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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

 WASHINGTON D.C., 20460

OFFICE OF

CHEMICAL SAFETY AND

POLLUTION PREVENTION

 PC Code: 038501

 DP Barcode: D429589

Date: December 9, 2015

MEMORANDUM

SUBJECT: Registration Review: Combined Problem Formulation and Environmental Fate,

Ecological Preliminary Risk Assessment and Endangered Species Assessment for 

Diphenylamine

TO: Roy Johnson, Chemical Review Manager

Jill Bloom, Team Leader

Risk Management and Implementation Branch 5

Pesticide Re-Evaluation Division (7508P)

FROM: Andrew Sayer, Ph.D., Biologist

Cheryl Sutton, Ph.D., Environmental Scientist

Environmental Risk Branch IV

Environmental Fate and Effects Division (7507P)

REVIEWED

BY: Thomas Steeger, Ph.D., Senior Advisor

James N. Carleton, Ph.D., Senior Fate Scientist

Environmental Risk Branch IV

Environmental Fate and Effects Division (7507P)

THROUGH: Jean Holmes, D.V.M., M.P.H., Branch Chief

Environmental Risk Branch IV

Environmental Fate and Effects Division (7507P)

The Environmental Fate and Effects Division (EFED) has completed a combined problem 

formulation and preliminary environmental fate and ecological risk assessment in support of the 

Registration Review of diphenylamine (PC Code 038501; CAS No: 122-39-4) as a plant growth 

regulator. 

EFED examined the most recent environmental fate and ecological risk assessment written in 

support of the 1997 Reregistration Eligibility Decision (RED) for diphenylamine in association 

with updated toxicity, exposure, and usage information to determine if additional data are needed 

to support the Registration Review of diphenylamine. In addition, EFED considered the latest 

Agency science policies and risk assessment methodologies. Because the database was 
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determined to be sufficient to assess the ecological risk for the sole registered use of 

diphenylamine, the preliminary risk assessment has been combined with the problem formulation 

for Registration Review. EFED’s understanding of the underlying fate and effects of 

diphenylamine have not changed since the earlier assessment in 1997 and no additional data are 

required at this time given the limited use of the compound as a post-harvest treatment; therefore,

this preliminary risk assessment does not differ substantially from the previous, and the reader is 

referred to the earlier document for a more detailed discussion of the available data. 

Risk Conclusions

Diphenylamine is plant-growth regulator registered for use as a post-harvest treatment on apples 

to prevent fruit scald. The chemical is classified as an indoor/food use pesticide, and is applied 

using truck or bin drenching, or thermal fogging. Diphenylamine is hydrolytically stable, but 

readily degrades via photolysis in water and through atmospheric oxidation. It transforms in 

aerobic soil, but forms dimers and polymers that may be more stable than the parent compound. 

It is only slightly mobile in soil, but may volatilize from soils and surface water.

Diphenylamine is classified as moderately toxic to freshwater fish, aquatic-phase amphibians,

and freshwater invertebrates on an acute exposure basis, and practically non-toxic to birds, 

reptiles and terrestrial-phase amphibians on an acute oral and subacute dietary exposure basis. 

Diphenylamine is practically non-toxic to mammals on an acute exposure basis, but effects have 

been observed in chronic studies and include reduction in mean body weights, body weight 

gains, changes in hematological parameters, splenic/kindey lesions, and increased signs of 

clinical toxicity. No studies have been submitted for estuarine/marine organisms, terrestrial 

invertebrates, terrestrial and aquatic plants; however, minimum exposure of these taxa to 

didphenylamine given its current limited use as a post-harvest treatment is expected. Chronic 

studies have not been submitted for taxa other than mammals. No additional relevant data were 

identified in the open literature.

The results of this preliminary risk assessment are similar to those identified in the 

environmental fate and ecological risk assessment written in support of the RED for 

diphenylamine in 1997. Diphenylamine is classified as an “indoor/food” use chemical and EPA

does not generally conduct quantitative ecological risk assessments for indoor/food use 

chemicals for which there are no significant exposure pathways to non-target organisms. Given 

the use patterns (i.e., truck or bin drenching with collection of drench water, or thermal fogging 

in an enclosed, sealed indoor space), the environmental fate properties (rapid photolysis, rapid

biotic transformation in soil, and rapid atmospheric oxidation of volatilized compound), and the 

limited amount of diphenylamine that will be available for environmental exposure as a direct 

result of these application methods, the likelihood of adverse effects on ecological systems from 

the post-harvest treatment use is considered to be minimal. Discharge of effluent containing 

diphenylamine is regulated by National Pollutant Discharge Elimination System (NPDES) 

permits. Disposal of drench water collected following application is not assessed here, as it is 

regulated under NPDES.
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Based on the low likelihood of exposure, EFED has made a No Effect (NE) determination for 

Federally threatened or endangered (hereafter referred to as “listed”) species and their designated 

critical habitat.

Uncertainties

There is some degree of uncertainty surrounding the environmental fate of diphenylamine. 

Although more data are available than typically are for indoor/food use pesticides, which require 

only hydrolysis data, there is not a full environmental fate dataset. Additionally, complete

information regarding the transformation products via biotic metabolism is not available. 

However, risk uncertainty associated with the lack of environmental fate data is offset by the fact 

that potential environmental exposure is expected to be minimal due to diphenylamine’s use as a 

post-harvest treatment. Exposure potential is further reduced by diphenylamine’s lability to 

photolytic and atmospheric oxidative degradation processes, particularly if the chemical is 

vented into the atmosphere as a vapor following thermal fogging. Although there is uncertainty 

concerning the environmental fate of the compound and its exposure potential associated with 

post-use disposal, drench wastes disposal is regulated under the NPDES permitting system and 

has not been further evaluated in this assessment.

Provided that use of diphenylamine as currently specified on the labels does not change, no 

additional data are recommended at this time.
Combined Problem Formulation, Environmental Fate,

Ecological Preliminary Risk Assessment and Endangered Species 

Assessment for the Registration Review of Diphenylamine

 

CAS 122-39-4 PC Code 038501

November 20, 2015

Prepared by

Andrew Sayer, Ph.D., Biologist

Cheryl Sutton, Ph.D., Environmental Scientist

U.S. Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

(EFED)

Environmental Risk Branch IV

1200 Pennsylvania Ave., NW

Mail Code 7507P

Washington, DC 20460

Reviewed by

Thomas Steeger, Ph.D., Senior Science Advisor 

James Carleton, Ph.D., Senior Fate Scientist

Jean Holmes, D.V.M., M.P.H., Branch Chief
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Table of Contents

1. Executive Summary.............................................................................................................. 7

2. Problem Formulation ......................................................................................................... 8

2.1. Conclusions from Previous Risk Assessments................................................................ 8

2.1.1. Ecological Risk Assessment...................................................................................... 9

2.1.2. Drinking Water Exposure Assessments.................................................................. 9

2.1.3 Clean Water Act Programs.......................................................................................... 9

2.2. Nature of Regulatory Action...................................................................................... 10

2.3. Stressor Source and Distribution .............................................................................. 10

2.3.1. Nature of the Chemical Stressor.......................................................................... 10

2.3.2. Overview of Pesticide Usage ................................................................................ 10

2.4. Receptors ................................................................................................................... 11

2.4.1. Aquatic and Terrestrial Effects........................................................................... 11

2.4.2. Ecosystems Potentially at Risk ......................................................................... 11

2.5. Assessment Endpoints ................................................................................................ 12

2.6. Risk Hypotheses......................................................................................................... 12

2.6.2. Potential Exposure Pathways and Effects.......................................................... 13

2.7. Analysis Plan .............................................................................................................. 13

2.7.1. Measures of Exposure........................................................................................ 13

2.7.1.1 Measures of Aquatic and Terrestrial Exposure ........................................................................13

2.7.2. Measures of Effect.............................................................................................. 13

2.8. Preliminary Identification of Data Gaps............................................................ 14

3. Analysis.............................................................................................................................. 14

3.1. Use Characterization .................................................................................................. 14

3.2. Exposure Characterization ........................................................................................ 15

3.2.1. Environmental Fate and Transport Characterization ...................................... 15

3.2.1.1. Transport and Mobility ............................................................................................................17

3.2.1.3. Field Studies ............................................................................................................................17

3.2.1.4. Bioaccumulation ......................................................................................................................17

3.2.1.5. Transformation Products..........................................................................................................18

3.2.2. Measures of Aquatic Exposure............................................................................ 18

3.2.2.1. Estimated Environmental Concentrations in Surface...............................................................18

3.2.2.2. Monitoring Data.......................................................................................................................19

3.2.3. Measures of Terrestrial Exposure....................................................................... 19

3.3. Ecological Effects Characterization .......................................................................... 19

3.3.1. Aquatic Organisms ............................................................................................... 19

3.3.2. Terrestrial Organisms.......................................................................................... 20

3.3.3. Review of Incident Data ....................................................................................... 22

4. Risk Characterization......................................................................................................... 23

4.1. Risk Description.......................................................................................................... 23

4.2.1. Risks to Aquatic Organisms................................................................................. 23

4.2.1.1. Freshwater Fish, Invertebrates, and Amphibians.....................................................................23

4.2.2. Risks to Terrestrial Organisms............................................................................ 23

4.2.2.1. Birds, Reptiles, and Terrestrial-phase Amphibians..................................................................23

4.2.2.2. Mammals .................................................................................................................................24

4.2.2.3. Terrestrial Invertebrates...........................................................................................................24

4.2.2.4. Terrestrial Plants......................................................................................................................24
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5. Endocrine Disruptor Screening Program (EDSP)........................................................... 24

6. Conclusions.......................................................................................................................... 25

7. References............................................................................................................................ 25

8. Appendix A. Submitted Studies for Diphenylamine....................................................... 27

9. Appendix B. Text from Memo (with CBI Redacted) from the DPA Task Force in 

Response to Use Questions from EPA....................................................................................... 29

List of Tables

TABLE 1. CHEMICAL PROFILE OF DIPHENYLAMINE. .................................................................................................................10

TABLE 2. CHEMICAL PROPERTIES AND ENVIRONMENTAL FATE PARAMETERS OF DIPHENYLAMINE. ...................................................15

TABLE 3: DIPHENYLAMINE ACUTE TOXICITY VALUES FOR AQUATIC ORGAMISMS...........................................................................20

TABLE 4. DIPHENYLAMINE ACUTE TOXICITY VALUES FOR BIRDS AND MAMMALS...........................................................................22
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1. Executive Summary

Diphenylamine is a plant growth regulator used only for post-harvest treatment of apples for 

control of scald, a physiological disorder that causes browning of the skin in storage rendering 

the apple unacceptable for fresh market. Diphenylamine prevents the oxidation of alphafarnesene, a volatile compound which naturally occurs in apples and leads to spoilage. It is 

classified as an indoor/food use chemical and does not have outdoor (field) or residential labeled 

applications. 

Applications are made post-harvest by either truck or bin drenching, which are conducted 

outdoors. Additionally, a drench or spray application is sometimes utilized as bins of fruit are 

moved beneath a conveyor; alternatively thermal fogging conducted in an enclosed, sealed

indoor space may be used. Drench wastes are collected and disposed of after re-use and a 

determination that the material is no longer suitable for re-use. Disposal of the drench waste is 

governed by NPDES permitting requirements. Venting of the chemical in vapor phase following 

indoor fogging is not expected to lead to non-target exposure due to expected degradation of 

diphenylamine in the atmosphere. Given these use practices and the fate of the vapor phase 

material, there are no significant environmental release pathways that would be expected to 

affect non-target plants or animals. 

Diphenylamine is hydrolytically stable at environmental pH’s, but readily degrades via aqueous 

photolysis and through atmospheric oxidation. It is susceptible to biotic transformation in 

aerobic soil; however, this process may lead to the formation of dimers and polymers that may 

be more stable than the parent compound. It is only slightly mobile in soil, but may volatilize 

from either dry or moist soils, as well as from surface water; volatilized material would then be 

subject to atmospheric oxidation.

Diphenylamine is classified as moderately toxic to freshwater fish, aquatic-phase amphibians and 

freshwater invertebrates on an acute exposure basis, and practically non-toxic to birds, reptiles 

and terrestrial-phase amphibians on an acute oral and subacute dietary exposure basis. 

Diphenylamine is practically non-toxic to mammals on an acute exposure basis, but effects 

observed in a reproduction study with rats include reduction in mean body weights and body 

weight gains, changes in hematological parameters, splenic/kindey lesions, and increased signs 

of clinical toxicity (e.g., bluish colored fluid in the cage and bluish colored staining of the coat in 

both sexes, and swelling of mammary gland(s) or palpable lateral-ventral masses, primarily in 

females). No studies have been submitted for estuarine/marine organisms, terrestrial 

invertebrates, terrestrial and aquatic plants. Chronic studies have not been submitted for taxa

other than mammals.

The results of this screening-level risk assessment are similar to those identified in the 

environmental fate and ecological risk assessment written in support of the RED for 

diphenylamine in 1997. Diphenylamine is an indoor/food use chemical and EPA does not 

generally conduct quantitative ecological risk assessments for indoor use chemicals for which 

there are no routes of exposure to non-target organisms. Given the patterns of diphenylamine use 

(i.e., truck or bin drenching with collection of drench water, or thermal fogging in an enclosed, 

sealed indoor space), the likelihood of exposure that would in turn lead to adverse effects on 
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ecological systems from the post-harvest treatment use is considered to be minimal. Potential 

aquatic and terrestrial exposure to diphenylamine from drench water disposal would be mitigated 

by rapid aqueous photolysis, rapid biotic transformation in soil, volatilization, and atmospheric 

oxidation of any volatilized compound. Discharge of effluent containing diphenylamine is 

regulated by National Pollutant Discharge Elimination System (NPDES) permits as indicated on 

end use product labeling. (At this time, some of the relevant diphenylamine product labels do 

not cite the NPDES permits, but the registrants have agreed to add the appropriate statements.) 

Exposure from the disposal of drench water collected following post-harvest treatment 

application is not assessed here, as it is regulated under NPDES. 

Based on the low likelihood of environmental exposure from the indoor/food use pattern, the 

NPDES permit for the drench water disposal, and the environmental fate properties of 

diphenylamine, EFED concludes that the post-harvest use of diphenylamine on apples will have 

'No Effect' (NE) on federally listed endangered or threatened terrestrial or aquatic species, or 

their designated critical habitats, as identified by the U.S. Fish and Wildlife Service and the 

National Marine Fisheries Service. EPA anticipates conducting no further analysis of potential 

risks to endangered or threatened species from diphenylamine for this use unless the Agency 

obtains data or information that would otherwise inform the Agency’s determination.

 

2. Problem Formulation

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

ecological risk assessment being conducted for the labeled uses of diphenylamine (PC Code 

038501; CAS No: 122-39-4). The problem formulation sets the objectives for the risk assessment 

and provides a plan for analyzing the data and characterizing the risk (USEPA 1998). 

As part of the Registration Review process, a Problem Formulation (PF) for this risk assessment 

has been developed simultaneously with the conduct of the Registration Review Preliminary 

Risk Assessment (PRA) itself, as it was determined that given the current uses available data are 

sufficient to conduct the risk assessment at this time. A separate Problem Formulation document 

will not be issued for diphenylamine.

2.1. Conclusions from Previous Risk Assessments

Most recently, in 2008, EFED assessed the ecological risk of a new diphenylamine product that 

used a post-harvest thermal fogging application technique to treat apples for scald during storage 

(DP340287), which was the same as the technique EFED reviewed previously for another 

diphenylamine product in June 2004 (DP303521). Both reviews concluded that the thermal 

fogging method of application would reduce potential exposures of terrestrial and aquatic 

environments to diphenylamine when compared with drench applications in open air facilities 

with discharge of spent drench material to orchards, and would reduce overall environmental 

loadings. Based on the limited potential exposure from the thermal fogging application 

technique, the potential risks to terrestrial and aquatic non-target organisms, including federally 

listed species, was determined to be even lower than that associated with the drench application. 

The ecological risk assessment written in support of the 1997 Reregistration Eligbility Decision 
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(RED) document for diphenylamine was issued in July 1997 (USEPA 1997). Conclusions are 

presented below.

2.1.1. Ecological Risk Assessment

The major environmental fate and ecological risk conclusions presented in the RED were as 

follows:

• Diphenylamine is stable towards hydrolysis at environmentally relevant pH values. It has 

a moderate solubility in water, a relatively high octanol/water partition coefficient (Kow), 

and a high vapor pressure. The high rate of aqueous photolysis and the susceptibility of 

the chemical in aerobic environments indicate that if diphenylamine were to reach surface 

waters, the parent compound would be short lived. However, aerobic biotic 

transformations result in dimers and polymers that may be more stable than the parent 

compound.

• Diphenylamine is moderately toxic to fish, aquatic-phase amphibians, and aquatic 

invertebrates on an acute exposure basis. It is practically non-toxic to birds, reptiles and 

terrestrial-phase amphibians on an acute and subacute exposure basis and it is practically 

non-toxic to mammals on an acute oral exposure basis. 

• Diphenylamine is classified as an indoor/food use chemical and EPA does not generally 

conduct quantitative ecological risk assessments for indoor/food use chemicals for which 

there are no significant exposure routes for non-target organisms. However, given the use 

patterns and the limited amount of diphenylamine that will be available for environmental 

exposure as a direct result of these application methods, the likelihood of adverse effects 

on ecological systems is considered to be minimal. Discharge of effluent containing 

diphenylamine is regulated by National Pollutant Discharge Elimination System (NPDES) 

permits. 

2.1.2. Drinking Water Exposure Assessments

A drinking water assessment (DWA) has not been conducted for diphenylamine, as the 

compound has been categorized in the past as an indoor/food use, for which a DWA was not 

required. 

2.1.3 Clean Water Act Programs 

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

under section 303(d) of the Clean Water Act. No Total Maximum Daily Loads (TMDLs) or 

water quality criteria have been developed for diphenylamine (USEPA 2015).
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2.2. Nature of Regulatory Action

The PRA is conducted as part of the Agency’s Registration Review process for pesticide active 

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

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

Registration Review. The Registration Review program is intended to ensure that, as the ability 

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

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

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

Through the new Registration Review program, EPA periodically reevaluates pesticides to make 

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

2.3. Stressor Source and Distribution

2.3.1. Nature of the Chemical Stressor

Diphenylamine is a plant growth regulator used for post-harvest treatment of apples for scald 

control. It is classified as an indoor/food use chemical and does not have outdoor (field) or 

residential labeled applications. Diphenylamine works as an antioxidant to prevent the oxidation 

of alpha-farnesene, a volatile compound which is present in apples and causes cold storage scald 

on the outside of the fruit (Ingle and D'Souza, 1989).

The chemical profile of diphenylamine is provided in Table 1. As described in Section 3.2.1.4, 

this screening-level ecological risk assessment focuses on diphenylamine parent only.

Table 1. Chemical Profile of Diphenylamine.

Common names Diphenylamine, DPA

IUPAC name/CAS name N-phenylaniline/N-phenylbenzenamine

Registered Product Names

No Scald DPA EC-283 (31% a.i.; EPA Registration 2792-45)

ecoFOG-100 (10% a.i.; EPA Reg. No. 64864-53)

Chemical name Diphenylamine

Structure

SMILES Notation N(c(cccc1)c1)c(cccc2)c2

Pesticide type Plant Growth Regulator (no longer used as a fungicide)

Chemical class Bridged Diphenyl 

(http://www.alanwood.net/pesticides/class_pesticides.html)

CAS number 122-39-4

Empirical formula (C6H5)2NH

Molecular mass 169.23 g mol-1 

2.3.2. Overview of Pesticide Usage
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Diphenylamine is a plant growth regulator used as a post-harvest treatment to prevent scald on

apples going to storage. Based on information provided by the Biologic and Economic Analysis 

Division (BEAD) in the BEAD Chemical Profile (BCP), diphenylamine application is made as a 

post-harvest treatment with dipping, drenching, spraying, and thermal fogging (USEPA 2015). 

However, the registrants for diphenylamine stated in a 2015 memo to EPA (from the 

Diphenylamine [DPA] Task Force; see Appendix B) that tank dipping is no longer used and is 

not being supported as a labeled use. Additional use details are provided in Appendix B, which 

consists of text from the DPA Task Force memo (with Confidential Business Information

redacted) in response to use questions recently posed by EPA. Use details were also previously 

provided in the 1997 RED chapter (USEPA 1997). Applications are made post-harvest by either 

truck or bin drenching, which are conducted outdoors and utilize a drench or spray application as 

bins of fruit are moved beneath on a conveyor; alternatively, thermal fogging is conducted in an

enclosed, sealed indoor space. Based on information in the BCP, diphenylamine end-use 

products are formulated as an emulsifiable concentrate, soluble concentrate, or pressurized gas.

Additional use information is presented in Section 3.1.

Following post-harvest drenching, the disposal of the collected drench water containing 

diphenylamine may include transfer to and storage in lagoons, or distribution to land (e.g., to 

orchard roads for dust abatement or to fields). Exposure and risk resulting from disposal of 

drench water collected following application are not assessed here, as such disposal is regulated 

under NPDES permits as indicated on end use product labels. Appendix B contains additional 

information on the disposal of drench waste under NPDES regulations.

2.4. Receptors

2.4.1. Aquatic and Terrestrial Effects

A receptor is a biological entity that is exposed to a stressor (USEPA 1998) and EPA relies on 

surrogate species to assess the potential for adverse effects to aquatic and terrestrial receptors 

from the use of a pesticide. Consistent with the process described in the Overview of the 

Ecological Risk Assessment Process in the Office of Pesticide Programs (USEPA 2004), this risk 

assessment uses a surrogate species approach in its evaluation of diphenylamine. Toxicity data 

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

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

included under these taxonomic groupings.

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

from the available open literature are used to evaluate potential direct effects of diphenylamine to 

aquatic and terrestrial receptors. The open literature studies are located through EPA’s database 

ECOTOX (http://cfpub.epa.gov/ecotox/), which provides a source for locating single chemical 

toxicity data for aquatic life, terrestrial plants, and wildlife. 

2.4.2. Ecosystems Potentially at Risk

Ecosystems at potential risk are often extensive in scope; therefore, it is not possible to identify 

such ecosystems in other than general terms in a screening-level assessment. In general terms, 
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terrestrial ecosystems potentially at risk are treated areas and areas immediately adjacent to 

treated areas. For diphenylamine, this includes terrestrial areas on which treated wastewater is 

disposed and areas adjacent to that. Aquatic ecosystems potentially at risk include water bodies 

adjacent to or downstream from treated areas and may include natural or impounded lentic 

systems, i.e., ponds, lakes, and reservoirs, and lotic (flowing) waterways, i.e., streams and rivers. 

Within water bodies, the water column, sediment, and pore water are all compartments of 

potential concern. Due to the limited use of diphenylamine as a post-harvest treatment on 

apples, and the lack of significant exposure pathways directly related to the post-harvest use as a 

drench or thermal fog, ecosystems potentially at risk are highly limited in scope. After use and 

re-use, drench waste water is collected and disposed of according to NPDES permitting 

requirements. Additionally, venting of the chemical in vapor phase following indoor fogging is 

not expected to lead to non-target exposure due to expected degradation of diphenylamine in the 

atmosphere (via rapid oxidation or photolysis), there are no significant release pathways.

2.5. Assessment Endpoints

Assessment endpoints represent the actual environmental values that are to be protected, defined 

by ecological entitities (species, community, etc.) and their attributes or characteristics (USEPA 

1998). Typically, ecological entities assessed include the following: birds, amphibians, reptiles, 

mammals, freshwater fish, terrestrial and aquatic invertebrates, and terrestrial and aquatic plants. 

The assessed attributes for any of these entities may include growth, survival, and/or 

reproduction. If risks are identified for given species/taxa based on a screening-level assessment,

then such risks might be expected to translate to higher levels of biological organization. For 

diphenylamine, however, use patterns and environmental fate data suggest it will not be 

sufficiently available in the environment to be a cause of concern for ecological entities.

2.6. Risk Hypotheses

For diphenylamine, the following risk hypothesis is employed for the ecological risk assessment:

The exposure pathway of diphenylamine used in accordance with the label has low 

potential to result in adverse effects on the survival, growth, and reproduction of nontarget terrestrial and aquatic organisms.

Additional discussion can be found in Section 4.1, Risk Characterization.
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2.6.2. Potential Exposure Pathways and Effects

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 include a source, a release mechanism, an environmental transport medium, a point of 

exposure for ecological receptors, and a feasible route of exposure. The potential exposure 

pathways and effects of the registered use of diphenylamine are mediated by the fact that the 

compound is exclusively an indoor/food use (post-harvest treatment of apples). The normally 

assessed routes of environmental exposure are not relevant for diphenylamine. The two

diphenylamine application methods are truck or bin drenching, with collection of drench water;

and thermal fogging, which is done in an enclosed, sealed indoor space. Additionally, any 

diphenylamine released to the air as a vapor in limited amounts following venting of storage 

spaces where thermal fogging is conducted is expected to rapidly degrade via atmospheric 

oxidation and photolysis. The disposal of drench water containing diphenylamine may lead to 

non-target organism exposure if such water is stored in lagoons or distributed to land, for 

example to orchard roads for dust-abatement purposes. However, exposure resulting from 

disposal of drench water collected following post-harvest application is not assessed here, as 

such disposal is regulated under NPDES as indicated on end use product labels. Furthermore, 

neither application method is expected to result in spray drift. Appendix B contains additional 

information on the disposal of drench waste under NPDES permits.

2.7. Analysis Plan 

2.7.1. Measures of Exposure

2.7.1.1 Measures of Aquatic and Terrestrial Exposure 

Standard exposure modeling is not applicable to the indoor/food use registered for 

diphenylamine, precluding the need for the determination of estimated environmental 

concentrations (EEC). The sole registered use of diphenylamine as a post-harvest treatment on 

apples is not anticipated to result in aquatic exposure from either the thermal fogging application 

(an indoor use in a sealed, enclosed room) or from the outdoor (truck and bin) drenching use, 

after which the drench waste is collected and subsequently disposed of in accordance with 

NPDES permits. 

Exposure estimates using the Screening Tool for Inhalation Risk (STIR, v. 1.0, 11/23/2010) and 

Screening Imbibition Program (SIP, v. 1.0) were not conducted for diphenylamine due to the 

indoor/food use pattern, low acute and sub-acute toxicity to avian taxa, short atmospheric

oxidation half-life, and NPDES permit regarding the disposal of drench water.

2.7.2. Measures of Effect 

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

conducted with a limited number of surrogate test species. The test species are not intended to be 

representative of the most sensitive species but rather were selected based on their ability to 
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thrive under laboratory conditions. The acute measures of effect used in this screening-level 

assessment are the LD50 (Lethal Dose), LC50 (Lethal Concentration), and EC50 (Effects 

Concentration). These are measures of acute toxicity which result in 50% of the respective effect 

in tested organisms. The biological endpoint for the chronic measure of exposure is the NOAEL 

(No Observed Adverse Effect Level). Toxicity studies were submitted for freshwater fish and 

invertebrates, birds, and mammals. The endpoints used for risk characterization were 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 were considered to be scientifically valid). 

2.8. Preliminary Identification of Data Gaps

The database on the environmental fate and transport properties of diphenylamine is complete

with respect to the required studies for indoor/food use pesticides, for which only hydrolysis data 

are required to be submitted to EPA. Acceptable studies were submitted for hydrolysis, aqueous 

photolysis, aerobic soil metabolism and adsorption/leaching. A submitted anaerobic aquatic 

metabolism study was classified as not acceptable. Since the compound is used only for postharvest treatment of apples as an indoor/food use (fumigation in storage) or as a drench with 

recycled and collected treatment water, environmental fate data requirements are limited to 

hydrolysis data. Additional data on photolysis and metabolism of diphenylamine are also 

available, but are not required for this post-harvest use.

There are no ecological effects data gaps for diphenylamine with respect to the required studies 

for indoor/food use pesticides. No studies have been submitted for estuarine/marine organisms, 

terrestrial invertebrates, terrestrial and aquatic plants. Chronic studies have not been submitted 

for taxa other than mammals. However, given the current use pattern, these data were not 

deemed to be necessary to complete the risk assessment. Only acute studies are required for fish 

and aquatic invertebrates because of the indoor/food use.

3. Analysis

3.1. Use Characterization

Diphenylamine is used as a post-harvest treatment as a plant growth regulator to prevent scald on 

apples going to storage. Applications are made post-harvest by either truck or bin drenching, 

which is conducted outdoors and utilizes drench or spray application as bins of fruit are moved 

beneath on a conveyor, with collection and subsequent disposal of drench wastes in accordance 

with NPDES permits. Alternatively, application may be done via thermal fogging conducted in 

an enclosed, sealed indoor space. Additional information on use provided by the DPA Task 

Force is presented in a memo in Appendix B. As stated in the memo, 

“The application rate is application of 100 gallons of product to 30 bins of apples. The 

application rate ranges from 1000 – 2200 ppm with an average 1500 ppm. The number of 

apple bins typically treated in one day depends on the region of the country and apple 

production. Application can range from 1000- 5000 apple bins/day with an average of 

2500 apple bins/day could be treated depending on the size of the packing house.” 
-Page 15 of 31-

Based on information in the memo, “The typical thermal fogging room can hold from a minimum 

of 500 apple bins to a maximum of 6,000 apple bins with an average room holding 1,800 apple 

bins.” The DPA Task Force also stated in the memo, “The primary application is drench which 

is >50% of applications followed by thermal fogging at approximately 25% of applications. 

Over the few years, more facilities have been converting to thermal fogging and it is expected to 

continue.” The registrants reiterated this information orally during a teleconference following 

the Office of Pesticide Programs’ (OPP) receipt of the memo in response to OPP’s questions on 

use.

3.2. Exposure Characterization

3.2.1. Environmental Fate and Transport Characterization

Diphenylamine is moderately soluble in water, and has a moderately high vapor pressure, 

indicating that it has intermediate to high volatility under field conditions and may volatilize in

the environment if present on dry, non-adsorbing surfaces. Based on its Henry’s Law Constant, 

diphenylamine may also volatilize from water. While diphenylamine is stable to hydrolysis, it

degrades rapidly via aqueous photolysis, with a half-life of 4.4 hours. Its estimated atmospheric 

oxidation half-life is 0.6 hours, estimated using a quantitative structure-activity relationship 

(QSAR) software (EPI Suite v.4.11). Diphenylamine transforms rapidly in aerobic soil (half-life 

<1 day), although it forms more structurally complex dimers and polymers via metabolism (most 

of which contained dimeric diphenylamine with an additional unit of aniline), which may be 

more stable than the parent compound. Degradation in aerobic soil occurs to some extent, and

one of the products of aerobic metabolism is CO2 (18% of the applied by study termination at 1 

year). Unextracted residues (up to 58% of the applied by 184 days) were also formed in 

laboratory metabolism studies. In soils, parent diphenylamine is only slightly mobile, based on

organic carbon partition coefficient (Koc) values in five soils and using the FAO soil mobility

classification scheme (FAO, 2000). Chemical property and environmental fate data for 

diphenylamine are presented in Table 2. 

Table 2. Chemical Properties and Environmental Fate Parameters of Diphenylamine.

Chemical/Fate Parameter Value Description/Comments Source (MRID)/ 

Classification

Selected Physical/Chemical Parameters

Chemical name diphenylamine ˗ ˗

Molecular mass 169.23 g mol-1 ˗ USEPA 1997

Vapor pressure (25°C) 6.39 x10-4 Torr

Intermediate to high 

volatility possible from dry, 

non-sorbing surfaces.

USEPA 1997

Water solubility (25°C) 39.4 mg/L USEPA 1997

Octanol-water partition 

coefficient (Log KOW) 3.59 USEPA 1997
-Page 16 of 31-

Chemical/Fate Parameter Value Description/Comments Source (MRID)/ 

Classification

Henry’s Law Constant 

(25°C) 3.6 x 10-6

 atm-m3/mole

Calculated from MW, VP, 

WS. Indicates the compound 

may volatilize from moist 

soil or water surfaces.

˗

Atmospheric oxidation halflife (hours; 25°C) 0.64

Estimated value. Based on 

reaction with hydroxyl 

radicals. No reaction with 

ozone.

EPI Suite

v.411/AopWin 

v1.92

Persistence

Hydrolysis half-life (days)

pH 5, 25°C

pH 7, 25°C

pH 9, 25°C

316

352

358

Essentially stable to 

hydrolysis.

42660001

(Acceptable)

Aqueous photolysis half-life 

@25°C; pH 7 (hours) 4.4 Rapidly photodegrades in 

clear, shallow water.

42958201

(Acceptable)

Soil photolysis half-life 

(25°C) No data. Data are not required. ˗

Aerobic soil metabolism 

half-life (days; 25°C) <1

Transformed to dimers and 

polymers possibly more 

stable than the parent. High 

unextracted residues by day 

3.

42964201 

(Acceptable)

Anaerobic soil metabolism 

half-life (25°C) No data. Data are not required. ˗

Aerobic aquatic metabolism 

half-life (25°C) No data. Data are not required. ˗

Anaerobic aquatic 

metabolism half-life (25°C) No data. Data are not required. 43080901(Not Acceptable)

Mobility

Freundlich soil-water 

partition coefficients (KF);

21.4 (loamy sand) 

13.8 (loam) 

4.9 (silt loam)

16.4 (silty clay loam)

151.6 (clay)

˗ 43412701

(Acceptable)

Organic carbon-normalized 

soil partition coefficients 

(KFOC)

3622 (loamy sand) 

3962 (loam) 

1212 (silt loam)

6593 (silty clay loam)

5143 (clay)

Slightly mobile in soils. 43412701

(Acceptable)

Field Dissipation

Terrestrial field dissipation 

half-life No data Data are not required. ˗

Fish Bioconcentration
-Page 17 of 31-

Chemical/Fate Parameter Value Description/Comments Source (MRID)/ 

Classification

Fish bioconcentration factors 

(steady-state); depuration 

rate

No data Data are not required. ˗

3.2.1.1. Transport and Mobility

In a batch equilibrium study of diphenylamine conducted on five soils, diphenylamine was only 

slightly mobile in soil based on the Koc values (MRID 43412701). In aged soil columns, 

diphenylamine residues were somewhat mobile in silt loam soil columns (with <1.9% found in 

the last two segments and the leachate), and slightly mobile in loamy sand, loam and clay soil 

columns (with 0.11-0.48% of the applied in the last two column segment or leachates). Because 

this chemical is used indoors or with collected drench waste, there is a low likelihood that it will 

runoff to surface waters. However, if collected drench material is applied to orchard roads or 

other outdoor surfaces, rather than held in lined storage lagoons, there is a potential for 

diphenylamine to reach surface waters via runoff events. The susceptibility of the chemical to 

aqueous photolysis and to biotic degradation in aerobic environments indicate that if it were to

be released to soils or reach surface waters, the parent compound has a high likelihood of being 

readily dissipated.

There is also a potential for transport via volatilization, based on diphenylamine’s vapor pressure 

as well as the high level of volatiles (up to 70% of the applied) detected in the submitted 

anaerobic aquatic metabolism study. However, volatilized diphenylamine is expected to rapidly 

degrade through atmospheric oxidation, and possibly aqueous photolysis if it is present on 

particulate matter along with sufficient moisture. 

3.2.1.2. Degradation 

Diphenylamine rapidly degraded in water via photolysis (half-life of 4.4 hours) in laboratory 

studies, forming several major transformation products (MRID 42958201). In aerobic loam soil 

(MRID 42964201), diphenylamine transformed with a metabolism half-life of <1 day, but 

formed dimers and polymers that are structurally more complex and may be more stable than the 

parent compound (USEPA 1997). Information on the biotic metabolism of diphenylamine in 

anaerobic soil or aquatic environments is not available. 

3.2.1.3. Field Studies

Field dissipation data have not been submitted and are not required for diphenylamine based on 

the current label use.

3.2.1.4. Bioaccumulation

Bioconcentration in fish data have not been submitted and are not required for diphenylamine 

based on the current label use. 
-Page 18 of 31-

3.2.1.5. Transformation Products

Submitted studies did not fully characterize transformation products. In the aquatic photolysis 

study, several major transformation products were formed: carbazole (maximum of 51.7% at 

10.5 hours, decreasing to non-detectable by 72-192 hours); hydroxydiphenylamine (OH-DPA; 

maximum of 16.3% at 36 hours, decreasing to 6.8% by 192 hours); and an hydroxylated tricyclic 

compound (first detected at 4 hours, increasing to 93.2% by 192 hours). Minor transformation 

products (not identified) were a total maximum of 5.9% of the applied.

In the aerobic soil metabolism study, 12 transformation products (<18.9% of the applied) were 

isolated, but were not identified. Additionally, some mineralization occurred, as CO2 was 17.9% 

of the applied after 365 days. Unextracted residues were >46.4% of the applied by day 3, and 

were a maximum of 57.9% at 184 days. Additional information about transformation products 

was obtained from an aged column leaching study (43413001), in which four degradates were 

identified in column soil samples. These included N,N-diphenylformamide (DPF), 4-nitro-Nphenylbenzenamine (NDPA), and two diphenylamine dimers (DPA-1, DPA-2).

3.2.2. Measures of Aquatic Exposure

3.2.2.1. Estimated Environmental Concentrations in Surface 

Water

Standard exposure modeling was not conducted for diphenylamine and estimated environmental 

concentrations (EEC) were not determined. The registered use of diphenylamine as a postharvest treatment on apples is not anticipated to result in aquatic exposure from either the 

fogging application (an indoor use in a sealed, enclosed room) or from the outdoor (truck and 

bin) drenching use, after which the drench waste is collected and subsequently disposed of in 

accordance with NPDES permits. As stated by the DPA Task Force in a memo to the Agency 

(see Appendix B), 

“Based on NPDES requirements, waste materials can be disposed of in lined lagoons, as 

dust abatement liquids or land applied. For the lined lagoon disposal, the waste solution 

is added to imperviously lined, in-ground, engineered structures, which rely largely upon 

evaporation for water removal. Dust abatement is the application of wastewater to 

unpaved bin storage lots and unpaved roads (i.e., orchard roads) for the purpose of dust 

suppression. Land application is an engineered system for applying wastewater to a 

vegetated land surface. DPA waste solutions are not discharged directly to surface 

waters.”

Thus, while there is the potential for aquatic exposure in surface water from storage in lined 

lagoons, or from use of the drench waste for dust abatement or land application, these

applications are regulated by NPDES. It is noted, however, that potential aquatic exposure from 

such applications would be mitigated by aqueous photolysis, volatilization, and atmospheric 

oxidation of any volatilized compound.
-Page 19 of 31-

3.2.2.2. Monitoring Data

EFED conducted a search (September 2015) of the United States Geological Services (USGS) 

National Water Quality Assessment (NAWQA) Program database 

(http://cida.usgs.gov/nawqa_queries_public/) and the California Department of Pesticide 

Regulation (CDPR) surface water and sediment database 

(http://cdpr.ca.gov/docs/emon/surfwtr/surfcont.htm). Based on the search results, no monitoring 

data are available for diphenylamine.

3.2.3. Measures of Terrestrial Exposure

Standard exposure modeling was not conducted for diphenylamine and estimated environmental 

concentrations (EEC) were not determined. The registered use of diphenylamine as a postharvest treatment on apples is not anticipated to result in terrestrial exposure from either the 

fogging application (an indoor use in a sealed, enclosed room) or from the outdoor (truck and 

bin) drenching use, after which the drench waste is collected. Disposal of drench waste, which 

may be stored in lagoons or applied to orchard fields and roads for dust abatement, is regulated 

by NPDES permit. Given the pattern of diphenylamine use, the likelihood of adverse effects on 

ecological systems from terrestrial exposure is considered to be minimal.

3.3. Ecological Effects Characterization 

A detailed description of the available ecotoxicity data for diphenylamine is provided in the 

Environmental Fate and Ecological Risk Assessment written in support of the RED for 

diphenylamine (USEPA 1997). Since the completion of that assessment, no new ecological 

effects data have been submitted to EPA. 

Since this is an indoor/food use chemical, and given the pattern of diphenylamine use, the 

likelihood of adverse effects on ecological systems is considered to be minimal. No further data 

are required. Discharge of effluent containing diphenylamine for manufacturing use is regulated 

by NPDES.

3.3.1. Aquatic Organisms 

Only acute studies are required for fish and aquatic invertebrates because of the indoor/food use. 

An overview of submitted aquatic organism studies can be seen in Table 3.

Freshwater Fish

One study with rainbow trout (Oncorhynchus mykiss) using the technical grade active ingredient 

(TGAI) was submitted to establish the toxicity of diphenylamine to freshwater fish (MRID 

43879001). The 96-hr LC50 is 2.2 mg a.i./L (parts per million; ppm), classifying diphenylamine 

as moderately toxic to freshwater fish on an acute exposure basis. Sublethal effects occurred at 

the three hightest treatment groups and included lethargy, erratic swimming, discoloration, loss 

of equilibrium, and lying on the bottom of the test chamber. 
-Page 20 of 31-

Freshwater Invertebrates

One study with the water flea (Daphnia magna) using the TGAI was submitted to establish the 

toxicity of diphenylamine to freshwater invertebrates for the food use (MRID 43878301). The 

48-hr LC50 is 1.2 ppm classifying diphenylamine as moderately toxic to freshwater invertebrates 

on an acute exposure basis. No sublethal effects were reported. 

 

Estuarine/Marine Fish

Estuarine/marine fish acute toxicity data are not required for diphenylamine because of the 

indoor/food use. No additional data were identified through ECOTOX.

Estuarine/Marine Invertebrates

Estuarine/marine invertebrate acute toxicity are not required for diphenylamine because of the 

indoor/food use. No additional data were identified through ECOTOX.

Chronic Effects

A freshwater fish early life-stage and freshwater invertebrate life-cycle test using TGAI are not 

required for diphenylamine because of the indoor/food use. No additional data were identified 

through ECOTOX.

Aquatic Plants and Algae

No data are available to assess the acute toxicity of diphenylamine to aquatic plants and algae. 

According to 40 CFR §158-Subpart G, plant data are not required for contained pesticide 

treatments.

Table 3: Diphenylamine Acute Toxicity Values for Aquatic Orgamisms.

Study Type Species Test Material

Endpoints

(mg a.i./L)

(Study Duration)

Toxicity 

Classification (MRID)

(Study Classification)

Acute toxicity to 

freshwater 

vertebrates

Rainbow trout 

(Oncorhynchus

mykiss)

TGAI (100% a.i.) LC50=2.2 mg a.i./L

(96-hour test)

Moderately toxic

(43879001)

(Acceptable)

Acute toxicity to 

freshwater 

invertebrates

Water flea

(Daphnia magna) TGAI (100% a.i.) EC50 =1.2mg a.i./L

(48-hour test)

Moderately toxic

(43878301)

(Acceptable)

3.3.2. Terrestrial Organisms 

An overview of submitted terrestrial organism studies can be seen in Table 4.

Birds

Only acute oral and subacute dietary studies are required for birds due to the indoor/food use. 

One acute oral toxicity study with the Bobwhite quail (Colinus virginlanus) using TGAI was 

conducted to establish the toxicity of diphenylamine to birds (MRID 43878901) as well as to 

reptiles and terrestrial-phase amphibians for which birds serve as surrogates. The 14-day LD50 is 
-Page 21 of 31-

>2,250 mg a.i./kg-bw (ppm) classifying diphenylamine as practically non-toxic to birds on an 

acute exposure basis. Reduced weight gain, however, was reported for males in the 2,250 ppm

treatment group. 

A study with the mallard duck (Anas platyrhynchos) using TGAI was conducted to establish the 

subacute dietary toxicity of diphenylamine to birds (MRID 43897101), reptiles and terrestrialphase amphibians. The 5-day LC50 is >5,205 mg a.i./kg-diet classifying diphenylamine as 

practically non-toxic to birds on a subacute dietary exposure basis. No mortalities or signs of 

toxicity were observed in the control or treatment groups. 

Chronic Effects

Avian reproduction studies using TGAI are not required for diphenylamine because of the 

intended indoor/food use and its reported low acute toxicity to avian taxa. No additional data 

were identified through ECOTOX.

Terrestrial Invertebrates

Terrestrial invertebrate studies are not required due to the indoor/food use of diphenylamine. No 

additional data were identified through ECOTOX.

Mammals

Acute oral and chronic mammalian toxicity studies with Sprague-Dawley rats (Rattus 

norvegicus) exposd to TGAI (99.9% a.i.) were submitted. In the acute study, the LC50 was 

reported to be 2.72 g/kg/day classifying diphenylamine as practically non-toxic on an acute 

exposure basis (Accession Number 00148523). 

A two-generation Sprague-Dawley rat reproductive study was conducted (MRID 42638101). 

Compound-related systemic toxicity was observed in a dose-related manner among both sexes

and generations at all dose levels. In general, females were more affected thanmales and F1

animals were more affected than F0 animals. Kidney, spleen, and liver appeared to be the target 

organs as evidenced by weight differences relative to control animals at 399 mg/kg/day in males,

131 and 448 mg/kg/day in females, and gross and microscopic findings at all dose levels in both 

sexes. The systemic toxicity NOAEL was less than 40/46 mg/kg/day in males and females, 

respectively. The LOAEL was 40/46 mg/kg/day in males and females, respectively, based on 

gross pathological findings in the spleen (enlarged, discolored, congestion, and hemosiderosis), 

and on microscopic findings in the kidney (brown pigment in the proximal convoluted tubule), 

liver (hepatic hypertrophy and brown pigment in the Kupffer cells), and spleen (congestion and 

hemosiderosis).

Terrestrial and Aquatic Plants

According to 40 CFR §158-Subpart G, terrestrial and aquatic plant studies are not required due 

to the indoor/food use of diphenylamine. No additional data were identified through ECOTOX. 
-Page 22 of 31-

Table 4. Diphenylamine Acute Toxicity Values for Birds and Mammals.

Study Type Species Test Material Endpoints

Toxicity 

Classification 

(MRID)

(Study 

Classification)

Acute oral toxicity 

to birds

Bobwhite quail

(Colinus 

virginianus)

TGAI (100% a.i.) LD50 >2250 mg a.i./kg bw

14-day test

Practically non-toxic

(43878901)

(Acceptable)

Subacute dietary 

toxicity to birds

Mallard duck

(Anas 

platyrhynchos)

TGAI (100% a.i.) LC50 >5205 mg a.i./kg diet

5-day test

Practically non-toxic

(43879101)

(Acceptable)

Acute oral toxicity 

to mammals

Sprague 

Dawley rats

(Rattus 

norvegicus)

TGAI (99.9% a.i.) LD50=2.72 g/kg/day 

14-day test

Practically non-toxic

(00148523)

(Acceptable)

Chronic 

mammalian 

toxicity

Sprague 

Dawley rats

(Rattus 

norvegicus)

TGAI (99.8% a.i.)

Males

NOAEL <40 mg/kg/day

LOAEL ≤40 mg/kg/day

Females

NOAEL <46 mg/kg/day

LOAEL ≤46 mg/kg/day

52-week test

Endpoints: gross 

pathological findings 

in the spleen 

(enlarged and 

discolored, 

congestion, and 

hemosiderosis), 

kidney abnormalities 

(brown pigment in 

proximal convoluted 

tubule), and liver 

abnormalities 

(hypertrophy and 

brown pigment in 

Kupffer cells)

(42638101)

(Acceptable)

3.3.3. Review of Incident Data 

The ecological incident information system (EIIS) is a database maintained by the Office of 

Pesticide Programs; the database contains ecological incidents that have been reported to the 

Agency. When available, EIIS includes date and location of an incident, type and magnitude of 

effects observed in various species, use(s) of pesticides known or suspected of contributing to the 

incident, and results of any chemical residue analysis or other analyses conducted during incident 

investigation. EIIS incidents are categorized according to the certainty that the incident resulted 

from pesticide exposure. 

Based on the 40 CFR §159.184, information on all known “major” incidents must be submitted 

to the Agency by the registrant(s). All ecological incidents considered “minor” only need to be 

aggregately reported in Aggregate Incident Reports (AIR) as quarterly counts of incidents by the 

registrant(s). Both EIIS and AIR were searched in September 2015 and no incidents for 

diphenylamine have been reported. Because of uncertainties regarding the extent to which 

incidents are reported to EPA, the absence of incident reports cannot be construed as the absence 

of incidents. 
-Page 23 of 31-

4. Risk Characterization

Diphenylamine is moderately toxic to freshwater fish, aquatic-phase amphibians, and freshwater 

invertebrates. It is practically non-toxic to birds, reptiles and terrestrial-phase amphibians on an 

acute and subacute exposure basis. EFED generally does not conduct quantitative ecological 

risk assessments for indoor/food use chemicals for which there are no exposure pathways to nontarget organisms. Given the pattern of diphenylamine use, and the lack of significant exposure 

pathways associated with the post-harvest treatment, the likelihood of adverse effects on 

ecological systems is considered to be minimal. Although this is an indoor/food use chemical, 

disposal of drench wastes containing diphenylamine following the post-harvest use is regulated 

by NPDES permit.

4.1. Risk Description

Diphenylamine is an indoor/food use chemical and it is not expected to be persistent or mobile in 

the environment as it is subject to rapid abiotic and biotic routes of degradation. A detailed 

description though of the available environmental fate and ecological effect data for 

diphenylamine is provided in the Environmental Fate and Ecological Risk Assessment written in 

support of the RED for diphenylamine (USEPA 1997). 

4.2.1. Risks to Aquatic Organisms 

4.2.1.1. Freshwater Fish, Invertebrates, and Amphibians

The susceptibility of the chemical to aqueous photolysis and to biotic degradation in aerobic 

environments indicate that if it were to be released to soils or reach surface waters, the parent 

compound has a high likelihood of being readily dissipated. Although diphenylamine is 

moderately toxic to aquatic animals, the likelihood of exposure from the indoor/food use and as a 

result of the environmental fate properties of the compound is considered low. No data are 

available to assess the toxicity of diphenylamine to estuarine/marine organisms as such data are 

not required for indoor uses; however, given the environmental fate profile of the compound and 

the chemical’s indoor use, the likelihood of exposure and hence risk is considered low. 

4.2.2. Risks to Terrestrial Organisms 

4.2.2.1. Birds, Reptiles, and Terrestrial-phase Amphibians

Diphenylamine is practically non-toxic to birds, reptiles and terrestrial-phase amphibians on an 

acute oral and subacute dietary exposure basis. Since this is an indoor/food use chemical, EPA

does not conduct avian risk assessments for such uses. However, given the pattern of 

diphenylamine use and the environmental fate properties of diphenylamine, the likelihood of 

exposure that could lead to adverse effects on ecological systems is considered to be minimal.
-Page 24 of 31-

4.2.2.2. Mammals

Diphenylamine is practically non-toxic to mammals on an acute exposure basis and given the 

chemical’s environmental fate profile and use, the likelihood of adverse effects from exposure is 

consider low. 

4.2.2.3. Terrestrial Invertebrates

Although terrestrial invertebrate testing is not required for diphenylamine because of the 

chemical’s use pattern, the likelihood of exposure is considered low.

4.2.2.4. Terrestrial Plants

Diphenylamine represents a relatively low likelihood of exposure to non-target plants based on 

its current use. Non-target plant testing is not required for diphenylamine because of the 

indoor/food use pattern. Release of the chemical into the air will result in rapid photolytic and 

atmospheric oxidative degradation processes with little exposure to non-target terrestrial plants.

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 Registration Review for diephenylamine, 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), diphenylamine 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 
-Page 25 of 31-

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, 20131 and includes some 

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. Diphenylamine is not on 

either list. 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.2

6. Conclusions

The risk hypothesis articulated in the problem formulation stated that “the exposure pathway of 

diphenylamine used in accordance with the label has low potential to result in adverse effects on 

the survival, growth, and reproduction of non-target terrestrial and aquatic organisms.” This 

hypothesis is supported by the results of this preliminary risk assessment written in support of 

Registration Review, as well as the environmental fate and ecological risk assessment written

previously in support of the RED for diphenylamine in 1997. Based on the low likelihood of 

exposure from the indoor/food use pattern, low toxicitiy to non-target organisms, the NPDES 

permit for the drench water disposal, and the environemental fate properties, the Agency 

concludes that the registration of the dipheylamine on post harvest apples will have 'no effect' 

(NE) on endangered or threatened terrestrial or aquatic species, or their designated critical 

habitats, as listed by the FWS and the NOAA’s NMFS. EPA anticipates conducting no further 

analysis of potential risks to endangered or threatened species from diphenylamine for this use 

unless the Agency obtains data or information that would otherwise inform the Agency’s 

determination.

7. References

Food and Agriculture Organization of the United Nations. 2000. FAO PESTICIDE DISPOSAL 

SERIES 8. Assessing Soil Contamination: A Reference Manual. Appendix 2. 

Parameters of pesticides that influence processes in the soil. Editorial Group, FAO 

Information Division: Rome. http://www.fao.org/DOCREP/003/X2570E/X2570E00.htm

Fletcher, J.S., J.E. Nellessen, and T.G. Pfleeger. 1994. Literature review and evaluation of the 

EPA food-chain (Kenaga) nomogram, and instrument for estimating pesticide residues on 

plants. Environmental Toxicology and Chemistry 13 (9):1383-1391.

Hoerger, F., and E.E. Kenaga. 1972. Pesticide residues on plants: Correlation of representative 

data as a basis for estimation of their magnitude in the environment. In F. Coulston and F. 

Korte, eds., Environmental Quality and Safety: Chemistry, Toxicology, and Technology, 

Georg Thieme Publ, Stuttgart, West Germany, pp. 9-28.

 1 See http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPPT-2009-0477-0074 for the final second list of 

chemicals.

2 http://www.epa.gov/endo/
-Page 26 of 31-

Ingle, M. and M. C. D'Souza. 1989. Physiology and control of superficial scald of apples: a 

review. Hort Science 24:28-31.

USEPA. 2015. BEAD Chemical Profile (BCP) for Registration Review: Diphenylamine

(038501). United States Environmental Protection Agency (USEPA). Biological and 

Economic Analysis Division. Office of Pesticide Programs. June 11, 2015.

USEPA. 2014. Estimation Program Interface (EPI) 

SuiteTM. http://www.epa.gov/opptintr/exposure/pubs/episuite.htm

USEPA. 2009a. Water models. Available online at http://www.epa.gov/oppefed1/models/water/.

USEPA. 2009b. ECOTOXicology Database, v. 4.0. Accessed on 12 April 2012. Available online 

at http://cfpub.epa.gov/ecotox/.

USEPA. 2009c. Guidance for Selecting Input Parameters in Modeling the Environmental Fate 

and Transport of Pesticides, Version 2.1. U.S. Environmental Protection Agency, Office 

of Prevention, Pesticides and Toxic Substances, Office of Pesticide Programs, 

Environmental Fate and Effects Division, October 22, 2009. Online 

at:http://www.epa.gov/pesticide-science-and-assessing-pesticide-risks/guidanceselecting-input-parameters-modeling

USEPA. 2006c, TerrPlant v. 1.2.2 User’s Guide. Office of Pesticide Programs, Environmental 

Fate and Effects Division, Washington, D.C. December 26, 2006.

USEPA. 2004. Overview of the Ecological Risk Assessment Process in the Office of Pesticide 

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

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

Pesticide Programs, Washington, D.C. Available online at 

http://www.epa.gov/oppfead1/endanger/consultation/ecorisk-overview.pdf.

USEPA. 1997. Environmental Fate Science Chapter for the Registration Elegibility Document 

for Diphenylamine. (DP Barcodes D231687, D208697, D208687, Dl98487) U.S. 

Environmental Protection Agency, (formerly the) Office of Prevention, Pesticides and 

Toxic Substances, Office of Pesticide Programs, Environmental Fate and Effects 

Division, July 1997.

USEPA. 1998. Guidelines for Ecological Risk Assessment. EPA/630/R-95/002F. Published in 63 

FR 26846; May 14, 1998. U.S. Environmental Protection Agency, Washington, DC. 

April, 1998.

USEPA. 1993b. Wildlife Exposure Factors Handbook. EPA/600/R-13/187a. Office of Research 

and Development, Washington, D.C.
-Page 27 of 31-

USEPA. 1992. Pesticides in Ground Water Database: A Compilation of Monitoring Studies: 

1971-1991: National Summary. U.S. Environmental Protection Agency, Washington, 

DC.

Willis, G.H. and L.L. McDowell. 1987. Pesticide persistence on foliage. Reviews of 

Environmental Contamination and Toxicology 100: 23-73.

8. Appendix A. Submitted Studies for Diphenylamine 

Environmental Fate Studies

MRID ? Citation

42660001 2059358 

2059359 

2059361 

summary

Baur, L. (1993) Hydrolysis of (carbon 14)-Ring-Diphenylamine in Water at pH 5, 

7, and 9: Lab Project Number: XBL 92084: RPT00119. Unpublished study 

prepared by XenoBiotic Labs, Inc. 82 p.

161-2 Photodegradation-water

42958201 2059360 

summary

Baur, L.; Robinson, R. (1993) Aqueous Photolysis of (carbon 14)-RingDiphenylamine: Lab Project Number: XBL 92087: RPT00123. Unpublished study 

prepared by XenoBiotic Laboratories, Inc. 106 p. 

162-1 Aerobic soil metabolism

42964201 2059360 

summary 

2059361

Liu, D. (1993) Aerobic Soil Metabolism of (carbon 14)-Ring-Diphenylamine: Lab 

Project Number: XBL 92082: RPT00139. Unpublished study prepared by 

XenoBiotic Labs, Inc. 98 p. 

162-3 Anaerobic aquatic metabolism

43080901 2059360 

summary 

2059361

Liu, D. (1993) Anaerobic Aquatic Metabolism of (carbon 14)-RingDiphenylamine: Lab Project Number: 92083: RPT00140. Unpublished study 

prepared by XenoBiotic Labs, Inc. 102 p. 

163-1 Leach/adsorption/desorption

43412701 2059360 

summary 

2059361

Reynolds, J. (1994) Adsorption and Desorption of (carbon 14)-RingDiphenylamine in Four Soils and One Sediment: Lab Project Number: 92086: 

RPT00163. Unpublished study prepared by XenoBiotic Lab., Inc. 123 p. 

43413001 2059360 

summary 

2059361

Kammerer, R. (1994) Aged Leaching of ((carbon 14)-Ring) Diphenylamine in 

Four Soils: Lab Project Number: XBL94011: RPT00184. Unpublished study 

prepared by XenoBiotic Lab., Inc. 139 p. 

Non-Guideline Studies

44775201 Morrissey, M. (1999) Diphenylamine (Purified Active Ingredient): Determination 
-Page 28 of 31-

of UV-Visible Absorption Spectrum: Final Report: Lab Project Number: 

COVANCE 6524-115. Unpublished study prepared by Covance Laboratories Inc. 

23 p. {OPPTS 830.7050}

Ecological Effects Studies 

71-1 Avian Single Dose Oral Toxicity

MRID Citation Reference

43878901 2059364 Palmer, S.; Beavers, J. (1995) Diphenylamine: An Acute Oral Toxicity Study with 

the Northern Bobwhite: Lab Project Number: 436-102: DLR54: 

436/100295/QLD.NC/CHP1053 . Unpublished study prepared by Wildlife 

International Ltd. 41 p. 

71-2 Avian Dietary Toxicity

MRID Citation Reference

43879101 2059366 Palmer, S.; Beavers, J. (1995) Diphenylamine: A Dietary LC50 Study with the 

Mallard: Lab Project Number: DLR52: 436-101: 

436/100295/MLCSDT.WC/CHP105. Unpublished study prepared by Wildlife 

International Ltd. 74 p. 

72-1 Acute Toxicity to Freshwater Fish

MRID Citation Reference

107141 Pitcher, F. (1972) No Scald DPA: Rainbow Trout (Salmo gairdneri)|: Test No. 499. 

(U.S. Agricultural Research Service, Pesticides Regulation Div., Animal Biology 

Laboratory; unpublished study; CDL:130356-A) 

43055201 Arce, G. (1993) Letter Sent to Office of Pesticide Programs dated December 10, 

1993 concerning results of a range-finding fish toxicity study. Prepared by Elf 

Atochem N. America, Inc. 11 p. 

43879001 2059365 Drottar, K.; Swigert, J. (1995) Diphenylamine Technical: A 96-Hour Flow-Through 

Acute Toxicity Test with the Rainbow Trout (Oncorhynchus mykiss): Final Report: 

Lab Project Number: SDR20: 436A-101: 436/100295/RBT-96H2/CHP105. 

Unpublished study prepared by Wildlife International Ltd. 99 p. 

72-2 Acute Toxicity to Freshwater Invertebrates

MRID Citation Reference

43878301 2059363 Drottar, K.; Swigert, J. (1995) Diphenylamine Technical: A 48-Hour Flow-
-Page 29 of 31-

Through Acute Toxicity Test with the Cladoceran (Daphnia magna): Final 

Report: Lab Project Number: SDR20: 436A-102: MP-DPAP-MA. Unpublished 

study prepared by Wildlife International Ltd. 97 p. 

9. Appendix B. Text from Memo (with CBI Redacted) from the DPA Task Force in 

Response to Use Questions from EPA

DPA TASK FORCE RESPONSE TO EPA QUESTIONS REGARDING 

DIPHENYLAMINE 

Are all applications indoors?

No, truck and bin drenching is done outside. Thermal fogging is performed inside a sealed, 

enclosed room but the applicators and thermofoggers are in an open area outside of the room.

• Describe how typical apple treatments for the allowed application methods such as 

thermal fogging, tank dipping, drenching, conveyor flooding, and spraying of apples 

are performed. Are all of these methods still used, allowed on labels, and supported for 

registration review? Explain the truck drenching use.

The vast majority of DPA application is to apple bins. Each bin contains approximately 900 

pounds of apples. Very little application to apples outside of bin would be performed. 

Thermal fogging is done in an enclosed storage room. The bins are placed in the chamber 

and the chamber is closed. DPA solution is mixed outside then “fogged” into the storage 

room using the appropriate equipment. 

Drenching or conveyor flooding (either chain or track drenching) is done by direct spray of 

the DPA solution on the apple bins in a stationary position or as the apples move past the 

spray nozzles on a chain or track driven conveyor belt. 

Truck drenching can be compared to a car wash. The truck pulls forward so that the front of 

bed is under the spray nozzle and the truck pulls forward until all bins in the truck bed are 

treated. The truck remains stationary in a draining area allowing the spray material to drain 

before putting bins in storage. Truck drenching may be done on as few as 20 bins and up to 

96 bins.

Tank dipping is no longer used and will not be supported. 

• Where does the used liquid go after use? How is used material disposed of? Does any 

waste material containing diphenylamine go down the drain of a storage facility or food 

processing facility? Are the drainage wastes covered by a NPDES permit or prohibited 

by label language? Is waste material applied outdoors such as to holding ponds, land 

application, or discharged directly to surface water.
-Page 30 of 31-

Liquids are collected after application and generally recycled for further applications. None 

of the waste material containing DPA goes down the drain of a storage facility or food 

processing facility. All discharges are in accordance with NPDES permits and the regulatory 

authority in each particular State or region. Based on NPDES requirements, waste materials 

can be disposed of in lined lagoons, as dust abatement liquids or land applied. For the lined 

lagoon disposal, the waste solution is added to imperviously lined, in-ground, engineered 

structures, which rely largely upon evaporation for water removal. Dust abatement is the 

application of wastewater to unpaved bin storage lots and unpaved roads (i.e., orchard roads) 

for the purpose of dust suppression. Land application is an engineered system for applying 

wastewater to a vegetated land surface. DPA waste solutions are not discharged directly to 

surface waters.

• How much is applied in a typical facility in one day (min, max, average)? How many 

apples are typically treated per day (min, max, average)?

The application rate is application of 100 gallons of product to 30 bins of apples. The 

application rate ranges from 1000 – 2200 ppm with an average 1500 ppm. The number of 

apple bins typically treated in one day depends on the region of the country and apple 

production. Application can range from 1000- 5000 apple bins/day with an average of 2500 

apple bins/day could be treated depending on the size of the packing house. Washington 

State is the largest producer and generally has large packing facilities which would be at the 

upper end of the range. In other regions of the country with less apple production, the daily 

number of bins treated would be at the lower end of the range. 

• What is the typical size of the room treated for the thermal fogging treatment (min, 

max, average)?

The typical thermal fogging room can hold from a minimum of 500 apple bins to a maximum 

of 6,000 apple bins with an average room holding 1,800 apple bins. 

• What is the total usage (lbs) per year for the last 5-10 years?

The total annual usage based on sales for DECCO and Pace is found in Tables 1 and 2. As 

this is confidential business information, it should be maintained as confidential. 

• Are drench wastes still disposed of in the field? Please describe.

As noted above, both dust abatement disposal and land applications are approved by NPDES 

permits.

• What are the main methods of application used now? Is it almost all fogging, or are the 

other methods (involving water) still used?

The primary application is drench which is >50% of applications followed by thermal 

fogging at approximately 25% of applications. Over the few years, more facilities have been 

converting to thermal fogging and it is expected to continue. The change to thermal fogging 
-Page 31 of 31-

over the last few years can be seen in the DECCO and Pace sales information found in 

Confidential Tables 1 and 2. 

• Are any drench or spray applications to apples conducted in outside environments (eg 

trucks, bins, etc)?

As discussed above, truck and bin drench and spray applications are conducted outdoors in 

areas designated for the application and permitting the collection of any runoff from the 

sprayed bins. Thermal fogging is done indoors. 

• When using foggers with room venting before reentry, explain the configuration of 

exhaust air piping and potential deposition near the site.

In general, room fogging is achieved by entry of the fog through a portal in the lower part of 

the chamber approximately 3 feet above the floor. Room cooling systems and humidifiers 

are turned off 12 hours prior to fumigation and during fumigation. All room air circulation 

fans are turned off prior to fumigation to allow DPA permeation throughout the room and 

turned on one hour after treatment. Venting is done through ceiling vents. Room cooling 

systems and humidifiers may be turned on several hours after completion of fumigation as all 

fogger should have been removed by that time. Venting is to the outside. 

• Is it your understanding that after the required room venting times on the label, no 

PPE is needed or used in practice? 

That is correct. 

• Are you aware your label mentions not to use paper wraps impregnated with DPA, but 

there are no registrations for wraps, or are wraps still used? 

Paper wraps impregnated with DPA are not produced or used. This appears to be a carryover 

from much older labels and should be removed. 

 

• Some labels allow a second treatment with prolonged storage (eg> 4 months), but some 

labels are silent on retreatment. What is the actual practice?

Retreatment is found on one registrants’ label (Pace). Use of a second treatment is permitted 

but is very seldom done, if at all.