UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D

. C. 20460

MEMORANDUM

Dat e: September 15

, 2015 OFFICE OF

CHEM I CAL SAFETY ANO
POLLUTION PREVENTION

SUB JE CT: Dicrotopho s : R ev i sed Hum an Health Ri sk Assessment fo r Reg i stration Review

of Dicrotopho s.

PC Co de: 03520 I

D ecis i o n No.: 454409

Petition No.: NA

Ri sk Assess m ent Type: Human H ealth Ri sk As ses sment

TX R No.: NA

MRID No.: NA

F ROM: Thurston G. Morton

, Chemist, RAB IV DP Barcod e: 428506

R eg i strat ion No.: NA

R eg ul ato r y Action: Reg Review

Case No.: 0145

C A S No

. : 141-66-2

40 CFR: § 180.299

Wade Britton

, Industrial Hygienist, RAB I V

Alexandra LaMa y, Bi olog i s t

, RAB V II 

# t{

Matthew Ll oyd, Industrial Hygienist

, RAB VII

Shalu Shelat, In dustrial Hygienist, RAB VI

## ~ 

# -tJ

. 1 1 . Anna Lowit

, Ph.D.

, Se nior Scient i st

, IO**'-)** {%

Elizabeth Holman

, Ph ys i ca l Scient i st, RA

John Liccione

, PhD, Toxicologist, RAB V

Health E ffect s Di vis i on (7509P) /

TH RO UGH: C harles Smith, Branch Chief

Risk Assessment Branch IV

Health Effects Divis i o n (7509P)

A nd

# 21/~ 

# _:__

Christine Olinger

, RARC Reviewer

# (;.~**,,,** - E li zabeth Mendez

, RARC**Reviewer _~** **_._ --....-=::::;i=-~** 

TO : Khue Nguyen and Ne i l A nd erson Risk Management a nd Im plementation Branch l

Pesticide Re- Eva lu ation Division (PRD) (7508P)

Pa ge I of971.0 Exec utive Summary

.................................................................... . ...................................... 4

2.0 H E D R ecom mendation s

.................................................................................... .. ......... ..... 6

2.1 Data Deficiencies

...... ... ..... ....... .. .. .. ....... ... . ... . ........ . ....................... . ...... ...... . ................. ... 7

2.2 Tolerance Co n s ideration s

................... ... ................... ... ......... .. .................................... . .. 7

2.2.1 Enforcement Analytical Method

............................................................................... 7

2.2.2 International Harmonization

.................................... .. .......... .. ..... ...... ..... ..... ...... .. ...... 7

2.2.3 Recommended Tolerance s

......................................................................................... 7

2.3 Label Recommendations

.. ... . ....... .. ... .. .. ........... .. ................................... . ......... .. .............. 8

2.3.1 R eco mmendation s from Residu e Reviews

... .................................. . ......... .. .......... . .... 8

2.3.2 Recommendation s from Occupational Assess ment

.......... .. .. . ... .. ........................ ..... 8

2.3.3 Recommendation s from Residential Assessment..

................................................... 8

3.0 Introducti o n

. ................................................................................................................. .... .. 8

3.1 C hemical Identity

............................................................................. .. ............................ 8

3.2 Physical/Chemical C hara cte ristic s

............... ... .......... .. .......... .. ..................................... 9

3.3 Pesticide Use Pattern

.... .. .......... .. .................... ... .......... ... ..... .. .. .. ..... ... . .. ...... .... ................ 9

3.4 An ticipated Ex posure Pathway s

............................................................................. . ... l 0

3.5 C onsideration of E nvironm e ntal Justice

.................. ... ......... ... ................................... l 0

4.0 Hazard C haracterization and Do se- Respon se Assessment

.......................................... I 0

4.1 Toxicology Studies Available for Analy s is

.................. . ....... .. . ... ..... ..... ....................... 11

4.2 Absorption, Distribution, Metabolism, & Exc retion (ADME)

...... . ........................ .. I I

4.2.1 Dermal Absorption

. . .. ..................... .. ....... .. .. ... ...... .. ........................ ... ....... .... . .. .. ...... . 1 2

4.3 Toxicological Effects

.................................................................................................... 12

4.3.2 Critical Durations of Exposure

.. .. .... .......... . ........ . ................................................... 13

4.4 Literature Re view on Neurodevelopment E ffect s

..................................................... 15

4.5 Safety Factor for Infant s and Children (FQPA SF)

.................................................. 20

4.5.1 Completeness of the Toxicology Database

..... ... ...... ...... ...... ........................ .... ... ..... 20

4.5.2 Ev idence of Ne urotoxici ty

........................................................................................ 21

4.5.3 Evidence of Sensitivity/Susceptibility in the Developing or Young A nimal..

...... 21

4.5.4 Residual U ncertainty in the Exposure Database

................................................... 21

4.6 Toxicity Endpoint and Point of D e partur e Selections

..................... .. ......... .. ............ 2 I

4.6.1 Do se-Res ponse Assessment

............................. .. .. .. .. .. .. .. ... .................... .. . ... . ............. 21

4.6.2 Recommendation for Co mbinin g Routes of Expos ure s for Risk A ss essment..

... 26

4.6.3 Cancer Classification and Risk Assess ment Recommendation

............................ 26

4.6.4 Summary of Points of Departure and Toxicity Endpoints Used in Human Risk

Assessment

............................................................................. ... ......... .. ......... .. .......... . .............. 27

4.7 En docrine Di s ruption

.... .. .................... .. .................... .. .......... .. .......... .. ......................... 29

5.0 Dietary Ex po sure a nd Ri s k Assessment

......................................................................... 30

5.1 Metabolite/Degradate Re s idue Profile

....... .. ........... ... ................................................ 30

5.1.1 Summary of Plant and Animal Metabolism Studies

........ .. ...... ...... ...... ..... ............ 30

5.1.2 S ummary of Environmental Degradation

.............................................................. 30

5.1.3 Comparison of Metabolic Pathways

..... ..... .......................................................... .. . 30

5.1.4 Residues of Co nc e rn S ummary a nd Rationale

............................ . ........... . .......... . .. 31

5.2 Food Re sid ue Profile

. .. .. . ... ...... ... ........ ...... ...... ... .......... .. ...... .. . ... ......... .. ........................ 31

5.3 Water Residue Profile

.................................................................................................. 3 1

5.4 Diet ary Risk A ss essment

.............................................................................................. 32

5.4.1 De s cription of Residue Data Use d in Dietary Assessment

.. ...... ... . . ...................... . 32

Page 2 of97Page 3 of 97



### 5.4.2 Percent Crop Treated Used in Dietary Assessment

................................ .............. 32

5.4.3 Acute Dietary Risk Assessment

................................ ................................ ............... 32

5.4.4 Steady State Dietary Risk Assessment

................................ ................................ .... 38

5.4.5 Cancer Dietary Risk Assessment

................................ ................................ ............. 42

6.0 Residential (Non

- Occupational) Exposure/Risk Characterization

............................. 43

6.1 Residential Handler Exposure

................................ ................................ .................... 43

6.2 Post

- Application Exposure

................................ ................................ .......................... 43

6.3 Residential Bystander Postapplication Inhalation Exposur e

................................ ... 43

6.4 Spray Drift

................................ ................................ ................................ .................... 43 6.4.1 Combined Risk Estimates from Lawn Deposition Adjacent to Applications

.......... 44

7.0 Aggregate Exposure/Risk Characterization

................................ ................................ .. 48

7.1 Acute Aggregate Risk

................................ ................................ ................................ ... 48

7.2 Short

- Term Aggregate Risk

................................ ................................ ........................ 48

7.3 Intermediate

- Term Aggregate Risk

................................ ................................ ........... 48

7.4 Chronic Aggregate Risk

................................ ................................ .............................. 48

7.5 Cancer Aggregate Risk

................................ ................................ ................................ 48

8.0 Cumulative Exposure/Risk Characterization

................................ ............................... 48

9.0 Occupational Exposure/Risk Characterization

................................ ............................ 49

9.1 Short

- and Intermediate

- term Handler Risk

................................ ............................. 49

9.2 Short

- /Intermediate

- Term Post

- Application Risk

................................ .................... 54

9.2.1 Occupational Post

- application Inhalation Exposure/Risk Estimates

.................. 54

9.2.2 Occupational Post

- application Dermal Exposure/Risk Estimates

....................... 54

10.0 References

................................ ................................ ................................ ......................... 58

A.1 Toxicology Data Requirements

................................ ................................ ................... 66

A.2 Toxicity Profiles

................................ ................................ ................................ ............ 67

A.3 Hazard Identification and Endpoint Selection

................................ .......................... 73

A.4 Executive Summaries

................................ ................................ ................................ ... 76 Appendix C. Physical/Chemical Properties

................................ ................................ ............. 97Page 4 of 97



### 1.0 Executive Summary

Dicrotophos is a broad spectrum organophosphate insecticide . The only dicrotophos end

- use formulation currently registered is a water

- miscible formulation which may be foliarly applied to established cotton plants or used as a tree injection treatment for ornamental and non

- food producing trees. It is classified as Restricted Use and m ay be purchased and used only by certified applicators or persons under their direct supervision.

The currently registered use on cotton ranges from an application rate of 0.2 to 0.5 lbs ai/acre via ground and aerial application. The applications are sp ecified to be conducted by closed system only. T he pre

- har vest interval (PHI) is 30 days

. Additionally, the micro

- injection use for ornamental trees is applied by closed system (capsule) and is not to be used on trees which will produce food within the y ear following treatment.

Hazard

Dicrotophos is a member of the organophosphate (OP) class of pesticides. Like other OPs , the initiating event in the adverse outcome pathway (AOP)/ mode of action (MOA), for dicrotophos

involves inhibition of the enzyme acetylcholinesterase (AChE) via phosphorylation of the serine residue at the active site of the enzyme. This inhibition leads to accumulation of acetylcholine and ultimately to neurotoxicity in the central and/or peripheral nervous system

. For dicrotopho s, AChE inhibition is the most sensitive endpoint in the toxicology database in multiple species, durations, lifestages, and routes

. OPs also exhibit a phenomenon known as steady state AChE

inhibition. A fter repeated dosing at the same dose level, the deg ree of inhibition comes into equilibrium with the production of new, uninhibited enzyme. Therefore, a steady state exposure assessments of 21 days and longer was conducted instead of the traditional chronic or long

- term

assessments

.

The toxicology database for dicrotophos is complete for risk assessment. There are acceptable studies available for toxicity endpoint selection

. Dicrotophos has high quality dose response data across multiple lifestages, durations, and routes for both re d blood cell ( RBC ) and brain AChE

inhibition

. High quality dermal and inhalation studies allow for route specific evaluation. Clinical signs of neurotoxicity can be found throughout the database of toxicity studies at doses much higher than those causing inhibition of AChE. No studies in the database of toxicology studies suggest quantitative sensitivity to dicrotophos, including all three components of the comparative ChE study (acute dosing in adults and juveniles; repeated dosing in adults and juvenile s; and gestational exposure)

. Qualitative susceptibility was observed in the reproduction and developmental neurotoxicity (DNT) studies, but the concern is low since clear no

- observed

adverse

- effect levels (NOAELs) were established and the benchmark dose (BMD) results using AChE inhibition are protective of the effects in these studies

. However, the Food Quality Protection Act (FQPA) Safety Factor (SF) has been retained for infants, children, youths, and women of childbearing age for all exposure scenarios due to uncertainty in the human dose

response relationship for neurodevelopmental effects ( s ee Section 4.4). As a result, a total uncertainty factor of 1000X was applied for all exposure scenarios, except dietary exposures for the adult population subgro up 50

- 99 years old where the FQPA SF does not apply (total uncertainty factor = 100X)

.Page 5 of 97



### D icrotophos is classified as "Suggestive evidence of carcinogenicity, but not sufficient to assess human carcinogenic potential”. This classification is based on the ev idence of increased tumor incidence for a single tumor type (thyroid) in a single species (mice) which raises a concern for carcinogenic effects, but is judged not sufficient for a conclusion as to human carcinogenic potential. In acute lethality studies , dicrotophos is acutely toxic (Category I for the oral and inhalation route and II for the dermal route). Dicrotophos is Category II for eye irritation and is a strong dermal sensitizer but is not irritating to the skin.

Dietary ( Food and W

ater) Exposure and Risk

Sufficient field trial data have been previously submitted for cotton undelinted seed and cotton gin byproducts. The tolerance for dicrotophos and its metabolite monocrotophos in/on cottonseed at 0.2 ppm is adequate. The tolerance for d icrotophos and its metabolite monocrotophos in/on cotton gin byproducts at 2.0 ppm also is adequate. Residues of dicrotophos and monocrotophos do not concentrate in cottonseed hulls, meal or refined oil, therefore tolerances are not required for these pr ocessed commodities.

The tolerance expression for dicrotophos has been reviewed and should be updated to be consistent with current policy

.

There are no CODEX, Canadian, or Mexican maximum residue levels (MRL s ) established for dicrotophos

. Therefore, in ternational harmonization is not an issue.

Average field trial residue along with 100 % crop treated were used in the dietary exposure

assessment s for cotton commodities. The entire distribution of daily time series drinking water outputs for the thir ty year simulation was used in the acute and steady state dietary exposure

assessments. The acute aggregate dietary exposure estimates are below HED’s level of concern (<100 % the a cute population adjusted dose ( aPAD ) ) for the U.S. population and all popu lation subgroups for all but one water scenario (NC Cotton Max Rate) . Combined dietary exposure from food and drinking water at the 95 th 

### percentile of exposure ranged from 11

- 50 % of the aPAD for the U.S. population and 19

- 130% of the aPAD for all infants <1 y ea r old), the most highly exposed population subgroup. The dietary exposure estimates for food only were ≤ 11% aPAD for all population subgroups. The steady state (2 day average) aggregate dietary (food and drinking water) exposure estimates using DEE M

- FCID with the 2

- day average option are above

HED’s level of concern for all maximum application rate cotton water scenarios. Combined dietary exposure from food and drinking water at the 95 th 

### percentile of exposure ranged from 10

- 52 % of the ss PAD for th e U.S. population and 50

- 32 0% of the ss PAD for all infants <1 y ea r old). All typical application rate (as determined by BEAD) cotton scenarios gave aggregate dietary (food and drinking water) exposure estimates <100% ssPAD. The dietary exposure

estimates for food only were ≤ 23% ssPAD for all population subgroups.

Spray Drift

A quantitative non

- occupational spray drift assessment was conducted for dicrotophos. Adult dermal risk estimates from indirect exposure to dicrotophos related to spray drift resul t in buffersPage 6 of 97



### of 20 0 feet for aerial applications and 50 feet for groundboom applications (i.e., MOEs < 1

, 00 0 at the edge of the field). Children’s ( 1 to < 2 years old ) total (combined dermal and incidental

oral ) risk estimates from indirect exposure to dicrotophos related to spray drift result in buffers

of 300 feet for both aerial and groundboom applications based on the screening level scenarios (i.e., MOEs < 1

, 00 0 at the edge of the field)

.

Occupational Expos ure and Risk

Based on the label

- defined protection for occupational handlers, engineering controls (ECs), all exposure scenarios assessed (not including flaggers) result in total (combined dermal and inhalation) risk estimates of concern (i.e., MOEs are < 1,000). HED does not have exposure data to assess dermal and inhalation exposures for flaggers with engineering controls; therefore, flagger risks were assessed in consideration of the maximum level of PPE (i.e., double layer, chemical resistant gloves, and PF10 respirator). At this level of PPE, occupational handler exposure for flaggers also result in a total risk estimate of concern.

HED has no exposure data appropriate for assessment of the tree injection use of dicrotophos. However, the exposure s and risks associated with this use (occupational handler and/or postapplication exposure) are not expected to exceed those estimated for the cotton use.

Occupational post

- application risks assessed are not of concern (i.e., MOEs >1000) on the day of

tr eatment (i.e., Day 0) for hand weeding activities and three days after application for scouting

activities in cotton.

Human Studies Review

This risk assessment relies in part on data from studies in which adult human subjects were intentionally exposed to a pesticide or other chemical. These data, which include Pesticide Handlers Exposure Database Version 1.1 (PHED 1.1); the Agricultural Handler Exposure Task Force (AHETF) database; the Agricultural Reentry Task Force (ARTF) database; and the

Residenti al SOPs (modified Turf SOP for Spray Drift ) are (1) subject to ethics review pursuant to 40 CFR 26, (2) have received that review, and (3) are compliant with applicable ethics requirements. For certain studies, the ethics review may have included review b y the Human Studies Review Board. Descriptions of data sources, as well as guidance on their use, can be found at the Agency website 1



### .

2.0 HED Recommendations

No additional residue chemistry data are required for registration review. No label changes are required based on residue ch emistry. Current tolerances need updated as previously discussed

.

1 http://www.epa.gov/pesticides/science/handler

- exposure

- data.html and http://www.epa.gov/pestici des/science/post

- app

- exposure

- data.htmlPage 7 of 97



### 2.1 Data Deficiencies

There are no data deficiencies for the registration review eligibility of dicrotophos.

2.2 Tolerance Considerations

2.2.1 Enforcement Analytical Method

For the purpose of registration review , adequate methods are available for the enforcement of plant commodity tolerances. Analytical methods for determination of dicrotophos residues of

concern in livestock commodities are not needed because tolerances need not be proposed for eggs, milk, and edible livestock tissues. The Pesticide Analytical Manual (PAM) Volume II (Section 180.299) lists two gas liquid chromatography ( GLC ) methods (designated as Methods A

a nd B) with KCl thermionic detection. Both of these methods detect residues of dicrotophos and monocrotophos, but not other cholinesterase

- inhibiting metabolites.

Samples collected from recently evaluated cotton field and processing studies were analyzed for dicrotophos and monocrotophos residues using a Gas Chromatography

– Flame Photometric

Detector Phosphorus Mode ( GC/FPD

- P ) method (designated as Method DIC

- AM

- 001) with a stated quantitation limit of 0.01 ppm for each analyte. This method has been subj ected to a successful independent laboratory validation.

2.2.2 International Harmonization

There are no CODEX, Canadian, or Mexican maximum residue levels (MRL) established for dicrotophos

. Therefore, international harmonization is not an issue.

2.2. 3 Recommended Tolerances

Sufficient field trial data have been submitted and reviewed for cotton undelinted seed and cotton gin byproducts. The combined residues of dicrotophos and monocrotophos in/on cottonseed samples treated and harvested according to the maximum label use directions ranged from <0.02 ppm to 0.13 ppm. T he tolerance for dicrotophos and its metabolite monocrotophos in/on cottonseed at 0.2 ppm is adequate

.

These data indicate that the combined residues of dicrotophos and monocrotophos in/on treated cotton gin byproducts ranged from 0.12 to 1.8 ppm following treatments according to the

maximum label use directions. The tolerance for dicrotophos and its metabolite monocrotophos

in/on cotton gin byproducts at 2.0 ppm is adequate

.

Based on the available cottonseed processing study which demonstrated that residues of dicrotophos and monocrotophos do not concentrate in cottonseed hulls, meal or refined oil, tolerances are not required for these processed commodities.

The tolerance expression for dicrotophos has been reviewed and should be updated as follows based on HED’s Interim Guidance on Tolerance Expressions (S. Knizner, 5/27/09).Page 8 of 97



### Tolerances are established for residues of the insecticide dicrotophos , including its

metabolite s and degradates, in or on the commodities in the table below. Compliance with the tolerance levels specified below is to be determined by measuring only the sum

of dicrotophos ( dimethyl phosphate of 3

- hydroxy

- N

, N

- dimethyl

- cis

- crotonamide ) and its

metabol ite [monocrotophos (dimethyl phosphate of 3

- hydroxy

- N

- methyl

- cis

crotonamide ) ] , calculated as the stoichiometric equivalent of dicrotophos, in or on the commodity

.

Cotton

, gin byproducts

................................ ................................ ..... 2 .0 ppm Cotton

, undelinted seed

................................ ................................ .... 0.2 ppm



### 2.3 Label Recommendations

2.3.1 Recommendations from Residue Reviews

No label changes are needed for the residue chemistry.

2.3.2 Recommendations from Occupational Assessment

HED recommends that the directions for use on the “enclosed pamphlet” on the tree injection product labe l (EPA Reg No. 7946

- 11) be made more explicitly tied to the physical product label. The current product label references an enclosed pamphlet for general user directions.

2.3.3 Recommendations f rom Residential Assessment

Dicrotophos is currently registered as a Restricted Use Pesticide therefore there are currently no registered (or proposed) residential uses for dicrotophos.

3.0 In troduction

3.1 Chemical Identity

Table 3.1 Test Compound Nomenclature

Chemical Structure

Empirical Formula C 8 H 16 NO 5 P

Common Name Dicrotophos

IUPAC name [( E )

- 4

- dimethylamino

- 4

- oxobut

- 2

- en

- 2

- yl] dimethyl phosphate

CAS Name (1 E )

- 3

- (dimethylamino)

- 1

- methyl

- 3

- oxo

- 1

- propenyl dimethyl phosphate

CAS Registry Number 141

- 66

- 2

End

- use product/EP Bidrin 8, Bidrin XP, Bidrin XP II, Inject

- A

- Cide B

Chemical Class OrganophosphatePage 9 of 97



### 3.2 Physical/Chemical Characteristics

Dicrotophos is a mixture of the E

- and Z

- isomers in which the E

- isomer is pesticidally active. Technical dicrotophos is a yellow to dark amber liquid at room temperature with a boiling point

of 111

- 112 C at 0.022 mm Hg (extrapolated to 398

- 399 C at 760 mm Hg), density of 1.19

- 1.22 g/mL at 20 C, and vapor pressure of 1 x 10

- 4 

### mm Hg at 20 C. Dicrotophos is miscible (mixable in all proportions) with water, acetone, alcohol, acetonitrile, chloroform, methylene chloride, and xylene. Dicrotophos is only slightly soluble in kerosene and diesel fuel.

3.3 Pesticide Use Pattern

The only dicrotophos end

- use formulation currently registered is a water

- miscible f ormulation

, which may be applied foliarly to established cotton plants or used as a tree injection treatment for

ornamental and non

- food producing trees. It is classified a s Restricted Use and may be purchased and used only by certified applicators or persons under their direct supervision.

Table 3. 3 . Summary of Directions for Use of Dicrotophos

.

Applic. Timing, Type, and Equip. Formulation

[EPA Reg. No.] Applic.

Rate (l b ai/A) Max. No.

Applic. per

Season Max.

Seasonal Applic. Rate (lb ai/A) PHI

(days) Use Directions and

Limitations

Cotton
Early Season (emergence to

pre

- bloom), Apply by air or ground

5481

- 448 0.2 1 0.2 (during this growth period) NS E ngineering controls/closed system only Do not graze livestock on

treated fields

Late Season Use (first

bloom to 30 days prior to harvest), Apply by air or ground 0.5 2 1.0 (during this growth period) 30 E ngineering controls/closed system only

The minimum application

interval between applications is 14 days; Do not graze livestock on

treated fields

Apply by air or ground 5481

- 552 0.4 NS 1.0 30 E ngineering controls/closed system only Do not graze livestock in

treated areas or cut treated crops for feed, do not feed gin trash, Apply by air or ground 5481

- 9024 0.4 NS 1.0 30 E ngineering controls/closed system only

Ornamental Trees

Micro

- injection 7946

- 11 NS NS NS NA Closed system only This product is not to be

used on trees which will produce food within the year following treatmentPage 10 of 97



### 3.4 Anticipated Exposure Pathways

The Pesticide Re

- Evaluation Division has requested a registration review assessment of human health risk to support the registered use s of dicrotophos . Humans may be exposed to dicrotophos in food and drinking water, since dicrotophos may be applied directly to growing crops and application may result in dicrotophos reaching surface and ground water sources of drinking

water. There are no residential uses of dicrotophos , so there is not li kely to be exposure in

residential or non

- occupational settings. In an occupational setting, applicators may be exposed while handling the pesticide prior to application, as well as during application. There is a potential for post

- application exposure f or workers re

- entering treated fields.

3.5 Consideration of Environmental Justice

Potential areas of environmental justice concerns, to the extent possible, were considered in this human health risk assessment, in accordance with U.S. Executive Order 1 2898, "Federal Actions to Address Environmental Justice in Minority Populations and Low

- Income Populations," ( http://www.epa.gov/compliance/environment aljustice/resources/policy/exec_order_12898.pdf ). As a part of every pesticide risk assessment, OPP considers a large variety of consumer subgroups according to well

- established procedures. In line with OPP policy, HED estimates risks to population subgroups from pesticide exposures that are based on patterns of that subgroup’s food and water consumption, and activities in and around the home that involve pesticide use in a residential setting. Extensive data on food consumption patterns are compiled by the USDA under the National Health and Nutrition Survey/What We Eat in America (NHANES/WWEIA) and are used in pesticide risk assessments for all registered food uses of a pesticide. These data are analyzed and categorized by subgroups based on age and ethnic group. Additionally, OPP is able to assess dietary exposure to smaller, specialized subgroups and exposure assessments are performed when conditions or circumstances warrant. Whenever appropriate, non

- dietary exposures based on home use of pesticide products and associated risks for adult applicators and for toddlers, youths, and adults entering or playing on treated areas postapplication are evaluated. Further considerations are currently in development as OPP has committed resources and expertise t o the development of specialized software and models that consider exposure to bystanders and farm workers as well as lifestyle and traditional dietary patterns among specific subgroups.

4.0 Hazard Characterization and Dose

- Response Assessment

Dicrotophos is a member of the organophosphate (OP) class of pesticides. Like other OPs , the initiating event in the adverse outcome pathway (AOP)/ mode of action (MOA), for dicrotophos

involves inhibition of the enzyme acetylcholinesterase (AChE) via pho sphorylation of the serine residue at the active site of the enzyme. This inhibition leads to accumulation of acetylcholine and ultimately to neurotoxicity in the central and/or peripheral nervous system (see Figure 1). For dicrotophos, AChE inhibition is the most sensitive endpoint in the toxicology database in multiple species, durations, lifestages, and routes . AChE inhibition is the focus of this hazard

characterization ; t he availability of reliable AChE inhibition dose response data is one of the k ey determinants in evaluating the toxicology database.Page 11 of 97 

### Figure 1 . Adverse outcome pathway for OPs

4.1 Toxicology Studies Available for Analysis

The toxicology database for dicrotophos is complete for risk assessment. There are acceptable studies available for toxicity endpoint selection; they include:

 subchronic oral toxicity studies in rats, mice and dogs

 chronic oral toxicity stud ies in rats and dogs

 carcinogenicity studies in rats and mice

 developmental studies in rats and rabbits

 reproduction study in rats

 acute and subchronic neurotoxicity studies in rats

 developmental neurotoxicity (DNT) study in rats

 acute and repeated comparative cholinesterase (ChE) studies in juvenile and adult

rats

 repeated, gestational ChE study in pregnant rat and fetuses

 delayed neurotoxicity study in hens

 subchronic dermal toxicity in rats

 in vitro dermal penetration studies in rats and humans

 repeated dosing inhalation studies in rats

 immunotoxicity study in rats

 complete mutagenicity study battery

 metabolism studies in rats

4.2 Absorption, Distribution, Metabolism, & E xcretion (ADME)

Some OPs require metabolic activation to the oxon met abolite. However, dicrotophos is not one

of these OPs (see chemical structure in Table 3.1). Instead, dicrotophos as the parent active ingredient is an AChE inhibiting chemical. Generally, absorption and distribution are rapid with

extensive metabolism and no accumulation in the tissues. Metabolism generally leads to detoxification, although a small amount (3%) of administered dicrotophos is converted internally

to monocrotophos which has comparable biological activity as the parent compound.

In a r at metabolism study, rats were administered [ 14 

### C]dicrotophos as a single dose at levels of 0.5 or 3 mg/kg or a repeat dose of 0.5 mg/kg/day for 14 days and excreta were collected out to 96 hours post

- dose. Following oral dosing, dicrotophos was rapidly ab sorbed in male and female

rats and excreted in the urine

. Consistent with the results of AChE studies, there was little or no influence of sex, dose or route of administration on the rate of absorption. Dicrotophos was 

# Target
Tissue

Dose Phosphor

ylation of

the active
site of Neurotoxi city Accumula
tion of acetylchol

inePage 12 of 97



### absorbed and distributed quickly whi ch is consistent with the time to peak effect of 1 hour post

dosing for brain and blood AChE inhibition in adult rats. T he major ity of the radioactivity ( 58

- 75 %) was eliminated via urine within the first 12 hours. Total recovery at 96 hours post

- dosing

was 97

- 99% of the administered dose with urine comprising a total of 82

- 86%, feces comprising 2

- 4%, and approximately 5

- 7% of the radioactivity recovered in expired air. Less than 3% of administered radioactivity remained in the tissues/carcass at 96 hours.

In rats, d icrotophos is extensively metabolized via N

- demethylation and oxidation of the N

methyl moiety yielding intact OP ( O

- desmethyldicrotophos) , which may be further dealkylated. Metabolism also proceed s via demethylation and dealkylation of the phosphate moiety forming various acetoacetamide and acetobutamide products along with dimethyl phosphate

. Hydroxylation of the N

- methyl group followed by N

- demethylation is another metabolic pathway producing N

- methyl

- N

- hydroxymethyl dicrotophos, mono crotophos and N

hydroxymethyl monocrotophos. Characterized metabolites exceeded 83% of the dose with

un metabolized dicrotophos accounting for only 3

- 7% of the administered dose

. Hydroxydicrotophos ( (E) and (Z) ) accounted for as much as 20% of the dose an d m o nocrotophos accounting for 3%.

4.2.1 Dermal Absorption

There is one in vivo dermal penetration rat study (MRID 45099501) and one in vitro human and rat epidermis absorption study (MRID 45099502) for dicrotophos. The 28

- day dermal rat toxicity study (MRID 46484501) includes quality AChE dose response inhibition data and is being relied upon for the dermal risk assessment. Using the “triple pack” approach, if in vitro

data obtained using animal skin is shown to be a good predictor of animal in vivo dermal absorption for a chemical, then the identical technique performed in vitro with human skin may be useful in extrapolating human dermal abs orption

. Mathematically, the PoD derived from the

28

- day dermal rat toxicity study has been adjusted to account for greater rat skin permeability (4

- 72 fold) compared to human skin ( c alculations are provided in Section 4.5.1)

4.3 Toxicological Effects

D icrotophos has high quality dose response data across multiple lifestages, durations, and routes

for both RBC and brain AChE inhibition . Many of these studies have been evaluated using benchmark dose modeling techniques . Based on Table 4.3.2. 1, brain and RBC AChE inhibition

are remarkably similar ( 0.023

- 0.310 mg/kg/day) for all lifestages evaluated (adults, juveniles, pregnant dams, and fetuses) in oral studies. Available studies with adult animals show similar findings in gavage and dietary studies

. High quality studies in the dermal and inhalation routes allow for route specific evaluation.

Clinical signs of neurotoxicity can be found throughout the database of experimental toxicity studies at doses much higher than those causing inhibition of AChE. In the acute neurotoxicity study, clinical signs (decreased activity, decreased pupil response, flaccid appearance) were observed at a dose of 5 mg/kg

, but not at 0.5 mg/kg. In the subchronic neurotoxicity study, decreased motor activity was obser ved at a dose of 2.03 mg/kg/day

, but not at 0.45 mg/kg/day

. In both the rat and rabbit developmental studies, maternal clinical signs (fasciculations in rats;Page 13 of 97



### diarrhea and mucus on feces in rabbits) of neurotoxicity were observed at 1.0 mg/kg/day

, but not at 0.5 mg/kg/day.

No studies in the database of toxicology studies suggest quantitative sensitivity to dicrotophos. In the acute and repeated comparative ChE studies, juvenile rats, pregnant dams, fetuses and

non

- pregnant adults show similar results in both blood and brain measurements. In the rat and rabbit developmental studies, neither study showed effects on the fetus whereas the dams showed significant neurotoxicity. Qualitative sensitivity was observed in the reproduction and DNT

studies. In t he reproductive toxicity study, percent of live born pups and whole litter losses were observed at the same dose (0.25 mg/kg/day) where reduced body weight was observed in parental animals 2



### . In the DNT, morphometric changes in the brain of male and female offspring

on post

- natal day ( PND ) 12 were observed at lowest

- observed adverse effect level ( LOAEL ) of 0.4 mg/kg/day (NOAEL is 0.05 mg/kg/day) whereas there were no observed effects on the dams at 0.4 mg/kg/day

. It is noteworthy that the doses used in the DNT and reproductive studies were approximately 10

- fold and 8

- fold higher, respectively, than the steady state BMDL 10 

### s (at or near 0.03 mg/kg/day) for all lifestages throughout the database suggesting that the parental animals in the reproductive toxicity and DNT studies were exhibiting substantial AChE inhibition.

Moreover, BMD results using AChE inhibition are protective for the effects on the pups observed in the DNT and reproductive toxicity studies.

In accordance with the Agency's Draft Cancer Ris k Assessment Guidelines (July 2, 1999), dicrotophos is classified as showing "Suggestive evidence of carcinogenicity, but not sufficient to assess human carcinogenic potential”. This classification is based on the evidence of increased

tumor incidence for a single tumor type (thyroid) in a single species (mice) which raises a concern for carcinogenic effects, but is judged not sufficient for a conclusion as to human carcinogenic potential. Dicrotophos was negative in three acceptable genetoxicity assays (M RID 43603301, 43591401, 43603302) and satisfy the guideline requirements. These assays, however, do not exclude the possibility of direct interaction with DNA, based on suggestive evidence of clastogenic effects seen in the mouse lymphoma assay. The CARC recommended that an in vivo comet assay on the target organ be conducted to examine possible interaction with DN A

. An immunotoxicity study (MRID no. 48404101) is available which shows effects at doses much higher than those resulting in AChE inhibition and used for PoD derivation.

In acute lethality studies, dicrotophos is acutely toxicity (Category I for the oral a nd inhalation route and II for the dermal route). Dicrotophos is Category II for eye irritation and is a strong dermal sensitizer but is not irritating to the skin.

4.3.2 Critical Durations of Exposure

One of the key elements in risk assessment is the appropriate integration of temporality between the exposure and hazard assessments. One advantage of an AOP understanding is that human health risk assessments can be refined, focused on the most relevant durations of exposure. The following text provid es an analysis of the temporal pattern of AChE inhibition from acute, single dosing and repeated dosing studies in laboratory animals for dicrotophos. This analysis provides

2 AChE inhibition were not measured in the dicrotophos reproductive toxicity or DNT studies.Page 14 of 97



### the basis for determining which exposure durations are appropriate for assessing human health

risk. Table 4.3.2. 1 provides a summary of the selected results from experimental toxicology studies with dicrotophos. Dicrotophos has extensive AChE inhibition data; for purposes of trend evaluation but to limit the size of the table, data from only a single sex (female) are shown 3



### .

Table 4.3.2.1

– Dicrotophos BMD 10 Results (mg/kg/day) for Brain and RBC ChE Inhibition Over Time in

Female Adult Rats

Days of dosing Brain RBC

1 a 0.120 0.310

15 b 0.028 0.036

28 c 0.077 0.171

35 d 0.048 0.026

37 b 0.023 0.038

63 d 0.044 0.057

98 d 0.045 0.058

371 e 0.047 0.040

735 e 0.042 0.053

a MRID 4615320 6 CCA Acute Study

– Single Dose

b MRID 46153201 Developmental Neurotoxicity Study (i.e., gestational CCA data) ; Results for maternal rats.

c MRID 4615320 8 CCA Repeat Study

– 4 weeks

d MRID 43980201 Subchronic Neurotoxicity Study

e MRID 44527802 Chronic Toxicity Study



### As show in Table 4.3.2.1, the acute BMD value s (0.12 mg/kg in brain and 0.31 mg/kg in RBC )

are the largest in the table

, whereas BMD values from 15 days of dosing up to 2 years are remarkably similar. OPs exhibit a phenomenon known as steady state AChE inhibition. A fter repeated dosing at the same dose level, the degree of inhibition comes into equilibrium with the producti on of new, uninhibited enzyme. At this point, the amount of AChE inhibition at a given

dose remains consistent across duration. In general, OPs reach steady state within 2

- 3 weeks but this can vary among OPs. In the case of dicrotophos the results in Ta ble 4.3.2.1 show a clear pattern of steady state reached by 15 days of exposure. In addition to the consistency across durations, the data across multiple studies (gestational data from the DNT, subchronic neurotoxicity study, and chronic toxicity study) are similar. Given the results in Table 4.3.2.1,

f or dicrotophos, acute (single day) and steady state durations are appropriate for human health risk assessment. As such, endpoint selection discussed below focuses on acute, single day effects and steady state effects.

Although there are rat data at a shorter time period (i.e., 15 days) than 21 days, exposure assessments of 21 days and longer will be conducted for all routes of exposure (i.e., oral, dermal and inhalation) for all single chemical OP a ssessments. Although the durations of the toxicity and exposure assessments may differ, an exact match is not necessary and would suggest a level

3 Note: Only the BMD, not the BMDL, estimates are shown in Table 4.3.2.1. According to the BMD guidance, the

central est imate (i.e., the BMD) is used for purposes of comparison.Page 15 of 97



### of precision that the toxicity data do not support. Given this, the 21

- day and longer exposure

assessment is s cientifically supportable and also provides consistency with the OP cumulative

risk assessment across the OPs.

4.4 Literature Review on Neurodevelopment Effects

For the OPs, historically the Agency has used inhibition of AChE as the POD for human health risk assessment; at present time, this policy continues. This science policy is based on decades

of work which shows that AChE inhibition is the initial event in the pathway to acute cholinergic neurotoxicity. The use of AChE inhibition data for deriving PODs was supported by the FIFRA SAP (2008, 2012) for chlorpyrifos as the most robust source of dose

- response data for extrapolating risk and is the source of data for PODs for dicrotophos . A detailed review of the epidemiological studies used in this review can be found either in the 2014 chlorpyrifos revised

human health risk assessment (D424485, D. Drew et al, 12/29/2014) or in the 2015 literature

review for oth er organophosphates (OPP/USEPA; D331251; 9/15/15).

Newer lines of research on OPs in the areas of potential AOPs, in vivo animal studies, and notably epidemiological studies in mothers and children, have raised some uncertainty about the agency’s risk a ssessment approach with regard to the potential for neurodevelopmental effects in fetuses and children. Many of these studies have been the subject of review by the agency over the last several years as part of efforts to develop a risk assessment for chl orpyrifos (D424485, D. Drew et al, 12/29/2014). Initially, t he agency focused on studies from three US cohorts: 1) The Mothers and Newborn Study of North Manhattan and South Bronx performed by the Columbia Children’s Center for Environmental Health (CCCE H) at Columbia University; 2) the

Mt. Sinai Inner

- City Toxicants, Child Growth and Development Study or the “Mt. Sinai Child Growth and Development Study;” and 3) the Center for Health Assessment of Mothers and Children of Salinas Valley (CHAMACOS) conduct ed by researchers at University of California Berkeley. The agency has evaluated these studies and sought external peer review (FIFRA SAP reviews in 2008 and 2012; federal panel, 2013 4 

### ) and concludes they are of high quality. In the

three US epidemiology cohort studies, mother

- infant pairs were recruited for the purpose of studying the potential health effects of environmental exposures during pregnancy on subsequent child development. Each of these cohorts evaluated the association between prenatal chlorp yrifos and/or OP exposure (with adverse neurodevelopmental outcomes in children through age 7

years ) . For the 2014 chlorpyrifos revised human health risk assessment (D424485, D. Drew et al, 12/29/ 2014) , EPA included epidemiologic research results from t hese three US prospective birth cohort studies but primarily focused on the results of CCCEH since this cohort has published studies on the association between cord blood levels of chlorpyrifos and neurodevelopmental outcomes. The agency retained the FQPA 10X Safety Factor (SF) in the 2014 chlorpyrifos revised risk assessment, in large part, based on the findings of these studies.

In the 2015 updated literature review (OPP/USEPA; D331251; 9/15/15), the agency conducted a systematic review expanding the sco pe of the 2012/2014 review focused on US cohort studies with particular emphasis on chlorpyrifos. The expanded 2015 review includes consideration of the epidemiological data on any OP pesticide, study designs beyond prospective cohort studies,

4 http://www.regulations.gov/#!documentDetail;D=EPA

- HQ

- OPP

- 2008

- 0850

- 0170Page 16 of 97



### and non

- U.S . based studies. The updated literature review identified seven studies which were

relevant (Bouchard et al., 2010; Fortenberry et al., 2014; Furlong et al., 2014; Guodong et al., 2012; Oulhote and Bouchard , 2013; Zhang et al., 2014; Shelton et al., 2014). These seven studies have been evaluated in context with studies from the 2012/2014 review ( D424485, D. Drew et al, 12/29/2014 ). Only a brief summary is provided below.

The OP exposure being assessed in many of these studies used concentrations of urin ary dialkyl phosphate metabolites (DAPs) as the urinary biomarker. Total DAPs is a non

- specific measure of OP exposure and is the sum of six separate molecules

- three dimethyl alkylphosphate (DMAP) molecules of DMP, DMTP, DMDTP, and three diethyl alkylph osphate (DEAP) molecules of DEP, DETP, and DEDTP. Each metabolite is a breakdown product from multiple OPs (Table 4.4.1; CDC, 2008) 5 

### . Specifically, DMP, DMTP, and DMDTP are associated with 18, 13, and 5 OPs, whereas DEP, DETP, and DEDTP are associated wi th 10, 10, and 4 OPs, respectively. Thus, using urinary DAPs alone as an exposure measure, it is not possible to separate the exposure and associated effects for single, specific OPs.

Table 4.4.1.CDC Table of organophosphate pesticides and their dialky l phosphate metabolites (2008).

Pesticide DMP DMTP DMDTP DEP DETP DEDTP

Azinphos methyl X X X
Chlorethoxyphos X X Chlorpyrifos X X Chlorpyrifos methyl X X Coumaphos X X Dichlorvos (DDVP) X

Diazinon X X Dicrotophos X

Dimethoate X X X

Disulfoton X X X

Ethion X X X

Fenitrothion X X

Fenthion X X Isazaphos

- methyl X X

Malathion X X X

Methidathion X X X Methyl parathion X X

Naled X Oxydemeton

- methyl X X

Parathion X X

Phorate X X X

Phosmet X X X Pirimiphos

- methyl X X Sulfotepp X X Temephos X X

Terbufos X X X

5 http://www.cdc.gov/nchs/data/nhanes/nhanes_03_04/l26opd_c_met_organophosphorus_pesticides.pdfPage 17 of 97

Tetrachlorviphos X

Trichlorfon X
DMP = dimethylphosphate; DEP = diethylphosphate; DMTP = dimethylthiophosphate; DMDTP = dimethyldithiophosphate; DETP = diethylthiophosphate; DEDTP = diethyldithiophosphate.



### For studies which measured urinary 3,5,6

- trichloro

- 2

- pyridinol ( TCPy) (e.g., Fortenberry et al, 2014; Eskenazi et al, 2007; Whyatt et al, 2009), this metabolite can be d erived from chlorpyrifos, chlorpyrifos

- methyl, and the herbicide triclopyr. TCPy is also the primary environmental degradate of chlorpyrifos, chlorpyrifos

- methyl, and triclopyr; thus exposure can be found directly on food treated with these pesticides. C CCEH studies have largely used chlorpyrifos measured in cord blood as the specific biomarker (e.g., Lovasi et al, 2010; Whyatt et al, 2004; Rauh et al, 2011). The CHARGE study (Shelton et al, 2015) did not measure biomarkers but instead used geospatial an alysis to focus on the residential proximity to OP exposure using data from the California Department of Pesticide Regulation, with five OPs accounting for a total of 73% of the pesticide applied near residential settings (chlorpyrifos, acephate, diazinon, bensulide, and dimethoate).

Similarly, DAPs can be found directly on food following OP applications (Zhang et al, 2008; Chen et al, 2012). Specifically, studies have shown that DAPs may form as environmental degradates from abiotic hydrolysis, photoly sis, and plant metabolism (Zhang et al, 2008; Chen et al, 2012; Racke et al, 1994). Furthermore, since these DAPs are excreted more rapidly and extensively than the parent OPs (Zhang et al, 2008; Forsberg et al, 2008), direct exposure to DAPs may lead to an overestimate of OP exposure when using urinary DAPs as a biomarker of OP exposure. The agency recognizes that this is a source of uncertainty when using DAPs for assessing OP exposure and will continue to monitor this issue in future assessments.

Wi th respect to neurological effects near birth, the CHAMACOS and Mt. Sinai cohorts measured neurological effects at birth, and observed a putative association with total DEAP, total DMAP, and total DAP exposure (Engel et al., 2007; Young et al., 2005) . Similarly, a Chinese study (Zhang et al., 2014) reported sta tistically significant associations between for total DEAPs, total DMAPs, and total DAPs prenatal OP pesticide exposure and neonatal neurodevelopment assessed 3 days after birth. However, another cross

- sectional Chinese study, Guodong et al (2012), observ ed no association with urinary DAPs and a developmental quotient score for 23

- 25

month old children.

The 3 US cohorts (CCCEH, Mt. Sinai, CHAMACOS) each reported evidence of impaired mental and psychomotor development, albeit not consistent by age at time of testing (ranging from 6 month to 36 months across the three cohorts). Attentional problems and ADHD were reported by three prospective cohorts [Rauh et al, 2006; Eskenazi et al., 2007; Marks et al, 2010 ; and Fortenberry et al (2014)] investigators with additional support from a case control study, Bouchard et al. (2010). The exposure metric varied among these studies. Specifically, Fortenberry et al (2014) found suggestive evidence of an association wi th TCPy and ADHD in boys whereas statistically significant associations were observed by Rauh et al (2006) with chlorpyrifos exposure and ADHD

. Eskenazi et al (2007) reported associations with total DMAPs and total DAPs and ADHD; Marks et al (2010) report ed associations with total DEAP, DMAP, and total DAP exposure and ADHD. In a national cross

- sectional study of Canadian

children , using 2007

- 2009 data for children age 6

- 11 years (Oulhote and Bouchard , 2013), therePage 18 of 97



### were no overall statistically significan t associations observed between child urinary DEAP, DMAP, or total DAP metabolite levels and parentally reported behavioral problems. In contrast, Bouchard et al. (2010), looking at U.S. children age 8

- 15 years in the 2000

- 2004 National Health

and Nutriti on Examination Survey (NHANES), observed a positive association between attention and behavior problems and total DAPs and DMAPs, but not DEAPs. As part of their analysis, Oulhote and Bouchard (2013) noted that their outcome assessment for behavioral prob lems may not have been as sensitive as Bouchard et al (2010), which may in part account for

the difference in the observed results from these studies.

In addition, the 3 US cohorts and the CHARGE study have reported suggestive or positive

associations b etween OP exposure and autism spectrum disorders (Rauh et al., 2006; Shelton et al., 2014; Eskenazi et al, 2007; Furlong et al., 2014). Specifically, Furlong et al (2014) documented suggestive evidence of an association between total DEAP exposure and rec iprocal social responsiveness among blacks and boys. Eskenazi et al (2007) reported a statistically significant association between pervasive developmental disorder (PDD) and total DAP exposure, whereas Eskenazi et al (2010) reported non

- significant, but suggestive, increased odds of PDD of 2.0 (0.8 to 5.1; p=0.14). Rauh et al (2006) documented a significant association between PDD and specifically chlorpyrifos exposure. Both PDD and reciprocal social responsiveness are related to the autism spectrum dis order. Using a different exposure assessment method (geospatial analysis and residential proximity to total OP exposure), Shelton et al (2014) also showed statistically significant associations between total OP exposure and ASD. While these studies vary in the magnitude of the overall strength of association, they have consistently observed a positive association between OP exposure and ASD. Finally, CCCEH, Mt. Sinai, CHAMACOS have reported an inverse relation between the respective prenatal

measures of chlorpyrifos and intelligence measures at age 7 years (Rauh et al. ,2011; Engel et al.,
2011; Bouchard et al., 2011 )

.

Across the epidemiology database of studies, the maternal urine, cord blood, and other (meconium) measures provide evidence that exposure did occur to the fetus during gestation but

the actual l evel of such exposure during the critical window(s) of susceptibility is not known. While significant uncertainties remain about the actual exposure levels experienced by mothers and infant participants in the children’s health cohorts, it is unlikely tha t these exposures resulted in AChE inhibition. As part of the CHAMACOS study, Eskenazi et al. (2004) measured AChE activity and showed that no differences in AChE activity were observed. The biomarker data (chlorpyrifos) from the Columbia University stud ies are supported by the agency’s dose reconstruction analysis using the PBPK

- PD model (D424485, D. Drew et al, 12/29/2014)

. Following the recommendation of the FIFRA SAP (2012), the agency conducted a dose reconstruction analysis of residential uses avai lable prior to 2000 for pregnant women and young

children inside the home. The PBPK

- PD model results indicate for the highest exposure considered (i.e., indoor broadcast use of a 1% chlorpyrifos formulation) <1% RBC AChE inhibition was produced in pregnan t women. While uncertainty exists as to actual OP exposure at (unknown) critical windows of exposure, EPA believes it is unlikely individuals in the epidemiology studies experienced RBC AChE inhibition.Page 19 of 97



### A review of the scientific literature on potential modes of action/adverse outcome pathways (MOA/AOP) 6 

### leading to effects on the developing brain was conducted for the 2012 FIFRA SAP meeting (USEPA, 2012) and updated for the December 2014 chlorpyrifos revised risk assessment (D424485, D. Drew et al, 12/29/ 2014). In short, multiple biologically plausible hypotheses and pathways are being pursued by researchers that include targets other than AChE inhibition, including cholinergic and non

- cholinergic systems, signaling pathways, proteins, and

others. Howeve r, no one pathway has sufficient data to be considered more credible than the

others. The fact that there are, however, sparse AOP data to support the in vitro to in vivo extrapolation, or the extrapolation from biological perturbation to adverse conseque nce significantly limits their quantitative use in risk assessment. The SAP concurred with the agency in 2008 and 2012 about the lack of definable key events in a MOA/AOP leading to developmental neurobehavioral effects. However, since the 2014 literatur e review, there are no substantive changes in the ability to define and quantitate steps in an MOA/AOP leading from exposure to effects on the developing brain. Published and submitted guideline DNT laboratory

animal studies have been reviewed for OPs as part of the 2012/2014 review (D424485, D. Drew et al, 12/29/2014) and the updated 2015 review (OPP/USEPA; D331251; 9/15/15). Neurobehavioral alterations in laboratory animals were often reported, albeit at AChE inhibiting doses, but there was generally a lack of consistency in terms of pattern, timing, or dose

- response for these effects, and a number of studies were of lower quality. However, this information does provide evidence of long

- lasting neurodevelopmental disorders in rats and mice following

ges tational exposure.

At this time, a MOA(s)/AOP(s) has/have not been established for neurodevelopmental outcomes. This growing body of literature does demonstrate, however, that OPs are biologically active on a number of processes that affect the developing brain. Moreover, there is a large body of in vivo laboratory studies which show long

- term behavioral effects from early life exposure, albeit at doses which cause AChE inhibition. EPA considers the results of the toxicological studies relevant to the human population, as qualitatively supported by the results of epidemiology studies. The agency acknowledges the lack of established MOA/AOP pathway and uncertainties associated lack of ability to make strong causal linkages and unknown window(s) of susceptibility. These unce rtainties do not undermine or reduce the confidence in the findings of the epidemiology studies. The epidemiology studies reviewed in the 2012/2014 and 2015 literature reviews represent different investigators, locations, points in time, exposure assessme nt procedures, and outcome measurements. Despite all these differences in study design, with the exception of two negative studies in the 2015 literature review (Guodong et al, 2012; Oulhote

and Bouchard , 2013), authors have identified associations with n eurodevelopmental outcomes associated with OP exposure across four cohorts and twelve study citations. Specifically, there is evidence of delays in mental development in infants (24

- 36 months), attention problems and autism spectrum disorder in early child hood, and intelligence decrements in school age children who were exposed to OPs during gestation. Investigators reported strong measures of statistical association across several of these evaluations (odds ratios 2

- 4 fold increased in some instances),

and observed evidence of exposures

- response trends in some instances, e.g. , intelligence

measures.

6 Mode of action (MOA) and adverse outcome pathways (AOPs) describe a set of measureable key events that make up the biological processes leading to an adverse outcome and the causal linkages between such events.Page 20 of 97



### As section 408(b)(2)(C) of the FFDCA instructs EPA, in making its “reasonable certainty of no harm” finding, that in “the case of threshold effects, an additio nal tenfold margin of safety for the pesticide chemical residue and other sources of exposure shall be applied for infants and children

to take into account potential pre

- and postnatal toxicity and completeness of data with respect to exposure and toxicit y to infants and children .” Section 408 (b)(2)(C) further states that “the Administrator may use a different margin of safety for the pesticide chemical residue only if, on the basis of reliable data, such margin will be safe for infants and children.” Gi ven the totality of the evidence, there is sufficient uncertainty in the human dose

- response relationship for neurodevelopmental effects which prevents the agency from reducing or removing the statutory 10X FQPA Safety Factor. For the dicrotophos DRA, a v alue of 10X has been applied. Similarly, a database uncertainty factor of 10X will be retained for occupational risk assessments. The agency will continue to evaluate the epidemiology studies and pursue approaches for quantitative or semi

- quantitative co mparisons between doses which elicit AChE inhibition and those which are associated with neurodevelopmental outcomes prior to a revised

human health risk assessment.

4.5 Safety Factor for Infants and Children (FQPA SF)

The database of toxicology studie s for dicrotophos is complete

. N eurotoxicity is the most sensitive effect in all species, routes, and lifestages and is being used in deriving PoDs

. No quantitative sensitivity was observed in any experimental laboratory study in the database, including all three components of the comparative ChE study (acute dosing in adults and juveniles; repeated dosing in adults and juveniles; and gestational exposure). Qualitative susceptibility was observed in the reproduction and DNT studies but the concern is low since clear NOAELs were established and the BMD results using AChE inhibition are protective of the

effects in these studies.

As noted above, the lack of an established MOA/AOP makes quantitative use of the epidemiology studies in risk assessment challe nging, particularly with respect to determining

dose

- response, critical duration of exposure, and window(s) of susceptibility. However, exposure levels in the range measured in the epidemiology studies are likely low enough that they are unlikely to resu lt in AChE inhibition. Epidemiology studies consistently identified associations with neurodevelopmental outcomes associated with OP exposure such as delays in mental development in infants (24

- 36 months), attention problems and autism spectrum disorder in early childhood, and intelligence decrements in school age children. Therefore, there is a need to protect children from exposures that may cause these effects; this need prevents the agency from reducing or removing the statutory FQPA Safety Factor. Thus, the FQPA 10X Safety Factor will be retained for dicrotophos for the population subgroups that include infants, children, youths, and women of childbearing age for all exposure scenarios.

4. 5 .1 Completeness o f the Toxicology Database

The database of toxicology studies for dicrotophos is complete and includes developmental studies in rat and rabbit, a reproductive toxicity study, a DNT, and a comparative ChE study with three components (acute, repeated, gestational).Page 21 of 97



### As discussed in Section 4.4, there is uncertainty in the human dose

- response relationship for neurodevelopmental effects and this warrants retention of the FQPA Safety Factor for the population subgroups that include infants, children, youths, and women of childbearing ag e for all exposure scenarios.

4. 5 .2 Evidence of N eurotoxicity

Dicrotophos is an OP with a neurotoxic AOP ; neurotoxicity is the most sensitive effect in all species, routes, and lifestages and is being used in deriving PoDs

.

4. 5 .3 Evidence o f Sensitivi ty/Su sceptibility in the Developing o r Young Animal

Rat and rabbit developmental studies are available and do not show any quantitative susceptibility. Similarly, the reproductive toxicity study and developmental neurotoxicity (DNT) study do not show any quantitative lifestage susceptibility. Qualitative susceptibility observed in the DNT and reproductive toxicity studies were only observed at much higher doses than being used for points of departure derivation. The comparative ChE study is available an d provides AChE quality dose response data from potentially susceptible lifestages (i.e., fetuses, pregnant dams, post

- natal pups). T he CCA study does not show any lifestage sensitivity to AChE inhibition with dicrotophos.

As discussed in Section 4.4, there is uncertainty in the human dose

- response relationship for neurodevelopmental effects and this warrants retention of the FQPA Safety Factor for the population subgroups that include infants, children, youths, and women of childbearing age for all exp osure scenarios.

4. 5 .4 Residual Uncertainty in the Exposure Datab ase

There are no residual uncertainties in the exposure database. The refined dietary risk assessment

uses average field trial residue , estimated drinking water concentrations from maximum application rate, and 100 % crop treated and will not underestimate dietary exposure to dicrotophos

.

4. 6 Toxicity Endpoint and Point of D eparture Selections

4. 6 .1 Dose

- Response Assessment

Table 4. 6 .4.1 summarizes the dicrotophos toxicity endpoints and PoDs selected from an evaluation of the database. This endpoint selection was based on a weight of the evidence evaluation using the following considerations:

 Relative sensitivity of the brain and RBC compartments : For dicrotophos, across most studies, durations, lifestages, and routes, the brain and RBC compartments tend to be similarly sensitive. As such, OPP has emphasized the brain data in PoD derivation as these data represent the target tissue and brain data tend to be less variable than RBC

data.Page 22 of 97



###  Potentially susceptible populations (fetuses, juveniles, pregnancy ): The available AChE data across multiple lifestages (adults, pregnant adults, fetuses, juveniles) show no lifestage sensitivity.

 Route of exposure: It is preferred to match, to the de gree possible, the route of exposure in the toxicity study with that of the exposure scenario(s) of interest . In the case of dicrotophos, there are oral , dermal, and inhalation studies which contain quality dose response AChE data.

 Duration of exposure: It is preferred to match, to the degree possible, the duration of toxicity study with that of the exposure duration of interest. In the case of dicrotophos, there are single day and steady state oral studies but only steady state dermal and

inhalation stu dies

.

 Consistency across studies: In cases where multiple datasets are available for a single duration, it is important to evaluate the extent to which data are consistent (or not) across studies. The dicrotophos database has striking consistency across studies which allows for PoDs to be derived from multiple critical studies thereby increasing the confidence in

such values.

De scription s of the primary toxicity studies used for selecting toxicity endpoints and PoDs for various exposure scenario s are presented in A ppendix 3 of this document. Summary tables of BMD analyses can be found in Appendix 2 and the technical details of the analysis can be found

in the BMD memo (Liccione & Holman, D414900, 1/28/14 )

Consistent with risk assessment s for other AChE

- inhibiting compounds, OPP has used a benchmark response (BMR) level of 10% and has thus calculated BMD 10 

### s and BMDL 10 

### s ( s ee Appendix 1 for summary of OPP’s ChE policy) . The BMD 10 

### is the estimated dose where ChE is inhibited by 10% compared to b ackground. The BMDL 10 

### is the lower confidence bound on the

BMD 10



### . As a matter of science policy, the a gency uses the BMDL, not the BMD, for use as the

PoD (USEPA, 2012)

. All BMD/BMDL modeling for all individual datasets was completed using USEPA BMD Sof

tware, version 2.2; an exponential model was used to fit the data, with the assumption of constant variance across each dataset. BMD results from the OP Cumulative Risk Assessment (( CRA (2002, 2006 ) ) were included in the endpoint selection weight of

evide nce evaluation.

Acute Dietary ( all populations )

As shown in Appendix Table 2.1, results of single dosing exposures with dicrotophos are consistent across multiple datasets for both RBC and brain data including pups ages post

- natal day (PND) 8, 15, and 22 in addition to adult male and female rats.

A P oD for the acute dietary (all populations) exposure scenario was derived from the results of a high quality, well

- conducted CCA rat study (MRID 46153205). A BMDL 10 

### of 0. 07 mg/kg/day associated with brain ChE inhibition in male and female pups (PND 8 & 1 5) was selected as a suitable PoD for the acute dietary (all populations) exposure scenario. The corresponding

BMD 10 

### was 0.08 mg/kg/day.Page 23 of 97



### Brain cholinesterase inhibition was selected for the PoD since the brain is a principal target organ for organopho sphate pesticides, and the brain ChE data was more robust than RBC ChE data. Data from the PND 8 and 15 pups represent highly exposed sub

- populations (infants and young children) and thus are appropriate for PoD derivation.

An uncertainty factor of 100 0X (10X to account for interspecies extrapolation, 10X for intraspecies variation, and 10X for FQPA SF due to uncertainty in the human dose

- response relationship for neurodevelopmental effects ( s ee Section 4.4) ) is applied to the BMDL 10 

### of 0.07 mg/kg/day. As a result, t he acute population adjusted dose (aPAD) is 0.00 0 07 mg/kg/day. The only population subgroup that the FQPA safety factor is not retained is adults 50

- 99; therefore,

the a PAD for this population subgroup is 0.0007 mg/kg/day.

Steady

- State Die tary (all populations)

Table 4.3.2.1 and Appendix Table 2.2 show remarkable similarity in BMD estimates across multiple studies, durations, lifestages, and compartments in studies 15 days and longer. Because of this consistency, OPP has elected to use BM D/BMDL estimates reported in the OP CRA (2002, 2006) for deriving the steady state oral PoD. Results of the OP CRA incorporate multiple studies together in a single BMD/BMDL analysis and are thus highly robust. Specifically, in the OP CRA, EPA performed a sophisticated statistical analysis using nonlinear mixed effects

models which allow for combining the results of multiple studies and multiple time points into a single BMD estimate. These procedures were reviewed favorably by the FIFRA SAP in February 2002.

In the case of dicrotophos, for the OP CRA, the available AChE da ta at durations of 21 days and longer in adult rats were extracted from the subchronic neurotoxicity study and the chronic study rat study (MRIDs 43980201 and 44527802). The plot of the brain AChE data from these studies is depicted in Figure 4. 6 .1 below. A BMDL 10 

### of 0. 03 mg/kg/day associated with brain ChE inhibition in male and female adult rats was selected as a suitable PoD for the steady

- state dietary (all populations) exposure scenario. The corresponding BMD 10 

### was 0.04 mg/kg/day.

An uncertaint y factor of 1000X (10X to account for interspecies extrapolation, 10X for intraspecies variation, and 10X for FQPA SF due to uncertainty in the human dose

- response relationship for neurodevelopmental effects ( s ee Section 4.4 )) is applied to the BMDL 10 

### of 0 .03 mg/kg/day

. As a result, t he steady

- state population adjusted dose ( ssPAD ) is 0.00 0 0 3 mg/kg/day. The only population subgroup that the FQPA SF is not retained is adults 50

- 99; therefore, the ssPAD for this population subgroup is 0.0003 mg/kg/day.Page 24 of 97



### Fig ure 4. 6 .1. BMD results from the OP CRA (2002, 2006) for dicrotophos (Extracted from
USEPA, 2002, Appendix III.B.1)

Incidental Oral, Steady State

For the purpose of assessing potential risk associated with incidental oral exposure from steady

state durations resulting from spray drift

, OPP selected the dose (P o D) and endpoint from the OP CRA (USEPA, 2002 and 2006) . Quantitation of incidental oral risks was performed using the

BMDL 1 0 

### value of 0.03 mg/kg, based on brain ChE inhibiti on and the BMD 1 0 

### of 0.04 mg/kg. These values do not represent the sub

- populations of interest (infants, toddlers, young children) for incidental oral exposure. However, the results of repeated dosing study in juvenile rats (PND

12

- 18) are similar to thos e in adults. Thus data from adults are protective of any effects in the

young. A total uncertainty factor of 1000X is appropriate for incidental oral exposures (10X for interspecies extrapolation, 10X for intraspecies variation, and a 10X FQPA SF due to uncertainty

in the human dose

- response relationship for neurodevelopmental effects ( s ee Section 4.4) ).

Dermal, Steady State

A steady state d ermal PoD was selected from a 28

- day dermal toxicity study (MRID 4 6484501 ) in rats based on brain ChE inhibition ( BMDL 10 

### = 2.1 mg/kg/day ; BMD 10 

### = 3.3 mg/kg/day ) in

the female rat

. It is noted that although there were no adequate model fits (based on statistical goodness of fit results) to the male data , a visual examination of the graphical display of thePage 25 of 97



### resul ts indicated comparable fits as observed with the female data. There were no significant differences between RBC and brain ChE inhibition in the dermal toxicity study.

A refined dermal equivalent dose (RDD) for human skin may be derived from the in vitro human and rat epidermis absorption study (MRID 45099502) to account for the differences in skin permeability across species. In the in vitro study, the amount of radiolabel dicrotophos was 4 to 72 fold higher in rat epidermis compared to human epide rmis. The RDD was calculated by the following formula:

Refined Dermal Equivalent Dose (RDD) (mg/kg/day) =

Dermal PoD (mg/kg/day) x Animal In Vitro Absorption (%)

Human In Vitro Absorption (%)

Us ing the equation above, the PoD derived from the 28

- day dermal rat toxicity study can be refined to account for higher skin permeability in rat compared to human skin. Therefore, the refined dermal dose for human skin to use as the PoD is 9.33 mg/kg/day. The calculations are

shown in the table below.

Table 4. 6 .1. Calculations Used to Derive a Refined Dermal Equivalent Dose

“Triple Pack” Data Study/Information Type In vivo Rat

(24 hr) In vitro Rat

(24 hr) In vitro Human

(24 hr) Animal i n vitro

Human in vitro

Dose 4 μg/cm 2 

### 32.9 47.1 10.6 4.44

Dose 40 μg/cm 2 

### 34.9 57.7 12.2 4.73

Refined Dermal Equivalent Dose Calculation Study/Information Type Rat Dermal

PoD ( BMDL 10 

### ) RDD = PoD x Animal In Vitro

Human In Vitro

28

- day dermal toxicity study 2.1 mg/kg/day 2.1 x 4.44 = 9.33 mg/kg/day

Please note that the dermal absorption value from in vivo and in vitro studies at 24 hours were

used in estimation of h uman adjusted dermal absorption value because there was continued absorption after skin washing. The 24 hour animal in vitro absorption value was also considered to be a good predictor animal in vivo absorption ( in vitro / in vivo ≈ 1) . Additionally, the dermal absorption values at the low dose were used for refinement as they represented the most

conservative estimate.

A total uncertainty factor of 1000X is appropriate for dermal exposures (10X for interspecies extrapolation, 10X for intraspecies variation, and a 10X FQPA SF for residential as sessments or a database uncertainty factor in occupational assessments due to uncertainty in the human dose

response relationship for neurodevelopmental effects ( s ee Section 4.4) ).Page 26 of 97



### Inhalation , Steady State

A steady state inhalation PoD was selected from a 28

- day inhalation toxicity study (MRID

4 8146702 ) in female rats based on brain ChE inhibition ( BMDL 10 

### = 0.62 μg/L/day or 0.00062 mg/L/d ay ; BMD 10 

### = 0.67 μg/L/day or 0.00067 mg/L/d ay)

. Although the model fit of the

female data did not achieve an adequate statistical goodness of fit value (i.e., p values), a visual examination of the graphical display of the dose response indicated a comparable fit as observed with the male data ( BMDL 10 

### = 0.61 μg/L/day ; BMD 10 

### = 0.69 μg/L/day ; acceptable

p value) , and the fit adequately described the female ChE dose response pattern. Therefore, and in order to be consistent with the endpoints derived for oral and dermal exposure, the agency is using the female brain ChE data rather than the male data. The particle size distribution from this study suggests that most particles were well below the respirable range for an aerosol (1

- 3 μm), suggesting that the exposure was mainly via a gas. A human equivalent concentration (HEC) was not generated from this study based on the following conditions: 1) exposure was via gas and not particles thus resulting in an Regional Gas Dose Ratio ( RGDR ) instead of Regional Deposited Dose Ratio ( RDDR ) ; and 2) the effects observed were only systemic (AChE inhibition) withou t portal of entry effects (e.g., irritation). Concentrations were not adjusted for a continuous exposure basis as is done for an HEC.

For steady state inhalation exposures, a total uncertainty factor of 1000X was applied ( 10X for interspecies extrapol ation, 10X for intraspecies variation and a 10X for residential assessments or a database uncertainty factor in occupational assessments due to uncertainty in the human

dose

- response relationship for neurodevelopmental effects (see Section 4.4)).

4. 6 .2 Recommendation for Combining Routes of Exposures for Risk Assessment

PoDs for the oral, dermal, and inhalation routes are all derived from brain AChE inhibition. The data do not support any differences in response across different lifestages or sexes. T hus, all routes can be aggregated.

4. 6 .3 Cancer Classification and Risk Assessment Recommendation

In accordance with the Agency's Draft Cancer Risk Assessment Guidelines (July 2, 1999), dicrotophos is classified as showing "Suggestive evidence of carcin ogenicity, but not sufficient to assess human carcinogenic potential”. This classification is based on the evidence of increased tumor incidence for a single tumor type (thyroid) in a single species (mice) which raises a concern for carcinogenic effects, b ut is judged not sufficient for a conclusion as to human carcinogenic potential. Quantitative risk assessment for dicrotophos using the Reference Dose (RfD) approach will adequately account for all chronic toxic effects, incl uding carcinogenicity

. Quantif ication of risk using the RfD approach requires comparison of the chronic exposure to pesticide residues to the chronic RfD, a quantitative measure of hazard likely to result from long term exposure to dicrotophos.Page 27 of 97



### 4. 6 .4 Summary of Points of Departure a nd Toxicity Endpoints Used in Human Risk

Assessment

Table 4. 6 .4.1 Summary of Toxicological Doses and Endpoints and Points of Departure for Dicrotophos

Exposure/

Scenario Point of

Departure Uncertainty

Factors a Level of Concern

for Risk

Assessment Study and Toxicological Effects

Acute Dietary (all populations, except adults 50

- 99 ) BMDL 10 =

0.07mg/kg/day UF A = 10x

UF H = 10x FQPA SF = 1 0 x a PAD = 0.0 0 007 mg/kg/day BMD 10 = 0.08 mg/kg/day

CCA Study (MRID 4615205) in the rat

– PND 8, 15, & 22

Inhibition of brain ChE in rat pups.

Acute Dietary ( Adults 50

- 99 ) BMDL 10 =

0.07mg/kg/day UF A = 10x

UF H = 10x FQPA SF = 1x a PAD = 0.0007 mg/kg/day BMD 10 = 0.08 mg/kg/day

CCA Study (MRID 4615205) in the rat

– PND 8, 15, & 22

Inhibition of brain ChE in rat pups.

Steady

- State Dietary (all populations except
adults 50

- 99 ) BMDL 10 =

0.03 mg/kg/day UF A = 10x

UF H = 10x FQPA SF = 1 0 x ss PAD = 0.00 0 03

mg/kg/day BMD 10 = 0.04 mg/kg/day

Subchronic and chronic toxicity studies (OP CRA 2002, 2006; MRID’s

43980201 and 44527802)

Inhibition of brain ChE in adult rat

Steady

- State Dietary ( Adults 50

- 99 ) BMDL 10 =

0.03 mg/kg/day UF A = 10x

UF H = 10x FQPA SF = 1x ss PAD = 0.0003

mg/kg/day BMD 10 = 0.04 mg/kg/day

Subchronic and chronic toxicity studies (OP CRA 2002, 2006; MRID’s

43980201 and 44527802)

Inhibition of brain ChE in adult rat

Incidental Oral Steady State BMDL 10 =

0.03 mg/kg/day UF A = 10x

UF H = 10x FQPA SF = 1 0 x Residential LOC =

1,000 BMD 10 = 0.04 mg/kg/day

Subchronic and chronic toxicity studies (OP CRA 2002, 2006; MRID’s

43980201 and 44527802)

Inhibition of brain ChE in adult rat

Dermal Steady State (21 days and longer) BMDL 10 =

2.1 mg/kg/day

RDD = 9.33 mg/kg/day UF A = 10x

UF H = 10x FQPA SF = 1 0 x Residential LOC =

1,000 BMD 10 = 3.3 mg/kg/day

28

- day dermal toxicity study (MRID 46484501) in rats

Inhibition of brain ChE in adult rat.Page 28 of 97

Exposure/

Scenario Point of

Departure Uncertainty

Factors a Level of Concern

for Risk

Assessment Study and Toxicological Effects

Inhalation Steady State (21 days and longer) BMDL 10 =

0.00062 mg/L/day (0.162 mg/kg/day)* UF A = 10x

UF H = 10x FQPA SF = 1 0 x Residential LOC =

1,000 BMD 10 = 0.00067 mg/L/day

(0.175 mg/kg/day)*

28

- day inhalation toxicity study (MRID 48146702)

Inhibition of brain ChE in adult rat.

Cancer (oral, dermal, inhalation) Classification: "Suggestive evidence of carcinogenicity, but not sufficient to assess human carcinogenic

potential ”

. Point of Departure (PoD) = A data point or an estimated point that is derived from observed dose

- response data and used to mark the beginning of extrapolation to determine risk associated with lower environmentally relevant human exposures. NOAEL = no ob served adverse effect level. LOAEL = lowest observed adverse effect level. UF = uncertainty factor. UF A = extrapolation from animal to human (interspecies). UF H = potential variation in sensitivity among members of the human population (intraspecies). FQPA SF = FQPA Safety Factor. PAD = population adjusted dose (a = acute, c = chronic). RfD = reference dose. RfC = reference concentration.. RDD = refined equivalent dermal dose. MOE = margin of exposure. LOC = level of concern. N/A = not applicable. *conversion to oral mg/kg based on 0.00062 g/L x 1 x 6x 43.5 x 1 = 0.162 mg/kg/day. See Appendix 4 for further details. 0.00067 g/L x 1 x 6 x 43.5 x 1 = 0.175

^9.33 mg/kg/day is derived by multiplying the rat PoD of 2.1 by 4.44 (comparison of human to r at absorption); 2.1 x 4.44 = 9.33. See Appendix 4 for further details on this conversion.

a FQPA SF retained for infants, children, youths, and women of childbearing age for all exposure scenarios due to uncertainty in the human dose

- response relationsh ip for neurodevelopmental effects ( s ee Section 4.4). This includes all exposure scenarios, except the dietary exposure scenarios for the population subgroup adults 50

- 99 for which the FQPA SF has been reduced to 1X

.

Table 4. 6

. 4 .2 Summary of Toxicological Doses and Endpoints for Dicrotophos for Use in Occupational Human Health

Risk Assessments

Exposure/

Scenario Point of

Departure Uncertainty

Factors Level of Concern

for Risk

Assessment Study and Toxicological Effects

Dermal Single Day Steady

- State BMDL 10 =

2.1 mg/kg/day

RDD = 9.33 mg/kg/day UF A =10x

UF H =10x

UF DB = 10x a Occupational LOC

for MOE = 100 0 28

- day dermal toxicity study (MRID

46484501) in rats

BMD 10 = 3.3 mg/kg/day

Inhibition of brain ChE in adult rat

.

Inhalation Single Day Steady

- State BMDL 10 =

0.000 62 mg/L/day (0.1 62 mg/kg /day )* UF A =10x

UF H =10x

UF DB = 10x a Occupational LOC

for MOE = 100 0 28

- day inhalation toxicity study (MRID

48146702)

BMD 10 = 0.000 67 mg/L/day (0.1 75 mg/kg /day )*

Inhibition of brain ChE in adult rat

Cancer (oral, dermal, inhalation) Classification : "Suggestive evidence of carcinogenicity, but not sufficient to assess human carcinogenic

potential ”

. Point of Departure (P o D) = A data point or an estimated point that is derived from observed dose

- response data and used to mark the beginning of extrapolation to determine risk associated with lower environmentally relevant human exposures. NOAEL = no observed adverse effect level. LOAEL = lowest observed adverse effect level. UF = uncertainty factor. UF A = extrapolation from animal to human (interspecies). UF H = potential variation inPage 29 of 97

sensitivity among members of the human population (intraspecies). UF DB = Database uncer tainty. MOE = margin of exposure. LOC = level of concern. N/A = not applicable. *conversion to oral mg/kg based on 0.00062 mg/L/day x 1 x 6x 43.5 x 1 = 0.162 mg/kg/day. 0.00067 g/L x 1 x 6 x

43.5 x 1 = 0.175 See Appendix A2 for further details on this conversion.

^9.33 mg/kg/day is derived by multiplying the rat PoD of 2.1 by 4.44 (comparison of human to rat absorption); 2.1 x 4.44 = 9.33. See Appendix 4 for further details on this conversion.

a UF DB for occupational d ermal and inhalation exposures = database uncertainty factor for uncertainty in the human

dose

- response relationship for neurodevelopmental effects ( s ee Section 4.4).



### 4. 7 Endocrine Disruption

As required by FIFRA and FFDCA, EPA reviews numerous studies to assess potential adverse outcomes from exposure to chemicals. Collectively, these studies include acute, subchronic and chronic toxicity, including assessments of carcinogenicity, neurotoxicity, developmental, reproductive, and general or systemic toxicity. These studies include endpoints which may be susceptible to endocrine influence, including effects on endocrine target organ histopathology, organ weights, estrus cyclicity, sexual maturation, fertility, pregnancy rates, reproductive loss,

and se x ratios in offspring. For ecological hazard assessments, EPA evaluates acute tests and chronic studies that assess growth, developmental and reproductive effects in different taxonomic groups. As part of its reregistration decision for dicrotophos, EPA re viewed these data and selected the most sensitive endpoints for relevant risk assessment scenarios from the existing hazard database. However, as required by FFDCA section 408(p), dicrotophos is subject to the endocrine screening part of the Endocrine Disr uptor Screening Program (EDSP).

EPA has developed the EDSP to determine whether certain substances (including pesticide active and other ingredients) may have an effect in humans or wildlife similar to an effect produced by a “naturally occurring estrog en, or other such endocrine effects as the Administrator may designate.” The EDSP employs a two

- tiered approach to making the statutorily required determinations. Tier 1 consists of a battery of 11 screening assays to identify the potential of a

chemical s ubstance to interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal systems. Chemicals that go through Tier 1 screening and are found to have the potential to interact with E, A, or T hormonal systems will proceed to the next stage of the ED SP where EPA will determine which, if any, of the Tier 2 tests are necessary based on the available data. Tier 2 testing is designed to identify any adverse endocrine

- related effects caused by the substance, and

establish a dose

- response relationship betwe en the dose and the E, A, or T effect.

Under FFDCA section 408(p), the Agency must screen all pesticide chemicals. Between October 2009 and February 2010, EPA issued test orders/data call

- ins for the first group of 67 chemicals, which contains 58 pesticid e active ingredients and 9 inert ingredients. A second list of chemicals identified for EDSP screening was published on June 14, 2013 7 

### and includes some pesticides including dicrotophos scheduled for registration review and chemicals found in water.

Neithe r of these lists should be construed as a list of known or likely endocrine disruptors.

7 See http://www.regulations.gov/#!documentDetail;D=EPA

- HQ

- OPPT

- 2009

- 0477

- 0074 for the final second list of

chemicals.Page 30 of 97



### Dicrotophos is on List 2. List 2 represents the next set of chemicals for which EPA intends to

issue test orders/data call

- ins in the near future. For further information on the status of the EDSP, the policies and procedures, the lists of chemicals, future lists, the test guidelines and the Tier 1 screening battery, please visit our website. 8



### 5.0 Dietary Exposure and Risk Assessment

5.1 Metaboli te/Degradate Residue Profile

5.1.1 Summary of Plant and Animal Metabolism Studies

The requirement for plant metabolism is fulfilled based on an acceptable cotton metabolism study. Based on the metabolites identified, the major pathway is the stepwise de methylation and hydrolysis of the phosphate group, with subsequent conjugation of acetoacetamide, monocrotophos, and N

- methylacetoacetamide. The results of the cotton metabolism study were presented to the HED Metabolism Committee which concluded both dic rotophos and its metabolite monocrotophos should be included in the tolerance expression, and both compounds should be included for dietary exposure assessment.

The requirements for animal metabolism are fulfilled. Acceptable goat and hen metabolism

s tudies have been submitted and evaluated. Neither dicrotophos nor monocrotophos were detected in eggs and poultry tissues, or milk and ruminant tissues; the metabolites found in animals are structurally similar to those found in cotton. Since the HED Met abolism Committee previously concluded that dicrotophos and monocrotophos are the residues of concern, HED

concluded that tolerances are not needed in livestock

.

5.1.2 Summary of Environmental Degradation

The most significant degradation pathway for dicrotophos is aerobic soil metabolism (half

- life = 3 days). Dicrotophos is relatively more persistent to hydrolysis with a half

- life of 72 days. Dicrotophos is stable to hydrolysis. Dicrotophos is mobile with adsorption coefficients (K D 

### ) ranging from o f 0. 1 to 3.58 mL/g. A full summary of adsorption/desorption data can be found in the Dicrotophos RED. It is not appropriate to use K OC 

### to characterize the mobility of dicrotophos because adsorption coefficients do not sufficiently correlate with soil org anic carbon content.

Use of K D 

### rather than K OC 

### is consistent with previous assessments. However, adsorption strongly correlates with clay content (r 2 

### = 0.92).

5.1.3 Comparison of Metabolic Pathways

Metabolism in rats generally leads to detoxification , although a small amount of dicrotophos is converted internally to monocrotophos. In cotton, the major pathway is the stepwise demethylation and hydrolysis of the phosphate group, with subsequent conjugation of acetoacetamide, monocrotophos, and N

- meth ylacetoacetamide. The metabolites found in animals are structurally similar to those found in cotton.

8 http://www.epa.gov/endo/Page 31 of 97



### 5.1.4 Residues of Concern Summary and Rationale

Table 5.1.4 Summary of Metabolites and Degradates to be included in th e Risk

Assessment and Tolerance Expression

Matrix Residues included in Risk

Assessment Residues included in Tolerance Expression

Plants Primary Crop Dicrotophos and Monocrotophos Dicrotophos and Monocrotophos

Rotational Crop Dicrotophos and Monocrotophos Dicrotophos and Monocrotophos

Livestock Ruminant Dicrotophos and Monocrotophos Dicrotophos and Monocrotophos

Poultry Dicrotophos and Monocrotophos Dicrotophos and Monocrotophos

Drinking Water Dicrotophos Not Applicable



### 5 .2 Food Residue Profile

HED has previously evaluated residue data depicting the magnitude of dicrotophos residues of concern in/on cottonseed and cotton gin byproducts. The application rates represent 1x the maximum registered rates. The combined residues of dicrotophos and monocrotophos in/on

tr eated cottonseed ranged from <0.02 ppm (nondetectable) to 0.13 ppm. The combined residues of dicrotophos and monocrotophos in/on treated cotton gin byproducts ranged from 0.12 ppm to 1.8 ppm.

HED has evaluated residue data pertaining to the potential for concentration of dicrotophos residues of concern in the processed commodities of cotton. The cotton processing data indicate that dicrotophos and monocrotophos residues did not concentrate in hulls, meal, and refined oil processed from cottonseed bearing detectable dicrotophos residues and nondetectable monocrotophos residues. Tolerances are, therefore, not required for the processed commodities

of cotton.

5.3 Water Residue Profile

This revised assessment (A. Shelby, 8/13/15/, D 427440) changes the cotton percent cropped area (PCA) from 33% to 21% based on updated guidance (EPA, 2014a), incorporates application rate and application date recommendations made by the Biological and Economic Analysis Division (EPA, 2014b) and addresses commen ts on the original assessment made by Stone Environmental on behalf of the registrant, AMVAC (MRID 49582601). Registrant comments are addressed in

more detail in the EFED drinking water assessment memo (A. Shelby, 8/13/15/, D 427440)

.

Based on SWCC (Surfa ce Water Concentration Calculator v1.106) modeling runs results from the Texas Cotton scenario, the maximum estimated surface water exposure concentrations for dicrotophos and assuming maximum application rates for current uses are:Page 32 of 97 

### 8.75 μg/L for the 1 in 10 year annual peak concentration 0.507 μg/L for the 1

- in

- 10 year annual average, and 0.306 μg/L for the 30 year annual average

Based on ground water modeling results (PRZM

- GW), the maximum estimated groundwater exposure concentration from six vul nerable scenarios for dicrotophos is 0.0003 μg/L for acute and chronic exposure based on post breakthrough average

. Since the predicted concentrations in ground water are well below those calculated for surface water, surface water exposures are the

drive r for dicrotophos drinking water exposure.

Daily time series outputs for the thirty year simulation were provided to HED for use in dietary exposure modeling.

Table 5.3. Summary of Estimated Surface Water and Groundwater Concentrations for Dicrotophos.

SWCC

Scenario Application rate

and timing 1

- in

- 10

- year

peak (ppb) 1

- in

- 10

- year 21

day average (ppb) 1

- in

- 10

- year

annual average (ppb) Simulation

average (ppb) Mississippi

Cotton Maximum Rate 6.09 4.01 0.381 0.199

Typical Rate

- BEAD dates 3.21 1.67 0.193 0.0860

Typical Rate

- 14 day interval 4.49 2.45 0.204 0.0834

North

Carolina

Cotton Maximum Rate 7.73 4.94 0.507 0.306

Typical Rate 1.62 1.05 0.0901 0.0503

Texas

Cotton Maximum Rate 8.75 4.63 0.430 0.222

Typical Rate

- BEAD dates 3.66 2.12 0.238 0.0934

Typical Rate

- 14 day interval 3.69 2.09 0.217 0.0839



### 5.4 Dietary Risk Assessment

5.4.1 Description of Residue Data Used in Dietary Assessment

Average field tria l residue w as used in the dietar y exposure assessment for cottonseed oil

. The

entire distribution of daily time series drinking water outputs for the thirty year simulation w as used in the acute and steady state dietary exposure assessments.

5.4.2 Percent Crop Treated Used in Dietary Assessment

A conservative 100 percent crop treated (% CT) was used in the acute and steady state dietary

exposure assessment.

5.4.3 Acute Dietary Risk Assessment

Dicrotophos acute dietary exposure assessment were conducted using the Dietary Exposure

Evaluation Mode l software with the Food Commodity Intake Database DEEM

- FCIDTM, VersionPage 33 of 97



### 3.16, which incorporates consumption data from USDA’s National Health and Nutrition Examination Survey, What We Eat in America, (NHANES/WWEIA ). This dietary survey was

conducted from 2 003 to 2008. The analys e s w as performed to support the registration review of dicrotophos

. Since average field trial residue and 100 percent crop treated was used, the exposure at the 95 th 

### percentile of regulation will be used for reporting purposes.

An alyses were conducted using water distributions from three cotton producing areas at the maximum label application rate and the typical label application rate.

The acute aggregate dietary exposure estimates are below HED’s level of concern (<100 % the

a cute population adjusted dose ( aPAD ) ) for the U.S. population and all population subgroups for all but one water scenario (NC Cotton Max Rate) . Combined dietary exposure from food and drinking water at the 95 th 

### percentile of exposure ranged from 11

- 50 % of the aPAD for the U.S. population and 19

- 130% of the aPAD for all infants <1 y ea r old), the most highly exposed population subgroup. The dietary exposure estimates for food only were ≤ 11% aPAD for all population subgroups.

Table 5.4.3.1 Results o f Acute Dietary Exposure Analysis for Dicrotophos (Food Only)

Population Subgroup aPAD (mkd) 95 th Percentile

Exposure (mkd) % aPAD

General U.S. Population 0.0 0 007 0.0000 04 5.7

All Infants (< 1 year old) 0.0 0 007 0.000002 2.6

Children 1

- 2 years old 0.0 0 007 0.000008 11

Children 3

- 5 years old 0.0 0 007 0.0000 08 11

Children 6

- 12 years old 0.0 0 007 0.0000 06 8.2

Youth 13

- 19 years old 0.0 0 007 0.0000 04 5.1

Adults 20

- 49 years old 0.0 0 007 0.0000 02 3.4

Adults 50

- 99 years old 0.0 0 07 0.0000 02 <1

Females 13

- 49 years old 0.0 0 007 0.0000 02 3.5

* The values for the highest exposed population is bolded.Page 34 of 97

Table 5.4.3.2 Results of Acute Dietary Exposure Analysis for Dicrotophos (Food and Drinking Water) MS Cotton Typical Rate

– BEAD Date of Application

Population Subgroup aPAD (mkd) 95 th Percentile

Exposure (mkd) % aPAD

General U.S. Population 0.0 0 007 0.0000 11 15

All Infants (< 1 year old) 0.0 0 007 0.000024 35

Children 1

- 2 years old 0.0 0 007 0.000017 25

Children 3

- 5 years old 0.0 0 007 0.0000 16 23

Children 6

- 12 years old 0.0 0 007 0.0000 12 17

Youth 13

- 19 years old 0.0 0 007 0.0000 09 12

Adults 20

- 49 years old 0.0 0 007 0.0000 10 15

Adults 50

- 99 years old 0.0 0 07 0.0000 10 1.4

Females 13

- 49 years old 0.0 0 007 0.0000 10 14

* The values for the highest exposed population is bolded.

Table 5.4.3.3 Results of Acute Dietary Exposure Analysis for Dicrotophos (Food and Drinking Water) MS Cotton Typical Rate

– 14 D ay Retreatment I nterval

Population Subgroup aPAD (mkd) 95 th Percentile

Exposure (mkd) % aPAD

General U.S. Population 0.0 0 007 0.0000 10 14

All Infants (< 1 year old) 0.0 0 007 0.000020 29

Children 1

- 2 years old 0.0 0 007 0.0000 16 23

Children 3

- 5 years old 0.0 0 007 0.0000 15 21

Children 6

- 12 years old 0.0 0 007 0.0000 11 16

Youth 13

- 19 years old 0.0 0 007 0.0000 08 11

Adults 20

- 49 years old 0.0 0 007 0.0000 09 13

Adults 50

- 99 years old 0.0 0 07 0.0000 09 1.3

Females 13

- 49 years old 0.0 0 007 0.0000 09 13

* The values for the highest exposed population is bolded.Page 35 of 97

Table 5.4.3.4 Results of Acute Dietary Exposure Analysis for Dicrotophos (Food and Drinking Water) MS

Cotton Max Rate

Population Subgroup aPAD (mkd) 95 th Percentile

Exposure (mkd) % aPAD

General U.S. Population 0.0 0 007 0.0000 20 29

All Infants (< 1 year old) 0.0 0 007 0.0000 49 70

Children 1

- 2 years old 0.0 0 007 0.0000 30 43

Children 3

- 5 years old 0.0 0 007 0.0000 27 38

Children 6

- 12 years old 0.0 0 007 0.0000 19 28

Youth 13

- 19 years old 0.0 0 007 0.0000 15 22

Adults 20

- 49 years old 0.0 0 007 0.0000 20 28

Adults 50

- 99 years old 0.0 0 07 0.0000 19 2.8

Females 13

- 49 years old 0.0 0 007 0.0000 20 28

* The values for the highest exposed population is bolded.

Table 5.4.3.5 Results of Acute Dietary Exposure Analysis for Dicrotophos (Food and Drinking Water) TX Cotton Typical Rate

– BEAD Date of Application

Population Subgroup aPAD (mkd) 95 th Percentile

Exposure (mkd) % aPAD

General U.S. Population 0.0 0 007 0.0000 10 15

All Infants (< 1 year old) 0.0 0 007 0.000023 32

Children 1

- 2 years old 0.0 0 007 0.000017 24

Children 3

- 5 years old 0.0 0 007 0.0000 16 23

Children 6

- 12 years old 0.0 0 007 0.0000 12 17

Youth 13

- 19 years old 0.0 0 007 0.0000 08 12

Adults 20

- 49 years old 0.0 0 007 0.0000 10 14

Adults 50

- 99 years old 0.0 0 07 0.0000 09 1.3

Females 13

- 49 years old 0.0 0 007 0.0000 10 14

* The values for the highest exposed population is bolded.Page 36 of 97

Table 5.4.3.6 Results of Acute Dietary Exposure Analysis for Dicrotophos (Food and Drinking Water) TX Cotton Typical Rate

– 14 D ay Retreatment I nterval

Population Subgroup aPAD (mkd) 95 th Percentile

Exposure (mkd) % aPAD

General U.S. Population 0.0 0 007 0.0000 10 14

All Infants (< 1 year old) 0.0 0 007 0.000021 30

Children 1

- 2 years old 0.0 0 007 0.0000 16 23

Children 3

- 5 years old 0.0 0 007 0.0000 15 21

Children 6

- 12 years old 0.0 0 007 0.0000 11 16

Youth 13

- 19 years old 0.0 0 007 0.0000 08 11

Adults 20

- 49 years old 0.0 0 007 0.0000 09 13

Adults 50

- 99 years old 0.0 0 07 0.0000 09 1.2

Females 13

- 49 years old 0.0 0 007 0.0000 09 13

* The values for the highest exposed population is bolded.

Table 5.4.3.7 Results of Acute Dietary Exposure Analysis for Dicrotophos (Food and Drinking Water) TX

Cotton Max Rate

Population Subgroup aPAD (mkd) 95 th Percentile

Exposure (mkd) % aPAD

General U.S. Population 0.0 0 007 0.0000 22 31

All Infants (< 1 year old) 0.0 0 007 0.00005 3 76

Children 1

- 2 years old 0.0 0 007 0.0000 33 47

Children 3

- 5 years old 0.0 0 007 0.0000 29 41

Children 6

- 12 years old 0.0 0 007 0.0000 21 30

Youth 13

- 19 years old 0.0 0 007 0.0000 16 24

Adults 20

- 49 years old 0.0 0 007 0.0000 21 30

Adults 50

- 99 years old 0.0 0 07 0.0000 21 3.0

Females 13

- 49 years old 0.0 0 007 0.0000 21 30

* The values for the highest exposed population is bolded.Page 37 of 97

Table 5.4.3.8 Results of Acute Dietary Exposure Analysis for Dicrotophos (Food and Drinking Water) NC Cotton Typical Rate

Population Subgroup aPAD (mkd) 95 th Percentile

Exposure (mkd) % aPAD

General U.S. Population 0.0 0 007 0.0000 08 11

All Infants (< 1 year old) 0.0 0 007 0.000013 19

Children 1

- 2 years old 0.0 0 007 0.000013 18

Children 3

- 5 years old 0.0 0 007 0.0000 12 18

Children 6

- 12 years old 0.0 0 007 0.0000 09 13

Youth 13

- 19 years old 0.0 0 007 0.0000 06 9.2

Adults 20

- 49 years old 0.0 0 007 0.0000 07 9.9

Adults 50

- 99 years old 0.0 0 07 0.0000 06 <1

Females 13

- 49 years old 0.0 0 007 0.0000 07 9.7

* The values for the highest exposed population is bolded.

Table 5.4.3.9 Results of Acute Dietary Exposure Analysis for Dicrotophos (Food and Drinking Water) NC

Cotton Max Rate

Population Subgroup aPAD (mkd) 95 th Percentile

Exposure (mkd) % aPAD

General U.S. Population 0.0 0 007 0.0000 35 50

All Infants (< 1 year old) 0.0 0 007 0.0000 92 130

Children 1

- 2 years old 0.0 0 007 0.0000 52 75

Children 3

- 5 years old 0.0 0 007 0.0000 46 66

Children 6

- 12 years old 0.0 0 007 0.0000 33 48

Youth 13

- 19 years old 0.0 0 007 0.0000 26 38

Adults 20

- 49 years old 0.0 0 007 0.0000 35 50

Adults 50

- 99 years old 0.0 0 07 0.0000 35 5.0

Females 13

- 49 years old 0.0 0 007 0.0000 35 50

* The values for the highest exposed population is bolded.Page 38 of 97



### 5.4.4 Steady State Dietary Risk Assessment

The DEEM acute module was used to conduct steady

- state assessments using the steady

- state endpoint, two

- day average dietary exposure, and 21

- day rolling water averages. The steady

- state
assessments are refined using average field trial residue, 100% crop treated, and default processing factors. EFED provided daily time

- series outputs that simulate 29 years of residue s of ethoprop in water for multiple scenarios as mentioned previously. These distributions were

converted into 21

- day rolling averages and incorporated into R esidue D istribution F ile s (RDFs)

that were used in DEEM for water, direct all sources and water, indirect all sources.

The steady state (2 day average) aggregate dietary (food and drinking water) exposure estimates using DEEM

- FCID with the 2

- day average option are above HED’s level of c oncern for all maximum application rate cotton water scenarios. Combined dietary exposure from food and drinking water at the 95 th 

### percentile of exposure ranged from 10

- 52 % of the ss PAD for the U.S. population and 50

- 32 0% of the ss PAD for all infants <1 y ea r old). All typical application rate (as determined by BEAD) cotton scenarios gave aggregate dietary (food and drinking water) exposure estimates <100% ssPAD. The dietary exposure estimates for food only were ≤ 23% ssPAD for all population subgroups.

Table 5.4.4.1 Results of Steady State Dietary Exposure Analysis for Dicrotophos (Food Only)

Population Subgroup ssPAD (mkd) 95 th Percentile

Exposure (mkd) % aPAD

General U.S. Population 0.00003 0.000003 10

All Infants (< 1 year old) 0.00003 0.000002 5.9

Children 1

- 2 years old 0.00003 0.000007 22

Children 3

- 5 years old 0.00003 0.000007 23

Children 6

- 12 years old 0.00003 0.000005 17

Youth 13

- 19 years old 0.00003 0.000003 11

Adults 20

- 49 years old 0.00003 0.000002 7.3

Adults 50

- 99 years old 0.0003 0.000002 <1

Females 13

- 49 years old 0.00003 0.000002 7.5

* The values for the highest exposed population is bolded.Page 39 of 97

Table 5.4.4.2 Results of Steady State Dietary Exposure Analysis for Dicrotophos (Food and Drinking Water) MS Cotton Typical Rate

– BEAD Date of Application

Population Subgroup ssPAD (mkd) 95 th Percentile

Exposure (mkd) % aPAD

General U.S. Population 0.00003 0.000011 16

All Infants (< 1 year old) 0.00003 0.000025 83

Children 1

- 2 years old 0.00003 0.000017 58

Children 3

- 5 years old 0.00003 0.000016 52

Children 6

- 12 years old 0.00003 0.000012 39

Youth 13

- 19 years old 0.00003 0.000009 29

Adults 20

- 49 years old 0.00003 0.000010 35

Adults 50

- 99 years old 0.0003 0.000010 3.3

Females 13

- 49 years old 0.00003 0.000010 34

* The values for the highest exposed population is bolded.

Table 5.4.4.3 Results of Steady State Dietary Exposure Analysis for Dicrotophos (Food and Drinking Water) MS Cotton Typical Rate

– 14 D ay Retreatment I nterval

Population Subgroup ssPAD (mkd) 95 th Percentile

Exposure (mkd) % aPAD

General U.S. Population 0.00003 0.000010 14

All Infants (< 1 year old) 0.00003 0.000022 72

Children 1

- 2 years old 0.00003 0.000016 53

Children 3

- 5 years old 0.00003 0.000015 48

Children 6

- 12 years old 0.00003 0.000011 36

Youth 13

- 19 years old 0.00003 0.000008 27

Adults 20

- 49 years old 0.00003 0.000010 32

Adults 50

- 99 years old 0.0003 0.000009 3.0

Females 13

- 49 years old 0.00003 0.000009 31

* The values for the highest exposed population is bolded.Page 40 of 97

Table 5.4.4.4 Results of Steady State Dietary Exposure Analysis for Dicrotophos (Food and Drinking Water) MS Cotton Max Rate

Population Subgroup ssPAD (mkd) 95 th Percentile

Exposure (mkd) % aPAD

General U.S. Population 0.00003 0.000021 30

All Infants (< 1 year old) 0.00003 0.000053 180

Children 1

- 2 years old 0.00003 0.000032 110

Children 3

- 5 years old 0.00003 0.000028 94

Children 6

- 12 years old 0.00003 0.000020 68

Youth 13

- 19 years old 0.00003 0.000016 53

Adults 20

- 49 years old 0.00003 0.000021 68

Adults 50

- 99 years old 0.0003 0.000020 6.6

Females 13

- 49 years old 0.00003 0.000020 68

* The values for the highest exposed population is bolded.

Table 5.4.4.5 Results of Steady State Dietary Exposure Analysis for Dicrotophos (Food and Drinking Water) TX Cotton Typical Rate

– BEAD Date of Application

Population Subgroup ssPAD (mkd) 95 th Percentile

Exposure (mkd) % aPAD

General U.S. Population 0.00003 0.000011 15

All Infants (< 1 year old) 0.00003 0.000023 78

Children 1

- 2 years old 0.00003 0.000017 56

Children 3

- 5 years old 0.00003 0.000015 51

Children 6

- 12 years old 0.00003 0.000011 38

Youth 13

- 19 years old 0.00003 0.000008 28

Adults 20

- 49 years old 0.00003 0.000010 33

Adults 50

- 99 years old 0.0003 0.000009 3.2

Females 13

- 49 years old 0.00003 0.000010 33

* The values for the highest exposed population is bolded.Page 41 of 97

Table 5.4.4.6 Results of Steady State Dietary Exposure Analysis for Dicrotophos (Food and Drinking Water) TX Cotton Typical Rate

– 14 D ay Retreatment I nterval

Population Subgroup ssPAD (mkd) 95 th Percentile

Exposure (mkd) % aPAD

General U.S. Population 0.00003 0.000010 14

All Infants (< 1 year old) 0.00003 0.000022 74

Children 1

- 2 years old 0.00003 0.000016 53

Children 3

- 5 years old 0.00003 0.000015 49

Children 6

- 12 years old 0.00003 0.000011 36

Youth 13

- 19 years old 0.00003 0.000008 27

Adults 20

- 49 years old 0.00003 0.000010 32

Adults 50

- 99 years old 0.0003 0.000009 3.0

Females 13

- 49 years old 0.00003 0.000009 31

* The values for the highest exposed population is bolded.

Table 5.4.4.7 Results of Steady State Dietary Exposure Analysis for Dicrotophos (Food and Drinking Water) TX Cotton Max Rate

Population Subgroup ssPAD (mkd) 95 th Percentile

Exposure (mkd) % aPAD

General U.S. Population 0.00003 0.000022 32

All Infants (< 1 year old) 0.00003 0.000057 190

Children 1

- 2 years old 0.00003 0.000034 110

Children 3

- 5 years old 0.00003 0.000030 100

Children 6

- 12 years old 0.00003 0.000022 73

Youth 13

- 19 years old 0.00003 0.000017 57

Adults 20

- 49 years old 0.00003 0.000022 73

Adults 50

- 99 years old 0.0003 0.000021 7.1

Females 13

- 49 years old 0.00003 0.000022 73

* The values for the highest exposed population is bolded.Page 42 of 97

Table 5.4.4.8 Results of Steady State Dietary Exposure Analysis for Dicrotophos (Food and Drinking Water) NC Cotton Typical Rate

Population Subgroup ssPAD (mkd) 95 th Percentile

Exposure (mkd) % aPAD

General U.S. Population 0.00003 0.000008 11

All Infants (< 1 year old) 0.00003 0.000015 50

Children 1

- 2 years old 0.00003 0.000013 43

Children 3

- 5 years old 0.00003 0.000012 40

Children 6

- 12 years old 0.00003 0.000009 30

Youth 13

- 19 years old 0.00003 0.000006 21

Adults 20

- 49 years old 0.00003 0.000007 24

Adults 50

- 99 years old 0.0003 0.000007 2.2

Females 13

- 49 years old 0.00003 0.000007 23

* The values for the highest exposed population is bolded.

Table 5.4.4.9 Results of Steady State Dietary Exposure Analysis for Dicrotophos (Food and Drinking Water) NC Cotton Max Rate

Population Subgroup ssPAD (mkd) 95 th Percentile

Exposure (mkd) % aPAD

General U.S. Population 0.00003 0.000036 52

All Infants (< 1 year old) 0.00003 0.000097 320

Children 1

- 2 years old 0.00003 0.000053 180

Children 3

- 5 years old 0.00003 0.000046 150

Children 6

- 12 years old 0.00003 0.000033 110

Youth 13

- 19 years old 0.00003 0.000027 90

Adults 20

- 49 years old 0.00003 0.000036 120

Adults 50

- 99 years old 0.0003 0.000036 12

Females 13

- 49 years old 0.00003 0.000036 120

* The values for the highest exposed population is bolded.



### 5.4.5 Cancer Dietary Risk Assessment

D icrotophos is classified as showing "Suggestive evidence of carcinogenicity, but not sufficient to assess human carcinogenic potential”. Quantitative risk assessment for dicrotophos using the Reference Dose (RfD) approach will adequately acco unt for all chronic toxic effects, incl uding carcinogenicity

.Page 43 of 97



### 6.0 Residential (Non

- Occupational) Exposure/Risk Characterization

There are no registered (or proposed) residential uses for dicrotophos at this time. However, that does not preclude non

- occu pational exposure to dicrotophos

.

6.1 Residential Handler Exposure

HED uses the term “handlers” to describe those individuals who are involved in the pesticide application process. There are currently no registered or proposed residential uses for dicrotophos; therefore a residential handler assessment was not performed.

6.2 Post

- Application Exposure

There are currently no registered or proposed residential uses for dicrotophos

. The potential for

non

- occupational exposure from agricultural applic ations of dicrotophos has been assessed

below in Section 6.4.

6. 3 Residential Bystander Postapplication Inhalation Exposure

Volatilization of pesticides may be a source of post

- application inhalation exposure to individuals nearby pesticide applications. The agency sought expert advice and input on issues related to volatilization of pesticides from its Federal Insecticide, Fungicide, and Rodenticide Act Scientific Advisory Panel (SAP) in December 2009, and received the SAP’s final report on March 2, 2010 (http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html). The agency has evaluated the SAP report and has developed a Volatilization Screening Tool and a subsequent Volatilization Screening Analysis ( http://www.regulations.gov/#!docketDetail;D=EPA

- HQ

- OPP

- 2014

- 0219 ). During Registration Review, the agency will utilize this analysis to determine if data (i.e., flux studies, route

- specific inhalation t oxicological studies) or further analysis is required for dicrotophos.

6. 4 Spray Drift

Off

- target movement of pesticides can occur via many types of pathways and it is governed by a variety of factors. Sprays that are released and do not deposit in the application area end up off

target and can lead to exposures to those it may directly contact. They can also deposit on surfaces where contact with residues can eventually lead to exposures ( e.g. , children playing on lawns where residues have deposited next to treated fields). The potential risk estimates from these residues can be calculated using drift modeling coupled with methods employed for residential risk assessments for turf products.

The approach to be used for quantitatively incorporating sp ray drift into risk assessment includes assessing exposures for children (1 to 2 years old) and adults who have contact with turf where residues are assumed to have deposited via spray drift thus resulting in an exposure scenario. Aside from the predicted residues available for transfer, the routes of exposure and assessment methodology is analogous to how exposures to turf products are considered in risk assessment.Page 44 of 97



### In order to evaluate the drift potential and associated risks, an approach based on dri ft modeling coupled with techniques used to evaluate residential uses of pesticides was utilized. Essentially, a residential turf assessment based on exposure to deposited residues has been completed to address drift from the agricultural applications of dicrotophos. In the spray drift scenario, the deposited residue value was determined based on the amount of spray drift that may occur at varying distances from the edge of the treated field using the AgDrift (v2.1.1) model. Exposures

were considered for 50 feet wide lawns where the nearest side of the property was directly adjoining the treated field (at field edge) and at varied distances up to 300 feet downwind of a

treated field. Once the deposited residue values were determined, the remainder of the spray drift assessment was based on the algorithms and input values specified in the recently revised (2012) Standard Operating Procedures for Residential Risk Assessment (SOPs)

.

A screening approach was developed for situations where specific label guid ance for application parameters is not available. 9 

### AgDrift is appropriate for use only when applications are made by aircraft, airblast sprayers, and groundboom sprayers. When AgDrift was developed, a series of screening values (i.e., the Tier 1 option) were incorporated into the model and represent each equipment type and use under varied conditions. The screening options specifically recommended in this methodology were selected because they are plausible and represent a reasonable upper bound level of drift for common application methods in agriculture. In all cases, each scenario is to be evaluated unless it is not plausible based on the anticipated use pattern (e.g., herbicides are not typically applied to tree canopies) or specific label prohibitio ns (e.g., aerial applications are not all owed). Section 6.4.1 provides the screen ing level drift related risk estimates along with additional risk management options if necessary. These drift estimates represent plausible options for pesticide labels.

6. 4 .1 Combined Risk Estimates from Lawn Deposition Adjacent to Applications

The spray drift risk estimates are based on an estimated deposited residue concentration as a result of the screening level agricultural application scenarios. Dicrotophos is use d on cotton and can be applied via groundboom and aerial equipment at a maximum application rate of 0.5 lbs ai/acre. The recommended drift scenario screening level options are listed below:

 Groundboom applications are based on the AgDrift option for hig h boom height and using very fine to fine spray type using the 90 th 

### percentile results.

 Aerial applications are based on the use of AgDrift Tier 1 aerial option for a fine to medium spray type and a series of other parameters which will be described in m ore detail below (e.g., wind vector assumed to be 10 mph in a downwind direction for entire application/drift event).

In addition to the screening level spray drift scenarios described above, additional results are provided which represent viable drift reduction technologies (DRTs) that represent potential risk management options. In particular, different spray qualitie s have been considered as well as the

9 http://www.agdrift.com/Page 45 of 97



### impact of other application conditions (e.g., boom height, use of a helicopter instead of fixed wing aircraft, crop canopy conditions).

Dermal risk estimates were estimated for adults

. For adults, when an endpoint is not sex

- specific (i.e., the endpoints are based on developmental or fetal effects) a body weight of 80 kg is typically used in risk assessment; however, in this case, a female

- specific body weight of 69 kg

was used. While the endpoint of concern, brain A ChE inhibition, is not sex

- specific, the female

specific body weight was used to protect for pregnant women due to uncertainty in the human

dose

- response relationship for neurodevelopmental effects ( s ee Section 4.4). Dermal and

incidental oral risk estima tes for children 1<2 years old were combined because the toxicity endpoint for each route of exposure is the inhibition of brain cholinesterase (ChE). The total applicable LOC is 1000, so MOEs < 1000 represent risk estimates of concern. Adult dermal risk estimates from indirect exposure to dicrotophos related to spray drift result in buffers of 200 feet for aerial applications (i.e., MOEs ≥ 1000 at the edge of the field) and 50 feet for groundboom applications. Children’s (1 to < 2 years old) dermal and incidental oral risk estimates from indirect exposure to dicrotophos related to spray drift result in buffers of 300 feet for both aerial and groundboom applications based on the screening level scenarios.

Results are presented in Tables 6. 4 .1 and 6. 4 .2 and indicate that there are risks of concern for both aerial and groundboom applications. Appropriate drift reduction technologies such as changing the spray type/nozzle configuration to coarser spray applications may result in less drift

and reduced risk concerns (i.e., higher MOEs) from aerial applications. Similarly, using coarser sprays and lowering boom height for groundboom sprayers reduces risk concerns.

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 46 of 97 Table 6. 4 .1. Adult Risk Estimates (MOEs) Related to Indirect Exposure to Spray Drift for Dicrotophos for the Dermal Route of Exposure

Crop/Rate Group Spray Type/

Nozzle Configuration Appl.

Rate (lb ai/A) TTR

(ug/cm2) At

Edge 10

Feet 25

Feet 50

Feet 75

Feet 100

Feet 125

Feet 150

Feet 200

Feet 250

Feet 300

Feet

Cotton

Aerial Fine to Medium

0.5 0.056 170 210 250 330 440 560 680 790 1,000 1,300 1,500

Medium to

Coarse 200 280 370 520 740 980 1,200 1,500 2,000 2,700 3,300

Coarse to Very

Coarse 230 350 520 810 1,200 1,500 2,000 2,400 3,300 4,300 5,400

Very Fine to

Fine 120 130 140 160 190 220 250 280 340 400 450

AT401, M, 10 mph, 37% SD 180 230 300 410 550 720 880 1,000 1,300 1,700 2,000

WASP, M, 10 mph, 37% SD 200 250 330 500 680 880 1,100 1,300 1,700 2,000 2,400

AT401, C, 10 mph, 25% SD 220 300 430 640 910 1,200 1,500 1,800 2,500 3,300 3,900

WASP, C, 10 mph, 25% SD 250 350 510 810 1,100 1,500 1,900 2,400 3,300 4,300 4,800

AT401, VC, 10 mph, 20% SD 250 370 600 980 1,400 1,900 2,400 3,100 4,300 5,400 7,200

WASP, VC, 10 mph, 20% SD 310 490 750 1,200 1,700 2,300 3,100 3,600 5,400 6,100 7,200

Groundboom High Boom

Very fine to

Fine 230 460 770 1,200 1,700 2,100 2,500 3,100 3,900 5,400 6,100

Low Boom Very

fine to Fine 500 1,300 2,100 3,300 4,300 5,400 6,100 7,200 8,600 11,000 14,000

High Boom Fine

to
Medium/Coarse 880 2,300 3,300 4,800 6,100 7,200 8,600 8,600 11,000 14,000 14,000

Low Boom Fine

to
Medium/Coarse 1,300 3,600 5,400 7,200 8,600 11,000 14,000 14,000 21,000 21,000 21,000

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 47 of 97 Table 6. 4 .2. Children (1<2 years old) Risk Estimates (MOEs) Related to Indirect Exposure to Spray Drift for Dicrotophos for the Combined Dermal and Oral Routes of Exposure

Crop/Rate Group Spray Type/

Nozzle Configuration Appl. Rate

(lb ai/A) TTR

(ug/cm2) At

Edge 10

Feet 25

Feet 50

Feet 75

Feet 100

Feet 125

Feet 150

Feet 200

Feet 250

Feet 300

Feet

Cotton

Aerial Fine to

Medium

0.5 0.056 13 16 20 26 35 45 54 63 83 100 120

Medium to

Coarse 16 22 30 42 59 77 97 120 160 210 260

Coarse to Very

Coarse 19 27 42 64 92 120 150 190 260 340 430

Very Fine to

Fine 9 10 11 13 15 17 19 22 27 32 36

AT401, M, 10 mph, 37% SD 15 19 24 32 44 57 70 81 110 130 160

WASP, M, 10 mph, 37% SD 16 20 26 40 54 70 85 100 130 160 190

AT401, C, 10 mph, 25% SD 17 24 34 51 72 95 120 140 200 260 310

WASP, C, 10 mph, 25% SD 20 28 41 64 90 120 150 190 260 340 380

AT401, VC, 10 mph, 20% SD 19 30 47 77 110 150 190 240 340 430 570

WASP, VC, 10 mph, 20% SD 25 39 60 95 140 180 240 280 430 490 570

Groundboom High Boom

Very fine to

Fine 18 37 61 97 140 170 200 240 310 430 490

Low Boom Very fine to

Fine 40 110 170 260 340 430 490 570 680 850 1,100

High Boom

Fine to

Medium/Coarse 70 180 260 380 490 570 680 680 850 1,100 1,100

Low Boom

Fine to

Medium/Coarse 100 280 430 570 680 850 1,100 1,100 1,700 1,700 1,700

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 48 of 97 7.0 Aggregate Exposure/Risk Characterization

In accordance with the FQPA, when there are potential residential exposures to a pesticide, aggregate risk assessment must consider exposures from three major routes: oral, dermal, and inhalation. There are three sources for these types of exposures: food , drinking water, and residential uses. In an aggregate assessment, exposures from relevant sources are added together and compared to quantitative estimates of hazard (e.g., a NOAEL or PAD), or the risks themselves can be aggregated. When aggregating ex posures and risks from various sources, HED considers both the route and duration of exposure. The registered dicrotophos uses are not anticipated to result in residential exposure.

7.1 Acute Aggregate Risk

T he acute exposure estimates provided in the Dietary Exposure Section represent acute aggregate

exposure.

7.2 Short

- Term Aggregate Risk

T he acute and steady state exposure estimates provided in the Dietary Exposure Section

represent aggregate exposure.

7.3 I ntermediate

- Term Aggregate Risk

No intermediate

- term exposure scenarios were identified for dicrotophos, therefore, no

intermediate

- term aggregate risk was calculated.

7.4 Chronic Aggregate Risk

No chronic exposure scenarios were identified for dicrotophos, therefore, no chronic aggregate

risk was calculated.

7.5 Cancer Aggregate Risk

Dicrotophos is classified as showing "Suggestive evidence of carcinogenicity, but not sufficient to assess human carcinogenic potential”. Quantitative risk assessment for dicrotophos using the Reference Dose (RfD) approach will adequately account for all chronic toxic effects, including carcinogenicity.

8.0 Cumulative Exposure/Risk Characterization

OPs, like dicrotophos, share the abili ty to inhibit AChE through phosphorylation of the serine residue on the enzyme leading to accumulation of acetylcholine and ultimately cholinergic neurotoxicity. This shared MOA/AOP is the basis for the OP common mechanism grouping per

OPP’s Guidance For Identifying Pesticide Chemicals and Other Substances that have a Common Mechanism of Toxicity (USEPA, 1999). The 2002 and 2006 CRAs used brain AChE inhibition in female rats as the source of dose response data for the relative potency factors and PODs for

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 49 of 97 each OP, including dicrotophos. Prior to the completion of Registration Review, OPP will update the OP CRA on AChE inhibition to incorporate new toxicity and exposure information

available since 2006.

As described in Section 4.4, OPP has retained the F QPA Safety Factor for OPs, including dicrotophos, due to uncertainties associated with neurodevelopmental effects in children and exposure to OPs. There is a lack of an established MOA/AOP for the neurodevelopment

outcomes which precludes the agency from formally establishing a common mechanism group per the Guidance For Identifying Pesticide Chemicals and Other Substances that have a Common Mechanism of Toxicity (USEPA, 1999) based on that outcome. Moreover, the lack of a recognized MOA/AOP and other unc ertainties with exposure assessment in the epidemiology studies prevent the agency from establishing a causal relationship between OP exposure and neurodevelopmental outcomes. The agency will continue to evaluate the epidemiology studies

associated with n eurodevelopmental outcomes and OP exposure prior to the release of the revised DRA. During this period, the agency will determine whether or not it is appropriate to apply the draft guidance document entitled, Pesticide Cumulative Risk Assessment: Framewo rk for Screening Analysis for the neurodevelopment outcomes.

9.0 Occupational Exposure/Risk Characterization

9.1 Short

- and Intermediate

- term Handler Risk

HED uses the term handlers to describe those individuals who are involved in the pesticide application process. HED believes that there are distinct job functions or tasks related to applications and exposures can vary depending on the specifics of each t ask. Job requirements (amount of chemical used in each application), the kinds of equipment used, the target being treated, and the level of protection used by a handler can cause exposure levels to differ in a manner specific to each application event.

Based on the anticipated use patterns and current labeling, types of equipment and techniques that can potentially be used, occupational handler exposure is expected from the registered uses of dicrotophos. The quantitative exposure/risk assessment deve loped for occupational handlers is based on the following scenarios:

 Mixer/Loader (aerial and groundboom equipment)

 Applicators (aerial and groundboom equipment)

 Flagger (from aerial spray applications)

The above exposure scenarios best represent the re gistered use pattern (i.e., cotton applications) for dicrotophos. Chemigation applications are prohibited on the product labels.

Dicrotophos is available as a Restricted Use product (EPA7946

- 11) for micro

- injection for systemic suppression of certain ins ects on ornamental trees. HED has no exposure data appropriate for assessment of the tree injection use of dicrotophos. However, the exposures and risks associated with this use (occupational handler and/or postapplication exposure) are not expected to ex ceed those estimated for the cotton use.

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 50 of 97 Occupational Handler Exposure Data and Assumptions

A series of assumptions and exposure factors served as the basis for completing the occupational handler risk assessments. Each assumption and factor is detailed below on an individual basis.

Application Rate : Product labels indicate that dicrotophos can be used at a maximum single application rate of 0.5 lbs ai/A. See Section 4 for additional information. The occupational handler assessment was completed assumi ng the single maximum application rate.

Unit Exposures: It is the policy of HED to use the best available data to assess handler exposure. Sources of generic handler data, used as surrogate data in the absence of chemical

- specific data,

include PHED 1.1 , the AHETF database, the Outdoor Residential Exposure Task Force (ORETF) database, or other registrant

- submitted occupational exposure studies. Some of these data are proprietary (e.g., AHETF data), and subject to the data protection provisions of FIFRA. The standard values recommended for use in predicting handler exposure that are used in this assessment, known as “unit exposures”, are outlined in the “Occupational Pesticide Handler Unit Exposure Surrogate Reference Table 10 

### ”, which, along with additiona l information on HED policy on use of surrogate data, including descriptions of the various sources, can be found at the Agency website 11



### .

Area Treated or Amount Handled: Based on HED ExpoSAC Policy 9.1, the amount treated or handled per day was assumed to be:

 200 acres for mixing/loading groundboom applications and applying via ground equipment on cotton,

 1200 acres for mixing/loading for aerial applications and applying via aircraft on cotton,

and

 350 acres for flagging for aerial application on cotton crops.

Body Weight : For adults, when an endpoint is not sex

- specific (i.e., the endpoints are based on developmental or fetal effects) a body weight of 80 kg is typically used in risk assessment; however, in this case, a female

- specific body weight of 69 kg was used. While the endpoint of

concern, brain ChE inhibition, is not sex

- specific, the female

- specific body weight was used to protect for pregnant women due to uncertainty in the human dose

- response relationship for neurodevelopmental effects ( s e e Section 4.4).

Absorption Factors: Since the steady

- state dermal point of departure POD was based on a route

- specific toxicity study, no absorption factor was necessary to estimate exposure. In addition, the POD was adjusted to account for the higher rat skin permeability compared to human skin.

A route

- specific inhalation study is available and was used in the assessment; no absorption factor is necessary to the inhalation assessment.

10 Available: http://www.epa.gov/opp00001/science/handler

- exposure

- tabl e.pdf

11 Available: http://www.epa.gov/pesticides/science/handler

- exposure

- data.html

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 51 of 97 Exposure Duration: HED typically classifies exposures from 1 to 30 days as short

- term and exposures 30 days to six

months as intermediate

- term. Exposure duration is determined by many things, including the exposed population, the use site, the pest pressure triggering the use of the pesticide, and the cultural practices surrounding that use site. For the organophosphate pesticides, the match between the toxicological endpoint selection and the exposure duration is different than HED’s approach for conventional chemicals. The endpoint selection for organophosphate pesticides involves a “single day” and “st eady state” approach based on an individual chemical’s cholinesterase inhibition. The steady state approach is appropriate for dicrotophos given the toxicological and exposure profile. The “steady state” endpoint selection for dicrotophos overlaps HED’s tr aditional short

- term exposure duration endpoint selection and is considered health protective for occupational handlers that apply commercially over longer periods of time (i.e., intermediate

- term exposures).

For most agricultural uses, it is reasonable t o believe that occupational handlers will not apply the same chemical every day for more than a one

- month time frame; however, there may be a large agribusiness and/or commercial applicators who may apply a product over a period of weeks (e.g. completing m ultiple applications for multiple clients within a region).

Dicrotophos is a RUP intended for broad spectrum application to cotton fields via aerial and ground equipment. The available product labels indicate that the product can be used in multiple applications per season (early and mid

- season use) with a minimum 14 day retreatment interval. The intended pests are similar in the early and mid

- season uses (boll weevils, spider mites, aphids, etc.).

Mitigation/Personal Protective Equipment: Estimates of dermal and inhalation exposure were

calculated based on the mi tigation of agricultural uses from the 2006 dicrotophos Reregistration Eligibility Decision (RED). Specifically, the RED required ECs such as closed cabs and closed mixing/loading systems for occupational handlers. All current dicrotophos labels indicate t his level of personal protection for occupational handlers.

Combining Exposures/Risk Estimates:

Dermal and inhalation risk estimates were combined in this assessment, since the toxicological effects for these exposure routes were similar. Dermal and inh alation risk estimates were combined using the following formula:

Total MOE = Point of Departure (mg/kg/day) ÷ Combined dermal + inhalation dose (mg/kg/day)



### Summary of Occupational Handler Non

- Cancer Exposure and Risk Estimates

Ba sed on the label

- defined protection for occupational handlers (engineering controls), all exposure scenarios assessed (not including flaggers) result in combined (dermal and inhalation) risk estimates of concern (i.e., MOEs are < 1,000). MOEs for these oc cupational handler exposure scenarios range from 78 to 870.

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 52 of 97 HED does not have unit exposure data for assessing dermal and inhalation exposure for flaggers with engineering controls. HED has presented flagger risk estimates in consideration of the

maximum level of PPE feasible (i.e., double layer, chemical resistant gloves, and PF10 respirator) even though engineering controls for flaggers are required on the registered product labels. Occupational handler exposures for flaggers also result in a combined risk estimate (dermal an d inhalation) of concern with an MOE = 290.

HED has no data to assess exposures to pilots using open cockpits. The only data available is for exposure to pilots in enclosed cockpits. Therefore, risks to pilots are assessed using the engineering contr ol (enclosed cockpits) and baseline attire (long

- sleeve shirt, long pants, shoes, and socks); pilots are not required to wear protective gloves. With this level of protection, no risk estimates of concern for applicators were identified.

The Agency match es quantitative occupational exposure assessment with appropriate characterization of exposure potential. While HED presents quantitative risk estimates for human flaggers where appropriate, agricultural aviation has changed dramatically over the past

two decades. According the 2012 National Agricultural Aviation Association (NAAA) survey of their membership, the use of GPS for swath guidance in agricultural aviation has grown steadily from the mid 1990’s. Over the same time period, the use of human flag gers for aerial pesticide applications has decreased steadily from ~15% in the late 1990’s to only 1% in the most recent (2012) NAAA survey. The Agency will continue to monitor all available information sources to best assess and characterize the exposure potential for human flaggers in agricultural aerial applications.

Table 9 .1 presents a summary of the occupational handler exposure and risk estimates for dicrotophos.

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 53 of 97 Table 9 .1. Steady

- State Occupational Handler Exposure and Risk Estimates for Dicrotophos

.

Exposure Scenario Crop or Target Dermal Unit

Exposure
(ug/lb ai) 1 Inhalation Unit

Exposure
(ug/lb ai) 1 Maximum

Application

Rate 2 Area

Treated or Amount

Handled Daily 3 Dermal Inhalation Total

Level of PPE

or EC Mitigation Level Dose (mg/kg/day) 4 MOE 5 Dose (mg/kg/day) 6 MOE 7 MOE 8

Mixer/Loader

Aerial Application Cotton EC

– 8.6 EC

– 0.083 0.5 1200 A/day 0.0748 120 0.000722 220 78

Groundboom Application Cotton EC

– 8.6 EC

– 0.083 0.5 200 A/day 0.0125 750 0.00012 1,400 490

Applicator

Aerial Application Cotton EC

– 2.1 EC

– 0.0049 0.5 1200 A/day 0.0181 520 0.0000426 3,800 460

Groundboom Application Cotton EC

– 5.1 EC

– 0.043 0.5 1200 A/day 0.00739 1,300 0.0000623 2,600 870

Flagger

Flagger

- from Aerial Application Cotton Double Layer/

Gloves/ PF10 Respirator

- 10.6 Baseline

– 0.035 0.5 350 A/day 0.027 350 0.0000888 1,800 290

1 PHED/ORETF (PPE= Personal Protective Equipment; EC= Engineering. Controls; PF10= Protection Factor 10).

2 Based on registered label (e.g. Reg. No. #5481

- 00448).

3 Exposure Science Advisory Council Policy #9.1.

4 Dermal Dose = Dermal Unit Exposure (ug/lb ai) x Conversion Factor (0.001 mg/ug) x Application Rate (lb ai/acre or gal) x Area Treated or Amount Handled (A) / BW (69 kg).

5 Dermal MOE = Dermal PoD (9.33 mg/kg/day)/Dermal Dose (mg/kg/day).

6 Inhalation Dose = Inhalation Unit Exposure (ug/lb ai) x Conversion Factor (0.001 mg/ug) x Application Rate (lb ai/acre or gal) x Area Treated or Amount Handled (A) / BW (69 kg).

7 Inhalation MOE = Inhalation BMDL10 (0.162 mg/kg/day)/ Inhalation Dose (mg/kg/day).

8 Total MOE = NOAEL (mg/kg/day) ÷ Dermal Dose + Inhalation Dose OR Total MOE = 1 ÷ (1/Dermal MOE + 1/Inhalation MOE).

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 54 of 97 9.2 Short

- /Intermediate

- Term Post

- Application Risk

HED uses the term post

- application to describe exposures that occur w hen individuals are present in an environment that has been previously treated with a pesticide (also referred to as re

entry exposure). Such exposures may occur when workers enter previously treated areas to perform job functions, including activities re lated to crop production, such as scouting for pests or harvesting. Post

- application exposure levels vary over time and depend on such things as the type of activity, the nature of the crop or target that was treated, the type of pesticide application,

an d the chemical’s degradation properties. In addition, the timing of pesticide applications, relative to harvest activities, can greatly reduce the potential for post

- application exposure.

Occupational post

- application dermal exposures are expected from t he dicrotophos cotton use.

Post

- application exposures are not anticipated from the tree injection use.

9.2.1 Occupational Post

- application Inhalation Exposure/Risk Estimates

There are multiple potential sources of post

- application inhalation exposure t o individuals performing post

- application activities in previously treated fields. These potential sources include volatilization of pesticides and resuspension of dusts and/or particulates that contain pesticides. The agency sought expert advice and inpu t on issues related to volatilization of pesticides from its Federal Insecticide, Fungicide, and Rodenticide Act Scientific Advisory Panel (SAP) in December 2009, and received the SAP’s final report on March 2, 2010 ( http://www.epa.gov/scipoly/SAP/meetings /2009/120109meeting.html ). The agency has evaluated the SAP report and has developed a Volatilization Screening Tool and a subsequent Volatilization Screening Analysis ( http://www.regulations.gov/#!docketDetail;D=EPA

- HQ

OPP

- 2014

- 0219 ). During Registration Review, the agency will utilize this analysis to determine if data (i.e., flux studies, route

- specific inhalation toxicological studies) or further analysis is required for dicrotophos.

In addition, the Agency is continuing to evaluate the available post

- application inhalation exposure data generated by the Agricultural Reentry Task Force. Given these two efforts, the Agency will continue to identify the need for and, subsequently, the way to incorporate occupational post

- application inhalation exposure into the agency's risk assessments.

9

. 2 .2 Occupational Post

- application Dermal Exposure/Risk Estimates

Occupational Post

- application Dermal Exposure Data and Assumptio ns

A series of assumptions and exposure factors served as the basis for completing the occupational

post

- application risk assessments. Each assumption and factor is detailed below on an individual

basis.

Exposure Duration: The endpoint selection for o rganophosphate pesticides involves a “single day” and “steady state” approach based on an individual chemical’s cholinesterase inhibition. The steady state approach is appropriate for dicrotophos given the toxicological and exposure profile. The “steady st ate”

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 55 of 97 endpoint selection for dicrotophos overlaps HED’s traditional short

- term exposure duration endpoint selection as well as being appropriately health protective for workers that are exposed over longer periods of time (i.e., intermediate

- term exposures)

.

Transfer Coefficients: It is the policy of HED to use the best available data to assess post

application exposure. Sources of generic post

- application data, used as surrogate data in the

absence of chemical

- specific data, are derived from ARTF exposure monitoring studies, and, as proprietary data, are subject to the data protection provisions of FIFRA. The standard values recommended for use in predicting post

- application exposure that are used in this assessment, known as “transfer coefficients”, are presented in the ExpoSAC Policy 3 12 

### ” which, along with additional information about the ARTF data, can be found at the Agency website 13



### .

Table 9 .2.2.1: Anticipated Post

- Application Activities and Dermal Transfer Coefficients.

Crops Policy Crop Group Category Transfer

Coefficients Activities

cm 2 /hr

Cotton Field/ Row Crop, Low/Medium 0 Irrigation, Mechanical Weeding

70 Hand Weeding

210 Scouting



### Application Rate: The application rates for dicrotophos on the available product labels range from 0.2 to 0.5 lbs ai/A, depending on the target pest. The occupational post

- application assessment was conducted at the maximum single application rate (0.5 lbs ai/A).

Body Weight: For adults, when an endpoint is not sex

- specific (i.e., the endpoints are based on developmental or fetal effects) a body weight of 80 kg is typically used in risk assessment; however, in this case,

a female

- specific body weight of 69 kg was used. While the endpoint of concern, brain ChE inhibition, is not sex

- specific, the female

- specific body weight was used to protect for pregnant women due to uncertainty in the human dose

- response relationship for neurodevelopmental effects ( s ee Section 4.4). Absorption Factor: Since the steady

- state dermal POD was based on a route

- s pecific toxicity study, no absorption factor was necessary to estimate exposure. The POD was adjusted to account for the higher rat skin permeability compared to human skin, however.

Exposure Time: The average occupational workday is assumed to be 8 hours.

Dislodgeable Foliar Residues: Chemical specific dislodgeable foliar residue (DFR) data have been submitted for dicrotophos use on cotton (see MRID 44731001). At two test sites (Mississippi and Texas), two applications

12 Available: http ://www.epa.gov/pesticides/science/exposac_policy3.pdf

13 Available: http://www.epa.gov/pesticides/science/post

- app

- exposure

- data.html

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 56 of 97 of Bidrin ® 

### 8, an emulsifiable concentrate formulation containing 84.2% active ingredient (E isomer), dicrotophos (8 lb ai/gal), were made to cotton foliage at the target rate of 0.5 lb ai/A/application for a total seasonal rate of 1.0 lb ai/A. At all sites, the highest average dicrotophos DFR value occurred immediately after the first application and dropped to below the LOQ by 14 days after application. The highest average DFR values (and percent of application rate) were 0.422 μ g/cm 2 

### (7.84 %) at the Mississippi site and 1.001 μg/cm 2 

### (18.23 %) at the Texas site. Following the second application, the highest average dicrotophos DFR value occurred immediately after application and dropped to below the LOQ by 7 days after application at the Mississippi site and by 14 days after application at the Texas site. The highest average DFR values (and percent of application rate) following application 2 were 0.180 μg/cm 2 

### (3.22 %) at the Mississippi site and 0.343 μg/cm 2 

### (6.13 %) at the Texas si te. 14 days is the minimal retreatment interval. HED determined that the Texas site data is more appropriate for use in human health risk assessment, as precipitation concerns make the Mississippi data significantly less reliable. Typically the DFR after multiple applications would be used for the regression analysis; however, residue data after the first application at the Texas site was used in this assessment as it provided higher dislodgeable residues values and is thus more conservative. See the sum mary of

this data in the table below.

Table 9 .2.2.2. Summary of Dicrotophos DFR Residues and Versar Regression Analysis Results for Cotton Leaves Treated with Dicrotophos

Statistic Texas

Application Rate (lb ai/A) Target Application Rate = 0.50 lb ai/A 0.49 (first application) 0.50 (second application) Measured Average Day 0 Residue (μg/cm 2 ) 1.001 (first application) 0.343 (second application) Predicted Day 0 Residue (μg/cm 2 ) 0.936

Slope

- 0.402

Half

- life (days) 1.7

R 2 0.945
Registrant’s predicted half

- life (days) 2.33 Registrant’s R 2 0.971



### Occupational Post

- application Non

- Cancer Dermal Exposure and Risk Estimate Equations The algorithms used to estimate non

- cancer exposure and dose for occupational post

- application

workers can be found in the supporting occupational and residential exposure assessment 14



### .

14 Dicrotophos. Occupational and Resident ial Exposure Assessment for the Registration Review Risk Assessment.

D 428507 , 9/15/15, W. Britton, M. Lloyd, A. Lamay, S. Shelat.

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 57 of 97 Occupational Post

- application Non

- Cancer Dermal Risk Estimates

Table 9 .2.2.3: Summary of Occupational/Commercial Post

- application Risk Estimates for Dicrotophos.
Crop/Site Activities DFR/TTR 1 DAT MOE 2

Steady State

Cotton Hand Weeding 0.94 0 1,200

0.084 6 14,000

Scouting 0.94 0 410

0.63 1 610

0.42 2 920

0.28 3 1,400

0.19 4 2,000

0.13 5 3,100

0.084 6 4,600

1. DFR derived from chemical

- specific study data (MRID 44731001). 2. MOE = POD (mg/kg/day) / Daily Dermal Dose. Daily Dermal Dose = [DFR/TTR (μg/cm 2 ) x TC x 0.001 mg/μg x 8 hrs/day ]  BW (69 kg)



### Cotton harvesting: Although dicrotophos can be applied to cotton after bloom, exposure to dicrotophos residues during harvesting or post

- harvest activities is expected to be negligible as residues are expected to be minimal after the label

- re quired 30

- day pre

- harvest interval and considering that dicrotophos dissipated with a half

- life of approximately 2 days from the terrestrial field studies (D276599). The assessment of pre

- harvest activities is expected to cover any harvest

- related exposur e to dicrotophos, which would not occur until 30

- days after application.

Restricted Entry Interval

The REI specified on the label of 6 days is based on the acute toxicity of dicrotophos and the mitigation specified in the dicrotophos RED. Dicrotophos is classified as Toxicity Category I via the oral and inhalation route, Toxicity Category II via the dermal route and for eye irritation, and Toxicity Category IV for skin irritation potential. It is a strong skin sensitizer. Steady

- state risk occupational post

- application risk estimates are not of concern (i.e., MOEs >1000) on the day of treatment (i.e., Day 0) for hand weeding activities and three days after application for scouting activities. Under 40 CFR 156.208 (c) (2), if the product contains only o ne active ingredient and it is in toxicity category I, the restricted entry interval shall be 48 hours. If the active ingredient is an organophosphorus ester that inhibits cholinesterase and that may be applied outdoors in an area where the average rainfal l is less than 25 inches per year, the restricted interval should be listed as 72 hours. Thus, the REI on the labels (6 days) meets the minimum requirements.

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 58 of 97 10.0 References

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- Picciotto, Irva. Neurodevelopmental disorders and prenatal residential proximity to agricultural pesticides: The CHARGE Study. Environmental Health Perspectives 122:1103

– 1109, 2014. U.S. Environmental Protection Agency. (2008). Draft Science Issue Paper: Chlorpyrifos Hazard and Dose Response

Characterization . http://www.epa.gov/scipoly/sap/meetings/2008/091608_mtg.htm U.S. Environmental Protection Agency. (2012). Draf t Issue Paper: Scientific Issues Concerning Health Effects of Chlorpyrifos. http://www.regulations.gov/#!documentDetail;D=EPA

- HQ

- OPP

- 2012

- 0040

- 0002 Young JG, Eskenazi B, Gladstone EA, Bradman A, Pedersen L, Johnson C, Barr DB, Furlong CE, Holland NT.

Asso ciation Between In Utero Organophosphate Pesticide Exposure and Abnormal Reflexes in Neonates. NeuroToxicology. 2005;26:199

– 209. Zhang, Ying, Han, Song, Liang, Duohong, Shi, Xinzhu, Wang, Fengzhi, Wei Liu, Zhang, Li, Chen, Lixin, Gu, Yingzi, Tian, Ying. Prenatal exposure to organophosphate pesticides and neurobehavioral development of neonates: A birth cohort study in Shenyang, China. PlosOne 47:80

– 85, 2014. Zhang X, Driver JH, Li Y, Ross JH, Krieger RI. (2008) Dialkylphosphates (DAPs) in fruits and vegetables may confound biomonitoring in organophosphorus insecticide exposure and risk assessment. J Agric Food Chem. 2008 Nov 26;56(22):10638

- 45. doi: 10.1021/jf8018084.

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 60 of 97 Ap pendix 1. Summary of OPP’s ChE Policy & Use of BMD Modeling

OPP’s ChE policy (USEPA, 2000 15 

### ) describes the manner in which ChE data are used in human health risk assessment. The following text provides a brief summary of that document to provide

context to points of departure selected.

AChE inhibition can be inhibited in the central or peripheral nervous tissue. Measurements of AChE or cholinesterase (ChE) inhibition in peripheral tissues (e.g., liver, diaphragm, heart, lung etc) are rare. As such, e xperimental laboratory studies generally measure brain (central) and blood (plasma and red blood cell, RBC) ChE. Blood measures do not represent the target tissue, per se, but are instead used as surrogate measures for peripheral toxicity in studies with laboratory animals or for peripheral and/or central toxicity in humans

. In addition, RBC measures represent AChE

, whereas plasma measures are predominately butyryl

- ChE (BuChE)

. Thus, RBC AChE data may provide a better representation of the inhibition in target tissues. As part of the dose response assessment, evaluations of neurobehavior and clinical signs are performed to consider the dose response linkage between AChE inhibition and apical outcomes.

Refinements to OPP’s use of ChE data have come in th e implementation of BMD approaches in dose response assessment. Beginning with the OP CRA, OPP has increased its use of BMD modeling to derive PoDs for AChE inhibiting compounds. Most often the decreasing exponential empirical model has been used.

OP P does have not a defined benchmark response (BMR) for OPs. However, the 10% level has been used in the majority of dose response analyses conducted to date. This 10% level represents a 10% reduction in AChE activity (i.e., inhibition) compared to backgr ound (i.e., controls). Specifically, t he BMD 10 

### is the estimated dose where ChE is inhibited by 10% compared to background. The BMDL 10 

### is the lower confidence bound on the BMD 10



### .

The use of the 10% BMR is derived from a combination of statistical and biological considerations. A power analysis was conducted by the Office of Research and Development (ORD) on over 100 brain AChE datasets across more than 25 OPs as part of the OP CRA (USEPA, 2002). This analysis demonstrated that 10% is a level that can be reliably measured in the majority of rat toxicity studies . In addition, the 10% level is generally at or near the limit of sensitivity for discern ing a statistically significant decrease in ChE activity in the brain compartment and is a response level close to the background brain ChE level. With respect to biological considerations, a change in 10% brain AChE inhibition is protective for downstrea m clinical signs and apical neurotoxic outcomes. With respect to RBC AChE inhibition, these data tend to be more variable than brain AChE data. OPP begins its BMD analyses using the 10% BMR for RBC AChE inhibition but BMRs up to 20% could be considered o n a case by case basis as long as such PoDs are protective for brain AChE inhibition, potential peripheral inhibition, and clinical signs of neurotoxicity.

15 USEPA (2000) Office of Pesticide Programs, US Environmental Protection Agency, Washington DC 20460. August 18, 2000 Office of Pesticide Programs Science Policy of The Use of Data on Cholinesterase Inhibition for Risk Assessments of Organophosphorous and Carbamate Pesticides.

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 61 of 97 Appendix 2

– Results for BMD/BMDL modeling for Dicrotophos

Appendix Table 2.1 BMD results of sing le dose studies.

Dicrotophos/Study Sex/age Compartment BMD Results BMD10 (mg/kg) BMDL10 (mg/kg)

MRID 46153205 CCA Acute Study

– Single Dose Male

PND8 Brain No reliable fit No reliable fit

Female

PND8 Brain 0.082 0.071

MRID 46153205 CCA Acute Study

– Single Dose Male

PND8 RBC 0.10 0.051

Female

PND8 RBC 0.11 0.059

MRID 46153205 CCA Acute Study

– Single Dose Male

PND15 Brain 0.079 0.070

Female

PND15 Brain No reliable fit No reliable fit

MRID 46153205 CCA Acute Study

– Single Dose Male

PND15 RBC No reliable fit No reliable fit

Female

PND15 RBC 0.10 0.067

MRID 46153205 CCA Acute Study

– Single Dose Male

PND22 Brain 0.23 0.13

Female

PND22 Brain No reliable fit No reliable fit

MRID 46153205 CCA Acute Study

– Single Dose Male

PND22 RBC 0.12 0.088

Female

PND22 RBC 0.14 0.099

MRID 46153206 CCA Acute Study

– Single Dose Adult Male

PND42 Brain 0.38 0.22

Adult Female

PND42 Brain 0.12 0.092

MRID 46153206 CCA Acute Study

– Single Dose Adult Male

PND42 RBC No reliable fit No reliable fit

Adult Female

PND42 RBC 0.31 0.20

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 62 of 97 Appendix Table 2.2 BMD results of repeated dosing studies ranging in duration from 7 days to 2 years.

Dicrotophos/Study Sex/age Compartment BMD Results BMD10 (mg/kg/day) BMDL10 (mg/kg/day)

MRID 46153204 CCA Repeat Study

– 7 days Adult Male

PND42 Brain 0.11 0.054

Adult Female

PND42 Brain No reliable fit No reliable fit

MRID 46153204 CCA Repeat Study

– 7 days Adult Male

PND42 RBC 0.072 0.051

Adult Female

PND42 RBC 0.095 0.069

MRID 46153204 CCA Repeat Study

– 7 days Pup Male

PND12 Brain 0.064 0.032

Pup Female

PND12 Brain 0.049 0.028

MRID 46153204 CCA Repeat Study

– 7 days Pup Male

PND12 RBC 0.045 0.042

Pup Female

PND12 RBC 0.024 0.017

MRID 46153208 CCA Repeat Study

– 4

- Weeks Adult Male Brain 0.060 0.015

Adult Female Brain 0.077 0.059

MRID 46153208 CCA Repeat Study

– 4

- Weeks Adult Male RBC 0.12 0.097

Adult Female RBC 0.17 0.042

MRID 46153201 Developmental Neurotoxicity in Rats Maternal Gestation Day 22 (~15D of dosing) Brain 0.028 0.021

Maternal Lactation Day 22 (~37D of dosing) Brain 0.023 0.017

MRID 46153201 Developmental Neurotoxicity in Rats Maternal Gestation Day 22 (~15D of dosing) RBC 0.036 0.028

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 63 of 97 Dicrotophos/Study Sex/age Compartment BMD Results BMD10 (mg/kg/day) BMDL10 (mg/kg/day)

Maternal Lactation Day 22 (~37D of dosing) RBC 0.038 0.029

MRID 46153201 Developmental Neurotoxicity in Rats Male Fetus Gestation Day 22 Brain 0.064 0.036

Female Fetus Gestation Day 22 Brain 0.094 0.064

MRID 46153201 Developmental Neurotoxicity in Rats Male Fetus Gestation Day 22 RBC 0.066 0.045

Female Fetus Gestation Day 22 RBC 0.049 0.033

Dicrotophos/Study Sex/age Compartment BMD Results BMD10 (mg/kg/day) BMDL10 (mg/kg/day)

MRID 43980201

Subchronic Neurotoxicity in Rats Male Adult 35D of dosing Brain 0.039 0.036

Female Adult 35D of dosing Brain 0.048 0.042

MRID 43980201

Subchronic Neurotoxicity in Rats Male Adult 63D of dosing Brain 0.041 a 0.035 a

Female Adult 63D of dosing Brain 0.044 0.041

MRID 43980201

Subchronic Neurotoxicity in Rats Male Adult 98D of dosing Brain 0.048 0.044

Female Adult 98D of dosing Brain 0.045 0.042

MRID 43980201

Subchronic Neurotoxicity in Rats Male

35D of dosing RBC 0.045 0.027

Female Adult 35D of dosing RBC 0.026 0.015

MRID 43980201

Subchronic Neurotoxicity in Rats Male Adult 63D of dosing RBC 0.048 0.022

Female Adult 63D of dosing RBC 0.057 0.033

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 64 of 97 Dicrotophos/Study Sex/age Compartment BMD Results BMD10 (mg/kg/day) BMDL10 (mg/kg/day)

MRID 43980201

Subchronic Neurotoxicity in Rats Male Adult 98D of dosing RBC 0.023 0.013

Female Adult 98D of dosing RBC 0.058 0.030

MRID 44527802 Chronic Toxicity in Rats (2 year) Male Adult 371D of dosing Brain 0.028 a 0.025 a

Female Adult 371D of dosing Brain 0.047 b 0.037 b

MRID 44527802 Chronic Toxicity in Rats (2 year) Male Adult 700D of dosing Brain 0.027 0.022

Female Adult 735D of dosing Brain 0.042 c 0.035 c

MRID 44527802 Chronic Toxicity in Rats (2 year) Male 371D of dosing RBC 0.039 d 0.034 d

Female 371D of dosing RBC 0.040 0.016

MRID 44527802 Chronic Toxicity in Rats (2 year) Male Adult 700D of dosing RBC No reliable fit No reliable fit

Female Adult 735D of dosing RBC 0.053 d 0.042 d

a Due to dose spacing issues, adequate statistical model fit (p>0.1) were not obtained for these specific analyses for Brain Ch E. However, they are listed here for characterization purposes, as these results are similar in magnitude to those obtained using the more robust techniques used in the 2006 CRA (which included the results of both the subchronic neurotoxicity and chronic toxicity brain ChE data).

b p=0.077 for model fit; based on visual inspection and taking into account the observed dose spacin g issues, this model fit is adequate.

c p=0.0896 for model fit; based on visual inspection and taking into account the observed dose spacing issues, this model fit i s adequate.

d Dropped high dose in order to improve model fit.

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 65 of 97 BMD results o f repeated exposure studies via the dermal and inhalation routes.



### Dicrotophos /Study Sex/age Compartment BMD Results

BMD10 BMDL10

MRID 46484501

28

- Day Dermal Toxicity Study Male Brain No reliable fit (p=0.062; 3.67 mg/kg/day) No reliable fit (p=0.062; 2.41 mg/kg/day)

Female Brain 3.35 mg/kg/day 2.14 mg/kg/day

MRID 46484501

28

- Day Dermal Toxicity Study Male RBC 3.1 5 mg/kg/day 2.12 mg/kg/day

Female RBC 3.6 5 mg/kg/day 2.54 mg/kg/day

MRID 48146702

28

- Day Inhalation Toxicity Study Male RBC 0.4 2 ug/L/day 0.34 ug/L/day

Female RBC 0.71 ug/L/day 0.49 ug/L/day

MRID 48146702

28

- Day Inhalation Toxicity Study Male Brain 0.68 ug/L/day 0.61 ug/L/day

Female Brain No reliable fit (p=0.01; 0.67 ug/L/day) No reliable fit (p=0.01; 0.62 ug/L/day)

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 66 of 97 A ppendix 3. Toxicology Profile and Executive Summaries

A.1 Toxicology Data Requirements
The requirements ( 40 CFR 158.500) for the food use for Dicrotophos are in Table A.1. Use of the new guideline numbers does not imply that the new (1998) guideline protocols were used.

Study Technical

Required Satisfied

870.1100 Acute Oral Toxicity

................................ ....................... 870.1200 Acute Dermal Toxicity

................................ .................. 870.1300 Acute Inhalation Toxicity

................................ .............. 870.2400 Primary Eye Irritation

................................ .................... 870.2500 Primary Dermal Irritation

................................ .............. 870.2600 Dermal Sensitization

................................ ..................... yes

yes

yes

yes

yes

yes yes

yes

yes

yes

yes

yes

870.3100 Oral Subchronic (rodent)

................................ ............... 870.3150 Oral Subchronic (nonrodent)

................................ ......... 870.3200 21/28

- Day Dermal

................................ ......................... 870.3250 90

- Day Dermal

................................ .............................. 870.3465 90

- Day Inhalation

................................ .......................... yes

yes

yes

no

yes yes

yes

yes

870.3700a Developmental Toxicity (rodent)

................................ .. 870.3700b Developmental Toxicity (nonrodent)

............................ 870.3800 Reproduction

................................ ................................ . yes

yes

yes yes

yes

yes

870.4100a Chronic Toxicity (rodent)

................................ .............. 870.4100b Chronic Toxicity (nonrodent)

................................ ........ 870.4200a Oncogenicity (rat)

................................ .......................... 870.4200b Oncogenicity (mouse)

................................ ................... 870.4300 Chronic/Oncogenicity

................................ ................... yes

yes

yes

yes

yes yes

yes

yes

yes

yes

870.5100 Mutagenicity

— Gene Mutation

- bacterial

..................... 870.5300 Mutagenicity

— Gene Mutation

- mammalian

................ 870.5xxx Mutagenicity

— Structural Chromosomal Aberrations

... 870.5xxx Mutagenicity

— Other Genotoxic Effects

....................... yes

yes

yes

yes yes

yes

yes

yes

870.6100a Acute Delayed Neurotoxicity (hen)

............................... 870.6100b 90

- Day Neurotoxicity (hen)

................................ .......... 870.6200a Acute Neurotoxicity Screening Battery (rat)

................. 870.6200b 90

- Day Neurotoxicity Screening Battery (rat)

.............. 870.6300 Develop. Neurotoxicity

................................ ................. CR

no

yes

yes CR yes

yes

yes

870.7485 General Metabolism

................................ ...................... 870.7600 Dermal Penetration

................................ ........................ 870.7800 Immunotoxicity

................................ ............................. yes CR

yes yes

yes

yes

Special Studies

Comparative Cholinesterase (rat)

............................... In vitro dermal penetration (human)

........................... -

- yes

yes

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 67 of 97 A.2 Toxicity Profiles

Table A.2.1 Acute Toxicity Profile

- Dicrotophos

Guideline No. Study Type MRID(s) Results Toxicity Category

870.1100 Acute oral

- Rat 00156063/

43893901 M/F LD 50 = 11/8

mg/kg I

870.1200 Acute dermal

- Rabbit 00156063 M/F LD50

876/476 = mg/kg II

870.1300 Acute inhalation

- Rat 46411001 LC 50 > 0.059 mg/L I

870.2400 Acute eye irritation

- Rabbit 00156063 Lesions reversed

by 14 days II

870.2500 Acute dermal irritation

- Rabbit 00156063 Non

- irritating IV

870.2600 Skin sensitization

– guinea pig 00156063 Strong sensitizer

—



### Table A.2.2 Subchronic, Chronic and Other Toxicity Profile

- Dicrotophos

Guideline

No. Study Type MRID No. (year)/

Classification /Doses Results

870.3100 90

- Day oral toxicity

rodents See Subchronic

Neurotoxicity study
870.6200b

870.3150 180

- Day oral

toxicity in

nonrodents 00013441

870.3200 21

- Day dermal

toxicity rats 4 5378201 ( 2001 )

0, 2, 5, 10, or 80 mg/kg/day Dermal and systemic NOAEL > 80 mg/kg/day

Dermal and systemic LOAEL was not established

Cholinesterase Inhibition NOAEL = Not established Cholinesterase Inhibition LOAEL = 2 mg/kg/day based on decreased erythrocyte cholinesterase activity in male rats and decreased plasma cholinesterase activity in female rats.

Acceptable/Guideline

870.3700a Prenatal

developmental in

rodents 00 161578 (1986 )

0, 0.1, 0.5, 1.0, or 2.0

m g/kg/day M aternal toxicity NOAEL = 0.5 mg/kg/day.

M aternal toxicity LOAEL = 1.0 mg/kg/day based on decreased body weight gain and fasciculations

D evelopmental toxicity NOAEL = 2.0 mg/kg/day (highest dose tested)

D evelopmental toxicity LOAEL = Not established

Acceptable/Guideline

870.3700b Prenatal

developmental in (New Zealand White) rabbits 45390701 ( 2001 )

0 , 0.5, 1.0, or 2.0 mg/kg/day Maternal toxicity NOAEL = 0.5 mg/kg/day.

M aternal toxicity LOAEL = 1.0 mg/kg/day based on clinical signs of toxicity

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 68 of 97 Table A.2.2 Subchronic, Chronic and Other Toxicity Profile

- Dicrotophos

Guideline

No. Study Type MRID No. (year)/

Classification /Doses Results

D evelopmental toxicity NOAEL = Not established

D evelopmental toxicity LOAEL = 0.5 mg/kg/day based on decreased male and female fetal body weights.

Acceptable/Guideline

870.3800 Reproduction and

fertility effects ( Alpk:AP f

SD ) rats 44296101 ( 1997 )

0, 0.5

, 5.0 or 10 /15/25 ppm for two generations

F 0 males: 0, 0.5

, 0.49 , and

2.53 mg/kg/day; F 0 females: 0, 0.5

, 0.53 , and 2.79 mg/kg/day; F 1 males: 0, 0.5

, 0.56 , and 1.15 mg/kg/day; F 1 females: 0, 0.6

, 0.59 , and

1.25 mg/kg/day dicrotophos ( 87.65 % ai) (dietary) Parental/Systemic NOAEL = 0.5 ppm (F 0 males/females: 0.5 / 0.5 mg/kg/day; F 1 males/females:

0.5/0.6 mg/kg/day). Parental/Systemic LOAEL = 5.0 ppm

Reproductive NOAEL = 0.5 ppm (F 0 males/females:

0.5 / 0.5 mg/kg/day; F 1 males/females: 0.5/0.6 mg/kg/day). Reproductive LOAEL = 5.0 ppm

Acceptable/Guideline

870.4100b Chronic toxicity

dogs 44328401 (1997 )

0, 0.025

, 0.1 or 1.0/0.5 mg/kg/day for one year. High

- dose dogs received 1.0 mg dicrotophos/kg/day for 13 weeks, after which they were not dosed for 7 days, and were then given 0.5 mg/kg/day from week 15

- 52. NOAEL = 0.025 mg/kg/day

LOAEL = 0.1 mg/kg/day based on decr eased body weight gain (26%; weeks 1

- 52) and food efficiency

in females.

Cholinesterase Inhibition NOAEL = 0.025 mg/kg/day Cholinesterase Inhibition LOAEL = 0.1 mg/kg/day based on statistically significantly decreased brain and plasma ChE.

Acceptable/Guideline

870.4200a Chronic toxicity /

Carcinogenicity

rat 44527802 ( 1998 )

0, 0.5

, 5 or 25 ppm (0, 0.02

, 0.25 or 1.42 mg/kg/day for male rats and 0, 0.03, 0.32, or 1.72 mg/kg/day for female

rats. NOAEL = 0.5 ppm ( 0.02 mg/kg/day for males and 0.03 mg/kg/day for females ).

LOAEL = 5 ppm (0.25 mg/kg/day for males and 0.32 mg/kg/day for females) based on decreased survival in male rats, and aspiration pneumonia and esophageal luminal dilatation in female rats

.

Cholinesterase Inhibit ion NOAEL = Not established Cholinesterase Inhibition LOAEL = 0.5 ppm (0.02 mg/kg/day for males and 0.03 mg/kg/day for females) based on statistically significantly decreased brain, erythrocyte and plasma ChE.

No evidence of carcinogenicity was observed in rats fed dicrotophos at dietary concentrations of 0.5, 5, or 25 ppm for 97

- 100 weeks for males and 105 weeks

for females.

Acceptable/Guideline

870.4200b Carcinogenicity

mice 44527801 (1) NOAEL = 10 /2 ppm ( 1.12/0.31 mg/kg/day) for males/females, respectively.

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 69 of 97 Table A.2.2 Subchronic, Chronic and Other Toxicity Profile

- Dicrotophos

Guideline

No. Study Type MRID No. (year)/

Classification /Doses Results

0, 2, 10, or 50 ppm (0, 0.22, 1.12, or 6.42 mg/kg/day for males and 0, 0.31, 1.58, or

9.06 mg/kg/day for females ) for up to 2 years. LOAEL = 50 ppm ( 6.42 mg/kg/day) for males based

on neurological signs, ki dney toxicity and thyroid

follicular cell adenomas. LOAEL = 10 ppm (1.58 mg/kg/day) for females

based on decreased survival rate.

Treatment for up to 105 weeks with dicrotophos resulted in a significant increase in Acceptable/Guideline

870.6100b Delayed

Neurotoxicity Study

Hen 44943901, 45170201 (1999)

Single oral gavage dose of 11 mg/kg Oral administration of dicrotophos at 11 mg/kg does not produce delayed neuropathy in the hen.

870.6200a Acute

Neurotoxicity
Rat (Oral gavage) 43759801 (1995)

0, 0.5, 5, or 10 mg/kg NOAEL = 0.5 mg/kg

LOAEL = 5 mg/kg based on clinical signs (principally decreased activity, upward curvature of spine, pinched in sides, flaccid appearance and decreased pupil response).

Acceptable/Guideline

870.6200b Subchronic

Neurotoxicity

Rat (Oral dietary) 43980201 (1995)

0, 0.5, 5, or 25 ppm (0, 0.04, 0.39, and 2.03 mg/kg/day in males and 0, 0.04, 0.45, and 2.38 mg/kg/day in females) Systemic NOAEL = 25 ppm (2.03 and 2.38 mg/kg/day in males and females, respectively)

System ic LOAEL = 5 ppm (0.39 and 0.45 mg/kg/day in males and females, respectively), based on changes in motor activity and body weight decreases

in both sexes.

Cholinesterase Inhibition NOAEL = Not determined

Cholinesterase Inhibition LOAEL = 0.5 ppm (0.04

mg /kg/day) based on cholinesterase inhibition in brain, plasma, and erythrocytes.

Acceptable/Guideline

870.6300 Developmental

Neurotoxicity

Rat (Oral gavage) 46153202 (2003)

0, 0.01, 0.05, or 0.4 mg/kg/day from GD7 through parturition to lactation day 7.

Pups 0, 0.01, 0.05, or 0.4 mg/kg/day from PND 8 to 22 Maternal systemic NOAEL ≥0.4 mg/kg/day (highest dose tested).

Maternal systemic LOAEL = Not identified

Offspring systemic NOAEL = Not established

Offspring systemic LOAEL = 0.4 mg/kg/day based

on morphometric changes in the brain of male and female offspring on PND 12.

Acceptable/Nonguideline

870.7485 Metabolism and

pharmacokinetics 43942001 (199 6 )

Labeled dicrotophos

administered to CD rats via In a 96

- hour rat metabolism study (MRID

43942001), [3

- 14 C]dicrotophos (98.9% ai) was

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 70 of 97 Table A.2.2 Subchronic, Chronic and Other Toxicity Profile

- Dicrotophos

Guideline

No. Study Type MRID No. (year)/

Classification /Doses Results

gavage as a single dose at 0.5 or 3 mg/kg or as a single dose at 0.5 mg/kg following

a 14

- day pretreatment with unlabeled dicrotophos at 0.5 mg/kg/day. administered to male and female CD rats (5 or 7
animals/sex/dose) by gavage as a single dose at
levels of 0.5 or 3 mg/kg, or as a single dose at 0.5
mg/kg following a 14

- day pretreatment with
unlabeled dicrotophos at 0.5 mg/kg/day. Five

additional rats/sex received a si ngle 0.5 mg/kg

intravenous dose in a 96

- hour study.

[ 14 C]Dicrotophos was rapidly absorbed by male and
female rats following oral and intravenous dosing.
The orally and intravenously administered
radioactivity was quantitatively recovered from each
dosing regimen; total recovery was 97

- 99% of the
dose. There was no difference in the relative pattern

of excretion between male and female rats and no
appreciable difference among dose levels or routes.
Greater than 80% of the radioactivity was recovered

in u rine during the first 24 hours from all dose
groups, and after 96 hours 83

- 88% was excreted in
urine and feces. Volatile radioactive products

accounted for 5

- 7% of the radioactivity. Only 1.1

- 2.6% of the dose was in the tissues/carcass. Liver

had the hi ghest percentage of the dose at 0.07

- 0.09%. The concentration of radioactivity was
highest in fat: 0.014

- 0.018 ppm for single oral and

intravenous low doses, 0.023

- 0.033 ppm for the oral
repeated low dose, and 0.106

- 0.124 ppm for the
single oral high dos e.

Dicrotophos metabolites were investigated in Day

- 1 urine. The results indicated that dicrotophos is extensively metabolized via N

- demethylation and

oxidation of the N

- methyl moiety yielding intact organophosphate products, which may be dealkylated. Metabolism may also proceed via demethylation and dealkylation of the phosphate moiety forming various acetoacetamide and acetobutamide products. Twenty

- one metabolic components were identified, including parent, 19 Phase 1 metabolites, and one conjugate

. Characterized metabolites exceeded 83% of the dose.

Un

- metabolized dicrotophos accounted for 3

- 7% of the doses. Hydroxydicrotophos accounted for up to 20% of the dose and monocrotophos accounted for up to 3%. Other intact organophosphates, numerous

a cetoacetamide and acetobutamide products, and one conjugate, N

- acetylmonocrotophos were identified, but were not separately quantified.

Acceptable/Guideline

870.7800 Immunotoxicity 48404101 (2011) Immunotoxicity NOAEL = 25 ppm (1.91 mg/kg/day)

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 71 of 97 Table A.2.2 Subchronic, Chronic and Other Toxicity Profile

- Dicrotophos

Guideline

No. Study Type MRID No. (year)/

Classification /Doses Results

Oral diet 0, 5, 15, or 25 ppm (0, 0.37, 1.14, or 1.91 mg/kg bw/day). Immunotoxicity LOAEL = Not established (> 25 ppm)

Systemic NOAEL = 25 ppm (1.91 mg/kg/day)

Systemic LOAEL = 5 ppm (0.37 mg/kg/day) based

on statistically significant depression in both erytrhocytes and brain cholinesterase activity.

Acceptable/Guideline

Comparative

Cholinesterase

Rat 46153205

- single oral gavage

dose of 0 or 5 mg dicrotophos

46153204

- single oral gavage dose of 0, 0.008, 0.02, 0.08, 0.4, or 1.0 mg/kg/day,

46153207

- repeated dose exposure via oral gavage of 0, 0.008, 0.02, or 0.4 mg/kg/day for 4 weeks

46153208

– repeated dose exposure via oral gavage of 0 or 0.4 mg dicrotophos for 4

or 8 weeks. For repeated oral exposure to dicrotophos, the

overall adult LOAEL for cholinesterase inhibition is 0.4 mg/kg/day based on brain and red blood cell; the

NOAEL is 0.08 mg/kg/day.

For repeat oral exposure to dicrotophos, the overall offspring LOAEL is 0.08 mg/kg/day based on brain and RBC; the NOAEL is 0.02 mg/kg/day.

Acceptable/Nonguideline

In Vitro Dermal

Penetration

Rat and Human skin 45099502 (1999) The invitro study results show that rat epidermis is more permeable than human epidermis.

Acceptable/Nonguideline

P o D Conversion Calculations

As summarized in Section 4.5.4, inhalation and dermal P o Ds were derived using the following conversion

calculations:

Inhalation BMDL 10

0.00062 mg/L/day (Female Brain AChE result from BMD modeling summarized in Appendix 1).

This value is converted to mg/kg/day using the equation:

mg/L x absorption x duration x conversion factor x activity factor

Absorption

- ratio of deposition a nd absorption in the respiratory tract compared to absorption by the oral route = 1

Duration

– duration of daily animal or human exposure (hr) = 6 hrs

Conversion factor

– a L/hr/kg factor which accounts for respiratory volume and BW for a given species and strain = 43.5 L/hr/kg

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 72 of 97 Activity factor

– accounts for increased exposure resulting from increased respiration (default is 1).

Therefore, the mg/kg/day value is: (0.00062 mg/L/day x 1 x 6 hrs x 43.5 L/hr/kg x 1 = 0.162 mg/kg/day

Inhalation BMD 10

Similar ly, the Inhalation BMD10 is derived using the 0.0007 mg/L/day result (Female Brain AChE result from
BMD modeling summarized in Appendix 1). This value is converted to mg/kg/day using the same equation above:

(0.00067 mg/L/day x 1 x 6 hrs x 43.5 L/hr/kg x 1 = 0.175 mg/kg/day.

Dermal Human Adjusted Point of Departure

9.33 mg/kg/day POD is derived by multiplying the rat PoD of 2.1 by 4.44 (comparison of human to rat absorption):

( 2.1 mg/kg/day) (4.44) = 9.33 mg/kg/day.

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 73 of 97 A.3 Hazard Identification and Endpoint Selection

A.3.1 Acute Dietary Reference Dose (aRfD)

– All Populations

Study Selected: Comparative Cholinesterase (CCA) Acute Studies in Rats

– Single Dose

MRID No.: 46153205 ; 46153206 Dose and Endpoint for Risk Assessment: A BMDL 10 

### of 0. 07 mg/kg/day associated with brain ChE inhibition in male and female pups was selected as a suitable PoD for the acute dietary (all populations) exposure scenario. The corresponding BMD 10 

### was 0.08 mg/kg/day. Comments about Study/Endpoint/Un certainty Factors: Brain cholinesterase inhibition was selected for the PoD since the brain is a principal target organ for organophosphate pesticides, and the brain ChE data was more robust than RBC ChE data. Data from the PND 8 and 15 pups represent h ighly exposed sub

- populations (infants and young children) and thus are appropriate

for PoD derivation. An uncertainty factor of 100X (10X to account for interspecies extrapolation and 10X for intraspecies variation) is applied to the BMDL 10 

### to obtain an aRfD of 0.0007 mg/kg/day. Based on the FQPA safety factor of 1 X , the acute population adjusted dose (aPAD)

is 0.0007 mg/kg/day.

Acute RfD (All Populations) = aPAD= (BMDL 10 ) 0.07 mg/kg = 0.0007 mg/kg (UF) 100



### A.3.2 Steady State Reference Dose (ssRfD)

– All Populations

Study Selected: Comparative Cholinesterase (CCA) Repeat Dose Studies in Rats

MRID No.: 43980201; 44527802

Dose and Endpoint for Risk Assessment: A BMDL 10 

### of 0. 03 mg/kg/day associated with brain

ChE in hibition in male and female adult rats was selected as a suitable PoD for the steady

- state dietary (all populations) exposure scenario. The corresponding BMD 10 

### was 0.04 mg/kg/day. Comments about Study/Endpoint/Uncertainty Factors: T he available AChE dat a at durations of 21 days and longer in adult rats (from the OP CRA) were extracted from the subchronic neurotoxicity study and the chronic study in rats. An uncertainty factor of 100X (10X to account for interspecies extrapolation and 10X for intraspeci es variation) is applied to

the BMDL 10 

### to obtain a ssRfD 16 

### of 0.000 3 mg/kg/day. Based on the FQPA safety factor of 1 X

, the steady

- state population adjusted dose ( ssPAD ) is 0.000 3 mg/kg/day.

ssRfD (All Populations)= ssPAD = (BMDL 10 ) 0.03 mg/kg/day = 0.0003 mg/kg/day (UF) 100



### A.3.4 Incidental Oral Exposure (Single Day)

Study Selected: Comparative Cholinesterase (CCA) Acute Study in Rats

– Single Dose

16 ssRfD: Reference dose derived from steady state duration

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 74 of 97 MRID No.: 46153205 Dose and Endpoint for Risk Assessment: A BMDL 10 

### of 0. 07 mg/kg/day associated with brain ChE inhibition in male and female pups was selected as a suitable PoD for assessing the potential risk associated with incidental oral exposure from a single day exposure scenario. The corresponding BMD 10 

### was 0.08 mg/kg/day. Comments about Study/Endpoint/Uncertainty Factors: Brain cholinesterase inhibition was selected for the PoD since the brain is a principal target organ for organophosphate pesticides,

and the brain ChE data was more robust than RBC ChE data. Data from t he PND 8 and 15 pups represent highly exposed sub

- populations (infants and young children) and thus are appropriate

for PoD derivation. The total UF is 100X (10X to account for interspecies extrapolation and 10X for intraspecies variation)

.

A.3.5 Inc idental Oral Exposure (Steady State)

Study Selected: Comparative Cholinesterase (CCA) Acute Study in Rats

– Single Dose

MRID No.: Dose and Endpoint for Risk Assessment: For the purpose of assessing potential risk associated with incidental oral exposure f rom steady state durations

, OPP selected the dose (P o D) and endpoint from the OP CRA (USEPA, 2002 and 2006)

. A BMDL 10 

### of 0. 03 mg/kg/day associated with brain ChE inhibition in adults was selected as a suitable PoD for assessing the potential risk associated with incidental oral exposure at steady

- state. The corresponding BMD 10 

### was 0.04 mg/kg/day. Comments about Study/Endpoint/Uncertai nty Factors: These values do not represent the

sub

- populations of interest (infants, toddlers, young children) for incidental oral exposure. However, the results of repeated dosing studies in juvenile rats (PND 12

- 18) are similar to those

in adults. Th us data from adults are protective of any effects in the young.

The total UF is 100X (10X to account for interspecies extrapolation and 10X for intraspecies variation)

.

A.3.6 Dermal Exposure (Single Day and Steady State )

Study Selected: 28

- day D ermal Toxicity Study

MRID No.: 46484501 ; 45099502 Dose and Endpoint for Risk Assessment: A BMDL 10 

### of 2.1 mg/kg/day associated with brain ChE inhibition in adult rats, following dermal exposure, was selected as a suitable PoD for assessing the potential ris k associated with dermal exposure (single day and steady

- state). The corresponding BMD 10 

### was 3.3 mg/kg/day. A refined dermal equivalent dose (RDD) for human skin was derived using data from an in vitro human and rat epidermis absorption study (MRID

4509 9502) to account for differences in skin permeability across species. The RDD was calculated by the following formula:

Refined Dermal Equivalent Dose (RDD) (mg/kg/day) =

Dermal PoD (mg/kg/day) x Animal In Vitro Absorption (%)

Human In Vitro Absorption (%)

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 75 of 97 Using the equation above, the PoD derived from the 28

- day dermal rat toxicity study can be adjusted to account for higher skin permeability compared to human skin. Theref ore, the human adjusted dermal dose for use as the PoD is 9.33 mg/kg/day 17 

### . The calculations are shown in

Table 4.5.1. Comments about Study/Endpoint/Uncertainty Factors: A dermal study that measure s AChE inhibition after a single exposure is not availabl e for dicrotophos. Therefore, the 28

- day dermal study is the only study available and was used for both th e single day and the steady

- state dermal

assessment. The total UF is 100X (10X to account for interspecies extrapolation and 10X for intraspecies va riation)

. Note: Although human information has been used to derive a human adjusted PoD, the full 10X interspecies factor is retained. The adjustments made here relate only to dermal adsorption, not to systemic pharmacokinetics which impact species differences in internal dosimetry and not to pharmacodynamics which relate to species differences in AChE

inhibition.

A.3.7 Inhalation Exposure (Single Day and Steady State)

Study Selected: 28

- day Inhalation Toxicity Study

MRID No.: 48146702

Dose and E ndpoint for Risk Assessment: A BMDL 10 

### of 0.62 μ g/ L /day or 0.00062 mg/L/day associated with brain ChE inhibition in female rats, following inhalation exposure, was selected as a suitable PoD for assessing the potential risk associated with inhalation exposu re (single day and steady

- state). The corresponding BMD 10 

### was 0.67 μ g/ L /day or 0.00067 mg/L/day.

Comments about Study/Endpoint/Uncertainty Factors: An inhalation study that measure s AChE inhibition after a single exposure is not available for dicroto phos. Therefore, the 28

- day inhalation study is the only study available and was used for both th e single day and the steady

state inhalation assessment. The particle size distribution from this study suggests that most particles were well below the respirable range for an aerosol (1

- 3 μm), suggesting that the exposure was mainly via a gas. A human equivalent concentration (HEC) was not generated

from this study based on the following conditions: 1) exposure was via gas and not particles thus resulting in an RGDR instead of RDDR; and 2) the effects observed were only systemic (AChE inhibition) without portal of entry effects (e.g., irritation). Concentrati ons were not adjusted for a continuous exposure basis as is done for an HEC. For steady state inhalation exposures, a total uncertainty factor of 100 X was applied (10X for interspecies uncertainty factor and 10X for intraspecies variability and a 1X F QPA SF)

.

17 9.33 mg/kg/day is derived by mult iplying the rat PoD of 2.1 by 4.44 (2.1x4.44 =9.33)

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Page 76 of 97 A.4 Executive Summaries

A.4.1 Subchronic Toxicity

870.3100 90

- Day Oral Toxicity

– Rat

See Subchronic Neurotoxicity study 870.6200b [MRID 43980201]

870.3150 90

- Day Oral Toxicity

– Non

- Rodent [00013441]

[TBA]

870.3200 21/28

- Day Dermal Toxicity

– Rat

In a repeated dose dermal toxicity study (MRID 45378201), groups of 10 male and 10 female Crl:CD(SD)BR rats received applications of 0, 2, 5, 10, or 80 mg/kg/day Dicrotophos (87.6%, Batch No. 403001B) in deionized water, 6 hours/day for 21 days in a 28

- day period. Additional groups of 5 male and 5 female rats were assigned to each dose level and designated as satellite animals for assessment of brain, erythrocyte, and plasma cholinesterase activity.

There were no deaths, clinical si gns, dermal, hematology or clinical chemistry, opthalmological or gross or histopathological effects attributable to treatment. No treatment

- related body weight or food consumption effects were observed and there were no treatment

- related effects on organ weight. No treatment

- related Functional Observational Battery (FOB) or motor activity effects

were noted.

There was a decrease in brain cholinesterase activities in males and females in hte 10 mg/kg/day (males: p<0.01, 27% decrease; females p<0.05, 26 % decrease) and 80 mg/kg/day (males : p<0.01, 57% decrease; females p<0.01, 65% decrease) treatment groups compared to controls. Erythrocyte cholinesterase activities were decreased for males in all treatment groups (p<0.01,

11

- 46% decrease) and for femal es at 5 (p<0.05, 16% decrease, 10 (p<0.01, 23% decrease, or 80 (p<0.01, 57% decrease) mg/kg/day compared to controls. Plasma cholinesterase activities were decreased for females in all treatment groups (p<0.01, 38

- 70% decrease) and for males at 10 (p<0.05 , 16% decrease) or 80 mg/kg/day (p<0.01, 35% decrease).

The dermal and systemic NOAEL for Dicrotophos in rats are >80 mg/kg/day. The dermal and systemic LOAELs were not identified. The NOAEL for cholinesterase inhibition is not

identified and the LOAE L for cholinesterase inhibition is 2 mg/kg/day based on decreased erythrocyte cholinesterase activity in male rats and decreased plasma cholinesterase activity in female rats.

This study is classified as Acceptable/Guideline and does satisfy the guideline requirements for a repeated

- dose dermal study [OPPTS 870.3200 (§82

- 2)] in rats.

870.3465 Subchronic Inhalation

– Rat

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 77 of 97 In a subchronic inhalation toxicity study (MRIDs # 48146702 & 48146701), dicrotophos (88.9% purity; batch/lot # GB101309

- 01) was administered to 4 groups of Cr1:CD® (SD) rats 10/sex/concentration by dynamic nose only exposure at concentrations of 0, 0.1, 0.75, or 3.0 μg/L for 6 hours per day, 5 days/week for a total of 20 days.

There were no compound related effects in mortality, clinical signs, body weight, food consumption, hematology, clinical chemistry, organ weights, or gross and histologic pathology. Biologically significant, dose

- related reductions in erythr ocyte (M: ↓ 79%, F: ↓ 81% for the 0.75 μg/L and M: ↓ 48%, F: ↓ 64% for the 3.0 μg/L dose) and brain cholinesterase activity (M: ↓ 89%, F: ↓ 85% for the 0.75 μg/L and M: ↓ 65%, F: ↓ 62% for the 3.0 μg/L dose), were observed in both sexes exposed to 0.75 and 3.0 μg/L, respectively.

The LOAEL is 0.75 μg/L /day, based on biologically significant reductions in erythrocyte and brain cholinesterase activity in both sexes. The NOAEL is 0.1 μg/L /day.

This subchronic inhalation toxicity study in the rat is Accept able, Non

- guideline and dose not satisfy the guideline requirement for a subchronic inhalation study OPPTS 870.3465; OECD 413 in the rat. The study animals were exposed to the test material over 20 days only, while OPPTS 870.3465; OECD 413 requires 90 days of exposure.

A .4.2 Prenatal Developmental Toxicity

870.3700a Prenatal Developmental Toxicity Study

– Rat

In a developmental toxicity study (MRID 00161578), 25 presumed pregnant Charles River Crl: CD(SD)BR rats per group were administered 5 mL/kg/day dicrotophos (89.7% a.i.) in water once daily, orally by gavage, at dosage levels of 0 (sterile water vehicle), 0.1, 0.5, 1.0, or 2.0 mg/kg/day, on gestation days 6 through 15 inclusive. Animals were observed daily (30 minutes

and 2 hours followi ng dose administration) and body weights and food consumption recoreded

on pre

- treatment day 0, on treatment days 6, 9, 12, and 15, and on post

- treatment days 18 and 20. On GD 20, dams were sacrificed, subjected to gross necropsy, and all fetuses examined externally. Approximately one

- half of each litter was processed for visceral examination and the remaining one

- half was processed for skeletal examination. All animals survived to terminal sacrifice. Significant levels of fasciculations were recorded in the 1.0 and 2.0 mg/kg groups, in 20 and 25 animals, respectively. Additionally, dams in the 2.0 mg/kg group exhibited tremors (20 animals), decreased limb tone (18 animals), gritting of teeth (15 animals), tachypnea (excessive, shallow breathing, 5 anima ls), and salivation (12 animals). Peak toxicological effects were observed generally 2 hours after dosing. Animals in the 2.0 mg/kg group also had increased levels of yellow urogenital staining, soft stool and dried red matter around the eyes and nose (r espectively, in 14, 10, and 9 animals). Significant mean body weight losses occurred in the two highest groups, 1.0 and 2.0 mg/kg, especially during the first three days of compound administration.

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Page 78 of 97 No clinical signs of toxicity were observed in any an imal. Maternal body weights, body weight gains, and food consumption were similar between the treated and control groups throughout the study. Maternal necropsy was unremarkable.

Therefore, the maternal toxicity NOAEL is 0.5 mg/kg/day and the maternal t oxicity LOAEL is 1.0 mg/kg/day, based on decreased body weight gain and fasciculations

.

No differences were observed between the treated and control groups for number of corpora lutea, number of implantation sites, live fetuses/dam, pre

- and post

- implanta tion losses, fetal body weights, or fetal sex ratios.

No treatment

- related external, visceral, or skeletal malformations/variations were observed in any fetus from any group.

Therefore, the developmental toxicity NOAEL is  2.0 mg/kg/day and the developmental toxicity LOAEL was not identified.

This study is classified as Acceptable/Guideline and satisfies the requirements for a developmental toxicity study [OECD 870.3700 (§83

- 3a)] in rats.

870.3700a Prenatal Developmental Toxicity Study

- Rat

In a developmental toxicity study (MRID 00263684), five groups of Sprague

- Dawley (Charles River Crl: CD [SD] Br) mated female rats (25/group) were administered single doses of 5 mL/kg/day test article (Bidrin technical, 89.7% a.i.) orally by gavage at le vels of 0 (sterile water vehicle), 0.1, 0.5, 1.0, or 2.0 mg/kg/day from (presumed) gestation day 6 through 15 inclusive, and survivors sacrificed on gestation day 20.

Prior to conducting the main developmental toxicity study, a preliminary dose

- selection investigation was performed, using 6 oral dosage levels (0, 0.5, 1.0, 5.0, 10.0 and 15.0 mg/kg/day) administered by gavage to groups of 8 mated Crl: CD[SD]Br females each from gestation days 6 through 15. Twenty

- three animals died, one to seven days after beginning treatment: 7/8 of the 5.0 mg/kg/day group, and all 8 of both 10.0 and 15.0 mg/kg/day groups. Numerous clinical signs of compound (OP) toxicity were evident in these animals. The single survivor on 5.0 mg/kg/day lost weight and ate less during th e study, and at scheduled necropsy (day 20) was found to have viable fetuses, apparently normal according to gross fetal examination. Animals of the second lowest dose group (1.0 mg/kg/day) manifested fasciculations (muscle twitching) 30 minutes following dosing, beginning on gestation day 14. No changes from control were noted at the LDT, 0.5 mg/kg/day group on fetal intrauterine survival, sex ratio, mean fetal weights, or gross examination. Based on these results, dose levels, as indicated above, for the definitive study were selected.

During the definitive study, animals were observed daily, and body weights and food consumption recorded periodically . Gross clinical, reproductive and fetal parameters were

recorded at termination. One

- half of each fet al litter was examined for soft tissue anomalies and

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 79 of 97 fetal kidneys graded for renal papillar development, while the remainder of each litter was prepared for skeletal examination; fetal values were reported both individually as well as by

litter. Statisti cal analyses were conducted on all relevant data sets.

No dams died, aborted or delivered spontaneously during the course of the study, but significant levels of fasciculation were recorded at 1.0 and 2.0 mg/kg/day (respectively, in 20 and 25 animals), as well as significant mean body weight losses and decreased food consumption (the latter recovered to control levels during the post

- treatment period, days 16 through 20, Additionally at the HDT, 20/25 dams had tremors, 18/25 decreased limb tone, 15/25 gr itting of the teeth, while shallow breathing was observed in 5/25, and salivation in 12. Finally, urogenital staining, soft stool and dried red ocular/nasal matter were common in HDT animals. No gross pathological changes attributable to test article wer e revealed; incidental findings unrelated to

treatment were described in a small number of animals at all doses.

No compound

- related adverse embryotoxic/fetotoxic effects in test animals compared to water controls were recorded for any fetal parameter. G ross external and/or visceral malformations were recorded in a few fetuses from different litters, equally distributed over the five dosage groups, while skeletal examinations revealed minor changes unremarkably similar in all groups (including controls).

Thus the maternal NOAEL in this rat study appears to be 0.5 mg/kg/day, and the maternal LOAEL for clinical toxicity 1.0 mg/kg/kg, while the developmental (fetal) NOAEL is 2.0 mg/kg/day, with the LOAEL greater than the HDT.

This study is classified as Acceptable/Guideline and satisfies the requirements for a develop

mental toxicity study [OECD 870.3700 (§83

- 3a)] in rats.

870.3700b Prenatal Developmental Toxicity Study

– Rabbit

In a developmental toxicity study (MRID 45390701), 28 presumed pregnant N ew Zealand white rabbits per group were administered dicrotophos (86.7% a.i.; Batch No.: 403001B, KB

- 80

- 9) aqueous solution by gavage at doses of 0, 0.5, 1.0, or 2.0 mg/kg/day on gestation days (GD) 5

- 29, inclusive. On GD 30, all surviving does were sacri ficed and the uteri were weighed and examined. All fetuses were examined for visceral anomalies by fresh dissection, sexed and

eviscerated. One

- half of the fetuses in each litter were fixed in 70% methylated spirits; after

24 hours, the heads were sectio ned along the fronto

- parietal suture line for examination of the brain. The remaining fetuses were decapitated and the bodies fixed in 70% methylated spirits and the heads fixed in Bouin’s solution for serial sectioning. All carcasses were then stained f or skeletal examination. Fetal defects were classified as major, minor, or variant. The degree of

ossification of the manus and pes were scored on a scale of 1 (good) to 6 (poor).

Two high

- dose animals were sacrificed in extremis on GD 29 due to sever ity of clinical signs of toxicity. One mid

- dose doe was sacrificed on GD 30 following signs of abortion. All remaining animals survived to terminal sacrifice. Clinical signs of toxicity in the high

- dose animals included shaking, increased breathing rate , wetness around the nose, mucus in the feces, and

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 80 of 97 diarrhea observed in 23

- 27 animals, and hunched posture, abnormal respiratory noise, salivation, subdued behavior, and staining in the genital area observed in 7

- 15 animals. In the mid

- dose group diarrhea and mucus in the feces were observed in 22 and 9 animals, respectively. No

treatment

- related clinical signs of toxicity were observed in the low

- dose group.

Covariant analyses based on GD 5 body weight, showed significantly (p  0.05) lower adjusted

mea n weights for the high

- dose group on GD 6, 29, and 30 as compared with the controls. The body weight gain in the high dose group was decreased (

- 27%) compared to the controls over the entire treatment period (GD 5

- 29). Contrary to this finding, the adju sted body weight was only slightly lower (4%) compared to controls. Therefore, the decreased maternal body weight gain in the high dose group possibly resulted from reduced fetal body weights. During the latter part of gestation, the high

- dose group gai ned less weight than the controls with weight gain 48% of

the control level for GD 20

- 30. Food consumption by the high

- dose group was significantly (68% of control; p  0.01) less than that of the controls for GD 26

- 30. Body weights, body weight changes, and food consumption in the low

- and mid

- dose groups were not affected by

treatment.

No treatment

- related lesions were observed in animals that were killed intercurrently. At scheduled necropsy, red or black spots on the glandular stomach were seen in 4, 4, 10, and

7 animals in the control, low

- , mid

- , and high

- dose groups, respectively. Other gross findings

occurred at a low incidence and were considered incidental to treatment.

Therefore, the maternal toxicity LOAEL for dicrotophos in rabbits is 1.0 mg/kg/day based on clinical signs of toxicity and the maternal toxicity NOAEL is 0.5 mg/kg/day.

All treated groups had slightly or significantly (p  0.05 or 0.01) greater numbers of implanta

tions/doe and live fetuses/doe, increased gravid uterine weight s, and decreased post

- implantation losses as compared with the control group. Mean fetal body weights were significantly (p  0.01)

decreased in the mid

- and high

- dose groups (8 and 10%, respectively) and were slightly less (4%) in the low

- dose group tha n that of the control group. When male and female fetuses were analyzed separately, significantly reduced body weights were found for the high

- dose males and females (p  0.01), the mid

- dose males (p  0.01), and the low

- dose males (p  0.05). The effects on fetal body weights in the low

- , mid

- and high

- dose groups are considered to be treatment

related.

The total number of fetuses (litters) examined in the control, low

- , mid

- , and high

- dose groups was 171(24), 224(25), 239(26), and 196(23), respectively. No treatment

- related external, visceral, or skeletal malformations/variations were observed in this study.

Therefore, the developmental toxicity LOAEL for dicrotophos in rabbits is 0.5 mg/kg/day based on decreased male and female fetal body weights. Th e developmental toxicity

NOAEL is not established.

This study is classified as Acceptable/Guideline and does satisfy the guideline requirements for a developmental toxicity study [OECD 870.3700 (§83

- 3b)] in rabbits.

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Page 81 of 97 A.4.3 Reproductive Toxicity

870.3800 Reproduction and Fertility Effects

- Rat

In a multi

- generation reproduction study (MRID 44296101), Dicrotophos (87.65% a.i.; Batch No. 403001 B) was administered to groups of 26 male and 26 female Alpk:AP f 

### SD rats (from the Rodent Breeding Unit, Alderley P ark) in the diet at concentrations of 0 0.5, 5.0, or 10/15/25 ppm for two generations. Two litters were produced in the first generation and one litter was produced in the second generation. Premating doses for the adult F 0 

### males were 0.5, 0.49, and

2.53 mg/kg/day and for the F 0 

### females were 0.5, 0.53, and 2.79 mg/kg/day, respectively. Premating doses for the adult F 1 

### males were 0.5, 0.56, and 1.15 mg/kg/dy and for the F 1 

### females were 0.6, 0.59, and 1.25 mg/kg/day, respectively. Due to a high mortality in the F 1a 

### pups in the 25 ppm group, the dietary concentration of dicrotophos was lowered to 10 ppm for four dams from lactation day 8 through termination of the litter. During mating, gestation, and lactation of

the F 1b 

### litters, high

- dose animals were gi ven diets containing 15 ppm. The control, low

- , and

mid

- dose F 1 

### pups were weaned onto the same diets as their parents. The F1 pups in the high dose group were weaned onto diets containing 10 ppm dicrotophos. Animals were given test or

control diet for 1 0 weeks then mated within the same dose group. All animals were exposed to test material either in the diet or during lactation until sacrifice. Clinical signs of toxicity were observed during premating weeks 2

- 5 as involuntary shaking of

the limbs in 5/2 6 F 0 

### males (p<0.05) and 11/16 F 0 

### females (p<0.01) given 25 ppm. No dose

- or

treatment

- related clincal signs of toxicity were observed inthe parental F 0 

### or F 1 

### animals given diets containing less than 25 ppm. No dose

- or treatment

- related gross abnormaliti es were observed in the F 0 

### or F 1 

### adults at necropsy; histopathological evaluations were not performed.

Mid and high

- dose F 0 

### males had significantly lower mean body weights as compared to controls (p<0.05 or 0.01). Food consumption was significantly (p< 0.01) reduced in the high

- dose F 0 

### males as compared with controls during premating. Food utilization was significantly (p<0.05 or 0.01) lower in the mid

- and high

- dose F 0 

### males as compared with the controls.

Mid and high

- dose F 0 

### females had significant ly lower mean body weights than the controls during premating (p<0.05 or 0.01). Food consumption by the high

- dose F 0 

### females was significantly (p<0.01) less at the beginning of premating, but was significantly (p<0.05 or 0.01) greater than the controls du ring latter premating. High

- dose F 0 

### females also had significantly (p<0.01) lower food utilization at the beginning of premating and then significantly (p<0.05) higher food utilization during latter premating weeks as compared with the controls.

Mean b ody weights of the mid

- and high

- dose F 1 

### males were significantly (p<0.01) lower than the controls during week 1 of the premating period. Food consumption by the F 1 

### males was similar between the treated and control groups throughout the premating period. Food utilization was significantly (p<0.05) reduced in the mid

- and high

- dose groups during early premating.

Mean body weights of all treated F 1 

### female groups were significantly (p<0.05 or 0.01) lower than the controls during week 1 of hte premating pe riod. No statistically significant differences in body weights occurred during the remainder of the premating period. In the high

- dose F 1 

### females, food consumption was significantly (p<0.05 or 0.01) greater than the controls during

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Page 82 of 97 most of the premating period and food utilization was significantly (p<0.05) greater during

weeks 8

- 10.

The Systemic Toxicity NOEL is 0.5 ppm and the Systemic Toxicity LOEL is 5.0 ppm based on lower body weights in the F 0 

### and F 1 

### males and females and reduced food utilizati on in

F 0 

### males and females and F 1 

### males.

High

- dose F0 females had significantly (p<0.05 or 0.01) lower body weights than the controls during gestation of litter A. No differences in body weights occurred between treated and control groups during gestatio n of litter B. During lactation of litter A, maternal body weights of

the mid

- and high

- dose animals were significantly (p<0.05 or 0.01) lower than the controls. During lactation of litter B, maternal body weights of the mid

- and high

- dose animals were

s ignificantly (p<0.05 or 0.01) lower than the controls. Food consumption by the treated F0 groups was greater than the controls during gestation of both the A and B litters with occasional statistical significance in the mid

- and high

- dose groups. In cont rast, food consumption by the high

- dose F0 females was significantly (p<0.05 or 0.01) less than the controls thoughout lactation of both litters (68

- 80%).

No treatment

- related differences in body weights were observed in the F1 females during gestation. However, all treated F1 groups had significantly (p<0.05 or 0.01) lower maternal body weights as compared with the controls during lactation. Food consumption was significantly (p<0.01) greater than the controls by the high

- dose F1 females throughout gest ation and once by the mid

- dose F1 females. In contrast, food consumption during lactation was occasionally significantly (p<0.05 or 0.01) less than the controls in all treated dams.

For the control, low

- , mid

- , and high

- dose F0 adults in production of li tter A, the proportion of successful matings was 70%, 67.9%, 85.7%, and 33.3% (p<0.01), respectively; the percent of live born pups was 97%, 99.2%, 98%, and 90.4% (p<0.05), respectively; and whole litter losses were 4/21, 0/19, 5/24, and 8/12 (p<0.05), res pectively. Whole litter losses during production of litter B were 4/22, 2/18, 6/23, and 10/19 (p<0.05), respectively. Whole litter losses by the F1 generation were 0/20, 1/23, 2/21, and 6/23 (p<0.05), for the control, low

- , mid

- , and high

- dose

groups, re spectively.

During lactation, no dose

- or treatment

- related clinical signs of toxicity or differences in pup body weights were observed in the offspring of either generation. For both litters produced by the F0 animals, there was a significant (p<0.05 or 0.01) decrease in the number of F1 pups/litter inthe high

- dose group after day 1 of lactation. Pup deaths in the high

- dose group resulted in significantly lower lactation indices of 56.6% (p<0.01) vs. 88.0% for the controls for litter A and 75.4% (p<0.05 ) vs 92.7% for the controls for litter B. The number of F2 pups/litter was significantly (p<0.01) decreased due to treatment in the mid

- and high

- dose groups as compared to controls after lactation day 1. Lactation indices for the control, low

- , mid

- , an d high

- dose F2 litters were 96.8%, 94.1%, 83.8% (p<0.05), and 75.6% (p<0.01), respectively.

The Reproductive Toxicity NOEL is 0.5 ppm and the Reproductive Toxicity LOEL is 5.0 ppm based on a reduced number of F2 pups/litter during lactation.

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 83 of 97 This study is classified as Acceptable/Guideline and satisfies the guideline requirement for a reproduction study (OPPTS 870.3800 §83

- 4) in rats.

A.4.4 Chronic Toxicity

870.4100a (870.4300) Chronic Toxicity

– Rat

See Carcinogenicity section below.

870.4100b Chronic Toxicity

- Dog In a chronic toxicity study (MRID 44328401), dicrotophos (87.65% w/w, Batch No. 403001 B) in corn oil was administered to 4 beagle dogs/sex/dose by capsule at doses of 0 (corn oil only), 0.025, 0.1, or 1.0/0.5 mg/kg/day f or 1 year (high

- dose dogs received 1.0 mg dicrotophos/kg/day for 13 weeks, after which they were not dosed for 7 days, and were then given 0.5 mg/kg/day

from week 15

- 52.

No animals died during the study. Treatment

- related clinical signs were seen primari ly at the high dose before it was lowered to 0.5 mg/kg/day, and were correlated with the inhibition of plasma and erythrocyte cholinesterase (ChE) activity. Signs included shaking and subdued behavior (2/4 or more dogs/sex during weeks 13

- 14 and in one fe male duing week 24); unsteady gait (one female at week 13) and a slight increase in the incidence/frequency of fluid feces, regurgitation, and vomiting (both sexes). High

- dose dogs also resisted dosing and males had reddening and peeling of the scrotal sk in with sores primarily during the first 14 study weeks.

Weekly body weights of high

- dose males were lower than those of controls (≤ 8.4%; p<0/05)
several times between weeks 5 and 14, and their week 1

- 14 body weight gain was 48% of

controls. After the high dose was lowered, the body weights improved and their overall weight gain was greater than of the controls. Weekly body weights of mid

- and high

- dose females were up to 10.3% lower than controls throughout the study (p<0.05 for weeks 6, 7 9, 14, 47, and 49

- 53 at one or both doses), and their overall weight gain and food efficiency were 74

- 78% of controls. There were no toxicologically significant differences from the controls for hematology, clinical chemistry, urinalysis, or ophthalmoscopic paramet ers, organ weights, or gross and microscopic pathology. No neoplastic lesions attributable to test article administration were reported.

Based on the 26% lower overall (week 1

- 52) body weight gain (and food efficiency) in mid

dose females, 0.1 mg/kg/da y is concluded to be the LOEL under the conditions of this study; the corresponding NOEL is 0.025 mg/kg/day. The reviewer disagrees with the study author that the body weight changes at the mid

- dose were not toxicologically significant and that only the h igh dose represents a LOEL for body weight changes.

Plasma, RBC, and brain ChE activities were inhibited by dicrotophos treatment thoughout most of the study in both sexes. The degree of inhibition was clearly dependent on the dose but not on the expos ure duration. At the high

- dose, the plasma, RBC, and brain ChE values were 36

- 64% of controls (p≤0.01) and neurologic impairment was clinically evident. At the mid

- dose, plasma ChE activity ws 55

- 61% of controls (p≤0.01) in both sexes, RBC ChE activity w as 83

- 91% of

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 84 of 97 controls (p≤0.05 or 0.01 for males only), and brain ChE was 81

- 88% of controls (p≤0.05 for females only). Although there were no visible neurological effects a the mid

- dose, because the parameter most germane to neurotoxicity, i.e. brain ChE, was statistically significantly inhibited in females (19%, p≤0.05), and plasma ChE was substantially inhibited in both sexes, the LOEL for ChE inhibition is considered to be 0.1 mg/kg/day, and the N OEL is 0.025 mg/kg/day. The reviewer disagrees with the study author that the high dose is the LOEL

for ChE inhibition.

This chronic oral toxicity study in dogs is classified as Acceptable/Guideline and satisfies the guideline requirement for a chronic oral toxicity study [OPPTS: 870.4100b (§83

- 1b )] in dogs.

A.4.5 Carcinogenicity

870.4200a Carcinogenicity Study

- Rat

In a chronic toxicity/carcinogenicity study (MRID 44527802 ), Dicrotophos (Lot No. 403004B, 878.65% (E isomer)) was administered to groups of 88 male and 88 female Alpk:Ap f 

### SD rats in

the diet at concentrations of 0, 0.5, 5, or 25 ppm (0, 0.02, 0.25, and 1.42 mg/kg/day for male rats and 0, 0.03, 0.32, and 1.74 mg/kg/day for females). Groups of 52 males and 52 females were designated for the main study and maintained on the treated food for up to 105 weeks. Groups of

12 males and 12 females were sacrificed at 52 weeks for interim evaluation at 52 weeks and study termination, respectively.

Survival was decreased to 26% in 25 ppm group males at week 97 (compared with 54% for controls) prompt ing termination of this group at this time; survival in the 5 ppm group males was only 19% at week 100 (compared with 49% for controls) prompting termination of the remaining groups at this time. Survival in females showed a dose

- related decrease at study termination (66, 46, 39, and 29% at 0, 0.5, 5, and 25 ppm, respectively). Numerous treatment

- related clinical signs related to respiration, gastrointestinal effects, urinary effects, and scabs and sores were observed in treated animals, particularly at 2 5 ppm in one or both sexes. Clinical signs indicative of cholinesterase inhibition were observed at 25 ppm in both sexes.

In 25 ppm group male rats, body weights were less than control weight up to week 90 of treatment. Females fed the 5 and 25 ppm di et gained 6

- 11% more weight than controls during the first year and 52

- 59% less weight than controls during the second year; overall weight gain was similar to that of control. Food consumption for both sexes fed the 25 ppm diet exceeded

that of controls by as much as 17

- 19% after 4 weeks of treatment. Food utilization (efficiency) calculated for the first 12 weeks of the study was decreased by 7% for 25 pm group males and was similar to that of controls for 25 ppm group females.

Treatment with 25 ppm caused a mild leukocytosis in both sexes characterized by significantly (p<0.01 or <0.05) elevated white blood cell counts (up to 142% of the control value in males and 179% in females). Statistically significant increases were noted for aspartate and alanine aminotransferase activities (up to 153 and 167%, respectively) in 25 pm group male and female

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 85 of 97 rats, but the increases could not be associated with microscopic lesions. Decreases in urine volumes for males during the first year ( 65

- 72% of control values) and for females throughout the study (56

- 76% of control values) were considered treatment related.

The only gross change considered treatment related were distended esophagus in male and female rats at 25 ppm and in female rats a t 5 ppm. This lesion was associated microscopically with luminal dilatation of the esophagus and aspiration pneumonia. The esophageal lesion occurred in 0/51, 1/51, 7/51 (p<0.01) and 12/52 (p<0.01) females and none of the males fed 0, 0.5, , or 25 ppm. Aspiration pneumonia occurred in 2/52, 4/52, 9/252 (p<0.01), and 21/52 (p<0.01) females, respectively, and 0/52, 0/52, 1/52, and 5/53 (p<0.05) males, respectively. In addition, alveolar macrophage infiltration (probably associated with aspiration of the t reated food) occurred in 2/52, 3/52, 1/52, and 12/53 (p<0.01) male rats, respectively; and atrophy/degeneration of the acinal epithelium in the Harderian gland occurred in 35/52, 30/52, 36/51, and 49/51 (p<0.01) female rats, respectively. Hepatitis occurr ed with statistically significant increased incidence in males at 25 ppm (12/52 vs 2/52 in controls, p p<0.01).

For chronic toxicity, the LOAEL is 5 ppm (0.25 mg/kg/day for males and 0.32 mg/kg/day for females), based on decreased survival in male rats, aspiration pneumonia and esophageal luminal dilatation in female rats. The NOAEL is 0.5 ppm (0.02 mg/kg/day for males and 0.03 mg/kg/day for females).

Cholinesterase activity was statistically significantly decreased at all dietary levels compared

with t he controls. At week 52 and study termination, respectively, brain cholinesterase activity in the 0.5 ppm group animals was inhibited by 19 and 12% for males and 23 and 18% for females, erythrocyte cholinesterase activity by 27 and 25% for males and 19 an d 39% for females and plasma cholinesterase activity by 27 and 25% for males and 19 and 39% for females. Only the plasma activity determined at study termination in 0.5 ppm group males was not statistically significant.

The LOAEL for cholinesterase inhib ition was 0.5 ppm (0.02 mg/kg/day for males and 0.03 mg/kg/day for females); a NOAEL was not established.

No evidence of carcinogenicity was observed in rats fed dicrotophos at dietary concentrations of 0.5, 5, or 25 ppm for 97

- 100 weeks for males and 105 weeks for females.

The chronic toxicity/carcinogenicity study in the rat is A cceptable/ G uideline and satisfies the guideline requirements for a chronic toxicity /carcinogenicity oral study (OPPTS 870.4200a ; §

83

- 1; ) in rats. A deficiency in male rats was the low survival at study termination; however, adequate numbers of animals were alive at 18 months to evaluate late

- developing lesions.

870.4200b Carcinogenicity (feeding)

- Mouse In an oncogenicity study (MRID 44527801), Dicrotophos (87.65% a.i., Bat ch No. 403001 B) was administered to groups of 55 male and 55 female C57BL/10J f 

### CD

- 1® Alpk mice in the diet at concentration of 0, 2, 10, or 50 ppm for up to 2 years. These concentrations resulted in a

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 86 of 97 nominal compound intake for each concentration level o f 0.22, 1.12, and 6.42 mg/kg/day for males; 0.31, 1.58, and 9.06 mg/kg/day for females for low

- , mid

- , and high

- dose, respectively.

Treatment with 50 ppm Dicrotophos resulted in a rapid decrease in survival in females after treatment week 86. High

- dose f emales were terminated at week 101 when their survival reached 25%. Survival of females at 10 ppm also rapidly decreased after about week 100 and was 38% at scheduled termination during week 104; 55% of control females survived. There was no

treatment

- rel ated effect on survival in males. Clinical signs observed during treatment only at 50 ppm included involuntary shaking of the limbs (males, 25%; females, 40%) seen from weeks 2 to 4, and rigidity and convulsions during handling (males, 13%; females, 29%) seen from week 39 to 40. Increased numbers of observations of opaque eyes were noted at the high dose in both sexes compared to the control groups. Ophthalmoscopic examinations during week 92 showed corneal opacities in all groups with a slight increase at the high dose in both sexes (males: control, 7%; 50 ppm, 14%, NS; females: control, 26%; 50 ppm, 40%, NS). The incidence of opaque eyes was also slightly increased in high

- dose mice during gross necropsy (males: control, 4%; 50 ppm 9%, NS; females: con trol, 18%; 50 ppm, 33%, p<0.05). Body weights of both sexes of mice at 50 ppm were generally up to about 12% lower than that of the controls for the first 12 weeks of the study but were the same or slightly greater than the controls during the second year of the study. Overall weight gains were comparable to the controls. The overall food efficiency values for the first 12 weeks in males at 50 ppm were about 20% (p<0.01) lower than the control values. Decreased food efficiency was not seen in treated fe males.

Increases in the incidence and severity of kidney tubular vacuolation were seen upon microscopic examination in males at 50 ppm compared to the controls (total incidence: control, 42%; 50 ppm 71%, p<0.01; lesions graded slight or moderate: control, 4%; 50 ppm, 22%, p<0.01). Kidney tubular vacuolation was seen in only 1 female.

The LOAEL is 50 ppm (6.42 mg/kg/day) for males based on neurological signs, kidney toxicity and thyroid follicular cell adenomas. For females, the LOAEL is 10 mg/kg /day (1.58 mg/kg/day) based on decreased survival rate. The NOAEL was 10 ppm (1.12 mg/kg/day) for males; and 2 ppm (0.31 mg/kg/day) for females.

Treatment for up to 105 weeks with Dicrotophos resulted in a significant increase in the incidence of thyroid follicular cell adenomas in male mice at 50 ppm (control, 0%, 50 ppm 10%, p<0.01, Cochran

- Armitage, p<0.05, Fishers exact test). Male mice had s ignificant increasing trend at p<0.01, and a significant difference in the pair

- wise comparison of the 50 ppm dose groups with the controls at p<0.05, for thyroid follicular cell adenomas. The incidence of thyroid

adenomas was not increased in females.

The CARC concluded that under the Draft Cancer Risk Assessment Guidelines (July 2, 1999), there is "Suggestive evidence of carcinogenicity, but not sufficient to assess human carcinogenic potential". The evidence from animal data is suggestive of carcino genicity, which raises a concern for carcinogenic effects, but is judged not sufficient for a conclusion as to human carcinogenic potential.

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 87 of 97 The study is classified as A cceptable/ G uideline and satisfies the guideline requirements for a carcinogenicity tox icity study in mice (OPPTS 870.4200 ; §83

- 5 ).

A.4.6 Mutagenicity

Mutagenicity Studies with Dicrotophos

Gene Mutation

870.5100

Salmonella/Escherichia

bacterial reverse mutation assay 43603301(1994) and 5000.0 μg/plate in the presence and absence of

mammalian metabolic activation (S9

- mix) Strains TA98, TA100, TA1535, TA1537, and TA 1538 of S. typhimurium were exposed to dicrotophos in vehicle from

con cen trations of 6.7 to 5000.0 μg/plate in the presence and

absence of mammalian metabolic activatio n (S9

- mix). There

was no evidence of induced mutant colonies over background.

Acceptable/Guideline

Gene Mutation

870.5300 mammalian cell gene mutation assay in

cultures of mouse lymphoma (L5178Y)

cells 43591401 (1995) concentrations of 0, 100,
500, 750, 1000, 2000, or 3000 μg/mL in the presence and absence of

mammalian metabolic activation (S9

- mix). Dose

- dependent and reproducible gene mutation was recorded in both the presence and absence of S9 activation at

non

- toxic doses of 750 μg/ml up to the c ytotoxic HDTs,

2000

- 3000 μg/ml.

Acceptable/Guideline

Cytogenetics 870.5395 Micronucleus assay in

mouse bone marrow

cells 43603302 (1994) Doses of 1.7, 3.3, and

6.6 mg/kg body weight Mice were administered single doses of Dicrotophos by i.p. injection, and bone marrow sampled for the presence of micronuclei in polychromatic erythrocyte. No increased incidences of micronuclei were found at doses up to a severely toxic level (6.6 mg/kg). Acceptable/Guideline



### A.4.7 Neurotoxicity

870.6100b Delayed Neurotoxicity Study

– Hen

In a delayed neurotoxicity range

- finding study (MRID 44943901), groups of 5 domestic hens were administered 0, 3, 5, 7, 9, 11, 15, or 20 mg/kg of dicrotophos (87.2% purity; Lot no. 8070030051) by gavage and observed for 7 days. The LD50 was 11 mg/kg with confidence limits of 9 and 15 mg/kg. As part of this study, the efficacy of atropine and 2

- pyridine aldoxime methiodide (2

- PAM) in preventing mortality was tested. In a 21

- day delayed neurotoxicity study (MRID 45170201), a group of 20 domestic hens was a dministered a single oral dose of 11 mg/kg of dicrotophos on day 0. Atropine and 2

- PAM were administered to prevent mortalities. An additional group of 12 birds was given 600 mg TOCP/kg as the positive control and a group of 12 hens served as the negati ve control. Toxicity assessments included clinical observations, assessment of ataxia, body weight and food consumption measurements, acetylcholinesterase

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 88 of 97 and neurotoxic esterase activities, and microscopic evaluation of the brain, spinal cord, and periph eral nerves.

In the 21

- day study, there were no mortalities, but dicrotophos

- treated hens showed clinical signs of toxicity beginning on day 1 and continuing in one hen through day 7. These signs included reduced reaction to external stimuli, wing droop, loss of coordination, lower limb weakness, and gaping. All hens in the negative and positive control groups appeared normal. Body weights and food consumption were reduced compared with the negative control group; body weights bur not food consumption w ere reduced in the positive control group. Differences were not significant in either group by day 21. Hens in the dicrotophos

- treated group showed slight ataxia up to day 13, whereas positive control birds showed slight ataxia on days 9

- 20. The early

c linical signs and slight ataxia which abated with time in the dicrotophos group are not considered a sign of delayed neurotoxicity. AChE was depressed by 84% (p<0.01) in the brain of the dicrotophos

- treated group, but NTE was non

- significantly reduced in the brain and spinal cord (8 and 25%, respectively). AChE activity in the brain and NTE activities in the brain and spinal cord were significantly reduced in the TOCP

- treated group (AChE by 21% and NTE in brain and spinal cord by 91% and 86%, respectively ). Neurohistopathological lesions indicative of delayed neuropathy were not observed in hens in any group. The single dose of 11 mg/kg was sufficiently high as mortalities occur at this dose without treatment with anticholinergics.

Therefore, under the conditions of this study, oral administration of Dicrotophos at 11 mg/kg does not produce delayed neuropathy in the hen.

870.6200a Acute Neurotoxicity Screening Battery

– Rat

In an acute neurotoxicity study (MRID 43759801) dicrotophos (87.65% ai) was a dministered by gavage to 10/sex/group to Sprague

- Dawley CD rats (20/sex/group) at dose levels of 0, 0.5, 5 or 10 mg/kg (in water, 10 ml/kg). The rats were evaluated for reactions in functional observations and motor activity measurements (3 hours, and 8 a nd 15 days postdosing). Two satellite groups (5/sex/group) were also included for the purpose of measuring plasma ChE and erythrocyte and brain AChE on days 1 and 8.

At 0.5 mg/kg, dicrotophos inhibited brain (21% in females and 22% in males) and eryth rocyte AChE (16% in females and 19% in males) and plasma ChE (46% in females and 38% in males) on day 1 (all depressions were statistically significant). Brain AChE and plasma ChE reached about 90% inhibition at 10 mg/kg. RBC AchE never exceeded 50% inhi bition. Brain AChE remained inhibited (7%

- 14%) for males at all doses by day 15. The NOEL and LOEL for ChE/AChE inhibition is < 0.5 mg/kg. At 5 mg/kg and above, dicrotophos produced clinical signs (prinicipally decreased activity, upward curvature of sp ine, pinched in sides, flaccid appearance and decreased pupil response in most or all animals and several other signs in some animals. Overall some 25 in males and 24 in females FOB parameters were reported affected by treatment in the 5 and/or 10 mg/kg d ose levels of dicrotophos. Motor activity was decreased. At 10 mg dicrotophos/kg produced deaths (7 females and 1 male) within 3 hours after dosing. Most

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 89 of 97 signs regressed after one day but some persisted for 3 or 4 days. The LOEL for neurotoxicity is

5 mg/kg based on clinical signs. The NOEL is 0.5 mg/kg.

This acute neurotoxicity study is classified Acceptable/Guideline and satisfies the guideline requirement for an acute neurotoxicity study [OPPTS 870.6200a (§ 81

- 8) ] in rats.

870.6200b Subchronic N eurotoxicity Screening Battery

– Rat In a subchronic oral neurotoxicity feeding study (MRID 43980201), 12 Alpk:APfSD rats/sex/group were fed diets containing 0, 0.5, 5, or 25 ppm dicrotophos (87.65% w/w, Batch No. 403001B) for 13 weeks. Two satellite grou ps, each with 6 Alpk:APfSD rats/sex/dose, were similarly treated and included for the purpose of measuring cholinesterase activity (ChE) at week 5 (Group A) and week 9 (Group B). The average consumption of test material in the 0, 0.5, 5, and 25 ppm dose g roups for males was 0, 0.04, 0.39, and 2.03 mg/kg/day and for females was 0, 0.04, 0.45, and 2.38 mg/kg/day.

There was no treatment

- related effect on mortality. Effects on body weights were minimal: weights were statistically significantly lower than co ntrols at the high dose (≤ 10.4%, p ≤ 0.05 or 0.01) during weeks 2

- 6 in males and 2

- 4 in females, and were correlated with decreased food consumption during weeks 1 and 2 (and decreased food efficiency in males). No notable changes were seen in behavior o r appearance upon clinical examination. Treatment

- related effects on motor activity were seen only at 25 ppm in both sexes: forelimb grip strength was decreased at weeks 9 and 14 in females (13

- 14%, p ≤ 0.05 or 0.01) and at week 5 in mals (14%, p≤ 0.05). Hindlimb grip strength was decreased only in females at week 9 (16%, p ≤ 0.05). The mean overall motor activity was decreased at week 9 in males (34%, respectively; p ≤ 0.01) and at weeks 9 and 14 in females (23 and 33%, respectively; p ≤ 0.05; p ≤ 0.01) . The neurotoxic effects, as well as the statistically significant increase in brain weight in 25 ppm males (≤ 5.2%), had no histopathological correlates. Based on the motor activity alterations and marginal body weight decreases in both sexes of rats, 25 ppm is identified as the LOEL and 5 ppm is the NOEL for systemic toxicity/neurotoxicity. Brain, plasma, and erythrocyte ChE activities were inhibited by dicrotophos treatment in all groups of rats, most markedly in the brain: 11

- 20% at 0.5ppm, 56

- 63% at 500m, and 87

- 90% at 25 ppm (p ≤ 0.01). ChE was inhibited slightly more in females. Based on the dose

- related inhibition in brain, plasma, and erythrocyte ChE activity, 0.5 ppm is the LOEL for ChE inhibition; a NOEL cannot be assigned because 0.5 ppm was the lowest dose tested.

This study is classified as Acceptable/Guideline, satisfying the guideline requirement for a subchronic oral neurotoxicity feeding study [OPPTS 870.6200b (§ 82

- 7) ] in the rat.

870.6300 Developmental Neurotoxicity

– Rat

In a developmental neurotoxicity study (MRID 46153202), dicrotophos (87.6% a.i., batch # 403001B) was administered by gavage to 30 parent female Alpk:AP f 

### SD Wistar

- derived rats/dose by gavage at dose levels of 0, 0.01, 0.05 or 0.4 mg/kg/day from gestation day ( GD) 7 through parturition to lactation day 7. Selected pups were dosed by gavage with 0, 0.01, 0.05 or 0.4

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 90 of 97 mg/kg/day from post natal days (PNDs) 8 to 22; pups were weaned on day 29 and the study was

terminated on PND 63. Doses were selected on the basis of a range

- finding study (MRID 46153201). A Functional Operational Battery (FOB) was performed on 30 dams/dose on GDs 10 and 17, and lactation days 2 and 9. On PND 5, litters were culled to yield four males and four females (as closely as possible). Off spring selected for F 1 

### generation were allocated (one/sex/litter) FOB, assessment of motor activity, assessment of auditory startle response habituation, assessment of learning and memory, and neuropathology at study termination (day 63 of age). On days 12 and 63, the whole brain was collected from 10 pups/sex from control and high dose groups for micropathologic examination and morphometric analysis. Pup physical development was assessed by body weight, and sexual maturation of females was assessed by age at vaginal opening. Maturation of males was assessed by age at completion of preputial separation. Cholinesterase activity, either in the dams or the offspring, was not measured in this study.

In dams during gestation and la ctation, no treatment

- related effects on mortality, clinical signs, body weight, body weight gain, food consumption, FOB, or reproductive parameters were noted. The maternal systemic NOAEL is  0.4 mg/kg/day, the highest dose tested. The maternal

LOAEL is not identified.

In offspring, there were no treatment

- related deaths or clinical signs or effects on birth weight, body weight or body weight gain pre

- or post

- weaning, clinical observations, developmental landmarks, FOB parameters, motor or locomotor ac tivity, auditory startle response, or learning and memory tests. At necropsy, no treatment

- related gross lesions or changes in absolute weight were seen.

The brain morphometric analyses revealed statistically significant decreases (9

- 14%  ) in cortex

m easurements in males at PND 12 and the overall width of the thalamus/cortex (5%  ) in males at PND 63. In females, measurements of the hippocampus at various levels are significantly
increased (7

- 10%  ) at PND 12 and the hippocampus length and thalamus wid th are decreased
(4

- 11%  ) at PND 63. These changes are considered related to treatment. Because of the changes seen at the high dose, morphometric data for all tissues (cortex, hippocampus, and thalamus) for the low and mid dose groups should be evaluat ed.

T he offspring systemic LOAEL is 0.4 mg/kg/day based on morphometric changes in the

brain of male and fem ale offspring on PND 12. The NOAEL is not established.

This study is classified Acceptable/Non g uideline and may be used for regulatory purposes . It does not, however, satisfy the guideline requirement for a developmental neurotoxicity study in rats (OPPTS 870.6300, §83

- 6); OECD 426 (draft) due to the lack of brain morphometric data at the low and mid dose groups and pending review of the positive control data.

A.4.8 Metabolism

870.7485 Metabolism

– Rat

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 91 of 97 In a 96

- hour rat metabolism study (MRID 43942001), [3

- 14 

### C]dicrotophos (98.9% ai) was administered to male and female CD rats (5 or 7 animals/sex/dose) by gavage as a single dose at

levels of 0.5 or 3 mg/kg, or as a single dose at 0.5 mg/kg following a 14

- day pretreatment with unlabeled dicrotophos at 0.5 mg/kg/day. Five additional rats/sex received a single 0.5 mg/kg

intravenous dose in a 96

- hour study.

[ 14 

### C]Dicrotophos was rapidly absorbed by male and female rats following oral and intravenous dosing. The orally and intravenously administered radioactivity was quantitatively recovered from each dosing regimen; total recovery was 97

- 99% of the dose. There was no difference in the relative pat tern of excretion between male and female rats and no appreciable difference among dose levels or routes. Greater than 80% of the radioactivity was recovered in urine during the first 24 hours from all dose groups, and after 96 hours 83

- 88% was excreted i n urine and feces. Volatile radioactive products accounted for 5

- 7% of the radioactivity. Only 1.1

- 2.6% of the dose was in the tissues/carcass. Liver had the highest percentage of the dose at 0.07

- 0.09%. The concentration of radioactivity was highest i n fat: 0.014

- 0.018 ppm for single oral and intravenous low doses, 0.023

- 0.033 ppm for the oral repeated low dose, and 0.106

- 0.124 ppm for the single oral high dose.

Dicrotophos metabolites were investigated in Day

- 1 urine. The results indicated that d icrotophos is extensively metabolized via N

- demethylation and oxidation of the N

- methyl moiety yielding intact organophosphate products, which may be dealkylated. Metabolism may also proceed via demethylation and dealkylation of the phosphate moiety formi ng various acetoacetamide and acetobutamide products. Twenty

- one metabolic components were identified, including parent, 19 Phase 1 metabolites, and one conjugate. Characterized metabolites exceeded 83% of the

dose. Un

- metabolized dicrotophos accounted for 3

- 7% of the doses. Hydroxydicrotophos accounted for up to 20% of the dose and monocrotophos accounted for up to 3%. Other intact organophosphates, numerous acetoacetamide and acetobutamide products, and one conjugate, N

acetylmonocrotophos were ident ified, but were not separately quantified.

This metabolism study in the rat is classified A cceptable /Guideline and satisfies the guideline requirement for a metabolism study [OPPTS 870.7485 ( § 85

- 1) ] in the rat. The nature of the metabolic products of dicrotophos in rats has been well characterized. However, numerous metabolites were identified in urine but not separately quantified, including several intact

or g anophosphates. In the event that a pa rticular class of components is deemed toxicologically significant, e.g., organophosphates, additional data to quantify these components may be required.

A.4.9 Immunotoxicity

870.7800 Immunotoxicity

In an immunotoxicity study (MRID # 48404101 ), Dicrotophos Technical (88.9%, batch #

GB1013 09

- 01 ) was administered to male HsdHanTM:WIST rats (10 /dose ) in diet at dose levels of 0, 5, 15, or 25 ppm (0, 0.37, 1.14, or 1.91 mg/kg bw/day , respectively ) for 28 days. Additionally, eight male rats received c yclophosphamide ( positive control) at 50 mg/kg

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 92 of 97 administered by i.p injection on Day 27. All ani mals (Group 1 to 5) were immuniz ed by intravenous injection of sheep red blood cells (SRBC 2 x 10 8 

### /mL, 1.0 mL/animal) on Day 25. A ll

a nimals were sacrificed by carbon dioxide asphyxiation on Day 29

. The following parameters

were measured and recorded: clinical observations, body weight and bodyweight gain, f ood

, water and compound consumption s , blood and brain cholinesterase activity , macroscopic pathology, o rga n weights

, and T

- cell dependent antibody response (TDAR) by plaque forming cell (PFC) assay.

All animals survived the treatment period. There were no treatment

- related clinical signs or compound toxicity. Body weights of males receiving 5 or 15 ppm were unaffected by treatment. A lower than control bodyweight gain (p<0.05) was observed in males receiving 25 ppm. Food and water consumptions

, gross pathological examination, thymus and brain weights, were not affected by treatment.

Erythrocyte and brain ace tylcholinesterase activity were reduced markedly, compared with the controls, at all dietary concen trations (p<0.01). The percentage reduction for brain acetylcholinesterase activity was 58, 81 and 86% at 5, 15 and 25 ppm, respectively. For erythrocytic ac etylcholinesterase activity the percentage reduction was 66, 83 and 86% at 5, 15 and 25 ppm, respectively

.

The cholinesterase inhibition LOAEL was 5 ppm (0.37 mg/kg/day) based on statistically significant depression in both erythrocytes and brain choline sterase activity; the NOAEL is

not established. The systemic toxicity LOAEL was 25 ppm (1.91 mg/kg/day) based on statistically significant decrease in body weight gains; the NOAEL is 15 ppm (1.14 mg/kg/day)

.

T here were sta tistically significant increases of spleen cellularity and total activity (PFC/spleen) at 25 ppm when compa red to the vehicle control . There was also a slight increase in specific activity ( PFC/10 6 

### viable cells ) but did not attained statistical significance . There were no statistically si gnificant changes at 5 or 15 ppm. There was a high inter

- individual variability noted in all the treatment groups as well as in the control group. Evaluation of individual animal data of this study did not show any trend or distribution that would demonst rate significant suppression of anti

- SRBC PFC response to sheep red blood cells (SRBC). Animals in positive control group, show ed a significant decrease of PFC response to a challenge with SRBCs

. This confirmed the ability of the test system to detect imm unosuppressive effects and confirmed the validity of the study design.

The Natural Killer (NK) cells activity was not evaluated in this study. The toxicology database

for dicrotophos does not reveal any evidence of treatment

- related effects on the immune system. The overall weight of evidence suggests that this chemical does not directly target the immune system. Under HED guidance, a NK cells activity assay is not required at this time.

Under conditions of this study, t he NOAEL for immunotoxicity is 25 ppm (1.91 mg/kg/day); the LOAEL wa s not established (>25 ppm).

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 93 of 97 This study is classified Acceptable/G uideline

, and satisfies the guideline requirement for an immunotoxicity study (OPPTS 870.7800) in rats

.

Special Studies

Comparative Cholinesterase Studies

A series of studies was performed to investigate the effect of dicrotophos on blood and brain cholinesterse (ChE) activity and to determine the peak time of ChE inhibition (ChEI) following both acute and repeated dosing in pre

- weaning, young, and older adult Alpk:AP f 

### SD rats. No plasma ChE activity was measured. The studies were conducted as follows:

 In a time

- course study (MRID 46153205), a single oral dose of 0 or 5 mg dicrotophos (86.9% a.i., Lot #403001B)/kg was administered by gavage to 1 5

- day

- or 42

- day

- old female rats (25/group).

 In acute exposure studies, single oral doses of dicrotophos (90.4% a.i., Lot # 403001B) were administered by gavage at doses of 0.0, 0.1, 0.3, 1.0 or 5.0 mg/kg to 5 male and 5 female

pre

- weaning rats of 8 , 15 and 22 days of age (MRID 46153205), and single oral doses of dicrotophos (87.6% a.i., Lot # 403001B) of 0.0, 0.1, 0.3, or 5.0 mg/kg were administered by gavage to groups of 15 young adult male and female rats (MRID 46153206).

 In repeat exposure stud ies, dicrotophos (90.4% a.i., Lot # 403001B ) 

### was administered by gavage at 0, 0.008, 0.02, 0.08, 0.4 or 1.0 mg/kg/day to pre

- weaning and young adult rats (5/sex) at 12 or 42 days age, respecti vely, for 7 days (MRID 4615320 4). In another study, 5

male and 5 female adult rats received test compound (87.6% a.i., Lot # 403001B) by gavage at 0, 0.008, 0.02, or 0.4 mg/kg/day for 4 weeks (MRID 46153208). For a bridging study (MRID 46153207), adult rats (10/sex) received daily gavage doses of 0.0 or 0.4 mg

dicr otophos (87.6% a.i, Lot # 403001B)/kg/day for 4 or 8 weeks.

Treatment

- related mortality was observed among pups receiving a single oral dose of 5 mg/kg (one of five males in the definitive study and three of 25 females in the time

- course study). At a

do se of 5 mg/kg, there was inhibition of RBC and brain ChE activity in pups and adults which correlated with clinical observations of tremors (all PND 8, 15, and 22 pups and 14/15 adult males and 15/15 adult females), splayed gait, shaking, and fast/irregula r breathing. Clinical signs of ChE activity inhibition were first seen in pups and young adult rats within approximately 30 minutes after dosing. In the pups the clinical effects were seen over a longer period than those in adults. No sex

- related differ ences were evident. The peak time of effect was reached by three hours in pups and one hour in adults. At the dose of 5 mg/kg, pups had greater ChE activity inhibition than adults in both compartments. In pups, dose

- dependent RBC and brain ChE activity inhibition was observed at single oral doses of  0.1 mg/kg (lowest dose
tested), while in adult rats dose

- dependent ChE activity inhibition was observed at doses of  0.3 mg/kg. Single doses of 0.1 mg/kg caused no significant effects in adult rats.

No mor tality or clinical signs were observed in repeat

- dose studies. There were no treatment

related effects on body or brain weight. Repeat oral administration for 7 days at 0.08 to PND 18

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 94 of 97 pups inhibited brain ChE activity by 15% (both sexes; NS) and RBC acti vity by 19 and 25% in male and female pups, respectively (both p<0.01). Young adults were affected at 0.4 mg/kg/day (brain: 23 and 36% ChEI in males and females, respectively; RBC: 47 and 38% ChEI in males and females, respectively). Inhibition was dose

- related. Repeated 7

- day exposure to  0.02 mg/kg/day or 0.08 mg/kg/day caused no significant ChE activity inhibition in pre

- weaning and adult rats, respectively. A daily dose of 0.4 mg/kg/day for 4 weeks to adult rats caused inhibition of ChE activity in both compartments which returned to al most normal after a 4

- week recovery period. No sex related differences were seen. Following repeat dosing at 0.4 mg/kg/day for 4 or 8 weeks, maximum inhibition was achieved within four weeks in adults (brain, 33

- 35%; RBC,

48

- 49%). Pre

- weaning rats were not tested in this study.

Overall, the results of all six studies together provide consistent evidence of greater sensitivity in young animals with respect to ChEI following acute and repeated dicrotophos exposure. This finding is further supported by the results of an earlier dev elopmental neurotoxicity study in rats (MRID 46153202) in which clinical signs and neuropathology were observed in pups at 0.4 mg dicrotophos/kg/day while no toxicity was evident in maternal animals indicating greater sensitivity of pups to dicrotophos tre atment.

For acute exposure :

the adult LOAEL for brain ChEI is 5 mg/kg (males), 0.3 mg/kg (females) the adult NOAEL for brain ChEI is 0.3 mg/kg (males), 0.1 mg/kg (females);

the PND 8, 15, and 22 LOAEL for brain ChEI is 0.1 mg/kg (both sexes) the PND 8, 15, and 22 NOAEL for brain ChEI is not determined (<0.1 mg/kg; both sexes);

the adult LOAEL for RBC ChEI is 0.3 mg/kg (both sexes) the adult NOAEL for RBC ChEI is 0.1 mg/kg (both sexes);

the PND 8, 15, and 22 LOAEL for RBC ChEI is 0.1 mg/kg (both sexes) the PND 8, 15, and 22 NOAEL for RBC ChEI is not determined (<0.1 mg/kg; both sexes).

For acute oral exposure to dicrotophos, the overall adult LOAEL for cholinesterase inhibition in rats is 0.3 mg/kg based on enzyme inhibition in brain and RBC; the adult NOAEL is 0.1 mg/kg.

For acute oral exposure to dicrotophos, the overall offspring LOAEL for cholinesterase inhibition in rats is 0.1 mg/kg based on enzyme inhibition in brain and RBC; the offspring NOAEL is not determined (<0.1 mg/kg).

For repeated expo sure :

the adult LOAEL for brain ChEI is 0.4 mg/kg/day (both sexes) the adult NOAEL for brain ChEI is 0.08 mg/kg (both sexes);

the offspring LOAEL for brain ChEI is 0.08 mg/kg/day (both sexes)

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 95 of 97 the offspring NOAEL for brain ChEI is 0.02 mg/kg/day (both sexes);

the adult LOAEL for RBC ChEI is 0.4 mg/kg/day (both sexes) the adult NOAEL for RBC ChEI is 0.08 mg/kg (both sexes);

the offspring LOAEL for RBC ChEI is 0.08 mg/kg/day (both sexes) the offspring NOAEL for RBC ChEI is 0.02 mg/kg/day (both sexes).

For repeated oral exposure to dicrotophos, the overall adult LOAEL for cholinesterase inhibition is 0.4 mg/kg/day based on brain and red blood cell; the NOAEL is

0.08 mg/kg/day.

For repeat oral exposure to dicrotophos, the overall offspring LOAEL is 0.08 mg/kg/day based on brain and RBC; the NOAEL is 0.02 mg/kg/day.

The cholinesterase activity measurements following acute and repeat oral doses of dicrotophos demonstrate greater susceptibility in juveniles than in adult rats. This susceptibility was

obs erved in terms of the dose level at which an effect was observed (i.e., the LOAEL for cholinesterase inhibition was lower for juveniles than for adults in both the acute and repeat

- dose studies). Although LOAELs were based on both RBC and brain ChEI, brai n ChEI was generally greater than RBC ChEI for both age groups in the acute study. This difference in RBC and brain

ChEI inhibition was not demonstrated in the 7

- day repeat dose study. The relative susceptibility

of dams and GD 20 fetuses was not address ed in this series of studies.

Taken together, these studies are classified as Acceptable/Nonguideline for the determination of RBC brain cholinesterase activities following treatment with dicrotophos in young adult and juvenile (pre

- weaning) rats. Main d eficiencies are omission of plasma ChE measurements and

lack of assessment in dams and fetuses

.

In Vitro Dermal Penetration

In an in vitro dermal absorption study (MRID 45099502), groups of six rat and six human epidermal samples were exposed to 1258, 417, 42.6, or 9.66 μg/cm 2 

### of aqueous 14 

### C

- dicro tophos per concentration and the amount of absorption determined at 0.5, 1, 2, 4, 10, and 24 h ours after application. At each time point, the amount of radioactivity present within six human and six rat epidermal chambers, collection fluid, carbon filters, epidermal samples, and receptor fluids was

determined.

The study results show that the rat epidermis was more permeable to dicrotophos than human epidermis, the absorption rate ranging from 4.8 times at the low dose to ~68 times faster at the high dose over a 24

- hour period. Likewise, the amount of radiolabeled dicrotophos crossing the rat epid ermal layer into the receptor fluid was 4

- 72 times greater than the human epidermis. The amount of dicrotophos absorbed by rat or human epidermis was related to the concentration applied, however absorption appeared to be saturated at the higher doses by both human and rat epidermal preparations. Rat epidermis absorbed an average of 272 μg/cm 2 

### and 230 μg/cm 2 

### of the concentrate and 1:10 dilution, respectively, suggesting saturated absorption. However, at a

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 96 of 97 1:1000 dilution, the amount absorbed by rat epide rmis was 24.6 μg/cm 2 

### , indicating absorption was proceeding at a submaximal rate. The maximal absorption rate of human epidermis was

consi derably less than rat epidermis and the data suggests that absorption was saturated at the three highest concentratio ns. At the concentrate, 1:10, and 1:100 dilutions, the absorption rate of human epidermis ranged from 3.8

- 5.9 μg/cm 2 

### of the amount applied over a 24

- hour period. The absorption rate of the 1:1000 dilution of dicrotophos was 1.0 μg/cm 2 

### , indicating that ab sorption

was not saturated.

Although there are differences in the in vitro absorption behavior of dicrotrophos from rat and human epidermis, no conclusions can be made from these results to the in vivo absorption of this

chemical. The in vitro results in the rat show higher absorption rates than those obtained from a companion in vivo study at similar applications (MRID 45099501, reviewed in a separate DER) where the maximum absorption was 35% of the applied dose at a 1/100 dilution application of

dicroto phos (contrast to 58% in vitro absorption at the same application rate) over 24 hour exposure and 26% of the applied dose absorption in vivo compared to 47% in vitro absorption over 10 hour exposure. The process of skin absorption in vitro is likely a pas sive process where

as in vivo absorption, it is an active process involving absorption, distribution (blood),

metabolism and excretion. Thus based on results of this in vitro study, no determination of the in

vivo dermal absorption of dicrotrophos in humans can be made.

In summary, the in vitro study results show that rat epidermis is more permeable than human epidermis. This in vitro dermal absorption study is Acceptable/Nonguideline for the deter

mination of ab sorption by rat and human epidermal skin.

### Dicrotophos Human Health Risk Assessment DP No. D428506

Page 97 of 97 Appendix C. Physical/Chemical Properties

Table C1. Physico

- Chemical Properties

Parameter Value Reference

Molecular Weight 237.19

pH

Water solubility (20°C) 11,990 43603202, 43603201

Solvent solubility (20°C to 25°C) miscible (mixable in all proportions) with water, acetone, alcohol, acetonitrile, chloroform, methylene chloride, and xylene

Vapor pressure (25°C) 7 x 10

- 5 43500401

Dissociation constant, pKa
Octanol/water partition coefficient, log K OW (25°C) 2.445 (E

- isomer) and 0.000481 (Z

- isomer)

Soil Half

- life (days) 8.1 (parent) 160826