UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

MEMORANDUM APRIL 22, 2009

Subject: Registration Review – Preliminary Problem Formulation for the Ecological Risk 

and Drinking Water Exposure Assessments for Tebupirimphos (PC Code 129086; 

D360013) 

To: Wilhelmena Livingston, Chemical Review Manager 

 Special Review Branch 

Special Review and Reregistration Division (SRRD) 

From: Brian Anderson, Biologist 

 James K. Wolf, Ph.D., Environmental Scientist 

 Environmental Risk Branch 3 

 Environmental Fate and Effects Division 

 Office of Pesticide Programs 

Through: Dana Spatz, Branch Chief 

 Environmental Risk Branch 3 

 Environmental Fate and Effects Division 

 Office of Pesticide Programs 

The Environmental Fate and Effects Division (EFED) has completed the preliminary problem 

formulation (attached) for the ecological risk, environmental fate, endangered species, and 

drinking water assessments to be conducted as part of the Registration Review of the 

organophosphate insecticide, tebupirimphos. The problem formulation draws information from 

both open literature and from studies submitted by the technical registrants in response to data 

requirements. This document is intended to provide an overview of what is currently known 

regarding the environmental fate and ecological effects associated with tebupirimphos and its 

degradation products and outlines uncertainties regarding attributes of the parent compound and 

its transformation products. It describes the preliminary ecological risk hypothesis and the 

processes that will be used during the completion of drinking water and ecological risk 

assessments in support of registration review. 

1 
 

Problem Formulation for the 

Ecological Risk and Drinking Water Exposure 

Assessments 

in Support of the Registration Review of 

Tebupirimphos 

Tebupirimphos (CAS No. 96182-53-5) 

 O-[2-(1,1-dimethylethyl)-5-pyrimidinyl] O-ethyl O-(1-methylethyl) phosphorothioate]

 

Prepared by:

Brian Anderson, Biologist 

James Wolf, Ph.D., Environmental Scientist 

Reviewed by: 

Dana Spatz, Branch Chief 

Date

April 22, 2009 

U. S. Environmental Protection Agency 

Office of Pesticide Programs 

Environmental Fate and Effects Division 

Environmental Risk Branch III 

1200 Pennsylvania Ave., NW 

Mail Code 7507P 

Washington, DC 20460

2 
Table of Contents

I. Purpose ...................................................................................................................................... 4 

II. Nature of Regulatory Action .................................................................................................... 4 

 A. Conclusions from Previous Risk Assessments.................................................................... 4 

1. Tebupirimphos Interim Registration Eligibility Decision, 2000......................................... 5 

Report on FQPA Tolerance Reassessment Progress and Interim Risk Management Decision 

Phostebupirim (Tebupirimphos) EPA-R-00-017, September 2000. ....................................... 5 

2. Drinking Water Exposure Assessment................................................................................ 5 

3. Organophosphate Cumulative Assessment and Tebupirimphos Reregistration Eligibility 

Decision, 2006 ........................................................................................................................ 6 

III. Stressor Source and Distribution............................................................................................6 

A. Mechanism of Action............................................................ 6 

 B. Overview of Pesticide Usage .............................................................................. 6 

C. Environmental Fate and Transport................................................................................... 10 

1. Physical and Chemical Properties................................................................................ 10 

2. Environmental Fate Summary ...................................................................................... 10 

a. Environmental Fate ...................................................................................................... 12 

b. Transformation Products.............................................................................................. 12 

c. Environmental Transport.............................................................................................. 13

 d. Bioaccumulation ................................................................................. ...13 

 e. Drinking Water Assessments ......................................................................... 13 

 f. Monitoring Data 14 

g. Water Treatment ........................................................................................................... 15

IV. Receptors.............................................................................................................................. 15

A. Effects to Aquatic Organisms..................................................................................... 16

B. Effects to Terrestrial Organisms ................................................................................. 17

C. Ecological Incidents.................................................................................................... 19

D. Ecosystems at Risk...................................................................................................... 19

V. Assessment Endpoints .......................................................................................................... 19

VI. Conceptual Model................................................................................................................. 20

A. Risk Hypotheses.............................................................................................................. 20

B. Diagram........................................................................................................................... 21 

VII. Analysis Plan Options........................................................................................................ 22

A. Ecological Risk Assessment ................................................................................................... 22

B. Endangered Species.......................................................................................................... 23 

C. Drinking Water Assessment.................................................................................................... 23

D. Clean Water Act...................................................................................................................... 24 

E. Anticipated Data Needs........................................................................................................... 25

1. Fate .................................................................................................................................. 26

 2. Effects................................................................................................................................ 31

VIII. Reference 36

Appendix A. 37 

3 
I. Purpose 

The purpose of this problem formulation is to provide a better understanding of the 

environmental fate and ecological effects of the registered uses of tebupirimphos (previously 

known as phostebupirim or MAT7484). Tebupirimphos is an organophosphate used as an “atplant” insecticide that is used to control corn rootworms, cutworms and other soil insect pests in 

field corn, sweet corn, popcorn, and corn grown for seed and silage. It is registered only for use 

on corn (terrestrial food and feed crops). There are no registrations for terrestrial non-food crops. 

This document will provide a plan for analyzing data relevant to tebupirimphos and for 

conducting updated ecological risk and drinking water assessments for its registered uses. 

Additionally, this problem formulation is intended to identify remaining data gaps, uncertainties 

and potential assumptions used to address those uncertainties relative to characterizing the 

ecological risk associated with the registered uses of tebupirimphos. 

II. Nature of Regulatory Action 

The Food Quality Protection Act of 1996 mandated the EPA to implement a new program for 

assessing the risks of pesticides, i.e., registration review.1 All pesticides distributed or sold in the 

United States generally must be registered by EPA. The decision to register a pesticide is based 

on the consideration of scientific data and other factors showing that it will not cause 

unreasonable risks to human health, workers, or the environment when used as directed on 

product labeling. The registration review program is intended to ensure that, as the ability to 

assess risk evolves and as policies and practices change, all registered pesticides continue to 

meet the statutory standard of no unreasonable adverse effects to human health and the 

environment. Changes in science, public policy, and pesticide use practices will occur over time. 

Through the new registration review program, the Agency periodically reevaluates pesticides to 

ensure that as change occurs, products in the marketplace can be used safely. 

As part of the implementation of the new Registration Review program pursuant to Section 3(g) 

of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA), the Agency is beginning its 

evaluation to determine whether tebupirimphos continues to meet the FIFRA standard for 

registration. This problem formulation for the environmental fate and ecological risk assessment 

chapter in support of the registration review is intended for the initial docket opening and public 

phase of the review process. 

A. Conclusions from Previous Risk Assessments 

The Agency has conducted previous ecological risk and drinking water exposure assessments on 

tebupirimphos that serve as a basis for this problem formulation. Each of the previous risk 

assessments is briefly discussed below. 

 

1 http://www.epa.gov/oppsrrd1/registration_review/

4 
1. Tebupirimphos Interim Registration Eligibility Decision, 2000 

Report on FQPA Tolerance Reassessment Progress and Interim Risk 

Management Decision Phostebupirim (Tebupirimphos) EPA-R-00-017, 

September 2000. 

The results of the Agency’s risk assessment for tebupirimphos are discussed in the September 

2000 Report on FQPA Tolerance Reassessment Progress (TRED) (USEPA, 2000) 

The human health risk assessment was based on estimated drinking water concentrations 

(EDWCs) presented in a 1998 drinking water assessment (P. Jennings; December 08, 1997). 

These EDWCs represent use on citrus at 0.153 lb a.i./A and were obtained using the Tier I SCIGROW model for ground water and the Tier I GENEEC models for surface water. The EDWCs 

were 0.006 ppb in ground water, and 1.89 ppb and 0.86 ppb, respectively, for acute (peak) and 

chronic (56-day average) exposure in surface water. Because dietary risk assessments based on 

exposures solely from food do not exceed levels of concern, both acute and chronic drinking 

water levels of comparison (DWLOCs) were calculated and compared to EPA model estimates 

and monitoring results. For the most sensitive subgroup (children <1 year), the acute (19.04 ppb) 

and the chronic (1.65 ppb) DWLOCs did not indicate a risk concern from potential exposure to 

tebupirimphos residues in drinking water. No monitoring data or model estimates were 

considered for tebupirimphos-oxon in this assessment. 

The Agency also completed a screening-level ecological risk assessment (dated November 30, 

1999, addendum dated April 4, 2001) in support of the registered uses of tebupirimphos. 

Completion of the organophosphate (OP) cumulative assessment (USEPA 2006) resulted in 

finalization of the tebupirimphos TRED (USEPA 2006). 

The previous ecological risk assessments for corn (D288456, D350993, 2009) determined that 

tebupirimphos posed an acute risk above the Agency’s concern levels to small birds (including 

terrestrial-phase amphibians and reptiles as surrogate species) and mammals that consume 

tebupirimphos granules; piscivorous birds and mammals that consume fish species with 

bioaccumulated tebupirimphos residues; and fish, aquatic-phase amphibians, and crustaceans 

inhabiting water bodies exposed to tebupirimphos residues via off-site runoff. Potential chronic 

risk also exceeded concern levels for freshwater and estuarine/marine crustaceans inhabiting 

water bodies exposed to tebupirimphos residues via runoff. Potential risks to other non-target 

taxonomic groups did not exceed concern levels. Due to lack of toxicity data for bees and 

terrestrial plants, the risks to those taxa from tebupirimphos exposure is unknown. Also, 

potential risks to wildlife and plants from degradation product, OMAT, are unknown. 

2. Drinking Water Exposure Assessment 

A drinking water exposure assessment was completed in 2008 (D356184) using Tier II 

PRZM/EXAMS surface water modeling for proposed new corn use (increased rate and use area). 

The proposed new rate is 0.26 lbs ai/A. The exposure in drinking water from the current 

maximum application was also provided to HED. This assessment estimated the drinking water 

concentrations for the parent compound only. This assumed that 100 percent of the 

5 
tebupirimphos is transformed to tebupirimphos-oxon through chlorination and the toxicities are 

similar or equal. 

3. Organophosphate Cumulative Assessment and Tebupirimphos

Reregistration Eligibility Decision, 2006 

Because the Agency determined that tebupirimphos shares a common mechanism of toxicity 

with the structurally-related organophosphates insecticides, a cumulative human health risk 

assessment for the OP pesticides was necessary before the Agency could make a final 

determination of reregistration eligibility of tebupirimphos. The cumulative assessment was 

finalized in 2006, http://www.epa.gov/pesticides/cumulative/common_mech_groups.htm#op 

(USEPA 2006). 

The OP cumulative relied on a combined assessment methodology of modeling and monitoring 

data for human health exposure via drinking water. Unlike other assessments, the cumulative 

approach focused on regions of high OP use. No ecological risks were evaluated in the OP 

cumulative process. The Agency requested human health toxicity data on tebupirimphos-oxon to 

further refine estimates. 

 III. Stressor Source and Distribution 

A. Mechanism of Action 

Tebupirimphos [O-[2-(1,1-dimethylethyl)-5-pyrimidinyl] O-ethyl O-(1-methylethyl) 

phosphorothioate] is a non-systemic, broad-spectrum soil organophosphate (OP) insecticide. 

The CAS number and PC Code for tebupirimphos are 96182-53-5 and 129086, respectively. 

Several formulations containing tebupirimphos also contain the active ingredient cyfluthrin (PC 

Code 128831 and CAS No. 68359-37-5). Only tebupirimphos is discussed in this document. The 

mechanism of action for tebupirimphos is through inhibition of acetylcholinesterase, an enzyme 

that is necessary for normal nerve function. OP class pesticides react with a serine hydroxyl 

group within the enzyme active site, phosphorylating this hydroxyl group and yielding a 

hydroxylated "leaving group". This process inactivates the enzyme and blocks the degradation of 

the neurotransmitter acetylcholine. The synaptic concentrations of acetylcholine then build up 

and hyperexcitation of the central nervous system (CNS) occurs. 

Tebupirimphos is a pyrimidine phosphorothionate organophosphate (OP). An important bioactivation step occurs for OP pesticides containing a sulfur atom attached to the phosphorus by a 

double bond (e.g., phosphorothionates). For these compounds, oxidative desulfuration may occur 

to form an oxon (i.e., tebupirimphos oxygen analog) that has been found in some OPs to be more 

toxic than the parent compound. 

B. Overview of Pesticide Usage 

 

6 
Tebupirimphos is used as an insecticide on terrestrial food and feed crops and terrestrial feed 

crops. The BEAD screening level usage report states that tebupirimphos is an “at-plant” granular 

insecticide that is used to control corn rootworms, cutworms and other soil insect pests in field 

corn, sweet corn, popcorn, and corn grown for seed and silage. Based on usage data provided by 

the Biological and Economic Analysis Division (BEAD), on average, roughly 500,000 pounds of 

tebupirimphos is applied annually to corn crops (Table 1). Most of the tebupirimphos use is on 

corn (non-sweet) with a small amount (1000 lb a.i.) applied annually to sweet corn. 

Table 1. Screening Level of Usage in Agricultural (SLUA) of Tebupirimphos 

(Source: BEAD SLUA report September 26, 2008) [All number rounded] 

Crop Pounds A.I. Percent Crop 

(Average) 

Percent Crop 

(Total) 

Corn 500,000 5 10 

Sweet Corn 1,000 <12 5 

Rice1 <2.53 <1 <2.5 

Sorghum1 <5004 <1 <2.5 

Sunflowers1 <500 <1 <1 

1 These crops were not known to be listed on active end use product registrations when this 

report was run.

2

<1' indicates less than 1 percent of crop is treated. 

3

<2.5' indicates less than 2.5 percent of crop is treated.

4

<500' indicates less than 500 pounds of active ingredient. 

 

 

The SLUA data sources used in the BEAD assessment include: USDA-NASS (United States 

Department of Agriculture's National Agricultural Statistics Service) 2001-2006, Private 

Pesticide Market Research, 2001-2007, NPUD 2002 (National Pesticide Use Database) of the 

CropLife America Foundation and California, DPR data. These results reflect amalgamated data 

developed by the Agency and are releasable to the public. 

 

Currently, tebupirimphos (Aztec® Insecticide) is only registered for use on corn. The labels 

restrict its use to Arkansas, Colorado, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, 

Louisiana, Michigan, Minnesota, Missouri, Montana, Nebraska, Nevada, New Mexico, North 

Dakota, Ohio, Oklahoma, Pennsylvania, South Dakota, Tennessee, Texas, Utah, Vermont, West 

Virginia, Wisconsin, and Wyoming. As shown in Figure 1, based on U.S. Geological Survey 

(USGS) National Water Quality Assessment Program (NAWQA) data from 2002, tebupirimphos 

is used on corn, primarily in the mid-portion and corn belt of the United States. Local uses have 

been granted for Louisiana, Mississippi, and Texas (Table 2). 

7 
Figure 1. Map of Estimated Annual Agricultural Use of Tebupirimphos in 2002. 

http://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=02&map=m2024 

Application information for tebupirimphos is summarized in Table 2. 

There are three registered products containing tebupirimphos, Aztec® 2.1 % (EPA Reg. 264-

813), Aztec®3.78% (EPA Reg. 264-839) and Aztec® 4.67 % (EPA Reg. 264-811) Aztec 

Granular insecticide contains two active ingredients (Table 2), tebupirimphos and cyfluthrin. 

Tebupirimphos is limited to ground incorporation application methods such as band, T-band, and 

in-furrow. Only the band method specifies a minimum incorporation depth (1-inch). Single 

application rates range from 0.144 to 0.146 pounds active ingredient/acre (lbs a.i./A) and 

seasonal application rates are up to 0.146 lbs a.i./A. The registrant has recently proposed to 

increase the maximum use rate (0.20 to 0.26 lb a.i./A) and decrease allowable row spacing (20 

inch spacing). These proposed changes have not yet been approved.

8 
Table 2. Maximum Tebupirimphos1

 Crops, Use Rates and Management Practices (Generalized 

Screening Level Portrayal of the Current Label Uses as of 08/11/08). 

Maximum Rate 

per Application 

Maximum 

Application Rate per 

period 

Use Site 

FOOD/FEE

D USES 

(Use Group 

Code) lb product/1K lb ai/A/crop cycle or 

year 

 Application Equipment 

 //Type (Reg # Code) 

corn (silage) 

(*B1) 

0.0083 to 0.0084 0.144 to 0.146 Soil incorporation equipment 

//Soil band treatment/ Soil in-furrow 

treatment/ Soil treatment 

 (T-banding) (a),(b),(c) 

corn, field 

(*A2) 

0.0083 to .0084~ 0.144 to 0.146 Soil incorporation equipment 

//Soil band treatment/ Soil in-furrow 

treatment/ Soil treatment 

(T-banding) (a),(b),(c) 

corn, pop 

(*A2) 

0.0083 to 0.0084~ 0.144 to 0.146 Soil incorporation equipment 

//Soil band treatment/ Soil in-furrow 

treatment/ Soil treatment 

(T-banding) (a),(b),(c) 

corn, sweet 

(*A2) 

0.0083 to 0.0084~ 0.144 to 0.146 Soil incorporation equipment 

//Soil band treatment/ Soil in-furrow 

treatment/ Soil treatment 

 (T-banding) (a),(b),(c) 

1

 All products are granular formulations 

2 1K linear feet is 1000 linear feet. 

3

 USE GROUP CODES: A2 = TERRESTRIAL FOOD+FEED CROP; B1= TERRESTRIAL FEED CROP 

Use Site/Registration Number(s) for Maximum Dosages with Reg # Codes 

FOOD/FEED USES 

corn (silage) 264-811(b), 264-812(c), 264-813(c), 264-839(a), LA01000800(b), LA04000200(c), 

LA04001000(b), MS04000100(c), MS04000600(b), TX04000100(b), TX04002400(b) 

corn, field 264-811(b), 264-812(c), 264-813(c), 264-839(a), LA01000800(b), LA04000200(c), 

LA04001000(b), MS04000100(c), MS04000600(b), TX04000100(b), TX04002400(b) 

corn, pop 264-811(b), 264-812(c), 264-813(c), 264-839(a), LA01000800(b), LA04000200(c), 

LA04001000(b), MS04000100(c), MS04000600(b), TX04000100(b), TX04002400(b) 

corn, sweet 264-811(b), 264-812(c), 264-813(c), 264-839(a), LA01000800(b), LA04000200(c), 

LA04001000(b), MS04000100(c), MS04000600(b), TX04000100(b), TX04002400(b) 

9 
C. Environmental Fate and Transport 

1. Physical and Chemical Properties 

Chemical name: O-[2-(1,1-dimethylethyl)-5-pyrimidinyl] O-ethyl O-(1-methylethyl) 

phosphorothioate] 

Trade name(s): Aztec® 2.1 Granular Insecticide, Aztec® 3.78 Granular Insecticide, and 

Aztec® 4.67 Granular Insecticide 

Physical/Chemical properties: 

Molecular formula: C13H23N2O3PS 

 Molecular weight: 318.37 g/mol 

 Physical state: Colorless liquid 

 Melting point: Not known 

 Vapor pressure: 3.8 x 10-05 @ 20oC mm Hg 

 3.75 x 10-04 @ 25oC mm Hg;

 Solubility (20°C): 5.5 mg/L water; 

Octanol/Water Partition Coefficient: logKow = 4.19 @ 22 oC 

2. Environmental Fate Summary 

Based on available environmental fate data, tebupirimphos degradation appears to be primarily 

due to abiotic process (hydrolysis and photolysis in water). Hydrolysis half-lives range between 

47 to 41 days (pH 5 to pH 9) and photolysis in water is < 2 days. Photolysis on soil would be 

minimal, since tebupirimphos is soil incorporated. Tebupirimphos appears to be quite persistent 

to microbial degradation in the environment based upon soil metabolism studies (half-lives of 55 

to 1849 days). The vapor pressure of tebupirimphos (>10-05 mm Hg) is high enough that 

volatilization may be an important route of dissipation. Based on the relatively high Freundlich 

Kads values (12.4 to 15.6 mL/g) and Kocs (1022 to 2674 mL/goc), tebupirimphos is expected to be 

slightly mobile in soil. 

A number of degradation products, in addition to CO2 were identified in environmental fate 

studies (Table 3). The metabolite, OMAT (or oxon), was determined by the Health Effects 

Division (HED) to be of toxicological concern. The chemical names are listed in Appendix A. 

10 
Table 3: Environmental fate data for tebupirimphos. 

Study Value (units) Major Degradate 

Minor Degradates 

Source 

MRID# (other) 

Hydrolysis (t1/2) 

@ pH 5 47days 

@ pH 7 45 days 

@ pH 9 41 days 

DIMET (27%) 

TBHP (5%) 

42005465 

Aqueous 

Photolysis (t1/2) 

31 hrs in sterile aqueous 

solution at pH 5 

DBMAT (37%) 

DIMAT (10%) 

TBHP (5%) 

OMAT (5%) 

42005466 

Photolysis on 

Soil (t1/2) 106 days DBMAT (14%) 

TBHP (2%) 

42005467 

Air Photolysis 

(t1/2) No Data 

Aerobic Soil 

Metabolism (t1/2) 55 to 1849 days 

CO2 (31%) 

OMAT (<1 to 5.6%) 

TBHP (1 to 3.8%) 

IMATS (3%) 

42005468 

44299803 

Anaerobic Soil 

Metabolism (t1/2) 279 days 

IMATS (5%) 

TBHP (4%) 

CO2 (8%) 

42005468 

Anaerobic 

Aquatic 

Metabolism 

No Data 

Aerobic Aquatic 

Metabolism (t1/2) No Data 

Mobility 

Freundlich Kads

Tebupirimphos

12.4 to 15.6 

[Koc 1022 to 2674] 

OMAT

1.1 to 5.3 

42005469 

42005970 

Vapor Pressure 

3.75 x 10-4 mm Hg at 25 oC 

3.8 x 10-05 mm Hg at 20 oC 

(TRED) 

(D199163) 

Terrestrial Field 

Dissipation (t1/2) 

14 to 39 days OMAT 43092702 

43092703 

Fish 

Accumulation 

BCF: Whole body – 660X, 

Fillet – 110X, Viscera 

1100X 

TBHP, 

OMAT, 

HTBHP 

42005433 

42005475 

42005476 

logKow 4.19 Estimated with EPI 

Suite 

11 
a. Environmental Fate 

Hydrolysis, Photolysis: Tebupirimphos is degraded by abiotic hydrolysis. Hydrolysis half-lives 

are 47, 45, and 41 days at pH 5, pH 7, and pH 9, respectively. The soil photolysis and aqueous 

photolysis half-lives were 106 and 1.29 days, respectively. Although OMAT was detected in 

aqueous photolysis studies, it was not a major breakdown product. 

Aerobic soil metabolism: Two aerobic soil metabolism studies (MRID 42005468, 44299803) 

were submitted to the Agency. The aerobic soil metabolism study (MRID 42005468) provides 

acceptable data (DP 0171349). 

The aerobic soil metabolism study (MRID 44299803), which used three soils and three 

application rates, did not meet guideline requirements. Issues included no confirmation of 

aerobic conditions, no report on radiochemical purity of the pyrimidinyl ring-labeled 

tebupirimphos test material, and detections limit were not reported for HPLC and TLC analysis. 

The registrant addressed the deficiencies in a second study. The major observed degradation 

product was CO2. Other identified degradation products included TBHP, IMATS, and OMAT 

(the oxygen analog of tebupirimphos (or oxon) reached a maximum 5.6 % of applied 

radioactivity). The registrant used nonlinear regression to estimate “half-life” of tebupirimphos; 

half-lives ranged from 55 to 1849 days. The estimated half-lives increased with increasing 

application rates. For two of the soils with the lowest application rate, the estimated half-lives 

using nonlinear regression were 55 and 82 days, which tended to underestimate the residues 

remaining after 100 days. 

b. Transformation Products

A number of degradation products were identified in the environmental fate studies (Table 3). 

The maximum percent of applied radioactivity of these degradates are listed in Table 3. Three of 

these degradation products DIMET, DIMAT, and DBMAT were either measured at greater than 

10% of applied radioactivity in one or more of the environmental fate studies. OMAT, a 

degradate of toxicological concern was detected as minor degradation product (< 10% of 

applied) in the aqueous photolysis and aerobic soil metabolism studies. 

There are no submitted studies on the persistence of OMAT or the other degradation products. 

OMAT is one of several environmental transformation (aerobic metabolism, aqueous hydrolysis, 

terrestrial field dissipation) products of tebupirimphos. Although, EFED does not have enough 

data to determine (quantify) the persistence of OMAT in the environment, the environmental fate 

data indicate that OMAT is not a major environmental degradate (< 6 percent), but it is more 

mobile in soil than tebupirimphos. These limited data suggest that the “slow microbial 

transformation” of tebupirimphos will control the rate and amount of OMAT formed, thus, the 

OMAT concentrations should be less then the tebupirimphos concentrations. There are no data 

12 
for photodegradation in air, which may be a possible pathway for transformation of OPs to an 

oxygen analog.

c. Environmental Transport 

Based on the Freundlich Kads values (12.4 to 15.6 mL/g) and Koc values (1022 to 2674 mL/goc), 

tebupirimphos is classified as slightly mobile in soil according to the mobility classification 

scheme adopted by EFED (Bradbury, 2006; FTT, 2006). However, based upon limited number 

of samples, Kads was negatively correlated with organic carbon content. The OMAT 

transformation product which is structurally similar to tebupirimphos appears to be more mobile 

(Freundlich Kads = 1.4 to 3.6 mL/g ) than the parent chemical).. No data are available for the 

other degradation products. 

No laboratory volatility studies are available. The vapor pressure of tebupirimphos has been 

reported as ranging between 3.8 x 10-05 to 3.75 x 10-04 mm Hg at 20 and 25 oC, respectively. 

Laboratory volatility studies for tebupirimphos have been requested because the vapor pressure 

is >10-05 mm Hg (D19063, June 1994). The calculated Henry’s Law constant ranges between 

2.89 x 10-06 to 2.89 x 10-05 atm m3

/mol. Although no air monitoring data are available for 

tebupirimphos or tebupirimphos oxon , another OP, methidathion and it’s oxon, which have a 

similar vapor pressure of 2.5 x 10-06 mm Hg and lower Henry’s Law constant (3.97 x 10-09 atm 

m3

/mol), have been measured in air samples (Aston and Seiber, 1997). 

 d. Bioaccumulation

Tebupirimphos accumulated in fish with maximum bioconcentration factors of 110, 660 and 

1100x in edible tissues (fillet), whole body, and viscera, respectively. Depuration was minimal 

(2%) after 14 days. The estimated Kow also indicates the potential to bioaccumulate (logKow - 

4.19). Given the toxicity profile of tebupirimphos and Kow, these data suggest that 

tebupirimphos accumulation should be evaluated in registration review with respect to potential 

risks to organisms that consume aquatic animals that have accumulated the pesticide.

 e. Drinking Water Assessments

The human health risk assessment for the TRED (USEPA, 2000) was based on estimated 

drinking water concentrations (EDWCs) from a 1997 drinking water assessment (P. Jennings; 

December 08, 1997). These EDWCs represent use on corn at 0.153 lb a.i./A and were obtained 

using the Tier I SCI-GROW model for ground water and the Tier I GENEEC models for surface 

water. The EDWCs were 0.006 ppb in ground water, and 1.89 ppb and 0.86 ppb, respectively, 

for acute (peak) and chronic (56-day average) exposure in surface water. Ground water 

concentration was estimated to be 0.013μg/L. No monitoring data or model estimates were 

considered for tebupirimphos-oxon in this assessment. 

A Tier II drinking water assessment was prepared in 2008, in response to the registrants request 

to increase the use area and the application rate (0.27 lb a.i/A) of tebupirimphos on corn 

13 
(D356184). Surface water concentrations were estimated using PRZM and EXAMS models. 

Ground water concentrations were estimated using the Tier 1 SCI-GROW model. The Tier 2 

estimates for acute (peak), chronic (annual average), and long term average for tebupirimphos in 

surface water are 6.11, 0.66, and 0.35 μg/L, respectively. The estimated ground water 

concentrations using SCI-GROW is 0.028 μg/L, for acute and chronic exposure. These 

estimates used the persistence of parent tebupirimphos and the mobility of the (Kads of the 

tebupirimphos. Exposure then was based upon 100 percent conversion of the tebupirimphos to 

tebupirimphos-oxen during water treatment. 

 f. Monitoring Data

A monitoring study was initiated by the USEPA and USGS (Blomquist et al., 2001) to assess 

water quality in drinking water reservoirs. In this pilot study, twelve water-supply reservoirs and 

Community Water Systems (CWS) were selected based on vulnerability for pesticide 

contamination. Small watersheds with high pesticide use and high runoff potential were given 

the highest priority in the selection process. Other factors considered were representation across 

pesticide use areas, integration with ongoing monitoring efforts, and feasibility of monitoring. 

A sampling strategy was designed to measure pesticide concentrations in raw and finished 

drinking water as well as in reservoir outflow samples to provide an integrated water 

concentration for the reservoir watershed. For each site visit, the following three water samples 

were collected: 1) raw water from the intake spigot of the public water system, 2) finished-water 

at the compliance tap at the entry point to the distribution center, and 3) ambient reservoir water 

sample at the reservoir outlet. Sampling was designed to coincide with the period of intensive 

pesticide use, such as the post-pesticide application season. During a four- month postapplication period, each site was sampled quarterly for one year with biweekly sampling 

collection. In addition, two sites were sampled at weekly intervals for six months after the 

application season to improve the estimate of peak concentrations for short-lived compounds. 

Raw and finished drinking water samples were taken at most sampling times, and each water 

sample was analyzed using the USGS analytical schedules 2001, 9060, and 9002. Finished 

water samples were not quenched to eliminate chemical oxidation from residual chlorine. Out of 

186 pesticides and degradation products analyzed, 46 were organophosphorus (OP) pesticides 

and their degradation products. Tebupirimphos and the oxygen analog (OMAT) were analytes in 

the monitoring study. 

There were no detections of tebupirimphos in the USEPA/USGS Pilot Reservoir Study in raw or 

finished water samples (Blomquist, 2001). OMAT was detected at low concentrations in 3 of 

316 samples of raw water samples (Table 4). 

14 
Table 4. Summary statistics for tebupirimphos and degradation product OMAT (Blomquist et al., 

2001).

Raw Finished 

Chemical LOD 1

No. 

samples 

No. 

detects 

% 

Detected 

Max.

μg/L

Mean

μg/L

No. 

samples

No. 

detects 

% 

Detected 

Max. 

μg/L 

Mean

μg/L

Tebupirimphos 0.016 316 0 0 .0 0. 220 .0 0 .nd2 nd 

OMAT 0.008 316 3 0.9% 0.007 0.005 220 .0 0 nd nd 

1 LOD = Limit of Detection. The value reported is the most common limit of detection. For some chemicals, the LOD 

varied during method development.

2 nd is no detection.

A cursory review of open literature sources and assessments from other regulatory agencies 

reveals that there are a limited number of studies monitoring for tebupirimphos and its oxon 

degradation products in various media. Additional monitoring data will be evaluated when the 

risk assessment is prepared, including the USGS NAWQA database and the Pesticide Data 

Program as well as in open literature or other available data sources. 

g. Water Treatment 

Water treatment of surface water often includes chlorination as a disinfection process. 

Laboratory studies show that tebupirimphos forms tebupirimphos-oxon during chlorination. In a 

study conducted by the Biological and Economic Analysis Division (BEAD) of OPP and cited in 

the 2006 OP Cumulative (Section II.E.1 (USEPA, 2006), tebupirimphos was shown to be 

unstable in untreated water for 72 hours. Upon chlorination, the tebupirimphos formed an oxon 

(OMAT) within 1-hour of chlorination and was stable at least for 72 hours (Kamel et al, 2008). 

These results suggest that water (chlorination) treatment of tebupirimphos can lead to 

transformation to tebupirimphos-oxon, and that the oxon may be stable enough to pass through 

the distribution system to the tap. At the time this study was conducted, analytical methods were 

in development and had not yet gone through sufficient QA/QC to support quantitative results 

and so the conclusion is strictly qualitative. 

The Health Effects Division (HED) determined that tebupirimphos and oxygen analog of 

tebupirimphos (previously identified as OMAT) should be considered in the drinking water 

assessment (USEPA, 2008). 

IV. Receptors 

Consistent with the process described in the Overview Document (USEPA, 2004), the risk 

assessment for tebupirimphos will rely on a surrogate species approach. Toxicological data 

generated from surrogate test species, which are intended to be representative of broad 

taxonomic groups, are used to extrapolate to potential effects on a variety of species (receptors) 

included under these taxonomic groupings. 

15 
Acute and chronic toxicity data from studies submitted by pesticide registrants along with the 

available open literature are used to evaluate the potential direct and indirect effects of 

tebupirimphos on aquatic and terrestrial receptors. Toxicity studies for the technical grade active 

ingredient (TGAI), the typical end-use product (TEP), and the oxon degradate will be considered 

in this ecological risk assessment. Open literature studies are identified using EPA’s ECOTOX 

database2, which employs a literature search engine for locating chemical toxicity data for 

aquatic life, terrestrial plants, and wildlife. Research papers accepted into the ECOTOX 

database are screened using standard procedures to ensure consistent, high quality information; 

these studies will be considered for use in the risk assessment. The Ecological Incident 

Information System (EIIS), which tracks incident reports submitted to EPA, is used to identify 

supportive, line of evidence information on exposure of aquatic and terrestrial receptors. Data 

from all of these sources can also provide insight into the direct and indirect effects of 

tebupirimphos on biotic communities from loss of species that are sensitive to the chemical and 

from changes in structure and functional characteristics of the affected communities. 

As described in the Agency’s Overview Document (U.S. USEPA, 2004), the most sensitive 

endpoint for each taxonomic group will be used to calculate risk quotients (RQs). Assessment 

endpoints include direct toxic effects on the survival, reproduction, and growth of terrestrial and 

aquatic life as well as indirect effects such as reduction in prey base and/or modification of 

habitat. 

Information used to evaluate tebupirimphos and it’s degradates of concern include registrantsubmitted studies and a comprehensive review of the open literature. Open literature is 

identified using the ECOTOX database. ECOTOX integrates three previously independent 

databases - AQUIRE, PHYTOTOX, and TERRETOX - into a system that includes toxicity data 

derived predominately from the peer-reviewed literature, for aquatic and terrestrial organisms. 

Other information that is used to evaluate toxicity and potential ecological risks includes use of 

the acute probit dose-response relationship to establish the probability of an individual effect and 

reviews of the Ecological Incident Information System (EIIS). A summary of the available 

ecotoxicity information and the incident information for tebupirimphos are provided below. 

A. Effects to Aquatic Organisms 

A summary of the most sensitive aquatic toxicity data for tebupirimphos based on a current 

Agency review of all submitted studies with fish, invertebrates, and aquatic plants is provided in 

Table 5. Data indicate that tebupirimphos is very highly toxic to fish and very highly to 

moderately toxic to invertebrates on an acute exposure basis. 

 

2

 http://www.epa.gov/ecotox 

16 
Table 5. - Summary of Acute and Chronic Toxicity Profile for Aquatic Animals and Plants Exposed 

to Tebupirimphos Technical. 

Acute Toxicity Chronic Toxicity 

Species 96-hr 

LC50/EC50

(μg a.i./L) 

48-hr EC50 

(μg a.i./L) 

Toxicity 

Classification 

(MRID) 

NOAEC / 

LOAEC 

(μg a.i./L) 

Endpoints 

(MRID) 

Freshwater Animals 

Bluegill sunfish 

(Lepomis macrochirus) 89 -- 

Very highly 

toxic 

(42005424) 

-- -- 

Fathead minnow 

(Pimephales promelas) -- -- -- 130 / 265 Growth (42784502) 

Water flea 

(Daphnia magna) -- 0.078 

Very highly 

toxic 

(42005428) 

0.011 / 0.022 Survival 

(42784503) 

Paper pondshell 

(freshwater mussel) 

(Anodonta imbecillis) 

2300 -- Moderately toxic 

(43048201) -- -- 

Estuarine/marine Animals 

Sheepshead minnow 

(Cyprinodon variegatus) 36 -- 

Very highly 

toxic 

(44193602) 

-- -- 

Mysid 

(Americanmysis bahia) 6.63 -- 

Very highly 

toxic 

(44169501) 

0.118 / 0.252 Reproduction 

(44314901) 

Eastern oyster 

(Crassostrea virginica) 958 -- Highly toxic (44193601) -- -- 

Aquatic Plants 

Species Endpoint (μg a.i./L) Effect (MRID) 

Freshwater green algae 

(S. capricornutum) 

96-hr EC50 = 630 

NOAEC = 240 Biomass (44187001) 

Duckweed 

(Lemna gibba) 

7-day EC50 = 8800 

NOAEC = 1840 Front count (44187002) 

B. Effects to Terrestrial Organisms 

A summary of the most sensitive terrestrial toxicity data for tebupirimphos based on all 

submitted studies with birds, mammals, honeybee, and terrestrial plants is provided in Table 6. 

The data indicate that tebupirimphos is highly to moderately toxic to birds and very highly to 

highly toxic to mammals on an acute exposure basis. No toxicity data with honeybees or 

terrestrial plants are available, the toxicity to these species exposed to the active ingredient is 

uncertain. A complete toxicity profile can be found in the EEB EUP Review document dated 

June 13 1995 and the data review memorandums dated June 24 1998, October 1 1998, and May 

15 2000. 

17 
Table 6 - Summary of Acute and Chronic Toxicity Profile for Terrestrial Animals and Plants 

Exposed to Tebupirimphos. 

Acute Toxicity Chronic Toxicity 

Species 48-hr LD50

(μg a.i./bee) 

Acute Oral 

LD50 

(mg a.i./kg 

bw)

Acute 

Dietary 

LC50 (mg 

a.i./kg diet) 

Toxicity 

Classification 

(MRID) 

NOAEC / 

LOAEC 

(mg a.i./kgdiet) 

Endpoints 

(MRID) 

Terrestrial Animals 

Bobwhite Quail 

(Colinus 

virginianus) 

-- 20.3 191 

Highly toxic 

(420054-05, 

-09 ) 

8.5 / 26 

Body weight 

gain 

(42005413) 

Mallard Duck 

(Anas 

platyrhynchos) 

-- -- 577 

Moderately 

toxic 

(42005410) 

9 / 19 Egg thickness 

(42784501) 

House Sparrow 

(Passer 

domesticus) 

-- 3.53 -- Highly toxic 

(42005415) -- -- 

White-footed 

Mouse 

(Peromyscus 

leucopus) 

-- -- 256 Highly toxic 

(42005412) -- -- 

Laboratory Rat 

(Rattus norvegicus) -- 1.8 -- 

Very highly 

toxic 

(42005436) 

5.0 

Tremors, 

body weight 

gains, 

cholinesterase 

inhibition 

(42005456) 

Honey Bee 

(Apis mellifera) No data -- -- No data -- -- 

Terrestrial Plants 

Crop Type of Study 

Species 

Endpoint 

(μg a.i./L) Effect (MRID) 

Seedling Emergence and Vegetative Vigor 

Monocots No data EC25 = No data 

NOAEC = No data No data 

Dicots No data EC25 = No data 

NOAEC = No data No data 

 

3 2.1% of the active ingredient in AZTEC 

18 
C. Ecological Incidents 

A preliminary review of the Ecological Incident Information System (EIIS)4

 maintained by the 

Agency’s Office of Pesticide Programs (OPP) did not find any incidents associated with 

tebupirimphos. Although no incidents were located, it should be noted that carcasses of small 

birds and mammals are often extremely difficult to find, and incidents are typically not reported 

unless kills are extensive. 

D. Ecosystems at Risk 

Tebupirimphos is formulated as a granule that may be applied by ground equipment in a band, Tband, or in-furrow to terrestrial habitats for agricultural and non-agricultural uses. The 

ecosystems potentially at risk are often extensive in scope; therefore, it may not be possible to 

identify specific ecosystems during the development of a nation-wide ecological risk assessment. 

However, in general terms, terrestrial ecosystems potentially at risk could include the treated 

field and immediately adjacent areas that may receive runoff. Areas adjacent to the treated field 

could include cultivated fields, fencerows and hedgerows, meadows, fallow fields or grasslands, 

woodlands, riparian habitats, and other uncultivated areas. 

Tebupirimphos has the potential to contaminate surface water after application via runoff for 

weeks to months post-application (i.e., aerobic soil metabolism half-lives of 55 to 1849 days). In 

general terms, aquatic ecosystems potentially at risk include water bodies adjacent to, or down 

stream from, the treated field and might include impounded bodies such as ponds, lakes and 

reservoirs, or flowing waterways such as streams or rivers. For uses in coastal areas, aquatic 

habitat also includes marine ecosystems, including estuaries. 

The similarity of tebupirimphos’s vapor pressure to methidathion (and subsequent detection) 

suggests that the volatilization of tebupirimphos from soil and water might result in off site 

exposure via atmospheric transport. 

V. Assessment Endpoints 

The most sensitive toxicity endpoints are used from surrogate test species to estimate treatmentrelated direct effects on acute mortality and chronic reproductive, growth, and survival 

assessment endpoints. Surrogate aquatic organisms include freshwater and estuarine/marine fish 

and invertebrates, and surrogate terrestrial animal species include birds and mammals. The risk 

assessment also assumes that reptiles and terrestrial-phase amphibians are approximately as 

sensitive to pesticide-induced effects as birds. These tests include short-term acute, subacute, 

and reproduction studies and are typically arranged in a hierarchical or tiered system that 

progresses from basic laboratory tests to applied field studies. 

For plants in terrestrial and semi-aquatic environments, the screening assessment endpoint is the 

perpetuation of populations of non-target species (crops and non-crop plant species). When data 

 

4 EIIS was accessed on 08 September 2008. 

19 
are available, endpoints assessed include emergence of seedlings and vegetative vigor. 

Terrestrial plant toxicity data for tebupirimphos are not available for consideration in this risk 

assessment. 

For aquatic plants, the assessment endpoint is the maintenance and growth of standing crop or 

biomass. When data are available, measurement endpoints for this assessment endpoint focus on 

algal and vascular plant (i.e., duckweed) growth rates and biomass measurements. There are no 

aquatic plant toxicity data for tebupirimphos available for consideration in this risk assessment. 

VI. Conceptual Model 

A. Risk Hypotheses 

Risk hypotheses are specific assumptions about potential adverse effects (i.e., changes in 

assessment endpoints) and may be based on theory and logic, empirical data, mathematical 

models, or probability models (USEPA 2004). For this assessment, the risk is stressor-initiated, 

where the stressor is the release of tebupirimphos to the environment. The following risk 

hypothesis is presumed for this screening-level assessment: 

Tebupirimphos, when used in accordance with current labels, can result in off-site 

movement of the compound and its oxon transformation product via runoff (both 

dissolved phase and with eroded sediment) and atmospheric transport via volatilization 

and expose non-target organisms. Application to soil, even with incorporation, may also 

result in exposure to non-target organisms as animals may be exposed to tebupirimphos 

from granules remaining on the soil surface. Monitoring studies have identified the 

presence of tebupirimphos in water. These potential exposure pathways may result in 

adverse effects on the survival, growth, and/or reproduction of non-target terrestrial and 

aquatic organisms, including Federally-listed threatened and endangered species. 

20 
B. Diagram 

The environmental fate properties of tebupirimphos and it’s degradates of concern are similar to 

other OPs which have been observed in surface water and air monitoring studies. Aston and 

Sieber, 1997; Menconi and Siepmann, 1996; Majewski and Capel, 1999; Vogel and Capel, 2008 

have identified the presence of methidathion and methidathion-oxon, an OP compound with 

comparable fate properties to tebupirimphos, in surface waters, air, fog, and rain. Therefore, 

runoff, and volatilization are possible transport pathways for tebupirimphos into aquatic and 

terrestrial environments. As depicted in Figure 2, these transport mechanisms (e.g. sources) for 

tebupirimphos granules applied by ground equipment may result in the movement of 

tebupirimphos into aquatic (water) and terrestrial (soil) habitats. The movement away from the 

site of application represents exposure pathways for a broad range of biological receptors of 

concern (non-target animals) and the potential attribute changes, i.e., effects such as reduced 

survivals, growth, and reproduction in the receptors. 

Figure 2. Conceptual model for effects of ground applications of granular tebupirimphos, 

and the degradate of concern, OMAT, on non-target aquatic and terrestrial organisms. 

21 
VII. Analysis Plan Options 

In Registration Review, pesticide ecological risk assessments will follow the Agency’s 

Guidelines for Ecological Risk Assessment, will be consistent with “Overview of the Ecological 

Risk Assessment Process in the Office of Pesticide Programs, U.S. Environmental Protection 

Agency” (“Overview Document”) (January 2004), and will be done in accordance with Section 7 

of the Endangered Species Act. 

A. Ecological Risk Assessment 

Previously completed screening level risk assessments and exceedances of Agency levels of 

concern indicate a need to further examine and refine acute and chronic risk to terrestrial and 

aquatic animals. Analysis of potential indirect effects on listed species is also required. 

Uncertainties remaining from previous assessments and potential paths forward are described 

below. 

1. Risk Assessment Methods 

A new use assessment was recently conducted on corn (February, 2009). Corn is the only 

registered use for tebupirimphos. The new use included an expanded area of the country to be 

treated as well as higher application rates Terrestrial exposures will be evaluated using the most 

current version of T-REX at the time of the assessment. Because tebupirimphos is formulated as 

a granule, the assessment will utilize the LD50/squre foot method for risk estimation. Also, 

because the chemical has shown potential to bioaccumulate, consideration will also be given to 

terrestrial and aquatic animals that consume organisms that have accumulated the pesticide. 

Surface water concentrations of tebupirimphos will be estimated using PRZM/EXAMS. 

At this time, OPP has not settled on a specific model for estimating atmospheric transport of 

pesticides and resulting exposure to organisms in areas receiving pesticide deposition from the 

atmosphere. However, a number of transport models are currently under evaluation for both 

human health and ecological risk assessment with the key model input being pesticide flux. The 

submission of data allowing estimation of flux rates for tebupirimphos and its degradates of 

concern, along with the requested photo-oxidation data are expected to enhance the Agency’s 

ability to predict exposures in aquatic and terrestrial habitats far from the treated site. It is 

anticipated that methods to describe the contributions of atmospheric transport and deposition of 

tebupirimphos and its degradates of concern to exposures to non-target organisms will be fully 

explored and capable of being incorporated into this risk assessment as part of registration 

review. 

A cursory review of open literature sources and assessments from other regulatory agencies 

reveals that there are a number of studies monitoring for tebupirimphos and its oxon in various 

media. A more thorough review of open literature sources will be conducted and data from these 

sources, as well as from any sources submitted during the public comment period, will be 

analyzed to characterize exposure and the potential for long range transport. 

22 
B. Endangered Species 

Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), EPA will 

evaluate risks to Federally-listed threatened and/or endangered (listed) species from registered 

uses of tebupirimphos. This assessment will be conducted in accordance with the Overview 

Document (USEPA 2004), provisions of the ESA, and the Services’ Endangered Species 

Consultation Handbook (USFWS/NMFS 1998). 

The assessment of effects associated with registrations of tebupirimphos is based on an action 

area. The action area is considered to be the area directly or indirectly affected by the federal 

action, as indicated by the exceedance of Agency Levels of Concern (LOCs) used to evaluate 

direct or indirect effects. The Agency’s approach to defining the action area under the provisions 

of the Overview Document (USEPA 2004) considers the results of the risk assessment process to 

establish boundaries for that action area with the understanding that exposures below the 

Agency’s defined LOCs constitute a no-effect threshold. For the purposes of this assessment, 

attention will be focused on the footprint of the action (i.e., the area where tebupirimphos 

application occurs), plus all areas where offsite transport (i.e., runoff, volatilization and longrange atmospheric transport, etc.) may result in potential exposure that exceeds the Agency’s 

LOCs. Specific measures of ecological effect that define the action area for listed species 

include any direct and indirect effects and/or potential modification of its critical habitat, 

including reduction in survival, growth, and reproduction as well as the full suite of sublethal 

effects available in the effects literature. Therefore, the action area extends to a point where 

environmental exposures are below any measured lethal or sublethal effect threshold for any 

biological entity at the whole organism, organ, tissue, and cellular level of organization. In 

situations where it is not possible to determine the threshold for an observed effect, the action 

area is not spatially limited and is assumed to be the entire United States. 

C. Drinking Water Assessment 

An updated drinking water assessment (DWA) may be conducted as part of Registration Review 

to support future human health risk assessments of tebupirimphos. The recent new use 

assessment (D350993) included the highest labeled application rates for the only labeled use 

(corn). An updated DWA will include modeling using Tier II PRZM/EXAMS surface water 

models and Tier I SCIGROW, as well as consideration of any monitoring data that may be 

available. 

Laboratory evidence indicates that chlorination of drinking water transforms tebupirimphos in 

treated water to tebupirimphos-oxon and that the oxon may persist long enough to pass through 

the distribution system to the tap in some systems depending on the sequence of treatment. 

Therefore, in future drinking water assessments of tebupirimphos, formation of tebupirimphosoxon will be considered. The available chlorination study is qualitative in nature and in order to 

account quantitatively for oxon formation, additional data will be needed. EFED has requested 

submission of a chlorination study. 

 

23 
D. Clean Water Act 

Tebupirimphos is not identified as a cause of impairment for any water bodies listed as impaired 

under section 303(d) of the Clean Water Act, based on information provided at 

http://oaspub.epa.gov/tmdl/waters_list.impairments?p_impid=3 (accessed 11/17/08).

The Agency invites submission of water quality data for this pesticide. To the extent possible, 

data should conform to the quality standards in Appendix B of the OPP Standard Operating 

Procedure: Inclusion of Impaired Water Body and Other Water Quality Data in OPP’s 

Registration Review Risk Assessment and Management Process (see: 

http://www.epa.gov/oppfead1/cb/ppdc/2006/november06/session1-sop.pdf), in order to ensure 

they can be used quantitatively or qualitatively in pesticide risk assessments. 

24 
E. Anticipated Data Needs 

The Agency expects to conduct a quantitative assessment of all degradates of toxicological 

concern in Registration Review. In the absence of data, the oxon degradate is presumed to be of 

greater toxicity than the parent, based on the toxicity profiles of similar organophosphate 

insecticides. The studies anticipated to be needed will provide data about the toxicity, formation, 

and fate of these oxons. 

 E.1. Fate Data Justifications

The need for oxon formation data is dependent on the results of the requested toxicity studies. 

That is, if oxon toxicity studies demonstrate that the oxon is not of sufficient toxicity to alter risk 

conclusions or to impact mitigation decisions, then a quantitative exposure assessment for the 

oxon would not be necessary and no additional fate data for the oxon would be needed. If 

toxicity of the oxon is shown to be important, then fate studies would be necessary to quantify 

potential oxon formation. If these new fate studies show that the oxons are formed in amounts 

that are too low to affect risk conclusion, then no further refinements would be necessary and the 

additional fate and transport studies on oxons would not be required. In all cases, of sufficient 

data are not available, the risk assessment will be based upon conservative assumptions. 

E. 2. Toxicity Data Justification

In the absence of data, risk assessment will assume that the oxon degradates are of toxicological 

concern. It is anticipated that in future risk assessments, quantification of risk specific to the 

oxon degradates will be implemented using either available toxicity data or established default 

assumption. For example, the OP Cumulative Assessment assumed that the toxicity of oxons to 

mammals could be up to 100 times greater than that of the parent, and for frogs and aquatic 

invertebrates, the available data suggests that the ratio of toxicity of the parent may be more than 

mammals. The Division (EFED) will develop a set of standard default assumptions at a later 

date. 

25 
1. Fate 

6.1 Environmental Fate and Exposure 

Study Title: Photodegradation in Water

Guideline Number: 835.2240 

Test Substance: Tebupirimphos, Tebupirimphos oxygen analog (oxon) 

Rationale for Requiring the Data 

Since tebupirimphos is applied to terrestrial crops, a study of photodegradation in water is required per 40 

CFR part 158, which was promulgated on October 26, 2007. Aquatic photolysis studies represent pesticide 

fate in water and provide data on pesticide dissipation and on the nature and persistence of photo-oxidation 

products. The aqueous photolysis study previously submitted (MRID 42005466) provides supplemental 

information but is insufficient to adequately characterize the transformation of tebupirimphos in water because 

tebupirimphos was radiolabeled on only the pyrimidine ring. Therefore, the fate of the phosphate portion of 

the molecule could not be determined and degradates containing this moiety, which could include oxidative 

products of toxicological concern, would not have been identified. 

Tebupirimphos-oxon (OMAT) is a degradation product of tebupirimphos that is of toxicological concern. 

Laboratory studies indicate that OMAT may occur in aquatic environments by multiple processes, either 

through biotic or abiotic transformation processes. Detections of tebupirimphos-oxon in surface water 

monitoring confirm its potential for occurrence in water. Therefore, it is necessary to understand the fate of 

tebupirimphos and OMAT in water. For this purpose, studies of photodegradation in water are required, using 

each compound as a test substance. 

The fate of tebupirimphos and it’s degradates in aquatic environments cannot be characterized without the 

requested data. The requested data would allow EPA to refine its estimates of drinking water exposure and of 

acute risk (mortality) and chronic risk (growth and reproduction) estimates for all aquatic and estuarine/marine 

organisms, and allow it to define an action area for endangered species. Risk mitigation strategies (e.g., 

determining maximum tebupirimphos application rate that results in an RQ below the LOC) cannot be 

evaluated without these data. 

Practical Utility of the Data 

How will the data be used? 

Aquatic photolysis studies of tebupirimphos and tebupirimphos-oxon will be used to characterize its potential 

dissipation through aquatic photolysis. 

Tebupirimphos-oxon is a degradate of toxicological concern. The additional data can be used to refine the 

current aquatic exposure estimates, which represent exposure to total toxic residues rather than to individual 

degradates. 

How could the data impact the Agency’s future decision-making? 

Without these required data, the fate of tebupirimphos cannot be fully characterized and exposure to 

potentially toxic degradates cannot be quantified. In the absence of acceptable data, estimates of potential 

exposure to the oxon degradate will be made based on conservative assumptions about transformation. The 

use of tebupirimphos might need to be restricted in areas where endangered species could be exposed. The 

lack of these data will limit the flexibility the Agency and registrants have in coming into compliance with the 

Endangered Species Act and could result in use restrictions for tebupirimphos which are unnecessarily severe. 

26 
Study Title: Photodegradation in Air

Guideline Number: 835.2370 

Test Substance: Tebupirimphos 

Rationale for Requiring the Data 

Since tebupirimphos is applied to terrestrial crops, a photodegradation study in air is conditionally required 

per 40 CFR part 158, which was promulgated on October 26, 2007. This study will provide data on 

photolytic pesticide dissipation and on the nature and persistence of photoproducts formed from 

tebupirimphos in the vapor phase. 

 

Although, there is no air monitoring data available for tebupirimphos or tebupirimphos-oxon, the OP, 

methidathion and its oxon (which have similar vapor pressure and Henry’s Law constant) have been 

detected in air samples. Monitoring studies have detected the photoproduct methidathion-oxon in air and on 

pine needles up to 20 km away from any use site, indicating that photodegradation in air is likely to be an 

important degradation pathway for methidathion, producing the toxic degradate methidathion-oxon. 

Because of the tebupirimphos vapor pressure and Henry’s Law constant are similar to methidathion, data 

on photodegradation in air is necessary to quantify this potential exposure.

Practical Utility of the Data 

How will the data be used? 

No acceptable photodegradation in air studies are currently available. This study will be used to 

characterize the environmental fate of tebupirimphos. In particular, these data will be used to quantify 

formation of tebupirimphos-oxon through photodegradation in air. Given the demonstrated potential for 

long range transport of photoproducts of methidathion (an OP with similar fate properties as 

tebupirimphos), persistence data from this study will be used to quantify the spatial extent of exposure to 

methidathion and its photoproducts in order to define an action area for endangered species and explore 

risk mitigation strategies. 

How could the data change the Agency’s decision or impact the Agency’s future decision-making? 

Without these data, the fate of tebupirimphos in the atmosphere cannot be fully characterized. The amount 

of transformation of tebupirimphos in air, its persistence, and the persistence of its photoproducts is 

uncertain and so the potential for long range transport of the parent and its oxon degradates would also be 

an uncertainty. In the absence of acceptable data, conservative assumptions will be made. The use of 

tebupirimphos might need to be restricted in areas where endangered species could be exposed. The lack 

of these data will limit the flexibility the Agency and registrants have in coming into compliance with the 

Endangered Species Act and could result in use restrictions for tebupirimphos which are unnecessarily 

severe. 

27 
Study Title: Volatility - laboratory

Guideline Number: 835.1410 

Test Substance: Tebupirimphos 

Rationale for Requiring the Data 

Since tebupirimphos is applied to terrestrial crops, a laboratory volatility study is conditionally required per 

40 CFR part 158, which was promulgated on October 26, 2007. Laboratory volatility studies are conducted 

to determine the rate and extent of volatilization from treated areas. The vapor pressure suggest that 

volatilization could be a route of dissipation from treated areas, which may have biological effects in 

nontarget organisms at some distance from the treated site, either through exposure in the vapor phase or 

through deposition to water or terrestrial surfaces. When volatilized, it is not known whether 

tebupirimphos residues are subject to photo-oxidation to toxic degradates. 

Data are not available to describe the volatility of tebupirimphos and OMAT from soil. Volatility data are 

necessary to quantitatively assess this potential route of exposure. Based upon the results of this study, a 

field volatility study may also be required to characterize potential exposure. 

Practical Utility of the Data 

How will the data be used? 

No volatility data for tebupirimphos and OMAT are currently available. This information can be used to 

estimate both near field and longer range transport exposures and so can be used to estimate the spatial 

extent of exposure to tebupirimphos and its oxon order to define an action area for endangered species and 

explore risk mitigation strategies. 

How could the data change the Agency’s decision or impact the Agency’s future decision-making? 

Volatility data will allow the agency to quantitatively address exposure and transport of tebupirimphos in 

air and possibly provide inputs for future modeling efforts. In the absence of acceptable data, conservative 

assumptions will be used to estimate the spatial extent of exposure. 

28 
Study Title: Aerobic Aquatic Metabolism

Guideline Number: 835.4300 

Test Substance: Tebupirimphos 

Rationale for Requiring the Data 

Since tebupirimphos is applied to terrestrial crops, an aerobic aquatic metabolism study is required per 40 CFR 

part 158, which was promulgated on October 26, 2007. Aerobic aquatic metabolism studies facilitate an 

understanding of a compound’s degradation in the water column or sediment under aerobic (oxygen-rich) 

conditions. These studies provide data on the dissipation of tebupirimphos through aerobic metabolism and on 

the nature and persistence of metabolites generated by pesticide interaction with microorganisms in a 

water/sediment system. The dataset for tebupirimphos does not include an aerobic aquatic metabolism study. . 

The aerobic soil metabolism study, however, demonstrated tebupirimphos oxon is formed. Tebupirimphosoxon is major degradate of tebupirimphos that is of toxicological concern. The study should be conducted to 

characterize the transformation of tebupirimphos in water and sediment. The study should be able to follow 

the fate of the pyrimidine and phosphate portions of the molecule (previous studies only radiolabeled the 

pyrimidine ring). 

Practical Utility of the Data 

How will the data be used? 

Tebupirimphos and its oxon degradate may occur in aquatic environments but there are no data available 

regarding their fate under these conditions. These data will be used to quantify the amount of tebupirimphosoxon or other toxic degradates that may be formed in water. 

How could the data impact the Agency’s future decision-making? 

Without these required data, the fate of tebupirimphos cannot be fully characterized and exposure to 

potentially toxic degradates cannot be quantified. The lack of these data will limit the flexibility the Agency 

and registrants have in coming into compliance with the Endangered Species Act and could result in use 

restrictions for tebupirimphos which are unnecessarily severe. 

29 
Study Title: Aerobic Soil Metabolism

Guideline Number: 835.4100 

Test Substance: Tebupirimphos-oxon 

Rationale for Requiring the Data 

At this time, there are no environmental fate data available to quantify exposure (both aquatic and 

terrestrial) for tebupirimphos oxon resulting from the transformation of applied tebupirimphos. Aerobic 

soil metabolism studies facilitate an understanding of a compound’s degradation in soil resulting from 

pesticide interaction with soil microorganisms in aerobic (oxygen-rich) conditions in the laboratory. 

The aerobic soil metabolism studies (MRIDs 42005468, 44299803) provide supplemental information but 

are inadequate to characterize the formation of transformation products without the pyrimidine ring. 

Therefore, the fate of the phosphate portion of the molecule could not be determined and degradates 

containing this moiety, which could include oxidative products of toxicological concern, would not have 

been identified. 

The Agency is asking for a minimum environmental fate data set for tebupirimphos oxon in order to 

estimate aquatic and terrestrial exposure. Without these data, exposure estimates will be based on 

conservative assumptions. For example, for other OP pesticides, aquatic exposures for human health have 

been estimated by predicting surface water concentrations of the parent compound and then assuming 

100% conversion to the oxon (with an adjustment for molecular weight ratios). Fate data for oxon 

degradates of tebupirimphos are necessary in order to address this uncertainty and provide a more realistic 

estimate of exposure. 

Practical Utility of the Data 

How will the data be used? 

This study will provide data to determine transformation rates for input into exposure modeling

How could the data change the Agency’s decision or impact the Agency’s future decision-making? 

Laboratory studies demonstrate that tebupirimphos can be transformed to tebupirimphos oxon. 

Environmental fate data for oxons will allow estimation of oxon exposures using standard Agency 

exposure models. The lack of these data will limit the flexibility the Agency and registrants have in 

complying with the Endangered Species Act and could result in use restrictions for tebupirimphos which 

are unnecessarily severe. 

 

 

30 
2. Effects 

Guideline Number: 850.2100 

Test Substance: Tebupirimphos 

Title: Acute oral LD50 in Passerine Birds 

Test Species: To be determined 

Rationale for Requiring the Data 

Acceptable acute oral toxicity data on passerine species are required under 40 CFR Part 158. There are no 

avian acute oral toxicity data available for passerine birds tested with the technical grade active ingredient 

of tebupirimphos. Tebupirimphos is classified as highly to moderately toxic to non-passerine birds. 

Previous assessments have identified potential risks to birds; therefore, potential risks to passerine birds are 

also anticipated to exceed LOCs. 

 

Practical Utility of the Data 

How will the data be used? 

These data are necessary to evaluate the extent of potential acute risk to avian species and will be used to 

calculate RQs for birds. 

How could the data change the Agency’s decision or impact the Agency’s future decision-making? 

If future risk assessments are performed without these data, the Agency would assume that tebupirimphos 

“may affect” birds, which are also used as a surrogate for terrestrial amphibians and reptiles (and listed 

species from other taxa indirectly). Although potential risks to birds is likely to exceed LOCs without 

submission of such data, the magnitude of potential risks cannot be quantified until these data are 

submitted. The lack of these data will limit the flexibility that the Agency and registrants have in coming 

into compliance with the Endangered Species Act and could result in use restrictions which could be 

unnecessarily severe. 

31 
Guideline Number: 850.1735; 850.1740 

Test Substance: Tebupirimphos 

Title: Sediment toxicity studies 

Test Species: Sediment organisms as specified in the guidelines 

Rationale for Requiring the Data 

There are no sediment toxicity data available for benthic invertebrates. The conditional requirements for 

the data are triggered based on the soil-binding ability and persistence of tebupirimphos. Since 

tebupirimphos has the potential for adsorption to sediment based on its estimated Koc (1845) and log Kow

(4.19), in addition to its persistence (55 to 1849 days) in the environment, a chronic sediment toxicity study 

with benthic invertebrates is required to support the terrestrial outdoor uses. Given the acute and chronic 

LOC exceedances for freshwater and estuarine/marine crustaceans reported in previous assessments, it is 

anticipated that benthic invertebrates would also be at risk from tebupirimphos exposures. 

Practical Utility of the Data 

How will the data be used? 

These data are necessary to evaluate the extent and duration of potential risks to sediment dwelling 

organisms and will be used to calculate RQs for sediment organisms. 

How could the data change the Agency’s decision or impact the Agency’s future decision-making? 

The value of these studies would be in quantifying and potentially refining risks to benthic invertebrates. 

Defining an action area for endangered species and exploring risk mitigation strategies cannot be evaluated 

without these data. Without these data, the Agency cannot determine if the current application rates may 

result in direct adverse effects to estuarine/marine fish and/or indirect effects to other listed species. If 

future endangered species risk assessments are performed without these data, the Agency will assume that 

tebupirimphos “may affect” benthic invertebrates (and other listed species indirectly), and use of 

tebupirimphos may need to be restricted in areas where listed species could be exposed. The lack of these 

data will limit the flexibility the Agency and registrants have in coming into compliance with the 

Endangered Species Act and could result in use restrictions for tebupirimphos which are unnecessarily 

severe. 

32 
Guideline Number: 850.4100 and 850.4150 

Test Substance: Tebupirimphos TEP 

Title: Seedling emergence and vegetative vigor studies (Tier 1 and, if triggeredTier 2) 

Test Species: Terrestrial plant species as specified by 850.4100 and 850.4150 

Rationale for Requiring the Data 

There are no toxicity data available for terrestrial monocots and dicots. A risk assessment for exposure to 

monocots and dicots is needed based on tebupirimphos uses on corn. A seedling emergence study with 

monocots and dicots is required to support the terrestrial outdoor use patterns that are expected to reach this 

environment. The data will be utilized to determine whether the Agency’s current measures are effective 

for protecting terrestrial plants. 

Risk to terrestrial plants has not been quantified in previous assessments, and no terrestrial plant seedling 

emergence or vegetative vigor toxicity data are currently available for tebupirimphos. Based on the 

updated data requirements in 40 CFR part 158 (October 2007), these data are required to support all 

terrestrial use patterns, including those relevant to tebupirimphos. (Tier II phytotoxicity tests would be 

required if a 25% or greater detrimental effect is found in one or more plant species in the Tier I tests). 

These phytotoxicity studies should be conducted using the maximum label application rate of 

tebupirimphos typical end-use product (TEP). Without these studies, the Agency would have to presume 

risk to listed and non-listed terrestrial plants and to organisms that depend on terrestrial plants for 

sustenance, shelter, or reproduction. Potential risks, however, would not be able to be quantified. 

Practical Utility of the Data 

How will the data be used? 

Tier I seedling emergence and vegetative vigor toxicity data will be used to quantitatively estimate 

potential risks to terrestrial plants associated with the use of tebupirimphos. These data will be used to 

define an action area for endangered species and explore risk mitigation strategies. The data will reduce 

uncertainties associated with the risk assessment for terrestrial plants and will improve the Agency’s 

understanding of the potential effects of tebupirimphos on terrestrial plants. In the absence of Tier I data, 

risk to terrestrial plants will be presumed. 

How could the data change the Agency’s decision or impact the Agency’s future decision-making? 

The value of these seedling emergence and vegetative vigor studies would be in quantifying and potentially 

refining risks to non-target terrestrial plants. Defining an action area for endangered species and exploring 

risk mitigation strategies cannot be evaluated without these data. Without terrestrial plant toxicity data for 

tebupirimphos, the Agency cannot determine if the current application rates of tebupirimphos may result in 

direct adverse effects to terrestrial plants and/or indirect effects (e.g., via loss of habitat/cover, riparian 

vegetation effects, etc.). If future endangered species risk assessments are performed without these data, 

the Agency will assume that tebupirimphos “may affect” terrestrial plants directly and listed species from 

other taxa indirectly, and use of tebupirimphos may need to be restricted in areas where listed species could 

be exposed. The lack of these data will limit the flexibility the Agency and registrants have in coming into 

compliance with the Endangered Species Act and could result in use restrictions for tebupirimphos which 

are unnecessarily severe. 

 

33 
Guideline Number: 850.2100; 850.2200 

Test Substance: Tebupirimphos-oxon 

Study Title: Avian acute oral toxicity 

Test Species: Acute LD50 in Mallard duck or bobwhite quail and a passerine species 

Rationale for Requiring the Data 

Rationale: Acceptable acute oral toxicity data have not been submitted for the degradate of toxicological 

concern for tebupirimphos. 

Data on the oxon degradate are required because of its structural similarity to parent chemical. The oxon 

degradates of other organophosphate pesticides have been shown to be considerably more toxic than parent 

chemical, and based on environmental fate studies, there is the potential for avian exposure to this 

degradate of concern. The oxon degradate could be found on avian food items due to photolysis or 

metabolism of the parent compound on soil or in water or leaf surfaces. 

Practical Utility of the Data 

How will the data be used? 

These data are necessary to evaluate the extent of potential acute risk to avian species and will be used to 

calculate acute dose or dietary based RQs for birds. 

How could the data change the Agency’s decision or impact the Agency’s future decision-making? 

If future risk assessments are performed without these data, the Agency would assume that tebupirimphos 

and its degradate of concern “may affect” birds, which are also used as a surrogate for terrestrial 

amphibians and reptiles (and listed species from other taxa indirectly). Although potential risks to birds is 

likely to exceed LOCs without submission of such data, the magnitude of potential risks cannot be 

quantified until these data are submitted. The lack of these data will limit the flexibility that the Agency 

and registrants have in coming into compliance with the Endangered Species Act and could result in use 

restrictions which could be unnecessarily severe. 

34 
Guideline Number: 850.1075; 850.1010 

Test Substance: Tebupirimphos-oxon 

Study Title: Acute LC50 in fish and aquatic invertebrates 

Test Species: Acute studies in bluegill sunfish and rainbow trout; acute study in daphnids

Rationale for Requiring the Data 

Acute toxicity studies on tebupirimphos-oxon with aquatic organisms have not been submitted. Based on 

strucutural similarity to parent chemical, this degradate may be as toxic or more toxic than parent chemical. 

Also, based on data from other organophosphate insecticides, the oxon may be considerably more toxic to 

aquatic organisms than the parent chemical. Environmental fate studies show that the oxon degradate can 

be formed through microbial metabolism and photolysis. Therefore, there is the potential for exposure to 

aquatic organisms. 

Practical Utility of the Data 

How will the data be used? 

These data are necessary to evaluate the extent of potential acute risks to aquatic species and will be used to 

characterize the magnitude and duration of potential risks to aquatic species. 

How could the data change the Agency’s decision or impact the Agency’s future decision-making? 

If future risk assessments are performed without these data, the Agency would assume that the pesticide 

and its degradates of concern “may affect” aquatic organisms, which are also used as a surrogate for 

aquatic amphibians (and listed species from other taxa indirectly). Although potential risks to aquatic 

organisms is likely to exceed LOCs without submission of such data, the magnitude of potential risks 

cannot be quantified until these data are submitted. The lack of these data will limit the flexibility that the 

Agency and registrants have in coming into compliance with the Endangered Species Act and could result 

in use restrictions which could be unnecessarily severe. 

35 
VIII. References 

Aston LS, Seiber JN. 1997. Fate of summertime airborne organophosphate pesticide residues in the Sierra Nevada 

Mountains. J Environ Qual. 26:1483–1492. 

Blomquist, J.D., J.M. Dennis, J.L. Cowles, J.A. Hetrick, R.D. Jones, and N.B. Birchfield. 2001. Pesticides in 

Selected Water-Supply Reservoirs and Finished Drinking Water, 1999-2000: Summary of Results from a 

Pilot Program. Open File Report 01-456. U.S. Department of Interior, United States Geological Survey, 

Baltimore, MD. 

Kamel, A., C. Byrne, C. Vigo, J. Ferrario, C. Stafford, G. Verdon, F. Siegelman, S. Knizner, and J. Hetrick. 2008. 

Oxidation of selected organophosphate pesticides during chlorination of simulated drinking water. Water 

Research. 43:522-534 

Menconi, M. and S. Siepmann. 1996. Hazard Assessment of the Insecticide Methidathion to Aquatic Organisms in 

the Sacramento-San Joaquin River Systems. California Department of Fish and Game. Administrative 

Report 96-1. 

U. S. Environmental Protection Agency. 2002. Interim Reregistration Eligibility Decision for Methidathion (List A, 

Case 0034). http://www.epa.gov/pesticides/reregistration/REDs/methidathion_ired.pdf. 

U.S. Environmental Protection Agency. 2004. Overview of the Ecological Risk Assessment Process in the Office 

of Pesticide Programs, U.S. Environmental Protection Agency. Endangered and Threatened Species 

Effects Determinations. Office of Prevention, Pesticides and Toxic Substances, Office of Pesticide 

Programs, Washington, D.C. January 23, 2004. http://www.epa.gov/espp/consultation/ecoriskoverview.pdf 

U. S. Environmental Protection Agency 2006. Organophosphorus Cumulative Risk Assessment 2006- Update. 

Prevention, Pesticides and Toxic Substances (EPA-HQ-OPP-2006-0618-0002). 

http://www.epa.gov/pesticides/cumulative/2006-op/op_cra_main.pdf 

U. S. Environmental Protection Agency 2007. 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/ 

U. S. Environmental Protection Agency. 2007b. Ecological Incident Information System. 

http://www.epa.gov/espp/consultation/ecorisk-overview.pdf 

U.S.Environmental Protection Agency. 2008. Fate of High Priority Organophosphate (OP) Pesticides During 

Drinking Water Treatment. EPA/600/R-08/089. September 2008. National Exposure Research Laboratory 

(NERL), Office of Research and Development. United States Environmental Protection Agency. Athens, 

Georgia. 

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. 

Vogel, J.R., M.S. Majewski, and P.D. Capel. 2008. Pesticides in Rain in Four Agricultural Watersheds in the United 

States. J Environ Qual 37:1101-1115. 

Washburn, A. 2003. The Environmental Fate of Methidathion. California Department of Pesticide Regulation. 

36 
Appendix A. 

Table 1. Chemical names for tebupirimphos and selected degradation products. 

Parent Chemical Name 

Tebupirimphos O-[2-(1,1-dimethylethyl)-5-pyrimidinyl] O-ethyl O-(1-methylethyl) 

phosphorothioate] 

Degradates 

OMAT 2-(1,1-dimethylethyl)-5-pyrimidinyl ethyl 1-methylethyl phosphate 

IMATS S-Ethyl O-(1-methylethyl) O-[2-(1-methylethyl)-5-pyrimidinyl] 

phosphorothioate 

DBMAT O-Ethyl O-(1methylethyl) O-(5-pyrimidinyl) phosphorothioate), 

DIMAT O-[2-(1,1-Dimethylethyl)-5-pyrimidnyl O-ethyl] O-ethyl O-hydrogen 

phosphorothioate 

DIMET O-[2-(1,1-Dimethylethyl)-5-pyrimidinyl] O-ethyl-O-hydrogenphosphorothioate 

HTBHP 2-(1,1-Dimethyl-2-hydroxyethyl)-5-hydroxypyrimidine 

TBHP 2-(1,1-dimethyl)-5-hydroxypyrimidine) 

37