UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

Date: July 10,2014 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

Subject: Dicrotophos. Occupational and Residential Exposure Assessment for the 

Registration Review Risk Assessment 

PC Code: 035201 

Decision No.: 454409 

Petition No.: NA 

Risk Assessment Type: Occupational/Residential Exposure Assessment 

TXRNo.:NA 

MRIDNo.: 44731001 

DP Barcode: 0418109 

Registration No.: NA 

Regulatory Action: Reg Review 

Case No.: 0145 

CAS No.: 141-66-2 

40 CFR: §180.299 

From: Shalu Shelat, Industrial Hygienist ' .J t.. ~ ---;; > 

Risk Assessment Branch VI 

And / / _____/ /L_ ~ Alexandra LaMay, Biologist t/l ~ ~~ Matthew Lloyd, Industrial Hygienist ./JIJJ 1 · 1 

Risk Assessment Branch VII . r :(~ 

Health Effects Division (75 9 ~ 

Through:,(UvElissa Reaves, Chief . ' 

Risk Assessment Branch IV I 

Health Effects Division (7509P) 

To: 

and 

Kelly O'Rouke 

Zaida Figueroa 

Exposure Science ;Kd 

Thurston Morton 

Risk Assessment Branch IV 

Division (7509P) 

Page I of32 
Introduction 

The Pesticide Reevaluation Division (PRD) requested that the Health Effects Division (HED) 

conduct an exposure and risk assessment for the currently registered uses of dicrotophos as part 

of the registration review process. Dicrotophos is registered for the use of cotton as well as a 

micro-injection application for ornamental trees. There are currently no registered nonoccupational (residential uses) for dicrotophos. 

It is HED policy to use the best available data to assess exposure. Several sources of generic 

data were used in this assessment as surrogate data in the absence of chemical-specific data, 

including [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; the Residential SOPs (modified Turf SOP for Spray Drift), other registrant-submitted 

studies (MRID 44 731 001)]. Some of these data are proprietary, and subject to the data 

protection provisions of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA). 

Note: This memorandum was reviewed by the Exposure Science Advisory Committee 

(ExpoSAC) on 09/26113. 

Page 2 of32 
Page 3 of 32

Table of Contents

1.0 Executive Summary............................................................................................................. 4

2.0 Risk Assessment Conclusions and Recommendations........................................................ 6

2.1 Summary of Risk Estimates............................................................................................. 6

2.2 Label Recommendations from Occupational Assessment............................................... 7

2.3 Label Recommendations from Residential Assessment .................................................. 7

2.4 Data Deficiencies and Requirements ............................................................................... 7

3.0 Hazard Characterization....................................................................................................... 7

4.0 Use Profile ......................................................................................................................... 10

5.0 Residential Exposure and Risk Estimates.......................................................................... 11

5.1 Residential Risk Estimates for Use in Aggregate Assessment ...................................... 11

5.2 Spray Drift...................................................................................................................... 11

5.2.1 Combined Risk Estimates From Lawn Deposition Adjacent to Applications............. 12

5.3 Residential Bystander Post-Application Inhalation Exposure ....................................... 16

6.0 Occupational Exposure and Risk Estimates ...................................................................... 16

6.1 Occupational Handler Exposure/Risk Estimates............................................................ 16

6.2 Occupational Post-application Exposure/Risk Estimates .............................................. 22

6.2.1 Occupational Post-application Inhalation Exposure/Risk Estimates...................... 22

6.2.2 Occupational Post-application Dermal Exposure/Risk Estimates.......................... 22

Appendix A. Summary of Occupational and Residential Non-cancer Algorithms..................... 27
Page 4 of 32

1.0 Executive Summary

This document presents an occupational and residential exposure and risk assessment for the 

currently registered uses of dicrotophos. Dicrotophos is registered for use on cotton as well as a 

micro-injection application for use on ornamental trees. There are currently no registered nonoccupational (residential uses) for dicrotophos. 

Use Profile:

Dicrotophos is a broad spectrum 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. 

All the available products are classified as Restricted Use and may be purchased and used only 

by certified applicators or persons under their direct supervision. As a Restricted Use pesticide,

the dicrotophos product labels contain substantial protective measures to prevent worker 

exposure; (Sections 4.0 and 6.0 provide more information on personal protective equipment). 

The currently registered application rates for the use on cotton ranges from 0.2 to 0.5 lbs ai/acre 

via ground and aerial application. The applications are specified to be conducted by closed 

system only. The pre-harvest intervals (PHI) is 30 days. Additionally, the micro-injection use 

for ornamental trees is applied by closed system and is not to be used on trees which will 

produce food within the year following treatment. 

This assessment addresses exposure and risk associated with the end-use products for 

dicrotophos when used as directed by occupational workers. There is a potential for 

occupational exposure associated with handler activities (i.e., mixing, loading, and applying) as 

well as with post-application activities (i.e., re-entering treated areas). There are no registered 

residential uses associated with dicrotophos at this time. There is, however, the potential for 

non-occupational exposure as a result of spray drift. A spray drift assessment was conducted for 

the cotton use application of dicrotophos. 

Exposure Duration:

For the organophosphate pesticides, the match between the toxicological endpoint selection and 

the exposure duration is different than HED’s approach for conventional chemicals. OPs exhibit 

a phenomenon known as steady state AChE inhibition. After repeated exposure at the same 

dose, the degree of inhibition comes into equilibrium with the production of new, uninhibited 

enzyme. At this point, the amount of AChE inhibition at a given dose remains consistent across 

duration. The endpoint selection for organophosphate 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 state” endpoint selection for dicrotophos overlaps with HED’s traditional short-term 

exposure duration endpoint selection and is consider health protective for occupational handlers 

that apply commercially over longer periods of time (i.e., intermediate-term exposures). Since 

chronic exposure is not expected for the registered uses and a cancer assessment was not 

conducted.

Hazard Profile:
Page 5 of 32

Dicrotophos is a member of the organophosphate (OP) class of pesticides. Like other OPs, the 

initiating event in the adverse outcome pathway (AOP), also often called the 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 dicrotophos, AChE inhibition is the most sensitive endpoint in the 

toxicology database in multiple species, durations, lifestages, and routes. Dicrotophos as the 

parent active ingredient is an AChE inhibiting chemical.

Endpoints and points of departure were selected for dermal, inhalation, and incidental oral routes 

of exposure. For the incidental oral exposure from steady state durations, a BMDL10 value of 

0.03 mg/kg, based on brain ChE inhibition, and the BMD10 of 0.04 mg/kg was selected as the 

point of departure (PoD) for dicrotophos from the OP Cumulative Risk Assessment (CRA). A 

steady state dermal PoD was selected from a 28-day dermal toxicity study in rats based on brain 

ChE inhibition (BMDL10 = 2.1 mg/kg/day; BMD10 = 3.3 mg/kg/day). 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. A steady state inhalation PoD was selected from a 28-day inhalation toxicity 

study (based on brain ChE inhibition (BMDL10 = 0.62 μg/L/day or 0.00062 mg/L/day; BMD10

= 0.67 μg/L/day or 0.00067 mg/L/day). A total uncertainty factor of 100X is appropriate for 

dermal, inhalation, and oral routes of exposures [10X for interspecies extrapolation, 10X for 

intraspecies variation and a 1X FQPA SF1]. 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.

Residential Exposure/Risk:

There are no currently registered non-occupational (residential) uses for dicrotophos. However, 

that does not preclude non-occupational exposure to dicrotophos.

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 result in buffers 

of 0 feet for groundboom and aerial applications, (i.e., MOEs ≥ 100 at the edge of the field). 

Children’s (1 to <2 year old) dermal and incidental oral risk estimates from indirect exposure to 

dicrotophos related to spray drift result in buffers of 250 feet for aerial applications and 75 feet 

for groundboom applications.

Occupational Handler Exposure:

No chemical-specific handler exposure data were submitted in support of this registration review 

assessment; therefore, HED relied on surrogate data in accordance with standard policies. 

Default assumptions established by the HED Science Advisory Council for Exposure 

(ExpoSAC) were used for parameters such as body weight and amount handled. A Total MOE 

approach was used as a risk metric since the toxicological effects for these exposure routes were 

similar. 

 

1 Applicable for the residential exposure assessment
Page 6 of 32

For mixer/loaders using the label-defined engineering controls, Total MOEs range from 91 to 

560 for aerial and groundboom, respectively. For applicators using the label defined engineering 

controls, Total MOEs range from 530 to 1,000 for aerial and groundboom applicators, 

respectively. Human flagging for aerial applications of dicrotophos resulted in a Total MOE of 

140. 

Occupational Post-application Exposure:

HED expects that post-application dermal exposure will occur since dicrotophos is applied postemergence as a foliar spray. Chemical-specific dislodgeable foliar residue (DFR) data were 

available and used for dicrotophos. HED has determined that steady-state risk estimates are of 

not of concern (i.e., MOEs >100) on the day of treatment (i.e., Day 0) for all of the postapplication exposure activities. Based on the Agency's current practices, a quantitative 

occupational post-application inhalation exposure assessment was not performed for dicrotophos

at this time. If new policies or procedures are put into place, the Agency may revisit the need for 

a quantitative occupational post-application inhalation exposure assessment for dicrotophos.

The acute toxicity data for dicrotophos show that this chemical is classified as 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. There were no systemic post-application risk estimates of 

concern on day 0 for all post-application activities. The reentry interval (REI) on the currently 

registered labels (6 days) meets the minimum requirements. 

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 

Residential SOPs (Turf SOP)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 by the Human Studies Review Board. 

Descriptions of data sources, as well as guidance on their use, can be found at the Agency 

website2. 

2.0 Risk Assessment Conclusions and Recommendations

2.1 Summary of Risk Estimates

The occupational handler assessment identified one exposure scenario that resulted in a risk 

estimate of concern (M/L for aerial applications to cotton with a calculated MOE of 91 and an 

LOC of 100). Total MOEs for the occupational handler scenarios range from 91 to 1,000 

depending on the exposure scenario. Additionally, there are no occupational post-application risk 

 

2 http://www.epa.gov/pesticides/science/handler-exposure-data.html and 

http://www.epa.gov/pesticides/science/post-app-exposure-data.html
Page 7 of 32

estimates of concern. The occupational post-application dermal MOEs range from 470 to 16,000

depending on the time (days) after treatment, and incorporated a chemical-specific DFR study. 

A spray drift assessment was completed for the currently registered uses of dicrotophos. The 

resulting risk estimates do exceed HED’s level of concern (MOEs < 100) for the combined 

dermal and incidental oral routes of exposure at the edge of the field. The spray drift assessment 

was completed at the maximum single application rate for cotton (0.5 lbs ai/acre) for the aerial 

and groundboom application methods. 

2.2 Label Recommendations from Occupational Assessment 

There are no label recommendations for the currently registered occupational uses of 

dicrotophos.

2.3 Label Recommendations from Residential Assessment

There are no currently registered non-occupational (residential) uses of dicrotophos.

2.4 Data Deficiencies and Requirements

There are currently no outstanding data requirements for dicrotophos.

3.0 Hazard Characterization

Acute Toxicity

The acute toxicity data for dicrotophos show that dicrotophos has a high acute toxicity category 

for acute oral and acute inhalation toxicity (Category I). It also has a Category II acute dermal 

toxicity. The data show acute eye irritation (Category II) and is a strong skin sensitizer but it not 

a dermal irritant (Category IV). 

Table 3.1 Acute Toxicity Profile - Dicrotophos

Guideline No. Study Type MRID(s) Results Toxicity Category

870.1100 Acute oral (rat) 00261098/

43893901

M/F LD50 = 11/8 

mg/kg

I

870.1200 Acute dermal (rat) 00261098 M/F LD50 = 

876/476 mg/kg

II

870.1300 Acute inhalation (rat) 46411001 LC50 > 0.059 

mg/L

I

870.2400 Acute eye irritation 00261098 Lesions reversed 

by 14 days

II

870.2500 Acute dermal irritation [species] 00261098 No irritation IV

870.2600 Skin sensitization [species] 00261098 Strong sensitizer --
Page 8 of 32

Toxicological PODs Used for Risk Assessment

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). 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. OPs exhibit a phenomenon known as steady state AChE inhibition. After 

repeated exposure at the same dose, the degree of inhibition comes into equilibrium with the 

production 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, pattern of steady state is reached at or near 

15 days of exposure. In addition to the consistency across durations, the data across multiple 

studies (repeat CCA study, gestational data from the DNT, subchronic neurotoxicity study, and 

subchronic rat toxicity study) are similar. For the purposes of the occupational and residential 

risk assessment, only the steady-state duration is relevant to the exposure scenarios.

The steady-state incidental oral PoD is selected from the OP CRA (USEPA, 2002 and 2006). 

The oral PoD is based on the BMDL10 value of 0.03 mg/kg, based on brain ChE inhibition and 

the BMD10 of 0.04 mg/kg. For steady state incidental oral exposures, a total uncertainty factor of 

100X was applied [10X for interspecies extrapolation, 10X for intraspecies variation and a 1X 

FQPA SF].

A steady state inhalation PoD was selected from a 28-day inhalation toxicity study (MRID 

48146702) in female rats based on brain ChE inhibition (BMDL10 = 0.62 μg/L/day or 0.00062 

mg/L/day; BMD10 = 0.7 μg/L/day or 0.0007 mg/L/day). 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). For 

steady state inhalation exposures, a total uncertainty factor of 100X was applied [10X for 

interspecies extrapolation, 10X for intraspecies variation and a 1X FQPA SF3].

A steady state dermal PoD was selected from a 28-day dermal toxicity study (MRID 46484501) 

in rats based on brain ChE inhibition (BMDL10 = 2.1 mg/kg/day; BMD10 = 3.3 mg/kg/day) in 

the female rat. 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. 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. Therefore, the refined dermal dose for human skin to use 

as the PoD is 9.33 mg/kg/day. A total uncertainty factor of 100X is appropriate for dermal 

exposures [10X for interspecies extrapolation, 10X for intraspecies variation and a 1X FQPA 

safety factor]. 

In accordance with the Agency's Draft Cancer Risk Assessment Guidelines (July 2, 1999), 

dicrotophos is classified as showing "Suggestive evidence of carcinogenicity, but not sufficient to 

 

3 For the relevant non-occupational exposure assessments
Page 9 of 32

assess human carcinogenic potential”. Although the mice study showed that dicrotophos was 

associated with evidence of increased tumor incidence for a single tumor type (thyroid), HED 

has determined that quantification of risk using a non-linear approach; i.e., RfD, for dicrotophos 

will adequately account for all chronic toxicity, including carcinogenicity, that could result from 

exposure to dicrotophos. 

A summary of the toxicological doses and endpoints for use in the occupational and residential 

exposure and risk assessment are provided in Table 3.2.

Table 3.2 Summary of Toxicological Doses and Endpoints and Points of Departure for Dicrotophos

Exposure

Scenario

Point of Departure

(mg/kg/day)

Study and Toxicological

Effects

Incidental Oral

Steady State

BMDL10 = 0.03 mg/kg/day

UFA = 10x

UFH = 10x

FQPA SF = 1x

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)

rat BMDL10 = 2.1 mg/kg/day

UFA = 10x

UFH = 10x

FQPA SF = 1x

Human Adjusted Dermal PoD = 

9.33 mg/kg/day1

BMD10 = 3.3 mg/kg/day

28-day dermal toxicity study (MRID 46484501) 

in rats

Inhibition of brain ChE in adult rat.

Inhalation

Steady State (21 

days and longer)

BMDL10 = 0.00062 

mg/L/day

(0.162 mg/kg/day)

UFA = 10x

UFH = 10x

FQPA SF = 1x

BMD10 = 0.0007 mg/L/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”.

1 Human Adjusted Dermal PoD = (2.1 x 4.44= 9.33 mg/kg/day)

Absorption

Since the steady-state dermal and inhalation PODs were based on route-specific toxicity studies, 

no absorption factors were necessary to estimate exposure.

Body Weight

The standard body weight for the general population (80 kg) was used for all exposure scenarios 

covered in this risk assessment since the endpoints selected were not developmental and/or fetal 

effects.
Page 10 of 32

4.0 Use Profile 

Dicrotophos is a broad spectrum insecticide and is currently registered as a water-miscible enduse 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 may be purchased and used only by certified applicators or persons under their direct 

supervision. As a Restricted Use pesticide, the dicrotophos product labels contain substantial 

protective measures to prevent worker exposure; (Sections 4.0 and 6.0 provide more information 

on personal protective equipment). 

Mixers and loaders for dicrotophos products must use closed system engineering controls, and 

wear long-sleeved shirt and long pants, chemical-resistant gloves, and a chemical-resistant apron. 

Applicators and flaggers for cotton applications must use either a closed cockpit (for airplanes) 

or enclosed cabs. Handlers/applicators for the micro-injection product must wear long-sleeved 

shirt and long pants, chemical resistant gloves, chemical-resistant footwear plus socks, and 

protective eyewear.

Table 3.1. Summary of Directions for Use of Dicrotophos.

Applic. 

Timing, Type, 

and Equip.

Formulation 

[EPA Reg. 

No.]

Applic. 

Rate (lb 

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

Engineering 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

Engineering 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

Engineering 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 Engineering 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 treatment
Page 11 of 32

5.0 Residential Exposure and Risk Estimates

There are currently no registered non-occupational (residential) uses for dicrotophos at this time.

5.1 Residential Risk Estimates for Use in Aggregate Assessment

Dicrotophos is a Restricted Use Pesticide (RUP) and there are no currently registered nonoccupational (residential) uses of dicrotophos. Based on the labeled use pattern and the exposure 

profile of dicrotophos, there is no recommended residential contribution to the aggregate risk 

assessment. 

5.2 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 offtarget 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 spray 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. 

In order to evaluate the drift potential and associated risks, an approach based on drift 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 guidance for application 

parameters is not available.4 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 

 

4http://www.agdrift.com/ 
Page 12 of 32

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 prohibitions 

(e.g., aerial applications are not allowed). Section 5.2.1 provides the screening level drift related 

risk estimates along with additional risk management options if necessary. These drift estimates 

represent plausible options for pesticide labels.

5.2.1 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 used 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 high boom height and 

using very fine to fine spray type using the 90th 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 more 

detail below (e.g., wind vector assumed to be 10 mph in a downwind direction for entire 

application/drift event).5

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 qualities have been considered as well as the 

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 calculated for adults. Dermal and incidental oral risk estimates 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 Level of Concern is 100 so 

MOEs < 100 represent risk estimates of concern. Adult dermal risk estimates from indirect 

exposure to dicrotophos related to spray drift result in buffers of 0 feet for groundboom and 

aerial applications, (i.e., MOEs ≥ 100 at the edge of the field). Children’s (1<2 year old) dermal 

and incidental oral risk estimates from indirect exposure to dicrotophos related to spray drift 

result in buffers of 75 feet for groundboom applications and 250 feet for aerial applications based 

on the screening level scenarios.

Results are presented in Tables 5.2.1.1 and 5.2.1.2 and indicate that the major risk concern is 

from aerial 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 

 

5 AgDrift allows for consideration of even finer spray patterns characterized as very fine to fine. However, this 

spray pattern was not selected as the common screening basis since it is used less commonly for most agriculture. If 

assessors identify this use pattern it should be used as the screening criteria and deposition values associated with it 

are provided in Table 1 below. Justification for including this spray quality should be included in any assessment 

based on specific label directions for its use.
Page 13 of 32

concerns (i.e., higher MOEs) from aerial applications. Similarly, using coarser sprays and 

lowering boom height for groundboom sprayers reduces risk concerns.
Page 14 of 32

Table 5.2.1.1 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 0.055575

190 240 290 390 510 650 790 920 1,200 1,500 1,800

Medium to 

Coarse 240 320 430 610 860 1,100 1,400 1,700 2,400 3,100 3,800

Coarse to Very 

Coarse 270 400 610 940 1,300 1,800 2,300 2,800 3,800 5,000 6,200

Very Fine to 

Fine 130 150 160 190 220 250 280 320 390 460 520

AT401, M, 10 

mph, 37% SD 210 270 350 470 640 830 1,000 1,200 1,600 1,900 2,400

WASP, M, 10 

mph, 37% SD 230 290 390 580 790 1,000 1,200 1,500 1,900 2,400 2,800

AT401, C, 10 

mph, 25% SD 250 350 500 740 1,100 1,400 1,700 2,100 2,900 3,800 4,500

WASP, C, 10 

mph, 25% SD 290 410 590 940 1,300 1,800 2,200 2,800 3,800 5,000 5,500

AT401, VC, 10 

mph, 20% SD 280 430 690 1,100 1,600 2,200 2,800 3,600 5,000 6,200 8,300

WASP, VC, 10 

mph, 20% SD 360 570 870 1,400 2,000 2,600 3,600 4,100 6,200 7,100 8,300

Groundboom

High Boom 

Very fine to 

Fine

270 530 890 1,400 2,000 2,500 2,900 3,600 4,500 6,200 7,100

Low Boom Very 

fine to Fine 590 1,600 2,500 3,800 5,000 6,200 7,100 8,300 9,900 12,000 17,000

High Boom Fine 

to 

Medium/Coarse

1,000 2,600 3,800 5,500 7,100 8,300 9,900 9,900 12,000 17,000 17,000

Low Boom Fine 

to 

Medium/Coarse

1,500 4,100 6,200 8,300 9,900 12,000 17,000 17,000 25,000 25,000 25,000
Page 15 of 32

Table 5.2.1.2 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 0.055575

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
Page 16 of 32

5.3 Residential Bystander Post-Application 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, 20106. The agency has evaluated the SAP report and has developed a Volatilization 

Screening Tool and a subsequent Volatilization Screening Analysis7. 

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.

6.0 Occupational Exposure and Risk Estimates

6.1 Occupational Handler Exposure/Risk Estimates

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 task. 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 developed 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 registered 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 insects on ornamental trees. HED has no specific data developed 

to represent tree injection treatment use; the exposure and risk associated with tree injection uses 

(occupational handler and/or postapplication exposure) will not be higher than the quantitatively 

assessed exposure scenarios addressed below.

Occupational Handler Exposure Data and Assumptions

 

6 http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html

7 http://www.regulations.gov/#!docketDetail;D=EPA-HQ-OPP-2014-0219
Page 17 of 32

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 assuming the single maximum application rate; lower 

application rates result in correspondingly higher exposures (i.e., lower risk to handlers).

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 Table8”, which, along with additional information on HED policy 

on use of surrogate data, including descriptions of the various sources, can be found at the 

Agency website9. 

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: The standard body weight for the general population (80 kg) was used for all 

exposure scenarios covered in this risk assessment since the endpoints selected were not 

developmental and/or fetal effects.

 

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.

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 

 

8 Available: http://www.epa.gov/opp00001/science/handler-exposure-table.pdf

9 Available: http://www.epa.gov/pesticides/science/handler-exposure-data.html
Page 18 of 32

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 “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 state” endpoint selection for dicrotophos 

overlaps HED’s traditional 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 to 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 multiple applications for multiple clients within a region).

Dicrotophos is a restricted use pesticide 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 mitigation of agricultural uses from the July, 2006 dicrotophos RED. 

Specifically, the RED required engineering controls such as closed cabs and closed 

mixing/loading systems for occupational handlers. All current dicrotophos labels indicate this 

level of personal protection for occupational handlers.

Occupational Handler Non-Cancer Exposure and Risk Estimate Equations

Potential daily exposures for occupational handlers were calculated using the following 

formulas:

Daily Exposure (mg ai /day) = UE (μg ai / lb ai) * CF * AR (lb ai /A) * AT (A /day) * 1E-3 mg/μg

where:

Daily Exposure = Amount (mg ai/day) that is available for dermal or inhalation absorption,

UE = Unit Exposure (μg ai / lb ai),

AR = maximum application rate according to label (lb ai /A), and

AT = daily acres treated (A /day).

The daily doses were calculated using the following formula:

Average Daily Dose (mg ai/kg/day) = [Daily Exposure (mg ai/day) * Absorption (%)]

Body Weight (kg)

where:

Average Daily Dose = Absorbed dose received from exposure to a pesticide in a given scenario (mg 

pesticide active ingredient/kg body weight/day),

Daily Exposure = Amount (mg ai/day) that is available for dermal or inhalation absorption,

Absorption Factor = A measure of the amount of chemical that crosses a biological boundary such as 

the skin and lungs (%), and
Page 19 of 32

Body Weight = Body weight determined to represent the population of interest in a risk 

assessment (kg).

Margin of Exposure: Non-cancer risk estimates for each application handler scenario are 

calculated using a Margin of Exposure (MOE), which is a ratio of the toxicological endpoint to 

the daily dose of concern. The daily dermal and inhalation dose received by occupational 

handlers were compared to the appropriate POD (i.e. BMDL10) to assess the risk to occupational 

handlers for each exposure route. All MOE values were calculated using the following formula:

MOE = POD (typically a BMDL10 in mg/kg/day) 

ADD (mg/kg/day)

where:

MOE = Margin of Exposure: value used by HED to represent risk or risk estimates (unitless),

POD = Point of Departure,

BMDL10 = Benchmark Dose Level (mg/kg/day): Dose level in a toxicity study, where no 

observed adverse effects occurred in the study, and

ADD = Average Daily Dose (mg/kg/day): the absorbed dose received from exposure to a 

pesticide in a given scenario.

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 inhalation 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

Based on the label-defined protection for occupational handlers (engineering controls), one

occupational handler exposure scenario results in a risk estimate of concern (M/L for aerial 

applications to cotton [0.5 lbs ai/A]; calculated MOE of 91 with an LOC of 100). The other 

occupational handler exposure scenarios assessed do not represent risk estimates of concern (i.e., 

all dermal and inhalation MOEs exceed the LOCs of 100) for the steady-state exposure 

assessment. Combined occupational handler risk estimates are presented using the Total MOE 

approach. Of the evaluated exposure scenarios, the lowest combined MOE is 91 (LOC =100; 

M/L for aerial applications to cotton). All the other combined MOEs for occupational handler 

scenarios range from 140 to 1,000.

In the case of dicrotophos, HED does not have unit exposure data for assessing dermal and 

inhalation exposure for flaggers with engineering controls. HED has presented flagger risk 

estimates at baseline PPE (i.e., long-sleeve shirt, long pants, shoes, socks, no respirator) even 

though engineering controls for flaggers are required on the registered product labels. The proper 

use of engineering controls significantly decreases handler exposure for this activity.
Page 20 of 32

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 control (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 matches 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 flaggers 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.

For mixer/loaders using the label defined engineering controls, Total MOEs range from 91 to 

560 for aerial and groundboom, respectively. For applicators using the label defined engineering 

controls, Total MOEs range from 530 to 1,000 for aerial and groundboom applicators, 

respectively. Human flagging for aerial applications of dicrotophos resulted in a Total MOE of 

140. 
Page 21 of 32

Table 6.1.1. Steady-State Occupational Exposure and Risk Estimates for Dicrotophos. All estimates are at engineering 

controls.

Exposure Scenario Crop or Target

Dermal Unit 

Exposure (ug/lb ai)1

Inhalation Unit

Exposure (ug/lb ai)1 Maximum 

Application 

Rate2

Area 

Treated or 

Amount 

Handled 

Daily3

Dermal Inhalation Total

Mitigation Level Mitigation Level Dose 

(mg/kg/day)4 MOE5 Dose (mg/kg/day)6 MOE7 MOE8

Mixer/Loader

M/L - Aerial Application Cotton EC – 8.6 EC – 0.083 0.5 1200 A/day 0.0645 140 0.000623 260 91

M/L - Groundboom 

Application Cotton EC – 8.6 EC – 0.083 0.5 200 A/day 0.0108 860 0.000104 1600 560

Applicator

Aerial Application Cotton EC – 2.1 EC – 0.0049 0.5 1200 A/day 0.0156 600 0.0000368 4400 530

Groundboom Application Cotton EC – 5.1 EC – 0.043 0.5 1200 A/day 0.00638 1500 0.0000538 3000 1,000

Flagger

Flagger- from Aerial 

Application Cotton Baseline - 11 Baseline – 0.35 0.5 350 A/day 0.0241 390 0.000766 210 140

1 PHED/ORETF (baseline or Eng. Controls [EC]).

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 (80 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 (80 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).
Page 22 of 32

6.2 Occupational Post-application Exposure/Risk Estimates

HED uses the term post-application to describe exposures that occur when individuals are 

present in an environment that has been previously treated with a pesticide (also referred to as reentry exposure). Such exposures may occur when workers enter previously treated areas to 

perform job functions, including activities related 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, 

and 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.

6.2.1 Occupational Post-application Inhalation Exposure/Risk Estimates

There are multiple potential sources of post-application inhalation exposure to 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 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, 201010. The Agency 

has evaluated the SAP report and has developed a Volatilization Screening Tool and a 

subsequent Volatilization Screening Analysis11. 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.

Although a quantitative occupational post-application inhalation exposure assessment was not 

performed, an inhalation exposure assessment was performed for occupational/commercial 

handlers. Handler exposure resulting from application of pesticides outdoors is likely to result in 

higher exposure than post-application exposure. Therefore, it is expected that these handler 

inhalation exposure estimates would be protective of most occupational post-application 

inhalation exposure scenarios.

6.2.2 Occupational Post-application Dermal Exposure/Risk Estimates

Occupational Post-application Dermal Exposure Data and Assumptions

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.

 

10 http://www.epa.gov/scipoly/SAP/meetings/2009/120109meeting.html

11 http://www.regulations.gov/#!docketDetail;D=EPA-HQ-OPP-2014-0219. 
Page 23 of 32

Exposure Duration: 

The endpoint selection for organophosphate 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 state” 

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 postapplication 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 312” which, along with 

additional information about the ARTF data, can be found at the Agency website13.

Table 6.2.2.1: Anticipated Post-Application Activities and Dermal Transfer Coefficients.

Crops Policy Crop Group Category Transfer 

Coefficients Activities

cm2/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: 

The standard body weight for the general population (80 kg) was used for all exposure scenarios 

covered in this risk assessment since the endpoints selected were not developmental and/or fetal 

effects.

Absorption Factor: 

Since the steady-state dermal POD was based on a route-specific 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.

 

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

13 Available: http://www.epa.gov/pesticides/science/post-app-exposure-data.html
Page 24 of 32

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 

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 μg/cm2 (7.84%) at the Mississippi site and 1.001 μg/cm2 (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/cm2 (3.22%) at the 

Mississippi site and 0.343 μg/cm2(6.13%) at the Texas site. 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 summary of 

this data in the table below.

Table 7. Summary of Dicrotophos DFR Residues and Versar Regression Analysis 

Results for Cotton Leaves Treated with Dicrotophos

Statistic Texas- 1

st application

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/cm2)

1.001 (first application)

0.343 (second application)

Predicted Day 0 Residue

(μg/cm2)

0.936

Slope -0.402

Half-life (days) 1.7

R

2 0.923

Registrant’s predicted half-life (days) 2.33

Registrant’s R2 0.971

Occupational Post-application Non-Cancer Dermal Exposure and Risk Estimate Equations
Page 25 of 32

Average Daily Dose (ADD): Potential daily exposures for occupational post-application workers 

were calculated using the following formulas:

Daily Exposure (mg ai /day) = TC (cm2/hr) * CF1 * DFRt (μg/cm2) * ET (hrs /day) * 1E-3 mg/μg

where:

Daily Exposure = Amount (mg ai/day) that is available for dermal absorption,

TC = Transfer coefficient (cm2/hr),

DFRt = Dislodgeable Foliar Residue on day “t” (μg/cm2), and

ET = Exposure Time (hours /day).

The daily doses were calculated using the following formula:

Average Daily Dose (mg ai/kg/day) = [Daily Exposure (mg ai/day) * Absorption (%)]

Body Weight (kg)

where:

Average Daily Dose = Absorbed dose received from exposure to a pesticide in a given scenario (mg 

pesticide active ingredient/kg body weight/day),

Daily Exposure = Amount (mg ai/day) that is available for dermal absorption,

Absorption Factor = A measure of the amount of chemical that crosses a biological boundary such as 

the skin (%), and

Body Weight = Body weight determined to represent the population of interest in a risk 

assessment (kg).

Margin of Exposure: Non-cancer risk estimates for each application handler scenario are 

calculated using a Margin of Exposure (MOE), which is a ratio of the toxicological endpoint to 

the daily dose of concern. The daily dermal dose received by occupational post-application 

workers was compared to the appropriate POD (i.e. BMDL) to assess the risk to occupational 

post-application workers. All MOE values were calculated using the following formula:

MOE = POD (BMDL in mg/kg/day) 

ADD (mg/kg/day)

where:

MOE = Margin of Exposure: value used by HED to represent risk or risk estimates (unitless),

POD = Point of Departure, and

ADD = Average Daily Dose (mg/kg/day): the absorbed dose received from exposure to a 

pesticide in a given scenario.

Occupational Post-application Non-Cancer Dermal Risk Estimates

Table 6.2.2.2: Summary of Occupational/Commercial Post-application Risk Estimates for Dicrotophos.

Crop/Site Activities DFR/TTR1 DAT MOE2

Steady State

Cotton

Hand Weeding 0.928 0 1,400

0.0832 6 16,000

Scouting 0.928 0 470

0.0832 6 5,200

1. DFR = from chemical-specific study data (MRID 44731001)
Page 26 of 32

2. MOE = POD (mg/kg/day) / Daily Dermal Dose. Daily Dermal Dose = [DFR/TTR (μg/cm2) x TC x 0.001 mg/μg x 8 hrs/day ]  BW (kg)

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-required 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 at 0 days after treatment is expected to 

cover any harvest-related exposure to dicrotophos, which would not occur until 30-days after 

application; all assessed post-application exposure activities are not of concern on the day of 

treatment.

Restricted Entry Interval

The REI specified on the label of 6 days is based on the acute toxicity of dicrotophos and the 

mitigations specified in the dicrotophos RED. Dicrotophos is classified as 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. Single day and steady-state post-application risk estimates were not 

a concern on day 0 (12 hours following application) for all post-application activities. Under 40 

CFR 156.208 (c) (2), if the product contains only one active ingredient and it is in toxicity 

category II, the restricted entry interval shall be 24 hours. If the active ingredient is an 

organophosphorus ester that inhibits cholinesterase and that may be applied outdoors in an area 

where the average rainfall is less than 25 inches per year, the restricted interval should be listed 

as 72 hours. Thus, the REI on the labels meets the minimum requirements.
Page 27 of 32

Appendix A. Summary of Occupational and Residential Non-cancer Algorithms

Spray Drift Non-cancer Post-application Algorithms

Modification To SOP Method To Account For Spray Drift and Residential Post-Application 

Hand to Mouth Algorithms

The modification to SOP 3.2.2 that has been made to account for spray drift only alters Equation 

3.4 from the SOPs. The modified equation is presented below and it should be used to evaluate 

potential risks from spray drift. This equation is the same except that an additional term has been 

included (DF or Drift Fraction) which provides an adjustment for the amount of drift that moves 

into and deposits in a non-target area such as a lawn. This equation applies to situations where 

TTR data are not available.

TTR= AR * DF * F * (1-D)t* CF2 * CF3

where:

TTR = turf transferable residue (μg/cm2)

DF = drift fraction of spray drift that deposits on lawns (unitless)

AR = application rate (lbs ai/ft2or lb ai/acre)

F = fraction of ai as transferable residue following application (unitless)

D = fraction of residue that dissipates daily (unitless)

t = post-application day on for exposure is being assessed (Day 0 in this SOP)

CF2 = weight unit conversion factor (4.54 x 108 μg/lb)

CF3 = area unit conversion factor (1.08 x 10-3ft2/ cm2or 2.47 x 10-8acre/cm2)

If chemical specific TTR data are available, the residue on Day 0 is used after it is adjusted based 

on the ratio of the applicable application rate for risk assessment (i.e., based on the crop of 

concern) and the application rate for the TTR study followed by an additional adjustment for the 

drift fraction factor like illustrated above.

Post-application Dermal Exposure Algorithm – Physical Activities on Turf

Exposure resulting from contacting previously treated turf while performing physical activities is 

calculated as shown below. Residential post-application exposure assessment must include 

calculation of exposure on the day of application. Therefore, though an assessment can present 

exposures for any day “t” following the application, it must include “day 0” exposure.

E = TTRt * CF1 * TC * ET

where:

E = exposure (mg/day);

TTRt = turf transferable residue on day t (μg/cm2);

CF1 = weight unit conversion factor (0.001 mg/μg);

TC = transfer coefficient (cm2/hr); and
Page 28 of 32

ET = exposure time (hr/day).

Dermal absorbed doses are calculated as:

BW

E AF D*



where:

D = dose (mg/kg-day);

E = exposure (mg/day);

AF = absorption factor (dermal); and

BW = body weight (kg).

Table A-1: Turf (Physical Activities) -- Inputs for Residential Post-application Dermal Exposure

Algorithm Notation Exposure Factor

(units) Point Estimate(s)

AR Application rate

(mass active ingredient per unit area) 0.5

F

Fraction of AR as TTR 

following application (if 

chemical-specific data is 

unavailable)

L/WP/WDG 0.01

Granules 0.002

FD

Daily residue dissipation 

(if chemical-specific data 

is unavailable)

(fraction)

L/WP/WDG 0.1

Granules 0.1

TC

Transfer 

Coefficient 

(cm2/hr)

L/WP/WDG

Adults 180,000

Children 1 < 2 years old 49,000

Granules

Adults 200,000

Children 1 < 2 years old 54,000

ET Exposure Time

(hours per day)

Adults 1.5

Children 1 < 2 years old 1.5

BW Body Weight

(kg)

Adults 80

Children 1 < 2 years old 11

L/WP/WDG = Liquids/Wettable Powders/Water-dispersible Granules

Post-application Hand-to-Mouth Exposure Algorithm– Physical Activities on Turf

Exposure from hand-to-mouth activity is calculated as follows (based on the algorithm utilized in 

the SHEDS-Multimedia model):

E = [HR * (FM * SAH) * (ET * N_Replen) * (1- (1- SE)

(Freq_HtM/N-Replen))]

where:

E = exposure (mg/day);

HR = hand residue loading (mg/cm2);

FM = fraction hand surface area mouthed / event (fraction/event);

SAH = typical surface area of one hand (cm2);
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ET = exposure time (hr/day);

N_Replen = number of replenishment intervals per hour (intervals/hour);

SE = saliva extraction factor (i.e., mouthing removal efficiency); and

Freq_HtM = number of hand-to-mouth contacts events per hour (events/hour).

and

SA * 2

Fai *DE

HR

H

hands



where:

HR = hand residue loading (mg/cm2);

Faihands = fraction ai on hands compared to total surface residue from dermal transfer coefficient 

study (unitless);

DE = dermal exposure (mg); and

SAH = typical surface area of one hand (cm2).

Dose, normalized to body weight, is calculated as:

BW

E

D 

where:

D = dose (mg/kg-day);

E = exposure (mg/day); and

BW = body weight (kg).

Table A-2: Turf (Physical Activities) – Inputs for Residential Post-application Hand-to-Mouth 

Exposure 

Algorithm 

Notation

Exposure Factor

(units) Point Estimate(s)

Faihands

Fraction of ai on hands 

from dermal transfer 

coefficient study

(unitless)

Liquid formulations 0.06

Granular formulations 0.027

DE Dermal exposure (mg) Calculated

SAH

Typical surface area of one hand (cm2), children 1 < 

2 years old 150

AR Application rate

(mass active ingredient per unit area) 0.5

HR Residue available on the hands (mg/cm2) Calculated via (DE * Faihands)/SAH

FM

Fraction hand surface area mouthed

(fraction/event) 0.127

N_Replen Replenishment intervals per hour 4
Page 30 of 32

Table A-2: Turf (Physical Activities) – Inputs for Residential Post-application Hand-to-Mouth 

Exposure 

Algorithm 

Notation

Exposure Factor

(units) Point Estimate(s)

(intervals/hr)

ET Exposure time 

(hrs/day) 1.5

SE Saliva extraction factor

(unitless) 0.48

Freq_HtM Hand-to-mouth events per hour

(events/hr) 13.9

BW Body Weight

(kg)

Children 1 < 2 years 

old 11

Occupational Non-cancer Handler Algorithms

Potential daily exposures for occupational handlers are calculated using the following formulas:

E=UE * AR * A * 0.001 mg/ug

where:

E = exposure (mg ai/day),

UE = unit exposure (μg ai/lb ai),

AR = maximum application rate according to label (lb ai A or lb ai/gal), and

A = area treated or amount handled (e.g., A/day, gal/day).

The daily doses are calculated using the following formula:

ADD= 

E * AF

BW

where:

ADD = average daily dose absorbed in a given scenario (mg ai/kg/day),

E = exposure (mg ai/day),

AF = absorption factor (dermal and/or inhalation), and

BW = body weight (kg).

Margin of Exposure: Non-cancer risk estimates for each application handler scenario are 

calculated using a Margin of Exposure (MOE), which is a ratio of the toxicological endpoint to 

the daily dose of concern. The daily dermal and inhalation dose received by occupational 

handlers are compared to the appropriate POD (i.e., NOAEL) to assess the risk to occupational 

handlers for each exposure route. All MOE values are calculated using the following formula:
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MOE= 

POD

ADD

where:

MOE = margin of exposure: value used by HED to represent risk estimates (unitless),

POD = point of departure (mg/kg/day), and

ADD = average daily dose absorbed in a given scenario (mg ai/kg/day).

Occupational Non-cancer Post-application Algorithms

Potential daily exposures for occupational post-application workers are calculated using the 

following formulas:

DFRt=AR * F* (1-D)t* (4.54E8

ug

lb) * (2.47E-8

A

cm2

)

where:

DFRt = dislodgeable foliage residue on day "t" (μg/cm2),

AR = application rate (lb ai/acre),

F = fraction of ai retained on foliage or 25% (unitless),

D = fraction of residue that dissipates daily or 10% (unitless), and

t = number of days after application day (days).

E=TC * DFR t* ET * 0.001

mg

ug

where:

E = exposure (mg ai/day),

TC = transfer coefficient (cm2/hr),

DFRt = dislodgeable foliar residue on day “t” (μg/cm2), and

ET = exposure time (hours/day).

The daily doses are calculated using the following formula:

ADD= 

E * AF

BW

where:

ADD = average daily dose absorbed in a given scenario (mg ai/kg/day),

E = exposure (mg ai/day),
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AF = absorption factor (dermal and/or inhalation), and

BW = body weight (kg).

Margin of Exposure: Non-cancer risk estimates for each scenario are calculated using a Margin 

of Exposure (MOE), which is a ratio of the toxicological endpoint to the daily dose of concern. 

The daily dermal dose received by occupational post-application workers is compared to the 

appropriate POD (i.e., NOAEL) to assess the risk to occupational post-application workers. All 

MOE values are calculated using the following formula:

MOE= 

POD

ADD

where:

MOE = margin of exposure: value used by HED to represent risk estimates (unitless),

POD = point of departure (mg/kg/day), and

ADD = average daily dose absorbed in a given scenario (mg ai/kg/day).