or equal to 24 hours.

Distance 

Field Size (acres)

Crop Type
Page 46 of 49 

Figure C-3. HED Tier 1 Air Exposure Model estimated exposure concentrations for vaporphase pirimiphos-methyl. 

Notes: 

1. Maximum EEC shown in yellow shading. 

Distance (m) 10 20 40 60 80

0 10.26 17.34 26.68 33.12 38.46

5 10.56 17.64 26.92 33.33 38.73

10 10.85 17.94 27.16 33.60 38.99

15 11.14 18.24 27.40 33.86 39.26

20 11.43 18.53 27.67 34.13 39.53

25 11.73 18.83 27.96 34.40 39.78

50 13.24 20.38 29.39 35.69 40.91

75 14.47 21.44 30.54 37.27 42.28

100 15.25 22.06 31.09 37.84 43.21

125 15.66 22.37 31.48 38.08 43.31

150 15.80 22.54 31.62 38.08 43.19

175 15.83 22.61 31.55 37.89 42.96

200 15.80 22.53 31.34 37.57 43.26

225 15.71 22.34 31.06 37.76 43.44

250 15.55 22.08 30.93 37.88 43.48

275 15.33 21.77 31.01 37.87 43.41

300 15.08 21.64 30.98 37.78 43.25

325 14.86 21.63 30.88 37.60 43.02

350 14.77 21.55 30.73 37.37 42.79

375 14.71 21.43 30.52 37.15 42.53

400 14.60 21.27 30.29 36.89 42.23

425 14.48 21.09 30.05 36.61 41.89

450 14.33 20.89 29.82 36.30 41.54

475 14.17 20.70 29.55 35.97 41.16

500 14.00 20.50 29.26 35.63 40.77

Bare soil
Page 47 of 49 

Appendix D. Drinking Water Exposure Screening Evaluation 

Table C-1. SIP model run for pirimiphos-methyl. 

Parameter Value 

Chemical name Pirimiphos-methyl 

Solubility (in water at 25oC; mg/L) 8.6 

 

Mammalian LD50 (mg/kg-bw) 2400 

Mammalian test species laboratory rat 

Body weight (g) of "other" mammalian species 

 

Mammalian NOAEL (mg/kg-bw) 0.87 

Mammalian test species laboratory rat 

Body weight (g) of "other" mammalian species 

 

Avian LD50 (mg/kg-bw) 40 

Avian test species northern bobwhite quail 

Body weight (g) of "other" avian species 

Mineau scaling factor 1.15 

 

Mallard NOAEC (mg/kg-diet) 

Bobwhite quail NOAEC (mg/kg-diet) 

NOAEC (mg/kg-diet) for other bird species 

Body weight (g) of other avian species 

NOAEC (mg/kg-diet) for 2nd other bird species 

Body weight (g) of 2nd other avian species 

Table 2. Mammalian Results 

Parameter Acute Chronic 

Upper bound exposure (mg/kg-bw) 1.4792 1.4792 

Adjusted toxicity value (mg/kg-bw) 1845.9854 0.6692 

Ratio of exposure to toxicity 0.0008 2.2105 

Conclusion* 

Drinking water exposure 

alone is NOT a potential 

concern for mammals 

Exposure through drinking 

water alone is a potential 

concern for mammals 

Table 3. Avian Results 

Parameter Acute Chronic 

Upper bound exposure (mg/kg-bw) 6.9660 6.9660 

Adjusted toxicity value (mg/kg-bw) 28.8172 0.0000 

Ratio of exposure to acute toxicity 0.2417 0.0000 

Conclusion* 

Exposure through drinking 

water alone is a potential 

concern for birds 

Due to insufficient data, risk 

cannot be precluded 

*Conclusion is for drinking water exposure alone. This does not combine all routes of exposure. Therefore, when aggregated 

with other routes (i.e., diet, inhalation, dermal), pesticide exposure through drinking water may contribute to a total exposure that 

has potential for effects to non-target animals.
Page 48 of 49 

Appendix E. Degradates Summary for Pirimiphos-Methyl 

Table E-1. Pirimiphos-methyl degradation products identified in environmental fate studies.

Degradate 

Identity Structure

Max% of 

Applied 

and Days 

Post 

Application

Comments

Hydrolysis (MRID Nos. 42982401 and 43177601) 

2(diethylamino)-4-

hydroxy-6-methyl 

pyrimidine 

(Non-OP degradate)

87.25%, 

30 days 

(pH5) 

22.51%, 

90 days 

(pH7) 

29.97%, 

60 days 

(pH9) 

pH5 study 

terminated at 30 

days. 

pH7 study 

terminated at 90 

days. 

pH9 study 

terminated at 60 

days. 

O-2 diethylamino-6-

methylpyrimidin-4-yl omethyl-phosphorothioate 

(OP Demethylated 

degradate)

4.99%, 

21 days 

(pH5) 

26.54%, 

90 days 

(pH7) 

18.17%, 

60 days 

(pH9) 

pH5 study 

terminated at 30 

days. 

pH7 study 

terminated at 90 

days. 

pH9 study 

terminated at 60 

days. 

Aerobic Soil Metabolism (MRID No. 135358) 

2(diethylamino)-4-

hydroxy-6-methyl 

pyrimidine 

(Non-OP degradate)

42.08%,, 

Peartree 

Sandy Loam 

(SL1) at 70 

days 

55.58%,, 

Frensham 

Sandy Loam 

(SL2) at 14 

days 

37.22%,, 

Gore Loam 

(L) at 14 days 

66.28 %,, 

Blackborough 

Peat (P) at 

210 days 

Studies in all soils 

terminated at 210 

days. 

N N

CH3

N

C

H2

C

H2

H3C CH3

HO

N N

CH3

N

C

H2

C

H2

H3C CH3

HO
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Table E-1. Pirimiphos-methyl degradation products identified in environmental fate studies.

Degradate 

Identity Structure

Max% of 

Applied 

and Days 

Post 

Application

Comments

Anaerobic Soil Metabolism (MRID No. 135358) 

2(diethylamino)-4-

hydroxy-6-methyl 

pyrimidine 

(Non-OP degradate)

61.4%,, 

Peartree 

Sandy Loam 

(SL1) at 14 

days 

37.22%,, 

Gore Loam 

(L) at 14 days 

Studies in all soils 

terminated at 210 

days. 

Findings from 

flooded water soil 

atmosphere 

reported. 

N N

CH3

N

C

H2

C

H2

H3C CH3

HO