UNITED STATES ENVIRONMEN TAL PROTECTION AGENCY WASHINGTON D.C., 20460

MEMORANDUM APRIL 22, 2009

Subject: Registration Review – Preliminary Problem Formulation for the Ecological Risk and Drinking Water Exposure Assessme nts for Tebupirimphos (PC Code 129086; D360013)

To: Wilhelmena Livingston, Chemical Review Manager Special Review Branch Special Review and Rere gistration 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 (E FED) 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 pr ovide an overview of wh at is currently known regarding the environmental fate and ecological effects associated with tebupirimphos and its degradation products and outlines uncertainties re garding attributes of the parent compound and its transformation products. It describes the preliminary ecological ri sk hypothesis and the processes that will be used during the completion of drinki ng 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 Previ ous Risk Assessments.................................................................... 4

1. Tebupirimphos Interim Registra tion Eligibility Decision, 2000......................................... 5 Report on FQPA Tolerance Reassessment Progr ess 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 Te bupirimphos 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 A ssessments ........................... .............................................. 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 th e 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, cutwor ms 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 analyz ing data relevant to tebupirimphos and for conducting updated ecological risk and drinking water assessments for its registered uses. Additionally, this problem formula tion is intended to identify rema ining data gaps, uncertainties and potential assumptions used to address thos e 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 mandate d 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 re gistered by EPA. The decision to register a pesticide is based
on the consideration of scientific data and other factors showing th at it will not cause unreasonable risks to human health, workers, or the environment when used as directed on product labeling. The registration re view program is intended to en sure that, as the ability to assess risk evolves and as policie s and practices change, all regist ered pesticides continue to meet the statutory standard of no unreasonabl e 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 Ag ency periodically reeval uates pesticides to ensure that as change occurs, products in the marketplace can be used safely.

As part of the implementation of the new Regist ration Review program purs uant to Section 3(g) of the Federal Insecticide, Fungi cide 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 en vironmental fate and ecological risk assessment chapter in support of the regist ration review is intended for th e initial docket opening and public phase of the review process.

A. Conclusions from Previous Risk Assessments

The Agency has conducted previous ecological ri sk and drinking water exposure assessments on tebupirimphos that serve as a basis for this probl em formulation. Each of the previous risk assessments is briefly discussed below

.

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

41. Tebupirimphos Interim Registra tion Eligibility Decision, 2000 Report on FQPA Tolerance Reassessment Progress and Interim Risk Management Decision Phostebupi rim (Tebupirimphos) EPA-R-00-017, September 2000.

The results of the Agency’s risk assessment fo r tebupirimphos are discus sed 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 wate r. 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 calc ulated 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 screeni ng-level ecological risk assessment ( dated November 30, 1999, addendum dated April 4, 2001 ) in support of the registered uses of tebupirimphos. Completion of the organophospha te (OP) cumulative assessme nt (USEPA 2006) resulted in finalization of the tebupiri mphos TRED (USEPA 2006).

The previous ecological risk assessments for corn (D288456, D350993, 2009) determined that tebupirimphos posed an acute risk above the Agen cy’s concern levels to small birds (including terrestrial-phase amphibians and reptiles as su rrogate 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 re sidues via off-site runoff. Potential chronic
risk also exceeded concern levels for freshwat er and estuarine/marine crustaceans inhabiting water bodies exposed to tebupirim phos residues via runoff. Pote ntial risks to other non-target taxonomic groups did not exceed concern levels. Du e to lack of toxicity data for bees and terrestrial plants, the risks to those taxa from tebupiri mphos 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 ne w 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

5tebupirimphos is transformed to tebupirimphos- oxon through chlorination and the toxicities are similar or equal.

3. Organophosphate Cumulative Assessment and Tebupirimphos Reregistration Elig ibility Decision, 2006

Because the Agency determined that tebupirim phos shares a common mechanism of toxicity with the structurally-related organophosphates insecticides, a cumulative human health risk assessment for the OP pesticides was necessa ry before the Agency could make a final determination of reregistrati on 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 asse ssment methodology of modeling and monitoring data for human health exposure via drinking wa ter. 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-dimethylet hyl)-5-pyrimidinyl] O -ethyl O -(1-methylethyl) phosphorothioate] is a non-system ic, broad-spectrum soil organophosphate (OP) insecticide. The CAS number and PC Code for tebupi rimphos are 96182-53-5 and 129086, respectively. Several formulations containing tebupirimphos also contain the active ingr edient cyfluthrin (PC Code 128831 and CAS No. 68359-37-5). Only tebupirim phos 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, phosphoryl ating this hydroxyl group and yielding a hydroxylated "leaving group". This pr ocess inactivates the enzyme a nd 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 phosphorothionat e organophosphate (OP). An important bioactivation step occurs for OP pe sticides 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

6Tebupirimphos is used as an insecticide on terrest rial food and feed crops and terrestrial feed crops. The BEAD screening level usag e report states that tebupirim phos is an “at-plant” granular
insecticide that is used to cont rol corn rootworms, cutworms and other soil insect pests in field corn, sweet corn, popcorn, and corn grown for s eed and silage. Based on usage data provided by the Biological and Economic Analysis Divi sion (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. S creening L evel of Usage in A gricultural (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 <1 2 5

Rice 1 <2.5 3 <1 <2.5 Sorghum 1 <500 4 <1 <2.5

Sunflowers 1 <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 pe rcent 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 a ssessment include: USDA-NASS (United States Department of Agriculture's National Agricu ltural Statistics Service) 2001-2006, Private Pesticide Market Research, 2001-2007, NPUD 2002 (National Pesticide Use Database) of the CropLife America Foundation and California, DPR da ta. 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, Ida ho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Michigan, Minnesota, Missouri, M ontana, Nebraska, Nevada, New Mexico, North Dakota, Ohio, Oklahoma, Pennsylvania, South Da kota, 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 Pr ogram (NAWQA) data from 2002, tebupirimphos is used on corn, primarily in the mid-portion and co rn belt of the United States. Local uses have been granted for Louisiana, Mi ssissippi, and Texas (Table 2).

7Figure 1 . Map of Estimated Annual Agri cultural Use of Tebupirimphos in 2002. http://water.usgs.gov/nawqa/pnsp/us age/maps/show_map.php?year=02&map= m2024

Application information for te bupirimphos is summarized in Table 2

.

There are three registered produc ts 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 tw o 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/acr e (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.

8Table 2. Maximum Tebupirimphos 1 Crops, Use Rates and Management Practices (Generalized Screening Level Portrayal of the Curren t 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)

9C. 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: C 13 H 23 N 2 O 3 PS 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: logK
ow = 4.19 @ 22 oC

2. Environmental Fate Summary

Based on available environmental fate data, tebup irimphos degradation appears to be primarily due to abiotic process (hydrolysis and photolysis in water). Hydr olysis half-lives range between 47 to 41 days (pH 5 to pH 9) and photolysis in wa ter is < 2 days. Photolysis on soil would be minimal, since tebupirimphos is soil incorporated . Tebupirimphos appears to be quite persistent to microbial degradation in th e environment based upon soil metabolism studies (half-lives of 55 to 1849 days). The vapor pr essure of tebupirimphos (>10 -05 mm Hg) is high enough that volatilization may be an important route of dissipation. Based on the relatively high Freundlich

K ads values (12.4 to 15.6 mL/g) and Kocs (1022 to 2674 mL/g
oc ), tebupirimphos is expected to be slightly mobile in soil.

A number of degradation products, in addition to CO 2 were identified in environmental fate studies (Table 3). The metabolite, OMAT (o r oxon), was determined by the Health Effects Division (HED) to be of toxicological concern. The chemical names are listed in Appendix A.

10Table 3: Environmental fate data for tebupirimphos.

Study Value (units) Major Degradate
Minor Degradates Source
MRID# (other)

Hydrolysis (t 1/2 ) @ pH 5 47days
@ pH 7 45 days
@ pH 9 41 days DIMET (27%)
TBHP (5%) 42005465

Aqueous Photolysis (t 1/2 ) 31 hrs in sterile aqueous solution at pH 5 DBMAT (37%)
DIMAT (10%)
TBHP (5%)
OMAT (5%) 42005466

Photolysis on Soil (t 1/2 ) 106 days DBMAT (14%)
TBHP (2%) 42005467

Air Photolysis (t 1/2 ) No Data

Aerobic Soil Metabolism (t 1/2 ) 55 to 1849 days CO 2 (31%)
OMAT (<1 to 5.6%)
TBHP (1 to 3.8%)
IMATS (3%) 42005468

44299803

Anaerobic Soil Metabolism (t 1/2 ) 279 days IMATS (5%)
TBHP (4%)

CO 2 (8%) 42005468

Anaerobic Aquatic
Metabolism No Data

Aerobic Aquatic Metabolism (t 1/2 ) No Data

Mobility

Freundlich K ads 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 (t 1/2 ) 14 to 39 days OMAT 43092702

43092703

Fish
Accumulation BCF: Whole body – 660X, Fillet – 110X, Viscera
1100X TBHP,

OMAT,

HTBHP 42005433

42005475

42005476

logK

ow 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, re spectively. The soil photolysis and aqueous photolysis half-lives were 106 and 1.29 days, respectively. Although OMAT was detected in aqueous photolysis studies, it wa s not a major breakdown product.

Aerobic soil metabolism : Two aerobic soil metabolism studies (MRID 42005468, 44299803) were submitted to the Agency. The aerobi c 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. Issu es included no confirmation of aerobic conditions, no report on radiochemical purity of the pyrimidinyl ring-labeled tebupirimphos test material, and detections limit we re not reported for HPLC and TLC analysis. The registrant addressed the deficiencies in a second study. The major observed degradation product was CO 2 . 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 us ed nonlinear regression to estim ate “half-life” of tebupirimphos; half-lives ranged from 55 to 1849 days. The es timated half-lives increased with increasing application rates. For two of the soils with the lowest applicati on 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 th ese degradates are listed in Table 3. Three of these degradation products DIMET, DIMAT, and DB MAT 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 degr adation 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 transfor mation (aerobic metabolism, aqueous hydrolysis, terrestrial field dissipation) products of tebupirimphos. A lthough, 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 envir onmental degradate (< 6 pe rcent), but it is more
mobile in soil than tebupirimphos. These limited data s uggest that the “slow microbial transformation” of tebupirimphos will control th e rate and amount of OMAT formed, thus, the
OMAT concentrations should be less then the tebupirimphos con centrations. There are no data

12for photodegradation in air, which may be a possi ble pathway for transfor mation of OPs to an oxygen analog.



### c. Environmental Transport

Based on the Freundlich K ads values (12.4 to 15.6 mL/g) a nd Koc values (1022 to 2674 mL/g
oc ), tebupirimphos is classified as slightly mobile in soil according to the mobility classification scheme adopted by EFED (Bradbury, 2006; F TT, 2006). However, based upon limited number of samples, K ads was negatively correlated with organic carbon content. The OMAT transformation product which is stru cturally similar to tebupirimphos appears to be more mobile (Freundlich K ads = 1.4 to 3.6 mL/g ) than the parent chemical). . No data are available for the other degradation products.

No laboratory volatility studies ar e available. The vapor pressu re 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 reques ted because the vapor pressure
is >10 -05 mm Hg (D19063, June 1994). The calculate d Henry’s Law constant ranges between
2.89 x 10 -06 to 2.89 x 10 -05 atm m 3 /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

m 3 /mol), have been measured in air samples (Aston and Seiber, 1997).



### d. Bioaccumulation

Tebupirimphos accumulated in fish with maxi mum bioconcentration factors of 110, 660 and 1100x in edible tissues (fillet), whole body, and vi scera, respectively. Depuration was minimal (2%) after 14 days. The estimated Kow also indicates the potential to bioaccumulate (logK
ow - 4.19). Given the toxicity profile of tebupiri mphos and Kow, these data suggest that tebupirimphos accumulation should be evaluated in re gistration review with respect to potential risks to organisms that consume aquatic an imals that have accumulated the pesticide.



### e

. Drinking Water Assessments

The human health risk asse ssment 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 wate r and the Tier I GEN EEC models for surface water. The EDWCs were 0.006 ppb in ground wa ter, and 1.89 ppb and 0.86 ppb, respectively, for acute (peak) and chronic (56-day averag e) 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 ra te (0.27 lb a.i/A) of tebupirimphos on corn

13(D356184). Surface water concentrations were es timated using PRZM and EXAMS models.
Ground water concentrations were estimated us ing 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 (K ads 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 th is pilot study, twelve wa ter-supply reservoirs and Community Water Systems (CWS) were select ed based on vulnerability for pesticide contamination. Small watersheds with high pest icide 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 concentr ations 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 spig ot of the public water system, 2) finished-water at the compliance tap at the entry point to the di stribution center, and 3) ambient reservoir water sample at the reservoir outlet. Sampling was de signed to coincide with the period of intensive pesticide use, such as the post-pesticide application s eason. 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 th e estimate of peak concentrations for short-lived compounds. Raw and finished drinking water samples were ta ken at most sampling times, and each water sample was analyzed using the USGS anal ytical schedules 2001, 9060, and 9002. Finished water samples were not quenched to eliminate chem ical oxidation from residual chlorine. Out of 186 pesticides and degradation products analy zed, 46 were organophosphorus (OP) pesticides and their degradation products. Tebupirimphos a nd the oxygen analog (OMAT) were analytes in the monitoring study.

There were no detections of tebupirimphos in th e USEPA/USGS Pilot Reservoir Study in raw or finished water samples (Blomqui st, 2001). OMAT was detected at low concentrations in 3 of 316 samples of raw water samples (Table 4).

14Table 4. Summary statistics for tebupirimphos a nd 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 .nd 2 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 a nd assessments from other regulatory agencies reveals that there are a limited number of studies monitoring for tebupirimphos and its oxon degradation products in various me dia. Additional monitoring da ta will be evaluated when the risk assessment is prepared, including the US GS NAWQA database a nd the Pesticide Data Program as well as in open literature or other available data sources.



### g. Water Treatment

Water treatment of surface water often include s 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 l east for 72 hours (Kamel et al, 2008). These results suggest that water (chlorinati on) 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 su fficient QA/QC to support quantitative results
and so the conclusion is strictly qualitative.

The Health Effects Division (HED) determin ed that tebupirimphos and oxygen analog of tebupirimphos (previously identif ied as OMAT) should be consid ered in the drinking water assessment (USEPA, 2008).



### IV. Receptors

Consistent with the process described in th e 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 poten tial effects on a variety of species (receptors)
included under these ta xonomic groupings.

15Acute 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 assessmen t. Open literature studies are identified using EPA’s ECOTOX
database 2 , which employs a literature search engine for locating chemical toxicity data for aquatic life, terrestria l plants, and wildlife. Research papers accepted into the ECOTOX database are screened using standa rd procedures to ensure consis tent, high quality information;
these studies will be considered for use in th e 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 insi ght into the direct a nd indirect effects of tebupirimphos on biotic communities from loss of species that are sensitive to the chemical and from changes in structure and functional ch aracteristics 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 t oxic effects on the survival, reproduc tion, and growth of terrestrial and aquatic life as well as indirect effects such as reduction in pr ey base and/or modification of
habitat.

Information used to evaluate tebupirimphos and it’s degradates of con cern 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 - in to a system that includes toxicity data derived predominately from the peer-reviewed literat ure, for aquatic and terre strial organisms.

Other information that is used to evaluate toxi city and potential ecological risks includes use of the acute probit dose-respons e relationship to establish the probabi lity of an individual effect and reviews of the Ecological Incide nt Information System (EIIS). A summary of the available ecotoxicity information and the incident informa tion for tebupirimphos are provided below.

A. Effects to Aquatic Organisms

A summary of the most sensitiv e 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 invertebrate s on an acute exposure basis.

2 http://www.epa.gov/ecotox

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

Species 96-hr
LC 50 /EC 50 (μg a.i./L) 48-hr EC 50 (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 EC 50 = 630
NOAEC = 240 Biomass (44187001)

Duckweed ( Lemna gibba ) 7-day EC 50 = 8800
NOAEC = 1840 Front count (44187002)

B. Effects to Terrestrial Organisms

A summary of the most sensit ive 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 ba sis. 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.

17Table 6 - Summary of Acute and Chronic Toxicity Profile for Terrestrial Animals and Plants Exposed to Tebupirimphos. Acute Toxicity Chronic Toxicity

Species 48-hr LD 50 (μg a.i. /bee) Acute Oral

LD 50 (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 ) -- 3.5 3
-- 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 EC 25 = No data
NOAEC = No data No data

Dicots No data EC 25 = No data
NOAEC = No data No data

3 2.1% of the active ingredient in AZTEC

18C. 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 incide nts 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 thatmay 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 ecosystem s potentially at risk could include the treated field and immediately adjacent areas that may recei ve runoff. Areas adjacent to the treated field could include cultivated fields, fencerows and hedgerows, meadows, fallow fields or grasslands, woodlands, riparian habitats, a nd 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 fro m surrogate test species to estimate treatmentrelated direct effects on acute mortality a nd chronic reproductive, growth, and survival assessment endpoints. Surrogate aq uatic 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 terr estrial-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 hierar chical or tiered system that progresses from basic laboratory te sts to applied field studies.

For plants in terrestria l and semi-aquatic environments, the screening assessment endpoint is the perpetuation of populations of non-target species (c rops and non-crop plant species). When data

4 EIIS was accessed on 08 September 2008.

19are available, endpoints assessed include emer gence of seedlings and vegetative vigor. Terrestrial plant toxicity data for tebupirimphos are not availa ble for consideration in this risk

assessment.

For aquatic plants, the assessment endpoint is th e maintenance and growth of standing crop or biomass. When data are available, measurem ent endpoints for this assessment endpoint focus on algal and vascular plant (i.e., duckweed) growth rates and bioma ss measurements. There are no aquatic plant toxicity data for tebupirimphos availa ble 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 th is assessment, the risk is stressor-initiated,
where the stressor is th e 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 trans formation product via runoff (both dissolved phase and with eroded sediment) and atmospheric transpor t via volatilization and expose non-target organisms. Application to soil, even with incorporation, may also result in exposure to non-targe t organisms as animals may be exposed to tebupirimphos from granules remaining on the soil surfa ce. Monitoring studie s have identified the presence of tebupirimphos in water. Thes e potential exposure pathways may result in adverse effects on the surviv al, growth, and/or reproduction of non-target terrestrial and aquatic organisms, including Federally-lis ted threatened and endangered species.

20B. Diagram

The environmental fate properties of tebupirimphos and it’s degradates of concern are similar to
other OPs which have been observed in surf ace water and air monitoring studies. Aston and Sieber, 1997; Menconi and Siepmann, 1996; Maje wski and Capel, 1999; Vogel and Capel, 2008 have identified the presence of methidathion and methidathi on-oxon, an OP compound with comparable fate properties to tebupirimphos, in su rface waters, air, fog, and rain. Therefore, runoff, and volatilization are possible transpor t 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 equi pment 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 gro und 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 Pes ticide Programs, U.S. Environmental Protection Agency” (“Overview Document”) (January 2004), a nd will be done in accordance with Section 7 of the Endangered Species Act.

A. Ecological Risk Assessment

Previously completed screening level risk asse ssments and exceedances of Agency levels of
concern indicate a need to further examine and re fine acute and chronic ri sk to terrestrial and aquatic animals. Analysis of potential indirect effects on liste d species is also required. Uncertainties remaining from previous assessm ents 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 in cluded an expanded area of the country to be treated as well as higher applica tion rates Terrestrial exposures will be evaluated using the most
current version of T-REX at the time of the asse ssment. Because tebupirimphos is formulated as a granule, the assessment will ut ilize the LD50/squre foot met hod for risk estimation. Also, because the chemical has shown potential to bio accumulate, consideration will also be given to terrestrial and aquatic animals that consume or ganisms 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 receivi ng 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 ra tes for tebupirimphos and its degradates of concern, along with the requested photo-oxidation data are expect ed to enhance the Agency’s ability to predict exposures in aquatic and terrestr ial habitats far from the treated site. It is anticipated that methods to describe the contribu tions of atmospheric transport and deposition of tebupirimphos and its degradates of concern to ex posures to non-target organisms will be fully explored and capable of being in corporated into this risk asse ssment as part of registration
review.

A cursory review of open literature sources a nd assessments from other regulatory agencies
reveals that there are a number of studies m onitoring 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 th e potential for long range transport.

22B. Endangered Species

Consistent with the Agency’s responsibility und er the Endangered Species Act (ESA), EPA will evaluate risks to Federally-listed threatened and/ or endangered (listed) sp ecies 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 regist rations of tebupirimphos is based on an action
area. The action area is considered to be the ar ea directly or indirectly affected by the federal action, as indicated by the exceedance of Agency Le vels of Concern (LOCs) used to evaluate
direct or indirect eff ects. The Agency’s approach to defi ning 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 understandi ng that exposures below the Agency’s defined LOCs constitute a no-effect threshold. For th e 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 modificat ion 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. Ther efore, the action area extends to a point where environmental exposures are belo w any measured lethal or subl ethal effect threshold for any biological entity at the whole organism, organ, ti ssue, and cellular level of organization. In situations where it is not possible to determin e the threshold for an observed effect, the action area is not spatially limited and is assume d 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 assessm ents 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 modeli ng using Tier II PRZM/EXAMS surface water models and Tier I SCIGROW, as well as consid eration of any monitoring data that may be
available.

Laboratory evidence indicates that chlorination of drinking wate r 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 sy stems depending on the se quence of treatment. Therefore, in future drinking water assessmen ts of tebupirimphos, formation of tebupirimphosoxon will be considered. The availa ble chlorination study is qualitativ e in nature and in order to account quantitatively for oxon formation, additional data will be needed. EFED has requested submission of a chlorination study.

23D. Clean Water Act

Tebupirimphos is not identified as a cause of impairment for any wa ter 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 B ody 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 qual itatively in pesticide risk assessments.

24E. 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 de gradate is presumed to be of greater toxicity than the pa rent, based on the toxicity pr ofiles of similar organophosphate insecticides. The studies anticipat ed 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 th e requested toxicity studies. That is, if oxon toxicity studies de monstrate that the oxon is not of su fficient 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 fa te data for the oxon would be needed. If toxicity of the oxon is shown to be important, th en fate studies would be necessary to quantify potential oxon formation. If these new fate studi es 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 woul d 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 assu me 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 av ailable toxicity data or established default assumption. For example, the OP Cumulative Asse ssment assumed that the toxicity of oxons to mammals could be up to 100 times greater than th at 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.

251. 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 ad equately characterize the transformati on 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 OM AT 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 re fine 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 tebupiri mphos and tebupirimphos-oxon will be used to characterize its potential dissipation through aquatic photolysis.

Tebupirimphos-oxon is a degradate of toxicological concer n. The additional data can be used to refine the current aquatic exposure estimates, which represent exposu re 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.

26Study Title: Photodegradation in Air
Guideline Number: 835.2370 Test Substance: Tebupirimphos Rationale for Requiring the Data

S ince tebupirimphos is applied to terrestrial crops, a p hotodegradation 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 Henr y’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 curre ntly available. This study will be used to
characterize the environmental fate of tebupirimphos. In particular, th ese 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 da ta from this study will be used to quan tify 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 rest rictions for tebupirimphos which are unnecessarily

severe.

27Study Title: Volatility - laboratory
Guideline Number: 835.1410 Test Substance: Tebupirimphos Rationale for Requiring the Data

Since tebupirimphos is applied to terre strial crops, a laborato ry volatility study is co nditionally 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

v olatilization could be a route of dissipation from tr eated 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 surf aces. 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 curren tly available. This information can be used to estimate both near field and longer range transport ex posures 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 an d transport of tebupirimphos in air and possibly provide inputs for fu ture modeling efforts. In the abse nce of acceptable data, conservative assumptions will be used to estimate the spatial extent of exposure.

28Study 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 pr ovide data on the dissipatio n 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.

29Study 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 ae robic (oxygen-rich) conditions in the laboratory.

The aerobic soil metabolism studies (MRIDs 42005468, 44299803) provide supplemental information but are inadequate to characterize the fo rmation 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. Withou t 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 concentr ations 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 nece ssary in order to address this uncer tainty 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 limi t 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.

302. 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 pote ntial 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 poten tial risks to birds is likely to exceed LOCs without submission of such data, the magnitude of potentia l 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.

31Guideline 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 K

oc (1845) and log K

ow (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 expl oring 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 perfor med 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 rest rictions for tebupirimphos which are unnecessarily

severe.

32Guideline Number: 850.4100 and 850.4150 Test Substance: Tebupirimphos TEP Title: Seedling emergence and vegetative vigo r 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 terrestria l outdoor use patterns that ar e 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 detrimen tal 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 terrestr ial 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 toxi city data will be used to quantitatively estimate potential risks to terrestrial plants associated with th e use of tebupirimphos. Th ese 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 fo r 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 fl exibility 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.

33Guideline Number: 850.2100; 850.2200 Test Substance: Tebupirimphos-oxon Study Title: Avian acute oral toxicity Test Species: Acute LD 50 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 pa rent 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 pote ntial acute risk to avian species and will be used to
calculate acute dose or diet ary 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, wh ich 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.

34Guideline Number: 850.1075; 850.1010 Test Substance: Tebupirimphos-oxon Study Title: Acute LC 50 in fish and aquatic invertebrates Test Species: Acute studies in bluegill sunf ish and rainbow trout; acute study in daphnids Rationale for Requiring the Data

Acute toxicity studies on tebupirimphos-oxon with aqua tic 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 pote ntial 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 thes e 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.

35VIII. 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 Rere gistration Eligibility Decision for Methidathion (List A, Case 0034). http://www.epa.gov/pesticides/rer egistration/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 Protec tion Agency. Endangered and Threatened Species Effects Determinations. Office of Prevention, Pe sticides 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/cumul ative/2006-op/op_cra_main.pdf

U. S. Environmental Protection Agency 2007. ECOTOXic ology 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. 2007 b . Ecological Incident Information System. http://www.epa.gov/espp/consultation/ecorisk-overview.pdf

U.S.Environmental Protection Agency. 2008. Fate of Hi gh 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 Ma rine 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. Ca pel. 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.

36Appendix A.

Table 1. Chemical names for tebupirim phos 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-pyrimid inyl ethyl 1-methylethyl phosphate

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

DBMAT O-Ethyl O-(1met hylethyl) O-(5-pyrimidinyl) phosphorothioate),

DIMAT O-[2-(1,1-Dimethylethyl)-5-pyrim idnyl O-ethyl] O-ethyl O-hydrogen phosphorothioate

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

HTBHP 2-(1,1-Dimethyl-2-hydr oxyethyl)-5-hydroxypyrimidine

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

37