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Problem Formulation for the Environmental Fate,

Ecological Risk, Endangered Species, and Drinking 

Water Exposure Assessments in Support of the 

Registration Review of Dichlobenil

Cl Cl

N

CAS Registry Number: 1194-65-6

PC Code: 027401

Prepared by:

Elyssa Gelmann, Biologist

Greg Orrick, Environmental Scientist

U. S. Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch II

1200 Pennsylvania Ave., NW

Mail Code 7507P

Washington, DC 20460

Reviewed by:

Kristina Garber, Senior Biologist

R. David Jones, Ph.D., Senior Agronomist

Brian Anderson, Branch Chief
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Table of Contents

1. Purpose....................................................................................................................................... 5

2. Nature of Regulatory Action...................................................................................................... 5

3. Conclusions from Previous Risk Assessments.......................................................................... 5

3.1. Ecological Risk Assessments.............................................................................................. 5

3.2. Drinking Water Exposure Assessments.............................................................................. 7

3.3. Clean Water Act Programs ................................................................................................. 8

3.3.1. Aquatic Life Criteria and Aquatic Life Benchmarks................................................... 8

3.3.2. Impaired Water Bodies................................................................................................ 8

4. Stressor Source and Distribution ............................................................................................... 9

4.1. Mechanism of Action........................................................................................................ 10

4.2. Overview of Pesticide Usage ............................................................................................ 10

4.3. Environmental Fate and Transport.................................................................................... 11

4.3.1. Mobility...................................................................................................................... 13

4.3.2. Degradation................................................................................................................ 13

4.3.3. Field Dissipation ........................................................................................................ 13

4.3.4. Transformation Products............................................................................................ 14

5. Receptors.................................................................................................................................. 17

5.1. Effects to Aquatic Organisms........................................................................................... 17

5.1.1. Freshwater Fish........................................................................................................... 19

5.1.2. Freshwater Invertebrates............................................................................................. 19

5.1.3. Estuarine/Marine Fish................................................................................................. 20

5.1.4. Estuarine/Marine Invertebrates................................................................................... 20

5.1.3. Aquatic Plants............................................................................................................. 20

5.2. Effects to Terrestrial Organisms....................................................................................... 21

5.2.1. Birds............................................................................................................................ 22

5.2.2. Mammals..................................................................................................................... 22

5.2.3. Terrestrial Invertebrates.............................................................................................. 23

5.2.4. Terrestrial Plants......................................................................................................... 23

5.3. Ecological Incidents.......................................................................................................... 24

6. Ecosystems Potentially at Risk ................................................................................................ 25

7. Assessment Endpoints ............................................................................................................. 25

8. Conceptual Model..................................................................................................................... 25

8.1. Risk Hypothesis................................................................................................................ 26

8.2. Conceptual Diagram ......................................................................................................... 26

9. Analysis Plan ........................................................................................................................... 29

9.1. Stressors of Concern ......................................................................................................... 30

9.2. Measures of Exposure....................................................................................................... 30

9.2.1. Aquatic Exposure........................................................................................................ 31

9.2.2. Terrestrial Exposure.................................................................................................... 32

9.3. Measures of Effect ............................................................................................................ 34

9.4. Integration of Exposure and Effects ................................................................................. 35

9.4.1. Deterministic and Probabilistic Assessment Methods................................................ 35

9.5. Endangered Species Assessments..................................................................................... 36

9.6. Drinking Water Assessment ............................................................................................. 36

10. Endocrine Disruptor Screening Program............................................................................... 37
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11. Preliminary Identification of Data Gaps................................................................................ 38

11.1. Environmental Fate.......................................................................................................... 38

11.2. Effects............................................................................................................................. 40

12. References.............................................................................................................................. 45

Appendix A. Sample Data Call-In Table...................................................................................... 51

List of Tables

Table 1. Labeled Dichlobenil Use Patterns of Maximum Exposure A........................................... 9

Table 2. Chemical Properties and Environmental Fate Parameters of Dichlobenil .................... 12

Table 3. Dichlobenil and Its Environmental Degradates............................................................. 15

Table 4. Summary of the Most Sensitive Endpoints from Aquatic Toxicity Studies for 

Dichlobenil.................................................................................................................................... 17

Table 5. Summary of the Most Sensitive Endpoints from Aquatic Toxicity Studies for BAM.. 18

Table 6. Summary of the Most Sensitive Endpoints from Terrestrial Toxicity Studies for 

Dichlobenil.................................................................................................................................... 21

Table 7. Summary of the Most Sensitive Endpoints from Terrestrial Toxicity Studies for BAM

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

Table 8. SIP Avian Results for Dichlobenil.................................................................................. 33

Table 9. SIP Mammalian Results for Dichlobenil........................................................................ 33

Table 10. STIR Avian (0.020 kg) Results for Dichlobenil........................................................... 33

Table 11. STIR Mammalian (0.15 kg) Results for Dichlobenil ................................................... 34

Table 12. Submitted Environmental Fate Data for Dichlobenil ................................................... 38

Table 13. Submitted Environmental Fate Data for the Dichlobenil Degradate, BAM................. 39

Table 14. Submitted Aquatic Ecological Effects Data for Dichlobenil....................................... 40

Table 15. Submitted Terrestrial Ecological Effects Data for Dichlobenil................................... 42

Table 16. Aquatic Ecological Effects Data for the Dichlobenil Degradate, BAM....................... 44

Table 17. Aquatic Ecological Effects Data for the Dichlobenil Degradate, BZZ ........................ 44

List of Figures

Figure 1. Estimated National Usage of Dichlobenil from 1999 to 2004 (USGS, 2012) .............. 11

Figure 2. Conceptual diagram depicting stressors, exposure pathways, and potential effects to 

aquatic organisms from the supported uses of dichlobenil. Dotted lines indicate exposure 

pathways that have a low likelihood of contributing to ecological risk. ...................................... 27

Figure 3. Conceptual diagram depicting stressors, exposure pathways, and potential effects to 

terrestrial organisms (terrestrial plants, terrestrial invertebrates, and dietary routes of exposure 

for terrestrial vertebrates) from the supported uses of dichlobenil............................................... 28

Figure 4. Conceptual diagram depicting stressors, drinking water and inhalation exposure 

pathways, and potential effects to terrestrial animals from the supported uses of dichlobenil. ... 29
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1. Purpose

The purpose of this problem formulation is to provide an understanding of the environmental fate 

and ecological effects of the registered uses of dichlobenil. Dichlobenil is a pre-emergence and 

sewer root-control benzonitrile herbicide first registered in 1964 and used on apples, bushberries, 

caneberries, cherries, cranberries, grapes, pears, rhubarb, tree nuts, plant nurseries, shelterbelts, 

and a large number of non-agricultural sites including ornamental areas, non-crop areas, 

residential areas including paths, patios, paved areas, and under paved areas, recreational areas, 

under pool/pond vinyl liners, drains, drain lines, irrigation supply systems, waste water systems, 

sewage systems, sewer lines, and storm sewers.

This document will provide a plan for analyzing data relevant to dichlobenil and for conducting 

environmental fate and ecological risk, and endangered species assessments for its registered

uses. Additionally, this problem formulation is intended to identify data gaps, uncertainties, and 

potential assumptions used to address those uncertainties, relative to characterizing the

ecological risk associated with the registered uses of dichlobenil. 

2. Nature of Regulatory Action

The Food Quality Protection Act of 1996 mandated the United States Environmental Protection 

Agency (EPA) to implement a new program for assessing the risks of pesticides, i.e., registration 

review (http://www.epa.gov/oppsrrd1/registration_review/). All pesticides distributed or sold in 

the United States generally must be registered by EPA. The decision to register a pesticide is 

based on the consideration of scientific data and other factors showing that it will not cause 

unreasonable risks to human health, workers, or the environment when used as directed on 

product labeling. 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, the Agency periodically reevaluates pesticides to 

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

As part of the implementation of the new Registration Review program pursuant to Section 3(g) 

of the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA), the Agency is beginning its 

evaluation to determine whether dichlobenil continues to meet the FIFRA standard for 

registration. This problem formulation for the environmental fate and ecological risk assessment 

chapter in support of the registration review is intended for the initial docket opening the public 

phase of the review process. 

3. Conclusions from Previous Risk Assessments

3.1. Ecological Risk Assessments

The Agency has conducted multiple ecological risk assessments on dichlobenil that serve as a 

basis for this problem formulation, including the Reregistration Eligibility Decision (RED), the 
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Pacific salmon and steelhead endangered species assessment, and three new use assessments. 

These assessments are briefly summarized below.

The RED document for dichlobenil (USEPA, 1998b) was issued in October 1998. The major 

ecological conclusions presented in the RED were as follows:

• Dichlobenil dissipates in the environment (on soil and in surface water) principally by 

volatilization. However, it is persistent under field conditions that reduce the potential 

for volatilization (i.e., cooler climates). When transformation proceeds through aerobic 

soil metabolism, the metabolite, 2,6-dichlorobenzamide (BAM) is generated (13.1% at 50 

weeks). Under conditions where dichlobenil does not volatilize there is potential for both 

dichlobenil and BAM to move to ground water in coarse-textured soils low in organic 

matter. Dichlobenil and its degradates exceed levels of concern for ground water quality.

• Except for the acute effects to freshwater mollusks and non-target plants, the 

concentrations of dichlobenil granules in the environment are not expected to cause either 

high acute or chronic levels of risk to non-target organisms. Restricted use triggers have 

been exceeded for birds and freshwater mollusks. Endangered species of birds, mollusks, 

aquatic invertebrates, fish and plants may be affected from the use of dichlobenil. For 

fish and aquatic invertebrates, risk is only anticipated at the highest application rate of 20 

lb a.i./A. The Agency mandated decreasing the maximum application rate to 10 lb a.i./A.

• Chronic risk to birds was not assessed due to lack of avian reproduction data. These 

studies were requested in a Data call-in. 

• The degradate, BAM, poses minimal acute or chronic risk to aquatic and terrestrial 

organisms. 

• Risks to non-target organisms from the wettable powder used for under-the-pavement 

and sewage line applications are considered to result in minimal exposure to the 

environment and therefore minimal risk to non-target organisms. 

• The EECs used for non-soil-incorporated uses are summarized in the table below. They 

can be found on page 64 (aquatic) and page 70 (terrestrial) of the RED.

Application rate 

(lb a.i./A), non-soil 

incorporated

Aquatic 1-in-10-year (μg/L) Terrestrial 

peak 21-day mean 56-day mean (mg/sq ft)

2 95 18 7 21

4 190 36 14 42

6 285 54 29 63

8 380 72 27 83

10 -- -- -- 104

20 951 180 67 208

The Pacific salmon and steelhead endangered species risk assessment was issued on July 31, 

2003 (USEPA, 2003). The assessment showed that dichlobenil was moderately toxic to 
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freshwater fish and estuarine invertebrates, slightly to moderately toxic to freshwater 

invertebrates and slightly toxic to estuarine fish. It was also toxic to aquatic vegetation. Acute 

and chronic risk quotients indicated no direct risk to endangered fish or aquatic invertebrate 

populations and low exposure potential to aquatic plants. The assessment concluded that 

dichlobenil did not present a direct effect on Pacific salmon and steelhead, indirect effects based 

on loss of their aquatic invertebrate food supply, or indirect effects based on loss of aquatic plant 

cover. The EECs from the RED were used for this assessment.

In 1997, a new use assessment was conducted for homeowner use of dichlobenil in septic 

systems (USEPA, 1997). Because of the small scale of the proposed use and the small amount 

of active ingredient (a.i.) applied (up to 10 grams a.i. per use), there was no concern of risk to 

non-target organisms. The assessment added that the larger, currently labeled use in municipal 

sewer systems could pose a risk to aquatic plants if treated sewer systems discharge directly into

natural water bodies or bypass sewage treatment equipment during periods of peak flow. 

A new use assessment for a granular formulation of dichlobenil on rhubarb at 2 lb a.i./A was 

conducted in 2005 (USEPA, 2005a). There was no concern of risk to aquatic animals from 

dichlobenil or BAM; however the assessment noted uncertainty in the chronic risk for freshwater

fish since there was no NOAEC established in the freshwater fish early-life stage study. There 

was no concern of risk to terrestrial animals from dichlobenil or BAM, however there was 

uncertainty in the assessment of chronic risk for birds since there was no NOAEC established in 

the avian reproduction study. A fugacity model indicated that estimated residue levels in soil 

invertebrates would not result in concern for mammals or birds. There was concern of risk to 

listed aquatic plants and to both listed and non-listed non-target terrestrial plants due to spray 

drift and runoff. The assessment noted that there was insufficient data on BAM to establish its 

potential environmental impacts, insufficient information to establish the aerobic aquatic 

metabolic degradation rate, and uncertainty in off-site transport due to the high volatility of 

dichlobenil. The aquatic 1-in-10-year peak, 21-day mean, and 60-day mean EECs were 26, 10, 

and 5.2 μg/L, respectively. The terrestrial EEC was 21 mg/sq ft.

A new use assessment in 2008 for rhubarb, bushberries, cranberry, and caneberry referred to and 

summarized the previously described assessments (USEPA, 2008). The 2005 new use 

assessment was referenced for the rhubarb use and the RED was referenced for the berry uses.

3.2. Drinking Water Exposure Assessments

A drinking water exposure assessment for the proposed new use on rhubarb was conducted for 

dichlobenil in 2005 (USEPA, 2005b). Exposure estimates of dichlobenil from currently labeled 

uses that produce maximum exposure (fruit and nut orchards and non-crop areas) were 298 μg/L 

(1-in-10-year peak), 4.6 μg/L (1-in-10-year annual mean), and 2.0 μg/L (30-year mean) for 

surface water and 9.3 μg/L for ground water.

In 2007, a drinking water exposure assessment was conducted for the dichlobenil degradate of 

concern, BAM (USEPA, 2007a). The assessment mentioned that BAM is also a degradate of the 

fungicide fluopicolide (PC code 027412). However, exposure estimates were only provided for 

BAM resulting from use of dichlobenil. Aggregate exposure from dichlobenil, fluopicolide, and 
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BAM produced from either parent compound was not estimated because each compound has 

different toxicity endpoints. BAM produced from dichlobenil was assessed separately from 

BAM produced from fluopicolide because exposure estimates of BAM produced from 

dichlobenil were an order of magnitude higher and resulted from use on non-crop areas, for

which fluopicolide is not labeled. Therefore, exposure estimates of BAM produced from the 

currently labeled use of dichlobenil that produces maximum exposure (non-crop areas) were 

used in the human health dietary risk assessment for BAM. These exposure estimates were 36 

μg/L (1-in-10-year peak), 15 μg/L (1-in-10-year annual mean), and 6.9 μg/L (30-year mean) for 

surface water and 89 μg/L for ground water (which was lowered to 56 μg/L in the dietary risk

assessment due to a reduction in the labeled maximum application rate).

3.3. Clean Water Act Programs

3.3.1. Aquatic Life Criteria and Aquatic Life Benchmarks

The Clean Water Act requires the Agency to publish water quality criteria that accurately reflect 

the latest scientific knowledge on the kind and extent of all identifiable effects on health and 

welfare that might be expected from the presence of pollutants in any body of water, including 

ground water. While these recommended criteria do not, in themselves, impose any 

requirements, states and authorized tribes can use them to develop water quality standards. An 

Aquatic Life Ambient Water Quality Criteria document has not been published for dichlobenil

(see url: http://www.epa.gov/waterscience/criteria/).

The Office of Pesticide Programs (OPP) publishes aquatic life benchmarks for freshwater species 

based on toxicity values for the most sensitive species from the most recent risk assessments. 

For dichlobenil, aquatic life benchmarks have been published and are listed in the table below 

(see url: http://www.epa.gov/oppefed1/ecorisk_ders/aquatic_life_benchmark.htm#benchmarks).

OPP Aquatic Life Benchmarks (μg/L freshwater)

Fish Invertebrates Nonvascular Plants Vascular Plants

Acute Chronic Acute Chronic Acute Acute

2,465 <330 1,850 560 1,000 30

3.3.2. Impaired Water Bodies

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

under section 303(d) of the Clean Water Act, based on information provided at 

http://iaspub.epa.gov/tmdl_waters10/attains_nation_cy.cause_detail_303d?p_cause_group_id=88

5.

No Total Maximum Daily Load (TMDL) criteria have been developed for dichlobenil, based on 

information provided at 

http://iaspub.epa.gov/tmdl_waters10/attains_nation.tmdl_pollutant_detail?p_pollutant_group_id

=885&p_pollutant_group_name=PESTICIDES. More information on impaired water bodies and 

TMDLs can be found at http://www.epa.gov/owow/tmdl/. The Agency invites submission of 

water quality data for this pesticide. To the extent possible, data should conform to the quality 
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standards in Appendix A of the OPP Standard Operating Procedure: Inclusion of Impaired 

Water Body and Other Water Quality Data in OPP’s Registration Review Risk Assessment and 

Management Process (see: 

http://www.epa.gov/oppsrrd1/registration_review/water_quality_sop.htm), in order to ensure 

they can be used quantitatively or qualitatively in pesticide risk assessments.

4. Stressor Source and Distribution

Dichlobenil is a nitrile, pre-emergent, nonselective herbicide used to control grasses, broadleaf

weeds, and root growth. It is registered for use on apples, bushberries, caneberries, cherries, 

cranberries, grapes, pears, rhubarb, tree nuts, plant nurseries, shelterbelts, and a large number of 

non-agricultural sites including ornamental areas, non-crop areas, residential areas including 

paths, patios, paved areas, and under paved areas, recreational areas, under pool/pond vinyl 

liners, drains, drain lines, irrigation supply systems, waste water systems, sewage systems, sewer 

lines, and storm sewers. It is formulated in 17 active or pending end-use products as a granule 

(80% of uses), liquid microencapsule, wettable powder, soluble concentrate, and emulsifiable 

concentrate. Treatment equipment include aircraft, backpack sprayers, foam applicators, foam 

making generators, granule applicators, ground equipment, handguns, package applicators, 

product containers, shaker cans, and spreaders. Table 1 lists the use patterns of maximum 

exposure for the current uses of dichlobenil.

Table 1. Labeled Dichlobenil Use Patterns of Maximum Exposure A

Use

Max. Single 

App. Rate

(lbs a.i./A)

Max. No. of 

App. per 

Year

Min. Reapp. 

Interval (d)

Max. Annual

App. Rate

(lbs a.i./A)

App. Method

Drains, drain lines, irrigation 

supply systems, waste water 

systems, sewage systems, 

sewer lines, and storm sewers

25.6 NS NS NS Foam application

Under asphalt, under vinyl 

pool/pond liners 12 NS NS NS B Soil treatment

Non-agricultural areas and 

under containerized nursery 

stock

10 NS NS NS Incorporate to a 

depth of 4-6 inches

Non-agricultural areas, 

ornamentals 8.0 NS NS NS Soil treatment

Apples, bushberries, cherries, 

grapes, pears, tree nuts 6.1 NS NS NS Soil treatment

Caneberries 4.0 NS NS NS Soil treatment

Cranberries 4.0 NS NS or 21 4.0 Soil treatment

Rhubarb 2.0 NS NS NS Soil treatment A

 NS means “not stated”. B

 Uses under asphalt and under vinyl pool and pond liners can be assumed to occur only once per site for a period 

of multiple years.
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4.1. Mechanism of Action

Dichlobenil is a cellulose biosynthesis inhibitor that leads to lack of cell structure integrity in 

plants and is herbicidally active on the roots and coleoptiles of susceptible weeds. Specifically, 

dichlobenil inhibits the enzyme cellulose synthase, which is involved in the synthesis of 

components of plant cell walls, preventing germination and meristem growth. The effects 

include stunted roots and shoots. Dichlobenil acts as a pre-emergence herbicide, applied after 

planting but before weeds germinate for agricultural uses.

4.2. Overview of Pesticide Usage

National pesticide usage data from the United States Geological Survey indicate that an average 

of 29,000 pounds of dichlobenil was applied per year to agricultural crops in the United States 

from 1999 to 2004 (see Figure 1; USGS, 2012). A Screening Level Usage Analysis conducted 

by the Agency indicates that usage of dichlobenil has generally decreased, with an average of 

less than 12,000 pounds applied annually to agricultural crops from 2000 to 2010 (year-specific 

usage was not provided; USEPA, 2011). The treated fraction of crops was reported to be 5% or 

less on average, with a maximum of 10% (USEPA, 2011).

The California Department of Pesticide Regulation reports a general decline of dichlobenil usage 

in the state from 80,000 pounds of dichlobenil applied in 2007 to 27,000 pounds applied in 2009 

(CDPR, 2011). Agricultural usage in the state is minimal. Landscape maintenance usage 

dropped by an order of magnitude (69,000 to 6,000 lbs applied) from 2007 to 2009, while 

sewage system usage increased from 0 to 12,000 lbs applied during the same time period 

(CDPR, 2011).
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Figure 1. Estimated National Usage of Dichlobenil from 1999 to 2004 (USGS, 2012)

4.3. Environmental Fate and Transport

Dichlobenil [2,6-dichlorobenzonitrile; CAS No. 1194-65-6; PC code 027401] dissipates in the 

environment (on soil and in surface water) principally by volatilization. However, it is persistent 

under field conditions that reduce the potential for volatilization (e.g., cooler climates). 

Dichlobenil photolyzes in shallow, clear surface waters (half-life of 10 days), but does not 

photolyze on soil. Under conditions where dichlobenil does not volatilize or photolyze, the 

compound persists. Dichlobenil slowly degrades in aerobic soil (half-life of 324 days) to 2,6-

dichlorobenzamide (i.e., BAM; 13% of the applied at 350 days). Biodegradation is negligible in 

aerobic and anaerobic aquatic systems. Dichlobenil does not bioconcentrate in fish and is not 

expected to bioaccumulate in aquatic ecosystems. There is potential for both dichlobenil and 

BAM to leach to ground water in vulnerable aquifers, such as those with coarse-textured soils 

low in organic matter. A selection of environmental fate and transport properties of dichlobenil 

is summarized in Table 2.
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Table 2. Chemical Properties and Environmental Fate Parameters of Dichlobenil

Parameter Value Source

Selected Physical/Chemical Parameters

Molecular mass (molecular formula) 172.01 g/mol (C7H3Cl2N) (Calculated)

Vapor pressure (20°C) 6.6 x 10-4 torr MRID 40600607

Aqueous solubility (25°C) 21 mg/L MRID 40600605

Henry’s Law Constant (20°C) 7.1 x10-6 atm-m3/mol (Calculated)

Log octanol-to-water partition coefficient

(log KOW)

2.700 MRID 40600608

Persistence

Hydrolysis half-life (22°C) pH 5: 2,200 d pH 7: 1,800 d

pH 9: 1,200 d

MRID 40548502/ 

41012101

Aqueous photolysis half-life (25°C) 10 d MRID 41709801

Soil photolysis half-life (25°C) No degradation observed MRID 43006801

Aerobic soil metabolism half-life

[dissipation half-life A] (24°C)

324 d [91 d] MRID 41340601/ 

43006803

Anaerobic aquatic metabolism half-life 

(20-29°C)

1,040 d MRID 41306001

Aerobic aquatic metabolism half-life 

[dissipation half-life A] (25°C)

No degradation observed [2.4 d] MRID 41149501

Mobility

Freundlich soil-water partition coefficients 

(KF); organic carbon-normalized 

Freundlich coefficients (KFOC)

0.3, 4.2, 7.4, 9.6, 10.5 L/kg;

133, 195, 262, 272, 323 L/kgOC

MRID 43611101

Maximum volatile concentration (23°C) 313 μg/m3 (24 hrs posttreatment) 

(35% volatilized by 4 d posttreatment)

MRID 43754001

Field Dissipation

Terrestrial field dissipation half-life; 

leaching depth

241 d (0-3” depth; Woodburn silt loam); 

leached to 50-60” depth

MRID 41385601

Aquatic field dissipation half-life 15 d (pond water), 21 d (top sediment), 

32 d (lower sediment)

MRID 41780601

69 d (pond water), 39 d (top sediment), 

variable concentrations (lower sediment)

MRID 41877301/ 

42191401

Fish Bioconcentration

Fish bioconcentration factors (steadystate); depuration rate32 (edible), 110 (inedible), 63 (whole); 

85% depuration in 1 day

MRID 40465801/ 

40465802 A Dissipation half-lives are shorter because they are corrected for volatilization.
Page 13 of 51

4.3.1. Mobility

Dichlobenil is soluble in water up to 21 mg/L (at 25°C; MRID 40600605). The compound is 

semi-volatile, with a vapor pressure of 6.6 x 10-4 torr and a Henry’s Law Constant of 7.1 x 10-6

atm·m3/mol at 20°C (MRID 40600607). The compound was observed to volatilize in multiple 

submitted laboratory studies, with an evaporation half-life of 2.4 days in an aerobic aquatic 

system at 25°C (MRID 41149501). EpiSUITE (v4.10) estimates a half-life in air of 1,510 hours 

(63 days) for dichlobenil, indicating that the compound may be subjected to long-range transport. 

Dichlobenil is moderately mobile in soil (KFOC range of 133-323L/kgOC; MRID 43611101). The 

compound was detected in the field at a soil depth of 60 inches (MRIDs 43564901 and -02).

Dichlobenil’s octanol-water partition coefficient (KOW) value is 501 (log KOW of 2.700; MRID 

40600608). EpiSUITE (v4.10) estimates an octanol-air partition coefficient (KOA) value for 

dichlobenil of 1.7 x 106. With a KOW >100 (501), a KOA >1.0 x 105 (1.7 x 106), and a half-life 

in air predicted to be >48 hrs (1,510 hrs), dichlobenil has characteristics consistent with 

compounds that bioaccumulate in terrestrial animals. However, fish bioconcentration factors are 

≤110 and depuration is rapid (85% depuration in 1 day; MRIDs 40465801 and -02), indicating 

that bioaccumulation of dichlobenil residues is not a primary concern in aquatic or terrestrial 

organisms.

4.3.2. Degradation

Dichlobenil photolyzes in water with a half-life of 10 days (MRID 41709801), but does not 

photolyze in soil (MRID 43006801). One major degradate, 4-chloro-2(3H)benzoxazolone 

(BZZ), was 19% of the applied and increasing in concentration at 21 days after treatment in the 

aqueous photolysis study. In the presence of moisture, dichlobenil does not hydrolyze 

substantially, with extrapolated hydrolysis half-lives of 1,200-2,200 days at pH 5-9 based on a 

150-day study (MRIDs 40548502 and 41012101).

Dichlobenil persisted in aerobic soil with a dissipation half-life of 91 days (at 24°C) and a 

degradation half-life (corrected for volatilization) of 324 days (MRIDs 41340601 and 

43006803). BAM was the only major degradate, at 13% of the applied at 350 days after 

treatment.

Dichlobenil was not observed to biodegrade in aerobic or anaerobic aquatic systems, with the 

exception that single replicates on two different intervals of the anaerobic aquatic metabolism 

study (day 217 and 339) contained degradates of dichlobenil totaling 18% and 14% of the 

applied, respectively (single degradates were no more than 7.2% of the applied). However, 

dichlobenil dissipated in aerobic aquatic conditions, with a half-life of only 2.4 days at 25°C due 

to volatilization (MRID 41149501).

4.3.3. Field Dissipation

Dichlobenil persisted in the field, dissipating from the top three inches of soil with a half-life of 

241 days in a Woodbum silt loam in Oregon (MRID 41385601). Dissipation appears to have 
Page 14 of 51

been due to biodegradation, leaching, and volatilization during the warmer months (the latter was 

observed via an increased rate of dissipation in soil). Monthly mean temperatures ranged from -

3 to 28 °C. Dichlobenil leached to the 50-60-inch sample depth, and BAM leached to the 

deepest sample depth (84-96-inch).

Dichlobenil was applied to one-third of a pond in Florida (MRID 41780601) and in Oregon 

(MRIDs 41877301 and 42191401). Dissipation half-lives were 15 days in the pond water, 21 

days in the top layer of sediment, and 32 days in the lower layers of sediment at the Florida site. 

At the Oregon site, dissipation half-lives were 69 days in the pond water and 39 days in the top 

layer of sediment. Concentrations in the lower sediment layers were too variable to calculate a 

dissipation half-life.

4.3.4. Transformation Products

The major organic degradates of dichlobenil in submitted environmental fate studies were BAM 

(in aerobic soil) and BZZ (in water under illumination). A variety of minor degradates were 

observed in the aqueous photolysis and anaerobic aquatic metabolism studies. Table 3

summarizes the transformation products of dichlobenil and their maximum amounts formed.

BAM (PC code 027402) is also a degradate of the fungicide fluopicolide (PC code 027412). 

Although BAM has a PC code, it is not a registered pesticide. BAM formed up to 13% of the 

applied in aerobic soil and was increasing in concentration at study termination. This degradate 

was detected in field studies at up to 4.9% of the maximum dichlobenil concentration in soil. 

Also, BAM leached to the deepest sampling depth (up to 84-96-inches deep) in each terrestrial 

field dissipation study. Submitted environmental fate studies of BAM indicate that the degradate 

is stable to hydrolysis, to aqueous photolysis, and to biodegradation in soil (MRIDs 45280303 

and 45575901). BAM is also mobile in soil, with Freundlich KOC values in five soils ranging 

from 34 to 54 L/kgOC (MRID 45539402).

BZZ formed up to 19% of the applied in irradiated water and was increasing in concentration at 

study termination (MRID 41709801). Dichlobenil field studies did not analyze for BZZ. Also, 

environmental fate studies conducted with BZZ have not been submitted. Therefore, the 

environmental fate of BZZ is not well understood.
Page 15 of 51

Table 3. Dichlobenil and Its Environmental Degradates

Code Name/ 

Synonym Chemical Name Chemical Structure Study Type Ref.

(MRID)

Maximum 

%AR (day)

Final %AR 

(study 

length)

PARENT

Dichlobenil 2,6-dichlorobenzonitrile

CAS No.: 1194-65-6

Formula: C7H3Cl2N

MW: 172.01 g/mol

Cl Cl

N

MAJOR TRANSFORMATION PRODUCTS

BAM 2,6-dichlorobenzamide

Formula: C7H5Cl2NO

MW: 190.03 g/mol Cl Cl

O NH2 Aq photolysis 41709801 3% (15 d) 3% (15 d)

Aerobic soil 41340601/ 

43006803 13% (350 d) 13% (350 d)

Anaerobic aquatic 41306001 7.2% A (217 d) n.d. B (370 d)

Terr dissipation 41385601 4.8% C (371 d) 3.4% C (540 d)

Aq dissipation 41877301/ 

42191401 1.8% D (113 d) <0.1% D (180 d)

BZZ 4-chloro2(3H)benzoxazolone

Formula: C7H4ClNO2

MW: 169.57 g/mol Cl

HN

O

O

Aq photolysis 41709801 19% (21 d) 19% (21 d)
Page 16 of 51

Code Name/ 

Synonym Chemical Name Chemical Structure Study Type Ref.

(MRID)

Maximum 

%AR (day)

Final %AR 

(study 

length)

MINOR TRANSFORMATION PRODUCTS

2,6-dichlorobenzoic 

acid

2,6-dichlorobenzoic acid

Formula: C7H4Cl2O2

MW: 191.01 g/mol Cl Cl

O OH Aq photolysis 41709801 4% (21 d) 4% (21 d)

Anaerobic aquatic 41306001 1.4% A (217 d) n.d. B (370 d)

2-chlorobenzonitrile 2-chlorobenzonitrile

Formula: C7H4ClN

MW: 137.57 g/mol Cl

N Aq photolysis 41709801 2% (21 d) 2% (21 d)

Anaerobic aquatic 41306001 6.4% A (217 d) n.d. B (370 d)

2-

hydroxybenzonitrile

2-hydroxybenzonitrile

Formula: C7H5NO

MW: 119.12 g/mol OH

N

Aq photolysis 41709801 4% (21 d) 4% (21 d)

Carbon dioxide Carbon dioxide

Formula: CO2

MW: 44.1 g/mol

O O Aerobic soil 41340601/ 

43006803 2.7% (280 d) 2.3% (350 d)

A Degradates were not consistently formed in this study and were not detected at most intervals. B n.d. means “not detected”.

C Terrestrial field study percentages represent the ratio of degradate concentration to the maximum parent concentration, both in the top layer of soil. D Aquatic field study percentages represent the ratio of degradate concentration to the maximum parent concentration, both in the top layer of sediment (BAM 

was not detected in the water samples).
Page 17 of 51

5. Receptors

Consistent with the process described in the Overview Document (USEPA, 2004), the risk 

assessment for dichlobenil will rely on a surrogate species approach. Toxicological data 

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

taxonomic groups, are used to extrapolate to 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 the 

available open literature are used to evaluate the potential direct and indirect effects of 

dichlobenil on aquatic and terrestrial receptors. These include toxicity data on the technical 

grade active ingredient, degradates, and when available, formulated products. The open 

literature studies are identified using EPA’s ECOTOXicology database (ECOTOX) (USEPA, 

2007c), which employs a literature search engine for locating chemical toxicity data for aquatic 

life, terrestrial plants, and wildlife. The evaluation of both sources of data can also provide 

insight into the direct and indirect effects of dichlobenil on biotic communities from loss of 

species that are sensitive to the chemical and from changes in structure and functional 

characteristics of the affected communities. 

Table 4 and Table 6 provide a summary of the aquatic and terrestrial taxonomic groups, 

respectively, and most sensitive surrogate species tested to characterize the potential acute and 

chronic ecological effects of dichlobenil. Table 5 and Table 7 provide this same information for 

the degradate BAM. No toxicity data were submitted or identified in the open literature for the 

degradate BZZ. A structural isomer, chlorzoxazone, has similar physical properties to BZZ and 

is pharmacologically active as a muscle relaxant at doses of 10-30 mg/kg/day. In addition, the 

tables provide a preliminary overview of the potential acute toxicity of dichlobenil by providing 

the acute toxicity classifications. Based on the available ecotoxicity information, the organisms 

facing the greatest hazard are aquatic and terrestrial plants, followed by moderate hazard to 

aquatic fish and invertebrates. 

5.1. Effects to Aquatic Organisms

Table 4. Summary of the Most Sensitive Endpoints from Aquatic Toxicity Studies for Dichlobenil

Taxonomic 

Group

Study 

Type

Surrogate Species Toxicity Value

(all units in terms of 

measured active 

ingredient)

MRID and 

Classification

Acute 

Toxicity 

Classification

Freshwater fish1

Acute

Rainbow Trout

(Oncorhynchus 

mykiss)

LC50 = 4.93 mg/L 40098001

Supplemental

Moderately 

toxic

Chronic 

(Early 

LifeStage)

Rainbow Trout

NOAEC = <0.33 mg/L

LOAEC = 0.33 mg/L

Endpoint: 34 day 

length

42224202

Supplemental --

Freshwater 

invertebrates Acute Water Flea 

(Daphnia magna) EC50 = 6.2 mg/L 40775001

Acceptable

Moderately 

toxic
Page 18 of 51

Taxonomic 

Group

Study 

Type

Surrogate Species Toxicity Value

(all units in terms of 

measured active 

ingredient)

MRID and 

Classification

Acute 

Toxicity 

Classification

Chronic Water Flea 

NOAEC = 0.56 mg/L

LOAEC = 1.0 mg/L

Endpoint: delayed 

reproduction

40775002, 

42224201

Acceptable

--

Estuarine/marine 

fish Acute

Sheepshead Minnow 

(Cyprinodon 

variegatus)

LC50 = 12.7 mg/L 43905403

Acceptable Slightly toxic

Estuarine/marine 

invertebrates Acute

Eastern Oyster 

(Crassostrea 

virginica)

EC50 = 1.63 mg/L 

Endpoint: shell growth

43905404

Acceptable

Moderately 

toxic

Aquatic plants 

and algae

Vascular Duckweed 

(Lemna gibba)

NOAEC = 0.006 mg/L

EC50 = 0.030 mg/L

40758203

Acceptable --

Nonvascular

Green Algae 

(Pseudokirchneriella 

subcapitata)

NOAEC = 0.16 mg/L

EC50 = 1.5 mg/L

40758201

Acceptable --

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

Table 5. Summary of the Most Sensitive Endpoints from Aquatic Toxicity Studies for BAM

Taxonomic 

Group

Study 

Type

Surrogate Species Toxicity Value

(all units in terms of

measured active 

ingredient)

MRID and 

Classification

Acute

Toxicity 

Classification

Freshwater fish1

Acute

Bluegill Sunfish 

(Lepomis 

macrochirus)

LC50 = 120 mg/L 40098001

Supplemental

Practically 

non-toxic

Chronic 

(Early 

Life 

Stage)

Rainbow Trout

NOAEC = 10 mg/L

LOAEC = 18 mg/L

Endpoints: 60 day 

offspring survival, 

length, weight

00156312 

Supplemental --

Freshwater 

invertebrates

Acute Water Flea EC50 = 184 mg/L 46708432

Acceptable

Practically 

non-toxic

Chronic Water Flea NOAEC = 320 mg/L

LOAEC = >320 mg/L

00156312 

Supplemental --

Aquatic plants 

and algae2

Nonvascular

Estuarine Algae 

(Chlorella 

pyreoidosa)

NOAEC = 10 mg/L

LOAEC = 32 mg/L

00156312 

Supplemental --

Nonvascular

Freshwater Algae 

(Scenedesmus 

pannonicus)

EC50 = 100 mg/L 00156312 

Supplemental --

1 Freshwater fish may be surrogates for aquatic-phase amphibians. 2 Toxicity endpoints presented, i.e., NOAEC or EC50, are the only ones available from the study.
Page 19 of 51

5.1.1. Freshwater Fish 

The acute toxicity of technical grade dichlobenil has been tested in five species of freshwater 

fish, rainbow trout (Oncorhychus mykiss), bluegill sunfish (Lepomis macrochirus), fathead 

minnow (Pimephales promelas), goldfish (Carassius auratus auratus), and green sunfish 

(Lepomis cyanellus). The 96-hr LC50 test results for freshwater fish ranged from 4.93 mg/L for 

rainbow trout (MRID 40098001) to 12.6 mg/L for green sunfish (MRID 40098001). Based on 

these studies, dichlobenil is classified as moderately toxic to freshwater fish on an acute basis. 

The acute toxicity of BAM has been tested in rainbow trout, bluegill sunfish, and guppy 

(Poecilia reticulaia). The 96-hr LC50 values ranged from 120 mg/L for rainbow trout (MRID 

40098001) to 275 mg/L for guppy (MRID 00156312). Based on these studies, BAM is classified 

as practically non-toxic to freshwater fish and aquatic-phase amphibians on an acute basis. On 

an acute exposure basis, BAM appears to be less toxic to fish compared to dichlobenil.

An early-life stage study with dichlobenil on rainbow trout demonstrated a statistically 

significant effect on offspring length at 34 days post-hatch at all concentrations tested (mean 

measured values of 0.33, 0.66, 1.2, 2.4, and 5.1 mg a.i./L) (MRID 42224202). Therefore, the 

NOAEC is <0.33 mg/L and the LOEC is 0.33 mg/L. This study is classified as supplemental and 

does not fulfill the guideline requirement due to the failure to establish a definitive NOAEC. 

An early-life stage study with BAM on rainbow trout demonstrated a NOEC of 10 mg/L and a 

LOAEC of 18 mg/L with effects on survival, length, and weight of offspring (MRID 00156312). 

On a chronic exposure basis, BAM appears to be less toxic to fish compared to dichlobenil.

5.1.2. Freshwater Invertebrates

The acute toxicity of technical grade dichlobenil has been tested in five species of freshwater 

invertebrates, including: scud (Gammarus fasciatus), sowbug (Asellus brevicaudus), water flea 

(Daphnia magna), glass shrimp (Palacmonetes kadiakensis), and seed shrimp (Cypridopsis 

vidua). The 48-hr EC50 for these studies ranged from 6.2 mg/L for D. magna (MRID 40775001) 

to 34.0 mg/L for the sowbug (MRID 00500149). Based on these studies, dichlobenil is classified 

as moderately toxic to freshwater invertebrates on an acute exposure basis. A study that tested a 

50% formulation of dichlobenil on five freshwater aquatic invertebrates (MRID 40094602) had 

similar results; the 48-hr EC50 ranged from 3.7 mg/L for a daphnid species (Daphnia pulex) to 

35.0 mg/L for the sowbug. 

The acute toxicity of BAM has also been tested in D. magna. The 48-hr EC50 for BAM was 184

mg/L (MRID 46708432). BAM is classified as practically non-toxic to freshwater invertebrates 

on an acute basis. On an acute exposure basis, BAM appears to be less toxic to freshwater 

invertebrates compared to dichlobenil.

A daphnid life-cycle study with dichlobenil demonstrated delayed reproduction at 1.0 mg/L and 

no effects were observed at 0.56 mg/L (MRID 40775002, 42224201). A daphnid life-cycle 

study with BAM showed no effects at the highest concentration tested, 320 mg/L (MRID 

00156312). Therefore, the NOAEC for chronic effects of freshwater invertebrate exposure to 
Page 20 of 51

BAM is 320 mg/L and the LOAEC is >320 mg/L. On a chronic exposure basis, BAM appears to 

be less toxic to freshwater invertebrates compared to dichlobenil.

5.1.3. Estuarine/Marine Fish

The acute toxicity of technical grade dichlobenil has been tested in one species of 

estuarine/marine fish, the sheepshead minnow (Cyprinodon variegatus). The 96-hr LC50 was 

12.7 mg/L in one study (MRID 43905403) and 14.0 mg/L in a second study (MRID 40228401). 

Based on these studies, dichlobenil is classified as slightly toxic to estuarine/marine fish on an 

acute basis. There are no chronic dichlobenil toxicity studies or acute or chronic BAM toxicity 

studies with estuarine/marine fish.

5.1.4. Estuarine/Marine Invertebrates

The acute toxicity of technical grade dichlobenil has been tested in three species of aquatic 

invertebrates including one mollusk, eastern oyster (Crassostrea virginica), and two 

crusteaceans, pink shrimp (Penaeus duorarum), and mysid shrimp (Mysidopsis bahia). A 96-hr 

study with eastern oyster larvae demonstrated an EC50 of 2.5 mg/L (MRID 40228401) whereas a 

96-hr study of eastern oyster shell growth demonstrated an EC50 of 1.63 mg/L (MRID 

43905404). A 48-hr study on pink shrimp had an EC50 of >1.0 mg/L (MRID 40228401) and a 

96-hr study on mysid shrimp had an LC50 of 2.35 mg/L (MRID 43905405). Based on these 

studies, dichlobenil is classified as moderately toxic to estuarine/marine invertebrates on an acute 

basis. There are no chronic dichlobenil toxicity studies or acute or chronic BAM toxicity studies 

with estuarine/marine invertebrates.

5.1.3. Aquatic Plants

The toxicity of technical grade dichlobenil was tested on one vascular and eight non-vascular 

plants. The NOEC and EC50 for duckweed (Lemna gibba) were 0.006 mg/L and 0.030 mg/L, 

respectively (MRID 40758203). For non-vascular plants, the NOEC ranged from 0.16 to 2.5 

mg/L for green algae (Pseudokirchneriella subcapitata) (MRID 40758201) and blue-green algae 

(Anabaena flos-aquae) (MRID 40758202), respectively. The EC50 ranged from 1.0 to 60 mg/L 

for a freshwater diatom (Navicula pelliculosa) (MRID 40758204) and three estuarine algae 

(Isochrysis galbana, Dunaliella tertiolecta, and Chlorococcum sp.) (MRID 40228401), 

respectively.

The toxicity of BAM was tested in one estuarine algae (Chlorella pyreoidosa), one freshwater 

algae (Scenedesmus pannonicus) (MRID 00156312), and one freshwater diatom (Navicula 

pelliculosa) (MRID 46708511). The EC50 for the estuarine algae was 100 mg/L, no NOEC was 

provided. The NOEC and LOEC for the freshwater algae were 10 and 32 mg/L, no EC50 was 

provided. No effects were seen in the freshwater diatom study at the highest concentration 

tested, 10 mg/L. No studies of BAM toxicity to vascular aquatic plants were identified.
Page 21 of 51

5.2. Effects to Terrestrial Organisms

Table 6. Summary of the Most Sensitive Endpoints from Terrestrial Toxicity Studies for 

Dichlobenil

Taxonomic 

Group

Study 

Type

Surrogate Species Toxicity Value

(all units in terms of 

measured active 

ingredient)

MRID and 

Classification

Acute 

Toxicity 

Classification

Birds1

Acute

Bobwhite quail

(Colinus 

virginianus)

LD50 = 683 mg/kg-bw 43469801

Acceptable Slightly toxic

Sub-acute 

dietary

Ring-necked 

pheasant 

(Phasianus 

colchicus)

LC50 = 1500 ppm 00022923

Supplemental Slightly toxic

Chronic Bobwhite quail NOAEC = <146 ppm

LOAEC = 146 ppm

45280301

Supplemental --

Mammals

Acute Oral

Laboratory rat 

(Rattus 

norvegicus)

LD50 = 4250 mg/kg-bw 00112500 Practically 

non-toxic

Acute 

Inhalation Laboratory rat LC50 = >3.3 mg/L 43335703 Toxicity 

Category III

Chronic

Laboratory rat 

(Rattus 

norvegicus)

NOAEL = 3 mg/kg/day

LOAEL = 15 mg/kg/day

Endpoint: reduced pup 

weight

41257303, 

42239101 --

Insects Acute 

contact

Honey bee 

(Apis mellifera L.) LD50 = >120 μg/bee 00018842Acceptable

Practically 

non-toxic

Terrestrial plants Seedling 

Emergence

Dicot – lettuce

(Lactuca sativa)

EC05 = 0.011 lb/A

EC25 = 0.023 lb/A

Endpoint: shoot dry 

weight

41280801

Supplemental --

Monocot – oat

(Avena sativa)

NOAEC = 0.084 lb/A

EC25 = 0.12 lb/A

Endpoint: shoot dry 

weight

41280801

Supplemental --

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

Table 7. Summary of the Most Sensitive Endpoints from Terrestrial Toxicity Studies for BAM

Taxonomic 

Group

Study 

Type

Surrogate 

Species

Toxicity Value

(all units in terms of 

measured active 

ingredient)

MRID and 

Classification

Acute 

Toxicity 

Classification

Mammals Acute

Mouse

(female)

(Mus 

musculus)

LD50 = 1144 mg/kg-bw 42940201 Slightly toxic
Page 22 of 51

Taxonomic 

Group

Study 

Type

Surrogate 

Species

Toxicity Value

(all units in terms of 

measured active 

ingredient)

MRID and 

Classification

Acute 

Toxicity 

Classification

Chronic

Rabbit 

(Oryctolagus 

cuniculus)

NOAEL = 10 mg/kg/day

LOAEL = 30 mg/kg/day

Endpoint: mortality

43003601, 

43265201 --

Terrestrial plants Seedling 

Emergence1

Dicot – pea

(Pisum 

sativum)

EC05 = 3.5 μg/kg soil

EC25 = >11.64 μg/kg soil

Endpoint: survival

46708506

Acceptable --

Monocot –

onion

(Allium cepa)

NOAEC = 0.722 μg/kg soil

EC25 = 6.3 μg/kg soil

Endpoint: shoot dry weight

46708506

Acceptable --

1 The study does not provide sufficient information to convert the toxicity values to lb a.i./A.

5.2.1. Birds

Acute oral and sub-acute dietary toxicity data for dichlobenil are available for mallard duck 

(Anas platyrhynchos), bobwhite quail (Colinus virginianus), and ring-necked pheasant 

(Phasianus colchicus) and dietary toxicity data are also available for Japanese quail (Coturnix 

japonica). Definitive acute oral LD50 values were 683 mg/kg-bw for the bobwhite quail (MRID 

43469801) and 1189 mg/kg-bw for the ring-necked pheasant (MRID 00160000). A mallard 

duck acute oral study showed no effects at the highest dose tested, 2000 mg/kg-bw (MRID 

00160000). The dietary LC50 values ranged from 1500 mg/kg-diet for the ring-necked pheasant 

(MRID 00022923) to >5200 mg/kg-diet for the mallard duck (MRID 40600602). Based on these 

studies, dichlobenil is classified as slightly toxic to birds on acute oral and sub-acute dietary 

bases. No studies on a passerine species have been submitted to U.S. EPA or identified in the 

open literature. No studies of BAM toxicity to birds were identified.

Two avian reproduction studies with dichlobenil were submitted to the Agency, one with the 

mallard duck and a second with the bobwhite quail. The bobwhite quail study failed to 

determine a definitive NOAEC, as hatchling weight and adult male body weight were 

significantly affected at the lowest concentration tested, 146 ppm (MRID 45280301). The 

mallard duck study found a NOAEC and LOAEC of 289 and 600 ppm, respectively, based on 

eggs laid, hatchlings, and 14-day old survivors (MRID 45280302).

5.2.2. Mammals

Acute oral and inhalation and chronic reproductive studies for laboratory rats were study 

submitted to the Health Effects Division (HED) and used to assess effects to mammalian 

wildlife. The acute oral toxicity of dichlobenil was tested in the laboratory rat (Rattus 

norvegicus) and the LD50 was found to be 4250 mg/kg-bw (MRID 00112500). Based on this 

study, dichlobenil is classified as practically non-toxic to mammals on an acute basis. The acute 

oral toxicity of BAM was tested in both the laboratory rat and the mouse (Mus musculus). The 

LD50 values ranged from 1144 mg/kg-bw for the female mouse (MRID 42940201) to 2330 

mg/kg-bw for the female rat (MRID 00111402). Based on these studies, BAM is classified as 

slightly toxic to mammals on an acute basis.
Page 23 of 51

A four hour acute inhalation study with dichlobenil on the laboratory rat was submitted to the 

agency (MRID 43335703). The study was performed using an 85.3% formulation due to 

clogging of the apparatus with technical dichlobenil above 0.25 mg/L. The LC50 was >3.3 mg/L. 

This result would normally place dichlobenil in Toxicity Category IV; however, because the 

respirable particle size was less than optimal (5.5 μm instead of an optimal size of 4 μm), 

Toxicity Category III was assigned as an added measure of protection.

Three mammalian reproduction studies with dichlobenil were submitted to the Agency, two with 

rats and one with rabbits (Oryctolagus cuniculus). One rat 2-generation study found a NOEL of 

3 mg/kg-bw/day and a LOAEL of 15 mg/kg/day (60 and 350 ppm in diet, respectively) based on 

reduced pup weight (MRID 41257303, 42239101). The study report indicates that palatability 

was an issue in the study and that no other endpoints were affected, up to 100 mg/kg/day. The 

two other studies were developmental toxicity gavage studies and reported a NOAEL / LOAEL 

of 20 / 60 mg/kg/day in the rat (MRID 00147437) and 45 / 135 mg/kg/day in the rabbit (MRID 

41257302). Major external, visceral, and skeletal defects were observed in the rabbit and 

decreased weight gain, food consumption, and food efficiency were observed in the rat. A 

developmental toxicity study using BAM was conducted on the rabbit. The NOAEL was 10 

mg/kg/day and the LOEL was 30 mg/kg/day based on mortality following a 6 day exposure 

(MRID 43003601, 43265201).

Dichlobenil and BAM toxicity endpoints for mammals are within approximately a factor of two 

on both acute and chronic exposure bases. BAM was somewhat more toxic to mammals than 

dichlobenil on an acute exposure basis but less toxic on a chronic exposure basis. Taking 

confidence intervals into account, BAM and dichlobenil appear to have similar toxicity to 

mammals.

5.2.3. Terrestrial Invertebrates

Toxicity of dichlobenil to terrestrial invertebrates was tested by an acute contact study using the 

honey bee (Apis mellifera). This study was acceptable and demonstrated an LD50 of >120 

μg/bee, classifying dichlobenil as practically non-toxic to terrestrial invertebrates (MRID 

00018842). No studies of BAM toxicity to terrestrial invertebrates were identified.

5.2.4. Terrestrial Plants

One terrestrial plant study with dichlobenil was submitted to the Agency using six dicots: 

soybean (Glycine max), lettuce, sugarbeet (Beta vulgaris), tomato (Solanum esculentum), 

cucumber (Cucumis sativa), and cabbage (Brassica oleraceae), and four monocots: corn (Zea 

mays), oat, wheat (Triticum aestivum), and onion (Allium cepa) (MRID 41280801). Seedling 

emergence, seedling germination, and vegetative vigor were tested; however the seedling 

germination and vegetative vigor studies were classified as invalid. The seedling emergence 

study was classified as supplemental because the lowest concentration tested was >EC25 for 

lettuce and the test compound was the technical active ingredient rather than a formulated 

product. The most sensitive dicot tested was lettuce with an EC05 of 0.011 lb a.i./A. The most 
Page 24 of 51

sensitive monocot tested was oat with a NOAEC of 0.084 lb a.i./A. The most sensitive endpoint 

for both species was the shoot dry weight. 

A seedling emergence study with BAM was submitted to the Agency using five dicots: 

sugarbeet, oilseed rape (Brassica napus), cucumber, soybean, and pea, and three monocots: corn, 

oat, and onion (MRID 46708506). The most sensitive dicot species was pea which resulted in an 

EC25, EC05, and NOAEC values of >11.64, 3.5, and 11.64 μg a.i./kg soil, respectively, based a 

statistically significant reduction in percent survival. The most sensitive monocot species was 

onion which resulted in an EC25 and NOAEC values of 6.3 and 0.722 μg a.i./kg soil, 

respectively, based a statistically significant reduction in dry weight. The study reported all 

application rates in terms of μg/kg soil soil without providing sufficient information to convert 

the nominal application rates to lbs a.i./A.

5.3. Ecological Incidents

A review of the Agency’s Ecological Incident Information System (EIIS, version 2.1.1), the 

‘Aggregate Incident Reports’ (v. 1.0) database, and the American Bird Conservancy’s Avian 

Monitoring Information System (AIMS) for ecological incidents involving dichlobenil was 

completed on 19 January 2012. The incidents identified in these sources and any other known 

incidents that occur before the registration review risk assessment is performed will be included 

in the assessment. The search of AIMS identified no ecological incidents involving dichlobenil. 

The search of EIIS returned two terrestrial plant incidents in Washington State attributed to 

dichlobenil use with “possible” certainty (USEPA, 2007b). Incident #I009786-020 occurred in 

January 2000 when a registered agricultural use of dichlobenil was applied to kinnikinnick (also 

known as bearberry). Thirty-five plants on the treated field were damaged. Incident #I013587-

060 occurred in April 1999 when a registered use of dichlobenil was applied to a right-of-way. 

A residential homeowner reported lawn damage as a result of spray drift from this application. 

The number of documented incidents in EIIS is believed to be a very small fraction of total 

mortality caused by pesticides for a variety of reasons. Incident reports for non-target organisms 

typically provide information only on mortality events and plant damage. Sub-lethal effects in 

organisms such as abnormal behavior, reduced growth and/or impaired reproduction are rarely 

reported, except for phytotoxic effects in terrestrial plants. An absence of reports does not 

necessarily equate to an absence of incidents given the nature of the incident reporting.

In addition to the incidents recorded in EIIS and AIMS, incidents have been reported to the 

Agency in aggregated incident reports. Pesticide registrants report certain types of incidents to 

the Agency as aggregate counts of incidents occurring per product per quarter. Ecological 

incidents reported in aggregate reports include those categorized as ‘minor fish and wildlife’ (WB), ‘minor plant’ (P-B), and ‘other non-target’ (ONT) incidents. ‘Other non-target’ incidents 

include reports of adverse effects to insects and other terrestrial invertebrates. For dichlobenil, 

registrants reported 9 minor plant incidents between 1995 and 2005, and no fish and wildlife or 

other non-target incidents. Unless additional information on these aggregated incidents becomes

available, they will be assumed to be representative of registered uses of dichlobenil in the risk 

assessment.
Page 25 of 51

6. 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 and immediately adjacent areas that may receive drift or runoff. Areas adjacent 

to the treated field 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 down stream from, the 

treated site 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.

7. 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, 1998a). For dichlobenil, the ecological entities include the following: birds, reptiles, 

terrestrial-phase amphibians, mammals, freshwater fish, freshwater aquatic-phase amphibians

and invertebrates, estuarine/marine fish and invertebrates, terrestrial plants, insects, aquatic 

plants, and algae. The attributes for each of these entities include growth, reproduction, and 

survival. 

8. 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 medium, a point of 

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

The conceptual model for dichlobenil provides a written description and visual representation of 

the predicted relationships between dichlobenil, potential routes of exposure, and the predicted 

effects for the assessment endpoint. A conceptual model consists of two major components: risk 

hypothesis and a conceptual diagram (USEPA, 1998a).
Page 26 of 51

8.1. Risk Hypothesis

A risk hypothesis describes the predicted relationship among the stressor, exposure, and 

assessment endpoint response along with the rationale for their selection. For dichlobenil, the 

following ecological risk hypothesis is being employed for this national-level ecological risk 

assessment:

Dichlobenil, when used in accordance with current labels, can result in off-site 

movement of the compound via runoff, leaching to ground water, spray drift and 

atmospheric transport leading to exposure of non-target plants and animals. 

Direct applications to and atmospheric deposition to foliar surfaces may serve as 

a major source of dichlobenil exposure to wildlife. Exposure in these 

environmental compartments will result in adverse effects upon the survival, 

growth, and reproduction of non-target terrestrial and aquatic organisms. These

non-target organisms include federally-listed threatened and endangered species. 

8.2. Conceptual Diagram

The environmental fate properties of dichlobenil indicate that direct spray, spray drift, leaching 

to ground water, atmospheric deposition, and runoff represent potential transport mechanisms of 

dichlobenil to aquatic and terrestrial organisms. These transport mechanisms (e.g., sources) are 

depicted in the conceptual models below (Figure 2, Figure 3, and Figure 4) and result in the 

movement of dichlobenil into aquatic (water and sediment) and terrestrial (soil and foliage) 

habitats. Use of dichlobenil in sewer drain and storm drain systems will also be assessed. The 

movement away from the site of application represents exposure pathways for a broad range of 

biological receptors of concern (non-target animals) and the potential attribute changes, i.e.,

effects such as reduced survival, growth and reproduction, in the receptors due to dichlobenil

exposure. 
Page 27 of 51

Figure 2. Conceptual diagram depicting stressors, exposure pathways, and potential effects to 

aquatic organisms from the supported uses of dichlobenil. Dotted lines indicate exposure pathways 

that have a low likelihood of contributing to ecological risk.
Page 28 of 51

Figure 3. Conceptual diagram depicting stressors, exposure pathways, and potential effects to 

terrestrial organisms (terrestrial plants, terrestrial invertebrates, and dietary routes of exposure for 

terrestrial vertebrates) from the supported uses of dichlobenil. 
Page 29 of 51

Figure 4. Conceptual diagram depicting stressors, drinking water and inhalation exposure 

pathways, and potential effects to terrestrial animals from the supported uses of dichlobenil.

As indicated in Figure 2, Figure 3, and Figure 4 above, the possible exposure mechanisms 

considered are direct application, spray drift, leaching to ground water, atmospheric transport, 

and runoff. In addition to exposure via ingestion of food items, drinking water and inhalation 

exposure pathways are considered for terrestrial vertebrates as well as ingestion of residues in 

dew by terrestrial invertebrates. EFED acknowledges the potential for a dermal exposure 

pathway, however at the present time, the Agency does not have a method to quantify these 

levels of exposure, and data are limited to quantify the contribution of such exposures to the 

toxic burden an organism experiences. Dermal exposure is not expected to be of concern for 

dichlobenil based on mammalian dermal toxicity and irritation data and the predominant use of 

granular formulations.

9. Analysis Plan 

In registration review, pesticide ecological risk assessments will follow the Agency’s Guidelines 

for Ecological Risk Assessment in compliance with the Overview Document (USEPA, 2004) 

and in accordance with Section 7 of the Endangered Species Act. In order to address the risk 

hypothesis, the potential for adverse effects on the environment is estimated. The use, 

environmental fate, and ecological effects of dichlobenil are characterized and integrated to 

assess the risks. This is accomplished using a risk quotient (ratio of exposure concentration to 
Page 30 of 51

effects concentration) approach. Although risk is often defined as the likelihood and magnitude 

of adverse ecological effects, the risk quotient-based approach does not provide a quantitative 

estimate of likelihood and/or magnitude of an adverse effect. However, as outlined in the 

Overview Document (USEPA, 2004), the likelihood of effects to individual organisms from 

particular uses of dichlobenil is estimated using the probit dose-response slope and either the 

level of concern (discussed below) or actual calculated risk quotient value. 

This analysis plan will be revisited and may be revised depending upon a full review of the data 

available in the open literature and the information submitted by the public in response to the 

opening of the Registration Review docket. 

9.1. Stressors of Concern

The stressors of ecological concern for terrestrial organisms are dichlobenil and its main 

degradate BAM. Submitted studies indicate that BAM toxicity to mammals is similar to that of 

dichlobenil. More specifically, BAM is slightly more acutely toxic and slightly less toxic on a 

chronic basis to mammals than dichlobenil. BAM is assumed to have similar toxicity to other 

terrestrial animals in the absence of data. Due to the difference in measurement units, 

assumptions will be made in the risk assessment to compare toxicity of dichlobenil and BAM to 

terrestrial plants.

The stressors of concern for aquatic organisms are dichlobenil and, pending results of requested 

ecotoxicity studies, the aquatic degradate BZZ. Submitted data indicate that BAM is orders of 

magnitude less toxic to fish, aquatic invertebrates, and aquatic plants than dichlobenil (see 

Section 5.1). If BZZ is found to be of similarly low toxicity, the stressor of concern for aquatic 

organisms will be dichlobenil alone.

Evaluation of pesticide mixtures is beyond the scope of this assessment because of the myriad 

factors that cannot be quantified based on the available data. Those factors include identification 

of other possible co-contaminants and their concentrations, differences in the pattern and 

duration of exposure among contaminants, and the differential effects of other physical/chemical 

characteristics of the receiving waters (e.g. organic matter present in sediment and suspended 

water). Evaluation of factors that could influence additivity/synergism is beyond the scope of 

this assessment and the capabilities of the available data to allow for an evaluation. However, it 

is acknowledged that not considering mixtures could over- or under-estimate risks depending on 

the type of interaction and factors discussed above. The assessment will, however, analyze the 

toxicity of formulated products (including formulations involving more than one active 

ingredient) and will determine whether formulated products are more toxic than the technical 

grade active ingredient data used for assessing both direct and indirect risks.

9.2. Measures of Exposure 

To estimate risks of dichlobenil exposures in aquatic and terrestrial environments, all exposure 

modeling and resulting risk conclusions will be based on maximum application rates and 

methods cited in Table 1 and will be estimated for each use of dichlobenil. Measures of 

exposure are based on aquatic and terrestrial models that predict estimated environmental 
Page 31 of 51

concentrations (EEC) of dichlobenil. The models used to predict aquatic EECs are the Pesticide 

Root Zone Model coupled with the Exposure Analysis Modeling System (PRZM/EXAMS), the 

provisional Tier II flooded agriculture model, PFAM, and the Down-the-Drain component of EFAST. Additional exposure models may be used to assess use in drains, drain lines, irrigation 

supply systems, waste water systems, sewage systems, sewer lines, and storm sewers if they are 

available. The model used to predict terrestrial EECs on food items is the Terrestrial Residue 

Exposure (T-REX). The model used to derive EECs relevant to terrestrial and wetland plants is

TerrPlant. These models are parameterized using relevant reviewed environmental fate data from 

registrant submissions and the literature; model input values will be consistent with the most 

recent version of the input parameter guidance (Version 2.1; USEPA, 2009).

9.2.1. Aquatic Exposure 

PRZM (v3.12.2; 5/15/2005) and EXAMS (v2.98.4.6; 4/25/2005) are simulation models coupled 

with the linkage program shell PE (v5.0; 11/15/06), which incorporates the standard scenarios 

developed by EFED. The models generate daily exposures and calculate 1-in-10-year EECs of 

dichlobenil that may occur in surface water bodies adjacent to application sites. PRZM 

simulates pesticide fate and transport as a result of leaching, direct spray drift, runoff and erosion 

from an agricultural field. EXAMS estimates environmental fate and transport of pesticides in a 

surface water body for a 30-year period. The combined model is designed to estimate pesticide 

concentrations found in water (standard pond) at the edge of the treated field. As such, it 

provides high-end values of the pesticide concentrations that might be found in ecologically 

sensitive environments following pesticide application. The location of the field is specific to the 

crop being simulated using site-specific information on the soils, weather, cropping, and 

management factors associated with the scenario. The crop/location scenario is intended to 

represent a high-end exposure site on which the crop is normally grown. Based on historical 

rainfall patterns, the receiving water body receives multiple runoff events during the years 

simulated. Weather and agricultural practices are simulated for 30 years so that the 10-year 

exceedance probability at the site can be estimated. The simulation is generated using 30 years 

of meteorological data, encompassing the years from 1961 to 1990. Additional information on 

these models can be found at: http://www.epa.gov/oppefed1/models/water/index.htm. 

The standard scenarios used for ecological pesticide assessments assume application to a 10-

hectare agricultural field that drains into an adjacent 1-hectare water body that is 2 meters deep 

(20,000 m3 volume) with no outlet. PRZM/EXAMS is used to estimate screening-level exposure 

of aquatic organisms to dichlobenil. The measure of exposure for aquatic species is the 1-in-10-

year return peak or rolling mean concentration. The 1-in-10-year peak is used for estimating 

acute exposures of direct effects to aquatic organisms. The 1-in-10-year 60-day mean is used for 

assessing chronic exposure to fish and aquatic-phase amphibians. The 1-in-10-year 21-day mean 

is used for assessing chronic exposure to aquatic invertebrates.

The provisional Tier II Pesticides in Flooded Applications Model (PFAM v0.70; pre-release) 

simulates pesticide transformation on and dissipation from flooded agricultural sites, such as rice 

paddies, following pesticide use. This model will be used to estimate exposure from the use of 

dichlobenil on cranberries. Up to 11 applications and up to 11 manually controlled changes in 

paddy water level can be modeled per year of simulation. A Variable Volume Water Model 
Page 32 of 51

(VVWM) post-processing model is used to simulate pesticide loading via released paddy water 

into a water body, the parameters of which are under development. Simulations are run using 30 

years of location-specific rainfall data. Peak and maximum mean exposure estimates that are 

expected once every ten years are generated based on daily values produced during the 

simulation. PFAM, its associated post-processor, and associated documentation are available online at: http://sites.google.com/site/pfamodel/.

The E-FAST model includes a Down-the-Drain component that estimates screening aquatic 

concentrations of compounds that are disposed of or used to treat sewage drains. This model 

will be used to estimate aquatic exposure from the following uses: drains, drain lines, irrigation 

supply systems, waste water systems, sewage systems, sewer lines, and storm sewers. Exposure 

is estimated in water bodies receiving outflow from sewage treatment facilities. E-FAST and 

associated documentation are available on-line at: 

http://www.epa.gov/oppt/exposure/pubs/efast.htm. If available, additional exposure models may 

be used to assess these uses as well. 

Pending results of aquatic toxicity studies on the aquatic degradate BZZ, this degradate will be 

included with dichlobenil in the residues of concern modeled for aquatic exposure.

9.2.2. Terrestrial Exposure 

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

to spray drift are derived using the T-REX model (version 1.4.1; 10/09/2008). This model 

incorporates the Kenega 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 Kenega, 1972). The 

Fletcher et al. (1994) modifications to the Kenega 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. Because dichlobenil and the degradate BAM have similar 

toxicity to terrestrial organisms, a total toxic residues approach will be used for terrestrial 

modeling.

The granular characterization module of T-REX will also be used as the majority of dichlobenil 

products are granular formulations. Terrestrial animals may be exposed to granular pesticides by 

intentionally or inadvertently ingesting granules when foraging for food or grit. They also may 

be exposed by other routes, such as by walking on exposed granules or drinking water 

contaminated by granules. According to the RED (p. 69), the registrant provided the following 

information as inputs for the granular characterization: “The smaller granule of the 4% granule 

formula (4G) (16/30 size), contains approximately 0.0216 mg a.i./granule; the larger granule of 

the 4G (8/30 size), contains approximately 0.1528 mg a.i./granule. According to information 

provided by Uniroyal and PBI Gordon, the large granule of the 4G is applied by air, the smaller 

granule of the 4G is applied by ground equipment or air. The 10% a.i. granule (10G) is 8/16 

mesh size and contains approximately 0.3276 mg a.i./granule.” These values will be used in the 

assessment unless updated information is provided by the registrants.
Page 33 of 51

The Screening Imbibition Program (SIP version 1.0; 6/15/2010) was used to calculate an upper 

bound estimate of dichlobenil exposure via drinking water using dichlobenil’s solubility (21 

ppm), the most sensitive acute and chronic avian toxicity endpoints (bobwhite quail, LD50 = 683

mg/kg-bw and NOAEC = 146 ppm, respectively) and the most sensitive acute and chronic 

mammalian toxicity endpoints (rat, LD50 = 4250 mg/kg-bw and NOAEL = 3 mg/kg-bw, 

respectively). Drinking water exposure alone was determined to be a potential pathway of 

concern for avian and mammalian species on a chronic basis. Results for avian and mammalian 

species are presented in Table 8 and Table 9, respectively. 

Table 8. SIP Avian Results for Dichlobenil

Parameter Acute Chronic

Upper bound exposure (mg/kg-bw) 17.0100 17.0100

Adjusted toxicity value (mg/kg-bw) 492.0534 14.3380

Ratio of exposure to acute toxicity 0.0346 1.1864

Conclusion*

Drinking water exposure 

alone is NOT a potential 

concern for birds

Exposure through drinking 

water alone is a potential 

concern for birds

Table 9. SIP Mammalian Results for Dichlobenil

Parameter Acute Chronic

Upper bound exposure (mg/kg-bw) 3.6120 3.6120

Adjusted toxicity value (mg/kg-bw) 3268.9324 2.3075

Ratio of exposure to toxicity 0.0011 1.5653

Conclusion*

Drinking water exposure 

alone is NOT a potential 

concern for mammals

Exposure through drinking 

water alone is a potential 

concern for mammals

*Conclusion is for drinking water exposure alone. This does not combine all routes of exposure. Therefore, when 

aggregated with other routes (i.e., diet, inhalation, dermal), pesticide exposure through drinking water may 

contribute to a total exposure that has potential for effects to non-target animals.

The Screening Tool for Inhalation Risk (STIR version 1.0; 11/23/2010) was used to calculate an 

upper bound estimate of dichlobenil exposure via inhalation using dichlobenil’s molecular 

weight (172 g/mole), vapor pressure (5.0 x 10-4 torr), highest granular application rate (10 lb 

a.i./A), most sensitive acute avian toxicity endpoint (bobwhite quail, LD50 = 683 mg/kg-bw), and 

most sensitive acute oral and inhalation mammalian toxicity endpoints (rat, LD50 = 4250 mg/kgbw and 4 hr LC50 >3.3 mg/L, respectively). The non-definitive mammalian inhalation endpoint 

results in a conservative estimate of the LC50 here. Inhalation alone was determined to be a 

potential pathway of concern for avian but not for mammalian species. This is based only on 

vapor inhalation, as droplet inhalation was not assessed for granular applications. Results for 

avian and mammalian species are presented in Table 10 and Table 11, respectively. 

Table 10. STIR Avian (0.020 kg) Results for Dichlobenil

Maximum Vapor Concentration in Air at Saturation (mg/m3) 4.63E+00

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 5.82E-01

Adjusted Inhalation LD50 2.96E+00

Ratio of Vapor Dose to Adjusted Inhalation LD50 1.97E-01 Proceed to Refinements
Page 34 of 51

Table 11. STIR Mammalian (0.15 kg) Results for Dichlobenil

Maximum Vapor Concentration in Air at Saturation (mg/m3) 4.63E+00

Maximum 1-hour Vapor Inhalation Dose (mg/kg) 7.31E-01

Adjusted Inhalation LD50 1.96E+02

Ratio of Vapor Dose to Adjusted Inhalation LD50 3.72E-03 Exposure not Likely Significant

The drinking water and inhalation pathways will be explored further with the development of 

SIP v.2.0 and STIR v.2.0 in the Ecological Risk Assessment. Detailed information about SIP 

v.1.0 and STIR v.1.0, as well as copies of the tools, can be found on the EPA’s website at 

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

EECs for terrestrial plants inhabiting dry and wetland areas are derived using TerrPlant (version 

1.2.2; 12/26/2006). This model uses estimates of pesticides in runoff and in spray drift to 

calculate EECs. EECs are based upon solubility, application rate and minimum incorporation 

depth. 

Available monitoring data will be used to qualitatively characterize exposure and compare with 

modeling results. The Agency is aware of monitoring conducted by Federal and state agencies 

and this route of exposure will be considered in the assessment to the extent that data on 

dichlobenil are available.

Two spray drift models, AgDisp (version 8.13; dated 12/14/2004) and AgDRIFT (version 2.01; 

dated 5/24/2001) will be used to assess exposures of terrestrial plants to dichlobenil deposited in 

terrestrial habitats by spray drift. AgDRIFT assesses risk out to 2,640 ft from the application site 

and AgDisp is then used if the risk extends beyond that range. Spray drift may occur during 

application of the liquid microencapsule formulation of dichlobenil that is applied via aerial 

spray to agricultural and non-agricultural areas. Spray drift is not a concern for the granular 

formulations. 

9.3. Measures of Effect

Ecological effect data are used as measures of direct and indirect effects to biological receptors. 

Data are obtained from registrant-submitted studies or from literature studies identified by 

ECOTOX. The ECOTOX database is searched in order to provide more ecological effects data 

to bridge existing data gaps. The most recent dichlobenil update in ECOTOX was in March 

2004. ECOTOX is a source for locating single chemical toxicity data and potential chemical 

mixture toxicity data for aquatic life, terrestrial plants, and wildlife. ECOTOX was created and 

is maintained by the US EPA, Office of Research and Development, and the National Health and 

Environmental Effects Research Laboratory's Mid-Continent Ecology Division (USEPA, 2007c).

Information on the potential effects of dichlobenil on non-target animals is also collected from 

the Ecological Incident Information System (EIIS; USEPA, 2007b). The EIIS is a database 

containing adverse effect (typically mortality) reports on non-target organisms where such 

effects have been associated with the use of pesticides. 
Page 35 of 51

Where available, sub-lethal effects observed in both registrant-submitted and open literature 

studies will be evaluated qualitatively. Such effects have included behavioral changes (e.g., 

lethargy, changes in coloration and olfaction). Quantitative assessments of risks, though, are 

limited to those endpoints that can be directly linked to the Agency’s assessment endpoints of 

impaired survival, growth and reproduction.

The assessment of risk for direct effects to non-target organisms makes the assumption that 

toxicity of dichlobenil to birds is similar to terrestrial-phase amphibians and reptiles. The same 

assumption is made for fish and aquatic-phase amphibians. 

The acute measures of effect used for animals in this screening-level assessment are the LD50, 

LC50 and EC50. LD stands for "Lethal Dose", and LD50 is the amount of a material, given all at 

once, that is estimated to cause the death of 50% of the test organisms. LC stands for “Lethal 

Concentration” and LC50 is the concentration of a chemical that is estimated to kill 50% of the 

test organisms. EC stands for “Effective Concentration” and the EC50 is the concentration of a 

chemical that is estimated to produce a specific effect in 50% of the test organisms. Endpoints 

for chronic measures of exposure for listed and non-listed animals are the NOAEL/NOAEC and 

NOEC. NOAEL stands for “No Observed-Adverse-Effect-Level” and refers to the highest tested 

dose of a substance that has been reported to have no harmful (adverse) effects on test 

organisms. The NOAEC (i.e., “No-Observed-Adverse-Effect-Concentration”) is the highest test 

concentration at which none of the observed effects were statistically different from the control. 

The NOEC is the No-Observed-Effects-Concentration. For non-listed plants, only acute 

exposures are assessed (i.e., EC25 for terrestrial plants and EC50 for aquatic plants); for listed 

plants, either the NOAEC or EC05 is used. 

9.4. Integration of Exposure and Effects

Risk characterization is the integration of exposure and ecological effects characterization to 

determine the potential ecological risk from the uses of dichlobenil listed in Table 1 and the 

likelihood of direct and indirect effects to non-target organisms in aquatic and terrestrial habitats. 

The exposure and toxicity effects data are integrated in order to evaluate the risks of adverse 

ecological effects on non-target species. For the assessment of dichlobenil risks, the risk 

quotient (RQ) method is used to compare exposure and measured toxicity values. EECs are 

divided by acute and chronic toxicity values. The resulting RQs are then compared to the 

Agency’s LOCs (USEPA, 2004). These criteria are used to indicate when uses of dichlobenil, as 

directed on the label, have the potential to cause adverse direct or indirect effects to non-target 

organisms. As noted previously, where data are lacking on the toxicity of dichlobenil, risk will 

be presumed.

 

9.4.1. Deterministic and Probabilistic Assessment Methods

The quantitative assessment of risk will primarily depend on the deterministic point-estimate 

based approach described in the risk assessment. An effort will be made to further qualitatively 

describe risk using probabilistic tools that the Agency has developed, provided sufficient data are 

available. These tools have been reviewed by FIFRA Scientific Advisory Panels and have been 
Page 36 of 51

deemed as appropriate means of refining assessments where deterministic approaches have 

identified risks.

9.5. Endangered Species Assessments

Consistent with the Agency’s responsibility under the Endangered Species Act (ESA), the

Agency will evaluate risks to federally listed threatened and/or endangered (listed) species from 

registered uses of dichlobenil. This assessment will be conducted in accordance with the 

Overview Document (USEPA, 2004), provisions of the ESA, and the Services’ Endangered 

Species Consultation Handbook (USFWS/NMFS, 1998).

The assessment of effects associated with the registration of dichlobenil is based on an action 

area. The action area is considered to be the area directly or indirectly affected by the federal 

action, as indicated by the exceedance of Agency LOCs used to evaluate direct or indirect 

effects. The Agency’s approach to defining the action area under the provisions of the Overview 

Document (USEPA, 2004) considers the results of the risk assessment process to establish 

boundaries for that action area with the understanding that exposures below the Agency’s 

defined LOCs constitute a no-effect threshold. For the purposes of this assessment, attention will 

be focused on the footprint of the action (i.e., the area where dichlobenil application occurs), plus 

all areas where offsite transport may result in potential exposure that exceeds the Agency’s 

LOCs. Specific measures of ecological effect that define the action area for listed species 

include any direct and indirect effects and/or potential modification of its critical habitat, 

including reduction in survival, growth, and reproduction as well as the full suite of sub-lethal 

effects available in the effects literature. Therefore, the action area extends to a point where 

environmental exposures are below any measured lethal or sub-lethal effect threshold for any 

biological entity at the whole organism, organ, tissue, and/or cellular level of organization. In 

situations where it is not possible to determine the threshold for an observed effect, the action 

area is not spatially limited and is assumed to be the entire United States.

9.6. Drinking Water Assessment

Drinking water exposure assessments will be conducted to support future human health risk 

assessments of dichlobenil. The drinking water assessments will incorporate model estimates of 

dichlobenil residues of concern, which are parent compound, BAM, and BZZ (USEPA, 1998b; 

DP barcode 399718, USEPA, 2012), in surface and ground waters. The dichlobenil residues of 

concern may be reevaluated pending receipt and review of additional environmental fate and 

toxicity data for dichlobenil and its degradates. BAM will be assessed alone because the 

compound has toxicity endpoints that are different from those of dichlobenil and fluopicolide. In 

the absence of toxicity data, BZZ is assumed to have similar toxicity to dichlobenil. Therefore, 

BZZ and dichlobenil will be assessed together using a total residues of concern approach.

Concentrations in surface waters will be estimated using PRZM/EXAMS and PFAM (see 

Section 9.2.1). Ground water estimates of concentrations will be estimated using the Tier I 

model Screening Concentration in Ground Water (SCI-GROW v2.3, Jul. 29, 2003) and/or 

PRZM-GW (under evaluation) according to current guidance. The drinking water assessments
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will also include a summary of available surface and ground water monitoring data. States are 

encouraged to submit monitoring data for review.

10. Endocrine Disruptor Screening Program

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 its most recent registration decision, 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), dichlobenil 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. Dichlobenil was included 

on that list and has been issued an order to conduct the Tier 1 testing. Once all required Tier 1 

and Tier 2 data have been received and reviewed, the endpoints and safety factors used for risk 

assessment purposes will be examined and a new risk assessment performed if necessary. For 

further information on the status of the EDSP, the policies and procedures, the list of 67 

chemicals, future lists, the test guidelines and the Tier 1 screening battery, please visit our 

website: http://www.epa.gov/endo/. 
Page 38 of 51

11. Preliminary Identification of Data Gaps 

11.1. Environmental Fate

Table 12 and Table 13 identify environmental fate studies by MRID that offer data for each

guideline requirement, as well as study classifications and whether or not further data are needed 

in order to support risk assessment.

Table 12. Submitted Environmental Fate Data for Dichlobenil

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Sufficient 

for 

EFED?

Current Additional Data Need

835.2120 Hydrolysis 40548502/ 

41012101

Acceptable Yes --

835.2240 Aqueous 

photolysis

40490001/ 

40490002

Unacceptable Yes --

41709801 Acceptable

835.2410 Soil photolysis 41119001 Unacceptable Yes --

43006801 Supplemental

835.4100 Aerobic soil 

metabolism

153745 Unacceptable No A guideline-compliant study of three

41340601/ additional soils is needed.

43006803

Acceptable

835.4200 Anaerobic soil 

metabolism

(None) (Not 

applicable)

Yes --

835.4300 Aerobic aquatic 

metabolism

41149501 Acceptable Yes --

835.4400 Anaerobic 

aquatic 

metabolism

41306001 Acceptable Yes --

835.1230

835.1240

Adsorption/ 

desorption and 

leaching

151561 Unacceptable Yes --

40600604 Unacceptable

41709802 Acceptable

43611101 Acceptable

835.1410 Volatility –

laboratory

43754001 Acceptable Yes --

835.6100 Terrestrial field 

dissipation

41149502/

41280802

Unacceptable Yes Analytical methods MRID 49725 and 

41149502 are upgradeable if validated by 

independent laboratories. However, 

independent laboratory validation is not 

needed to support the submitted field 

studies because they were submitted prior 

to 1996.

41170801 Unacceptable

41385601 Acceptable

43564901/ 

43522701

Supplemental

Analytical 

method in soil

49725 Upgradeable

41149502 Upgradeable
Page 39 of 51

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Sufficient 

for 

EFED?

Current Additional Data Need

835.6200 Aquatic field 

dissipation

41780601 Acceptable No Analytical methods MRID 38630, 42492, 

44712701, and 45321801 are upgradeable 

if validated by independent laboratories. 

A successful independent validation of 

MRID 45321801 is needed.

41877301/ 

42191401

Acceptable

Analytical 

method in water

38630 Upgradeable

42492 Upgradeable

44712701 Upgradeable

45321801 Upgradeable

165-4 

(850.1730)

Fish 

bioconcentration

41780601 Upgradeable Yes Additional data are not needed because 

dichlobenil’s KOW and fish BCF values 

indicate that the compound will not 

bioconcentrate in aquatic animals.

42191401 Upgradeable

40465801/

40465802

Supplemental

NonguidelineAnalytical 

method in mud

42495 Upgradeable (Not 

applicable)

Analytical methods MRID 42488, 42495, 

43924401, and 43924402 are upgradeable 

Analytical if validated by independent laboratories.

method in fish

42488 Upgradeable

Analytical 

method in 

saltwater

43924401 Upgradeable

43924402 Upgradeable

Table 13. Submitted Environmental Fate Data for the Dichlobenil Degradate, BAM

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Sufficient 

for 

EFED?

Current Additional Data Need

835.2240 Aqueous 

photolysis

45280303 Acceptable Yes --

835.4100 Aerobic soil 

metabolism

45575901 Acceptable Yes MRID 45575901 was conducted with only 

two soils. However, additional data are 

not needed because they are not expected 

to substantially change the study results.

835.4300 Aerobic aquatic 

metabolism

45539401 Unacceptable No A guideline-compliant study that confirms 

microbial activity throughout the study is 

needed.

835.1230 Adsorption/ 

desorption

45539402 Acceptable Yes --

NonguidelineAnalytical 

method in mud

42496 Upgradeable No Analytical methods MRID 42496, 42489, 

42494, 44712701, and 45321801 are

upgradeable if validated by independent 

laboratories. A successful independent 

validation of MRID 45321801 is needed.

Analytical 

method in fish

42489 Upgradeable

Analytical 

method in water

42494 Upgradeable

44712701 Upgradeable

45321801 Upgradeable

Environmental fate data for BZZ have not been submitted. Because BZZ is a residue of concern 

in drinking water exposure assessments, an adsorption/desorption study is needed.

To clarify, the following environmental fate data are needed for dichlobenil exposure 

assessment:
Page 40 of 51

Aerobic Soil Metabolism Study: Guideline 835.4100

A guideline-compliant aerobic soil metabolism study of three soils is needed for dichlobenil. 

These study data are useful for aquatic exposure modeling.

Aerobic Aquatic Metabolism Study: Guideline 835.4300

A guideline-compliant aerobic aquatic metabolism study of two systems is needed for BAM.

Microbial activity should be confirmed throughout the study. This study is important because 

BAM is a residue of concern in drinking water assessments for dichlobenil and fluopicolide.

Adsorption/Desorption Study: Guideline 835.1230

A guideline-compliant batch equilibrium study of five soils is needed for BZZ. This study is 

important because BZZ is a residue of concern in drinking water assessments for dichlobenil.

Independent Laboratory Validation: Part of Guideline 835.6200

Independent laboratory validation (ILV) is needed for the most recently submitted environmental 

chemistry method (ECM) in water, MRID 45321801. If independently validated, the level of 

quantitation (LOQ) for dichlobenil and BAM (0.10 μg/L) will be less than toxicological levels of 

concern for each compound. Without independent validation, there is uncertainty in the reported 

LOQ and whether the actual LOQ is less than toxicological levels of concern.

11.2. Effects

Table 14 and Table 15 identify ecological effects studies by MRID that offer data for each 

guideline requirement, as well as study classifications and whether or not further data are needed 

in order to support risk assessment. Rationale for the additional data requested is presented 

below the tables.

For the major degradate BAM, acute and chronic toxicity data are available for mammals, 

freshwater fish, and freshwater invertebrates and toxicity data is also available for terrestrial 

plants and for vascular and non-vascular aquatic plants. This data is nearly sufficient for the 

registration review risk assessment for dichlobenil, with one exception. Table 17 identifies an 

activated sludge respiration inhibition study that is needed for the effects assessment. A 

rationale for this request is presented below the table and in Appendix A.

For the major aquatic degradate BZZ, no toxicity data are available. Table 17 identifies 

ecological effects studies that are needed for the effects assessment and rationale for these 

requests is presented below the table.

Table 14. Submitted Aquatic Ecological Effects Data for Dichlobenil 

OCSPP

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Sufficient 

for 

EFED?

Current Additional Data Need

850.1010 Freshwater 

invertebrate 

acute toxicity

00500149 Supplemental Yes --

40094602 Supplemental

40775001 Acceptable
Page 41 of 51

OCSPP

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Sufficient 

for 

EFED?

Current Additional Data Need

850.1025

850.1035

850.1045

850.1055

Saltwater 

invertebrate 

acute toxicity 

40228401 Supplemental Yes --

43905404 Acceptable

43905405 Acceptable

850.1075 Freshwater fish 

acute toxicity 

00115756 Supplemental Yes --

43846901 Acceptable

40098001 Supplemental

850.1075 Saltwater fish 

acute toxicity 

40228401 Supplemental Yes --

43905403 Acceptable

850.1300 Freshwater 

invertebrate 

life cycle 

40775002/ 

42224201

Acceptable Yes --

850.1350 Saltwater 

invertebrates 

life cycle 

(None) (N/A) No A guideline compliant saltwater 

invertebrate life cycle test is needed.

850.1400 Freshwater fish 

early-life stage

42224202 Supplemental No A new guideline compliant study is 

needed to establish a definitive chronic 

NOAEC for freshwater fish. 

850.1400 Saltwater fish 

early-life stage

(None) (N/A) Yes --

850.1500 Fish life cycle (None) (N/A) Yes --

850.4400 Aquatic plant 

growth:

Tier II vascular 

plants

40758203 Acceptable Yes --

850.5400 Aquatic Plant 

Growth:

Tier II algae

40228401 Supplemental Yes --

40758201 Acceptable 

40758202 Acceptable

40758204 Acceptable

40758205 Acceptable

850.3300 Activated 

sludge 

respiration 

inhibition

(None) (N/A) No A study is needed to assess impacts to 

wastewater treatment facilities.

The following aquatic toxicity data are needed for dichlobenil ecological effects assessment:

Aquatic Invertebrate Life Cycle Test (Saltwater): Guideline 850.1350

Data regarding the chronic toxicity of dichlobenil TGAI to marine/estuarine invertebrates have 

not been submitted to the Agency. Acute toxicity data for marine/estuarine invertebrates are 

conditionally required under 40 CFR Part 158 (2010) data requirements for pesticides with 

outdoor uses. Dichlobenil may enter estuarine/marine systems through runoff from treated areas. 

The estimated 21-day EEC in water from the RED is >0.01 of the acute EC50 value for Eastern 
Page 42 of 51

oyster shell growth and the freshwater invertebrate life cycle study indicates that dichlobenil may 

affect reproductive physiology. Therefore, these data are necessary to determine if chronic 

exposure to dichlobenil TGAI may adversely affect the survival, growth, or reproduction of 

marine/estuarine invertebrates. 

Fish Early-Life Stage Test (Freshwater): Guideline 850.1400

Fish early-life stage data are required for one freshwater fish species. If the test species is not 

one for which an acute toxicity value is currently available, a 96-hr LC50 value on that species 

must also be provided. For dichlobenil, 96-hr LC50 values are available for the rainbow trout, 

bluegill sunfish, fathead minnow, goldfish, and green sunfish. One early-life stage test with the 

rainbow trout was submitted to the agency previously (MRID 40825101 / 42224202). This study 

does not fulfill the guideline requirement due to the failure to establish a NOAEC. Statistically 

significant reductions in length were seen at 34 days post-hatch in all concentrations tested. 

While this effect was not statistically significant at the two lowest concentrations at 60 days posthatch, the effect remained evident in the data and may have been biologically significant. 

Additionally, a transitory effect may have biological consequences of concern. Therefore, these 

data are necessary to determine the dichlobenil NOAEC and LOAEC for survival, growth, and 

reproduction of freshwater fish. 

Activated Sludge Respiration Inhibition: Guideline 850.3300

Data regarding the impact of dichlobenil TGAI to activated sludge are needed to assess impacts 

to wastewater treatment facilities (and, potentially, secondary impacts to aquatic organisms 

downstream from such facilities).

Table 15. Submitted Terrestrial Ecological Effects Data for Dichlobenil

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Sufficient 

for 

EFED?

Current Additional Data Need

850.2100 Avian oral 

toxicity

00160000 Supplemental No Acute oral toxicity data are necessary

for a passerine species. 43469801 Acceptable

850.2200 Avian dietary 

toxicity 

00022923 Supplemental Yes --

40600602 Acceptable

40600603 Acceptable

850.2300 Avian 

reproduction

45280301 Supplemental No A new guideline compliant study is 

needed to establish a definitive chronic 

NOAEC for an upland game species. 45280302 Acceptable

NonguidelineAvian 

inhalation

(None) (N/A) Yes An avian inhalation study is not 

requested due to the long terrestrial 

field dissipation half-lives, which 

indicate that the potential volatilization 

rate is not realized in the field, and the 

low screening RQ from the STIR 

model (0.2).

850.3020 Honey bee 

acute contact 

toxicity

00018842 Acceptable Yes --
Page 43 of 51

OCSPP 

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Sufficient 

for 

EFED?

Current Additional Data Need

850.3030 Honey bee 

residue on 

foliage

(None) (N/A) Yes --

850.3040 Field testing for 

pollinators

(None) (N/A) Yes --

850.4100 Terrestrial 

plant toxicity:

Tier II seedling 

emergence

41280801 Supplemental Yes --

850.4150 Terrestrial 

plant toxicity:

Tier II 

vegetative 

vigor

41280801 Invalid No A guideline compliant vegetative vigor 

study is needed.

The following terrestrial toxicity data are needed for dichlobenil ecological effects assessment:

Avian Acute Oral Toxicity Test (Passerine Species): Guideline 850.2100

Acute avian oral toxicity data are required for either one waterfowl or one upland game species 

and one passerine species under the 40 CFR Part 158 (2010) data requirements for conventional 

pesticides with outdoor uses. Submitted acute oral avian effects data show LD50s of 683 mg 

a.i./kg-bw for the bobwhite quail (MRID 43469801), 1189 mg a.i./kg-bw for the ring-necked 

pheasant, and >2,000 mg a.i./kg-bw for the mallard duck (MRID 00160000). Because passerine 

species have higher metabolic rates due to their smaller sizes than either waterfowl or upland 

game bird species and because they may utilize different metabolic pathways, they may be more 

or less sensitive to dichlobenil. The RED assessment demonstrated LOC exceedance from 

ingestion of dichlobenil granules to listed and non-listed birds based on the bobwhite quail LD50. 

A passerine study protocol should be submitted for review by the Agency prior to initiation of 

the study. 

Avian Reproduction: Guideline 850.2300

Avian reproduction data are required for one waterfowl and one upland game species for all 

outdoor use pesticides. These data were requested in the RED and subsequently submitted to the 

Agency. The study using the mallard duck was found to be an acceptable study. The study 

using the bobwhite quail was found to be supplemental and does not fulfill the guideline 

requirement due to the failure to establish a definitive NOAEC value. Reproductive effects were 

observed at the lowest concentration tested, 146 ppm (MRID 45280301). Therefore, an 

acceptable avian reproduction study for one upland game species, preferably the bobwhite quail, 

is necessary to determine the dichlobenil NOAEC and LOAEC for survival, growth, and 

reproduction of this species.

Terrestrial Plant Toxicity (Vegetative Vigor): Guideline 850.4150

Acceptable data regarding the toxicity of dichlobenil to terrestrial plants have not been submitted 

to the Agency. These data are required under the 40 CFR Part 158 (2010) data requirements for 

pesticides with outdoor uses. At the time of the RED, the Agency did not request a new 
Page 44 of 51

vegetative vigor study because vegetative vigor studies are not generally required for granular 

formulations. However, since 2007 dichlobenil has had a liquid microencapsule formulation 

registered that is applied via aerial spray. Vegetative vigor data are necessary to determine 

whether the outdoor use of the microencapsulated formulation of dichlobenil could adversely 

affect vegetative vigor of non-target plant species in the terrestrial environment. If a Tier I study 

exhibits a ≥25% effect, or if a NOAEC cannot be established when conducted as a limit test, a 

Tier II study is required.

Table 16. Aquatic Ecological Effects Data for the Dichlobenil Degradate, BAM

OCSPP

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Sufficient 

for 

EFED?

Current Additional Data Need

850.3300 Activated 

sludge 

respiration 

inhibition

(None) (N/A) No A study is needed to assess impacts to 

wastewater treatment facilities.

The following aquatic toxicity data are needed for dichlobenil ecological effects assessment:

Activated Sludge Respiration Inhibition: Guideline 850.3300

Data regarding the impact of the major aquatic dichlobenil degradate BAM to activated sludge 

are needed to assess impacts to wastewater treatment facilities (and, potentially, secondary 

impacts to aquatic organisms downstream from such facilities). A sample Data Call-In (DCI) 

table is provided in Appendix A.

Table 17. Aquatic Ecological Effects Data for the Dichlobenil Degradate, BZZ

OCSPP

Guideline

Data 

Requirement

Submitted 

Studies 

(MRID)

Study 

Classifications

Sufficient 

for 

EFED?

Current Additional Data Need

850.1075 Freshwater fish 

acute toxicity 

(None) (N/A) No A guideline compliant freshwater fish 

acute toxicity study is needed.

850.4400 Aquatic plant 

growth:

Tier II vascular 

plants

(None) (N/A) No A guideline compliant vascular aquatic 

plant study is needed.

The following aquatic toxicity data are needed for dichlobenil ecological effects assessment:

Fish Acute Toxicity Test (Freshwater): Guideline 850.1075

Data regarding the acute toxicity of major aquatic dichlobenil degradate BZZ to aquatic 

organisms have not been submitted to the Agency. Acute toxicity data for the freshwater fish 

rainbow trout (Oncorhychus mykiss), the most acutely sensitive freshwater aquatic animal to the 

parent, dichlobenil, are needed to determine if exposure to the degradate may adversely affect the 

survival of freshwater animals. High application rates and a lack of reliable toxicity estimates 

from ECOSAR, the Agency’s Ecological Structure Activity Relationships program, result in the 

need for empirical data.
Page 45 of 51

Vascular Aquatic Plant Toxicity Test: Guideline 850.4400

Data regarding the acute toxicity of aquatic dichlobenil degradate BZZ to aquatic plants have not 

been submitted to the Agency. Toxicity data for duckweed (Lemna gibba), the most sensitive 

aquatic plant to the parent, dichlobenil, are needed to determine if exposure to the degradate may 

adversely affect the survival or growth of freshwater plants. High application rates and a lack of 

reliable toxicity estimates from ECOSAR, the Agency’s Ecological Structure Activity 

Relationships program, result in the need for empirical data.

12. References 

MRID Citation

Environmental Fate and Product Chemistry Studies

40465801 Van Kampen, W.; Joustra, K.; Scherpenisse, P. (1987) The Identity of the 14C Residues in 

Aquarium Water, Viscera and Fillet Samples of Bluegill Sunfish of ABC-laboratories, 

Bioconcentration Study # 35168 with Dichlobenil: Laboratory Project ID C.201.62.001. 

Unpublished study prepared by Duphar B.V. 39 p. 

40465802 Forbis, A. (1986) Uptake, Depuration and Bioconcentration of 14C -dichlobenil to Bluegill Sunfish 

(Lepomis macrochirus): ABC Laboratory Project ID Report #35168. Unpublished study prepared 

by Analytical Bio-Chemistry Laboratories, Inc. 250 p. 

40548502 Buisman, P. (1983) Stability and Solubility of Dichlobenil in Water: Laboratory Project ID: 82-4 

AUV 82R008. Unpublished study prepared by Duphar B.V. 21 p. 

40600605 Van Berkel, M.; De Kok, H.; Olthof, J. (1987) Physical and Chemical Characteristics of 

Dichlobenil: Project ID: C.201.20.003. Unpublished study prepared by Duphar B.V. 15 p.

40600607 Jager, H.; Harteveld, J. (1987) The Vapour Pressure of 2,6-Dichlorobenzonitrile: Project ID: 

132386156. Unpublished study prepared by Prins Maurits Laboratorium, TNO. 19 p.

40600608 Thus, J. (1984) Determination by HPLC of the Log P Value of Dichlobenil and its Main 

Metabolite: Int. Doc. No. 56635/12/85. Un- published study prepared by Duphar B.V. 11 p.

41012101 Pouwelse, A. (1983) Stability and Solubility of Dichlobenil in Water Additional Data to Report 

56630/207/87 (MRID No. 40548502): Project ID: 82-4 AUV 82R008. Unpublished study 

prepared by Duphar B.V. 27 p. 

41149501 Gohdes, M. (1989) Aerobic Aquatic Metabolism of ?Carbon 14| Dichlo- benil: Final Report: 

Laboratory Project ID No. HLA 6015-360: Duphar Study No. C.201.62.004. Unpublished study 

prepared by Hazleton Laboratories America, Inc. 80 p. 

41306001 Saxena, A. (1989) Anaerobic Aquatic Metabolism of 14C -Dichlobenil: Lab Project Number: 

HLA/6015/361. Unpublished study prepared by Hazleton Laboratories America, Inc. 123 p. 

41340601 Walstra, P.; Groeneveld, A.; VanderLaan-Straathof, J.; et al. (1989) Aerobic Soil Metabolism of 

Dichlobenil in Sandy Loam: Project Number: C-201-62-007. Unpublished study prepared by 

Duphar B.V. 29 p.

41385601 Hughes, D. (1990) Determination of Dichlobenil and 2,6-Dichlorobenzamide in Soil from a 

Hillsboro, Oregon Field Trial: Lab Project Number: HLA 6012-182. Unpublished study prepared 

by Hazleton Laboratories America, Inc. 418 p. 

41709801 Boelhouwers, E.; Joustra, K.; Klein, G. et al. (1989) Photodegradation of [14C]Dichlobenil in 

Water: Lab Project Number: C.201.62.010. Unpublished study prepared by Duphar B.V. 74 p. 

41780601 Jacobson, B.; Judy, D.; Whithaus, M. (1991) Combined Aquatic Field Dissipation and 

Bioaccumulation Study on Aquatic Non-Target Organisms for Casoron 10G in Florida: Lab 

Project Number: 36831; 56635/63/90; C201.60.005. Unpublished study prepared by Analytical 

Bio-Chemistry Labs in coop. with Southern Ag. Research, Inc. 580 p. 

41877301 Jacobson, B.; Judy, D.; Whithaus, M. (1991) Combined Aquatic Field Dissipation and 

Bioaccumulation Study on Aquatic Non-Target Organisms for Casoron 10G in Oregon: Lab 

Project Number: 36832: 56635/01/91: C 201 60 006. Unpublished study prepared by Analytical 

Bio-chemistry Laboratories, Inc. 553 p. 
Page 46 of 51

MRID Citation

42191401 Jacobson, B. (1991) Combined Aquatic Field Dissipation and Bioaccumulation Study on Aquatic 

Non-target Organisms for Casoron 10G in Oregon: Lab Project Number: 36832: 56635/01/91: 

C20160006. Unpublished study prepared by ABC Laboratories, Inc. 7 p. 

43006801 Kabler, K.; Carpenter, M. (1993) Photodegradation Study of 14C-Dichlobenil on Soil Surface: 

Amended Final Report: Lab Project Number: 37135: CA-2853. Unpublished study prepared by 

Analytical Bio-Chemistry Labs, Inc. 41 p. 

43006803 Judy, D. (1993) A Comparison of the Udenhout Soil from the Netherlands with Soil Types from 

the United States: Final Report: Lab Project Number: 41226: 56835/50/93. Unpublished study 

prepared by ABC Labs, Inc. 22 p. 

43522701 Pouwelse, A.; van Loo, T. (1991) 2,6-Dichlorobenzonitrile and 2,6-Dichlorobenzamide Residues 

in Soil from a Dissipation Study of Casoron G (Germany 1989/1990). Addendum to Int. Doc. NO. 

56630/87/91: Lab Project Number: C/201/60/008: 56630/9/92: CA/2944. Unpublished study 

prepared by Solvay Duphar B.V. Analytical Development Dept. 11 p. 

43564901 Pouwelse, A.; van Loo, T. (1991) 2,6-Dichlorobenzonitrile and 2,6-Dichlorobenzamide Residues 

in Soil from 4 Terrestrial Field Dissipation Trials with Casoron G (Germany 1989/1990): Lab 

Project Number: C/201/60/008: 56630/87/91. Unpublished study prepared by Duphar B.V. 

Analytical Development Dept. 76 p. 

43754001 Van der Laan-Straathof, J. (1995) Determination of the Volatility of Dichlobenil from Casoron G4 Under Laboratory (Simulated Field) Conditions: Lab Project Number: C.201.62.020: 

56834/13/95. Unpublished study prepared by Solvay Duphar B.V. 33 p. 

45280303 Reynolds, J. (2000) Photolysis of [

14C] 2,6-Dichlobenzamide in Water Buffered at pH 5: Lab 

Project Number: XBL00041: RPT00626: 2000-088. Unpublished study prepared by XenoBiotic 

Laboratories, Inc. 84 p. 

45539401 Whitright, R. (2001) Aerobic Aquatic Metabolism of [14C] 2,6-Dichlobenzamide: Lab Project 

Number: 2000-089. Unpublished study prepared by Uniroyal Chemical Company. 125 p. 

45539402 Dzialo, D. (2001) Adsorption/Desorption of [14C] 2,6-Dichlobenzamide: Lab Project Number: 00-

1561: 00-2103: 01-86. Unpublished study prepared by Uniroyal Chemical Company 236 p. 

45575901 Griffen, D.S. (2002) Aerobic Soil Metabolism of 14C-2,6-Dichlorobenzamide (BAM): Study No. 

2000-103. Unpublished study prepared by Uniroyal Chemical Company, Inc. 141 p.

43611101 Thus, J.; van der Laan-Straathof, J. (1995) Adsorption/Desorption Test with Dichlobenil in Four 

Different Agricultural Soils and One Hydrosoil: Lab Project Number: C/201/62/019: 56835/53/94. 

Unpublished study prepared by Solvay Duphar B.V. Environmental Research Dept. 51 p. 

Ecological Effects Studies

00018842 Atkins, E.L., Jr., L.D. Anderson, E.A. Greywood (1969) Effect of Pesticides on Apiculture: 

Project No. 1499; Research Report CF-7501. (Unpublished Study Received May 8, 1971 under 

1F1174; Prepared by Univ. of California, Riverside, Dept. of Entomology, Submitted by Ciba 

Agrochemical Co., Summit, N.J., CDL:090973-B.

00022923 Hill, E.F.; Heath, R.G.; Spann, J.W.; et al. (1975) Lethal Dietary Toxicities of Environmental 

Pollutants to Birds: Special Scientific Report--Wildlife No. 191. (U.S. Dept. of the Interior, Fish 

and Wildlife Service, Patuxent Wildlife Research Center; unpublished report)

00112500 International Bio-Research, Inc. (1962) Acute Toxicity Study on Rats for Casoron. (Unpublished 

study received Oct 1, 1963 under 6F0500; submitted by Thompson-Hayward Chemical Co., 

Kansas City, KS; CDL:090576-B)

00147437 Koeter, H. (1984) Oral Embryotoxicity/Teratogenicity Study with Dichlobenil in Rats: Final 

Report: Report No. V 84.026/231045. Unpublished study prepared by Netherlands Organization 

for Applied Scientific Research. 109 p.

00156312 Van Leeuwen, C.J.; Maas, H. (1985) The Aquatic Toxicity of 2,6-Dichlorobenzamide (BAM), a 

Degradation Product of the Herbicide Dichlobenil. Environmental Pollution (Series A) 37:105-

115.

00160000 Hudson, R.; Tucker, R.; Haegele, M. (1984) Handbook of toxicity of pesticides to wildlife: Second 

edition. US Fish and Wildlife Service: Resource Publication 153. 91 p.

00500149 Sanders, H.O. (1970) Toxicities of some herbicides to six species of freshwater crustaceans. 

Journal of the Water Pollution Control Federation 42(8):1544-1550.
Page 47 of 51

MRID Citation

40094602 Johnson, W.; Finley, M. (1980) Handbook of Acute Toxicity of Chemicals to Fish and Aquatic 

Invertebrates: Resource Publication 137. USDI Fish and Wildlife Service, Washington, D.C. 98 p.

40098001 Mayer, F.; Ellersieck, M. (1986) Manual of Acute Toxicity: Interpretation and Data Base for 410 

Chemicals and 66 Species of Freshwater Animals. US Fish & Wildlife Service, Resource 

Publication 160. 579 p.

40228401 Mayer, F. (1986) Acute Toxicity Handbook of Chemicals to Estuarine Organisms: EPA/600/X86/231. Prepared by US EPA Environmental Research Laboratory, Gulf Breeze, Fl. 275 p.

40600601 Roberts, N.; Hakin, B. (1987) The Acute Oral Toxicity (LD50) of Dichlobenil to the Mallard 

Duck: PDR 474/871611. Unpublished study prepared by Huntingdon Research Centre Ltd. 24 p.

40600602 Roberts, N.; Hakin, B. (1987) The Dietary Toxicity (LC50) of Dichlobenil to the Mallard Duck: 

PDR 475/871500. Unpublished study prepared by Huntingdon Research Centre Ltd. 18 p.

40758201 Giddings, J. (1988) Toxicity of Dichlobenil to the Freshwater Green Alga: Laboratory Project ID 

11493-0787-6107-550. Unpublished study prepared by Springborn Life Sciences, Inc. 31 p.

40758202 Giddings, J. (1988) Toxicity of Dichlobenil to the Blue-green Alga: Anabaena flos-aguae: 

Laboratory Project ID 11493-0787-6107-550. Unpublished study prepared by Springborn Life 

Sciences, Inc. 28 p.

40758203 Giddings, J. (1987) Toxicity of Dichlobenil to the Freshwater Plant: Lemna gibba G3: Laboratory 

Project ID 11493-0787-6108-550. Unpublished study prepared by Springborn Life Sciences, Inc. 

22 p.

40758204 Giddings, J. (1988) Toxicity of Dichlobenil to the Freshwater Diatom: Navicula pelliculosa: 

Laboratory Project ID 11493-0787-6107-550. Unpublished study prepared by Springborn Life 

Sciences, Inc. 22 p.

40775001 Burgess, D. (1987) Acute Flow-Through Toxicity of Dichlobenil to Daphnia magna: Project ID. 

36180. Unpublished study prepared by Analytical Bio-Chemical Laboratories, Inc. 24 p.

40775002/

42224201

Forbis, A. (1988) Chronic Toxicity of Dichlobenil to Daphnia magna Under Flow-Through Test 

Conditions: Project ID 36181. Unpublished study prepared by Analytical Bio-Chemical 

Laboratories, Inc. 30 p.

41257302 Barker, L. (1989) Dichlbenil: Oral (Gavage) Teratology Study in the Rabbit (Experiment II): 

Repeat Study: Laboratory Project ID 5942-65/190: Duphar Report No. 56645/21/89. Unpublished 

study prepared by Hazleton UK. 143 p.

41257303 Leeming, N. (1989) Dichlobenil: 2 Generation Oral (Dietary Administration) Reproduction Study 

in the Rat: Laboratory Project ID 5798-65/18. Unpublished study prepared by Hazleton UK. 337 

p.

41280801 Eussen, J. (1989) The Effect of Dichlobenil on Seed Germination, Seedling Emergence and 

Vegetative Vigor of Non-target Terrestrial Plants: Lab Project Number: C/201/51/007: 

56656/30/89. Unpublished study prepared by Duphar B.V. Agrobiological Laboratory 

Boekesteyn. 72 p.

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MRID Citation

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Page 51 of 51

Appendix A. Sample Data Call-In Table

The following proposed Data Call-in table includes a rationale for requiring the activated sludge 

respiration inhibition data requested in this problem formulation, an explanation of the utility of 

the data, and an explanation for how the data might impact risk assessment, following the format 

provided by the Pesticide Re-evaluation Division.

Guideline Number: 850.3300

Study Title: Activated Sludge Respiration Inhibition

Rationale for Requiring the Data

The Agency has a limited understanding of the impact of dichlobenil and its major degradate BAM on 

wastewater treatment facilities following the use of dichlobenil in wastewater collection systems. 

Depending on how quickly and to what extent dichlobenil, BAM, or both compounds inhibit activated 

sludge respiration, use of dichlobenil in wastewater collection systems may or may not pose potential 

interference with wastewater treatment facilities (and potential secondary impacts to aquatic organisms 

downstream from such facilities).

In order to better understand the impact of dichlobenil and its major degradate BAM on wastewater 

treatment facilities following the use of dichlobenil in wastewater collection systems, the Agency is 

requiring an activated sludge respiration inhibition study of dichlobenil TGAI and of its major degradate 

BAM.

Practical Utility of the Data

How will the data be used?

Submission of an acceptable activated sludge respiration inhibition study will facilitate a better 

understanding of whether dichlobenil use in wastewater collection systems may impact wastewater 

treatment facilities. If data indicate that dichlobenil, BAM, or both compounds inhibit activated sludge 

respiration at concentrations relevant to wastewater treatment facilities, then the Agency could 

potentially determine that dichlobenil use in wastewater collection systems may impact wastewater 

treatment facilities and may result in secondary impacts to aquatic organisms downstream from such 

facilities. If data indicate that dichlobenil, BAM, or both compounds do not inhibit activated sludge 

respiration at concentrations relevant to wastewater treatment facilities, then the Agency could 

potentially determine that use of dichlobenil in wastewater collection systems is not expected to impact 

wastewater treatment facilities.

How could the data change the Agency’s decision, or impact the Agency’s future decisionmaking? 

In the absence of adequate activated sludge respiration inhibition data, dichlobenil use in wastewater 

collection systems will be assumed to pose a potential hazard to wastewater treatment facilities and to 

aquatic organisms downstream from such facilities. If the required data indicate that dichlobenil and 

BAM do not inhibit activated sludge respiration at concentrations relevant to wastewater treatment 

facilities, then risk assessment conclusions and associated labeled use precautions and/or restrictions 

could change.