-Page 2 of 102-

invertebrates (i.e. insects), and freshwater and estuarine/marine invertebrates. Table 1

summarizes the representative uses assessed and the taxa that may potentially be directly at risk 

from exposure to dicrotophos.

Summary

Dicrotophos is used on cotton with a maximum application rate of 0.5 lb a.i./ac and as a tree 

injection with maximum application rate contingent upon tree diameter. Dicrotophos is stable to 

photolysis, persistent to hydrolysis and metabolizes readily in aerobic and anaerobic 

environments. It is also mobile and does not bioaccumulate. Dicrotophos is very highly toxic to 

mammals, birds, and aquatic invertebrates on an acute basis; highly toxic to honey bees on an 

acute basis; slightly to moderately acutely toxic to fish; and minimally toxic to terrestrial and 

aquatic plants. In terms of its chronic toxicity profile, chronic risks exceeding established levels 

of concern are identified for birds, mammals, and aquatic invertebrates for dicrotophos used on 

cotton.

Basic Uncertainties 

The tree injection use pattern (EPA Reg. No. 7946-11) does not limit the number of applications 

that can be made in a given year or season. Further, the stated application rate is based on 

number of capsules for a given tree size. The number of capsules applied is the diameter of the 

tree at breast height, in inches, divided by two. However, the size of the capsule can be variable 

according to the label which would result in substantially different applications depending on 

capsule size (one to three milliliters). Given these uncertainties, maximum single application 

and maximum annual application cannot be precisely determined.

The fate of dicrotophos when injected into the tree is a considerable uncertainty. The suite of

chemical fate data EFED receives has little bearing on how a chemical behaves when injected 

into a tree. The rates of degradation in the tree, mobility to various parts of the tree, and 

formation of degradates cannot be characterized by current data. Further, the dispersion of 

dicrotophos-treated trees across various landscapes is a spatial uncertainty.

The understanding of dicrotophos half-lives in aerobic soil and aquatic metabolism are based 

upon on a single study testing only a single soil. The 2.7 day half-life is multiplied by an 

uncertainity factor (3X) to derive the model parameters but it must still be considered that one 

soil is being used to represent thousands of soils and microbial communities with variable types 

and rates of metabolism in addition to many aquatic environments with similar variability. 

The occurrence of monocrotophos, a metabolite of dicrotophos found in a cotton foliar residue 

study, in and/or on plant tissue is a considerable uncertainty in this assessment. Monocrotophos 

is known to be more toxic to avian species than dicrotophos on an acute basis, and while residues 

of monocrotophos on foliage are presumed to be lesser (on a mass per unit volume or mass per 

unit area basis), the enhanced toxicity of this compound may effectively extend the time of acute 

risk LOC exceedances following dicrotophos application. 
-Page 3 of 102-

The available avian acute and subacute studies are not robust. Many of the available studies lack 

a sufficient number of treatment levels; treatment level spacing is also problematic. For most 

studies, uncertainties would be reduced if additional study conduct details were available. 

Specifically, the percent active ingredient of the test material for the most sensitive acute oral 

and sub-acute dietary test species is a considerable uncertainty. The avian RQs reported in this 

assessment may underestimate toxicity since the compound purity was presumed to be technical 

grade. 

An acceptable foliar residue toxicity study with honey bees (OCSPP 850.3030) would allow for 

determination of a 24-h RT25. This data would reduce uncertainties surrounding the length of 

time post-application that residues of dicrotophos on foliage are toxic to honey bees.
Page 4 of 102

Table 1. Risk Resulting from Dicrotophos Exposure Presented by Taxon

Use Pattern Aquatic 

Invertebrates

Fish (surrogate 

for aquatic-phase 

amphibians)

Birds, 

(surrogate for 

reptiles and 

terrestrial-phase 

amphibians)

Mammals Plants Terrestrial 

Invertebrates

Cotton Acute risk:

Yes1

Chronic risk: 

Yes1

Acute risk:

Not expected

Chronic risk: 

Not expected

Acute risk: 

Yes1

Chronic risk: 

Yes1

Acute risk: 

Yes1

Chronic risk: 

Yes1

Terrestrial:

Not expected

Aquatic:

Not expected

Acute risk:

Yes1

Tree injection

Acute risk: 

Uncertain2

Chronic risk: 

Uncertain2

Acute risk:

Not expected

Chronic risk: 

Not expected

Acute risk: 

Uncertain2

Chronic risk: 

Uncertain2

Acute risk: 

Uncertain2

Chronic risk: 

Uncertain 2

Terrestrial:

Not expected

Aquatic:

Not expected

Acute risk:

Uncertain2

1 “Yes” indicates risk concerns for both listed and non-listed taxa

2 Risk is uncertain in the absence of data describing the dispersion of treated trees and magnitude of residues in tree tissue and exudate
Page 5 of 102

Additional Considerations for Listed Species

Based on this screening-level assessment, there are potential risks of direct effects to listed and 

non-listed freshwater and estuarine/marine invertebrates, mammals, birds (birds are surrogates 

for terrestrial phase reptiles and amphibians), and terrestrial invertebrates from the use of 

dicrotophos on cotton. Listed species of freshwater and estuarine/marine invertebrates, 

mammals, birds, and terrestrial invertebrates may also be affected through indirect effects 

because of the potential direct effects on listed and non-listed species. Potential direct effects on 

listed and non-listed freshwater and estuarine/marine invertebrates (cotton use pattern only), 

mammals, birds, and terrestrial invertebrates from the use of dicrotophos may be associated with 

modification of Primary Constituent Elements (PCEs) of designated critical habitats, where such 

designations have been made. However, at this current stage of the Registration Review process, 

it is premature to make effects determinations for listed species until further scientific analysis 

and refinements are conducted, based on recommendations received from the National Academy 

of Sciences’ (NAS) National Research Council (NRC) April 2013 report, available at

http://www.nap.edu/catalog.php?record_id=18344. The NAS report outlines recommendations 

on specific scientific and technical issues related to the development of pesticide risk 

assessments that are compliant with the Endangered Species Act (ESA) and the Federal 

Insecticide, Fungicide, and Rodenticide Act (FIFRA).

The EPA along with the U.S. Fish & Wildlife Service (USFWS), the National Marine Fisheries 

Service (NMFS) (collectively, the Services), and the U.S. Department of Agriculture (USDA), 

released a summary of their implementation plan for assessing risks of pesticides to listed species 

ahead of the stakeholder workshop held on November 15, 2013. This plan was developed in 

response to the NAS’ recommendations, including a common approach to risk assessment as a 

way of addressing scientific differences between EPA and the Services. During the workshop, 

the agencies received feedback from the public on the interim scientific approaches that were 

developed as part of the initial implementation of the NAS recommendations. These approaches 

will be jointly implemented and vetted as part of a phased iterative process. Once fully vetted, 

EPA will further refine the listed species effects determination portion of this risk assessment. 

To make effects determinations for individual listed species, useful refinements may include, but 

are not limited to, analyses of: 1) more detailed, species-specific ecological and biological data; 

2) more detailed and accurate information on dicrotophos use patterns; and 3) sub-county level 

spatial proximity data for the co-occurrence of potential effects areas and listed species and any 

designated critical habitat. Examples of such refinements are described below.

EFED is currently developing tools that are expected to further refine the assessment and are 

designed to support effects determinations for individual federally listed species and their 

designated critical habitats (where applicable). Scientific information obtained from the 

Services, and other reliable sources is being collated by EFED to address all currently listed 

species. This information is being stored in an Office of Pesticide Programs (OPP) Pesticide 

Registration Information SysteM (PRISM) listed species knowledgebase. The listed species 

knowledgebase consists of an information repository that houses biological and behavioral 

information relevant to individual species (e.g., habitat, diet, and life history, including specific 

temporal and spatial associations) and a document repository that contains supporting documents 

(e.g., USFWS recovery plans) and electronic information (e.g., GIS data files). For terrestrial 
-Page 6 of 102-

taxa, biological information relevant to the assessment (e.g., diet and body weight) will be used 

to parameterize exposure estimates using a method consistent with currently used methods in the 

T-REX and T-HERPS models. 

Refinements will also include more detailed analyses of the registered uses and specific use 

patterns that result in either “Likely to Adversely Affect” (LAA) or “Not Likely to Adversely 

Affect” (NLAA) determinations for federally listed species. The analyses may include more 

information on where, when, and how dicrotophos is used on all use sites. Actual usage data 

(when available) and national land-cover datasets that indicate potential use sites [e.g., National 

Land Cover Dataset (NLCD), Cropland Data Layer (CDL)] may be used to support a more 

refined analysis of where dicrotophos is reasonably expected to be used. Similarly, refinements 

on the timing of applications and a more in-depth exploration of agronomic practices for

dicrotophos may be included as part of the refinement.

The refinements based on individual species data; additional, detailed usage information, when 

available; and recommendations from the NRC report are expected to help to more accurately 

identify potential areas of effect and to better inform effects and habitat determinations for listed 

species and any designated critical habitats.
-Page 7 of 102-

Environmental Fate and Ecological Risk Assessment 

for the Registration of Dicrotophos

 

Dicrotophos

[(E)-4-dimethylamino-4-oxobut-2-en-2-yl] dimethyl phosphate

CAS Registry Number 0000141-66-2

PC Code 035201

Prepared by:

Andrew Shelby, Physical Scientist

Nathan Miller, Biologist

U. S. Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch VI

1200 Pennsylvania Ave., NW

Mail Code 7507P

Washington DC 20460

Reviewed by:

Brian Kiernan, Biologist, ERB VI

William P. Eckel, Ph.D, Senior Science Advisor, ERB VI

Mark Corbin, Branch Chief, ERB VI

July 10, 2014
-Page 8 of 102-

Table of Contents

1. Executive Summary ............................................................................................................ 10

2. Problem Formulation ......................................................................................................... 12

2.1. Nature of Regulatory Action..................................................................................................................12

2.2. Stressor Source and Distribution ..........................................................................................................12

2.2.1. Nature of Chemical Stressor..............................................................................................................12

2.2.2. Overview of Pesticide Usage.............................................................................................................13

2.3. Receptors.................................................................................................................................................13

2.3.1. Aquatic and Terrestrial Effects..........................................................................................................13

2.3.2. Ecosystems Potentially at Risk..........................................................................................................14

2.4. Assessment Endpoints............................................................................................................................14

2.5. Conceptual Model ...................................................................................................................................14

2.5.1. Risk Hypotheses................................................................................................................................15

2.5.2. Conceptual Diagram..........................................................................................................................15

2.6. Analysis Plan ...........................................................................................................................................17

2.6.1. Residues of Concern..........................................................................................................................17

2.6.2. Preliminary Identification of Data Gaps and Uncertainties...............................................................17

2.6.3. Evaluation of Multiple Active Ingredients, Mixtures and Formulated Products...............................18

2.6.4. Measures of Exposure .......................................................................................................................18

2.6.5. Measures of Effect.............................................................................................................................20

2.6.6. Integration of Exposure and Effects..................................................................................................21

3. Analysis............................................................................................................................. 22

3.1. Use Characterization..............................................................................................................................22

3.2. Exposure Characterization....................................................................................................................23

3.2.1. Environmental Fate and Transport Characterization .........................................................................23

N,N-dimethyl-3-oxobutanamide ..........................................................................................................................28

{[1-(dimethylcarbamoyl)propan-2-yl]oxy}(methoxy)phosphinic acid..............................................................28

3-hydroxy-N,N-dimethylbutanamide ..................................................................................................................28

3-[(dimethoxyphosphoryl)oxy]-N-methylbut-2-enamide...................................................................................28

3.2.2. Measures of Aquatic Exposure..........................................................................................................29

3.2.3. Measures of Terrestrial Exposure......................................................................................................33

3.3. Ecological Effects Characterization......................................................................................................35

3.3.1. Aquatic Toxicity Assessment ............................................................................................................36

3.3.2 Terrestrial Effects Characterization...................................................................................................40

4. Risk Characterization......................................................................................................... 45

4.1. Risk Estimation.......................................................................................................................................45

4.1.1. Aquatic Organisms............................................................................................................................46

4.1.2. Terrestrial Organisms........................................................................................................................48

4.2. Incident Database Review ............................................................................................................................53

4.3. Risk Description......................................................................................................................................55

4.3.1 Exposure to Aquatic Organisms........................................................................................................55

4.3.1.1. Risks to Aquatic Animals..................................................................................................................56

4.3.1.2. Risks to Aquatic Plants......................................................................................................................56

4.3.2. Exposure to Terrestrial Organisms....................................................................................................56

4.3.2.1. Risks to Mammals.............................................................................................................................56

4.3.2.2. Risk to Birds......................................................................................................................................60

4.3.2.3. Risk to Terrestrial Invertebrates........................................................................................................63

4.3.2.4. Risk to Terrestrial Non-target Plants.................................................................................................64

4.4. Uncertainties and Data Gaps.................................................................................................................65

4.4.1. Fate and Transport.............................................................................................................................65

4.4.2. Effects................................................................................................................................................65

5. Endocrine Disruptor Screening Program (EDSP)........................................................... 66
-Page 9 of 102-

6. Federally Threatened and Endangered (Listed) Species Concerns............................... 67

6.1. Action Area .............................................................................................................................................67

6.2. Taxonomic Groups Potentially at Risk.................................................................................................68

6.2.1. Probit Dose-Response Analysis ......................................................................................................73

6.2.2. Listed Species Occurrence Associated with Registered Uses.......................................................74

7. References............................................................................................................................ 75

7.1 Submitted Product Chemistry and Environmental Fate Studies.......................................................77

7.2. Submitted Ecotoxicity Studies (Retrieved from OPPIN November 19, 2012)...................................81

Appendices

Appendix A: PRZM/EXAMS output for highest cotton and tree injection scenarios ......... 87

Appendix B: Toxicity Categories and Levels of Concern ....................................................... 96

Appendix C: Example T-REX (v. 1.5) Input and Output for Dicrotophos........................... 97

Appendix D: STIR Results......................................................................................................... 99

Appendix E: SIP Results.......................................................................................................... 100

Appendix F: Accepted ECOTOX Data Table......................................................................... 101
-Page 10 of 102-

1. Executive Summary

The Environmental Fate and Effects Division (EFED) has completed the Registration Review 

preliminary ecological risk assessment for dicrotophos [(E)-4-dimethylamino-4-oxobut-2-en-2-

yl] dimethyl phosphate; CAS Registry Number 141-66-2; PC Code 035201) and its end-use 

products. Dicrotophos is broad-spectrum systemic organophosphate insecticide that provides 

control of insect pests on a contact basis while also being suitable for residual crop protection 

since it is readily taken up by plant tissue. It is currently registered for broadcast applications

only on cotton (applied as a liquid foliar spray via air or ground application equipment) and as a 

tree injection (applied as capsules into holes drilled in the tree trunk). This preliminary risk 

assessment examines the potential ecological risks associated with labeled uses of dicrotophos 

based on the best available scientific and commercial information on the use, environmental fate 

and transport, and effects of dicrotophos on nontarget organisms. 

Dicrotophos is expected to readily degrade in both terrestrial and aquatic environments under 

aerobic and anaerobic conditions, and is mobile and semivolatile to nonvolatile. Dicrotophos is 

not persistent in soil with a single aerobic half-life 2.7 days and a half-life of 8 days in anaerobic 

soil. Dicrotophos is relatively stable to hydrolysis (t1/2 = 72 days) and stable to photolysis. The 

major degradates of dicrotophos degrade readily in aerobic conditions. 

Aquatic exposure estimates for dicrotophos are presented for the parent compound and total 

toxic residues (i.e., parent dicrotophos plus transformation products: SD 6167, SD 11733, and 

SD 228001). Acute 1-in-10 year estimated environmental concentrations (EECs) in surface 

water for modeled cotton uses of dicrotophos ranged from 13 μg/L to 17 μg/L for total toxic 

residues, and 12 μg/L to 16 μg/L for parent dicrotophos alone. The highest reported surface 

water monitoring value (6.83 μg/L) is approximately half of the peak modeled values; higher 

dicrotophos detections may be found with more targeted monitoring approaches. Parent-only 

and total toxic residue concentrations are similar because dicrotophos dissipation is driven by 

aerobic metabolism and the dicrotophos transformation products metabolize readily. 

Terrestrial and aquatic exposure resulting from the tree injection use pattern— which cannot be 

assessed via EFED’s usual “pounds active ingredient per acre” application rate modeling 

paradigm— were evaluated according to multiple translocation and fate scenarios of varying 

degrees of conservatism (e.g., equal distribution across all tree tissue, 100% translocation to the 

leaves; described in detail in Section 3.2).

Dicrotophos is very highly toxic to aquatic invertebrates on an acute exposure basis. Chronic 

dicrotophos exposures adversely affected aquatic invertebrate growth, with length and weight 

reductions seen at concentrations as low as 1.7 μg ai/L in freshwater invertebrates and as low as 

6.15 μg ai/L in estuarine/marine invertebrates. Dicrotophos is slightly to moderately toxic to fish 

on an acute basis, and no adverse chronic effects were recorded at concentrations as high as 

9,880 μg ai/L in the available fish early life stage study. The screening level assessment with 

preliminary refinements concludes that the use of dicrotophos in accordance with registered 

labels results in acute and chronic risk to aquatic invertebrates that exceed both the Agency’s

acute and chronic risk Level of Concern (LOC), but does not result in acute or chronic risk to 

fish that exceeds the Agency’s LOCs. Estimates of risk to aquatic plants do not exceed the 
-Page 11 of 102-

Agency’s risk LOC.

Dicrotophos is very highly toxic to birds and mammals on an acute exposure basis, and available 

data suggest chronic toxicity concerns. A three-generation study on reproduction and fertility in 

Norway rats showed dicrotophos to cause chronic adverse effects in terms of decreased pup 

survival at 5 mg/kg-diet. In chronic avian reproduction testing, statistically significant effects to

egg production and female body weight were recorded at exposure concentrations as low as 1.5 

mg/kg-diet. The screening level assessment with preliminary refinements concludes that the use 

of dicrotophos in accordance with registered labels results in acute and chronic risk to avian and 

mammalian species that exceed both the Agency’s acute and chronic risk LOC. Dicrotophos is 

classified as highly toxic to honey bees, and the acute risk to terrestrial invertebrates exceeds the 

Agency’s risk LOC. No statistically significant effects to terrestrial plants were determined in 

Tier I testing with dicrotophos applied at the maximum label rate; risk to terrestrial plants does 

not exceed the Agency’s risk LOC. 

Specific to the dicrotophos tree injection use pattern, there is uncertainty in the acute and chronic 

risk estimates and corresponding risk LOC exceedances for birds, mammals, terrestrial 

invertebrates, and aquatic invertebrates in the absence of data describing the magnitude of 

residues in tree tissue and exudate(s) and the dispersion of treated trees across the landscape.

Potential effects to federally-listed endangered and threatened species (listed species) based on 

LOC exceedances require an in-depth listed species evaluation determining the potential cooccurrence of listed species and use patterns of dicrotophos. Identified potential risks to listed 

species are summarized in Table 1.

Table 1. Potential Effects to Federally Listed Taxa Associated with Direct Effects from the 

Registered Uses of Dicrotophos.

Listed Plant Taxon Potential Direct Effects

Terrestrial and semi-aquatic 

plants – monocots and dicots No

Aquatic nonvascular plants No

Aquatic vascular plants No

Listed Animal Taxon Potential Direct Effects

Acute Chronic

Terrestrial invertebrates Yes ND

Mammals Yes Yes

Birds Yes Yes

Reptiles Yes Yes

Amphibians Uncertain1 Uncertain1

Freshwater fish No No

Freshwater invertebrates Yes2 Yes2

Mollusks No ND

Estuarine/marine fish No No

Estuarine/marine invertebrates Yes2 Yes2

ND = Not determined

1 Freshwater fish are surrogates for aquatic-phase amphibians, and birds are surrogates for terrestrial-phase amphibians. Since direct effects 

are predicted for birds, but not for fish, it is presumed that amphibians consuming terrestrial food items may experience potential direct 

effects, whereas the potential for direct effects to aquatic-phase amphibians is unlikely.

2 Potential direct effects are uncertain for the tree injection use pattern.
-Page 12 of 102-

2. Problem Formulation

The purpose of problem formulation is to provide the foundation for the environmental fate and 

ecological risk assessment for the registration review risk assessment for the insecticide 

dictrotophos, [(E)-4-dimethylamino-4-oxobut-2-en-2-yl] dimethyl phosphate; CAS#: 141-66-2; 

PC code: 035201). The problem formulation sets the objectives for the risk assessment, 

establishes a risk hypothesis and conceptual model depicting potential risk, and provides a plan 

for analyzing the data and characterizing the risk associated with the uses of dicrotophos

(USEPA, 1998). 

2.1. Nature of Regulatory Action

Under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), all pesticides distributed 

or sold in the United States must be registered by the United States Environmental Protection 

Agency (USEPA). To determine whether a pesticide can be registered, the USEPA evaluates its 

safety to non-target species based on a wide range of environmental and health effects studies. 

In 1996, FIFRA was amended by the Food Quality Protection Act (FQPA), and EPA was 

mandated to implement a new program for the periodic review of pesticides, i.e., registration 

review1. The registration review program is intended to ensure that as the ability to assess risk 

evolves and as policies and practices change, all registered pesticides continue to meet the 

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

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

registration review program, the Agency periodically reevaluates pesticides to make sure that as 

changes occur, products in the marketplace can be used safely.

2.2. Stressor Source and Distribution

2.2.1. Nature of Chemical Stressor

Dicrotophos is a contact, systemic organophosphate insecticide. Organophosphates share a 

common mode of action, binding to the enzyme acetylcholinesterase (AChE), an important 

enzyme in the nervous system of animals. As dicrotophos binds to AChE, the availability of the 

neurotransmitter acetylcholine increases, resulting in paralysis from overstimulation of the 

nervous system. This mode of action is not specific to invertebrates and chemically-mediated 

effects are observed in vertebrates as well.

Dicrotophos is registered for use on cotton and in tree injections. This assessment is based on 

currently labeled maximum application rates for all uses. Specific use rates are discussed in

Section 3.1.

Four products containing dicrotophos are registered: Bidrin 8 (EPA Reg. No. 5481-448), Bidrin 

XP (EPA Reg. No. 5481-552), Bidrin XP II (EPA Reg. No. 5481-9024), and Mauget Inject-ACide B (EPA Reg. No. 7946-11). Bidrin 8, Bidrin XP, and Mauget Inject-A-Cide B are 82% 

dicrotophos. Bidrin XP and Bidrin XP II are co-formulated with bifenthrin (PC code: 128825), a 

 

1 http://www.epa.gov/oppsrrd1/registration_review/
-Page 13 of 102-

pyrethroid insecticide. Bidrin 8, Bidrin XP, and Bidrin XP II are labeled for use on cotton only. 

For use on cotton, dicrotophos can only be applied by ground spray or aerially. Mauget InjectA-Cide B is labeled for tree injection only.

2.2.2. Overview of Pesticide Usage

Though labels indicate potential use of dicrotophos, usage data allows for more accurate 

characterization of actual use of dicrotophos. Data for usage on cotton is derived from USDA 

National Agricultural Statistics Service, private pesticide market research, and the California 

Department of Pesticide Regulation2. Average annual amount of dicrotophos applied to cotton is 

900,000 pounds with an average percent crop treated of 15% and a maximum percent crop 

treated of 20%.

Usage information on the tree injection use pattern was provided by the product registrant, J.J. 

Mauget Co. The tree injection capsules distributed contain 82% dicrotophos active ingredient.

2.3. Receptors

2.3.1. Aquatic and Terrestrial Effects

In ecological risk assessment, a receptor is a biological entity that is exposed to a stressor 

(USEPA, 1998). Consistent with the process described in the Overview Document (USEPA, 

2004), this risk assessment uses a surrogate species approach in its evaluation of dicrotophos. 

Toxicity data generated using surrogate test species, which are intended to be representative of 

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

included under these broader taxonomic groupings. Table 2.1 provides the general taxonomic 

groups and surrogate species tested to evaluate potential ecological effects of dicrotophos to 

broad classes of non-target organisms. Within each of these taxonomic groups, a measure of 

effect is selected from among the available test data. 

Table 2.1. Taxonomic Groups and Test Species Evaluated for Assessing Potential 

Ecological Effects of Dicrotophos.

Organismal Group Typical Species

Birds1 Mallard duck (Anas platyrhynchos)

Bobwhite quail (Colinus virginianus)

Mammals Norway rat (Rattus norvegicus)

Invertebrates Honey bee (Apis mellifera L.)

Freshwater fish2 Bluegill sunfish (Lepomis macrochirus)

Rainbow trout (Oncorhynchus mykiss)

Fathead minnow (Pimephales promelas)

Freshwater invertebrates Water flea (Daphnia magna)

Midge (Chironomus riparius)

Estuarine/marine fish Sheepshead minnow (Cyprinodon variegatus)

Estuarine/marine invertebrates Mysid (Americamysis bahia)

Eastern oyster (Crassostrea virginica)

Terrestrial plants3 Monocots – Crop species, such as corn (Zea mays)

Dicots – Crop Species, such as soybean (Glycine max)

 

2 Dicrotophos is not registered for use on cotton in California
-Page 14 of 102-

Table 2.1. Taxonomic Groups and Test Species Evaluated for Assessing Potential 

Ecological Effects of Dicrotophos.

Organismal Group Typical Species

Aquatic plants and algae Duckweed (Lemna gibba) 

Freshwater Algae (Pseudokirchneriella subcapitata)

1 Birds represent surrogates for terrestrial-phase amphibians and reptiles.

2 Freshwater fish may be surrogates for aquatic-phase amphibians.

3 Four species of two families of monocots, of which one is corn; six species of at least four dicot families, of which one is soybeans.

2.3.2. Ecosystems Potentially at Risk 

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

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

assessment. However, in general terms, terrestrial ecosystems potentially at risk could include 

the treated field or tree(s) and immediately adjacent areas that may receive drift or runoff. Areas 

adjacent to the treated field or tree(s) could include cultivated fields, fencerows and hedgerows, 

meadows, fallow fields or grasslands, woodlands, riparian habitats, and other uncultivated areas. 

Aquatic ecosystems potentially at risk include water bodies adjacent to or downstream from use 

sites, and might include impounded bodies such as ponds, lakes and reservoirs, or flowing 

waterways such as streams or rivers including all adjacent off-channel habitats that are 

permanently or intermittently connected to flowing waters. For uses in coastal areas, aquatic 

habitat also includes marine ecosystems, including estuaries, embayments, and near-shore 

environments such as tidal marshes.

2.4. Assessment Endpoints

Assessment endpoints represent the actual environmental value that is to be protected, defined by 

an ecological entity (species, community, or other entity) and its attribute or characteristics 

(USEPA, 1998). For dicrotophos, ecological entities of potential concern include the following: 

birds, amphibians, reptiles, mammals, freshwater fish and invertebrates, estuarine/marine fish 

and invertebrates, non-target terrestrial plants, terrestrial invertebrates, and aquatic vascular and 

non-vascular plants. The attributes for each of these entities include growth, survival, and 

reproduction (Table 2.3 in Section 2.6.4).

2.5. Conceptual Model

For a pesticide to pose an ecological risk, it must reach ecological receptors in biologically 

significant concentrations. An exposure pathway is the means by which a pesticide moves in the 

environment from a source to an ecological receptor. For an ecological pathway to be complete, 

it must have a source, a release mechanism, an environmental transport mechanism, and a 

feasible route of exposure.

The conceptual model is intended to provide a written description and visual representation of 

anticipated relationships between dicrotophos, potential routes of exposure, and the predicted 

effects for the assessment endpoints. The conceptual model consists of two major components: 

risk hypotheses and a conceptual diagram (USEPA, 1998).
-Page 15 of 102-

2.5.1. Risk Hypotheses

For dicrotophos, the following generic ecological risk hypotheses are being employed for this 

screening-level risk assessment:

Given the currently labeled uses of dicrotophos and its environmental fate properties, 

there is a likelihood of exposure to non-target terrestrial and aquatic organisms. 

When used in accordance with the label, dicrotophos may result in potential adverse 

effects upon the survival, growth, and reproduction of non-target terrestrial and aquatic 

organisms. 

 2.5.2. Conceptual Diagram

The conceptual model is a graphical representation of predicted relationships between ecological 

receptors, both listed (threatened and endangered) and non-listed, and the stressors to which they 

may be exposed. A conceptual model specifies potential routes of exposure, biological receptor 

types, and effects endpoints of potential concern. 

Dicrotophos is expected to degrade quickly in both terrestrial and aquatic environments under 

aerobic and anaerobic conditions, and is considered mobile and nonvolatile. Aerobic and 

anaerobic metabolism are major routes of degradation. The major degradates of dicrotophos 

include SD6167, SD228001, and SD11733. 

Figure 2.1 depicts the stressors, exposure pathways, and potential effects to terrestrial organisms 

from currently labeled uses of dicrotophos. Figure 2.2 depicts the stressors, exposure pathways, 

and potential effects to aquatic organisms from currently labeled uses of dicrotophos. For both 

figures, dotted lines indicate exposure pathways that are expected to have a low likelihood of 

contributing to ecological risk. 

 

 
-Page 16 of 102-

Figure 2.1. Conceptual model for dicrotophos effects on terrestrial organisms.

Stressor

Source

Receptors

Attribute

Change

Dicrotophos applied to use site

Direct

application

Birds / Terrestrialphase amphibians 

/ reptiles / 

mammals

Seeds and 

Leaves

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Food chain

Reduction in prey

Habitat integrity

Reduction in primary productivity

Reduced cover

Community change

Terrestrial/riparian plants

grasses/forbs, fruit, terrestrial 

invertebrates 

Runoff

Mammals/ 

Birds

Exposure

Media

Soil

Ingestion

Ingestion

Ingestion

Ingestion

Dermal uptake/Ingestion

Root uptake

Wet/dry deposition

Mammals/Birds

/Amphibians

Ingestion
-Page 17 of 102-

Figure 2.2. Conceptual model for dicrotophos effects on aquatic organisms.

2.6. Analysis Plan

2.6.1. Residues of Concern

Major degradates of dicrotophos (i.e. those constituting greater than 10% of the applied radiation 

from environmental fate studies) are SD 6167, SD 11733, and SD228001. Dicrotophos readily 

metabolizes to SD 6167 in aerobic soil. Concentrations of SD 11733 and SD 228001were not 

determined in the aerobic soil metabolism study though formation is possible given other sources 

of radiation peaked during Day 1 of the study at 5.5% of applied radioactivity (See Table 3.4). 

Dicrotophos metabolizes to SD 11733 in anaerobic soil with concentrations as high as 12.7% of 

applied radioactivity at study conclusion (33 days).

2.6.2. Preliminary Identification of Data Gaps and Uncertainties 

The tree injection use pattern (EPA Reg. No. 7946-11) does not limit the number of applications 

that can be made in a given year or season. Further, the stated application rate is based on 

number of capsules for a given tree size. However, the size of the capsule can be variable 

according to the label which would result in substantially different applications depending on 

capsule size. The fate of dicrotophos when injected into the tree is also a great uncertainty. The 

Stressor

Source

Receptors

Attribute

Change

Dicrotophos applied to use site

Fish/aquatic-phase 

amphibians

Eggs 

Larvae 

Juveniles / Adults

Individual organisms

Reduced survival

Reduced growth

Reduced reproduction

Food chain

Reduction in algae

Reduction in prey

Habitat integrity

Reduction in primary productivity

Reduced cover

Community change

Surface water/

Sediment

Runoff

Aquatic Animals

Invertebrates

Vertebrates

Exposure

Media

Uptake/gills 

or integument

Ingestion Ingestion

Wet/dry deposition

Soil Groundwater

Uptake/gills 

or integument

Aquatic Plants

Non-vascular

Vascular

Uptake/cell, 

roots, leaves Riparian plant

terrestrial 

exposure 

pathways see 

Figure 2.1
-Page 18 of 102-

rates of degradation in the tree, mobility to various parts of the tree, and formation of degradates 

cannot be characterized by current data. Though it is not formed in soil metabolism, it is 

possible that monocrotophos is formed in the tree as it was found in a dicrotophos dislodgeable 

foliar residue study on cotton (MRID 44731001) 4 days following the last application at 1.6% of 

the maximum detected applied radioactivity and detected in a plant metabolism study (MRID 

13505). This degradate of dicrotophos is more toxic to many taxa than dicrotophos itself. 

2.6.3. Evaluation of Multiple Active Ingredients, Mixtures and Formulated 

Products

The Agency does not routinely include in its risk assessments an evaluation of mixtures of active 

ingredients, either those mixtures of multiple active ingredients in product formulations or those 

in the applicator’s tank. In the case of the product formulations of active ingredients (that is, a 

registered product containing more than one active ingredient), each active ingredient is subject 

to an individual risk assessment for regulatory decision regarding the active ingredient on a 

particular use site. If effects data are available for a formulated product containing more than 

one active ingredient, they may be used qualitatively or quantitatively in accordance with the 

Agency’s Overview Document and the Services’ Evaluation Memorandum (U.S. EPA 2004; 

U.S. FWS/NMFS 2004). 

In the case of dicrotophos, no data on the formulated products Bidrin XP and Bidrin XP II are 

available for fish, aquatic invertebrates, and aquatic and terrestrial plants and mammals. 

However, as these products contain bifenthrin, the effects on invertebrates are expected to be 

enhanced. 

2.6.4. Measures of Exposure 

Measures of exposure are based on aquatic and terrestrial models that estimate environmental 

concentrations of dicrotophos using labeled application rates and methods. For aquatic exposure 

the Tier II model Pesticide Root Zone Model (PRZM v3.12.2; May 12, 2005) linked with 

EXposure Analysis Modeling System (EXAMS v2.98.4.6; Apr. 25, 2005) via the 

PRZM/EXAMS model shell (PE v5.0, Nov. 15, 2006), i.e., PRZM/EXAMS) were used to 

estimate screening-level exposure concentrations in aquatic environments. The measure of 

exposure for aquatic species in surface water bodies receiving runoff and/or spray drift is a return 

frequency of 1-in-10 years of the estimated environmental concentrations (EEC), based on 30-

year simulations. The maximum 1-in-10 year return frequency concentration is used for 

estimating acute exposures to aquatic organisms (plants and animals); the 1-in-10 year 21-day 

mean concentration is used for assessing aquatic invertebrate chronic exposure; and the 1-in-10 

year 60-day mean concentration is used for assessing chronic exposure for fish (and aquaticphase amphibians for which fish serve as surrogates). EECs for dicrotophos include degradates 

of dicrotophos in total toxic residues (TTR) approach. These residues include SD 6167, SD 

11733, and SD228001.

Terrestrial wildlife are exposed to dicrotophos via consumption of residues on food items 

generated by spray applications. For spray applications, the T-REX model (Terrestrial Residue
-Page 19 of 102-

EXposure model; v. 1.5; March 22, 2012) is used to predict dietary exposure to dicrotophos 

residues on foliar surfaces and insects using the Kenaga nomogram as modified by Fletcher 

(Hoerger and Kenaga 1972, Fletcher et al. 1994). A default 35-day foliar dissipation half-life is

used for terrestrial exposure modeling in this assessment. Foliar dissipation data specific to 

dicrotophos (e.g., Willis and McDowell 1987) are not available. Use-specific input values, 

including number of applications, application rate and application interval are also inputs. 

To characterize potential nontarget bird and mammal exposure from spray drift alone, Tier 1 

modules in AgDRIFT (v. 2.1.1, December 2011) were used to estimate how far off-site spray 

drift exposure might occur at a level known to cause adverse effects in bird and mammal toxicity 

studies.

The Screening Tool for Inhalation Risk (STIR v.1.0, November 19, 2010) was used to calculate 

an upper bound estimate of exposure using dicrotophos’s vapor pressure and molecular weight 

for vapor phase exposure as well as the maximum application rate and method of application for 

spray drift. STIR incorporates results from several toxicity studies including acute oral and 

inhalation rat toxicity endpoints obtained from the “six-pack” of core studies, which are a series 

of six guideline studies that are submitted to the Registration Division of the Office of Pesticide

Programs for technical and formulated products3of a pesticide (LD50 8 mg/kg bw, MRID

43893901; and inhlation LC50 >0.059 mg/L, MRID 46411001, respectively) as well as the most 

sensitive acute oral avian toxicity endpoint (domestic goose LD50 1.22 mg/kg bw, MRID

00013439). Based on the results of the STIR model (Appendix D), exposure through inhalation 

of spray drift or the vapor phase of dicrotophos was determined to be a potential pathway of 

concern for avian species on an acute exposure basis but not, however, for mammalian species.

The analysis of the inhalation route in STIR does not consider that aggregation with other 

exposure pathways such as dietary, dermal, or drinking water may contribute to a total exposure 

that has a potential for effects to nontarget animals. However, the Agency does consider the 

relative importance of other routes of exposure in situations where data indicate that pesticide 

exposures through other routes may be potentially significant contributors to wildlife risk 

(USEPA 2004). The risk characterization section (Section 4.3), discusses the impact of 

consideration of other routes of exposure that have been identified as potentially important and 

the degree of certainty associated with screening-level risk assessment conclusions. Detailed

information about STIR v.1.0, as well as the tool, can be found on EPA’s website

(http://www.epa.gov/pesticides/science/models_pg.htm#terrestrial).

The Screening Imbibition Program (SIP v.1.0, released June 15, 2010) was used to calculate an 

upper bound estimate of exposure using dicrotophos’s solubility (11,990 mg/L, MRID

43603202), and compared to the most sensitive acute and chronic avian and mammalian toxicity 

endpoints (see Table 3.12). Drinking water exposure alone was determined to be a potential 

pathway of concern for avian and mammalian species on both an acute and a chronic exposure 

basis. For a sample of the output generated by SIP v.1.0, please see Appendix E.

 

3 Note that all STIR toxicity value inputs are the result of testing with technical grade active ingredient since no 

“six-pack” studies are available for dicrotophos formulated products. 
-Page 20 of 102-

2.6.5. Measures of Effect 

Measures of effect are obtained from a suite of registrant-submitted guideline studies that were 

conducted with a limited number of surrogate test species (Table 2.2). Additional ecotoxicity 

data on dicrotophos were located, based on a May 2012 query of the open literature in the 

publically available version of the ECOTOXicology database 

(ECOTOX; http://cfpub.epa.gov/ecotox/) to identify whether additional, more sensitive 

ecological effects data were available for dicrotophos; however, no more useful data were 

identified (USEPA 2012).

The acute measures of effect used in this baseline assessment are the LD50 (median Lethal Dose), 

LC50 (median Lethal Concentration) or EC50 (median Effects Concentration). These are 

measures of acute toxicity which result in 50% of the respective effect in tested organisms. The 

endpoints for chronic measures of exposure are the no observed adverse effect concentration 

(NOAEC) and the no observed adverse effect level (NOAEL). Toxicity studies were submitted 

for freshwater fish and invertebrates, estuarine/marine fish and invertebrates, aquatic plants, 

birds, mammals, bees, and other terrestrial invertebrates. The endpoints used for risk 

characterization are derived from studies which underwent review and were classified as 

“acceptable” (conducted under guideline conditions and considered to be scientifically valid) or 

“supplemental” (conditions deviated from guidelines but the results are considered to be 

scientifically valid). 

Table 2.2 lists the measures of environmental exposure and ecological effects used to assess the 

potential risks of dicrotophos to non-target organisms. The methods used to assess the risk are 

consistent with those outlined in the document “Overview of the Ecological Risk Assessment 

Process in the Office of Pesticide Programs” (USEPA, 2004).
-Page 21 of 102-

Table 2.2. Measures of Exposure and Measures of Effect Used in Assessing Potential Risks 

Associated with the Proposed Uses of Dicrotophos.

Assessment Endpoint Surrogate Species and Measures of 

Ecological Effect1 Measures of Exposure

Birds2

Survival

Lowest acute LD50 (single oral dose test) 

and LC50 (subacute dietary test)

Upper-bound residues on 

food items

Reproduction 

and Growth

Lowest NOAEC

(21-week reproduction test)

Mammals

Survival Lowest acute LD50 (single oral dose test)

Reproduction 

and Growth

Lowest NOAEC 

(2-generation reproduction test)

Aquatic Animals (Fish and 

invertebrates)3

Survival Lowest tested LC50 or EC50

(acute toxicity test)

Peak EECs4

Reproduction 

and Growth

Lowest NOAEC (early life-stage or full 

life-cycle tests)

21-day EECs for invertebrates 

and 60-day EECs for fish4

Terrestrial plants5 Survival and 

growth

Lowest EC25 (for non-listed plants) and 

corresponding NOAEC (for listed 

plants)

(endpoints derived for monocots and 

dicots from seedling emergence and 

vegetative vigor studies)

Estimates of runoff and spray 

drift to non-target areas

Insects6

Survival 

Lowest honeybee LD50 (acute contact 

test) Upper-bound residues on tall 

grass7

Aquatic plants (vascular 

and non-vascular)

Survival and 

growth

Lowest EC50 (for non-listed plants) and 

corresponding NOAEC or EC05 (for 

listed plants)

Peak EECs4

1 The most sensitive species tested within taxonomic groups is used for screening-level risk assessments.

2 Birds represent surrogates for terrestrial-phase amphibians and reptiles.

3 Freshwater fish represent surrogates for aquatic-phase amphibians.

4 Aquatic EECs are based on modeling described in Section 3.2.2.1.

5 Four species of two families of monocots - one is corn, six species of at least four dicot families, of which one is soybeans.

6 Risk to terrestrial invertebrates from dicrotophos use is quantitatively evaluated against the acute listed terrestrial invertebrate LOC of 0.4.

7 The tall grass residue value from the T‐REX model (v. 1.5) is used as a surrogate for dicrotophos concentrations in nectar and pollen.

2.6.6. Integration of Exposure and Effects

Exposure and toxicity data are integrated in order to evaluate the risks of adverse ecological 

effects on non-target species. For the screening-level risk assessment of dicrotophos, the 

deterministic risk quotient (RQ) method is used to compare estimated exposure concentrations 

with measured toxicity values. The RQ method involves dividing point estimates of 

environmental concentrations by acute and chronic toxicity values. The resulting unitless RQs 

are then compared to the Agency’s Levels of Concern (LOC) (USEPA, 2004) (Table 2.3). These 

criteria are used to indicate when applications of dicrotophos, as directed on the registered labels, 

have the potential to cause adverse effects to listed and non-listed non-target organisms.
-Page 22 of 102-

Table 2.3. Agency Risk Quotient (RQ) Metrics and Levels of Concern (LOC) Per Risk 

Class.

RISK CLASS RISK DESCRIPTION RQ LOC

Aquatic Animals (fish and invertebrates)

Acute Potential for effects to non-listed animals from acute 

exposures

Peak EEC/LC50

1 0.5

Acute 

Restricted Use

Potential for effects to animals from acute exposures

Risks may be mitigated through restricted use classification Peak EEC/LC50

1 0.1

Acute Listed 

Species

Listed species may be potentially affected by acute 

exposures

Peak EEC/LC50

1 0.05

Chronic Potential for effects to non-listed and listed animals from 

chronic exposures

60-day EEC/NOAEC 

(fish)

1

21-day EEC/NOAEC 

(invertebrates)

Aquatic Plants

Non-Listed Potential for effects to non-listed plants from exposures Peak EEC/LC50

1 1

Listed Potential for effects to listed plants from exposures Peak EEC/NOAEC 1

Terrestrial Animals (mammals and birds)

Acute Potential for effects to non-listed animals from acute 

exposures

EEC/LC50 (Dietary)

0.5

EEC/LD50 (Dose)

Acute 

Restricted Use

Potential for effects to animals from acute exposures

Risks may be mitigated through restricted use classification

EEC/LC50 (Dietary)

0.2

EEC/LD50 (Dose)

Acute Listed 

Species

Listed species may be potentially affected by acute 

exposures

EEC/LC50 (Dietary)

0.1

EEC/LD50 (Dose)

Chronic Potential for effects to non-listed and listed animals from 

chronic exposures EEC/NOAEC 1

Terrestrial and Semi-Aquatic Plants

Non-Listed Potential for effects to non-target, non-listed plants from 

exposures

EEC/ EC25 1

Listed Plant Potential for effects to non-target, listed plants from 

exposures

EEC/ NOAEC

1

EEC/ EC05

1 LC50 or EC50. 

3. Analysis

3.1. Use Characterization

Use patterns 

National Labels

Four products containing dicrotophos are registered: Bidrin 8 (EPA Reg. No. 5481-448), Bidrin 

XP (EPA Reg. No. 5481-552), Bidrin XP II (EPA Reg. No. 5481-9024), and Mauget Inject-ACide B (EPA Reg. No. 7946-11). Bidrin 8, Bidrin XP, and Mauget Inject-A-Cide B are 82% 

dicrotophos. Bidrin XP and Bidrin XP II are co-formulated with bifenthrin (PC code: 128825), a 
-Page 23 of 102-

pyrethroid insecticide. Bidrin 8, Bidrin XP, and Bidrin XP II are labeled for use on cotton only. 

Mauget Inject-A-Cide B is labeled for tree injection only. 

For use on cotton, dicrotophos can be applied only by ground spray or aerially. It can be applied 

early season (emergence to pre-bloom) at 0.2 lb a.i./A and late season (first bloom to 30 days 

prior to harvest) at 0.5 lb a.i./A. One application may be made early season and two applications 

may be made late season for a maximum seasonal application rate of 1.2 lbs a.i./A. Dicrotophos 

is applied to cotton to control thrips, cotton fleahoppers, aphids, spider mites, grasshoppers, boll 

weevils, leaf footed bug, plant bugs, and stink bugs. Products co-formulated with bifenthrin 

control additional pests.

For the tree-injection use pattern, application timing is dependent on the appearance or life stage 

of the target pest. Injections are made via holes drilled into the base of a given tree where 1, 2 or 

3 milliliter capsules are injected (82% a.i.). The number of capsules to be applied is determined 

by measuring the diameter of the tree at chest height and dividing by two. The size of the 

capsule is not specified in this application calculation. The following tree species are listed on 

the label: Ash, Beech, Birch, Flowering crabapples (non-crop), Dogwood, Elm, Black Gum, 

Hackberry, Linden, Locust, Maples (non-crop), Oaks, Pines, Flowering Stone Fruit (non-crop), 

Sycamore (Plane Tree), and Willow. The label contains no clause which explicitly limits 

applications to those species included on the label. 

Use patterns for dicrotophos are presented in Table 3.1. 

Table 3.1. Use Patterns for Dicrotophos

Crop Registration (application timing)

Max single 

application

Max season 

application

Min interval 

(days)

Tree Injection

National (Pest dependent)

Diameter of tree 

(inches) divided 

by two equals 

number of 3mL

capsules to insert Not specified Not specified

Cotton National (Emergence to 30 days 

pre-harvest) 0.5 lb a.i./A 1.24 14

3.2. Exposure Characterization

3.2.1. Environmental Fate and Transport Characterization

The general physical/chemical properties of dicrotophos are summarized in Table 3.2. 

Environmental fate and transport properties of dicrotophos are characterized in further detail in 

the following sections. The Agency’s understanding of these properties is limited by the 

available dataset. 

Table 3.2 General Physical and Chemical Properties of Dicrotophos

Property Value Reference

Chemical Name (E)-2-dimethylcarbamoyl-1-

 

4 An early season application at 0.2 lb/A is allowed by the dicrotophos cotton labels
-Page 24 of 102-

(IUPAC) methylvinyl dimethyl phosphate

CAS Registry Number 141-66-2 Dicrotophos RED

Molecular Formula C8H16NO5P Dicrotophos RED

Molecular Weight 

g/mol

237.19 Calculated

Physical State Yellow brown liquid MRID 40188003

Vapor Pressure, mmHg 7.0E-5 @ 25 oC MRID 43500401

Aqueous Solubility, 

mg/L

11,990 MRID 43603202, MRID 43603201

Octanol-Water 

Partition Coefficient 

(Log Kow)

0.3883 (E-isomer)

-3.318 (Z-isomer)

MRID 43603204

Henry’s Law Constant 3.13 E-11 atm-m3/mol Calculated from vapor pressure and solubility

When dicrotophos is released into the environment, it degrades quickly primarily via aerobic soil 

metabolism. Dicrotophos is not persistent (field dissipation half-life of 2.2 days) in the 

environment, is mobile in soil (estimated average Koc value is 73 ml/g o.c.), and has a very high 

solubility. It is not expected to accumulate in ground water because of its short half-life. A 

summary of the submitted environmental fate and transport data is summarized below in Table 

3.3.

Degradates of dicrotophos include SD 228001, resulting from demethylation at the phosphate 

group, and SD 6167 and SD 11733 resulting from cleavage at the phosphate group. SD 6167 

was detected in submitted hydrolysis, aerobic and anaerobic soil metabolism studies. SD 11733 

and SD 228001 were detected in the anaerobic soil metabolism and hydrolysis studies, 

respectively. 

Table 3.3 Environmental Fate Data Summary for Dicrotophos

Input Parameter Value Source/comment

Hydrolysis half-life pH 5: 117 days @ 25C

pH 7: 72 days @ 25C

pH 9: 28 day @ 25C

MRID 160823.

Aqueous Photolysis half-life Stable MRID 160824 

Soil Photolysis half-life Stable MRID 160825

Aerobic Soil metabolism half-life 2.7 days \ MRID 160826

Anaerobic Soil metabolism half-life 8 days MRID 160827

Degradation data on SD6167 was 

requested in DER

Anaerobic aquatic metabolism halflifeNo data Assumed stable

Aerobic Aquatic metabolism half-life No data Assumed stable

Organic carbon normalized soil 

partition coefficient Koc

73 mL/ g o.c. MRID 160828

Adsorption Coefficient 1.24 mL./g MRID 160828
-Page 25 of 102-

Input Parameter Value Source/comment

Terrestrial field dissipation 2.2 days

MRID 41114301

3.2.1.1. Transport and Mobility

Dicrotophos is transported off site primarily through spray drift leaching, and runoff for the 

cotton use pattern. Through the tree injection use pattern, dicrotophos is transported off site 

through run off, from residues contained within tree litter, and leaching.

Dicrotophos is not volatile, with a vapor pressure of 7.0E-5 torr at 25 oC and a Henry’s law 

constant of 3.13*10-11 atm-m3/mol. The reported log Kow for dicrotophos at 25oC for pH 7 was -

0.5.

Dicrotophos is mobile based on FAO Soil Mobility Classification Guidance (USEPA, 2006a), 

with estimated adsorption coefficients ranging from 0.07 to 3.58 mL/g. Adsorption correlates 

most with clay content as opposed to organic carbon content. Therefore the adsorption constant

(KD) is used for modeling purposes as opposed to the organic carbon partition coefficient (KOC).

3.2.1.2. Degradation

Dicrotophos hydrolyzes at all tested pHs with degradation increasing with increasing pH. Halflives range from 117 days to 28 days from pH 5 to pH 9 at 25oC (MRID 160823). It is stable to 

photolysis in water and on soil (MRIDs 160824 and 160825). 

Dicrotophos biodegrades quickly in aerobic soil, with a reported half-life of 2.7 days (parentonly half-life; MRID 160826). Dicrotophos readily metabolizes to SD 6167 in aerobic soil. 

Concentrations of SD 11733 and SD 228001were not determined in the aerobic soil metabolism 

study though formation is possible given other sources of radiation peaked during Day 1 of the 

study at 5.5% of applied radioactivity. Dicrotophos metabolizes to SD 11733 in anaerobic soil 

with concentrations as high as 12.7% of applied radioactivity at study conclusion (33 days). 

Figure 3.1 illustrates a predicted degradation pathway under aerobic conditions. 
-Page 26 of 102-

Figure 3.1 Predicted Transformation Pathway under Aerobic Conditions

3.2.1.3. Field Studies

One terrestrial field dissipation study has been submitted for a silt loam soil in Mississippi and 

Georgia though the data from Georgia is unacceptable (MRID 41114301). Dicrotophos 

dissipated with a half-life of 2.2 days from silt loam soil in Mississippi that was treated three 

times at 7-day intervals with 0.5 lb a.i./A resulting in a total of 1.5 lbs a.i./A applied. Residues 

were not detected below the 0-6 centimeter soil horizon. The application interval is shorter 

(current is 14 days) and seasonal application rate is higher (current is 1.2 lbs a.i./A) in this study 

than current label instructions. Degradates were not analyzed but residues would have likely 

been present with an aerobic soil metabolism (MRID 160826) detecting SD 6167 at 20% of 

applied radioactivity 5 days after application. 

Monitoring Data

Surface water monitoring data from the USGS National Water-Quality Assessment Program 

(NAWQA) and USDA’s Pesticide Data Program for dicrotophos indicate 57 detections in seven 

states (Colorado, Georgia, Louisiana, Minnesota, Mississippi, North Carolina, and Texas) from 

approximately 8,500 samples. The peak detection of 6.83 parts per billion occurred in 

Washington County, Mississippi on Bogue Phalia in 2005. All other detections were for 

concentrations less than 0.3 parts per billion.It appears targeted monitoring was occurring at the 

site as 14 samples resulted in 14 detections between the days of June 21 and August 24 from 

Dicrotophos

SD 

6167

SD 

22800

1

SD 

11733
-Page 27 of 102-

2005 to 2008. Sample frequency varied drastically though sampling occurred on consecutive 

days in some instances including the day following the peak detection of 6.83 ppb. The 

subsequent concentration was 0.17 ppb. This rapid reduction in concentration indicates that peak 

concentrations are highly likely to be missed without high frequency monitoring. NAWQA 

reports 65 detections from 99 samples in Mississippi indicating dicrotophos use areas are 

targeted among sampling sites. However, targeting monitoring high frequency monitoring 

around dicrotophos application and precipitation events is not necessarily occurring and peak 

detections may be missed 

No groundwater monitoring data for dicrotophos was found. However, occurrence of 

dicrotophos in groundwater may be expected since total toxic residues are mobile and persistent 

to hydrolysis and anaerobic metabolism. 

3.2.1.4. Bioconcentration

Dicrotophos is not expected to bioconcentrate due to its low log Kow (-3.318 to 0.3883) and low 

bioconcentration of a structurally similar chemical and metabolite, monocrotophos. 

Monocrotophos did not bioconcentrate to detectable levels in a static system (LOD = 0.03 ppm; 

MRID 155661). 

3.2.1.5. Environmental Degradates

The major degradates resulting from environmental degradation processes are SD 228001, SD 

6167, and SD 11733 (Table 3.4). These transformation products were identified in the 

environmental fate studies at concentrations >10% of the applied radioactivity and are 

considered in the environmental exposure assessment. 

In the neutral pH hydrolysis study, the demethylation product, SD 228001, formed at 

concentrations up to 18.8% of applied radioactivity 28 days after treatment. In an aerobic soil 

metabolism study, the phosphate group was cleaved forming SD 6167 at concentrations up to 

20.0% of applied radioactivity 5 days after treatment. In an anaerobic soil metabolism study, SD 

11733 formed at concentrations up to 12.6% of applied radioactivity 36 days after treatment. 

Considering the tree-injection use pattern, degradates found in foliar residue studies are of 

special interest as they provide some information related to plant metabolism. Monocrotophos

(dimethyl (E)-1-methyl-2-(methylcarbamoyl)vinyl phosphate), a demethylation product not 

found in environmental fate studies, was found in a dicrotophos dislodgeable foliar residue study 

on cotton (MRID 44731001) 4 days following the last application at 1.6% of the maximum 

detected applied radioactivity. This detection indicates that monocrotophos may form as a result 

of plant metabolism and could be a significant metabolite when injected in trees.
-Page 28 of 102-

Table 3.4. Table of Transformation Products Formed in Environmental Fate Studies

Common Name IUPAC Name Study in Which Found 

(Maximum % of Parent, or 

equivalent)

Reference 

MRID

SD 6167 N,N-dimethyl-3-

oxobutanamide

Aerobic soil metabolism 

(20.0%, 5 days after treatment) 160826

SD 228001 {[1-

(dimethylcarbamoyl)pr

opan-2-

yl]oxy}(methoxy)phos

phinic acid

Hydrolysis, pH 7 (18.8%, 28

days after treatment) 160823

SD 11733 3-hydroxy-N,Ndimethylbutanamide

Anaerobic soil metabolism 

(12.7%, 36 days after 

treatment)

160827

Monocrotophos 3-

[(dimethoxyphosphoryl

)oxy]-N-methylbut-2-

enamide Foliar residue study

(1.6%, 4 days after treatment)

44731001
-Page 29 of 102-

3.2.2. Measures of Aquatic Exposure

3.2.2.1. Surface Water Exposure to Dicrotophos

Surface Water Exposure to Dicrotophos

The Tier II model Pesticide Root Zone Model (PRZM v3.12.2; May 12, 2005; Carousel et al., 

undated) linked with EXposure Analysis Modeling System (EXAMS v2.98.4.6; Apr. 25, 2005; 

Burns, 2004) via the PRZM/EXAMS model shell (PE v5.0, Nov. 15, 2006), i.e., 

PRZM/EXAMS) were used to estimate screening-level exposure concentrations in aquatic 

environments. The PRZM model simulates pesticide movement and transformation on and 

across the agricultural field resulting from crop applications. The EXAMS model simulates 

pesticide concentrations in water due to loading via runoff, erosion, and spray drift, assuming a 

standard 1-ha pond, 2-m deep (20,000 m3) with no outlet that borders a 10-ha treated field. 

Simulations are for 30 years, from which the Agency estimates peak values that are expected to 

recur on average once every ten years, based on time series of daily estimated concentrations. 

The coupled PRZM and EXAMS models and user’s manuals are available from the U.S. 

Environmental Protection Agency Water Models web-page (USEPA, 2011b).

Exposure estimates generated using the standard pond are intended as surrogates for potential 

concentrations in a wide variety of vulnerable water bodies, including prairie potholes, playa 

lakes, vernal pools, other wetlands, man-made and natural ponds, and ephemeral and first-order 

streams. Innumerable site-specific factors will tend to make such water bodies more or less 

vulnerable than the standard pond. Static water bodies that have larger ratios of pesticide-treated 

drainage area to water body volume are generally expected to have higher peak concentrations 

than the standard pond’s EECs. Such water bodies may be smaller in size, and/or have larger 

drainage areas. However such water bodies may be more likely to overflow and discharge 

pesticide in their effluent, whereas the standard pond has no discharge. As watershed size 

increases, it becomes increasingly unlikely that the entire watershed is planted with a single crop 

that is all treated simultaneously with a pesticide. Headwater streams may have peak 

concentrations that are higher than those predicted for the standard pond, but such concentrations 

will likely persist for only short periods of time or distance, as they are carried downstream and 

diluted with water originating elsewhere.

The tree injection use pattern is not thought to be a significant source of aquatic exposure. 

Aquatic exposures could occur from the chemical entering soil environments and subsequently 

entering aquatic environments. This could occur if the chemical is translocated primarily to the 

leaves, and the leaves fall to the soil and decompose. This exposure pathway was proven 

realistic in a bioassay where leaves were collected from trees 72 hours after dicrotophos injection 

and blended leaves (100 mL water/g of foliage) were introduced into Daphnia pulex cultures. 

The bioassay results indicate that dicrotophos concentrations in the foliage were higher when the 

injections were made in multiple bore holes (the same application rate as the treatments with a 

single bore injection); daphnid mortality ranged from 74% to 100% in these multi-hole 

treatments (Donley, 1967). Dicrotophos degrades readily in soil, and through this process of 

translocation in the tree and potential foliage degradation over periods longer than 72 hours, it 

can be expected that dicrotophos will be substantially degraded before it reaches aquatic 
-Page 30 of 102-

environments. Preliminary EECs, assuming all dicrotophos applied to the tree is available on the 

soil surface, indicate values less than half those generated representing the cotton use pattern

(Table 3.6). The following conservative assumptions were made in the generation of tree 

injection EECs: 1) They were generated using the Florida Citrus PRZM/EXAMS scenarios, one 

of the more conservative PRZM/EXAMS scenarios. Dicrotophos is not likely to be used in 

citrus orchards though it is not specifically restricted on the label. 2) One 72” DBH tree is 

assumed to be treated per acre throughout the watershed of concern. Considering the labor 

intensive application method, it is not likely that trees will be consistently treated throughout a 

landscape and/or watershed 3) The model inputs assume all applied dicrotophos is translocated, 

undegraded, to the leaves which fall uniformly and make available the full application at a single 

point in time across all treated trees in a watershed. The complete availability of dicrotophos in 

foliage and the precise coordination of leaf abscission is highly unlikely but contributes to the 

conservativeness of the approach. 

The general chemical and environmental fate data for dicrotophos listed in Table 3.2-3.3 were 

used for generating model input parameters for PRZM and EXAMS (listed in Table 3.5). 

Chemical specific and model input values were chosen in accordance with current divisional 

guidance (USEPA, 2009). 

Table 3.5. PRZM/EXAMS input parameter values for dicrotophos. Use on cotton and tree 

injections

PARAMETER (units) VALUE(S) SOURCE COMMENT

Application Rate (kg a.i./ha) Cotton

Emergence= 0.2242

Bloom= 0.5605

Seasonal Max= 

1.345

Tree Injection

Single= 0.2556

Seasonal= 0.7668

Cotton

Emergence to pre-bloom = 0.2 lb

a.i./A

1

st bloom to 30 days pre-harvest = 

0.5 lb a.i./A with two applications 

allowed

Total annual application allowed = 

1.2 lb a.i./A

Tree injection

72 inch DBH tree assumed on one 

acre with 3mL capsules administered. 

Two retreatments are assumed.

Number of Applications 3

Interval between Applications 

(days)

14 Labeled interval for cotton. 

Assumed interval for tree injection

Molecular weight (g/mol) 237.19

Henry’s Law Constant (atmm3

/mol)

3.13 x 10-11 Dicrotopho

s RED

Vapor Pressure (torr) 7 x 10-5 43500401
-Page 31 of 102-

PARAMETER (units) VALUE(S) SOURCE COMMENT

Solubility in Water @ 20 OC, 

(mg/L or ppm)

11,990 43603202, 

43603201

Soil Partition Coefficient (mL/g) KD = 1.24 160828 Lowest non-sand KD is used because 

adsorption does not correlate with 

organic carbon content (An Rf study 

indicates SD 6167 is likely more 

mobile than parent dicrotophos 

[MRID 160829])

CAM (Chemical Application 

Method)

1 foliar spray; pre-plant or preemergence, unincorporated

Depth of Incorporation (inches) 0 –

Application efficiency (decimal) Cotton

0.95 

Tree Injection

1.00 

Cotton

Aerial application permitted on label

Tree Injection

No drift

Spray drift fraction (decimal) Cotton

0.05

Tree Injection

0.00

Application date (day/month) Crop Emergence 

date as specified by 

PRZM scenario and 

confirmed by OP 

cumulative

Initial application to cotton can be 

made from crop emergence to prebloom

Hydrolysis Half-life (days) 72 (parent)

990 (TTR)

160823 SD 6167 and SD228001 are included 

in TTR. SD11733 not detected in 

study.

Aqueous Photolysis Half-life @ 

pH 7 (days)

Stable 160824

Aerobic Aquatic Metabolism 

Half-life (days)

16.2 (parent)

17.4 (TTR)

SD 228001, SD 6167, and SD 11733 

are included in TTR.

TTR included in half-life estimation. 

2X aerobic soil metabolism 

parameter per Input Parameter 

Guidance1
-Page 32 of 102-

PARAMETER (units) VALUE(S) SOURCE COMMENT

Anaerobic Aquatic Metabolism 

Half-life (days)

48 (parent)

Stable (TTR)

160827

SD 228001, SD 6167, and SD 11733 

are included in TTR.

Parent anaerobic soil metabolism 

half-life = 8 days. 3X half-life due to 

single half-life value and 2X for 

estimating an aquatic half-life with a 

soil half-life per Input Parameter 

Guidance1.

Aerobic Soil Metabolism Halflife (days)8.1 (parent)

8.7 (TTR)

160826 Parent only and TTR half-lives 

calculated to be approximately the 

same (2.7 days and 2.9 days, 

respectively). TTR in this instance 

includes only SD 6167. Because 

only one half-life is available, 3X is 

used per Input Parameter Guidance1

1 “Input Parameter Guidance” refers to Guidance for Selecting Input Parameters in Modeling the Environmental Fate 

and Transport of Pesticides; Version 2.1, October 22, 2009. 

The modeled aquatic EECs resulting from the dicrotophos uses (listed in Table 3.6) were used 

for risk estimation in this screening-level assessment. The model input and output filenames 

supporting these values are listed in Appendix A. 

Table 3.6. Modeled Aquatic Surface Water 1-in-10-year EECs for Currently labeled Uses 

of Dicrotophos

Residues Modeled Crop Scenario 

(application date)

1-in-10 year 

peak daily, 

μg/L

1-in-10 year, 

peak 21-day 

average, μg/L

1-in-10 year, 

peak 60-day 

average, μg/L

Total Toxic 

Residues

MS Cotton 14.19 11.90 7.28

NC Cotton 12.89 10.31 7.71

TX Cotton 16.87 12.26 6.92

FL Citrus (Tree 

Injection) 8.91 5.80 4.25

Parent Only MS Cotton 13.98 10.40 5.85

NC Cotton 12.43 9.12 6.17

TX Cotton 16.33 10.73 5.54

3.2.2.2 Aquatic Spray Drift Exposure to Dicrotophos
-Page 33 of 102-

Spray drift exposure to aquatic organisms is also a viable exposure pathway. Concentrations of 

0.6 μg/L in water trigger the Acute Endangered Species LOC (0.05) (based on the Daphnia 

magna acute toxicity endpoint of 12.7 ppb). The 90th percentile mean of this concentration is 

achieved at distances up to 331 feet from the edge of field according to AgDRIFT v 2.0.10 for 

aerial applications. This buffer distance would be reduced in the case of non-listed species. The 

use of drift reduction technology (DRT) could reduce the distance necessary for to prevent 

exceedances of the LOC but DRT is not currently required on dicrotophos labels. Ground 

applications yielded concentrations as high as 0.6 ppb only up to three feet from the edge of field

though all broadcast uses allow aerial applications.

Spray drift exposure to dicrotophos was determined using the maximum single application rate 

(0.5 lb a.i./A for subsequent applications to cotton) The distance to water body from edge of field 

was determined for an initial average concentration of 0.6 ppb in Tier I Ground and Tier I Aerial 

aquatic assessments. The default ASAE Fine to Medium droplet size distribution was assumed.

Exposure from volatility off application site is not addressed due to the low volatility of 

dicrotophos.

3.2.3. Measures of Terrestrial Exposure

3.2.3.1. Terrestrial Wildlife

Exposure estimates for terrestrial organisms assumed to be in the target area or in an area 

exposed to off-site deposition are derived using the T-REX model (version 1.5.1, 03/22/2012). 

This model incorporates the Kenaga nomograph, as modified by Fletcher et al. (1994), which is 

based on a large set of field residue data. The upper limit values from the nomograph represent 

the upper bound of residue values from actual field measurements (Hoerger and Kenaga 1972). 

The Fletcher et al. (1994) modifications to the Kenaga nomograph are based on measured field 

residues from 249 published research papers, including information on 118 species of plants, 121 

pesticides, and 17 chemical classes. Based on these data, T-REX assumes a 35-day foliar 

dissipation half-life in the absence of other data. 

Terrestrial Exposure from Tree Injection Use Pattern

The dicrotophos tree injection use pattern presents a novel exposure pathway not considered in 

EFED’s standard exposure models. Tree injections are administered through drilled holes near 

the base of the tree which allows the pesticide to be conducted through the xylem (tissue for 

transporting sap) to the branches and leaves of the tree. This distribution results in 

concentrations in the leaves as much as thirty times higher than other surrounding plant tissues 

(Mota-Sanchez, et al., 2009). A conservative estimate of exposure would assume all pesticide is 

concentrated in the leaves. Martin, et al (1998) derived allometric equations for the estimation 

of various mass and volume attributes of deciduous tree species. For instance, total foliage of a 

red oak (Quercus rubra) can be estimated through the following equation:

Log(Y) = −2.514 + 2.326 ∗ log(DBH)
-Page 34 of 102-

where Y is the mass of the foliage in kilograms and DBH is the diameter of the tree at breast 

height in centimeters. Assuming a DBH of 20 inches (50.8 cm), the mass of the foliage is 28 kg 

or 63 lbs. Dicrotophos tree injections can be applied at a rate of 1 capsule per 2 inches of DBH. 

A capsule can have as much as three milliliters of formulated product and the formulated product 

is composed of 8 lbs of active ingredient per gallon. Given this:

20 in.DBH

1

×

1 capsule

2 in.DBH

×

3 mL

1 capsule ×

1 gallon

3785 mL

×

8 lbs a. i.

1 gallon = 0.0634 lbs a. i./tree

Distributing the application of dicrotophos evenly and exclusively to the foliage results in a dose 

of 0.001 lb of a.i./lb of foliage or 1,000 ppm.

A less conservative scenario is one in which the dose is evenly distributed throughout the 

sapwood and foliage. This even distribution may occur at a brief point in the tree injection 

application but shortly thereafter the dose would concentrate in its eventual repository, the 

foliage. Therefore this assumption may not be sufficiently conservative to address exposure to 

foliage. Sapwood includes the phloem, the facilitator of sucrose, and the xylem, the much larger 

facilitator of water and other nutrients. The xylem is thought to be the most effective element for 

conducting tree injection application to the leaves. The mass of the sapwood for the red oak, the 

same tree used in the calculation above, can be estimated through the following equation:

Log(Y) = −4.179 + 2.495 ∗ log(DBH)

where Y is the total sapwood volume in cubic meters. Assuming the same DBH of 20 inches 

and a red oak sapwood density of 740 kg/m3(Engineering Toolbox, 2012), the sapwood 

represents 880 kg or 1,942 lbs. Distributing the application of dicrotophos evenly and 

exclusively, as calculated previously, to the foliage and sapwood results in a dose of 0.00003 lb

a.i./lb of foliage or 31 ppm. 

These estimated concentrations can be compared indirectly to results from a study testing 

toxicity from exposure to foliage from dicrotophos injected trees (Donley, 1967). In the study, 

there was 74% to 100% mortality of Daphnia pulex after being exposed to 100 mL distilled 

water/g foliage. A similar mortality rate was seen when Dapnia magna were exposed to 20 to 30

μg/L dicrotophos (MRID 43787901). Given these two studies and assuming similar sensitivity

between the two Daphnia species, a concentration of 2 to 3 ppm may be assumed in the foliage 

of the Donley study. This estimate is an order of magnitude lower than the least conservative 

method for estimating tree injection exposure. Given the uncertainty in extrapolating toxicity 

across species and the indirect method of determining concentration, this is used to characterize 

the previous estimates as conservative but it also provides some validation for the tree injection 

exposure approach as a whole. 
-Page 35 of 102-

3.2.3.2. Terrestrial Plants

No significant effects to terrestrial plants were recorded in guideline plant studies. Therefore 

terrestrial spray drift modeling was not conducted.

3.3. Ecological Effects Characterization 

In screening-level ecological risk assessments, effects characterization describes the types of 

effects a pesticide can have on aquatic and terrestrial organisms. To date, toxicity tests for 

amphibian or reptiles are not required; birds are used as surrogates for reptiles and terrestrialphase amphibians and freshwater fish are used as surrogates for aquatic-phase amphibians. This 

characterization is based on the registrant-submitted toxicity data for birds, mammals, fish, 

invertebrates, and plants for dicrotophos.

This assessment evaluates the potential for dicrotophos to directly or indirectly affect listed 

species or modify designated critical habitat. As previously discussed in Section 2.7, assessment 

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

as well as indirect effects, such as reduction of the prey base or modification of habitat. In 

addition, potential modification of critical habitat is assessed by evaluating effects to the PCEs, 

which are components of the critical habitat areas that provide essential life cycle needs of listed 

entities. 

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

for each taxon is used for risk estimation. For this assessment, evaluated taxa include aquaticphase amphibians, freshwater fish, freshwater invertebrates, aquatic plants, birds (surrogate for 

terrestrial-phase amphibians), mammals, terrestrial invertebrates, and terrestrial plants. 

Toxicity endpoints are established based on data generated from guideline studies submitted by 

the registrant, and from open literature studies that meet the criteria for inclusion into the 

ECOTOX database maintained by EPA/Office of Research and Development (ORD) (U.S. EPA, 

2004). Open literature data presented in this assessment were obtained from ECOTOX 

information compiled in May 2012. In order to be included in the ECOTOX database, papers 

must meet the following minimum criteria:

(1) the toxic effects are related to single chemical exposure;

(2) the toxic effects are on an aquatic or terrestrial plant or animal species;

(3) there is a biological effect on live, whole organisms;

(4) a concurrent environmental chemical concentration/dose or application rate is 

reported; and

(5) there is an explicit duration of exposure.

Data that pass the ECOTOX screen are evaluated along with the registrant-submitted data, and 

may be incorporated qualitatively or quantitatively into this endangered species assessment. In 

general, effects data in the open literature that are more conservative than the registrantsubmitted data are considered. The degree to which open literature data are quantitatively or 

qualitatively characterized is dependent on whether the information is relevant to the assessment 
-Page 36 of 102-

endpoints (survival, reproduction, and growth) identified in Section 2.8. For example, endpoints 

such as behavior modifications are likely to be qualitatively evaluated, because quantitative 

relationships between modifications and reduction in species survival, reproduction, and/or 

growth are not available. 

In addition to registrant-submitted and open literature toxicity information, other sources of 

information, including use of the acute probit dose-response relationship to establish the 

probability of an individual effect and reviews of the Ecological Incident Information System 

(EIIS), are conducted to further refine the characterization of potential ecological effects 

associated with exposure to dicrotophos. A summary of the available aquatic and terrestrial 

ecotoxicity information, use of the probit dose-response relationship, and the incident 

information for dicrotophos are provided in Sections 4.1 through 4.4, respectively.

Toxicity data are available for monocrotophos, a pesticidal active ingredient (PC code: 058901) 

that was registered for use in the United States until its cancellation in 1991. Monocrotophos is a 

highly toxic metabolite (golden eagle LD50 = 0.2 mg/kg-bw) that can be formed by 

demethylation of dicrotophos. Laboratory studies on the degradation of dicrotophos do not 

indicate that monocrotophos forms in soil or water in any significant quantities. However, 

monocrotophos may be a significant metabolite in plants (MRIDs 44731001 and 13505). The 

amount of monocrotophos that can form from dicrotophos and the rate of formation and decline 

in and/or on foliage soon after application is an uncertainty.

No toxicity data were available on dicrotophos mixtures with other pesticides. Two multi-a.i.

products are registered for dicrotophos, Bidrin XP and Bidrin XP II. Bidrin XP contains 4 

pounds of 82% a.i. dicrotophos and 1 pound of 25.1% a.i. bifenthrin per gallon. Bidrin XP II 

contains 4 pounds of 43.1% a.i. dicrotophos and 1 pound of 10.8% a.i. bifenthrin per gallon.

3.3.1. Aquatic Toxicity Assessment

The most sensitive acute and chronic effects measurement endpoints associated with dicrotophos

exposure to freshwater and estuarine/marine species are summarized in Table 3.11. All 

acceptable and supplemental studies available for dicrotophos are described below.

Results of acute toxicity studies of freshwater and estuarine/marine organisms indicate that 

dicrotophos is slightly to moderately toxic to fish and very highly toxic to aquatic invertebrates

on an acute exposure basis. Statistically significant reductions in growth (i.e., length and weight) 

were seen in aquatic invertebrates chronically exposed to dicrotophos.
-Page 37 of 102-

Table 3.11. Most Sensitive Acute and Chronic Toxicity Data for Aquatic Organisms 

Exposed to Dicrotophos. 

Exposure 

Scenario

Species Affected 

Endpoint

Toxicity Measurement MRID

(Classification)

Freshwater Fish

Acute Rainbow trout

(Oncorhynchus 

mykiss)

Mortality 96-hr LC50 = 5.7 mg a.i./L

Slope: N/A

MRID 40098001

(Supplemental)

Chronic Fathead minnow

(Pimephales 

promelas)

Mortality NOAEC = 9.88 mg a.i./L MRID 48482901 

(Supplemental)

Freshwater Invertebrates

Acute Water flea

(Daphnia magna)

Immobility 48 hr EC50 0.0126 mg a.i./L

Slope: N/A

MRID 43787901

(Acceptable)

Chronic Water flea

(Daphnia magna)

Length 21- day NOAEC = 0.0017 mg a.i./L

LOAEC = 0.0028 mg a.i./L

MRID 44956501

(Supplemental)

Estuarine/Marine Fish

Acute Sheepshead 

minnow

(Cyprinodon 

variegatus)

Mortality 96-hr LC50 83.8 mg a.i./L

Slope: N/A

MRID 43603306

(Acceptable)

Chronic No studies available

Estuarine/Marine Invertebrates

Acute Mysid shrimp 

(Americamysis 

bahia)

Mortality 96-hr EC50 = 0.077 mg a.i./L

Slope: NA

MRID 43603305

(Acceptable)

Chronic Mysid shrimp

(Americamysis 

bahia)

♂+♀ length, 

♀ weight

21-day NOAEC= 0.00309 mg ai/L MRID 43893901

(Acceptable)

Aquatic Plants

7-day 

exposure

Duckweed

(Lemna gibba)

None 7-day EC50 >117 mg a.i./L

NOAEC = 117 mg a.i./L

MRID 48443703 

(Acceptable)

96-hour 

exposure

Marine alga

(Skeletonema 

costatum)

Cell density, 

biomass, and 

growth rate

96-hr EC50 >118 mg a.i./L

NOAEC = 14.3 mg a.i./L

MRID 48443701

(Acceptable)

3.3.1.1 Toxicity to Freshwater Fish

Acute Effects

TGAI

A 96-hour static acute exposure study (MRID 40098001, Supplemental) with fingerling (mean=

one gram) rainbow trout (Onchorhynchus mykiss) is available for dicrotophos. Ten trout were 

exposed to nominal concentrations of 0 (negative control), 4.2, 6.5, 10, 16, and 24 mg/L. 

Loading did not exceed 0.8 g/L. The 96-hour LC50 was 6.3 mg/L (5.7 mg a.i./L corrected for 

90% purity).

A 96-hour static acute exposure study (MRID 40098001, Supplemental) with juvenile (mean= 

one gram) bluegill sunfish (Lepomis macrochirus) is available for dicrotophos. At least ten fish 

were exposed to each treatment concentration, and at least six concentrations were tested (study 
-Page 38 of 102-

design information was generically summarized by this report and no greater detail was available 

on a chemical-by-chemical basis) (USFWS, 1980). The 96-hour LC50 was 24.2 mg/L (19.4 mg 

a.i./L corrected for 80% purity).

A 96-hour static acute exposure study (MRID 40098001, Supplemental) with juvenile (mean= 

1.4 grams) channel catfish (Ictalurus punctatus) is available for dicrotophos. Ten fish were 

exposed to nominal concentrations of 0, 65, 100, 160, 240, and 370 mg/L. The 96-hour LC50

was 77 mg/L (69 mg a.i./L corrected for 90% purity).

Chronic Effects

A 33-day fish early life stage (ELS) study (MRID 48482901; Supplemental) with fathead 

minnow (Pimephales promelas) is available for dicrotophos (87.7% a.i.). The fathead minnow

eggs used for the initiation of the definitive test were obtained from an in-house culture.

Fertilized eggs/embryos (80/level, <24 hours old) were exposed to Dicrotophos Technical at 

nominal concentrations of 0 (negative control), 0.33, 0.65, 1.3, 2.5, 5.0, and 10 mg ai/L. Meanmeasured concentrations were <0.174 (<MQL, control), 0.327, 0.590, 1.21, 2.45, 4.94, and 9.88 

mg ai/L, respectively. Minnows in two replicates of the control were redistributed following an 

inadvertent pooling event. Sublethal effects of edema and lying on the bottom were observed to 

varying degrees in the control and four treatment levels. No statistically or biologically 

significant effects on egg hatchability, larval survival, length, or wet weight were determined at 

any concentration tested and a NOAEC of 9.88 mg a.i./L is used in this assessment.

3.3.1.2. Toxicity to Freshwater Invertebrates

Acute Effects

TGAI

A 48-hour flow-through acute exposure study (MRID 43787901; Acceptable) with Daphnia 

magna is available for dicrotophos. Twenty daphnids per level were exposed to mean-measured 

concentrations of <0.77 (control and DMF control), 0.00209, 0.00340, 0.00488, 0.00872, 0.0149, 

and 0.0273 mg ai/L. The LC50 was 0.0126 mg ai/L; 10% mortality occurred in the lowest 

treatment and the NOAEC could not be determined (<0.00209 mg ai/L).

Chronic Effects

A 21-day chronic flow-through toxicity study (MRID 44956501, Supplemental) of dicrotophos

with Daphnia magna was submitted. Daphnids were cultured in house, and were <24 hours old 

at the start of the test. Four replicates (40 daphnids per level, 10 daphnids per replicate) were 

maintained for each treatment level. Mean-measured exposure concentrations were <0.1

(<MQL, control and DMF control), 0.00035, 0.00059, 0.00099, 0.0017, 0.0028, and 0.0044 mg 

ai/L. DMF solvent concentrations did not exceed 5 μL/L. The NOAEC and LOAEC were

determined to be 0.0017 mg ai/L and 0.0028 mg ai/L based on reductions in mean total length. 

No sublethal effects were reported.

3.3.1.3. Toxicity to Estuarine/Marine Fish
-Page 39 of 102-

Acute Effects

A 96-hour static acute study (MRID 43603306; Acceptable) tested the acute toxicity of 

dicrotophos technical (87.65% a.i.) to sheepshead minnow (Cyprinodon variegatus). Fish were 

exposed to mean-measured concentrations of 0 (control), 11.8, 21.7, 36.1, 62.7, and 102 mg ai/L. 

20 fish per test concentration were exposed. Mortalities and/or sublethal effects were observed

at all test concentrations. The 96-hour LC50 is 83.8 mg ai/L. Dicrotophos is classified as slightly

toxic to sheepshead minnow on an acute exposure basis.

Chronic Effects

No chronic estuarine/marine fish toxicity tests with TGAI or formulations of dicrotophos 

were submitted. 

3.3.1.4. Toxicity to Estuarine/Marine Invertebrates

Acute Effects

A 96-hour flow-through acute exposure study (MRID 43603305; Acceptable) with mysid shrimp 

(Americamysis bahia) is available for dicrotophos. Twenty mysids per level were exposed to 

mean-measured concentrations of 0 (nominal; control and triethylene glycol control), 0.020, 

0.035, 0.060, 0.115, and 0.184 mg ai/L. Triethylene glycol solvent concentrations did not exceed 

0.0016 mL/L. Sublethal effects of lethargic and/or erratic behavior were recorded in the three 

highest treatment levels. The 96-hr EC50 is 0.077 mg ai/L; the NOAEC is 0.035 mg ai/L based 

on erratic behavior at 0.060 mg ai/L. Dicrotophos is classified as very highly toxic to mysids on 

an acute exposure basis.

A 96-hour flow-through acute shell deposition study (MRID 43739801; Acceptable) with 

Eastern oyster (Crassostrea virginica), is available for dicrotophos. Twenty oysters per level 

were exposed to mean-measured concentrations of <0.47 (control), 15.3, 25.9, 40.6, 70.7, and 

125 mg ai/L. Shell growth in all treatments was less than that of the control, with growth 

inhibition ranging between 12 and 21 percent. A monotonic dose-response was observed 

through the second highest treatment (i.e., 70.7 mg ai/L). The EC50 is considered to be greater 

than 125 mg ai/L, the highest concentration tested.

Chronic Effects

A 28-day chronic exposure toxicity with mysids (MRID 43893901; Acceptable) is available for 

dicrotophos. Conducted under flow-through conditions, neonates less than 24 hours old were 

exposed to mean-measured concentrations of <0.00118 (<LOQ, control and triethylene glycol

control), 0.00309, 0.00615, 0.0108, 0.0223, and 0.0454 mg ai/L. Female body length and dry 

weight were the most sensitive endpoints assessed, with NOAEC and LOAEC values of 0.00309

and 0.00615 mg ai/L, respectively.

3.3.1.5. Toxicity to Aquatic Plants
-Page 40 of 102-

Studies were submitted for a freshwater vascular plant (duckweed, Lemna gibba) and two

phytoplanktonic nonvascular plants: a green algae (Pseudokirchneriella subcapitata) and a 

diatom (Skeletonema costatum). 

Vascular Aquatic Plants

A study (MRID 48443703; Acceptable) examining the effect of technical dicrotophos on the 

aquatic macrophyte duckweed was submitted. Three replicates were exposed to dicrotophos 

mean-measured concentrations of <LOQ (<1.99, control), 7.32, 14.8, 29.4, 59.2, and 117 mg 

ai/L. Frond numbers, dry weight, and growth rate all were promoted in the treatments as 

compared to the control, resulting in a non-definitive 7-day EC50 of > 117 mg a.i./L and a

NOAEC of 117 μg a.i./L. Chlorosis of fronds was noted in treatments exposed to dicrotophos 

concentrations greater than 14.8 mg ai/L.

Nonvascular Aquatic Plants

A study (MRID 48443702; Acceptable) examining the effect of technical dicrotophos on green 

algae (Pseudokirchneriella subcapitata) was submitted. Six control replicates and 3 replicates 

per treatment level were exposed to mean-measured concentrations of <LOQ (<1.99, control), 

3.78, 7.36, 14.6, 29.1, 58.6 and 118 mg ai/L. Maximum inhibitions of 25% (118 mg ai/L; cell 

density and yield) were recorded, and the 96-hour EC50 is > 118 mg ai/L. The NOAEC was 

statistically determined to be 29.1 mg ai/L.

A study (MRID 48443701; Acceptable) examining the effect of technical dicrotophos on 

Skeletonema costatum was submitted. Three replicates were exposed to dicrotophos meanmeasured concentrations of <LOQ (<1.99, control), 3.63, 7.21, 14.3, 28.4, 58.2 and 118 mg ai/L. 

Maximum inhibitions of 34 and 36% (118 mg ai/L; cell density and yield, respectively) were 

recorded, and the 96-hour EC50 is > 118 mg ai/L. The NOAEC was statistically determined to be 

14.3 mg ai/L.

3.3.2 Terrestrial Effects Characterization

The most sensitive acute and chronic toxicity reference values associated with dicrotophos 

exposure to mammals, birds, and terrestrial invertebrates are summarized in Table 3.12. The 

most sensitive measurement endpoints for terrestrial plants are presented in Table 3.13. 

Dicrotophos is very highly toxic to Norway rat (Rattus norvegicus) on an acute exposure basis. 

A three-generation study on reproduction in the rat showed dicrotophos to cause chronic toxicity 

effects and impacts on pup survival. 

An acute oral (dose-based) toxicity study with the domestic goose (Toulouse strain) indicated 

that dicrotophos is very highly toxic to the domestic goose when administered as a single oral 

dose. Passerines (i.e., house finch and house sparrow) did not exhibit heightened sensitivity to

dicrotophos, although dicrotophos retains its very highly toxic classification for these species. 
-Page 41 of 102-

Subacute dietary toxicity studies indicate that dicrotophos technical is also very highly toxic to 

bobwhite quail (Colinus virginianus) and Japanese quail (Coturnix japonica), and highly toxic to 

the mallard (Anas platyrhynchos) on a subacute dietary exposure basis. Treatment-related 

effects on both adult and offspring endpoints were reported in avian reproduction studies 

conducted with bobwhite quail and mallard. No studies evaluating toxicity of dicrotophos

formulations were submitted.

Results of available toxicity studies indicate that technical grade dicrotophos is highly toxic to 

honey bees (Apis mellifera) on an acute contact exposure basis. 

Terrestrial plants did not exhibit phytotoxic response to applications (made at the maximum label 

rate) of dicrotophos during Tier I seedling emergence and vegetative vigor testing.

Table 3.12. Dicrotophos Toxicity Measurement Endpoints for Terrestrial Animals.

Exposure 

Scenario

Species Exposure 

Duration

Toxicity Reference Value MRID 

(Classification)

Mammals

Acute

(Dose-based)

Laboratory rat

(Rattus 

norvegicus)

Single oral dose LD50 11.0 mg/kg bw (male)

LD50 8.0 mg/kg bw (female)

Acc. Nos. 261098

& 

43893901

Chronic

(Dietary-based)

Laboratory rat

(Rattus 

norvegicus)

ThreegenerationNOAEL = 2.0 mg/kg diet 

LOAEL = 5.0 mg/kg diet 

Endpoints based on decreased 

pup survival

Acc. No. 00013446 

(Supplemental)

Birds

Acute 

(Dose-based)

Domestic 

goose (Anser 

anser)

14-day single 

oral dose

LD50: 1.22 mg/kg bw MRID 00013439

(Supplemental)

House 

sparrow 

(Passer 

domesticus)

Single oral 

dose

LD50: 3 mg/kg bw Acc. No. 00160000

(Supplemental)

Acute 

(Dietary-based)

Bobwhite 

quail 

(Colinus 

virginianus)

7-day dietary LC50: 13 mg/kg diet MRIDs 00013707 & 

00063392

(Supplemental)

Mallard duck

(Anas 

platyrhynchos)

8-day dietary LC50: 94 mg/kg diet MRID 00022923

(Supplemental)

Chronic 

(Dietary-based)

Mallard duck

Anas 

platyrhynchos

ca. 20 week 

avian 

reproduction 

study

LOAEC: 3.0 mg ai/kg diet

NOAEC: 1.0 mg ai/kg diet 

(based on female weight at 

study termination)

MRID 44005501

(Acceptable)

Bobwhite 

quail 

Colinus 

virginianus

ca. 20 week 

avian 

reproduction 

study

LOAEC: 1.5 mg ai/kg diet

NOAEC: 0.5 mg ai/kg diet 

(based on eggs laid)

MRID 44005502

(Acceptable)

Terrestrial Invertebrates
-Page 42 of 102-

Table 3.12. Dicrotophos Toxicity Measurement Endpoints for Terrestrial Animals.

Exposure 

Scenario

Species Exposure 

Duration

Toxicity Reference Value MRID 

(Classification)

Acute

(Contact)

Honeybee 48-hour LD50 0.076 μg a.i./bee MRIDs 05004151 & 

05001991

(Acceptable)

Table 3.13. Dicrotophos Toxicity Measurement Endpoints for Terrestrial Plants.

Exposure 

Scenario

Taxon Toxicity Reference Value Reference

(Classification)

Seedling 

Emergence (Tier I)

Monocot EC25 > 1.0 lb a.i./A 

NOAEC = 1.0 lb a.i./A 

MRID 48482902

(Supplemental)

Dicot EC25 > 1.0 lb a.i./A 

NOAEC = 1.0 lb a.i./A 

Vegetative Vigor

(Tier I)

Monocot EC25 > 0.95 lb a.i./A 

NOAEC = 0.95 lb a.i./A 

MRID 48482903

(Acceptable)

Dicot EC25 > 0.95 lb a.i./A 

NOAEC = 0.95 lb a.i./A

In addition to the standard suite of laboratory toxicity studies, two field studies are available for

dicrotophos applied to cotton. Conducted in Alabama (MRID 40917001, Supplemental) and 

Arizona (MRID 40873701, Supplemental), these field studies evaluated effects to wildlife across 

fourteen replicate fields (eight treated and six control). In Alabama, two applications of 0.5 lb 

ai/A were made at a six day interval. In Arizona, three applications of 0.2 lb ai/A were separated 

by seven day intervals. Study results are potentially confounded by tank mixing of other 

insecticide active ingredients with dicrotophos. However, both studies identified treatment 

related mortalities, and residue analysis accompanied those determinations. In Alabama, 

external and internal dicrotophos residues were detected on indigo buntings as high as 17 ppm 

and 0.51 ppm, repectively. Further, both study reports include extensive lists of avian, 

mammalian, and hepetofaunal species documented in or around the treated fields. While neither 

study design is sufficiently robust for quantitative use in risk estimation, anecdotal information 

contained within the study reports is useful for risk characterization. 

3.3.2.1. Toxicity to Mammals

Acute Effects

The acute oral toxicity endpoint (LD50), based on Norway rat (Rattus norvegicus), is 11 mg/kgbw for males and 8.0 mg/kg-bw for females as reported by the Health Effects Division (HED) 

(MRIDs 261098 and 43893901; USEPA 2006). 

Chronic Effects
-Page 43 of 102-

A three-generation rat reproduction study reviewed by HED resulted in a NOAEL of 2 mg/kgdiet based on pup survival (Acc. 00013446). Mammalian reproduction was adversely affected at 

dicrotophos concentrations of 5 ppm and greater. 

3.3.2.2. Toxicity to Birds

Acute and Subacute Dietary

Acute 

Multiple avian acute toxicity studies are available for dicrotophos. In one avian acute toxicity 

study (Acc. No. 00013439; Supplemental), four domestic geese (Toulouse strain) per treatment 

group were exposed to technical (99% a.i.) dicrotophos and monitored for 14 days. Nominal 

concentrations of 0.0385, 0.385, 3.85, and 38.5 mg/kg-bw were delivered by stomach tube to 

geese ranging in weight from 2.96 to 4.50 kg. The diet during the observation period was shelled 

corn. The two lower treatment levels had no mortality after 14 days, whereas the two upper 

treatment levels had total mortality after 2 hours. The LD50 was determined to be 1.22 mg/kgbw.

Another avian acute toxicity study (Acc. No. 00160000; Supplemental) is available for 

dicrotophos. 12 male California quail (Callipepla californica), 18 months of age, were exposed 

to dicrotophos technical (80% a.i.). The LD50 was determined to be 1.89 mg/kg-bw (1.51 mg/kgbw when adjusted for purity).

Avian acute toxicity studies testing passerines are also available (Acc. No. 00160000; 

Supplemental). 16 male house sparrows (Passer domesticus) were exposed to technical 

dicrotophos (98% α isomer), and the LD50 was reported to be 3 mg/kg-bw. Eight pairs of male 

and female house finches (Carpodacus mexicanus) were exposed to technical dicrotophos (98% 

α isomer), and the LD50 was reported to be 2.83 mg/kg-bw. Neither sparrow nor finch ages were 

available. The study reports do not clarify whether the numbers of bobwhite, sparrows, or 

finches represent totals per treatment level or totals per test.

Subacute

An avian subacute dietary toxicity study (MRID 00013707; Supplemental) is available for 

dicrotophos. Bobwhite quail, 4-7 days old, were exposed to technical dicrotophos at levels of 1, 

3, 9, 27, and 610 mg/kg-diet for a period of four weeks. The dietary LC50 was 13 mg/kg-diet. 

A second avian subacute dietary toxicity study (Acc. No. 00022923; Supplemental) is available 

for dicrotophos. Five day old Mallard ducks (Anas platyrhynchos) were exposed to dicrotophos 

at eight different treatment concentrations; 10 birds per level; and the dietary LC50 was 

determined to be 94 mg/kg-diet. Ten day old Mallard ducks (Anas platyrhynchos) were also 
-Page 44 of 102-

exposed to dicrotophos but only five treatment concentrations were used; 10 birds per level; and 

the dietary LC50 was determined to be 144 mg/kg-diet. Dicrotophos is classified as highly to 

toxic very highly toxic to birds on a subacute dietary basis.

Chronic

A one-generation reproductive toxicity study (MRID 44005501; Acceptable) is available for

dicrotophos. Toxicity of chronic exposure to 6 replicate pens (2 males + 5 females) per level of 

16-month old mallard (Anas platyrhynchos) was assessed over ca. 20 weeks. Dicrotophos was 

administered to the birds mixed in the diet at nominal concentrations of 0, 1, 3, and 10 mg/kg. 

This study determined a NOAEC of 1 ppm, since significant reductions (ca. 8%) in female 

bodyweight were recorded at the 3 ppm level (the LOAEC). At 10 ppm, significant effects to 

mallard reproduction included egg production, embryo viability, hatchling production and 

survival, adult bodyweight, and thickness of eggshells.

A second one-generation reproductive toxicity study (MRID 44005502; Acceptable) is available 

for dicrotophos. Toxicity of chronic exposure to 20 pairs per level of 16-month old northern 

bobwhite quail (Colinus virginianus) was assessed over ca. 20 weeks. Dicrotophos was 

administered to the birds mixed in the diet at nominal concentrations of 0, 0.5, 1.5, and 5 mg/kg. 

Egg production and female body weight were significantly affected at the 1.5 ppm level, reduced 

by 25% and 9%, respectively. At 5 ppm, embryo viability, the number of 14-day old survivors, 

adult body weight, and adult mortality were significantly different from the control group. The 

NOAEC of this study is 0.5 mg/kg-diet; the LOAEC is 1.5 mg/kg-diet.

3.3.2.3. Toxicity to Terrestrial Invertebrates

Acute Effects

A 24-hour acute contact study (MRIDs 05004151 and 05001991; Acceptable) with honey bees 

(Apis mellifera) is available for dicrotophos. Two replicates of 10 bees were exposed to each of 

five or six concentrations of technical dicrotophos (study report generic for the testing of numerous 

chemicals; no further details pertaining to dicrotophos testing were available). This study reported 

an acute oral LD50 of 0.068 μg ai/bee, and an acute contact LD50 of 0.076 μg ai/bee. Dicrotophos 

is classified as highly toxic to honey bees on an acute dermal exposure basis.

Further, residues on foliage have been found to remain toxic to bees and other beneficial insects 

for as many as 16 days (MRIDs 05009353 and 05013577). In MRID 05013577 (Clinch, P.G., and 

T. Palmer-Jones, 1971), dicrotophos (85% EC) was applied as a pre-blossom spray to raspberries 

at a rate of 0.43 lb a.i./A six days before bloom. Hives were located near the treated area and bee 

mortalities were recorded through 16 days after application. By day 21, residual toxic effects of 

the spray application had subsided. In MRID 05009353 (Clinch, P.G., et al., 1973), dicrotophos 

(85% EC) was applied to flowering white clover at a rate of 0.45 lb a.i./A; honey bee mortality 

exceeding 50% was recorded for five days following application in the treated area. 

3.3.2.4. Toxicity to Terrestrial Plants
-Page 45 of 102-

The effect of Bidrin 8 Water Miscible Insecticide (TEP; 83.8% dicrotophos) on the Tier I seedling 

emergence (MRID 48482902, Supplemental) of monocot (corn, Zea mays; onion, Allium cepa; 

ryegrass, Lolium perenne; and oat, Avena sativa) and dicot (radish, Raphanus sativus; cucumber, 

Cucumis sativus; lettuce, Lactuca sativa; Sugarbeet, Beta vulgaris; soybean, Glycine max; and 

tomato, Lycopersicon esculentum) crops was studied at nominal concentrations of 0 (negative 

control) and 1 lb a.i./A. None of the monocot or dicot species were significantly affected at the 

maximum labeled rate, resulting in overall nominal NOAEC and EC25 values of 1.0 and >1.0 lb 

ai/A, respectively. 

The effect of Bidrin 8 Water Miscible Insecticide (TEP; 83.8% dicrotophos) on the Tier I 

vegetative vigor (MRID 48482903, Acceptable) of monocot (corn, Zea mays; onion, Allium cepa; 

ryegrass, Lolium perenne; and oat, Avena sativa) and dicot (radish, Raphanus sativus; cucumber, 

Cucumis sativus; lettuce, Lactuca sativa; Sugarbeet, Beta vulgaris; soybean, Glycine max; and 

tomato, Lycopersicon esculentum) crops was studied at mean-measured concentrations of <MQL 

(<0.0007 lb a.i./A, negative control), and 0.95 lb a.i./A. None of the monocot and dicot species 

were affected at the maximum labeled rate, resulting in overall mean-measured NOAEC and EC25

values of 0.95 and >0.95 lb ai/A, respectively.

3.4. ECOTOX Open Literature

A literature search in the Agency’s ECOTOX database (May 2012) resulted in one paper that

passed the ECOTOX and OPP acceptability screens and reported an endpoint more sensitive 

than those resulting from the submitted guideline studies. Meyers, S.M., 1990, reported a 5-day

LC50 for bobwhite quail of <12.5 mg/kg, although the lowest concentration tested, 20 ppm, adds 

uncertainty to the reliability of the reported LC50, which is less than 20 ppm. This paper has 

been received and a formal Open Literature Review Summary evaluation is being conducted; the 

review will be available for the final version of this risk assessment. For the time being, the 

endpoint will be used provisionally and qualitatively, pending review.

A study (Moser, V.C., 2011) examining age-related differences in acute neurotoxicity in the 

Norway rat (Rattus norvegicus) provides information useful for mammalian risk 

characterization; however, the reported endpoints are based on sublethal effects rather than 

mortality and will not be used as a quantitative measure of dicrotophos hazard.

The database also contains a number of studies that evaluated the effect of dicrotophos on target 

insects, though none of the studies result in more sensitive endpoints and are generally not 

endpoints used in Agency risk assessments.

4. Risk Characterization

4.1. Risk Estimation

Toxicity data and exposure estimates are used to evaluate the potential for adverse ecological 

effects on non-target species. This assessment for dicrotophos relies on the deterministic RQ 

method to provide a metric of potential risks. The RQ provides a comparison of exposure 

estimates to toxicity endpoints (i.e., the estimated exposure concentrations are divided by acute 
-Page 46 of 102-

and chronic toxicity values). The resulting unitless RQs are compared to the Agency’s LOCs, as 

shown in Table 2.3. LOCs are used by the Agency to indicate when the use of a pesticide, as 

directed by the label, has the potential to cause adverse effects to non-target organisms.

4.1.1. Aquatic Organisms 

The highest screening-level aquatic parent only EECs based on the maximum application rates 

for each proposed use pattern were used to derive RQs. These exposure estimates represent 

concentrations in surface water (Table 3.7). Peak EECs are used to represent acute exposure to 

fish, aquatic invertebrates and aquatic plants, and 21-day and 60-day average EECs represent 

chronic exposure to aquatic invertebrates and fish, respectively. Total toxic residue RQs are 

derived for characterization purposes, however, risk conclusions remain the same for all taxa

regardless of whether parent only or TTR are considered for risk estimation.

4.1.1.1. Fish and Invertebrates

Fish

Table 4.1 lists acute RQs calculated for fish (freshwater and estuarine/marine) and aquatic-phase 

amphibians exposed to dicrotophos, based on the peak EECs generated from PRZM/EXAMS 

modeling scenarios. Results of acute toxicity studies in freshwater and estuarine/marine fish 

(Table 3.13) indicate that dicrotophos is “moderately toxic” to fish on an acute exposure basis. 

However, RQs for uses of dicrotophos fall below the Agency’s acute risk to listed species LOC 

(0.05), as well as the Agency’s acute risk to non-listed species LOC of 0.5. 

Table 4.1. Acute Risk Quotients for Fish and Aquatic-phase Amphibians Exposed to 

Dicrotophos at the Upper-bound EECs Using the Most Sensitive of the Available 

Endpoints.

PRZM Scenario 

(standard unless 

noted)

1-in-10 year 

peak daily, 

μg/L

RQ

Freshwater LC50

5,700 μg ai/L

Estuarine/Marine

LC50

83,800 μg ai/L

Total Toxic Residues

TX Cotton 16.87 0.0030 < 0.001

Parent only

TX Cotton 16.33 0.0029 < 0.001

1 Acute risk to non-listed species LOC for aquatic fish is 0.5

2 Acute risk to listed species LOC for aquatic fish is 0.05

Chronic exposure RQs for fish were calculated with the endpoint derived from the guideline ELS 

study (Table 4.2). RQs for all scenarios fall below the Agency’s chronic risk LOC (1.0).

Table 4.2. Chronic Risk Quotients for Fish and Aquatic-phase Amphibians Exposed to 

Dicrotophos at the Upper-bound EECs Using the Most Sensitive of the Available 

Endpoints.
-Page 47 of 102-

PRZM Scenario 

(standard unless 

noted)

1-in-10 year 60-

day average, 

μg/L

RQ

NOAEC: 

9,880 μg ai/L

Total Toxic Residues

NC Cotton 7.71 <0.001

Parent only

NC Cotton 6.17 < 0.001

1 Chronic risk to listed and nonlisted aquatic animals is 1.0

Aquatic Invertebrates

Based on the available acute studies, dicrotophos is categorized as very highly toxic to Daphnia 

magna on an acute exposure basis. RQs for freshwater invertebrates exceed the acute risk LOC 

for listed species under every scenario modeled.

Mysids are much less acutely sensitive to dicrotophos than daphnids, although dicrotophos is still

classified as very highly toxic to mysid shrimp. Estuarine/marine invertebrate RQs exceed the 

acute risk LOC for listed species for all modeled scenarios (Table 4.3).

Table 4.3. Acute Risk Quotients for Aquatic Invertebrates Exposed to Dicrotophos at the 

Upper-bound EECs Using the Most Sensitive of the Available Endpoints.

PRZM Scenario 

(standard unless 

noted)

1-in-10 year 

peak daily, 

μg/L

RQ

FW LC50

12.7 μg ai/L

E/M LC50

77 μg ai/L

Total Toxic Residues

TX Cotton 16.87 1.33 0.22

Parent only

TX Cotton 16.33 1.29 0.21

1 Acute risk to non-listed species LOC for aquatic animals is 0.5

2 Acute risk to listed species LOC for aquatic animals is 0.05

Aquatic invertebrates exhibit sensitivity to dicrotophos in studies over chronic exposure 

durations. The chronic LOC (1.0) is exceeded for freshwater and estuarine/marine invertebrates 

for all PRZM scenarios modeled (Table 4.4). 

Table 4.4. Chronic Risk Quotients for Aquatic Invertebrates Exposed to Dicrotophos at 

the Upper-bound EECs Using the Most Sensitive of the Available Endpoints.

PRZM Scenario 

(standard unless 

noted)

1-in-10 year 21-

day average, 

μg/L

RQ

FW NOAEC: 

1.7 μg ai/L 

E/M NOAEC: 

3.09 μg ai/L

Total Toxic Residues

TX Cotton 12.26

7.2 3.97

Parent only
-Page 48 of 102-

TX Cotton 10.73

6.3 3.47

1 Chronic risk to listed and nonlisted aquatic animals is 1.0

4.1.1.2. Aquatic Plants

Exposure modeling data indicate that environmentally relevant concentrations of dicrotophos are 

orders of magnitude below levels which could potentially result in adverse effects to aquatic 

plant communities. Thus there is insufficient exposure for either the nonlisted or listed species 

LOC (1.0) to be exceeded (Table 4.5). 

Table 4.5. Acute Risk Quotients for Aquatic Vascular and Nonvascular Plants Exposed to 

Dicrotophos at the Upper-bound EECs Using the Most Sensitive of the Available 

Endpoints.

PRZM Scenario 

(standard unless 

noted)

1-in-10 

year peak 

daily, 

μg/L

Aquatic Vascular Plant RQs Nonvascular Plant RQs

EC50

μg ai/L

Nonlisted

> 117,000

NOAEC

μg ai/L

Listed

117,000

EC50

μg ai/L

Nonlisted

> 118,000

NOAEC

μg ai/L

Listed

14,300

Total Toxic Residues

TX Cotton 16.87 < 0.001 < 0.001 < 0.001 < 0.01

Parent Only

TX Cotton 

16.33 < 0.001 < 0.001 < 0.001 < 0.01

1 Plant LOC is 1.0. Bold indicates exceeds LOC

4.1.2. Terrestrial Organisms 

4.1.2.1. Mammals

Based on the available acute toxicity data, the LD50 for dicrotophos is 11 mg/kg for male rats, 

and 8 mg/kg for female rats, respectively. Therefore, dicrotophos is categorized as “very highly 

toxic” to mammals on an acute exposure basis. RQs exceed the acute non-listed species LOC 

(0.5) by a factor of up to 23X (short grass). Table 4.6 lists maximum acute EECs and RQs for 

all of the proposed use rates based on the upper 90th percentile Kenaga values. The acute listed 

species LOC is 0.1. With an RQ of 0.07, only the large mammal granivore forage class does not 

result in an LOC exceedance. Further discussion of the predicted exposure values relative to the 

levels at which mortality was observed is provided as part of the risk description in Section 

4.2.4.

Based on the proposed maximum application rates on cotton, there are chronic dose-based 

exposure concerns for mammals of all size classes for the short grass, tall grass, broadleaf plant, 

fruits/pods, arthropods, and and granivore sub-classes. RQs exceed the LOC by a factor of up to 

915X (short grass). Table 4.7 lists maximum chronic dose-based EECs and RQs based on the 
-Page 49 of 102-

upper 90th percentile Kenaga values for applications to cotton. Additionally, there are 

exceedances for chronic dietary-based exposure for all forage types assessed (Table 4.8).
-Page 50 of 102-

Table 4.6. Mammalian Acute Dose-based RQs for the Use of Dicrotophos on Cotton. Bold indicates exceedance of the LOC.

Rate

(# apps; 

interval)

Size 

Class

(grams)

Adjusted 

LD50

EECs and RQs

Short Grass Tall Grass Broadleaf 

Plants

Fruits/Pods/

Seeds Arthropods Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

0.5 (2; 

14d)

15 17.58 201.1 11.4 92.18 5.2 113.1 6.4 12.57 0.71 78.77 4.5 2.79 0.16

35 14.23 139.0 9.8 63.71 4.5 78.2 5.5 8.69 0.61 54.44 3.8 1.93 0.14

1000 6.15 32.2 5.2 14.77 2.4 18.1 3.0 2.01 0.33 12.62 2.1 0.45 0.073

Acute risk to non-listed species LOC for mammals is 0.5

Acute risk to listed species LOC for mammals is 0.1

Table 4.7. Mammalian Chronic Dose-based RQs for the Use of Dicrotophos on Cotton. Bold indicates exceedance of the LOC.

Rate

(# apps; 

interval)

Size 

Class

(grams)

Adjusted 

NOAEL

EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/

Seeds Arthropods Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

0.5 (2; 

14d)

15 0.22 201.12 915.08 92.18 419.41 113.13 514.73 12.57 57.19 78.77 358.40 2.79 12.71

35 0.18 139.00 781.65 63.71 358.26 78.19 439.68 8.69 48.85 54.44 306.15 1.93 10.86

1000 0.08 32.23 419.00 14.77 192.04 18.13 235.69 2.01 26.19 12.62 164.11 0.45 5.82

Chronic risk LOC for mammals is 1.

Table 4.8. Mammalian Chronic Dietary-based* RQs for the Use of Dicrotophos on Cotton. Bold indicates exceedance of the LOC. 

Rate

(# apps; 

interval)

NOAEC 

(ppm)

EECs and RQs

Short Grass Tall Grass Broadleaf 

Plants

Fruits/Pods/

Seeds Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

0.5 (2; 14d)1 0.1 210.94 105 96.68 48 118.66 59.33 13.18 6.59 82.62 41.31

*Size class not used for dietary risk quotients

Chronic risk LOC for mammals is 1.
-Page 51 of 102-

4.1.2.2. Birds

Based on the available toxicity data, the avian acute dose-based and sub-acute dietary endpoints 

used for risk assement are 1.22 mg/kg-bw and 13 mg/kg-diet, respectively. Dicrotophos is 

classified as “very highly toxic” to birds on both an acute and sub-acute basis. 

RQs for acute dose-based exposure exceed the acute non-listed species LOC (0.5) for all size 

classes and foraging groups by at least two fold and as much as 926X (small bird, short grass) 

(Table 4.9). 

On a sub-acute basis, RQs for all size classes and foraging groups exceed the acute non-listed 

species LOC (0.5) by at least two fold and as much as 32X. RQs resulting from sub-acute

dietary exposure are depicted in Table 4.10. 

On a chronic dietary basis, RQs for all size classes and foraging groups exceed the the chronic 

LOC (1.0) by at least 26X and as much as 422X (Table 4.11).
-Page 52 of 102-

Table 4.9. Avian Acute Dose-based RQs for the Use of Dicrotophos on Cotton. Bold indicates exceedance of the LOC.

Rate

(# apps; 

interval)

Size 

Class

(grams)

Adjusted 

LD50

EECs and RQs

Short Grass Tall Grass Broadleaf Plants Fruits/Pods/

Seeds Arthropods Granivore

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

0.5 (2; 

14d) 20 0.52 240.24 463.30 110.11 212.34 135.14 260.60 15.02 28.96 94.10 181.46 3.34 6.43

100 0.66 137.00 207.53 62.79 95.12 77.06 116.73 8.56 12.97 53.66 81.28 1.90 2.88

1000 0.93 61.34 65.78 28.11 30.15 34.50 37.00 3.83 4.11 24.02 25.76 0.85 0.91

Acute risk to non-listed species LOC for birds is 0.5

Acute risk to listed species LOC for birds is 0.1

Table 4.10. Avian Sub-acute Dietary-based* RQs for the Use of Dicrotophos on Cotton. Bold indicates exceedance of the LOC.

Rate

(# apps; 

interval)

LC50

(ppm)

EECs and RQs

Short Grass Tall Grass Broadleaf 

Plants

Fruits/Pods/

Seeds Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

0.5 (2; 14d) 13 210.94 16.23 96.68 7.44 118.66 9.13 13.18 1.01 82.62 6.36

*Size class not used for dietary risk quotients

Acute risk to non-listed species LOC for birds is 0.5

Acute risk to listed species LOC for birds is 0.1

Table 4.11. Avian Chronic Dietary-based RQs for the Use of Dicrotophos on Cotton. Bold indicates exceedance of the LOC.

Rate

(# apps; 

interval)

NOAEC

(ppm)

EECs and RQs

Short Grass Tall Grass Broadleaf 

Plants

Fruits/Pods/

Seeds Arthropods

EEC RQ EEC RQ EEC RQ EEC RQ EEC RQ

0.5 (2; 14d) 0.5 210.94 421.9 96.68 193.4 118.66 237.31 13.18 26.37 82.62 165.24

Chronic risk LOC for birds is 1.0
-Page 53 of 102-

4.1.2.3. Terrestrial Invertebrates 

Dicrotophos is classified as highly toxic to honeybees on an acute contact exposure basis. Per 

the Pollinator SAP white paper (USEPA, 2012), tall grass EECs were calculated separately for 

acute oral and acute contact exposure, according to the following equations:

 Oral toxicity EEC = (Single application rate) × (110 μg a.i./g per 1 lb a.i.) × (0.29 g/day)

 Contact toxicity EEC = (Single application rate) × (2.7 μg a.i./bee per 1 lb a.i.) 

Acute oral and contact tall grass EECs of 15.95 μg ai/bee and 1.35 μg ai/bee were divided by the 

acute oral and contact LD50’s of 0.068 μg ai/bee and 0.076 μg ai/bee, respectively, resulting in 

acute oral and contact RQs of 234.6 and 17.8, respectively. The initial screening level RQs

determined for honey bees (Table 4.12) exceed the terrestrial invertebrate LOC (0.4) by more 

than two orders of magnitude on an oral toxicity basis, and more than an order of magnitude on a 

contact toxicity basis; however, these estimates of risk are considered within the context of other 

lines of evidence. More discussion on the ratio between the LD50 and the expected exposure is 

presented in the Risk Description section.

Table 4.12. Terrestrial Invertebrate Oral and Contact Toxicity RQs for the Use of Dicrotophos 

on Cotton. Bold indicates exceedance of the LOC.

Rate

(lb a.i./A)

LD50 (μg 

a.i./bee)

EECs and RQs

Tall Grass

EEC RQ

Oral toxicity

0.068 15.98 234.56

0.5 Contact toxicity

0.076 1.35 17.76

Acute risk LOC for terrestrial invertebrates is 0.4

4.1.2.4. Non-target Terrestrial Plants

Ten different crop species were treated with dicrotophos at the maximum label rate during Tier I 

seedling emergence and vegetative vigor testing. No definitve effects endpoints were 

determined from those tests and risk to terrestrial plants is presumed to be negligible. 

4.2. Incident Database Review

A review of the Ecological Incident InformationSystem (EIIS) database for incidents involving 

dicrotophos was conducted on December 5, 2012. Four incidents for dicrotophos are reported in 

the database (Appendix D). Of these, two occurred from use on agricultural areas, one incident 

resulted from a disposal site, and one use site was undefined. The 1976 incident resulting from 

the disposal site (B0000-400-19; probable) occurred in Washington State and mortalities of 

American wigeon, common pintail, and mallard were reported. An incident associated with rice 
-Page 54 of 102-

in Texas (B0000-400-20; probable) involved ingestion of dicrotophos-treated rice, and 

mortalities of red-winged blackbird, great-tailed grackle, brown-headed cowbird, and mourning 

dove were reported. In 1991, dicrotophos applied to cotton in Lauren county, GA (I000922-001; 

unlikely) was associated with mortalities of hundreds of catfish, bream, and bass in a pond 20 to 

50 yards from the treated field. In 2002, dicrotophos used in Desha county, AR (I018980-029; 

highly probable) is associated with the mortalities of 200 greater snow geese, one coyote, and at 

least one hawk species.

Similarly, a search of the Avian Incident Monitoring System (AIMS; 

http://www.abcbirds.org/abcprograms/policy/toxins/aims/aims/index.cfm) was conducted on 

December 5, 2012. AIMS is a database administered by the American Bird Conservancy that 

contains publicly available data on reported avian incidents involving pesticides. Nine incidents 

involving dicrotophos were found. Seven incidents are reported from Texas; one from Arkansas; 

and one from Washington state. All but three incidents have certainty classifications as 

“unlikely;” one of these three incidents was already captured by EIIS (B0000-400-19; probable). 

A 1996 incident from Harris county, Texas (US Fish and Wildlife Service Law Enforcement 

Division Case No. 96-0296) is classified as highly likely; one red-tailed hawk and 11 passerine 

birds were assessed as moribound. A 2000 incident from Pulaski county, Arkansas (US Fish and 

Wildlife Service Law Enforcement Division Case No. 00-0197) involving dicrotophos and 

mevinphos is classified as highly likely; mortalities of dove, grackle, cowbird, and blackbird 

were reported. Two other incidents involving misapplication of pesticide-treated seed were 

reported and more than 1,000 bird mortalities are associated with these incidents.

Pesticide registrants report certain types of incidents to the Agency as aggregate counts of 

incidents occurring per product per quarter. One aggregated fish and wildlife incident has been 

reported to the Agency associated with dicrotophos. It was submitted in the summer of 2004. 

Unless further information regarding this aggregate incident is discovered, it will be assumed 

that it resulted from registered use.

The number of reports listed in the EIIS database are believed to be only a small fraction of the 

total incidents involving organism mortality and damage caused by pesticides. Few resources are 

assigned to incident reporting. Reporting by states is only voluntary, and individuals discovering 

incidents may not be informed on the procedure of reporting these occurrences. Additionally, 

much of the database is generated from registrant-submitted incident reports. In addition, 

incident reports for non-target organisms typically provide information only on mortality events 

and plant damage incidents. Impacts to non-commercial beneficial insects and other invertebrates 

are not likely to be reported. Except for phytotoxic effects in terrestrial plants, sublethal effects 

for organisms such as reduced growth or impaired reproduction are rarely reported. Because of 

these logistical difficulties, EIIS is most likely a minimal representation of all pesticide-related 

ecological incidents.

Therefore, the weight of evidence based on the currently available data suggests that direct 

effects to avian and mammalian species are expected from the currently registered use of 

dicrotophos. 
-Page 55 of 102-

4.3. Risk Description

The results of risk estimation indicate that registered uses of dicrotophos yield acute and chronic 

LOC exceedances for aquatic invertebrates (freshwater and estuarine/marine). RQs calculated 

for fish and aquatic plants did not result in LOC exceedances.

Acute and chronic risk to birds and mammals from dicrotophos is indicated on both a dietary and 

dose basis. Acute risk to terrestrial invertebrates is indicated based on dermal contact toxicity 

and exposure estimates. Risk to terrestrial plants is presumed to be neglible, based on the 

nondefinitive endpoints determined from Tier I studies with crop species.

Several refinements to the risk determinations may be attempted in the final version of this risk 

assessment. These refinements include consideration of biological factors of individual listed 

species and the potential co-occurence of listed species and registered use sites where 

dicrotophos may be used.

4.3.1 Exposure to Aquatic Organisms

Surface water EECs resulting from applications of dicrotophos to cotton are conservative 

estimates of exposure for the use of dicrotophos as a broadcast insecticide. Application practices 

were conservatively modeled by using maximum application rates and minimum application 

intervals. Environmental fate data were conservatively represented by using the 90th percentile 

mean of metabolism half-life estimates. Finally, scenario selection was conservatively 

performed by modeling run-off prone soils that drain to a small pond without an outlet. Low 

EECs for dicrotophos come as a result of high metabolism rates. However, modeling values are 

only two times larger than the highest reported monitoring value and higher monitoring values 

may be found with more targeted monitoring approaches.

The tree injection use pattern is not expected to appreciably contribute to aquatic exposure. 

Theoretically, aquatic exposures could result from dicrotophos entering soil environments, which

could occur if the chemical is translocated primarily to the leaves, and the leaves fall to the soil 

and decompose. Dicrotophos degrades readily in soil, and through this process of translocation 

in the tree and foliage degradation, it can be expected that dicrotophos will be substantially 

degraded before it reaches aquatic environments. Therefore, discussion of dicrotophos risk to 

aquatic animals (Section 4.3.1.1) is limited to exposure resulting from the registered use on 

cotton.

Spray drift exposure to aquatic organisms is also a viable exposure pathway. Concentrations of 

0.6 ppb in water trigger the Endangered Species LOC (based on Daphnia magna toxicity 

endpoint of 12.7 ppb). This concentration is achieved at distances up to 331 feet from the edge 

of field according to AgDRIFT v 2.01 for aerial applications. Ground applications yielded 

maximum concentrations only as high as 0.6 ppb at three feet from the edge of field; therefore 

spray drift resulting from ground applications would be of limited concern, especially in 

comparison to aerial applications. Note that all broadcast uses allow aerial applications.
-Page 56 of 102-

4.3.1.1. Risks to Aquatic Animals

Based on the available data, risk to freshwater or estuarine/marine fish is not expected on an 

acute exposure basis. The highest RQ from all modeled use patterns is 0.003, well below the 

listed species LOC of 0.05. Neither is chronic risk to fish expected; RQs are all less than 0.001.

The acute non-listed species LOC (0.5) for effects to freshwater invertebrates and acute restricted 

use LOC (0.1) for effects to estuarine/marine invertebrates are exceeded, with RQs as high as 

1.33 and 0.22 for freshwater and estuarine species, respectively. Chronic risk LOCs (1.0) are 

also exceeded; RQs were determined to be as high as 7.2 and 3.97 for freshwater and estuarine 

invertebrates, respectively. Both acute and chronic toxicity data indicate that freshwater 

invertebrates are more sensitive than estuarine/marine invertebrates to dicrotophos exposure.

4.3.1.2. Risks to Aquatic Plants

Based on the available toxicity information on Lemna gibba and Pseudokirchneriella 

subcapitata, the use of dicrotophos on cotton does not result in RQ exceedances of the LOC for 

listed aquatic plants, since all RQs are less than 0.01. 

4.3.2. Exposure to Terrestrial Organisms

Dicrotophos is registered for use as a foliar spray on cotton and also as a tree injection for 

ornamental trees. Each use pattern has unique exposure uncertainties; therefore, discussion of 

terrestrial exposure will be subdivided according to use pattern. Specific to the cotton use 

pattern, application practices were conservatively modeled by using maximum application rates 

and minimum application intervals. The spray drift model AgDrift provides helpful bounds 

which define the spatial extent of risk concern resulting from off-field drift at currently registered 

dicrotophos application rates. Sections 4.3.2.1., 4.3.2.2., and 4.3.2.3. contain descriptive 

characterization of the AgDrift output and the associated off-field risk implications for 

mammals, birds, and terrestrial insects, respectively.

4.3.2.1. Risks to Mammals

Cotton use pattern

Acute upper bound Kenaga RQs derived for mammals in the Risk Estimation section of this 

assessment indicate acute listed mammalian risk LOC (0.1) exceedances for all but 1000 gram 

granivore mammals (RQ = 0.07). Based on the EEC values from T-REX and the LD50 from the 

available acute rat study, the highest RQ value for 15 gram mammals foraging on short grass—

the most sensitive size class and forage item combination— is 11.44. 

When assessing potential chronic risk to mammals, in accordance with the overview document, 

the dietary-based NOAEC is converted to a dose-based NOAEL using data from the HED study, 
-Page 57 of 102-

which can be scaled to different mammalian size classes. The dose-based RQs are calculated 

using a body weight adjusted and consumption-weighted equivalent dose, as determined in the 

study. The adjustments account for the fact that smaller-sized animals have to consume more 

food in terms of their body weight than larger animals and that there is differential sensitivity to 

chemicals based on body size. By expressing the Kenaga nomogram-estimated residues in terms 

of daily equivalent dose, estimated environmental concentrations can then be compared to the 

dose-based NOAEL. Dose-based and dietary-based chronic RQs exceed the LOC (1.0) for all 

forager types. Dose-based chronic RQs range from 5.82 to 915, and dietary based chronic RQs 

range from 6.59 to 105. The exceedances for dicrotophos are greater than 915-fold (dose-based) 

and 100-fold (dietary-based) for short grass mammalian foragers. These exceedances are based 

on reduced pup survival observed in a three-generation rat reproduction study. Since terrestrial 

application residues exceed 2 mg ai/kg dietary item (i.e., the mammalian reproduction NOAEC) 

for at least 105 days (fruits/pods/seeds) and as many as 250 days (short grass) following the first 

application of dicrotophos, there is a high degree of confidence in the prediction of adverse 

chronic effects.

EECs exceed the mammalian acute non-listed species LOC (0.5) for 164 days after application 

for short grass, assuming a 35-day half life and two applications of 0.5 lb a.i./A applied at a 14-

day interval (Figure 4.1). With the same model input parameters, EECs exceed the mammalian 

acute non-listed species LOC for 116 to 134 days following application for all other forage types 

except fruits/pods/seeds, where the mammalian acute non-listed species LOC is exceeded for 23

days following the first application.

Even under a less conservative T-REX exposure scenario, mean Kenaga acute and chronic RQs 

exceed the acute listed species or chronic LOC for all size classes and forage types, except for 

granivores with RQs (acute dose-based) less than the acute listed species LOC for all size 

classes. 

To spatially examine the potential risk of spray drift, simulations were performed with the 

program AgDRIFT. It was determined that spray drift EECs yield acute dose-based RQs that 

exceed the acute listed species LOC (0.1) for short grass even at the model limit (997 feet from 

the treated field). However, spray drift is not of acute dose-based risk concern for listed 

granivore mammals. AgDRIFT also indicates that spray drift EECs yield chronic dietary RQs 

that exceed the LOC (1.0) for short grass even at the model limit (997 feet from the treated field). 

Even considering the least conservative forage class (fruits/pods), RQs resulting from spray drift 

EECs would exceed the chronic LOC at least as far as 650 feet from the treated field.

One of the uncertainties regarding chronic RQs for dicrotophos is the use of the 35 day default 

foliar dissipation half-life. In some fate studies, dicrotophos is shown to degrade much more 

quickly. In an effort to address this uncertainty, RQs were modeled using a hypothetical three 

day half-life. Use of a three day half-life results in a 40% reduction in the RQs (e.g. 5.82 to 

3.44). However, even if data were available to reduce the foliar dissipitation half-life used in the 

model to three days, all size class and forage class exceedances would remain, albeit not as far 

off-field as for the 35-day half life assumption.
-Page 58 of 102-

Tree Injection Use Pattern

The tree injection use pattern is a potential avenue of dicrotophos exposure for mammals. 

Without an understanding of the systemic nature of dicrotophos in the tree, it is not possible to 

accurately estimate dicrotophos concentrations by plant tissue type and thereby associate dietary 

items with an exposure magnitude. Mammalian diets could consist of bark, foliage, nuts, or 

some combination of the three and, in the absence of plant tissue residue data (and dissipation 

rates), are all plausible exposure pathways. While crop tree species have been off-labeled, trees 

that produce mast would not be considered crop tree species. Depending on the translocation of 

tree-injected dicrotophos to seeds, mast producing species such as oaks could forseeably be of 

exposure concern for nut-consuming mammals.

Since a mammalian acute dietary toxicity endpoint (i.e., an LC50) is not available, the chronic 

NOAEL (2.0 mg/kg diet) serves as a conservative estimate of acute dietary-based toxicity. 

Given the conservative assumption that dicrotophos exclusively accumulates in the foliage of 

injected trees resulting in an exposure to concentrations of 1,000 ppm, the dietary RQ for 

mammals is 500. Given the assumption that dicrotophos is evenly distributed through sapwood 

and foliage of injected trees resulting in an exposure to concentrations of 31 ppm, the dietary RQ 

for mammals is 15.5. This RQ exceeds the non-listed species LOC (0.5) by more than 30 fold. 

Note that the assumption of even distribution is not conservative if considering herbivorous 

consumption of leaves, bark, or seeds alone. Still, these assumptions represent a spectrum of 

presumed exposure with all conclusions indicating the tree injection use pattern produces 

exceedances of the acute LOC.
-Page 59 of 102-

Figure 4.1. Mammalian LOCs Superimposed on Residue Decline Curve
-Page 60 of 102-

4.3.2.2. Risk to Birds

Cotton Use Pattern

The southeastern United States and Mississippi Valley, some of the largest cotton growing areas 

of the country, fall within the delineation of two major migratory corridors traveled by 

neotropical migrant birds: the Mississippi and Atlantic flyways. Two field studies conducted in 

the late 1980’s on dicrotophos-treated cotton fields in Alabama and Arizona documented the 

occurence of numerous avian and herpetile species in wildlife surveys. In Alabama, 75 species 

of bird were identified during surveys, with 29 of those species using the cotton fields. In 

Arizona, 102 species of birds were identified during surveys, 36 of those species observed within 

the borders of the cotton field.

Similar to the mammalian chronic EECs, acute avian EECs are calculated on both a dietary and 

dose basis. For the cotton use, acute dose-based upper bound Kenaga RQs exceed the acute nonlisted species LOC (0.5) for all size classes and foraging groups. Sub-acute dietary and chronic 

dietary upper bound Kenaga RQs exceed the acute non-listed species LOC (0.5) and chronic 

LOC (1.0), respectively, for all forager group types. Considering the magnitude of acute nonlisted species LOC exceedances, as much as 926-fold, there is a high degree of certainty that 

avian species will be adversely affected by dicrotophos applied to cotton. 

EECs exceed both the avian acute listed species LOC (0.1) and avian chronic LOC (1.0) for 270

days and 320 days, respectively, after first application for short grass, assuming a 35-day half life 

and two applications of 0.5 lb a.i./A applied at a 14-day interval (Figure 4.2). With the same 

model input parameter, EECs exceed the avian acute non-listed species LOC (0.5) for 140 to 160 

days following application for all other forage types except fruits/pods/seeds, where the avian 

acute non-listed species LOC is no longer exceeded after day 48. Since terrestrial application 

residues exceed 0.5 mg ai/kg dietary item (i.e., the avian reproduction NOAEC) for more than 

267 days following the first application of dicrotophos for all forager types except consumers of 

fruits/nuts/seeds (dicrotophos residues above the NOAEC through day 180), there is a high 

degree of confidence in the prediction of adverse chronic effects. Even under a less conservative 

T-REX exposure scenario, mean Kenaga acute and chronic RQs exceed the acute listed species 

or chronic LOC for all size classes and forage types. 

To spatially examine the potential risk of spray drift, simulations were performed with the spray 

drift modeling program AgDRIFT. It was determined that spray drift EECs yield acute dosebased RQs that exceed the acute listed species LOC (0.1) for short grass even at the model limit 

(997 feet from the treated field), and for all other forage classes at least 730 feet from the treated 

field. Spray drift EECs yield subacute dietary RQs that exceed the acute listed species LOC 

(0.1) for short grass even at the model limit (997 feet from the treated field), and for all other 

forage classes at least 108 feet from the treated field. Spray drift EECs yield chronic dietary RQs 

that exceed the LOC (1.0) for short grass even at the model limit (997 feet from the treated field), 

and for all other forage classes at least 250 feet from the treated field. 

The STIR model output indicates that inhalation may be an exposure pathway of concern for 

avian species. Considering that the available acute mammalian inhalation toxicity study used a 
-Page 61 of 102-

supersaturated solution and recorded no mortalities, and that exposure to droplets in the field 

would be expected to be of a lesser duration (i.e., less than four hours), inhalation is not regarded 

as the primary route of exposure eliciting observed avian toxicological response.

One of the uncertainties regarding chronic RQs for dicrotophos is the use of the 35 day default 

foliar dissipation half-life. In some fate studies, dicrotophos is shown to degrade much more 

quickly. In an effort to address this uncertainty, RQs were modeled using a hypothetical three 

day half-life. Use of a three day half-life results in a 40% reduction in the RQs (e.g. 5.82 to 

3.44). However, even if data were available to reduce the foliar dissipitation half-life used in the 

model to three days, all forage class exceedances would remain, albeit not as far off-field as for 

the 35-day half life assumption.
-Page 62 of 102-

Figure 4.2. Avian LOCs Superimposed on Residue Decline Curve

Chronic LOC 

Avian acute 

LOC

Avian acute listed 

species LOC
-Page 63 of 102-

Birds are generally used as surrogates for terrestrial-phase amphibians and reptiles. However, 

these taxa are poikilotherms (body temperature varies with environmental temperature) while 

birds are homeotherms (temperature is regulated, constant, and largely independent of 

environmental temperatures). Therefore, they tend to have much lower metabolic rates and 

lower caloric intake requirements than birds or mammals. As a consequence, birds are likely to 

consume more food than amphibians on a daily dietary intake basis, assuming similar caloric 

content of the food items. The use of avian food intake allometric equation as a surrogate to 

reptiles and amphibians is likely to result in an over-estimation of exposure and risk for reptiles 

and terrestrial-phase amphibians. Therefore, T-REX has been refined to the Terrestrial 

Herpetofaunal Exposure and Residue Program Simulation (T-HERPS) model (v1.0, 5/15/2007), 

which allows for an estimation of food intake for poikilotherms using the same basic procedure 

as T-REX to estimate food intake. It is possible that the final listed species effects determination 

will utilize T-HERPS as a refinement, should exposure of herpetofauna be deemed likely. 

Tree Injection Use Pattern

The tree injection use pattern is a potential route of dicrotophos exposure for avian species. 

Without an understanding of the systemic nature of dicrotophos in the tree, it is not possible to 

accurately estimate dicrotophos concentrations by plant tissue type and thereby associate dietary 

items with an exposure magnitude. In contrast to mammalian species which are likely to 

consume bark, foliage, nuts, or some combination of the three, birds would more likely consume

fruits, nuts, and seeds; encountering dicrotophos residues (if present) through those dietary items. 

While the label stipulates that this product is not for use on crop species, it is important to 

understand that even the ornamental varieties of many tree species still produce fruits, nuts, or 

seeds that are attractive forage items for birds. Secondary exposure is also of concern for avian 

species that forage on insects, which may encounter dicrotophos residues via their insect prey.

The subacute dietary exposure endpoint for birds is an LC50 of 13 mg/kg diet or 13 ppm. Given 

the conservative assumption that dicrotophos exclusively accumulates in the foliage of injected 

trees resulting in an exposure to concentrations of 1,000 ppm, the dietary RQ for birds is 77 (for 

the purposes of this exercise, the foliage is considered an appropriate surrogate for 

fruits/nuts/seeds). Assuming even distribution of dicrotophos throughout the sapwood, foliage, 

and nuts/fruits/seeds of injected trees results in an exposure concentration of 31 ppm, with a 

corresponding avian dietary RQ of 2.4. This RQ exceeds the non-listed species LOC (0.5) by 

more than 4 fold. Note that the assumption of even distribution is not conservative if considering 

herbivorous consumption of fruits, nuts, or seeds alone. Still, these assumptions represent a 

spectrum of presumed exposure with all conclusions indicating the tree injection use pattern 

produces exceedances of the acute LOC.

4.3.2.3. Risk to Terrestrial Invertebrates

Of the available data on various non-target terrestrial insects, honeybees are the most sensitive 

terrestrial invertebrate species. Dicrotophos is classified as highly toxic to honeybees on an 
-Page 64 of 102-

acute contact exposure basis, with an LD50 of 0.076 μg ai/bee. The honey bee acute oral LD50 is 

0.068 μg ai/bee. RQs for terrestrial invertebrates were calculated separately for acute oral and 

contact exposure, using tall grass EECs of 15.95 μg ai/bee and 1.35 μg ai/bee, divided by the 

acute oral and contact LD50’s of 0.068 μg ai/bee and 0.076 μg ai/bee, respectively. The resulting 

RQs for acute oral and contact exposure, 234.6 and 17.8, respectively, are compared to a LOC of 

0.4 as discussed in the Pollinator SAP white paper (USEPA, 2012). Thus, the RQ exceeds the 

LOC by more than an order of magnitude. However, the screening level RQ values are based on 

model-generated exposure values which are intended to be conservative. Also, the RQ values

are based on effects to individual bees under laboratory conditions and there is uncertainty 

regarding the potential effects to bee colonies under actual use conditions. Residues on foliage 

have been found to remain toxic to bees and other beneficial insects for as long as 16 days 

(MRID 05013577). Although the risk estimates suggest that terrestrial invertebrates may be 

impacted by dicrotophos use and that indirect effects to plants with obligate relationships to 

insect species may result, there are relatively few incident reports for dicrotophos and none of 

these reports involved bees. Since dicrotophos is used on cotton and since cotton is used by 

some beekeepers to produce honey, the proximity of bee colonies to dicrotophos use areas may 

be high; however, in a survey of pesticide residues in managed bee colonies (Mullin et al. 2010),

no dicrotophos residues were reported. While the absence of bee kill incident data cannot be 

construed as the absence of incidents and while the Mullin et al. 2010 study cannot be considered 

an exhaustive investigation of pesticide residues in honey bee colonies, these sources of 

information serve as lines of evidence that the screening-level risk estimates while high may not 

accurately reflect the risk. Although other organophosphate pesticides have been detected in bee 

colonies and have been associated with bee kill events, these data may reflect the more 

widespread use of the organophosphates on a range of pollinator-attractive crops. Also, since 

organophosphate insecticides such as dimethoate have been used as reference toxicants in both 

laboratory and semi-field based studies, it is possible that high toxicity of these compounds 

results in the loss of the scout and forage bees and that sufficiently large quantities of toxicant 

may not be transported back to the colony to result in colony-level effects. At this time, there is 

uncertainty regarding the actual risks of dicrotophos use to bees given the lack of colony-level 

studies; however, the other lines of evidence available for the compound do not indicate that the 

compound is being detected in colonies nor have bee incidents been reported to have been 

associated with the use of the compound.

Specific to the tree injection use pattern, potential exposure of non-target insect pollinator species

to dicrotophos is plausible, although the magnitude of residue concentrations is uncertain in the 

absence of residue data from dicrotophos-treated trees. Many of the tree species listed on the label 

(e.g., ash, crabapple, linden, locust, maple, stone fruit trees) are attractive sources of pollen and/or 

nectar for insect pollinators.

4.3.2.4. Risk to Terrestrial Non-target Plants

Since no adverse effects were reported in either the seedling emergence or vegetative vigor

studies at the maximum dicrotophos application rate, phytotoxic effects are not expected on the

use sites. Effects offsite are also not expected as exposures would be below the maximum 

application rate. 
-Page 65 of 102-

4.4. Uncertainties and Data Gaps

4.4.1. Fate and Transport

The tree injection use pattern (EPA Reg. No. 7946-11) does not limit the number of applications 

that can be made in a given year or season. Further, the stated application rate is based on 

number of capsules for a given tree size. However, the size of the capsule can be variable 

according to the label which would result in substantially different applications depending on 

capsule size. Given these uncertainties, maximum single application and maximum annual 

application cannot be precisely determined.

The fate of dicrotophos when injected into the tree is also a great uncertainty. The suite of 

chemical fate data EFED receives has little bearing on how a chemical behaves when injected 

into a tree. The rates of degradation in the tree, mobility to various parts of the tree, and 

formation of degradates cannot be characterized by current data. Though it is not detected in soil 

metabolism studies, it is possible that monocrotophos is formed in the tree as monocrotophos 

was formed in foliar dislodgeable residue study (MRID 44731001). The study showed 

detections of monocrotophos over the level of quantitation after each of two applications in 

Texas. Monocrotophos was not detected in the Mississippi test. This degradate of dicrotophos is 

more toxic to many taxa than dicrotophos itself. 

Dicrotophos degrades readily in aerobic soil with a half-life of 2.7 days and is the dominant route 

of dissipation. Model estimates for aerobic soil and aquatic metabolism rely on only one study 

testing one soil to derive model parameters. The 2.7 day half-life is multiplied by uncertainity 

factors to derive the parameters but it must still be considered that one soil is being used to 

represent thousands of soils and microbial communities with variable types and rates of 

metabolism in addition to many aquatic environments with similar variability. 

4.4.2. Effects 

The formation and decline of monocrotophos residues in and/or on plant tissue is a considerable 

uncertainty in this assessment. Monocrotophos is known to be more toxic to avian species than 

dicrotophos on an acute basis, and while residues of monocrotophos on foliage are presumed to 

be lesser (on a mass per unit volume or mass per unit area basis), the enhanced toxicity of this 

compound may effectively extend the time of acute risk LOC exceedances following dicrotophos 

application. 

The available avian acute and subacute studies are not robust. Many of the available studies 

were not performed in accordance with the current guidelines. Fewer treatment levels than 

recommended (four instead of five) is one shortcoming of the studies. Treatment levels were 

poorly selected, such that few, if any, concentrations or doses resulted in partial kills, meaning 

that mortalities by treatment were commonly zero or 100 percent. For most studies, uncertainties 

would be reduced if additional study conduct details were available. Specifically, the percent 

active ingredient of the test material for the most sensitive acute oral and sub-acute dietary test 

species is a considerable uncertainty. The avian RQs reported in this assessment may 

underestimate toxicity since the compound purity was presumed to be technical grade. 
-Page 66 of 102-

An acceptable foliar residue toxicity study with honey bees (OCSPP 850.3030) would allow for 

determination of a 24-h RT25. This data would reduce uncertainties surrounding the length of 

time post-application that residues of dicrotophos on foliage are toxic to honey bees.

A chronic fish study with an estuarine/marine species exposed to dicrotophos is not available. 

While it is uncertain whether estuarine/marine fish species may be more sensitive to dicrotophos 

exposure of chronic duration than freshwater species, available data indicate that 

estuarine/marine species are nearly 14 fold less sensitive to dicrotophos exposure of acute 

duration than freshwater fish species tested.

5. Endocrine Disruptor Screening Program (EDSP)

As required by FIFRA and FFDCA, EPA reviews numerous studies to assess potential adverse 

outcomes from exposure to chemicals. Collectively, these studies include acute, subchronic and 

chronic toxicity, including assessments of carcinogenicity, neurotoxicity, developmental, 

reproductive, and general or systemic toxicity. These studies include endpoints which may be 

susceptible to endocrine influence, including effects on endocrine target organ histopathology, 

organ weights, estrus cyclicity, sexual maturation, fertility, pregnancy rates, reproductive loss, 

and sex ratios in offspring. For ecological hazard assessments, EPA evaluates acute tests and 

chronic studies that assess growth, developmental and reproductive effects in different 

taxonomic groups. As part of the Preliminary Problem Formulation for Registration Review 

(USEPA, 2008), EPA reviewed 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 Disruptor 

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 estrogen, or other such endocrine effects as the Administrator 

may designate.” The EDSP employs a two-tiered approach to making the statutorily required 

determinations. Tier 1 consists of a battery of 11 screening assays to identify the potential of a 

chemical substance to interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal 

systems. Chemicals that go through Tier 1 screening and are found to have the potential to 

interact with E, A, or T hormonal systems will proceed to the next stage of the EDSP where EPA 

will determine which, if any, of the Tier 2 tests are necessary based on the available data. Tier 2 

testing is designed to identify any adverse endocrine-related effects caused by the substance, and 

establish a dose-response relationship between the dose and the E, A, or T effect. 

Under FFDCA section 408(p), the Agency must screen all pesticide chemicals. Between 

October 2009 and February 2010, EPA issued test orders/data call-ins for the first group of 67 

chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. A second list 

of chemicals identified for EDSP screening was published on June 14, 20135and includes some 

 

5 See http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0477-0074 for the final second list of 

chemicals.
-Page 67 of 102-

pesticides scheduled for registration review and chemicals found in water. Neither of these lists 

should be construed as a list of known or likely endocrine disruptors. 

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.6

6. Federally Threatened and Endangered (Listed) Species Concerns

Section 7 of the Endangered Species Act, 16 U.S.C. Section 1536(a)(2), requires all federal 

agencies to consult with the National Marine Fisheries Service (NMFS) for marine and 

anadromous listed species, and/or the United States Fish and Wildlife Service (USFWS) for 

listed wildlife and freshwater organisms, if they are proposing an "action" that may affect listed 

species or their designated critical habitat. Each federal agency is required under the Act to 

ensure that any action they authorize, fund, or carry out is not likely to jeopardize the continued 

existence of a listed species or result in the destruction or adverse modification of designated 

critical habitat. To jeopardize the continued existence of a listed species means "to engage in an 

action that reasonably would be expected, directly or indirectly, to reduce appreciably the 

likelihood of both the survival and recovery of a listed species in the wild by reducing the 

reproduction, numbers, or distribution of the species" (50 C.F.R. § 402.02).

To facilitate compliance with the requirements of the Endangered Species Act (subsection 

(a)(2)), the Office of Pesticide Programs has established procedures to evaluate whether a 

proposed registration action may directly or indirectly appreciably reduce the likelihood of both 

the survival and recovery of a listed species in the wild by reducing the reproduction, numbers, 

or distribution of any listed species (USEPA, 2004). After the Agency’s screening level risk 

assessment is conducted, if any of the Agency’s listed species’ LOCs are exceeded for either 

direct or indirect effects, an analysis is conducted to determine if any listed or candidate species 

may co-occur in the area of the proposed pesticide use or areas downstream or downwind that 

could be contaminated from drift or runoff/erosion. If listed or candidate species may be present 

in the proposed action area, further biological assessment is undertaken. The extent to which 

listed species may be at risk is considered, which then determines the need for the development 

of a more comprehensive consultation package, as required by the Endangered Species Act.

The federal action addressed herein is the proposed registration renewal of dicrotophos on 

agricultural (i.e., cotton) and silvicultural use sites and it is expected that its use as a tree 

injection pesticide could occur nationwide.

6.1. Action Area 

For listed species assessment purposes, the action area is considered to be the area affected 

directly or indirectly by dicrotophos use and not merely the immediate area where dicrotophos is 

applied. At the initial baseline, the risk assessment considers broadly described taxonomic 

 

6 http://www.epa.gov/endo/
-Page 68 of 102-

groups and conservatively assumes that listed species within those broad groups are co-located 

with the pesticide treatment area. This means that listed terrestrial plants and wildlife are 

assumed to be located on or adjacent to the treated site and listed aquatic organisms are assumed 

to be located in a surface water body adjacent to the treated site. 

6.2. Taxonomic Groups Potentially at Risk 

If the assumptions associated with the baseline action area result in RQs that are below the listed 

species LOCs, a "no effect" determination conclusion is made with respect to listed species in 

that taxa, and no further refinement of the action area is necessary. Furthermore, RQs below the 

listed species LOCs for a given taxonomic group indicate no concern for indirect effects on listed 

species that depend upon the taxonomic group for which the RQ was calculated. However, in 

situations where the screening assumptions lead to RQs in excess of the listed species LOCs for a 

given taxonomic group, a potential for a "may affect" conclusion exists and may be associated 

with direct effects on listed species belonging to that taxonomic group or may extend to indirect 

effects upon listed species that depend upon that taxonomic group as a resource. In such cases, 

additional information on the biology of listed species, the locations of these species, and the 

locations of use sites are considered to determine the extent to which screening assumptions 

regarding an action area apply to a particular listed organism. These subsequent refinement steps 

will consider how this information would impact the action area for a particular listed organism 

and potentially include areas of exposure that are downwind and downstream of the pesticide use 

site.

Assessment endpoints, exposure pathways, and the conceptual models addressing registered 

dicrotophos uses, and the associated exposure and effects analyses conducted for the dicrotophos 

baseline risk assessment are in Sections 2 to 3. The assessment endpoints used in the baseline 

risk assessment include those defined operationally as reduced survival and reproductive 

impairment for both aquatic and terrestrial animal species and survival, reproduction, and growth 

of aquatic and terrestrial plant species from both direct acute and chronic exposures. These 

assessment endpoints are intended to address the standard set forth in the Endangered Species 

Act requiring federal agencies to ensure that any action they authorize does not appreciably 

reduce the likelihood of both the survival and recovery of a listed species in the wild by reducing 

the reproduction, numbers, or distribution of the species. Risk estimates (RQs) which, 

integrating exposure and effects, are calculated for broad based taxonomic groups in the 

screening-level risk assessment presented in Section 4.

Data on exposure and effects collected under laboratory and sometimes field conditions are 

evaluated in the screening-level risk assessment for nonlisted and listed species. Both acute 

endangered species and chronic risk LOCs are considered in the baseline risk assessment to 

identify potential effects (or absence thereof) to listed species. This section identifies direct 

effect concerns, by taxa that are triggered by exceeding endangered LOCs in the screening-level

risk assessment (Table 6.1) Where applicable, an evaluation of the potential probability of 

individual effects for exposures that may occur at the established listed species LOC is presented 

in Section 6.2.1. Data on exposure and effects collected under field and laboratory conditions 

are evaluated to make determinations on the predictive utility of the direct effect screening 

assessment findings to listed species. 
-Page 69 of 102-

Additional Considerations for Listed Species

Based on this screening-level assessment, there are potential risks of direct effects to listed and 

non-listed freshwater and estuarine/marine invertebrates, mammals, birds (birds are surrogates 

for terrestrial phase reptiles and amphibians), and terrestrial invertebrates from the use of 

dicrotophos on cotton. Listed species of freshwater and estuarine/marine invertebrates, 

mammals, birds, and terrestrial invertebrates may also be affected through indirect effects 

because of the potential direct effects on listed and non-listed species. Potential direct effects on 

listed and non-listed freshwater and estuarine/marine invertebrates (cotton use pattern only), 

mammals, birds, and terrestrial invertebrates from the use of dicrotophos may be associated with 

modification of Primary Constituent Elements (PCEs) of designated critical habitats, where such 

designations have been made. However, at this current stage of the Registration Review process, 

it is premature to make effects determinations for listed species until further scientific analysis 

and refinements are conducted, based on recommendations received from the National Academy 

of Sciences’ (NAS) National Research Council (NRC) April 2013 report, available at

http://www.nap.edu/catalog.php?record_id=18344. The NAS report outlines recommendations 

on specific scientific and technical issues related to the development of pesticide risk 

assessments that are compliant with the Endangered Species Act (ESA) and the Federal 

Insecticide, Fungicide, and Rodenticide Act (FIFRA).

The EPA along with the U.S. Fish & Wildlife Service (USFWS), the National Marine Fisheries 

Service (NMFS) (collectively, the Services), and the U.S. Department of Agriculture (USDA), 

released a summary of their implementation plan for assessing risks of pesticides to listed species 

ahead of the stakeholder workshop held on November 15, 2013. This plan was developed in 

response to the NAS’ recommendations, including a common approach to risk assessment as a 

way of addressing scientific differences between EPA and the Services. During the workshop, 

the agencies received feedback from the public on the interim scientific approaches that were 

developed as part of the initial implementation of the NAS recommendations. These approaches 

will be jointly implemented and vetted as part of a phased iterative process. Once fully vetted, 

EPA will further refine the listed species effects determination portion of this risk assessment. 

To make effects determinations for individual listed species, useful refinements may include, but 

are not limited to, analyses of: 1) more detailed, species-specific ecological and biological data; 

2) more detailed and accurate information on dicrotophos use patterns; and 3) sub-county level 

spatial proximity data for the co-occurrence of potential effects areas and listed species and any 

designated critical habitat. Examples of such refinements are described below.

EFED is currently developing tools that are expected to further refine the assessment and are 

designed to support effects determinations for individual federally listed species and their 

designated critical habitats (where applicable). Scientific information obtained from the 

Services, and other reliable sources is being collated by EFED to address all currently listed 

species. This information is being stored in an Office of Pesticide Programs (OPP) Pesticide 

Registration Information SysteM (PRISM) listed species knowledgebase. The listed species 

knowledgebase consists of an information repository that houses biological and behavioral 

information relevant to individual species (e.g., habitat, diet, and life history, including specific 
-Page 70 of 102-

temporal and spatial associations) and a document repository that contains supporting documents 

(e.g., USFWS recovery plans) and electronic information (e.g., GIS data files). For terrestrial 

taxa, biological information relevant to the assessment (e.g., diet and body weight) will be used 

to parameterize exposure estimates using a method consistent with currently used methods in the 

T-REX and T-HERPS models. 

Refinements will also include more detailed analyses of the registered uses and specific use 

patterns that result in either “Likely to Adversely Affect” (LAA) or “Not Likely to Adversely 

Affect” (NLAA) determinations for federally listed species. The analyses may include more 

information on where, when, and how dicrotophos is used on all use sites. Actual usage data 

(when available) and national land-cover datasets that indicate potential use sites [e.g., National 

Land Cover Dataset (NLCD), Cropland Data Layer (CDL)] may be used to support a more 

refined analysis of where dicrotophos is reasonably expected to be used. Similarly, refinements 

on the timing of applications and a more in-depth exploration of agronomic practices for

dicrotophos may be included as part of the refinement.

The refinements based on individual species data; additional, detailed usage information, when 

available; and recommendations from the NRC report are expected to help to more accurately 

identify potential areas of effect and to better inform effects and habitat determinations for listed 

species and any designated critical habitats.
-Page 71 of 102-

Table 6.1. Preliminary Conclusions for Potential Direct Effects to Federally Listed Taxa Associated with the Registered Uses of Dicrotophos, Based on 

Best Available Data.

Listed Plant Taxon Potential Direct Effects

Terrestrial and semiaquatic plants –

monocots and dicots

No effect

Aquatic vascular and 

nonvascular plants No effect

Listed Animal Taxon

Potential Direct Effects

Acute Notes Chronic Notes

Terrestrial invertebrates Yes

1 Effect to aquatic invertebrates uncertain for the 

tree injection use pattern.

2 Estuarine/marine acute invertebrate RQ exceeds 

LOC by 3.4 fold for cotton use pattern. 

ND

3 Effect to aquatic invertebrates uncertain for

the tree injection use pattern.

4 No effect to estuarine/marine fish species 

from chronic aquatic exposure to the TGAI, 

unless estuarine/marine fish

are more than 1000 times as

sensitive as the fathead minnow tested

in MRID 48482901.

Mammals Yes Yes

Birds Yes Yes

Reptiles Yes Yes

Amphibians (terrestrial 

phase) Yes Yes

Amphibians (aquatic 

phase) No effect No effect

Freshwater fish No effect No effect

Freshwater 

invertebrates Yes1 Yes3

Molluscs No effect ND
-Page 72 of 102-

Listed Plant Taxon Potential Direct Effects

Estuarine/marine fish No effect No effect4

Estuarine/marine 

invertebrates Yes1,2 Yes3

ND Not determined.
-Page 73 of 102-

6.2.1. Probit Dose-Response Analysis 

The Agency uses the probit dose-response relationship as a tool for providing additional 

information on the potential for acute direct effects to aquatic and terrestrial animals (USEPA, 

2004). As part of this evaluation, the acute RQ for listed species is presented in terms of the 

chance of an individual event (i.e., mortality or immobilization) should exposure at the EEC 

actually occur for a species with sensitivity to dicrotophos on par with the acute toxicity endpoint 

selected for RQ calculation. To accomplish this interpretation, the Agency uses the slope of the 

dose-response relationship available from the toxicity study used to establish the acute toxicity 

measures of effect for each taxonomic group that is relevant to this assessment. The individual 

effects probability associated with the acute RQ is based on the mean estimate of the slope and 

an assumption of a probit dose-response relationship. In addition to a single effects probability 

estimate based on the mean, upper and lower estimates of the effects probability are also 

provided to account for variance in the slope, if available. Based on the available acute toxicity 

for dicrotophos, a summary of the probit dose-response analysis is provided in Table 6.2. If no 

dose response information is available to estimate a slope for this analysis, a default slope 

assumption of 4.5 (with lower and upper bounds of 2 to 9) (Urban and Cook, 1986) is used. 

Individual effect probabilities are calculated based on an Excel spreadsheet tool IECV1.1 

(Individual Effect Chance Model Version 1.1) developed by the U.S. EPA, OPP, Environmental 

Fate and Effects Division (June 22, 2004). The model allows for such calculations by entering 

the mean slope estimate (and the 95% confidence bounds of that estimate) as the slope parameter 

for the spreadsheet. The desired threshold for the probability of an individual effect is entered as 

the listed species LOC. In addition, the probability of an individual effect is also derived based 

on the calculated acute RQ, if available.

The probabilities of an individual acute direct effect (i.e., mortality) for each taxa for which there 

is a definitive RQ are presented in Table 6.2. These reflect a default average slope of 4.5 (e.g.

chance is 1 in 4.3 X 105). If the true dose response curve were shallower, the chance of an 

individual effect increases (e.g. slope of 2, chance is 1 in 48). 
-Page 74 of 102-

Table 6.2. Summary of Dicrotophos Probit Dose Response Analysis for Listed Species

Taxa (study type) Acute Effect

Slope (95% C.I.)

Chance of Individual 

Effect at Listed Species 

LOC (95% C.I.)

Chance of Individual 

Effect at Derived Acute 

RQ (95% C.I.)

Bird oral dose

Mortality 

Default Slope = 4.5 

(2 – 9)

1 in 2.9E+05

(1 in 44 to 1 in 8.9E+18) 1 in 2.34 to 1 in 11

Bird dietary

Mortality 

Default Slope = 4.5 

(2 – 9)

1 in 2.9E+05

(1 in 44 to 1 in 8.9E+18) 1 in 1.97 to 1 in 1 2

Mammal oral dose

Mortality 

Default Slope = 4.5 

(2 – 9)

1 in 2.9E+05

(1 in 44 to 1 in 8.9E+18) 1 in 6.38E+06 to 1 in 13

Freshwater fish

Mortality 

Default Slope = 4.5 

(2 – 9)

1 in 4.18E+08

(1 in 216 to 1 in 

1.75E+31)

1 in 5.25E+264

(1 in 1.23E+06 to 1 in 

7.46E+102)

Estuarine/marine fish

Mortality 

Default Slope = 4.5 

(2 – 9)

1 in 4.18E+08

(1 in 216 to 1 in 

1.75E+31)

1 in 6.12E+615

(1 in 1.45E+13 to 1 in 

3.80E+242)

Freshwater invertebrates

Immobilization 

Slope = 3.3

(-1 – 7.7)

1 in 1.14E+05

(1 in 1 to 1 in 1.57E+23)

1 in 1.316

(1 in 2.42 to 1 in 1.05)

Estuarine/marine 

invertebrates 

Immobilization 

Slope = 5.3

(-7.7 – 18)

1 in 3.73E+11

(1 in 1 to 1 in 

7.23E+120)

1 in 7.75E+027

(1 in 1 to 1 in 1.45E+24)

1 Acute RQ for bird (oral) 0.91-463

2 Acute RQ for bird (dietary) 1.01-16.2

3 Acute RQ for mammal 0.073-11.4

4 Acute RQ for freshwater fish 0.004

5Acute RQ for estuarine/marine fish 0.0002

6 Acute RQ for freshwater invertebrates = 1.65

7 Acute RQ for estuarine/marine invertebrates = 0.27

Based on the model output, the chance of individual effect at the derived acute RQ may be 

considered “likely” for avian dose and dietary exposure, and for freshwater invertebrate 

exposure. The chance of individual effect at the derived acute RQ is not as probable for 

freshwater fish, estuarine/marine invertebrates, and mammals (exposed to an oral dose). 

6.2.2. Listed Species Occurrence Associated with Registered Uses

The screening-level risk assessment for dicrotophos assumes that it may be applied nationwide, 

including U.S. territories and possessions. Therefore, no federally listed species are excluded 

from the screening level analyses, unless otherwise indicated (e.g., if only listed due to Similarity 

of Appearance to another listed species). A spatial co-occurrence analysis that compares the best 

available data regarding dicrotophos potential and documented use areas and listed species 

occurrence is needed to more explicitly address potential risk to listed species of concern.
-Page 75 of 102-

7. References

Donley, D.E. 1967. Distribution of Bidrin in the Foliage of Treated Trees. Journal of Economic 

Entomology. 60(6): 1583-1585.

Engineering Toolbox. http://www.engineeringtoolbox.com/wood-density-d_40.html. Accessed 

December 7, 2012

Flickinger, E.L., D.H. White, C.A. Mitchell, and T.G. Lamont. 1984. Monocrotophos and

dicrotophos residues in birds as a result of misuse of organophosphates in Matagorda 

County, Texas. J. Assoc. Off. Anal. Chem. 67:827-828.

Kuhns, M. 2012. Getting Chemicals into Trees without Spraying. Utah State University 

Cooperative Extension. NR/FF/020. 

http://extension.usu.edu/files/publications/publication/NR_FF_020pr.pdf

Martin, J.G.; B.D. Kloeppel, T.L. Schaefer, D.L. Kimbler, S.G. McNulty. 1998. Aboveground 

biomass and nitrogen allocation of ten deciduous southern Appalachian tree species. 

Canadian Journal of Forest Research. 28: 1648-1659. 

http://coweeta.uga.edu/publications/136.pdf

Meyers, S.M. 1990. Effects of Northern Bobwhite (Colinus virginianus) Age and Weight on 

Results of the Avian Dietary Toxicity Test. Bulletin of Environmental Contamination and 

Toxicology. 45(5):667-674. November 1990.

Mota-Sanchez, D; B.M. Cregg, D.G. McCullough, T.M. Poland, R.M. Hollingworth. 2009. 

Distribution of trunk-injected 14C-imidacloprid in ash trees and effects on emerald ash 

borer (Coleoptera: Buprestidae) adults. Crop Protection 28: 655-661. 

http://naldc.nal.usda.gov/download/32582/PDF

Moser, VC. 2011. Age-related differences in acute neurotoxicity produced by mevinphos, 

monocrotophos, dicrotophos, and phosphamidon. Neurotoxicology and Teratology. 

33(4):451-457. July-August 2011.

United States Environmental Protection Agency (USEPA). 1993. Wildlife Exposure Factors 

Handbook. EPA/600/R-13/187a. Office of Research and Development, Washington, D.C.

U.S. Environmental Protection Agency. 1998. Guidelines for Ecological Risk Assessment. 

Risk Assessment Forum, Office of Research and Development, Washington, D.C. 

EPA/630/R-95/002F. April 1998. 

U.S. Environmental Protection Agency. 2000. Risk Characterization Handbook. Science Policy 

Council, U.S. Environmental Protection Agency, Washington, D.C. 20460. EPA 100-B00-002. December 2000.

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

Endangered and Threatened Species Effects Determinations. Office of Prevention, 

Pesticides and Toxic Substances, Office of Pesticide Programs, Washington, D.C. 

January 23, 2004.

U.S. Environmental Protection Agency. 2006. Reregistration Eligibility Decision for 

Dicrotophos, U.S. Environmental Protection Agency, Washington, D.C. 20460. Case no. 

0145. July 2006.

U.S. Environmental Protection Agency. 2008. Preliminary Problem Formulation for 

Registration Review for Dicrotophos, U.S. Environmental Protection Agency, 

Washington, D.C. 20460. DP Barcode 348184. May 6, 2008.

U.S. Environmental Protection Agency. 2010. User’s Guide: Screening Tool for Inhalation Risk

Version 1.0, U.S. Environmental Protection Agency, Washington, D.C. 20460. 

November 23, 2010.

U.S. Environmental Protection Agency. 2010. Release of SIP (Screening Imbibition Program) 

version 1.0 for use in the Environmental Fate and Effects Division. U.S. Environmental 

Protection Agency, Washington, D.C. 20460. July 6, 2010.

U.S. Environmental Protection Agency. 2012. White Paper in Support of the Proposed Risk 

Assessment Process for Bees. Office of Chemical Safety and Pollution Prevention, 

Office of Pesticide Programs, Environmental Fate and Effects Division, Washington, 

D.C. September 11, 2012.

United States Fish and Wildlife Service (USFWS). 1980. Handbook of Acute Toxicity of 

Chemicals to Fish and Aquatic Invertebrates. Summaries of Toxicity Tests Conducted at 

Columbia National Fisheries Research Laboratory, 1965-78. Resource Publication 137. 

Washington, DC.

Willis, G.H. and L.L. McDowell. 1987. Pesticide persistence on foliage. Reviews of 

Environmental Contamination and Toxicology 100: 23-73.
-Page 77 of 102-

7.1 Submitted Product Chemistry and Environmental Fate Studies

161-1 Hydrolysis (DICROTOPHOS)

MRID DOC NUM Citation Reference

39210 Brown, N.P.H.; Forster, A.S.; Furmidge, C.G.L. (1966) Stability of 

agricultural chemicals. Hydrolytic and thermal stabilities of 

phosphorylated crotonamides. Journal of the Science of Food and 

Agriculture 17(?/Nov):510-517. (Also~In~unpublished submission 

received Mar 18, 1980 under 6F1851; submitted by Shell 

Chemical Co., Washington, D.C.; CDL:099341-U) 

115287 Shell Chemical Co. (19??) Hydrolytic Decomposition of Bidrin. 

(Unpublished study received Oct 7, 1982 under 201-142; CDL: 

248514-C) 

115288 Brown, N.; Forster, A.; Furmidge, C. (1966) Stability of agricultural chemicals. 1. Hydrolytic and thermal stabilities of 

phosphorylated crotonamides. J. Sci. Fd Agric. 17(11):510-517. 

(Also In unpublished submission received Oct 7, 1982 under 201-

142; submitted by Shell Chemical Co., Washington, DC; CDL: 

248514-D) 

160823 2031336 Stearns, S.; Lee, P. (1986) Aqueous Hydrolysis of [Carbon 14]-SD 

3562: RIR-22-002-86. Unpublished study prepared by Shell Agricultural Chemical Co. with summary of environmental fate data 

appended. 26 p. 

161-2 Photodegradation-water

MRID DOC NUM Citation Reference

160824 2031337 Stearns, S.; Lee, P. (1986) Aqueous Photolysis of [Carbon 14]-SD 

3562: RIR-22-003-86. Unpublished study prepared by Shell Agricultural Chemical Co. 20 p. 

161-3 Photodegradation-soil

MRID DOC NUM Citation Reference

87962 Shell Chemical Company (1964) ?Study of the Chemical SD 9129 

and Bidrin^(R)I|. (Compilation; unpublished study received May 

17, 1972 under 201-157; CDL:000875-M) 

115292 Osgerby, J.; Woodburn, A. (1965) The Adsorption and 

Decomposition of Bidrin and Azodrin in Soil: Project Progress 

Report PPR. FD 48/65. (Unpublished study received Oct 7, 1982 

under 201-142; prepared by Shell Research, Ltd., Eng., submitted 

by Shell Chemical Co., Washington, DC; CDL:248514-J) 
-Page 78 of 102-

115293 Osgerby, J.; Clarke, D. (1965) The Stability of Bidrin in Soil: 

Project Progress Report PPR. FD/5/65. (Unpublished study received Oct 7, 1982 under 201-142; prepared by Shell Research, 

Ltd., Eng., submitted by Shell Chemical Co., Washington, DC; 

CDL:248514-K) 

160825 2031338 Powell, W.; Hernandez, H.; Lee, P. (1986) Soil Surface Photolysis 

of [Carbon 14]-SD 3562: RIR-22-013-86. Unpublished study prepared by Shell Agricultural Chemical Co. 20 p. 

161-4 Photodegradation-air

MRID DOC NUM Citation Reference

28576 2031331 Hall, W.E.; Saliman, P.M. (1963) Sunlamp Stability of SD 9129 

and Bidrin^(R)I Insecticide. (Unpublished study received Mar 18, 

1980 under 6F1851; submitted by Shell Chemical Co., 

Washington, D.C.; CDL:099341-M) 

162-1 Aerobic soil metabolism

MRID DOC NUM Citation Reference

13470 2031328 Osgerby, J.M.; Clarke, D. (1965) Project Progress Report PPR 

FD/5/ 65: The Stability of Bidrin in Soil: Project F18. Includes 

method dated Feb 1, 1965. (Unpublished study received Jan 28, 

1966 under 201-142; prepared by Shell Research, Ltd., submitted 

by Shell Chemical Co., Washington, D.C.; CDL:000834-AM) 

85766 Moore, C.A. (1971) The Degradation of Two Insecticides by Soil 

Microorganisms: ?Submitter| 33364. Masters' thesis, Mississippi 

State Univ., Dept. of Entomology. (Unpublished study received 

Oct 21, 1981 under 3125-306; submitted by Mobay Chemical 

Corp., Kansas City, Mo.; CDL:246088-H) 

115292 Progress report Osgerby, J.; Woodburn, A. (1965) The Adsorption and 

Decomposition of Bidrin and Azodrin in Soil: Project Progress 

Report PPR. FD 48/65. (Unpublished study received Oct 7, 1982 

under 201-142; prepared by Shell Research, Ltd., Eng., submitted 

by Shell Chemical Co., Washington, DC; CDL:248514-J) 

115293 Progress report Osgerby, J.; Clarke, D. (1965) The Stability of Bidrin in Soil: 

Project Progress Report PPR. FD/5/65. (Unpublished study received Oct 7, 1982 under 201-142; prepared by Shell Research, 

Ltd., Eng., submitted by Shell Chemical Co., Washington, DC; 

CDL:248514-K) 

160826 2031339 Hernandez, H.; Stearns, S.; Lee, P. (1986) Aerobic Soil 

Metabolism of SD 3562: RIR-22-006-86. Unpublished study 

prepared by Shell Agricultural Chemical Co. 26 p. 

162-2 Anaerobic soil metabolism
-Page 79 of 102-

MRID DOC NUM Citation Reference

160827 2031340 Hernandez, H.; Stearns, S.; Lee, P. (1986) Anaerobic Soil 

Metabo- lism of SD 3562: RIR-22-011-86. Unpublished study 

prepared by Shell Agricultural Chemical Co. 31 p. 

163-1 Leach/adsorp/desorption

MRID DOC NUM Citation Reference

28571 Osgerby, J.M.; Woodburn, A.T. (1965) The Adsorption and 

Decomposi- tion of Bidrin and Azodrin in Soil: PPR. FD 48/65. 

(Unpublished study received Mar 18, 1980 under 6F1851; 

prepared by Shell Re- search, Ltd., submitted by Shell Chemical 

Co., Washington, D.C.; CDL:099341-B) 

87957

Same as 28571

Osgerby, J.M.; Woodburn, A.T. (1965) The Adsorption and 

Decomposi- tion of Bidrin and Azodrin in Soil: PPR. FD 48/65. 

(Unpublished study received May 17, 1972 under 201-157; 

prepared by Shell Re- search, Ltd., England, submitted by Shell 

Chemical Co., Washing- ton, D.C.; CDL:000875-B) 

160828 2031341 Stearns, S.; Hernandez, H.; Lee, P. (1986) Soil Adsorption and 

De- sorption of SD 3562: RIR-22-001-86. Unpublished study 

prepared by Shell Agricultural Chemical Co. 32 p. 

160829 2031342 Hernandez, H.; Stearns, S.; Lee, P. (1986) Soil Thin-layer Mobility 

of SD 3562 and Its Soil Degradates: RIR-22-010-86. Unpublished 

study prepared by Shell Agricultural Chemical Co. 15 p. 

163-2 Volatility – lab

MRID DOC NUM Citation Reference

160825 Powell, W.; Hernandez, H.; Lee, P. (1986) Soil Surface Photolysis 

of [Carbon 14]-SD 3562: RIR-22-013-86. Unpublished study prepared by Shell Agricultural Chemical Co. 20 p. 

43500401 2031347 Atkins, R. (1994) Laboratory Volatility of ((carbon 13)/(carbon 14)) 

Dicrotophos: Lab Project Number: 837: 1635. Unpublished study 

prepared by PTRL East, Inc. 67 p. 

164-1 Terrestrial field dissipation

MRID DOC NUM Citation Reference

115294 Compilation Shell Chemical Co. (1973) Bidrin Insecticide Soil Dissipation Data. 

(Compilation; unpublished study received Oct 7, 1982 under 201-

142; CDL:248514-L) 

115295 2031334 Bosio, P.; Soulie, L. (1975) Pesticide Breakdown in Soil: Part 1: 
-Page 80 of 102-

Bidrin: Group Research Report BEGR.0101.75. (Unpublished 

study received Oct 7, 1982 under 201-142; prepared by Shell 

Chimie, Fr., submitted by Shell Chemical Co., Washington, DC; 

CDL: 248514-M) 

41114301 2031346 Lee, P. (1989) Field Soil Dissipation Study with Dicrotophos: Project ID: AMR-1189-88. Unpublished study prepared by E.I. du 

Pont de Nemours and Co., Inc., and En-Cas Analytical Laboratories. 95 p. 

165-1 Confined rotational crop

MRID DOC NUM Citation Reference

42210903 Nathan, E. (1992) Confined Accumulation Study of Dicrotophos 

on Rotational Crops: Lab Project Number: DICR/ENV 1. 

Unpublished study prepared by E. I. du Pont de Nemours and 

Co., Inc. 7 p. 

44101001 O'Neal, S. (1996) A Confined Rotational Crop Study with (carbon 

13)(carbon 14)-Dicrotophos: Lab Project Number: 868: 1897. 

Unpublished study prepared by PTRL East, Inc. 199 p. 

165-4 Bioaccumulation in fish

MRID DOC NUM Citation Reference

155661 2031335 Schultz, D.; Krudop, W. (1976) Bio-accumulation of Azodrin 

Insecticide in Fish - Residue Levels of Azodrin and Two 

Metabolites (SD 12657 and SD 11319) in Rainbow Trout 

Resulting from the Exposure to 0.5 PPM Azodrin in Water: 

Reference No. RIR-24-633-76-A. Unpublished study prepared by 

Shell Develop- ment Co. 13 p. 

201-1 Droplet size spectrum

MRID DOC NUM Citation Reference

42210901 Mullin, L. (1992) Spray Drift Field Evaluation and Droplet Size 

Spectrum of Du Pont Bidrin Insecticide: Lab Project Number: 

DICR/ECO 1. Unpublished study prepared by E.I. du Pont de 

Nemours and Co., Inc. 4 p. 
-Page 81 of 102-

7.2. Submitted Ecotoxicity Studies (Retrieved from OPPIN November 19, 2012)

71-1 Avian Single Dose Oral Toxicity

MRID Citation Reference

13438 Brown, V.K.; Ferrigan, L.W.; Stevenson, D.E. (1964) Technical Mem- orandum: 

Toxicological Investigations with Bidrin: Number Tox 31/64. (Unpublished study 

received Jan 28, 1966 under 201-142; prepared by Shell Research, Ltd., submitted by 

Shell Chemical Co., Washington, D.C.; CDL:000834-D) 

13439 Doyle, R.L.; Elsea, J.R. (1963) Toxicity Studies on Bidrin in Geese: N-279. 

(Unpublished study received Jan 28, 1966 under 201-142; prepared by Hill Top 

Research Institute, Inc., sub- mitted by Shell Chemical Co., Washington, D.C.; 

CDL:000834-E) 

13707 Gough, B.J.; Shellenberger, T.E.; Escuriex, L.A. (1967?) Acute Tox- icity of a Series 

of Organophosphate Pesticides to Bobwhite and Japanese Quail. (Unpublished study 

received Sep 13, 1974 under 2724-169; prepared by Gulf South Research Institute, 

submitted by Zoecon Industries, Inc., Dallas, Tex.; CDL:128306-A) 

98480 Grue, C.E. (1979) Response of common grackles to dietary concen- trations of four 

organophosphate pesticides. Taken from: Ab- stracts: 49th Annual Meeting of the 

Cooper Ornithological Society; Jun 15-18, 1979. The Society. (Abstract no. 71; 

also~In~unpublished submission received Oct 26, 1979 under 476- 2028; submitted 

by Stauffer Chemical Co., Richmond, Calif.; CDL:243641-J) 

102038 Hudson, R.; Tucker, R.; Haegele, M. (1972) Effect of age on sensi- tivity: Acute oral 

toxicity of 14 pesticides to mallard ducks of several ages. Toxicology and Applied 

Pharmacology (22):556- 561. (Also In unpublished submission received Oct 26, 1977 

under 1016-69; submitted by Union Carbide Corp., Arlington, VA; CDL:096397-E) 

5008363 Hudson, R.H.; Haegele, M.A.; Tucker, R.K. (1979) Acute oral and percutaneous 

toxicity of pesticides to mallards: correlations with mammalian toxicity data. 

Toxicology and Applied Pharmacology 47(3):451-460. 

71-2 Avian Dietary Toxicity

MRID Citation Reference

28592 Shellenberger, T.E.; Newell, G.W.; Adams, R.F.; et al. (1964?) Cholinesterase 

Inhibition and Toxicological Evaluations of Two Organophosphate Pesticides in 

Japanese Quail. (Unpublished study received Mar 18, 1980 under 6F1851; prepared 

by Stanford Research Institute, Dept. of Toxicology, submitted by Shell Chemical Co., 

Washington, D.C.; CDL:099341-AN) 

63392 Shellenberger, T.E. (1967) Letter sent to Ralph F. Glasser dated Mar 28, 1967 

?Toxicological evaluation of bobwhite and Japanese quail with Azodrin and Bidrin|. 

(Unpublished study received Jun 2, 1971 under 1F1062; prepared by Gulf South 

Research Insti- tute, submitted by Shell Chemical Co., Washington, D.C.; CDL: 

091826-Q) 

90901 Grue, C.E. (1979) Response of Common Grackles to Dietary Concentra- tions of Four 

Organophosphate Pesticides. (U.S. Fish and Wild- life Service, Patuxent Wildlife 

Research Center; unpublished study; CDL:241307-L) 
-Page 82 of 102-

115300 Hill, E. (1981) Subacute dietary toxicities of dicrotophos and dieldrin in time-replicated 

trials with young ring-necked pheasants and mallards. Avian and Mammalian Wildlife 

Toxicology 2:105-120. (Also In unpublished submission received Oct 7, 1982 under 

201-142; submitted by Shell Chemical Co., Washington, DC; CDL:248514-T) 

115301 Hill, E.; Camardese, M. (1981) Subacute toxicity testing with young birds: Response 

in relation to age and interest variability of LC50 estimates. Avian and Mammalian 

Wildlife Toxicology 2:41-65. (Also In unpublished submission received Oct 7, 1982 

under 201-142; submitted by Shell Chemical Co., Washington, DC; CDL:248514-U) 

131892 Grue, C. (1982) Response of common grackles to dietary concentra- tions of four 

organophosphate pesticides. Archives of Environ- mental Contamination and 

Toxicology 11:617-626. (Also In unpub- lished submission received Sep 2, 1983 

under 100-643; submitted by Ciba-Geigy Corp., Greensboro, NC; CDL:251199-D) 

71-4 Avian Reproduction

MRID Citation Reference

28592 Shellenberger, T.E.; Newell, G.W.; Adams, R.F.; et al. (1964?) Cholinesterase 

Inhibition and Toxicological Evaluations of Two Organophosphate Pesticides in 

Japanese Quail. (Unpublished study received Mar 18, 1980 under 6F1851; prepared 

by Stanford Research Institute, Dept. of Toxicology, submitted by Shell Chemical Co., 

Washington, D.C.; CDL:099341-AN) 

43871601 Wetherill, G. (1995) Draft Statistical Analysis of Data from A Reproduction Study in 

Bobwhite Quail: Lab Project Number: AVC 5. Unpublished study prepared by 

Huntingdon Research Centre Ltd. 7 p. 

43871602 Cameron, D. (1995) Effects of Dietary Administration of Dicrotophos on Reproduction 

in the Mallard Duck: Status Report at Week 23: Lab Project Number: AVC 6. 

Unpublished study prepared by Huntingdon Research Centre Ltd. 16 p. 

44005501 Cameron, D. (1996) Dicrotophos: Mallard Duck Dietary Reproduction and Preliminary 

Studies: Lab Project Number: AVC 6: AVC 6/960138. Unpublished study prepared by 

Huntingdon Life Sciences, Ltd. 259 p. 

44005502 Cameron, D. (1996) Dicrotophos: Bobwhite Quail Dietary Reproduction and 

Preliminary Studies: Lab Project Number: AVC 5: AVC 5/960137. Unpublished study 

prepared by Huntingdon Life Sciences, Ltd. 313 p. 

71-5 Simulated or Actual Field Testing

MRID Citation Reference

13439 Doyle, R.L.; Elsea, J.R. (1963) Toxicity Studies on Bidrin in Geese: N-279. 

(Unpublished study received Jan 28, 1966 under 201-142; prepared by Hill Top 

Research Institute, Inc., sub- mitted by Shell Chemical Co., Washington, D.C.; 

CDL:000834-E) 

63393 Welch, J.F. (1968) Letter sent to Director, Bureau of Sport Fish- eries & Wildlife dated 

May 14, 1968: Bidrin-wildlife relation- ship investigations. (U.S. Fish & Wildlife 

Service, Denver Wildlife Research Center; unpublished study; CDL:130022-C) 

151814 Skelsey, J.; Boultinghouse, R. (1972) Wildlife Test (Bird Toxicity) Using Azodrin 
-Page 83 of 102-

Insecticide and Bidrin Insecticide. Unpublished study prepared by Shell Development 

Co. 7 p. 

40873701 Palmer, D.; Krueger, H.; Jaber, M. (1988) Dicrotophos: An Evalua- tion of its Effects 

upon Wildlife on and around Cotton Fields in Southwestern Arizona: Wildlife 

International Ltd. Project No. 112-181. Unpublished study prepared by Wildlife 

International Ltd. 345 p. 

40917001 Sheeley, D.; Dingledine, J.; Krueger, H.; et al (1988) Dicrotophos: An Evaluation of Its 

Effects upon Wildlife on and Around Cotton Fields in Southeastern Alabama: Proj. No. 

112-180; AMR 1246-88. Unpublished study prepared by Wildlife International Ltd. 326 

p. 

72-1 Acute Toxicity to Freshwater Fish

MRID Citation Reference

13531 Henderson, C.; Pickering, Q.H.; Tarzwell, C.M. (1959) The Toxicity of Organic 

Phosphorus and Chlorinated Hydrocarbon Insecticides to Fish: Report No. 4276. 

(Unpublished study received Mar 4, 1966 under unknown admin. no.; prepared by 

U.S. Public Health Service, Robert A. Taft Sanitary Engineering Center, submitted by 

Mobay Chemical Corp., Agricultural Div., Kansas City, Mo.; CDL:130685-B) 

63391 Cope, O.B. (1965) Letter sent to M.J. Sloan dated Nov 3, 1965 (Tox- icity tests of 

Bidrin on bluegill sunfish). (U.S. Fish and Wildlife Service, Fish-Pesticide Research 

Laboratory; unpub- lished study; CDL:091826-M) 

99910 McCann, J. (1970) ?Bidrin 8: Bluegill (Lepomis macrochirus)|: Test No. 276. (U.S. 

Agricultural Research Service, Pesticides Regulation Div., Animal Biology Laboratory; 

unpublished study; CDL:132073-A) 

72-2 Acute Toxicity to Freshwater Invertebrates

MRID Citation Reference

13531 Henderson, C.; Pickering, Q.H.; Tarzwell, C.M. (1959) The Toxicity of Organic 

Phosphorus and Chlorinated Hydrocarbon Insecticides to Fish: Report No. 4276. 

(Unpublished study received Mar 4, 1966 under unknown admin. no.; prepared by 

U.S. Public Health Service, Robert A. Taft Sanitary Engineering Center, submitted by 

Mobay Chemical Corp., Agricultural Div., Kansas City, Mo.; CDL:130685-B) 

63391 Cope, O.B. (1965) Letter sent to M.J. Sloan dated Nov 3, 1965 (Tox- icity tests of 

Bidrin on bluegill sunfish). (U.S. Fish and Wildlife Service, Fish-Pesticide Research 

Laboratory; unpub- lished study; CDL:091826-M) 

43787901 Davis, J.; Cunningham, F. (1995) Dicrotophos Technical: Acute Toxicity to the Water 

Flea (Daphnia magna) Under Flow-Through Test Conditions: Lab Project Number: 

J9407001D. Unpublished study prepared by AMVAC Chemical Corp. and Toxicon 

Environmental Sciences. 56 p. 

72-3 Acute Toxicity to Estuarine/Marine Organisms

MRID Citation Reference
-Page 84 of 102-

43603305 Jones, F.; Davis, J. (1995) Dicrotophos Technical: Acute Toxicity to the Mysid 

(Mysidopsis bahia) Under Flow-Through Test Conditions: Lab Project Number: 

J9407001G. Unpublished study prepared by Toxikon Environmental Sciences. 48 p. 

43603306 Jones, F.; Davis, J. (1995) Dicrotophos Technical: Acute Toxicity to the Sheepshead 

Minnow (Cyprinodon variegatus) Under Flow-Through Test Conditions: Lab Project 

Number: J9407001E. Unpublished study prepared by Toxikon Environmental 

Sciences. 48 p. 

43739801 Cunningham, F.; Davis, J. (1995) Dicrotophos Technical: Acute Effect On New Shell 

Growth of the Eastern Oyster (Crassostrea virginica): Lab Project Number: 

J9407001F: J9407001C. Unpublished study prepared by Toxikon Environmental 

Sciences. 50 p. 

72-4 Fish Early Life Stage/Aquatic Invertebrate Life Cycle Study

MRID Citation Reference

13533 Farbenfabriken Bayer, Aktiengesellschaft (19??) Comparative Tests Determining Fish 

Toxicity and Mosquito Effect Using Fish Species Lebistis reticulatus(Pet.) and 

Platypoecilus maculatus (Gue.) and Larvae of Aedes aegypti? L.: Report No. 5337. 

(Unpublished study received Mar 4, 1966 under unknown admin. no.; submitted by 

Mobay Chemical Corp., Agricultural Div., Kansas City, Mo.; CDL:130685-D) 

13819 Shell Chemical Company (1962) Toxicity of SD 3562 and SD 4294 to Fish 

(?~Gambusia sp.~?). (Unpublished study including letter dated May 25, 1962 from 

E.T. White to W.R. Smith, received Jan 24, 1963 under 201-274; prepared in 

cooperation with Doctors Gamble Brothers and Archer Clinic; CDL:000970-I) 

43893901 Davis, J.; Cunningham, F. (1996) Dicrotophos Technical: Chronic Toxicity to the 

Mysid (Mysidopsis bahia) Under Flow-Through Conditions: Lab Project Number: 

J9407001H: J9503013. Unpublished study prepared by Toxikon Environmental 

Sciences. 88 p. 

44956501 Hahne, R. (1999) Chronic Toxicity of Dicrotophos Technical-During the Complete LifeCycle of Daphnia magna Under Flow-Through Test Condititons: Lab Project Number: 

44978. Unpublished study prepared by ABC Laboratories, Inc. 46 p. {OPPTS 

850.1300} 

141-1 Honey bee acute contact

MRID Citation Reference

162751 Stevenson, J. (1968) Laboratory studies on the acute contact and oral toxicities of 

insecticides to honeybees. Ann. appl. Biol. 61:467-472. 

850.1400 Fish early-life stage toxicity test

MRID Citation Reference

48037002 Habig, C. (2010) Dicrotophos: Request for a Waiver from Freshwater Fish Early Life 

Stage Testing. Project Number: 0902870/000/E0T0/2010/001, 

0902870/000/E0T0/0310/0001. Unpublished study prepared by Exponent, Inc. 7 p.
-Page 85 of 102-

48482901 Hicks, S. (2011) Dicrotophos Technical: Early Life-Stage Toxicity Test with the 

Fathead Minnow, Pimephales promelas, under Flow-Through Conditions. Project 

Number: 66150. Unpublished study prepared by ABC Laboratories, Inc. 80 p.

850.4100 Terrestrial plant toxicity, Tier 1 (seeding emergence)

MRID Citation Reference

48037003 Habig, C. (2010) Dicrotophos: Request for a Waiver from Seedling Emergence and 

Vegetative Vigor Testing. Project Number: 0902870/000/E0T0/2010/002, 

0902870/000/E0T0/3010/0002. Unpublished study prepared by Exponent, Inc. 7 p.

48482902 Lee, B. (2011) Bidrin 8 Water Miscible Insecticide: Effects on the Seedling Emergence 

and Growth of Non-Target Terrestrial Plants (Tier I). Project Number: 66145. 

Unpublished study prepared by ABC Laboratories, Inc. 72 p.

850.4150 Terrestrial plant toxicity, Tier 1 (vegetative vigor)

MRID Citation Reference

48037003 Habig, C. (2010) Dicrotophos: Request for a Waiver from Seedling Emergence and 

Vegetative Vigor Testing. Project Number: 0902870/000/E0T0/2010/002, 

0902870/000/E0T0/3010/0002. Unpublished study prepared by Exponent, Inc. 7 p.

48482903 Lee, B. (2011) Bidrin 8 Water Miscible Insecticide: Effects on the Vegetative Vigor of 

Non-Target Terrestrial Plants (Tier 1). Project Number: 66146. Unpublished study 

prepared by ABC Laboratories, Inc. 69 p.

850.4400 Aquatic plant toxicity test using Lemna spp. Tiers I and II

MRID Citation Reference

48037001 Habig, C. (2010) Dicrotophos: Request for a Waiver from Aquatic Plant Testing. 

Project Number: 0902870/000/E0T0/2010/003, 0902870/000/E0T0/0310/0003. 

Unpublished study prepared by Exponent, Inc. 7 p.

48443703 Rebstock, M. (2011) Dicrotophos: Growth Inhibition Test with the Freshwater Aquatic 

Plant, Duckweed, Lemna gibba. Project Number: 66147, 800/AQU/006. Unpublished 

study prepared by ABC Laboratories, Inc. 69 p.

850.5400 Algal toxicity, Tiers 1 and II

MRID Citation Reference

48037001 Habig, C. (2010) Dicrotophos: Request for a Waiver from Aquatic Plant Testing. 

Project Number: 0902870/000/E0T0/2010/003, 0902870/000/E0T0/0310/0003. 

Unpublished study prepared by Exponent, Inc. 7 p.

48443701 Rebstock, M. (2011) Dicrotophos: Static Growth Inhibition Test with the Marine 

Diatom, Skeletonema costatum. Project Number: 66149, 800/AQU/004. Unpublished 

study prepared by ABC Laboratories, Inc. 64 p.
-Page 86 of 102-

48443702 Rebstock, M. (2011) Dicrotophos: Static Toxicity Test with the Green Alga, 

Pseudokirchneriella subcapitata. Project Number: 66148, 800/AQU/005. Unpublished 

study prepared by ABC Laboratories, Inc. 65 p.
-Page 87 of 102-

Appendix A: PRZM/EXAMS output for highest cotton and tree injection scenarios

COTTON

stored as TXcotton.out

Chemical: dicrotophos

PRZM environment: TXcottonOP.txt modified Thuday, 14 June 2007 at 10:24:14

EXAMS environment: pond298.exv modified Tueday, 26 August 2008 at 05:14:08

Metfile: w13958.dvf modified Tueday, 26 August 2008 at 05:14:44

Water segment concentrations (ppb)

Year Peak 96 hr 21 Day 60 Day

90 Day Yearly

1961 2.516 2.329 1.718 1.279

0.9903 0.2616

1962 2.619 2.423 2.018 1.665

1.289 0.3387

1963 2.411 2.23 1.773 1.217

0.9238 0.2385

1964 2.597 2.405 1.815 1.344

1.037 0.2698

1965 17.57 16.6 13.02 7.447

5.427 1.415

1966 3.735 3.484 3.044 2.1

1.595 0.4197

1967 4.168 3.873 3.113 2.2

1.649 0.4289

1968 9.188 8.549 6.597 4.273

3.168 0.835

1969 4.288 3.996 3.207 2.146

1.597 0.4182

1970 17.05 15.97 12.37 6.948

5.045 1.316

1971 2.685 2.486 1.951 1.497

1.148 0.3019

1972 15.22 14.18 11.3 6.74

4.817 1.244

1973 3.22 2.998 2.524 1.996

1.543 0.4086

1974 4.467 4.125 3.39 2.255

1.653 0.4303

1975 8.157 7.743 5.752 3.912

2.963 0.7861

1976 7.266 6.822 6.279 5.305

3.991 1.04
-Page 88 of 102-

1977 3.449 3.204 2.804 2.385

1.786 0.4623

1978 8.543 7.893 6.362 4.208

3.023 0.7827

1979 19.76 18.52 14.02 8.329

6.262 1.653

1980 3.826 3.588 2.861 1.935

1.423 0.3721

1981 6.303 5.864 5.142 3.184

2.36 0.6205

1982 5.838 5.416 4.32 2.932

2.206 0.5706

1983 6.438 6.091 5.155 3.327

2.463 0.6511

1984 2.396 2.211 1.809 1.24

0.9408 0.2446

1985 2.456 2.273 1.672 1.236

0.9504 0.2482

1986 10.86 10.47 8.236 5.8

4.159 1.072

1987 2.975 2.758 2.343 1.77

1.349 0.3602

1988 4.469 4.155 3.214 2.167

1.626 0.4266

1989 9.831 9.061 6.862 4.324

3.226 0.8406

1990 8.755 8.068 6.471 3.876

2.778 0.717

Sorted results

Prob. Peak 96 hr 21 Day 60 Day

90 Day Yearly

0.032258064516129 19.76 18.52 14.02 8.329

6.262 1.653

0.0645161290322581 17.57 16.6 13.02 7.447

5.427 1.415

0.0967741935483871 17.05 15.97 12.37 6.948

5.045 1.316

0.129032258064516 15.22 14.18 11.3 6.74

4.817 1.244

0.161290322580645 10.86 10.47 8.236 5.8

4.159 1.072

0.193548387096774 9.831 9.061 6.862 5.305

3.991 1.04

0.225806451612903 9.188 8.549 6.597 4.324
-Page 89 of 102

-

3.226 0.8406

0.258064516129032 8.755 8.068 6.471 4.273

3.168 0.835

0.290322580645161 8.543 7.893 6.362 4.208

3.023 0.7861

0.32258064516129 8.157 7.743 6.279 3.912

2.963 0.7827

0.354838709677419 7.266 6.822 5.752 3.876

2.778 0.717

0.387096774193548 6.438 6.091 5.155 3.327

2.463 0.6511

0.419354838709677 6.303 5.864 5.142 3.184

2.36 0.6205

0.451612903225806 5.838 5.416 4.32 2.932

2.206 0.5706

0.483870967741936 4.469 4.155 3.39 2.385

1.786 0.4623

0.516129032258065 4.467 4.125 3.214 2.255

1.653 0.4303

0.548387096774194 4.288 3.996 3.207 2.2

1.649 0.4289

0.580645161290323 4.168 3.873 3.113 2.167

1.626 0.4266

0.612903225806452 3.826 3.588 3.044 2.146

1.597 0.4197

0.645161290322581 3.735 3.484 2.861 2.1

1.595 0.4182

0.67741935483871 3.449 3.204 2.804 1.996

1.543 0.4086

0.709677419354839 3.22 2.998 2.524 1.935

1.423 0.3721

0.741935483870968 2.975 2.758 2.343 1.77

1.349 0.3602

0.774193548387097 2.685 2.486 2.018 1.665

1.289 0.3387

0.806451612903226 2.619 2.423 1.951 1.497

1.148 0.3019

0.838709677419355 2.597 2.405 1.815 1.344

1.037 0.2698

0.870967741935484 2.516 2.329 1.809 1.279

0.9903 0.2616

0.903225806451613 2.456 2.273 1.773 1.24

0.9504 0.2482

0.935483870967742 2.411 2.23 1.718 1.236

0.9408 0.2446
-Page 90 of 102-

0.967741935483871 2.396 2.211 1.672 1.217

0.9238 0.2385

0.1 16.867 15.791 12.263 6.9272

5.0222 1.3088

Average of yearly averages: 0.639126666666667

Inputs generated by pe5.pl - Novemeber 2006

Data used for this run:

Output File: TXcotton

Metfile: w13958.dvf

PRZM scenario: TXcottonOP.txt

EXAMS environment file: pond298.exv

Chemical Name: dicrotophos

Description Variable Name Value Units

Comments

Molecular weight mwt 237.19 g/mol

Henry's Law Const. henry 3.13E-11 atm-m^3/mol

Vapor Pressure vapr 7E-5 torr

Solubility sol 11990 mg/L

Kd Kd 1.24 mg/L

Koc Koc mg/L

Photolysis half-life kdp 0 days Halflife

Aerobic Aquatic Metabolism kbacw 17.4 days Halfife

Anaerobic Aquatic Metabolism kbacs 0 days Halfife

Aerobic Soil Metabolism asm 8.7 days Halfife

Hydrolysis: pH 7 990 days Halflife

Method: CAM 1 integer See 

PRZM manual

Incorporation Depth: DEPI 0 cm

Application Rate: TAPP 0.2242 kg/ha

Application Efficiency: APPEFF 0.95 fraction

Spray Drift DRFT 0.05 fraction of 

application rate applied to pond

Application Date Date 16-4 dd/mm or 

dd/mmm or dd-mm or dd-mmm

Interval 1 interval 14 days Set to 0 

or delete line for single app.

app. rate 1 apprate 0.5605 kg/ha

Interval 2 interval 14 days Set to 0 
-Page 91 of 102-

or delete line for single app.

app. rate 2 apprate 0.5605 kg/ha

Record 17: FILTRA

IPSCND 1

UPTKF

Record 18: PLVKRT

PLDKRT

FEXTRC 0.5

Flag for Index Res. Run IR EPA Pond

Flag for runoff calc. RUNOFF none none, monthly 

or total(average of entire run)

TREE INJECTION

stored as FLcitrus.out

Chemical: dicrotophos

PRZM environment: FLcitrusSTD.txt modified Tueday, 29 May 2007 at 12:45:56

EXAMS environment: pond298.exv modified Tueday, 26 August 2008 at 05:14:08

Metfile: w12844.dvf modified Tueday, 26 August 2008 at 05:14:22

Water segment concentrations (ppb)

Year Peak 96 hr 21 Day 60 Day

90 Day Yearly

1961 1.04 0.9764 0.7329 0.448

0.3241 0.0824

1962 1.534 1.416 1.042 0.6315

0.4555 0.116

1963 6.039 5.668 4.19 2.351

1.658 0.4186

1964 9.764 9.025 7.685 5.63

4.097 1.042

1965 0.8907 0.8266 0.6418 0.4133

0.3177 0.08435

1966 1.089 1.004 0.8656 0.4982

0.3548 0.09032

1967 0.6773 0.623 0.5161 0.2942

0.2076 0.05286

1968 7.704 7.199 5.473 3.263

2.364 0.6136

1969 3.688 3.478 3.016 2.016

1.455 0.3724

1970 2.943 2.713 2.121 1.209

0.8513 0.2159

1971 6.843 6.335 4.538 2.519
-Page 92 of 102-

1.849 0.4726

1972 6.413 5.93 4.417 3.107

2.257 0.5729

1973 2.158 1.967 1.398 1.072

0.8126 0.211

1974 1.474 1.356 0.9645 0.5847

0.4249 0.1088

1975 2.844 2.618 1.942 1.069

0.7712 0.1987

1976 11.94 11.25 8.242 4.631

3.389 0.8855

1977 8.17 7.708 5.674 4.333

3.16 0.8092

1978 1.664 1.516 1.092 0.7439

0.5682 0.1495

1979 1.852 1.714 1.295 0.9563

0.7415 0.1951

1980 2.058 1.933 1.471 1.002

0.7355 0.1891

1981 5.576 5.124 3.618 1.963

1.401 0.3592

1982 1.704 1.58 1.336 1.011

0.756 0.1951

1983 2.419 2.218 1.616 0.8657

0.6114 0.1559

1984 6.077 5.605 4.13 2.334

1.659 0.4199

1985 1.266 1.167 0.9541 0.6007

0.446 0.1156

1986 0.8556 0.7828 0.5874 0.3149

0.2432 0.06331

1987 4.849 4.465 3.227 1.88

1.344 0.3401

1988 6.376 5.908 4.49 3.549

2.62 0.6688

1989 0.08765 0.08312 0.05917

0.03765 0.02748 0.00848

1990 8.996 8.25 5.815 3.032

2.126 0.5409

Sorted results

Prob. Peak 96 hr 21 Day 60 Day

90 Day Yearly

0.032258064516129 11.94 11.25 8.242 5.63

4.097 1.042
-Page 93 of 102-

0.0645161290322581 9.764 9.025 7.685 4.631

3.389 0.8855

0.0967741935483871 8.996 8.25 5.815 4.333

3.16 0.8092

0.129032258064516 8.17 7.708 5.674 3.549

2.62 0.6688

0.161290322580645 7.704 7.199 5.473 3.263

2.364 0.6136

0.193548387096774 6.843 6.335 4.538 3.107

2.257 0.5729

0.225806451612903 6.413 5.93 4.49 3.032

2.126 0.5409

0.258064516129032 6.376 5.908 4.417 2.519

1.849 0.4726

0.290322580645161 6.077 5.668 4.19 2.351

1.659 0.4199

0.32258064516129 6.039 5.605 4.13 2.334

1.658 0.4186

0.354838709677419 5.576 5.124 3.618 2.016

1.455 0.3724

0.387096774193548 4.849 4.465 3.227 1.963

1.401 0.3592

0.419354838709677 3.688 3.478 3.016 1.88

1.344 0.3401

0.451612903225806 2.943 2.713 2.121 1.209

0.8513 0.2159

0.483870967741936 2.844 2.618 1.942 1.072

0.8126 0.211

0.516129032258065 2.419 2.218 1.616 1.069

0.7712 0.1987

0.548387096774194 2.158 1.967 1.471 1.011

0.756 0.1951

0.580645161290323 2.058 1.933 1.398 1.002

0.7415 0.1951

0.612903225806452 1.852 1.714 1.336 0.9563

0.7355 0.1891

0.645161290322581 1.704 1.58 1.295 0.8657

0.6114 0.1559

0.67741935483871 1.664 1.516 1.092 0.7439

0.5682 0.1495

0.709677419354839 1.534 1.416 1.042 0.6315

0.4555 0.116

0.741935483870968 1.474 1.356 0.9645 0.6007

0.446 0.1156

0.774193548387097 1.266 1.167 0.9541 0.5847

0.4249 0.1088
-Page 94 of 102-

0.806451612903226 1.089 1.004 0.8656 0.4982

0.3548 0.09032

0.838709677419355 1.04 0.9764 0.7329 0.448

0.3241 0.08435

0.870967741935484 0.8907 0.8266 0.6418 0.4133

0.3177 0.0824

0.903225806451613 0.8556 0.7828 0.5874 0.3149

0.2432 0.06331

0.935483870967742 0.6773 0.623 0.5161 0.2942

0.2076 0.05286

0.967741935483871 0.08765 0.08312 0.05917

0.03765 0.02748 0.00848

0.1 8.9134 8.1958 5.8009 4.2546

3.106 0.79516

Average of yearly averages: 0.324937333333333

Inputs generated by pe5.pl - Novemeber 2006

Data used for this run:

Output File: FLcitrus

Metfile: w12844.dvf

PRZM scenario: FLcitrusSTD.txt

EXAMS environment file: pond298.exv

Chemical Name: dicrotophos

Description Variable Name Value Units

Comments

Molecular weight mwt 237.19 g/mol

Henry's Law Const. henry 3.13E-11 atm-m^3/mol

Vapor Pressure vapr 7E-5 torr

Solubility sol 11990 mg/L

Kd Kd 1.24 mg/L

Koc Koc mg/L

Photolysis half-life kdp 0 days Halflife

Aerobic Aquatic Metabolism kbacw 17.4 days Halfife

Anaerobic Aquatic Metabolism kbacs 0 days Halfife

Aerobic Soil Metabolism asm 8.7 days Halfife

Hydrolysis: pH 7 990 days Halflife

Method: CAM 1 integer See 

PRZM manual

Incorporation Depth: DEPI 0 cm
-Page 95 of 102-

Application Rate: TAPP 0.2556 kg/ha

Application Efficiency: APPEFF 1.0 fraction

Spray Drift DRFT 0.0 fraction of 

application rate applied to pond

Application Date Date 29-4 dd/mm or 

dd/mmm or dd-mm or dd-mmm

Interval 1 interval 14 days Set to 0 

or delete line for single app.

app. rate 1 apprate 0.2556 kg/ha

Interval 2 interval 14 days Set to 0 

or delete line for single app.

app. rate 2 apprate 0.2556 kg/ha

Record 17: FILTRA

IPSCND 1

UPTKF

Record 18: PLVKRT

PLDKRT

FEXTRC 0.5

Flag for Index Res. Run IR EPA Pond

Flag for runoff calc. RUNOFF none none, monthly 

or total(average of entire run)
-Page 96 of 102-

Appendix B: Toxicity Categories and Levels of Concern

 

 Table B1. Categories of Toxicity for Aquatic Organisms

LC50 (ppm) Toxicity Category

< 0.1 Very highly toxic

> 0.1 - 1 Highly toxic

> 1 - 10 Moderately toxic

> 10 - 100 Slightly toxic

> 100 Practically nontoxic

Table B2. Categories of Toxicity for Terrestrial Organisms

Oral dose LD50 (mg/kg-bw) Toxicity Category

< 10 Very highly toxic

10 - 50 Highly toxic

51 - 500 Moderately toxic

501 - 2000 Slightly toxic

> 2000 Practically nontoxic

Dietary LC50 (ppm) Toxicity Category

< 50 Very highly toxic

50 - 500 Highly toxic

501 - 1000 Moderately toxic

1001 - 5000 Slightly toxic

> 5000 Practically nontoxic

Table B3. Categories of Toxicity for Honey Bee

Bee Acute Contact LD50 (μg/bee) Toxicity Category

<2 Highly toxic

2 – 10.99 Moderately toxic

> 11 Practically nontoxic

Table B4. Levels of Concern for Terrestrial and Aquatic Organisms

Taxa Acute LOC Chronic LOC

Avian

1

(terrestrial phase amphibians) 0.1 1

Mammalian

2

0.1 1

Terrestrial plants31

Aquatic Animals4(aquatic phase

amphibians)

0.05 1

Insects 50.05 1

Used in RQ calculations:

1 LD50 and estimated NOEL

2 LD50 and NOEC

3 EC25

4 LC/EC50 and estimated and reproductive NOEC

5 LD50 per EFED’s CRLF Steering Committee
-Page 97 of 102-

Appendix C: Example T-REX (v. 1.5) Input and Output for Dicrotophos

Table C.1. T-REX Model Inputs: Chemical Application Scenarios and Body Mass for Assessed

Species.
-Page 98 of 102-

Table C.2. Avian and Mammalian Toxicity Endpoints for RQ Calculation.
-Page 99 of 102-

Appendix D: STIR Results
-Page 100 of 102-

Appendix E: SIP Results
-Page 101 of 102-

AppendixF: AcceptedECOTOX Data Table

The code list for ECOTOX can be found at: http://cfpub.epa.gov/ecotox/blackbox/help/codelist.pdf

Chemical Name Ref # Genus Species Common Name Effect Group Effect Meas Endpt1 Endpt2 Dur Preferred Mean Dur Unit Preferred Conc #1 Author Reported Mean

Conc #1 Purity Adjusted in Preferred Unit

Mean

Conc #2 Purity Adjusted in Preferred Unit

Mean Conc Units Preferred % Purity

Dicrotophos 112447 Caenorhabditis elegans Nematode BEH BEH NMVM EC50 0.208333333 d 1.11 1.11 mM 100

Dicrotophos 112447 Caenorhabditis elegans Nematode MOR MOR MORT LC50 0.166666667 d 35.03 35.03 mM 100

Dicrotophos 25114 Carica papaya Papaya GRO GRO HGHT LOAEL 28 d 0.062 0.062 AI % 100

Dicrotophos 25114 Carica papaya Papaya GRO GRO HGHT NOAEL 28 d 0.031 0.031 AI % 100

Dicrotophos 87491 Callirhytis cornigera Parasitic Wasp POP POP ABND LOAEL 30.44d 2 2 ml 100

Dicrotophos 87491 Callirhytis cornigera Parasitic Wasp PHY IMM PARA LOAEL 30.44d 2 2 ml 100

Dicrotophos 87491 Callirhytis cornigera Parasitic Wasp POP POP ABND NOAEL 336d 2 2 ml 100

Dicrotophos 87491 Callirhytis cornigera Parasitic Wasp POP POP ABND LOAEL 60.88d 2 2 ml 100

Dicrotophos 87491 Callirhytis cornigera Parasitic Wasp POP POP ABND LOAEL 60.88d 2 2 ml 100

Dicrotophos 87491 Callirhytis cornigera Parasitic Wasp POP POP ABND NOAEL 60.88d 2 2 ml 100

Dicrotophos 87491 Callirhytis cornigera Parasitic Wasp POP POP ABND NOAEL 60.88d 2 2 ml 100

Dicrotophos 87491 Callirhytis cornigera Parasitic Wasp POP POP ABND NOAEL 60.88d 2 2 ml 100

Dicrotophos 93416 Microplitis croceipes Braconid Parasitoid Wasp MOR MOR MORT NR-LETH 1 d 0.28 0.28 AI kg/ha 100

Dicrotophos 93416 Microplitis croceipes Braconid Parasitoid Wasp MOR MOR MORT NR-LETH 1 d 0.28 0.28 AI kg/ha 100

Dicrotophos 93416 Cardiochiles nigriceps Braconid Wasp MOR MOR MORT NR-LETH 1 d 0.28 0.28 AI kg/ha 100

Dicrotophos 93416 Cardiochiles nigriceps Braconid Wasp MOR MOR MORT NR-LETH 1 d 0.28 0.28 AI kg/ha 100

Dicrotophos 114809 Hypera postica Weevil POP POP ABND LOAEL 21 d 1 1 AI lb/acre 100

Dicrotophos 98221 Cryptolaemus montrouzieri Mealybug Destroyer MOR MOR MORT LT50 1 d 0.0477 0.0477 AI % w/w 100

Dicrotophos 98221 Cryptolaemus montrouzieri Mealybug Destroyer MOR MOR MORT LT50 1 d 0.477 0.477 AI % w/w 100

Dicrotophos 98221 Metaphycus luteolus Brown Scale Parasite MOR MOR MORT LT50 1 d 0.0477 0.0477 AI % w/w 100

Dicrotophos 98221 Metaphycus luteolus Brown Scale Parasite MOR MOR MORT LT50 1 d 0.477 0.477 AI % w/w 100

Dicrotophos 98221 Aphytis melinus Red Scale Parasite MOR MOR MORT LT50 1 d 0.0477 0.0477 AI % w/w 100

Dicrotophos 98221 Aphytis melinus Red Scale Parasite MOR MOR MORT LT50 1 d 0.477 0.477 AI % w/w 100

Dicrotophos 98221 Lindorus lophanthae Black Lady Beetle MOR MOR MORT LT50 1 d 0.0477 0.0477 AI % w/w 100

Dicrotophos 98221 Lindorus lophanthae Black Lady Beetle MOR MOR MORT LT50 1 d 0.477 0.477 AI % w/w 100

Dicrotophos 88810 NR Thysanoptera Thrip Order POP POP ABND NOAEL 6 d 0.2 0.2 AI lb/acre 100

Dicrotophos 79345 Gossypium hirsutum Cotton POP POP BMAS NOAEL 173d 0.1 0.1 AI lb/acre 100

Dicrotophos 79345 Frankliniella fusca Tobacco Thrip POP POP ABND LOAEL 7 d 0.1 0.1 AI lb/acre 100

Dicrotophos 88060 Frankliniella sp. Common Thrip POP POP ABND NOAEL 5 d 0.33 0.33 AI lb/acre 100

Dicrotophos 88060 Frankliniella sp. Common Thrip POP POP ABND LOAEL 5 d 0.33 0.33 AI lb/acre 100

Dicrotophos 88060 Frankliniella sp. Common Thrip POP POP ABND NOAEL 2 d 0.33 0.33 AI lb/acre 100

Dicrotophos 88060 Frankliniella sp. Common Thrip POP POP ABND NOAEL 2 d 0.33 0.33 AI lb/acre 100

Dicrotophos 101655 NR Pentatomidae Stink Bug Family POP POP ABND NOAEL gs 8 8 fl oz/acre 100

Dicrotophos 101655 NR Pentatomidae Stink Bug Family POP POP ABND LOAEL gs 8 8 fl oz/acre 100

Dicrotophos 101655 NR Pentatomidae Stink Bug Family POP POP ABND NOAEL gs 8 8 fl oz/acre 100

Dicrotophos 101655 Gossypium hirsutum Cotton POP POP BMAS NOAEL hv 8 8 fl oz/acre 100

Dicrotophos 101655 Gossypium hirsutum Cotton POP POP BMAS NOAEL hv 8 8 fl oz/acre 100

Dicrotophos 101655 Gossypium hirsutum Cotton POP POP BMAS NOAEL hv 8 8 fl oz/acre 100

Dicrotophos 64843 Gallus domesticus Domestic Chicken BCM ENZ ACHE IC50 7 d 55 55 ppm 100

Dicrotophos 64843 Gallus domesticus Domestic Chicken MOR MOR MORT LD50 7 d 7.97 7.97 ppm 100

Dicrotophos 64843 Gallus domesticus Domestic Chicken BCM ENZ CEST IC50 7 d 55 55 ppm 100

Dicrotophos 150470 Gossypium hirsutum Cotton GRO GRO HGHT LOAEL 23 d 0.25 0.25 AI lb/acre 100

Dicrotophos 150470 Gossypium hirsutum Cotton POP POP BMAS NOAEL hv 0.25 0.25 AI lb/acre 100

Dicrotophos 150470 NR Thripidae Thrip Family POP POP ABND LOAEL 8 d 0.25 0.25 AI lb/acre 100

Dicrotophos 101406 Lipaphis erysimi Turnip Aphid MOR MOR MORT NR-LETH 8 d 0.24 0.24 % 100

Dicrotophos 101406 Diaeretiella rapae Parasitoid Wasp GRO DVP EMRG LOAEL 8 d 0.24 0.24 % 100

Dicrotophos 29481 Oryza sativa Rice POP POP BMAS NOAEL hv 2.5 2.23 lb/acre 100

Dicrotophos 29481 Oryza sativa Rice POP POP BMAS NOAEL hv 2.5 2.23 lb/acre 100

Dicrotophos 29481 Oryza sativa Rice GRO GRO HGHT NOAEL hv 0.3 0.3 % 100

Dicrotophos 29481 Oryza sativa Rice GRO MPH LGTH NOAEL hv 0.3 0.255 % 85

Dicrotophos 29481 Oryza sativa Rice GRO GRO NLEF NOAEL hv 0.3 0.255 % 85

Dicrotophos 96420 Apis mellifera Honey Bee MOR MOR MORT LD50 1 d 0.076 0.076 ug 100

Dicrotophos 96420 Apis mellifera Honey Bee MOR MOR MORT LD90 1 d 0.1 0.1 ug 100

Dicrotophos 96420 Apis mellifera Honey Bee MOR MOR MORT LD50 1 d 0.068 0.068 ug 100

Dicrotophos 96420 Apis mellifera Honey Bee MOR MOR MORT LD90 1 d 0.2 0.2 ug 100

Dicrotophos 88074 Aphis gossypii Cotton Aphid POP POP ABND LOAEL 2 d 0.3 0.3 AI lb/acre 100

Dicrotophos 88074 Aphis gossypii Cotton Aphid POP POP ABND LOAEL 3 d 0.4 0.4 AI lb/acre 41

Dicrotophos 88074 Aphis gossypii Cotton Aphid POP POP ABND LOAEL 3 d 0.4 0.4 AI lb/acre 100

Dicrotophos 88773 Aphis gossypii Cotton Aphid POP POP ABND NOAEL 30 d 0.2 0.2 AI lb/acre 100

Dicrotophos 88773 Gossypium hirsutum Cotton POP POP BMAS NOAEL hv 0.2 0.2 AI lb/acre 100

Dicrotophos 88773 Gossypium hirsutum Cotton GRO GRO GGRO NOAEL hv 0.2 0.2 AI lb/acre 100

Dicrotophos 88773 NR Thripidae Thrip Family POP POP ABND LOAEL 7 d 0.2 0.2 AI lb/acre 100

Dicrotophos 156321 Neozygites fresenii Fungus POP POP ABND NOAEL 20 d 0.56 0.49952 lb/acre 100

Dicrotophos 156321 Neozygites fresenii Fungus POP POP ABND NOAEL 20 d 0.56 0.49952 lb/acre 100

Dicrotophos 156321 Aphis gossypii Cotton Aphid POP POP ABND NOAEL 20 d 0.56 0.56 AI kg/ha 100

Dicrotophos 156321 Aphis gossypii Cotton Aphid POP POP ABND NOAEL 20 d 0.56 0.56 AI kg/ha 100

Dicrotophos 154178 Hypothenemus hampei Coffee Borer Beetle MOR MOR MORT LC50 1.083333333 d 0.039114 0.039114 AI % 100

Dicrotophos 154178 Hypothenemus hampei Coffee Borer Beetle MOR MOR MORT LC50 1.083333333 d 0.00998 0.00998 AI % 100

Dicrotophos 50386 Anas platyrhynchos Mallard Duck MOR MOR MORT LOAEL 30 d 0.25 0.25 mg/kg bdwt 98

Dicrotophos 39755 Colinus virginianus Northern Bobwhite Quail MOR MOR MORT NR-LETH 8 d 20 18 ppm 90

Dicrotophos 39755 Colinus virginianus Northern Bobwhite Quail MOR MOR MORT LC50 7 d 12.5 11.25 ppm 90

Dicrotophos 39755 Colinus virginianus Northern Bobwhite Quail MOR MOR MORT NR-LETH 8 d 28 25.2 ppm 90

Dicrotophos 39755 Colinus virginianus Northern Bobwhite Quail MOR MOR MORT LC50 7 d 18.7 16.83 ppm 90

Dicrotophos 39755 Colinus virginianus Northern Bobwhite Quail MOR MOR MORT NR-LETH 8 d 40 36 ppm 90

Dicrotophos 39755 Colinus virginianus Northern Bobwhite Quail MOR MOR MORT LC50 8 d 15.8 14.22 ppm 90

Dicrotophos 39755 Colinus virginianus Northern Bobwhite Quail MOR MOR MORT NR-LETH 8 d 56 50.4 ppm 90

Dicrotophos 39755 Colinus virginianus Northern Bobwhite Quail MOR MOR MORT LC50 8 d 27 24.3 ppm 90

Dicrotophos 39755 Colinus virginianus Northern Bobwhite Quail MOR MOR MORT LC50 8 d 30.8 27.72 ppm 90

Dicrotophos 39755 Colinus virginianus Northern Bobwhite Quail MOR MOR MORT NR-ZERO 8 d 20 18 ppm 90
-Page 102 of 102-

Chemical Name Ref # Genus Species Common Name Effect Group Effect Meas Endpt1 Endpt2 Dur Preferred Mean Dur Unit Preferred Conc #1 Author Reported Mean

Conc #1 Purity Adjusted in Preferred Unit

Mean

Conc #2 Purity Adjusted in Preferred Unit

Mean Conc Units Preferred % Purity

Dicrotophos 39755 Colinus virginianus Northern Bobwhite Quail MOR MOR MORT NR-LETH 8 d 56 50.4 ppm 90

Dicrotophos 39755 Colinus virginianus Northern Bobwhite Quail MOR MOR MORT NR-ZERO 8 d 20 18 ppm 90

Dicrotophos 39755 Colinus virginianus Northern Bobwhite Quail MOR MOR MORT NR-LETH 8 d 56 50.4 ppm 90

Dicrotophos 39755 Colinus virginianus Northern Bobwhite Quail MOR MOR MORT LC50 8 d 29.9 26.91 ppm 90

Dicrotophos 39755 Colinus virginianus Northern Bobwhite Quail MOR MOR MORT LC50 8 d 14 12.6 ppm 90

Dicrotophos 39755 Colinus virginianus Northern Bobwhite Quail MOR MOR MORT LC50 8 d 29 26.1 ppm 90

Dicrotophos 50181 Coturnix japonica Japanese Quail BEH FDB FCNS LOAEL 1 d 26 26 ppm 85

Dicrotophos 50181 Coturnix japonica Japanese Quail BEH FDB FCNS LOAEL 2 d 26 26 ppm 85

Dicrotophos 50181 Coturnix japonica Japanese Quail BEH FDB FCNS LOAEL 3 d 26 26 ppm 85

Dicrotophos 50181 Coturnix japonica Japanese Quail BEH FDB FCNS LOAEL 4 d 26 26 ppm 85

Dicrotophos 50181 Coturnix japonica Japanese Quail BEH FDB FCNS LOAEL 5 d 26 26 ppm 85

Dicrotophos 63269 NR Arachnida Spider/Mite Class POP POP ABND NOAEL 14 d 0.45 0.45 AI kg/ha 100

Dicrotophos 63269 Geocoris sp. Big-Eye Bug POP POP ABND NOAEL 14 d 0.45 0.45 AI kg/ha 100

Dicrotophos 63269 Geocoris sp. Big-Eye Bug POP POP ABND NOAEL 14 d 0.45 0.45 AI kg/ha 100

Dicrotophos 63269 Orius insidiosus Minute Pirate Bug POP POP ABND LOAEL 14 d 0.45 0.45 AI kg/ha 100

Dicrotophos 63269 Orius insidiosus Minute Pirate Bug POP POP ABND NOAEL 14 d 0.45 0.45 AI kg/ha 100

Dicrotophos 63269 NR Arachnida Spider/Mite Class POP POP ABND NOAEL 14 d 0.45 0.45 AI kg/ha 100

Dicrotophos 153435 NR Cicadellidae Leafhopper Family POP POP ABND LOAEL 70 d 0.1 0.1 % 100

Dicrotophos 153435 NR Cicadellidae Leafhopper Family POP POP ABND NOAEL 70 d 0.1 0.1 % 100

Dicrotophos 153435 NR Lepidoptera Moth And Butterfly Order POP POP ABND LOAEL 70 d 0.1 0.1 % 100

Dicrotophos 153435 Gossypium sp. Cotton REP REP SEPD NOAEL 70 d 0.1 0.1 % 100

Dicrotophos 153435 Gossypium sp. Cotton POP POP BMAS NOAEL 70 d 0.1 0.1 % 100

Dicrotophos 114803 Sorghum bicolor ssp. bicolor Grain Sorghum POP POP BMAS NOAEL hv 0.5 0.5 AI lb/acre 100

Dicrotophos 114803 Sorghum bicolor ssp. bicolor Grain Sorghum POP POP BMAS NOAEL hv 0.5 0.5 AI lb/acre 100

Dicrotophos 36627 Anas platyrhynchos Mallard Duck MOR MOR MORT NR-ZERO 14 d 32 32 ppm 85

Dicrotophos 36627 Anas platyrhynchos Mallard Duck MOR MOR MORT NR-ZERO 0.75d 2.4 2.4 mg/kg bdwt 85

Dicrotophos 36627 Anas platyrhynchos Mallard Duck MOR MOR MORT NR-ZERO 40 d 16 16 ppm 85

Dicrotophos 155866 Microplitis croceipes Braconid Parasitoid Wasp MOR MOR MORT NR-LETH 1 d 0.28 0.28 AI kg/ha 100

Dicrotophos 155866 Microplitis croceipes Braconid Parasitoid Wasp MOR MOR MORT NR-LETH 1 d 0.28 0.28 AI kg/ha 100

Dicrotophos 155866 Cardiochiles nigriceps Braconid Wasp MOR MOR MORT NR-LETH 1 d 0.28 0.28 AI kg/ha 100

Dicrotophos 155866 Cardiochiles nigriceps Braconid Wasp MOR MOR MORT NR-LETH 1 d 0.28 0.28 AI kg/ha 100

Dicrotophos 155867 Rattus norvegicus Norway Rat BEH BEH NMVM NOAEL LOAEL d 1.06 1.0494 2.1087mg/kg bdwt 99

Dicrotophos 155867 Rattus norvegicus Norway Rat BCM ENZ CEST ED50 d 0.749 0.74151 mg/kg bdwt 99

Dicrotophos 155867 Rattus norvegicus Norway Rat BCM ENZ CEST ED50 d 0.447 0.44253 mg/kg bdwt 99

Dicrotophos 155867 Rattus norvegicus Norway Rat BEH BEH NMVM ED50 d 1.58 1.5642 mg/kg bdwt 99

Dicrotophos 155867 Rattus norvegicus Norway Rat BCM ENZ CEST LOAEL d 0.213 0.21087 mg/kg bdwt 99

Dicrotophos 155867 Rattus norvegicus Norway Rat BCM ENZ CEST LOAEL d 0.213 0.21087 mg/kg bdwt 99

Dicrotophos 155867 Rattus norvegicus Norway Rat BCM ENZ CEST LOAEL d 0.213 0.21087 mg/kg bdwt 99

Dicrotophos 155867 Rattus norvegicus Norway Rat BCM ENZ CEST LOAEL d 0.213 0.21087 mg/kg bdwt 99

Dicrotophos 155867 Rattus norvegicus Norway Rat BEH BEH NMVM NOAEL LOAEL d 0.213 0.21087 1.0494mg/kg bdwt 99

Dicrotophos 155867 Rattus norvegicus Norway Rat BCM ENZ CEST ED50 d 0.314 0.31086 mg/kg bdwt 99

Dicrotophos 155867 Rattus norvegicus Norway Rat BCM ENZ CEST ED50 d 0.36 0.3564 mg/kg bdwt 99

Dicrotophos 155867 Rattus norvegicus Norway Rat BEH BEH NMVM ED50 d 1.21 1.1979 mg/kg bdwt 99

Dicrotophos 155867 Rattus norvegicus Norway Rat BCM ENZ CEST LOAEL d 0.107 0.10593 mg/kg bdwt 99

Dicrotophos 155867 Rattus norvegicus Norway Rat BCM ENZ CEST NOAEL LOAEL d 0.107 0.10593 0.21087mg/kg bdwt 99

Dicrotophos 155867 Rattus norvegicus Norway Rat BCM ENZ CEST ED50 d 0.431 0.42669 mg/kg bdwt 99

Dicrotophos 155867 Rattus norvegicus Norway Rat BCM ENZ CEST ED50 d 0.403 0.39897 mg/kg bdwt 99

Dicrotophos 105685 Coturnix japonica Japanese Quail BCM ENZ CEST LOAEL 0.041666667 d 3 3 mg/kg bdwt 85

Dicrotophos 105685 Coturnix japonica Japanese Quail BCM ENZ CEST LOAEL 0.041666667 d 3 3 mg/kg bdwt 85

Dicrotophos 105685 Coturnix japonica Japanese Quail BCM ENZ CEST LOAEL 0.041666667 d 3 3 mg/kg bdwt 85

Dicrotophos 105685 Coturnix japonica Japanese Quail BCM ENZ CEST LOAEL 0.041666667 d 3 3 mg/kg bdwt 85

Dicrotophos 67192 Megachile rotundata Alfalfa Leafcutter Bee MOR MOR MORT LD50 1 d 1.2 1.2 ppm 82