registration review of pyridaben. This document recommends studies that should be included in a 

generic data call-in (DCI) to address uncertainties surrounding the environmental fate and 

potential ecological effects of pyridaben. 

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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

Problem Formulation for the Environmental Fate, 

Ecological Risk, Endangered Species, and Drinking 

Water Exposure Assessments in Support of the 

Registration Review of Pyridaben 

N

N

CH3

3CH

CH3

O

S

Cl

C

H2

CH3

CH3

CH3

2-tert-butyl-5-(4-tert-butylbenzylthio)-4-chloropyridazin-3(2H)-one 

CAS Registry Number: 96489-71-3 

PC Code: 129105 

Prepared by:

Kristina Garber, Biologist 

Reuben Baris, Environmental Scientist 

Reviewed by: 

Brian Kiernan, Biologist 

Cheryl Sutton, Ph.D., Environmental Scientist 

Mark Corbin, Branch Chief ERB6 

Marietta Echeverria, Acting Branch Chief ERB4

U. S. Environmental Protection Agency 

Office of Pesticide Programs 

Environmental Fate and Effects Division

Environmental Risk Branch IV 

1200 Pennsylvania Ave., NW 

Mail Code 7507P 

Washington, DC 20460

August 26, 2010 

-3 of 62-
Table of Contents 

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

2. Problem Formulation .............................................................................................................. 5 

2.1. Nature of Regulatory Action........................................................................................... 5 

2.2. Conclusions from Previous Risk Assessments ............................................................... 5 

2.2.1. Ecological Risk Assessments.................................................................................. 5 

2.2.2. Drinking Water Exposure Assessments.................................................................. 6 

3. Stressor Source and Distribution ............................................................................................ 6 

3.1. Mechanism of Action...................................................................................................... 6

3.2. Overview of Pesticide Use and Usage............................................................................ 7 

3.3. Environmental Fate and Transport.................................................................................. 8 

3.4. Degradates of Concern.................................................................................................. 10 

3.5. Water Quality................................................................................................................ 11 

4. Receptors............................................................................................................................... 12 

4.1. Effects of Pyridaben to Aquatic Organisms.................................................................. 12 

4.2. Effects of Pyridaben to Terrestrial Organisms.............................................................. 14 

4.3. Effects of Pyridaben’s Degradates of Concern to Non-Target Organisms................... 15 

4.4. Incident Databases Review........................................................................................... 15 

4.5. Ecosystems Potentially at Risk ..................................................................................... 16 

5. Consideration of Persistent, Bioaccumulative and Toxic Properties of Pyridaben .............. 16 

6. Assessment Endpoints .......................................................................................................... 17 

7. Conceptual Model................................................................................................................. 18 

7.1. Risk Hypothesis ............................................................................................................ 18 

7.2. Conceptual Diagram ..................................................................................................... 18 

8. Analysis Plan ........................................................................................................................ 20 

8.1. Stressors of Concern ..................................................................................................... 20 

8.2. Measures of Exposure................................................................................................... 21 

8.3. Measures of Effect ........................................................................................................ 22 

8.4. Integration of Exposure and Effects ............................................................................. 23 

8.5. Deterministic and Probabilistic Assessment Methods.................................................. 24 

8.6. Endangered Species Assessments................................................................................. 24 

8.7. Drinking Water Assessment ......................................................................................... 25 

8.8. Preliminary Identification of Data Gaps....................................................................... 25 

8.8.1. Environmental Fate Data ...................................................................................... 25 

8.8.2. Effects Data........................................................................................................... 27 

9. References............................................................................................................................. 32 

9.1. Scientific Literature and Government Publications...................................................... 32 

9.2. Submitted Environmental Fate and Product Chemistry Studies................................... 33 

9.3. Submitted Effects Studies............................................................................................. 34 

APPENDIX A: Current Registrations for Pyridaben................................................................... 37 

APPENDIX B: Characterization of Environmental Fate Data for Pyridaben ............................. 38 

APPENDIX C: Characterization of Ecological Effects Data for Pyridaben ............................... 43 

APPENDIX E: PRZM/EXAMS Input Parameters...................................................................... 51 

APPENDIX F: Data Call-In Tables............................................................................................. 52 

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1. Purpose 

The purpose of this problem formulation is to provide an understanding of what is known about 

the environmental fate and ecological effects of pyridaben, considering its currently registered 

uses. Pyridaben is a selective contact insecticide and miticide that controls pests in apples, citrus 

(including non-bearing nursery beds), cranberries, grapes, pears (including Asian varieties), 

stone fruit (e.g., apricots, cherries, nectarines, peaches, plums, and prunes), tree nuts (e.g., 

almond, beech, brazil, butternut, cashew, chestnut, chinquapin, filbert, hickory, macadamia, 

pecan, black walnut, English walnut, and pistachios), and commercially grown ornamentals. This 

document provides a plan for analyzing data relevant to pyridaben and for conducting 

environmental fate, ecological risk, endangered species, and drinking water exposure 

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 pyridaben. 

2. Problem Formulation 

2.1. Nature of Regulatory Action 

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

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

Agency (EPA). In determining whether a pesticide can be registered in the United States, the 

Agency evaluates its safety to non-target species based on a wide range of environmental and 

health effects studies. In 1996, FIFRA was amended by the Food Quality Protection Act, and the 

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

registration review (http://www.epa.gov/oppsrrd1/registration_review/). The Registration 

Review program is intended to ensure that, as the ability to assess risk evolves and as policies 

and practices change, all registered pesticides continue to meet the statutory standard of no 

unreasonable adverse effects to human health and the environment. Changes in science, public 

policy, and pesticide use practices will occur over time. Through the Registration Review 

program, the Agency periodically reevaluates pesticides to make sure that as change occurs, 

products in the marketplace can be used safely. 

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

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

evaluation of pyridaben to determine whether it continues to meet the FIFRA standard for 

registration. This problem formulation for the environmental fate, ecological risk, endangered 

species, and drinking water exposure assessments in support of the registration review will be 

posted in the initial docket that will open the public phase of the review process. 

 

2.2. Conclusions from Previous Risk Assessments 

2.2.1. Ecological Risk Assessments 

Pyridaben is a contact insecticide/miticide that was first registered in 1996 for use on citrus 

groves, apple orchards, pears, and almonds (Case No. 015679). In 2004, an ecological risk 

assessment was conducted for proposed new uses of pyridaben on strawberries, hops, tropical 

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fruit, and stone fruit (D285563+). The assessment concluded that pyridaben (parent only), at the 

proposed maximum use rates, exceeds acute and chronic risk levels of concern for freshwater 

fish and invertebrates, acute risk for estuarine/marine fish and invertebrates, and chronic risk for 

birds and mammals for the proposed uses. 

EFED recently (August 2010) completed an ecological risk assessment of a special local needs 

use of pyridaben on pears in the state of Washington. This assessment concluded that based on 

maximum application rates, exposure levels and available effects data, pyridaben applied to 

pears in Washington at 0.75 lb a.i./A, has the potential to cause effects to survival, growth and 

reproduction of aquatic animals and terrestrial mammals and effects to the reproduction of birds, 

terrestrial-phase amphibians and reptiles. This includes non-listed and listed species. Because 

pyridaben is highly toxic to bees on an acute exposure basis, there is potential for acute effects to 

beneficial insects. Effects to non-listed terrestrial and wetland plants are not expected; however, 

risks to listed plants cannot be precluded. Because no toxicity data are available to characterize 

the effects of pyridaben to aquatic plants, risks to aquatic plants cannot be precluded. There is 

also potential for indirect effects to species that depend on those that may be directly affected by 

pyridaben (i.e., fish, aquatic and terrestrial invertebrates, mammals and birds). 

2.2.2. Drinking Water Exposure Assessments 

The Agency conducted three drinking water exposure assessments for pyridaben from 1999 to 

2004 in support of the establishment of tolerances for use on cranberries, and the proposed new 

uses on strawberries, hops, tropical fruit, and stone fruit (USEPA, 1999a&b; USEPA, 2004a). 

The most recent assessment (USEPA, 2004a) reported screening-level acute and chronic 

concentrations of pyridaben in surface water at 5.5 μg/L and 1.4 μg/L, respectively, and a 

screening-level ground water concentration of 0.006 μg/L, which is the same concentration 

reported for ground water in the 1999 assessments (D258903 & D259315). The Agency 

concluded that pyridaben is not likely to be a significant ground water contaminant. However, 

the Agency noted that compounds such as pyridaben with Koc values greater than 9995 ml/g are 

beyond the scope of the regression data used in SCI-GROW development; therefore, if ground 

water contamination by pyridaben is a concern, the Agency recommended a higher tier ground 

water exposure assessment be considered, regardless of the concentration returned by SCIGROW. In the 2004 assessment, estimated drinking water concentrations (EDWCs) were 

reported for pyridaben only (parent only). Degradates identified by the Health Effects Division to 

be of toxicological concern (PB 7 and PB9) were not included in the drinking water assessment 

since they were not identified in fate studies great enough to impact environmental modeling 

inputs for pyridaben. 

3. Stressor Source and Distribution 

3.1. Mechanism of Action 

Pyridaben is a selective contact pesticide used to control a wide variety of mites and other 

insects. It is an inhibitor of glutamate-dependent mitochondrial respiration in both vertebrates 

and invertebrate systems and specifically inhibits NADH:CoQ oxidoreductase activity 

(Hollingworth et al. 1994). 

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3.2. Overview of Pesticide Use and Usage 

Currently, there are seven national registrations (Section 3) for formulated products that contain 

pyridaben. These formulations are water soluble packets, wettable powders, or aqueous 

suspensions. There are three registrations for technical pyridaben that are used to create 

formulated products. In addition, there are six special local needs [SLNs; Section 24(c)] 

registrations. These special local needs registrations apply to greenhouse tomatoes grown in 

Arizona, Maine, Minnesota, Pennsylvania, and Texas, and pears grown in Washington. The 

greenhouse uses will not be considered in ecological risk assessments associated with pyridaben 

since exposure to non-target organisms is not expected from the greenhouse uses of pyridaben. A 

list of the registrations is provided in Appendix A. 

Pyridaben is registered for use on citrus, cranberries, grapes, stone fruits and tree nuts applied 

twice at a single maximum application rate of 0.5 lb a.i./A (annual maximum rate is 1.0 lbs 

a.i./A/yr). Pyridaben is also registered on apples and pears for one application (per season) at a 

maximum single application of 0.5 lb a.i./A. Currently, there is an active SLN in Washington for 

pears that allows for one application (per season) at a maximum single application of 0.75 lb 

a.i./A. Pyridaben is also registered for use on commercially grown ornamental plants at a single 

maximum rate of 1.0 lb a.i./A (per season). Applications are allowed by ground spray only, with 

the exception of chemigation applications that may be made to cranberries. Aerial applications of 

pyridaben are prohibited on product labels. Maximum single application rates for pyridaben, 

number of applications per year, application intervals and application methods are provided in 

Table 3.1. 

TABLE 3.1. Maximum Use Patterns and General Management Practices for Pyridaben. 

Use 

Single max 

application 

rate (lb a.i./A) 

Number 

of app. 

per year 

Application 

interval (d) 

Annual max 

application rate 

(lbs a.i./A/yr) 

Application 

method(s) 

Almonds 0.5 2 30 1.0 Ground spray 

Apples 0.5 1 30 0.5 Ground spray 

Apricots1 0.5 2 30 1.0 Ground spray 

Beech Nut 0.5 2 30 1.0 Ground spray 

Brazil Nut 0.5 2 30 1.0 Ground spray 

Butternut 0.5 2 30 1.0 Ground spray 

Cashew 0.5 2 30 1.0 Ground spray 

Cherries1 0.5 2 30 1.0 Ground spray 

Chestnut 0.5 2 30 1.0 Ground spray 

Chinquapin 0.5 2 30 1.0 Ground spray 

Citrus 0.5 2 90 1.0 Ground spray 

Cranberries2 0.5 2 30 1.0 Ground spray, 

chemigation 

Filbert 0.5 2 30 1.0 Ground spray 

Grapes 0.5 2 30 1.0 Ground spray 

Hickory 0.5 2 30 1.0 Ground spray 

Macadamia 0.5 2 30 1.0 Ground spray 

Nectarines 0.5 2 30 1.0 Ground spray 

Peaches 0.5 2 30 1.0 Ground spray 

Pear 0.5 1 30 0.5 Ground spray 

Pear (SLN)3 0.75 1 30 0.75 Ground spray 

-7 of 62-
Use 

Single max 

application 

rate (lb a.i./A) 

Number 

of app. 

per year 

Annual max Application Application application rate interval (d) method(s) (lbs a.i./A/yr) 

Pecan 0.5 2 30 1.0 Ground spray 

Pistachio 0.5 2 30 1.0 Ground spray 

Plums 0.5 2 30 1.0 Ground spray 

Prunes 0.5 2 30 1.0 Ground spray 

Ornamental Plants4 1.0 1 No successive 

treatments 

1.0 Ground spray 

Stone Fruit 0.5 2 30 1.0 Ground spray 

Walnut (Black and English) 0.5 2 30 1.0 Ground spray 

NA = not applicable 

SLN = special local needs registration 

1

 Except in California. 

2

 Allowed only in CT, DE, ME, MA, NH, NJ, RI, and VT. 

3

 Allowed in Washington only. 

4

 Use on greenhouse and outdoor ornamental plants and foliage crops. 

3.3. Environmental Fate and Transport 

Pyridaben (2-tert-butyl-5-(4-tert-butylbenzylthio)-4-chloropyridazin-3(2H)-one, 

CAS RN: 96489-71-3) is a semi-volatile, hydrophobic compound that is hardly mobile in soil 

based on the FAO soil mobility classifications (Koc’s >10,000) (USEPA, 2006). Pyridaben is 

semi-volatile, with a vapor pressure of 8.21 x 10-5 torr (MRID 42676103) and a unitless Henry's 

Law Constant of 0.07 (calculated). However, based on the compound's tendency to sorb to soil 

(Koc > 10,000; MRID 42680155) and plants (LogKow = 6.37; MRID 42676103), pyridaben is 

not expected to volatilize when applied to the surfaces of soil or plants. Pyridaben dissipates in 

the environment through abiotic and biotic degradation (primary route of degradation is 

photolysis, both aqueous and from soil). The compound is persistent in aerobic soil (half-life of 

110 days). Pyridaben is stable to hydrolysis at pH 5, 7, and 9. The persistence of pyridaben in 

aquatic environments (both aerobic and anaerobic) is uncertain as there are no acceptable studies 

available that report this data. However due to its high tendency to bind to soil, it is likely to 

partition quickly to the sediment in aquatic environments. Terrestrial field dissipation data 

indicate that the compound dissipates, with dissipation half-lives (DT50s) in the top 12” of soil 

ranging from 12 to 14 days (DT90s ranged from 120 to 629 days); the compound was not 

detected below 12”. The field studies illustrate that initially pyridaben degrades rather quickly, 

but tends to persist much longer at lower concentrations once the DT50 has been achieved (i.e., 

the compound degrades much slower after the initial DT50). 

Table 3.4 summarizes the submitted environmental fate data for pyridaben. Additional 

characterization of the submitted environmental fate data is located in Appendix B. 

There was one major degradate (4-tert-butyl benzyl a1coho1, B-3) was identified in the 

definitive aqueous photolysis study, however it was not found at >10% in the quantitative 

portion of the study. There were no major degradates of pyridaben identified in the remaining 

environmental fate studies. There were several minor degradates that were identified, some with 

concentrations approaching 10% of the applied at the study termination (e.g., PB-4). These 

compounds include: 

• 2-tert-Butyl-5-(4-tert-butylbenzylsulfinyl)-4-chloropyridazin-3(2H)-one (PB-4), 

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• 2-tert-Butyl-5-[4-(1-carboxy-1-methylethyl)benzylthio]-4-chloropyridazin-3(2H)-one (PB-7), 

• 2-tert-butyl-4-chloro-5-[4-(1,1-dimethyl-2-hydroxyethyl) benzylthio]pyridazin-3(2H)-one (PB-9), 

• 2-tert-Butyl-4-(4-tert-butylbenzoyl)-pyridazin-3(2H)-one-5-sulfonic acid (P-14), 

• 2-tert-Butyl-4-(4-tert-butylbenzyl)-pyridazin-3(2H)-one-5-sulfonic acid (PB-14), and 

• 4-Chloropyridazin-3(2H)-one-5-sulfonic acid (PB-16). 

Bioconcentration data are available from two separate BCF laboratory studies involving rainbow 

trout (MRID 43792113). After 28 days of exposure to pyridaben (0.11 μg a.i./L), whole fish 

BCF values (based on total radioactivity) were 342 and 439 (μg/kg-ww per μg/L). Metabolites 

were identified in the fish tissue; however, their levels were not quantified. Identified metabolites 

included: PB-5, PB-7, PB-9, PB-10, PB-11, PB-12 and PB-13. In a life cycle test with fathead 

minnows (Pimephales promelas), BCF values ranged 1168 to 3780 in larval and adult fish 

exposed to pyridaben (MRID 43792106). 

As discussed in USEPA 2008, several authors, including Kelly and Gobas (2003), Armitage and 

Gobas (2007) and Kelly et al. (2007), conclude that chemicals with Log KOA >5 and Log KOW>2 

may biomagnify in terrestrial food chains. The estimated Log KOA of 9.1 (EPIsuite, v.4.0) 

combined with the measured Log Kow value of 6.37 suggest that bioaccumulation of pyridaben 

in air-breathing organisms is possible. As with aquatic organisms, bioaccumulation may be 

limited by metabolism of pyridaben. 

TABLE 3.4. General Chemical Properties and Environmental Fate Properties of 

Pyridaben. 

Parameter Value Reference (MRID #)

Physical/Chemical Parameters

Molecular mass 364.9 42676103 

Vapor pressure (20°C) 8.21 x 10-5 torr 42676103 

Henry’s Law Constant (20oC) 6.84 x 10-3 Calculated (VP/Wsol) 

Water solubility (20°C) 0.012 mg·L-1 42676103 

Octanol-water partition coefficient (KOW) (25°C, 

pH not reported) 

2,344,228 

Log Kow = 6.37 

42676103 

Mobility

Organic carbon partitioning coefficient (KOC, L·kg1

) 

64,600 (sand) 

34,900 (sandy loam) 

87,900 (silt loam, low CEC) 

78,700 (silt loam, high CEC) 

42680155 

Persistence in Water

Hydrolysis half-life (25°C, pH 5, 7, & 9) Stable 42680153 

Aqueous photolysis half-life (25°C) 0.06 day† 43680427 

Aerobic aquatic metabolism half-life no data none 

Anaerobic aquatic metabolism half-life no data none 

Persistence in Soil

Soil photolysis half-life (25°C) 11 days 43792110 

Aerobic soil metabolism half-life (25°C) 110 days 42680154 

Anaerobic soil metabolism half-life (25oC) Stable 43680128 

Field Dissipation

Terrestrial field dissipation half-life; maximum 

leaching depth 

14 days; 0-12” (CA citrus) 

12 days; 0-6” (FL Citrus) 

43680430 

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Parameter Value Reference (MRID #)

Aquatic Bioconcentration 

Bioconcentration Factor (BCF) in fish 342-439 

1168-3780 

43792113, 

43792106 †

 The previously accepted study on aqueous photolysis (MRID 436804-27) used acetone (a known photosensitizer) as a co-solvent and reported a 

halflife of 5.3 minutes. A preliminary study in the same submission, however, used acetonitrile as a co-solvent, and EFED determined the halflife to be 40 minutes for this study. Therefore input would be corrected to account for partial sunlight (720 minutes), thus 0.06 day.

3.4. Degradates of Concern 

HED has identified two degradates of concern: PB-7 and PB-9 to be included in the drinking 

water exposure assessment (D230656). Both degradates are similar in structure to parent 

pyridaben. These degradates are considered of to be of concern in the ecological risk assessment 

of pyridaben. However, the estimated environmental concentrations (EECs) generated in the 

ecological assessment will use environmental fate data for the parent only, since these two 

degradates were found at such low concentrations in the aerobic and anaerobic soil metabolism 

studies. Half-lives calculated for pyridaben do not differ from half-lives calculated for total 

residues of concern (i.e., pyridaben + PB-7 + PB-9). Thus adding them into the exposure 

expression would not impact the estimated exposure concentrations.

Table 3.5. Estimated (using EpiSuite v.4.0) Chemical Properties of Pyridaben and Its 

Degradates of Concern 

Parameter (units) Pyridaben 

(measured)* 

PB-7** PB-9*** 

Molecular mass (g/mol) 364.9 352.8 338.9 

Vapor pressure (Torr, 25°C) 2.9e-8 

(8.21 x 10-5 ) 

1.1e-10 6.4e-12 

Water solubility (mg/L @ 25°C) 0.018 

(0.012) 

6.9 40.2 

Octanol-water partition coefficient (Log KOW) (25°C) 5.5 

(6.4) 

3.4 2.6 

*measured values from Table 3.4 provided in parentheses for reference purposes. 

**Smiles code: c1cc(C(O)=O)ccc1CSC2=C(Cl)C(=O)N(C(C)(C)C)N=C2 

***Smiles code: c1cc(CO)ccc1CSC2=C(Cl)C(=O)N(C(C)(C)C)N=C2

N

N

CH3

3CH

CH3

O

S

Cl

C

H2

CH3

CH3

CH3

Pyridaben 

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N

N

CH3

3CH

CH3

O

S

Cl

C

H2

CH3

CH3

O

OH

PB-7 

N

N

CH3

3CH

CH3

O

S

Cl

C

H2

CH3

CH3

H2

OH

PB-9 

Figure 3.1. Structures of Pyridaben and Its Degradates of Concern for Drinking Water and 

Ecological Risk Assessments. 

3.5. Water Quality 

Pyridaben is not identified as a cause of impairment for any water bodies under section 303(d) of 

the Clean Water Act1. In addition, no Total Maximum Daily Loads (TMDL) have been 

developed for pyridaben2 and there are no aquatic life criteria for pyridaben3. 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 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/oppfead1/cb/ppdc/2006/november06/session1-sop.pdf), in order to ensure 

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

No monitoring data were available for pyridaben. Neither the USGS’s NAWQA program nor the 

California Department of Pesticide Regulation monitoring studies included pyridaben as an 

analyte. 

 

1

 based on information provided at 

http://iaspub.epa.gov/tmdl_waters10/attains_nation_cy.cause_detail_303d?p_cause_group_id=885, accessed Jan. 

26, 2010 

2

 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, accessed Jan. 26, 2010 3

 based on information provided at http://www.epa.gov/waterscience/criteria/aqlife/index.html

-11 of 62-
 

4. Receptors 

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

assessment for pyridaben relies 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 the potential effects on a variety of species (receptors) included under 

these taxonomic groupings. To adequately capture the risk from pyridaben use, the toxicity and 

potential exposure of non-target animals to pyridaben will be considered. The most sensitive 

endpoints from the available toxicity data for pyridaben will be used to quantify risk. 

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 pyridaben 

to aquatic and terrestrial receptors. This includes toxicity on the technical grade active 

ingredient, degradates, and when available, formulated products. The open literature studies are 

identified through EPA’s ECOTOXicology (ECOTOX) database, which employs a literature 

search engine for locating chemical toxicity data for aquatic life, terrestrial plants, and wildlife 

(USEPA, 2007f). The evaluation of both sources of data may also provide insight into the direct 

and indirect effects of pyridaben 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. A preliminary review of open literature data from ECOTOX on pyridaben was 

conducted as part of this Problem Formulation to help identify data gaps. Nine studies were 

identified in ECOTOX. These studies contain effects data for terrestrial invertebrates, aquatic 

animals and algae. A more complete review of the data from ECOTOX will be conducted for 

evaluation for possible quantitative and/or qualitative inclusion in this risk assessment. 

A summary of the most sensitive data representing non-target organisms exposed to pyridaben in 

aquatic and terrestrial habitats is provided in Sections 4.1 and 4.2. Additional toxicity data are 

summarized in Appendix C. A summary of ecological incidents associated with pyridaben and a 

description of ecosystems potentially at risk are provided in Sections 4.3 and 4.4, respectively. 

4.1. Effects of Pyridaben to Aquatic Organisms 

Pyridaben is very highly toxic to fish and invertebrates (freshwater and estuarine/marine) on an 

acute exposure basis. Chronic toxicity data are available from a full life cycle test conducted with 

the fathead minnow (Pimephales promelas). Growth (length and weight) of the F0 and F1

generations, as well as survival of the F1 generation were significantly decreased relative to 

controls at 0.555 μg a.i./L (NOAEC = 0.277 μg a.i./L; MRID 43792106). Because the rainbow 

trout (Oncorhynchus mykiss) is more sensitive on an acute exposure basis when compared to the 

fathead minnow, the acute to chronic ratio (ACR; 8.3) from MRID 43792106 is used to derive a 

chronic endpoint for the rainbow trout which is 0.087 μg a.i./L. In a chronic study with the water 

flea (Daphnia magna), time to reproduction was significantly affected at 0.086 μg a.i./L 

(NOAEC = 0.044 μg a.i./L; MRID 43680408). In a chronic study with mysid shrimp 

(Mysidopsis bahia), no reproductive, growth or survival effects were observed in exposures as 

high as 0.13 μg a.i./L (MRID 43680409). No data are available to quantify the toxicity of 

pyridaben to sediment-dwelling invertebrates. In a Tier II test with green algae (Selenastrum 

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capricornutum), an EC50 was estimated as >665 μg a.i./L. A Tier I toxicity test with duckweed 

(Lemna gibba) exposed to 16.2 μg a.i./L pyridaben resulted in a no decrease in frond production 

compared to the solvent control and a 7% decrease in frond production compared to the negative 

control. The most sensitive acute and chronic toxicity endpoints for aquatic animals and plants 

exposed to pyridaben are provided in Table 4.1. These endpoints may be considered for 

calculating risk quotients in future risk assessments of pyridaben. 

TABLE 4.1. Summary of the Most Sensitive Endpoints from Submitted Aquatic Toxicity 

Studies for Pyridaben. 

Taxa 

represented 

Species 

(common name) 

Toxicity Value 

(μg a.i./L) 

Citation 

(MRID) 

Comments 

96-hr LC50 = 

0.72 43680402 Slope = 6.9 (95% C.I. = 4.4-9.3) 

freshwater fish 

and aquaticphase 

amphibians 

Oncorhynchus 

mykiss (rainbow 

trout) NOAEC = 0.087 

See 

comments 

Acute and chronic toxicity data are 

available for fetched minnows 

(Pimephales promelas) exposed to 

pyridaben (96-h LC50 = 2.3 μg a.i./L; 

NOAEC = 0.277 μg a.i./L; ACR = 8.3; 

MRID 43792106). Because the rainbow 

trout is more sensitive on an acute 

exposure basis, the ACR is used to derive 

a NOAEC for the rainbow trout. 

48-hr EC50 = 

0.53 42680111 Slope = 6.4 (95% C.I. = 4.2-8.6) 

freshwater 

invertebrates 

Daphnia magna 

(waterflea) NOAEC = 0.044 43680408 

Study classification is Acceptable. 

LOAEC = 0.086 μg/L based on delayed 

time to reproduction. 

96-hr LC50 = 

17.2 43680406 Slope = 4.7 (95% C.I. = 2.2-7.2) 

Estuarine/ 

Marine fish 

Cyprinodon 

variegates

(Sheepshead 

minnow) NOAEC = 2.1 See 

comments 

Derived using ACR for fathead minnow 

(8.3) and acute toxicity value for 

sheepshead minnow. 

96-hr EC50 = 

 0.67 43680405 Slope = 3.1 (95% C.I. = 1.8-4.5) Estuarine/ 

Marine 

Invertebrates 

Mysidopsis 

bahia (mysid 

shrimp) NOAEC = 0.13 43680407 

A LOAEC was not established in this 

study because no effects were observed at 

any treatment level. 

Selenastrum 

capricornutum 

(green algae) 

EC50 >665 

NOAEC <20.8 43680421 Due to a poor dose-response relationship, a reliable EC05 could not be calculated. 

Aquatic Plants 

Lemna gibba 

(duckweed) 

EC50 and 

NOAEC >16.2 43680422 

Estimated from tier 1 test where no 

biologically significant effects to 

duckweed were observed at 16.2 μg 

a.i./L. Note that these effects values are 

greater than pyridaben’s solubility in 

water (i.e., 12 μg/L). 

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4.2. Effects of Pyridaben to Terrestrial Organisms 

Pyridaben is classified practically non-toxic to birds on an acute oral exposure basis. On a 

subacute dietary basis, pyridaben is classified as slightly toxic to birds. Reproductive (decreases 

in eggs laid, eggs set, viable embryos, live 3 week embryos, normal hatchlings and hatch 

survival) and parental effects (decrease in size of adult male testes and decrease in number of 

female ovaries) were observed in mallard ducks fed pyridaben at levels as low as 500 mg/kg-diet 

(LOAEC). The resulting no observed adverse effects concentration (NOAEC) was 100 mg/kgdiet. 

Pyridaben is moderately toxic to mammals on an acute oral exposure basis. In a 2-generation 

reproduction study, the LOAEC for pyridaben parental toxicity was 80 mg/kg-diet based on 

decreased body weights, body weight gains and food efficiency. The resulting NOAEC was 28 

mg/kg-diet. No reproductive effects were observed at any test level, resulting in a reproductive 

LOAEC >80 mg/kg-diet. 

Pyridaben is highly toxic to honey bees (LD50 = 0.024 μg a.i./bee). Available foliar residue 

studies indicate that pyridaben can cause mortality (> 20%) in honey bees up to 24 hours after 

application (MRID 43680424). 

Seedling emergence and vegetative vigor data are available for 6 species of dicots and 4 species 

of monocots exposed to technical pyridaben (MRIDs 436804-19 and -20). In these studies, <25% 

decrease in dry weight was observed in plants exposed to 0.5 lb a.i./A pyridaben (compared to 

controls). Because no data are available at the highest single application rate (i.e., 1.0 lb a.i./A), 

there is uncertainty in the potential effects of pyridaben on terrestrial plants. 

The most sensitive acute and chronic toxicity endpoints for terrestrial animals exposed to 

pyridaben are provided in Table 4.2. These endpoints may be considered for calculating risk 

quotients in future risk assessments of pyridaben. 

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TABLE 4.2. Summary of the Most Sensitive Endpoints from Submitted Terrestrial 

Toxicity Studies for technical Pyridaben. 

Taxa 

represented Species Toxicity Value 

Citation 

(MRID) Comments 

LD50>2500 mg/kgbw 42680105 

LC50 = 4688 

mg/kg-diet 42680107 

Birds, 

terrestrial-phase 

amphibians and 

reptiles

Anas platyrhynchos 

(Mallard Duck) 

NOAEC = 100 

mg/kg-diet 43792101 

LOAEC = 500 mg/kg-diet based 

on reproductive and parental 

effects 

Mus sp. (mouse) LD50 = 383 

mg/kg-bw Female 42680120 LD50 for males = 424 Study conducted with TGAI 

Terrestrial 

mammals Rattus norvegicus

(laboratory rat)

NOAEC = 

 28 mg/kg-diet 

42680143 

42680144 

NOAEL = 2.2 and 2.4 mg/kgbw/day for males and females 

respectively 

LOAEC = 80 mg/kg-diet based on 

parental effects. No reproductive 

effects were observed. 

LOAEL = 6.3 and 7.8 mg/kg-bw 

for males and females, respectively 

Terrestrial 

invertebrates 

Apis mellifera 

(Honey bee) 

LD50 = 0.024 

μg/bee 43680423 Slope = 3.31 

Non-target 

terrestrial and 

wetland plants 

10 species of 

monocots and 

dicots 

EC25 >0.5 lb a.i./A 43680419 

43680420 

<25% effects to dry weight were 

observed in all 10 test species for 

Tier 1 seedling emergence and 

vegetative vigor tests. 

4.3. Effects of Pyridaben’s Degradates of Concern to Non-Target Organisms 

As stated previously, HED has identified PB-7 and PB-9 as degradates of concern for human 

health. No empirical data are available from registrant-submitted studies or from the literature to 

characterize the toxicity of PB-7 and PB-9 to non-target organisms. ECOSAR (v.1.0) and 

ASTER were run to estimate the toxicity of these degradates to aquatic organisms (Appendix D). 

When the estimated toxicity values generated by ECOSAR and ASTER are compared to 

available empirical data (Table 4.1), both tools predict acute toxicity values for fish and 

invertebrates exposed to pyridaben that are 1-2 orders of magnitude less toxic when compared to 

empirical data. This suggests that ECOSAR and ASTER may not be appropriate tools for 

estimating the toxicity of pyridaben and its degradates. Therefore, in the absence of data to the 

contrary and given the structural similarities of PB-7 and PB-9 to the parent, it will be assumed 

that the toxicities of PB-7 and PB-9 are equivalent to that of pyridaben. Available toxicity data 

for pyridaben (Tables 4.1 and 4.2) will be used as surrogates for characterizing the effects of PB7 and PB-9 to non-target aquatic and terrestrial organisms. 

4.4. Incident Databases Review 

Searches of the EIIS (Environmental Incident Information System) database for ecological 

incidents (run on April 27, 2010) and AIMS (run on August 9, 2010) identified no incidents 

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involving pyridaben. One note of uncertainty associated with these databases is the nature of 

reporting of incidents. Pyridaben exposure incidents may have occurred that were not reported 

due to various factors, such as a lack of reporting, or a lack of witnessing of effects. Therefore, 

the absence of incident reports does not necessarily indicate the absence of incidents. 

4.5. 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 and sediment 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, embayment’s, and 

near shore environments. 

5. Consideration of Persistent, Bioaccumulative and Toxic Properties of Pyridaben 

The EPA’s PBT Profiler is a screening-level tool that provides estimates of the persistence, 

bioaccumulation, and chronic toxicity to fish. When pyridaben is run through the PBT profiler, 

the tool indicates that pyridaben may have persistent, bioaccumulative and toxic characteristics. 

This conclusion is supported by empirical environmental fate and effects data available for 

pyridaben. 

For pyridaben, the persistence conclusion is based on the estimated aerobic metabolism halflives for sediment, water and soil (Table 5.1); this does not account for photodegradation in soil, 

which could be a significant degradation pathway in the natural environment during periods of 

intense light. Empirical data are available from an aerobic soil metabolism study where the halflife (110 d) was a 92% of the estimated value (120 d); however, both the estimated and the 

empirical soil metabolism half-lives are sufficient to consider pyridaben persistent according to 

the PBT profiler’s definition (i.e., t 1/2 ≥ 60 d). No empirical aquatic or sediment metabolism data 

are available for which to compare the estimated half-lives for these media. 

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Table 5.1. Estimated (via PBT profiler) and empirical half-lives (in days) for pyridaben in 

different media. 

Media Estimated Empirical 

Water* 60 No data 

Soil* 120 110** 

Sediment* 540 No data 

Air 0.37 No data 

*Represents biodegradation. Estimated using BIOWIN; this estimate does not account for photodegradation. 

**MRID 42680154

The bioaccumulation conclusion for pyridaben is based on an estimated BCF for fish of 16,000. 

The PBT profiler’s threshold for concluding that a chemical is bioaccumulative is a BCF of 

1000. Empirical BCFs from two separate laboratory studies involving rainbow trout (MRID 

43792113) were 342 and 439. In a life cycle test with fathead minnows (Pimephales promelas), 

BCF values ranged 1168 to 3780 in larval and adult fish exposed to pyridaben (MRID 

43792106). Differences in BCF values observed in the 30-d rainbow trout and full life cycle 

fathead minnow tests may be attributed to the durations of the studies. Based on the Kow of 

pyridaben, the time required to reach steady state may be greater than 30 days, which would 

result in underestimation of BCF values obtained from the rainbow trout studies. Regardless of 

these differences, empirical BCF values are 1-2 orders of magnitude below the PBT profiler’s 

estimated BCF. One reason for this overestimate may be a lack of consideration of metabolism 

of pyridaben by fish, which was observed in the laboratory BCF study. KABAM (KOW (based) 

Aquatic BioAccumulation Model; version 1.0) was used to estimate a fish BCF that considers 

metabolism (see Appendix B). When the metabolism rate is estimated from the empirical BCF 

studies, estimated BCF for fish is 5740, which is on the same order of magnitude as the empirical 

BCF values observed in fathead minnows. Although metabolism reduces the bioconcentration 

potential of pyridaben, the estimated and empirical BCF data are still sufficient to consider 

pyridaben bioaccumulative (i.e., BCF ≥ 1000) according to the PBT profiler’s definition. 

The PBT profiler considers a chemical “toxic” when its chronic value is below 10,000 μg/L. The 

chronic value is the geometric mean of the NOAEC and LOAEC from a chronic fish study (i.e.

the MATC). The estimated chronic value for pyridaben is 4 μg/L. The MATC from the full life 

cycle test conducted with the fathead minnow exposed to pyridaben was 0.392 μg/L (MRID 

43792106), which is an order of magnitude below the PBT profiler’s estimated chronic value. 

6. Assessment Endpoints 

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

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

(USEPA, 1998). For pyridaben, the ecological entities may include the following: birds, 

mammals, terrestrial-phase amphibians, reptiles, freshwater fish and invertebrates, aquatic-phase 

amphibians, estuarine/marine fish and invertebrates, terrestrial plants, terrestrial invertebrates, 

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

survival. The proposed assessment endpoints for pyridaben are provided in Tables 4.1 and 4.2. 

No endpoints have been established for aquatic plants. 

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7. 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 pyridaben provides a written description and visual representation of 

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

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

risk hypothesis and a conceptual diagram (USEPA, 1998). 

Based on the submitted environmental fate data and previous assessments in support of the 

original registration and Section 24c registrations, the pyridaben vapor pressure suggests that the 

chemical is semi-volatile; however, it is not expected to volatilize due to its tendency to sorb to 

soil (high Koc) and plants (high Koc and Kow). Given that pyridaben will sorb to soil, there is 

potential for it to be transported via wind eroded soil with sorbed compound, thus may be a 

concern for long range transport. Persistence in aqueous environments is uncertain. The 

compound is unlikely to leach to ground water due to its adsorptive potential, however it may 

move to surface water bodies through spray drift, and/or in runoff events that are accompanied 

by erosion. Estimated and empirical bioconcentration data indicate that bioaccumulation of 

pyridaben may occur, but it will be significantly reduced by metabolism of the compound by 

aquatic organisms. A previous ecological risk assessment concluded that pyridaben (parent 

only), at the maximum use rates, exceeds acute and chronic risk levels of concern for freshwater 

fish and invertebrates, acute risk for estuarine/marine fish and invertebrates, and chronic risk for 

birds and mammals. 

7.1. 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 pyridaben, the 

following hypothesis will employed for the ecological risk assessment associated with 

registration review: 

Given the uses of pyridaben and its environmental fate properties, there is a likelihood of 

exposure of non-target terrestrial and aquatic organisms to pyridaben and its degradates 

of concern (PB-7 and PB-9). When used in accordance with the label, pyridaben results 

in potential adverse effects upon the survival, growth, and reproduction of non-target 

terrestrial and aquatic organisms. 

7.2. Conceptual Diagram 

The environmental fate properties of pyridaben indicate that runoff, spray drift, and direct spray 

represent potential transport mechanisms of pyridaben to aquatic and terrestrial habitats where 

non-target organisms may be exposed. The potential transport mechanisms (i.e., sources) of 

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pyridaben are depicted in the conceptual models below (Figures 7.1 and 7.2) along with the 

receptors of concern and the potential attribute changes in the receptors due to exposures of 

pyridaben. 

Pyridaben applied to use site 

Degradation to PB-7 and PB-9 

Spray drift 

Fish/aquatic-phase 

amphibians 

Eggs 

Larvae 

Juveniles / Adults 

Individual organisms 

Reduced survival 

Reduced growth 

Reduced reproduction 

Food chain 

Reduction in algae 

Reduction in prey 

Habitat integrity 

Reduction in primary productivity

Reduced cover 

Community change 

Surface water/ 

Sediment 

Runoff 

Aquatic Animals 

Invertebrates 

Vertebrates 

Uptake/gills 

or integument 

Ingestion Ingestion

Long-range 

atmospheric 

transport 

Wet/dry deposition 

Soil Ground water 

Uptake/gills 

or integument 

Aquatic Plants 

Non-vascular 

Vascular 

Uptake/cell, 

roots, leaves Riparian plant

terrestrial 

exposure 

pathways (see 

Figure 6.2) 

Stressor 

Source 

Exposure 

Media 

Receptors 

Attribute 

Change 

FIGURE 7.1. Conceptual Model for Pyridaben Effects on Aquatic Organisms. Dotted 

Lines Indicate Exposure Pathways that Have a Low Likelihood of Contributing to 

Ecological Risk. 

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Pyridaben applied to use site 

Stressor Degradation to PB-7 and PB-9 

Source 

Receptors 

Attribute 

Change 

Direct 

application Spray drift 

Birds / Terrestrialphase amphibians / 

reptiles / mammals

Terrestrial 

invertebrates 

Individual organisms 

Reduced survival 

Reduced growth 

Reduced reproduction 

Food chain 

Reduction in prey 

Habitat integrity 

Reduction in primary productivity

Reduced cover 

Community change 

Terrestrial/riparian plants 

grasses/forbs, fruit, seeds 

(trees, shrubs) 

Runoff 

Mammals

Exposure 

Media 

Soil 

Ingestion 

Ingestion

Ingestion

Ingestion

Dermal uptake/Ingestion 

Long-range 

atmospheric 

transport 

Root uptake 

Wet/dry deposition 

Birds / 

Amphibians 

Ingestion 

FIGURE 7.2. Conceptual Model for Pyridaben Effects on Terrestrial Organisms. 

8. Analysis Plan 

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 pyridaben are characterized and 

integrated to assess the risks. Risk quotients (RQs) will be derived for pyridaben residues of 

concern by dividing estimated environmental concentrations (EEC) by the most sensitive 

endpoint from the relevant, available toxicity data for the pyridaben residues of concern. 

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. 

8.1. Stressors of Concern 

Pyridaben and its degradates PB-7 and PB-9 are considered the stressors of concern in the risk 

assessment. The PB-7 and PB-9 degradates are identified as stressors of concern for drinking 

water and ecological risk assessments because HED has identified these two degradates of 

concern (D230141 and D230656; Oct and Nov 1996). Both degradates are similar in structure to 

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parent pyridaben. These degradates are considered of to be of concern in the ecological risk 

assessment of pyridaben. However, half-lives calculated for pyridaben do not differ from halflives calculated for total residues of concern (i.e., pyridaben + PB-7 + PB-9). Thus adding them 

into the exposure expression would not significantly impact the estimated exposure 

concentrations. 

Available toxicity data for environmental mixtures of pyridaben with other pesticides will be 

presented as part of the ecological risk assessment. It is expected that the toxic effect of 

pyridaben, in combination with other pesticides used in the environment, is likely to be a 

function of many factors including but not necessarily limited to: (1) the exposed species, (2) the 

co-contaminants in the mixture, (3) the ratio of pyridaben and co-contaminant concentrations, (4) 

differences in the pattern and duration of exposure among contaminants, and (5) the differential 

effects of other physical/chemical characteristics of the receiving waters (e.g. organic matter 

present in sediment and suspended in water). Quantitatively predicting the combined effects of 

all these variables on mixture toxicity to any given taxa with confidence is beyond the 

capabilities of the available data and methodologies. However, a qualitative discussion of 

implications of the available pesticide mixture effects data on the confidence of risk assessment 

conclusions will be addressed as part of the uncertainty analysis. 

8.2. Measures of Exposure 

In order to estimate risks of pyridaben exposures in aquatic and terrestrial environments, all 

exposure modeling and resulting risk conclusions will be made based on maximum application 

rates for the currently registered uses. Measures of exposure are based on aquatic and terrestrial 

models that predict estimated environmental concentrations (EEC) of pyridaben using maximum 

labeled application rates and application methods that have the greatest potential for off-site 

transport of the chemical. The models used to predict aquatic EECs are the Pesticide Root Zone 

Model coupled with the EXposure Analysis Modeling System (PRZM/EXAMS). For exposure 

to sediment dwelling organisms, predicted pore water EECs are generated using the Pesticide 

Root Zone Model coupled with the EXposure Analysis Model System (PRZM/EXAMS). If long 

range transport potential (LRTP) is of concern, The “OECD Pov and LRTP Screening Tool” 

(version 2.04

) will be used in evaluating the overall persistence (Pov), and LRTP of pyridaben. 

The OECD Tool requires estimated degradation half-lives in soil, water and air, and partition 

coefficients between air and water and between octanol and water as chemical-specific input 

parameters to calculate persistence and the metrics of LRTP. The model used to predict 

terrestrial EECs on food items is T-REX. The model used to derive EECs relevant to terrestrial 

and wetland plants is TerrPlant. These models are parameterized using environmental fate data 

from studies submitted by registrants and from the scientific literature. 

PRZM (v3.12.2, May 2005) and EXAMS (v2.98.4.6, April 2005) are simulation models coupled 

with the graphical user interface, PE (v5.0, November 2006) to generate daily exposures and 1-

in-10-year EECs of pyridaben that may occur in surface water bodies adjacent to application 

sites receiving pyridaben through runoff and spray drift. PRZM simulates pesticide application, 

movement and transformation on an agricultural field and the resultant pesticide loadings to a 

receiving water body via runoff, erosion, and spray drift. EXAMS simulates the fate of the 

 

4

 Available online at: http://www.oecd.org/document/17/0,3343,en_2649_34373_40754961_1_1_1_1,00.html

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pesticide and resulting concentrations in the water body. The standard watershed geometry used 

for ecological pesticide assessments assumes 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. The composite model PRZM/EXAMS is used to estimate exposure of aquatic organisms 

to pyridaben at a location that is expected to be more vulnerable than most locations where a 

specific crop is crown. Therefore, the resulting exposure estimates are expected to be protective 

of aquatic wildlife in most locations. Measures of exposure for aquatic species include the 1-in10-year peak and 1-in-10-year rolling mean concentrations. 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 aquatic invertebrate chronic exposure. Appendix E includes a 

summary of PRZM/EXAMS input parameters as well as an example output for applications of 

pyridaben on pears in Washington. 

KABAM v.1.0 is used to estimate potential bioaccumulation of pyridaben in freshwater aquatic 

food webs and subsequent risks to mammals and birds via consumption of contaminated aquatic 

prey. At this time, no tool is available in EFED to quantify the bioaccumulation potential of 

pyridaben in terrestrial food webs. 

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, 10/08/2008). This model 

incorporates the Kenaga nomograph, as modified by Fletcher et al. (1994), which is based on a 

large set of actual field residue data. The upper limit values from the nomograph represent high 

end residue values from actual field measurements (Hoerger and Kenaga, 1972). The Fletcher et 

al. (1994) modifications to the Kenaga nomograph are based on measured field residues from 

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

and 17 chemical classes. Given that no suitable data on interception and subsequent dissipation 

from foliar surfaces is available for pyridaben, the EFED default foliar dissipation half-life of 35 

days is used based on high-end dissipation values for pesticides reported by Willis and 

McDowell (1987). 

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

1.2.2, 12/26/2006). This model estimates exposure by calculating residues in runoff and in spray 

drift. These calculations are solely based upon inputs of solubility, application rate, and 

minimum incorporation depth. 

The AgDRIFT spray drift model (v2.01; May 2001) is used to assess exposures of organisms to 

pyridaben that is deposited on terrestrial habitats by spray drift. 

8.3. Measures of Effect 

 

Ecological effects 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 provides more ecological effects data in an attempt to bridge 

existing data gaps. 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 

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created and is maintained by the USEPA, Office of Research and Development, and the National 

Health and Environmental Effects Research Laboratory's Mid-Continent Ecology Division. 

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

Ecological Incident Information System (EIIS; USEPA 2007e). 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. Any new incident reports beyond what 

have already been discussed in this problem formulation will be reviewed. 

Incidents reported in the aggregate incident reports and the Avian Incident Monitoring System 

(AIMS) will also be searched. AIMS is a database administered by the American Bird 

Conservancy (it was partially funded by the EPA). It contains publicly available data on reported 

avian incidents involving pesticides (online at: 

http://www.abcbirds.org/abcprograms/policy/pesticides/aims/aims/index.cfm). 

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

studies will be evaluated qualitatively. Such effects may include behavioral changes (e.g., 

lethargy and changes in coloration). 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 pyridaben 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 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. 

8.4. Integration of Exposure and Effects 

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

determine the potential ecological risk from the use of pyridaben 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 

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non-target species. For the assessment of pyridaben 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 Levels of Concern (LOC) 

(USEPA, 2004b). These criteria are used to indicate when pyridaben use, as directed on the 

labels, has the potential to cause adverse direct or indirect effects to non-target organisms. In 

addition, incident data from EIIS, aggregate incident reports, and AIMS will be considered as 

part of the risk characterization. 

8.5. 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. Depending on the risk manager’s need for 

additional information regarding risk, an effort will be made to further describe risk using 

probabilistic tools that the Agency has developed. These tools have been reviewed by FIFRA 

Scientific Advisory Panels (http://www.epa.gov/scipoly/sap/index.htm) and have been deemed 

as appropriate means of refining assessments where deterministic approaches have identified 

risks. 

8.6. 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 pyridaben. This assessment will be conducted in accordance with the 

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

Species Consultation Handbook (USFWS/NMFS, 1998). 

The action area is used to identify all listed (threatened and endangered) species and designated 

critical habitat that could be affected by the Federal action. The Federal action is the 

authorization or registration of pesticide use or uses as described on the label(s) of pesticide 

products containing a particular active ingredient. The action area is defined by the Endangered 

Species Act as, “all areas to be affected directly or indirectly by the Federal action and not 

merely the immediate are involved in the action” (50 CFR §402.2). Based on an analysis of the 

Federal action, the action area is defined by the actual and potential use of the pesticide. 

In the case of nationwide ecological risk assessment conducted for pyridaben under Registration 

Review, the action area will encompass the entire United States and its territories. The purpose 

of defining the action area as the entire United States and its territories is to ensure that the initial 

area of consideration encompasses all areas where pyridaben may be used now and in the future, 

including the potential for off-site transport via spray drift and downstream dilution. 

Additionally, the concept of a nationwide action area takes into account the potential for direct 

and indirect effects and any potential modification to critical habitat based on ecological effect 

measures associated with reduction in survival, growth, and reproduction, as well as the full suite 

of sublethal effects available in the effects literature. It is important to note that the nationwide 

action area does not imply that direct and/or indirect effects and critical habitat modification are 

expected to or are likely to occur over the full extent of the action area, but rather to identify all 

listed species and critical habitat that may potentially be affected by the action. The Agency will 

-24 of 62-
use more rigorous analysis including consideration of available land cover data, toxicity data, 

and exposure information to determine areas where individual listed species and designated 

critical habitat may be affected or modified via endpoints associated with reduced survival, 

growth, or reproduction. 

8.7. Drinking Water Assessment 

A drinking water assessment will be conducted to support future human dietary exposure 

assessments of pyridaben. Concentrations of pyridaben plus the identified residues of concern 

(pyridaben + PB-7 + PB-9) in surface water will be estimated using PRZM/EXAMS (see 

description in Section 7.2). However, the contribution of the two residues of concern (PB-7 and 

PB-9) are expected to have little impact on the persistence of the exposure estimates since both 

of these degradates were formed in minor amounts (<10%) in fate studies (e.g., anaerobic soil 

metabolism) that do not significantly impact the environmental modeling. Ground water 

exposure estimates for pyridaben plus the residues of concern will be estimated using the 

Screening Concentration in Ground Water (SCI-GROW) model (v.2.3, July 2003) followed by a 

higher tier model if necessary. It is important to note that compounds such as pyridaben with Koc

values greater than 9995 ml/g are beyond the scope of the regression data used in SCI-GROW 

development. Therefore, if ground water contamination by pyridaben is a concern, the Agency 

recommends that a higher tier ground water exposure assessment be considered, regardless of the 

concentration returned by SCI-GROW. The drinking water assessment will also include a 

summary of available surface and ground water monitoring data. 

8.8. Preliminary Identification of Data Gaps 

8.8.1. Environmental Fate Data 

The studies submitted to fulfill environmental fate data requirements for pyridaben are not 

sufficient to conduct an exposure assessment; six requirements have not been met: 1) An 

acceptable aerobic aquatic metabolism study has not been submitted. Conditional data was 

submitted to the Agency but was classified as unacceptable. This study is necessary in order to 

describe the fate of pyridaben in surface water bodies down-gradient from terrestrial use sites. 2) 

There is only one acceptable aerobic soil metabolism study conducted on one soil. Conditional 

data was submitted to fulfill this requirement, but the studies were found unacceptable. This 

study needs to be conducted on at least four relevant soils of different organic carbon content, 

pH, clay content, and microbial biomass in order to begin to understand the variability in aerobic 

biodegradation of pyridaben in the environment. 3) Submission of an anaerobic aquatic 

metabolism study is necessary to understand the degradation of pyridaben in oxygen-limiting 

environments. 4) Submission of a storage stability study is essential in order to be confident that 

any degradation measured in the test system was due solely to the environment of that test 

system, and not due to handling and storage. Lastly, although not necessary for exposure 

assessment, submission of an environmental chemistry method in water and in soil, as well as 

associated independent laboratory validations for these methods is also necessary in order to 

support enforcement and monitoring purposes at the federal, state, and local levels (5th and 6th

data requirements). 

-25 of 62-
Due to the bioaccumulation potential of pyridaben, EFED is requesting a bioconcentration study 

with the oyster and an aquatic food chain transfer study. 

Draft Data Call-In (DCI) tables for the requested data are provided in APPENDIX F. Table 8.1

identifies 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 

(i.e., whether there is a data gap). 

TABLE 8.1. Environmental Fate Data Requirement Table for Pyridaben.

OPPTS 

Guideline 

Data Requirement Submitted 

Studies 

(MRID) 

Classification Data 

Gap? 

Comments 

835.2120 Hydrolysis 42680153 Acceptable No -- 

835.2240 Aqueous photolysis 43680127 Acceptable No -- 

835.2410 Soil photolysis 43792110 Acceptable No -- 

42680154 Acceptable Only one soil was acceptable. 

47576104 Unacceptable 

835.4100 Aerobic soil 

metabolism 

47583301 Unacceptable 

Yes 

835.4200 Anaerobic soil 

metabolism 

43680128 Acceptable No -- 

835.4300 Aerobic aquatic 

metabolism 

47576105 Unacceptable Yes 

835.4400 Anaerobic aquatic 

metabolism 

-- -- Yes No data submitted 

42680156 Supplemental 

42680155 Supplemental 

44008302 Supplemental 

835.1230 

835.1240 

Adsorption/ 

desorption and 

leaching 

43792111 Supplemental 

No No additional data needed 

Terrestrial field 43909904 Supplemental 

dissipation 

43680430 Supplemental 

No Studies were downgraded since there is 

no acceptable storage stability study 

conducted for the longest duration of 

storage from sampling to analysis. 

Confined terrestrial 

field dissipation 

43680429 Supplemental No Not a required study. Provides 

supplemental data on the dissipation of 

pyridaben in terrestrial environments. 

835.6100 

Storage Stability 42680103 Unacceptable Yes Interim study submitted. Need final study 

conducted for the longest sample storage 

duration in the unconfined field 

dissipation study. 

Aquatic 

Microcosm Study 

43792108 Supplemental No Not a required study. Provides 

supplemental data on the dissipation of 

pyridaben in aquatic environments. 

835.6200 

Confined aquatic 

dissipation 

43792112 Supplemental No Not a required study. Provides 

supplemental data on the dissipation of 

pyridaben in aquatic environments. 

850.1710 Oyster 

bioconcentration 

none Not applicable Yes No data submitted 

850.1730 Fish Supplemental 43792114 Does not fulfill guideline. 

bioconcentration Acceptable 43792113 

No 

Supersedes MRID 43792114 

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OPPTS 

Guideline 

Data Requirement Submitted Classification Data Comments 

Studies Gap? 

(MRID) 

850.1850 Aquatic food chain 

transfer 

none Not applicable Yes No data submitted 

835.6200 Analytical method 

in water 

-- -- Yes No data submitted 

835.6100 Analytical method 

in soil 

-- -- Yes No data submitted 

8.8.2. Effects Data 

Although many submissions have been made to provide data on the effects of pyridaben to 

aquatic and terrestrial organisms, data gaps still exist (Tables 8.2-8.4). Data gaps include the 

following: avian acute oral toxicity for a passerine species, acute toxicity with estuarine/marine 

fish, estuarine/marine fish early-life stage toxicity, estuarine/marine invertebrate full life cycle 

toxicity, aquatic vascular and non-vascular plant and terrestrial plant toxicity. These data gaps 

are discussed below. 

TABLE 8.2. Available Ecological Effects Data for Terrestrial Animals Exposed to 

Pyridaben and Remaining Data Gaps.

Guideline Description MRID Classification Data Gap? Comments 

850.2100 Avian oral toxicity 42680105 Acceptable 

42680106 Acceptable 

Yes* 

850.2200 Avian dietary 42680107 Acceptable 

toxicity 42680108 Acceptable 

No 

850.2300 Avian reproduction 43792101 Acceptable 

43792102 Acceptable 

No 

850.3020 Honeybee acute 

contact toxicity 43680423 Acceptable No 

850.3030 Honey bee residue 

on foliage 43680424 Acceptable No 

850.3040 Field testing for 

pollinators none Not applicable Yes** 

*At this time, EFED is not 

requesting data to fulfill this 

data gap. 

**These data are required 

because data from a residual 

toxicity study (MRID 

43680424) indicates 

extended residual toxicity. 

Avian acute oral toxicity with a passerine species 

According to the 40 CFR 158, acute oral toxicity data are required for a passerine species. 

Because no acute oral toxicity data have been submitted for a passerine species exposed to 

pyridaben, this is a data gap. Available acute oral toxicity data for birds (MRIDs 426801-05 and 

-06) indicate that pyridaben is classified practically non-toxic to birds on an acute oral exposure 

basis. Therefore, EFED is not requesting oral toxicity data for passerines exposed to pyridaben. 

It should be noted that no acute oral toxicity data for passerines exposed to pyridaben have been 

identified in the scientific literature (using ECOTOX) and no ecological incidents involving birds 

exposed to pyridaben have been identified (using EIIS). 

-27 of 62-
Field testing for pollinators 

According to 40 CFR Part 158, this study is required if any of the following are met: 1) data 

from other sources (Experimental Use Permit program, university research, registrant submittals, 

etc.) indicate potential adverse effects on colonies, especially effects other than acute mortality 

(reproductive, behavioral, etc.); 2) data from residual toxicity studies indicate extended residual 

toxicity; or 3) data derived from studies with terrestrial arthropods other than bees indicate 

potential chronic, reproductive or behavioral effects. In a foliar residue study MRID (43680424), 

pyridaben residues aged 24 h caused mortality (> 20%) in honey bees. Therefore, the second 

condition relevant to this data requirement is met and submission of a field study of the effects of 

pyridaben on pollinators is required (Guideline 850.3040). Pyridaben registrants must submit a 

study protocol for review by the Agency prior to initiation of the field testing for pollinators 

study. 

TABLE 8.3. Available Ecological Effects Data for Aquatic Animals Exposed to Pyridaben 

and Remaining Data Gaps.

Guideline Description MRID Classification Data 

Gap? Comments 

42680109 Acceptable 

42680110 Acceptable 

43680401 Acceptable 

43680402 Acceptable 

850.1075 Freshwater fish – 

Acute toxicity 

43680403 Supplemental 

No 

850.1075 Saltwater fish – 

Acute toxicity 43680406 Supplemental Yes 

43680404 Acceptable 850.1010 Freshwater invertebrates – 

Acute toxicity 42680111 Acceptable 

No 

850.1025 43680405 Acceptable 

850.1035 

850.1045 

850.1055 

Saltwater invertebrates – 

Acute toxicity * 43680407 Supplemental 

No 

43680408 Acceptable 850.1300 Freshwater invertebrate – 

life cycle test 43680410 Supplemental 

No 

850.1350 Saltwater invertebrates – 

life cycle test 43680409 Supplemental Yes 

850.1400 Freshwater fish – 

early life stage test none Not applicable No** 

850.1400 Saltwater fish – 

early life stage test Not available Not applicable Yes 

850.1500 Freshwater fish - lifecycle 43792106 Acceptable No 

850.1735 Whole sediment: acute 

freshwater invertebrates Not available Not applicable Yes 

none 

Whole sediment: chronic 

freshwater invertebrates Not available Not applicable Yes 

*Data are required for 

one estuarine/marine 

mollusk and one 

estuarine/marine 

invertebrate. These data 

are submitted for 

Guidelines 850.1025 

(MRID 43680407) and 

850.1035 (MRID 

43680405), respectively. 

No data have been 

submitted under 

850.1045 and 850.1055. 

**Chronic toxicity data 

for a freshwater fish are 

available from a full life 

cycle study. 

 

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Acute toxicity to estuarine/marine fish 

Acute toxicity data are available for sheepshead minnow exposed to pyridaben (Cyprinodon 

variegates; MRID 43680406). This study was classified supplemental because the highest test 

concentration resulted in 50% mortality, leading to uncertainty in the established LC50. 

Submission of acceptable acute toxicity data for estuarine/marine fish (guideline 850.1075) will 

reduce uncertainty associated with the acute endpoint and increase confidence in risk 

conclusions. 

Chronic toxicity to estuarine/marine fish 

Chronic toxicity data are not available for estuarine/marine fish. The updated Part 158 data 

requirements, specify that an early life-stage study is required for estuarine/marine fish for 

chemicals that have the potential to enter estuarine/marine water. In addition, these data may be 

required when the acute LC50 for an estuarine/marine fish is <1 mg/L, and when reproductive 

effects are observed in other aquatic organisms. Because pyridaben use sites may overlap with 

watersheds of estuarine/marine environments, pyridaben has the potential to enter 

estuarine/marine environments. In addition, the LC50 for sheepshead minnow exposed to 

pyridaben is <1 mg/L (MRID 43680406) and reproductive effects have been observed in 

freshwater fish (MRID 43792106) and invertebrates (MRIDs 43680408 and 43680410) exposed 

to pyridaben. Therefore, an early life stage test (guideline 850.1400) is required for pyridaben. 

Chronic toxicity to estuarine/marine invertebrate 

Supplemental chronic toxicity data are available for mysid shrimp exposed to pyridaben 

(43680409). This study was classified supplemental due to poor control performance and lack of 

observed effects at any treatment level. Submission of acceptable chronic toxicity data for 

estuarine/marine invertebrates (Guideline 850.1350) will reduce uncertainty associated with the 

chronic endpoint that is currently available and will increase confidence in risk conclusions. 

Whole sediment toxicity to freshwater invertebrates 

No data are currently available to characterize the acute or chronic toxicity of pyridaben to 

sediment dwelling invertebrates. The updated Part 158 data requirements, published in October 

2007, specify that acute and chronic toxicity data for sediment invertebrates are conditionally 

required if the half-life of the pesticide in sediment >10 days in aerobic soil or aquatic 

metabolism studies and if any of the following conditions exist: a) the Kd is ≥50; b) the log Kow

is ≥3 or c) the Koc is ≥1000. Since the half-live of pyridaben in soil under aerobic conditions is 

>10 days, the Log Kow is >3 and the Koc is >1000, acute and chronic toxicity data for one species 

of sediment-dwelling invertebrate are required for pyridaben. Pyridaben registrants must 

submit a study protocol for review by the Agency prior to initiation of the chronic toxicity 

study with sediment dwelling invertebrates.

-29 of 62-
TABLE 8.4. Available Ecological Effects Data for Plants Exposed to Pyridaben and 

Remaining Data Gaps.

Guideline Description MRID Classification Data 

Gap? Comments 

850.4100 Terrestrial Plant toxicity: 

seedling emergence (Tier 1) 43680419 Supplemental Yes 

850.4150 Terrestrial Plant toxicity: 

vegetative vigor (Tier 1) 43680420 Acceptable* Yes 

43680422 Supplemental 850.5400 Aquatic Plant Growth: algae 

(Tiers 1 and 2) 43680421 Supplemental 

Yes** 

850.4400 Aquatic Plant Growth: 

vascular plants (Tier 1) 43680422 Supplemental Yes** 

*Although this study is 

classified acceptable, it was 

conducted with TGAI. 

Because no data are 

available from studies 

conducted with a typical 

end use product, this 

guideline is not fulfilled. 

**Although Tier 1 studies 

are available for 1vascular 

and 4 non-vascular aquatic 

plants, these studies did not 

test up to the limit 

concentration of 100 mg/L. 

Terrestrial plants: seedling emergence and vegetative vigor 

Tier 1 data were submitted for seedling emergence and vegetative vigor studies were plants were 

exposed to 0.5 lb a.i./A technical pyridaben. There are two uses of pyridaben (SLN on Pears and 

ornamentals) that have single application rates that exceed 0.5 lb a.i./A. In addition, the 40 

CFR158 requires that Tier I seedling emergence and vegetative vigor tests are conducted with 

typical end use product. Therefore, guidelines 850.4100 and 850.4150 are data gaps. In order to 

fulfill these guidelines, additional Tier 1 seedling emergence and vegetative vigor studies are 

required. These studies must be conducted at the highest single application rate for pyridaben 

(1.0 lbs a.i./A on ornamentals) and with a typical end use product containing pyridaben. If the 

Tier I data result in significant decreases in endpoints compared to controls or >25% effects to 

any test species, Tier II data should be submitted for that species. 

Aquatic Plant Growth: algae 

Supplemental Tier I data are available for four species of algae exposed to <20 μg a.i./L 

pyridaben (MIRD 43680422). In addition, a supplemental Tier II study is available for green 

algae exposed to pyridaben (MRID 43680421). In order to fulfill the guideline requirement for 

algae, additional Tier I data must be submitted for four species of algae exposed to pyridaben at a 

concentration of 100 mg a.i./L (limit test). If the Tier I data result in >50% effects to any test 

species, Tier II data should be submitted for that species. 

Aquatic Plant Growth: vascular plants 

Supplemental Tier I data are available for duckweed exposed to <20 μg a.i./L pyridaben (MIRD 

43680422). In order to fulfill the guideline requirement for aquatic vascular plants, additional 

Tier I data must be submitted for a vascular aquatic plant (i.e., duckweed) exposed to pyridaben 

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at a concentration of 100 mg a.i./L (limit test). If the Tier I data result in >50% effects to the test 

species, Tier II data should be submitted for that species. 

-31 of 62-
9. References 

9.1. Scientific Literature and Government Publications 

Armitage, J.M. and F.A.P.C. Gobas. 2007. A terrestrial food-chain bioaccumulation model for POPs. Environmental 

Science and Technology, 41 (11): 4019-4025. 

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

(Kenaga) nomogram, an instrument for estimating pesticide residues on plants. Environ. Tox. Chem.

13:1383-1391. 

Hoerger, F. and E. E. Kenaga. 1972. Pesticide Residues on Plants: Correlation of Representative Data as a Basis 

for Estimation of their Magnitude in the Environment. In F. Coulston and F. Korte, eds., Environmental 

Quality and Safety: Chemistry, Toxicology, and Technology, Georg Thieme Publ., Stuttgart, West 

Germany, pp. 9-28. 

Hollingworth, R.M., K.I. Ahammadsahib, G. Gadelhak, J.L. McLaughlin. 1994. New inhibitors of Complex I in the 

mitochondria1 electron transfer chain with activities as pesticides. Biochem. Soc. Trans. 22,23 0 23 3. 

Kelly, B.C. and F.A.P.C. Gobas. 2003. An Arctic terrestrial food-chain bioaccumulation model for persistent 

organic pollutants. Environmental Science and Technology, 37(13): 2966-2974. 

Kelly, B.C.; Ikonomou, M.G.; Blair, J.D.; Morin, A.E. and F.A.P.C. Gobas. 2007. Food web-specific 

biomagnifications of persistent organic pollutants. Science, 317: 236. 

USEPA. 1998. Guidelines for Ecological Risk Assessment. EPA/630/R-95/002F. Risk Assessment Forum, Office 

of Research and Development, Washington, D.C. April 1998. Online at: 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=12460 

USEPA. 1999a. Tier I Estimated Environmental Concentrations of Pyridaben in Drinking Water for Tolerance 

Petition for the use on Cranberry (DP 258903). USEPA/OPP/EFED, Washington, DC 20460. 

USEPA. 1999b. Tier II Drinking Water EECs for Use in the Human Health Risk Assessment (DP 259315). 

USEPA/OPP/EFED, Washington, DC 20460. 

USEPA. 2004a. Drinking Water Exposure Screening Assessment for Proposed Uses of Pyridaben on Strawberries, 

Hops, Tropical Fruit and Stone Fruit. USEPA/OPP/EFED, Washington, DC 20460. 

USEPA. 2004b. Overview of the Ecological Risk Assessment Process in the Office of Pesticide Programs. U.S. 

Environmental Protection Agency, Office of Prevention, Pesticides and Toxic Substances, Office of 

Pesticide Programs, Washington DC. January 23, 2004. 

USEPA. 2006. Standardized Soil Mobility Classification Guidance. U.S. Environmental Protection Agency, 

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

and Effects Division, Memorandum. Apr. 21, 2006. 

USEPA. 2008. White paper on methods for assessing ecological risks of pesticides with persistent, bioaccumulative 

and toxic characteristics. Submitted to the FIFRA Scientific Advisory Panel for review and comment. 

United States Environmental Protection Agency, Environmental Fate and Effects Division. Available 

online at: 

http://www.epa.gov/scipoly/sap/meetings/2008/october/sap_pbt_whitepaper_final_Oct_7_08d.pdf. 

U.S. Fish and Wildlife Service (USFWS) and National Marine Fisheries Service (NMFS). 1998. Endangered 

Species Consultation Handbook: Procedures for Conducting Consultation and Conference Activities Under 

Section 7 of the Endangered Species Act. Final Draft. March 1998. 

-32 of 62-
9.2. Submitted Environmental Fate and Product Chemistry Studies 

42676103 Sato, T. (1993) Physical and Chemical Characteristics of Pyridaben (NC-129) Acaricide and Insecticide 

Technical Grade Active Ingredient and Manufacturing-use Product: Lab Project Number NCI-129-

H506. Unpublished study prepared by Battelle, Ricerca, Inc., and Chemicals Inspection & Testing Inst. 

402 p. 

42680153 O'Connor, J. (1992) NC-129: Determination of Hydrolysis as a Function of pH: Final Report: Lab 

Project Number: 92/NAS106/0374: 92/11493. Unpublished study prepared by Life Science Research, 

Ltd. 131 p. 

43680427 O'Connor, J. (1995) NC-129: Photodegradation in Water: Final Report: Lab Project Number: 94/11765: 

94/0160: 94/NAS101/0160. Unpublished study prepared by Pharmaco LSR Ltd. 304 p. 

43792110 O'Connor, J. (1995) NC-129: Photodegradation on Soil: Final Report: Lab Project Number: 94/0044: 

94/11766: NAS/102. Unpublished study prepared by Pharmaco-LSR Ltd. 331 p. 

42680154 O'Connor, J. (1993) NC-129: A Study of Aerobic Soil Metabolism: Lab Project Number: NAS/099/NC129: 92/NAS099/0211: 93/10100. Unpublished study prepared by Life Science Research, Ltd. 541 p. 

47576104 Crowe, A. (2002) Pyridaben - Aerobic Soil Metabolism (Route of Degradation). Project Number: 

NAS/341. Unpublished study prepared by Huntingdon Life Sciences, Ltd. 99 p. 

43680428 O'Connor, J. (1994) NC-129--A Study of Anaerobic Metabolism plus First Amendment: Final Report: 

Lab Project Number: 94/10947: 94/NAS103/0285: 93/NAS103/0546. Unpublished study prepared by 

Pharmaco LSR Ltd. 412 p. 

42680155 O'Connor, J. (1992) NC-129: Determination of Soil Adsorption/Desorption Properties: Lab Project 

Number: LSR 92/0172: 92/11152. Unpublished study prepared by Life Science Research, Ltd. 202 p. 

42680156 O'Connor, J. (1993) NC-129: Determination of the Mobility of NC-129 and Its Degradates by Soil 

Column Studies: Lab Project Number: NAS/105/NC-129: 92/NAS105/0215: 93/10099. Unpublished 

study prepared by Life Science Research, Ltd. 415 p. 

43360701 Winkler, V. (1994) BASF Response to EPA Review of NC-129: Determination of the Mobility of NC129 and its Degradates by Soil Column Studies: Lab Project Number: 94/5110: LSR 92/NAS 105/0215: 

93/10099. Unpublished study prepared by BASF Corp. 53 p. 

43792111 O'Connor, J. (1995) NC-129: Determination of the Mobility of NC-129 and its Degradates by Soil 

Column Studies: Amended Final Report: Lab Project Number: 94/1164: 94/11764: NAS/105. 

Unpublished study prepared by Pharmaco LSR Ltd. 431 p. 

44008302 Morgan, P. (1996) P-14: Determination of the Adsorption/Desorption Properties in Soils: Final Report: 

Lab Project Number: NAS/176: 95/NAS176/1199: 96/5038. Unpublished study prepared by Huntingdon 

Life Sciences Ltd. 51 p. 

43680429 Venkatesh, K. (1995) Confined Terrestrial Field Dissipation of (carbon 14)-BAS 300 I: Lab Project 

Number: 95/5012: M9019: M9317. Unpublished study prepared by BASF Corp. and Agvise Labs. 100 

p. 

43680430 Clark, J.; Jackson, S.; Qiu, J. (1995) Pyridaben Soil Dissipation in Citrus Groves: Lab Project Number: 

95/5052: 93002: ER 95004. Unpublished study prepared by Grayson Research Ltd. 1322 p. 

43792112 Singh, M. (1995) Confined Aquatic Dissipation of Pyridaben (BAS 300 I) in a Simulated Microcosm 

Environment: Lab Project Number: 95/5020: 93013: M9418. Unpublished study prepared by Toxicon 

Environmental Sciences and BASF Corp. 177 p. 

43909904 Clark, J.; Jackson, S.; Qiu, J. (1995) Pyridaben Soil Dissipation in Apple Orchards in the USA: Through 

-33 of 62-
180 Days: Summary Report: Lab Project Number: RCN 94164: RCN 94165: 95/5178. Unpublished 

study prepared by Grayson Research, Ltd.; ACDS Research, Inc.; and Qualls Agricultural Labs. 892 p. 

43680432 Singh, M. (1994) Dissipation of (Carbon 14)-BAS 300 I in an Outdoor Confined Aquatic Ecosystem: 

Lab Project Nos. 94/5182; 91118; M9316. Unpublished study prepared by BASF Corp. and Wildlife 

International Ltd. 134 p. 

43680433 Smith, M. (1995) HPLC Method for Residue Determinations of Pyridaben (BAS 300 I) Metabolite, P-16 

in Pond Water, Sediment, and Soil: Lab Project Number: 95/5011: D9307: 93065. Unpublished study 

prepared by BASF Corp. 65 p. 

43792113 Jenkins, W. (1994) NC-129: Determination of its Accumulation in the Rainbow Trout Under FlowThrough Exposure Conditions: (Final Report): Lab Project Number: 94/10081: 93/NAS087: 

93/NAS088. Unpublished study prepared by Pharmaco:LSR, Ltd. 376 p. 

43792114 Ohuchiyama, N. (1987) Test on Bioaccumulation of NC-129 in Carp: Test Number: 6208: Final Report: 

Lab Project Number: 88/0573. Unpublished study prepared by Kyushu Lab. 60 p. 

9.3. Submitted Effects Studies 

42680105 Grimes, J.; Jaber, M. (1986) The Acute Oral Toxicity with the Mallard (NC-129): Final Report: Lab 

Project Number: 221-102: 88/0600. Unpublished study prepared by Wildlife International, Ltd. 23 p. 

42680106 Grimes, J.; Jaber, M. (1986) NC-129: An Acute Oral Toxicity Study with the Bobwhite: Final Report: 

Lab Project Number: 221-101: 88/0598. Unpublished study prepared by Wildlife International, Ltd. 21 p. 

42680107 Grimes, J.; Jaber, M. (1987) NC-129: A Dietary LC50 Study with the Mallard: Final Report: Lab Project 

Number: 221-106: 88/0601. Unpublished study prepared by Wildlife International, Ltd. 25 p. 

42680108 Grimes, J.; Hinken, C.; Jaber M. (1986) NC-129: A Dietary LC50 Study with the Bobwhite: Final Report: 

Lab Project Number: 221-105: 88/0599. Unpublished study prepared by Wildlife International, Ltd. 24 p 

42680109 Willis, C.; Wilson, I. (1987) The Acute Toxicity of NC-129 to Rainbow Trout: Final Report: Lab Project 

Number: AFT/86/022B: 88/0596. Unpublished study prepared by Aquatox, Ltd. 40 p. 

42680110 Willis, C. (1988) The Acute Toxicity of NC-129 to Bluegill Sunfish: Final Report: Lab Project Number: 

LSR/87/NAS021/600: 87/NAS021/600: 88/0595. Unpublished study prepared by Life Science Research, Ltd. 51 p. 

42680111 Willis, C.; Wilson, I. (1987) The Acute Toxicity of NC-129 to Daphnia Magna: Final Report: Lab Project 

Number: AFT/86/024: 88/0594. Unpublished study prepared by Aquatox, Ltd. 35 p. 

42680119 Yanagita, T. (1990) Acute Toxicity Study by Oral Administration of NC-129 in Rats: Lab Project 

Number: ML-303F: 90/0585. Unpublished study prepared by Preclinical Research Laboratories Central Institute for 

Experimental Animals. 102 p. 

42680120 Yanagita, T. (1990) Acute Toxicity Study by Oral Administration of NC-129 in Mice: Lab Project 

Number: ML-303E: 90/0586. Unpublished study prepared by Preclinical Research Laboratories Central Institute for 

Experimental Animals. 94 p 

42680143 Tesh, J. et al. (1989) NC-129: Effects of Dietary Administration upon Reproductive Performance in the 

Rat: Dose Range-Finding Study: Lab Project Number: LSR 88/0025: 88/0025: 89/0372. Unpublished study prepared 

by Life Science Research. 94 p. 

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42680144 Willoughby, C. (1990) NC-129: Reproductive Performance Study in Rats Treated Continuously through 

Two Successive Generations--Volumes I and II: Lab Project Number: LSR 89/NAS033/0937: 89/NAS033/0937: 

89/0937: 90/0046. Unpublished study prepared by Life Science Research. 724 p. 

43680401 Ward, G. (1994) Pyridaben Technical: Acute Toxicity to Bluegill, Lepomis macrochirus, Under FlowThrough Conditions: Lab Project Number: 94/5002: 93062: ER93046. Unpublished study prepared by Toxikon 

Environmental Sciences. 33 p. 

43680402 Ward, G. (1994) Pyridaben Technical: Acute Toxicity to Rainbow Trout, Oncorhynchus mykiss, Under 

Flow- Through Conditions: Lab Project Number: 94/5001: 93142: ER93047. Unpublished study prepared by 

Toxikon Environmental Sciences. 33 p. 

43680403 Bootman, J.; Jenkins, W.; O'Connor, J. (1989) NC-129: 21-Day Rainbow Trout Toxicity Study Under 

Flow-Through Conditions: Lab Project Number: 89/0258: 88/NAS041/0824: 88/0824. Unpublished study prepared 

by Life Sciences Research Ltd. 41 p. 

43680404 Graves, W.; Swigert, J. (1993) Pyridaben Technical A.I.: A 48-Hour Flow-Through Acute Toxicity Test 

with the Cladoceran (Daphnia magna): Lab Project Number: 93/5169: ER 93057: 92076. Unpublished study 

prepared by Wildlife International Ltd. 45 p. 

43680405 Morrow, J. (1993) Pyridaben (BAS 300 I-Tech. A.I.): Acute Toxicity to the Mysid, Mysidopsis bahia, 

Under Flow-Through Test Conditions: Lab Project Number: 93/5171: 92017: ER93039. Unpublished study prepared 

by Toxikon Environmental Sciences. 36 p. 

43680406 Morrow, J.; Ward, G. (1993) Pyridaben Technical: Acute Toxicity to the Sheepshead Minnow, 

Cyprinodon variegatus, Under Flow-Through Test Conditions: Lab Project Number: 93/5155: 92018: ER93058. 

Unpublished study prepared by Toxikon Environmental Sciences. 33 p. 

43680407 Ward, G. (1994) Pyridaben (BAS 300 I-Tech. A.I.): Acute Effect on New Shell Growth of the Eastern 

Oyster, Crassostrea virginica: Lab Project Number: 94/5024: 93074: ER93048. Unpublished study prepared by 

Toxikon Environmental Sciences. 44 p. 

43680408 Drottar, K.; Swigert, J. (1994) (Carbon 14)-Pyridaben: A Flow-Through Life Cycle Toxicity Test with the 

Cladoceran, Daphnia magna: Lab Project Number: 94/5074: 93063: ER 94001. Unpublished study prepared by 

Wildlife International Ltd. 61 p. 

43680409 Holmes, C.; Machado, M. (1995) (Carbon 14)Pyridaben (BAS 300 I) Technical--Chronic Toxicity to 

Mysids (Mysidopsis bahia) Under Flow-Through Conditions: Final Report: Lab Project Number: 95/5018: 93033: 

ER95001.Unpublished study prepared by Springborn Labs, Inc. 180 p. 

43680410 Jenkins, W.; Jenkins, C.; O'Connor, J. (1989) NC-129: 21-Day Juvenile Production Study Using Daphnia 

magna Under Semi-Static Test Conditions: Lab Project Number: 89/0271: 88/0700. Unpublished study prepared by 

Life Science Research Ltd. 45 p. 

43680419 Elliott, D. (1992) Tier 1 Seed Germination/Seedling Emergence Nontarget Phytotoxicity Study Using 

Pyridaben (BAS 300 I-Tech. a.i.): Lab Project Number: 92/5161: 92013: ER92041. Unpublished study prepared by 

Pan- Agricultural Labs, Inc. 93 p. 

43680420 Blackburn, R. (1992) Tier 1 Vegetative Vigor Nontarget Phytotoxicity Study Using Pyridaben (BAS 300 

I-Tech. a.i.): Lab Project Number: 92/5160: 92012: ER92040. Unpublished study prepared by Pan-Agricultural 

Labs, Inc. 70 p. 

43680421 Jenkins, W. (1988) Determination of the EC50 of NC-129 to Selenastrum capricornutum Under NonAxenic Conditions: Lab Project Number: 88/0597: 87/NAS027/897. Unpublished study prepared by Life Science 

Research Ltd. 46 p. 

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43680422 Hughes, J.; Jackson, S. (1994) Tier 1 Non-Target Aquatic Plant Toxicity Study on BAS 300..I 

(Pyridaben): Lab Project Number: 95/5064: 93008: ER 93034. Unpublished study prepared by Malcolm Pirnie, Inc. 

and Huntingdon Analytical Services. 106 p. 

43792101 Beavers, J.; Sipler, O.; Mitchell, L. et al. (1994) Pyridaben Technical (NC 129): A Reproduction Study 

with the Mallard: Lab Project Number: 94/10237: 147-159: 72W0021/929008. Unpublished study prepared by 

Wildlife International Ltd. and BASF Corp. 208 p. 

43792102 Beavers, J.; Sipler, O.; Mitchell, L.; et al. (1994) Pyridaben Technical (NC 129): A Reproduction Study 

with the Northern Bobwhite: Lab Project Number: 94/10238: 147-158: 71W0021/929019. Unpublished study 

prepared by Wildlife International, Ltd. and BASF Corp. 206 p. 

43792103 Motohashi, F.; Sakamoto, S. (1991) Acute Toxicity Study of 20% WP-Formulation of NC-129 to FreshWater Fish Under Paddy Field Condition: (The First Test): Lab Project Number: 91-504. Unpublished study 

prepared by Nissan Chemical Industries Ltd.'s Shiraoka Research Station of Biological Science. 35 p. 

43792104 Motohashi, F.; Sakamoto, S. (1991) Acute Toxicity Study of 20% SC-Formulation of NC-129 to FreshWater Fish Under Paddy Field Condition: (The Second Test): Lab Project Number: 91-519: 91/11266. Unpublished 

study prepared by Nissan Chemical Industries Ltd.'s Shiraoka Research Station of Biological Science. 36 p. 

43792105 Motohashi, F.; Sakamoto, S. (1991) Acute Toxicity Study of 20% WP-Formulation of NC-129 to FreshWater Fish Under Paddy Field Condition: (The Third Test): Lab Project Number: 91-527: 91/11267. Unpublished 

study prepared by Nissan Chemical Industries Ltd.'s Shiraoka Research Station of Biological Science. 36 p. 

43792106 Rhodes, J.; Leak, T.; Holmes, C. (1995) Full Life-Cycle Toxicity of BAS 300 I (Pyridaben) to the 

Fathead Minnow (Pimephales promelas) Under Flow-Through Conditions: Lab Project Number: 40571: 92160: 

ER94070. Unpublished study prepared by ABC Labs, Inc. and BASF Corp. 1310 p. 

43792107 Springer, T.; Jackson, B.; Reed, C. et al. (1994) Acute Toxicity (96 Hour LC 50) of BAS 300 11 I to 

Bluegill Sunfish in Outdoor Studies: Lab Project Number: 94/5181: 147-146: 91096. Unpublished study prepared by 

Wildlife International Ltd. and BASF Corp. 114 p. 

43792108 Rand, G.; Holmes, C. (1995) Pyridaben (BAS 300 11 I): An Outdoor Aquatic Microcosm Study: Lab 

Project Number: ER 94066: 92077: J9203004. Unpublished study prepared by Toxikon Environmental Sciences; 

Huntingdon Analytical Services; and A & L Midwest Labs, Inc. 677 p. 

44039601 Cunningham, F. (1996) Pyridaben: An Outdoor 96-Hour Static Acute Toxicity Test with the Saltwater 

Mysid, (Mysidopsis bahia): Lab Project Number: J9509002: 96/5075: J9509002/BASF 95121. Unpublished study 

prepared by Toxikon Environmental Sciences. 202 p. 

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APPENDIX A: Current Registrations for Pyridaben 

Section 3 registrations for formulated 

products: 

7969-106 

7969-125 

7969-202 

7969-225 

81880-3 

81880-4 

81880-5 

81880-6 

Section 3 registrations for technical 

pyridaben: 

7969-110 

7969-164 

33906-16 

Special local needs registrations for 

pyridaben: 

AZ070009 

ME080001 

MN080010 

PA070003 

TX070009 

WA090017 

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APPENDIX B: Characterization of Environmental Fate Data for Pyridaben 

B.1. Transport and Mobility 

Pyridaben (2-tert-butyl-5-(4-tert-butylbenzylthio)-4-chloropyridazin-3(2H)-one) is a white, 

crystalline solid that has a melting point of 108-110oC (MRID 42676103). It has a low solubility 

in water (0.012 ppm @ 20oC; MRID 42676103). Based on a low vapor pressure 8.21 x 10-5 torr 

(25oC; MRID 42676103) and Henry’s Law Constant 6.84 x 10-3atm·m3/mole (estimated, 

EpiSuite v4.0), pyridaben has the potential to volatilize from treated sites; however, due to the 

compound’s high propensity to bind to soil particles it, it is unlikely that it will volatilize. 

Due to pyridaben’s low solubility, low vapor pressure, and high level of binding (Kads = 108-

6600; MRID 42680155), it is likely that the chemical would remain bound to the soils during 

runoff events. According to the FAO soil mobility classification scheme, pyridaben is hardly 

mobile (Koc > 10,000; USEPA, 2006). Therefore, it would reach adjacent bodies of water when 

the runoff events are accompanied by erosion. Pyridaben is unlikely to leach to ground water. 

B.2. Bioaccumulation 

Based on pyridaben’s Log Kow (6.37; MRID 42676103), bioaccumulation in aquatic ecosystems 

is potentially a concern. 

Bioconcentration data are available from two separate laboratory studies involving rainbow trout 

(MRID 43792113). These studies were conducted according to similar methods, but are 

distinguished by the position of the radiolabels on the pyridaben molecule. After 28 days of 

exposure to pyridaben (0.11 μg a.i./L), whole fish BCF values (based on total radioactivity) were 

342 and 439 (μg/kg-ww per μg/L). In a life cycle test with fathead minnows (Pimephales 

promelas), BCF values ranged 1168 to 3780 in larval and adult fish exposed to pyridaben (MRID 

43792106). 

In the BCF studies with rainbow trout, the rate constant for the depuration phase of the two 

experiments was 0.18 d-1 (kT). Metabolites were identified in the fish tissue; however, their levels 

were not quantified. Identified metabolites included: PB-5, PB-7, PB-9, PB-10, PB-11, PB-12 

and PB-13 (illustrated below in Table A1). The presence of these metabolites indicate that 

metabolism of pyridaben may alter the bioaccumulation potential of pyridaben through 

transformation. 

Differences in BCF values observed in the 30-d rainbow trout and full life cycle fathead minnow 

tests may be attributed to the durations of the studies. Based on the Kow of pyridaben, the time 

required to reach steady state may be greater than 30 days, which would result in 

underestimation of BCF values obtained from the rainbow trout studies. For this reason, 

KABAM was run to estimate BCF values considering metabolism and steady state conditions. 

Using a Log Kow value of 6.37, KABAM (v.1.0) estimates a fish BCF of 1.1x105 for pyridaben. 

This value assumes no metabolism of the parent compound. The sum of the loss rate constants 

for KABAM (i.e., k2, kE and kG) is 0.012 d-1, which is an order of magnitude lower than the kT

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value estimated from the laboratory BCF studies. A metabolism rate constant can be estimated 

by subtracting the estimated loss rate constants for respiration, fecal elimination and growth 

dilution from the empirical kT from MRID 43792113. The result is an estimated kM = 0.17, 

which indicates that metabolism is likely the dominant elimination pathway for pyridaben, 

leading to much lower bioconcentration of total pyridaben residues than expected when 

considering the Kow of pyridaben. When kM is considered, the estimated BCF for a 3.6 g fish 

(similar to the weight of the test fish in the laboratory BCF studies) is 5740. This revised 

estimated BCF is 2 orders of magnitude lower than the estimated BCF that assumes no 

metabolism. Although this estimated value is 1 order of magnitude above the empirical BCF 

values from the rainbow trout studies (342 and 439), it is consistent with the maximum BCF for 

fathead minnows (3780) reported by the full life cycle study authors. 

B.3. Degradation 

It appears that photolysis constitutes the major degradation pathway for pyridaben in water (t 1⁄2 

= 5 minutes; MRID 43680427). Aerobic soil metabolism is expected to play a minor role in the 

degradation of the chemical (t 1⁄2 = 110 days; MRID 42680154). Pyridaben degrades to 

numerous minor degradates (Table B1), at relatively low levels; no major organic degradates 

(>10% of the applied) were observed, except for B-3 identified in the definitive aqueous 

photolysis study. Pyridaben is stable to hydrolysis at pH 5, 7 and 9 (MRID 42680153) and is 

stable in soil under anaerobic conditions (MRID 43680128). 

Based on results of a soil photolysis study (MRID 43792110), pyridaben appears to have a 

biphasic degradation profile (quickly at the beginning, likely due to soil photolysis, and more 

slowly afterwards). The initial half-life of pyridaben on soils exposed to a xenon arc lamp was 11 

days. Multiple degradates, at <10% of the applied were formed. It appears that the soil photolysis 

could enhance the aerobic soil metabolism as evidenced by the formation of additional levels of 

C02, as compared to the control (unexposed samples). 

In an aerobic soil metabolism study (MRID 42680154), pyridaben degraded slowly, with a 

registrant calculated half-life of 86 days (reviewer calculated half-life of 110 days) in sandy loam 

soil (only one soil, CA sandy loam, was acceptable; MRID 42680154). Only minor non-volatile 

degradates were identified. Among them, the following were identified: PB-4, PB-7, and PB-14, 

as well as other unidentified compounds and CO2. 

Evidence suggests that anaerobic soil metabolism does not constitute an important route of 

degradation for pyridaben. Anaerobic soil metabolism studies were conducted on two soils: a 

Florida sand soil, and a California sandy loam soil (MRID 43680128). The study started with 

incubation of the soils under aerobic conditions, followed by establishment of anaerobic 

conditions by maintaining a nitrogen atmosphere. As a result of the establishment of anaerobic 

conditions the degradation of pyridaben essentially ceased. In addition, the release of C02

decreased substantially and ultimately ceased. Multiple degradates were observed throughout, 

the study at <8% of the applied, including PB-4, PB-14, PB-5, PB-9, PB-11, B-I, B-3, and B-7.

-39 of 62-
Table B.1. Pyridaben and Its Radiolabeled Degradates

Common 

Name Chemical Name Chemical Structure Study Type Maximum %AR A (day)

Parent 

Pyridaben 2-tert-butyl-5-(4-tertbutylbenzylthio)-4-

chloropyridazin-3(2H)-one

N

N

CH3

3CH

CH3

O

S

Cl

C

H2

CH3

CH3

CH3

-- -- 

Major Radiolabeled Degradates (>10% AR)

B-3 Unknown Unknown Aqueous Photolysis 20% (30 

min) 

CO2 Carbon dioxide O C O

Minor Radiolabeled Degradates 

PB-4 

2-tert-butyl-5-(4-tertbutylbenzylsulfinyl)-4- 

chloropyridazin-3(2H)-one

N

N

CH3

3CH

CH3

O

S

Cl

O C

H2

CH3

CH3

CH3

Aerobic Soil Metabolism 

 

Anaerobic Soil Metabolism 

< 10% (2 

months) 

<8% 

PB-5 

5-(4-tert-Butylbenzylthio)-

4-chloropyridazin-3(2H)-

one 

Anaerobic Soil Metabolism 

Fish Bioaccumulation 

<8% 

PB-7 

2-tert-butyl-5-[4-(1-

carboxy-1-

methylethyl)benzylthio]-3-

chloro-pyridazin-3(2H)-one

N

N

CH3

3CH

CH3

O

S

Cl

C

H2

CH3

CH3

O

OH

Aerobic Soil Metabolism 

Anaerobic Soil Metabolism 

Fish Bioaccumulation 

< 10% (2 

months) 

< 8% 

PB-9 

2-tert-Butyl-4-chloro-5-[4-

(1,1-dimethyl-2-

hydroxyethyl)benzylthio]py

ridazin-3(2H)-one 

N

N

CH3

3CH

CH3

O

S

Cl

C

H2

CH3

CH3

H2

OH

Anaerobic Soil Metabolism <8% 

PB-11 

5-(4-tert-Butylbenzylthio)-

4-chloro-2-(1,1-dimethyl-2-

hydroxyethyl)-pyridazin3(2H)-one 

Anaerobic Soil Metabolism <8% 

-40 of 62-
Common Maximum Chemical Name Chemical Structure Study Type Name %AR A (day)

PB-12 

5-(4-tert-Buthylbenzylthio)-

2-(1-carboxy-1-

methylethyl)-4-

chloropyridazin-3(2H)-one

Fish Bioaccumulation 

PB-14 

2-tert-Butyl-4-

chloropyridazin-3(2H)one5-sulphonic acid. 

N

N

CH3

3CH

CH3

O

S O3H

Cl Aerobic Soil Metabolism 

Aqueous Photolysis 

< 10% (6 

months) 

7% (6 hours)

PB-16 4-Chloropyridazin-3-(2H)-

one-5-sulfonic acid. 

NH

N

O

S O3H

Cl

Aqueous Photolysis 5% (4-6 

hours) 

B-1 Unknown Unknown -- 

B-7 2-(4-Carboxyphenyl)-2-

methylpropionic acid 

CH3

CH3

O

OH

O

OH -- 

A. %AR means “percent of applied radioactivity”. 

B.4. Field Dissipation 

Four terrestrial field dissipation studies were conducted to support the registration of pyridaben, 

two in apple orchards, and two in citrus groves. For the orchard studies pyridaben was applied 

twice at 0.6 lbs a.i./A with an application interval of 30 days (MRID 43909904), and for the 

citrus grove study pyridaben was applied twice at 0.5 lbs a.i./A with an application interval of 30 

days (MRID 43680430). For the apple orchards studies, conducted in New York and 

Washington, the registrant reported DT50’s for pyridaben after the first and second applications. 

The DT50’s were consistent with a range of 6-12 days. For the citrus grove studies, conducted in 

California and Florida, the registrant reported overall nonlinear DT50’s, which were 14 days in 

California, and 12 days in Florida. Calculated DT50’s and DT90’s from each study are 

summarized below in Table B.2. 

Table B.2. Summary of DT50s from Terrestrial Field Dissipation Studies for Pyridaben. 

Study DT50 Comments DT90 MRID 

New York Apples 7.5 days Mean of two 

values 

214 days 43909904 

Washington Apples 10 days Mean of two 

values 

188 days 43909904 

Florida Citrus 12 days None 120 days 43680430 

California Citrus 14 days None 629 days 43680430 

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It should be noted that in all cases the initial rate of dissipation of pyridaben was faster, likely 

due to soil photolysis, with some potential for volatilization, with much slower dissipation 

afterwards (calculated DT90s ranged from 120 to 629 days). Parent pyridaben remained in the 

upper 0-6" soil level, except for rare trace levels in the 6-12" soil level in Washington and 

California only. Six metabolites of pyridaben were monitored: P-14, P-16, PB-4, PB-7, PB-9, 

and PB-14, Trace levels of some of these compounds were occasionally detected in the 0-6" soil 

level only. 

There are also three additional supplemental studies that are discussed below. In a Confined 

Terrestrial Field Dissipation study (MRID 43792112), 14C-pyridaben was applied to a loamy 

sand. Based on non-linear DT50’s, the following results were reported: 

 DT50 pyridazinone labeled parent 71 days 

 DT50 benzene labeled parent 1 day 

There were glaring differences in the DT50’s for the two labels. Despite the differences in 

DT50s it was apparent in both studies that the degradation of pyridaben was biphasic. Essentially 

all the residues remained in the 0-3" soil depth. The following degradates were monitored and 

found only in small amounts (<2.85% of the total applied) : PB-4, PB-7, PB-9, PB-14, P-14, and 

P-16. 

In another supplemental study, an Outdoor Aquatic Microcosms study of pyridaben (MRID 

43792108), conducted in Palm Beach County, Florida, three levels of application were used: 

0.34 μg/L, 3.4 μg/L, and 34 μg/L. Based on the results obtained, post-application half-lives for 

the low, mid, and high treatment concentrations in water were 28.5, 21.2, and 23.0 hours, 

respectively. The residue concentrations of pyridaben in sediment at the highest application rate 

(34 ppt) gave a DT50 of approximately 9.8 days. 

Thirdly, a supplemental confined Aquatic field dissipation study was conducted using 

radiolabeled pyridaben (MRID 43792112). Pyridaben degraded rapidly to a large number of 

minor products after 3 DAT. The half-life for the benzene label was 0.28 days, and for the 

pyridazinone label it was 0.99 days. 

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APPENDIX C: Characterization of Ecological Effects Data for Pyridaben 

C.1. Effects to Aquatic Organisms 

Toxicity to aquatic fish and invertebrates is categorized using the definitions provided in Table 

C1 (U.S. EPA, 2004). Toxicity categories for aquatic plants have not been defined. 

Table C1. Categories of Acute Toxicity for Fish and Aquatic Invertebrates. 

LC50 (mg a.i./L) Toxicity Category 

< 0.1 Very highly toxic 

> 0.1 - 1 Highly toxic 

> 1 - 10 Moderately toxic 

> 10 - 100 Slightly toxic 

> 100 Practically nontoxic 

The available acute and chronic toxicity data for aquatic organisms exposed to pyridaben are 

from registrant-submitted studies conducted in the laboratory. The data summarized below 

correspond to exposures involving the technical grade active ingredient (TGAI) pyridaben. 

Some supplemental data are available from outdoor mesocosm studies that were conducted with 

formulated products containing pyridaben (MRIDs 43792103, 43792104, 43792105, 43792108, 

44039601, 53792107). These studies are not described in this problem formulation, but may be 

considered for characterization purposes in future risk assessments of pyridaben. 

An ECOTOX search that was conducted on September 15, 2009, identified several studies 

containing acute and chronic toxicity data for aquatic organisms (Rand and Clark 2000a; Rand 

and Clark 2000b; Rand et al. 2000; Rand et al. 2001). Rand and Clark 2000a present acute and 

chronic toxicity data for several species of freshwater and estuarine/marine fish and 

invertebrates. The reported details of these studies (i.e., concentration range tested, slope, effect 

and NOEC) are consistent with those provided by the registrant in the flow through tests for 

these species that are described below. Rand and Clark 2000b, Rand et al. 2000 and Rand et al. 

2001 present effects data from microcosms, which are not considered for this problem 

formulation. 

C.1.1. Freshwater Fish 

Pyridaben is very highly toxic to freshwater fish on an acute exposure basis. The most sensitive 

acute endpoint is a 96-h LC50 of 0.72 μg a.i./L for rainbow trout (Oncorhynchus mykiss; MRID 

43680402). Registrant submitted acute toxicity data for fish exposed to pyridaben are 

summarized in Table C2. 

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Table C2. Acute toxicity data for freshwater fish exposed to pyridaben (TGAI; 98-100% 

a.i.). LC50 values are based on mean-measured concentrations. 

Species Common 

name 

Flow/static 96-h LC50 

(μg a.i./L) 

95% C.I. Slope Citation 

(MRID) 

Lepomis Flow 3.43 3.13-3.80 4.95 43680401 

macrochirus 

Bluegill 

sunfish Static (renewal) 2.52 1.85-3.2 5.01 42680110 

Flow 0.72 0.63-0.83 6.86 43680402 

Static (renewal) 2.3 1.9-2.68 5.68 42680109 

Oncorhynchus 

mykiss 

Rainbow Trout 

Flow 3.2 NA NA 43680403 

NA = not available 

Chronic toxicity data are available from a full life cycle test conducted with the fathead minnow 

(Pimephales promelas). Growth (length and weight) of the F0 and F1 generations, as well as 

survival of the F1 generation were significantly decreased relative to controls at 0.555 μg a.i./L. 

The resulting study NOAEC was 0.277 μg a.i./L (MRID 43792106).This study reported a 96-h 

LC50 of 2.3 μg a.i./L for fish (30-d old) from the same lot that was tested in the full life cycle test. 

Although the study report did not provide the raw mortality data for the acute test, these data can 

be used to characterize the acute to chronic ratio (i.e., LC50/NOEC = 8.3) of pyridaben to fathead 

minnows. 

C.1.2. Freshwater Invertebrates 

Pyridaben is very highly toxic to freshwater invertebrates on an acute exposure basis. Data are 

available from two acute studies involving Daphnia magna. In a static test, the 48-h EC50 was 

0.53 (0.47-0.61) μg a.i./L (MRID 42680111). In a flow-through test, the 48-h EC50 was 1.02 

(0.90-1.16) μg a.i./L (MRID 43680404). 

In a registrant submitted chronic semi-static study with D. magna, a decrease in adult survival 

(10% relative to controls) and a decrease in reproduction (6% decrease in number of offspring 

per female) was observed at the lowest treatment level, resulting in a NOAEC <0.013 μg a.i./L 

(MRID 43680410). This study was classified supplemental and will not be used for establishing 

the chronic endpoint for freshwater invertebrates due to high variability in exposure 

concentrations (average declines of >40% in concentration within 2 days of exposure). 

In a second chronic study with D. magna, time to reproduction was significantly affected at 

0.086 μg a.i./L, with a NOAEC of 0.044 μg a.i./L (MRID 43680408).The second study was 

conducted under flow-through conditions, with consistent exposure concentrations. Therefore, 

the NOAEC from this study is considered more reliable than the NOAEC derived from MRID 

43680410. This NOAEC will be used in future ecological risk assessments of pyridaben. 

C.1.3. Estuarine/marine Fish 

Pyridaben is very highly toxic to estuarine/marine fish on an acute exposure basis. This is based 

on one 96-h LC50 value of 17.2 (13.3-26.5) μg a.i./L for sheepshead minnow (Cyprinodon 

variegates; MRID 43680406). This study was classified supplemental because the highest test 

concentration resulted in 50% mortality, leading to uncertainty in the established LC50. 

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C.1.4. Estuarine/marine Invertebrates 

Pyridaben is very highly toxic to estuarine/marine invertebrates on an acute exposure basis. This 

is based on a 96-h LC50 value of 0.67 (0.54-0.94) μg a.i./L for mysid shrimp (Mysidopsis bahia;

MRID 43680405) and a 96-h EC50 of 5.7 μg a.i./L for reduction of shell deposition in the 

Eastern oyster (Crassostrea virginica; MRID 43680407). 

In a 35-d chronic flow-through study with mysid shrimp, no reproductive, growth or survival 

effects were observed in exposures as high as 0.13 μg a.i./L (MRID 43680409). This study was 

classified supplemental due to poor control performance and lack of observed effects at any 

treatment level. Despite this uncertainty, this endpoint will be used in future risk assessments of 

pyridaben if no additional acceptable or supplemental data are available. 

C.1.5. Aquatic Plants 

Data from Tier 1 studies are available for 4 species of non-vascular plants (Navicula pelliculosa, 

Skeletonema costatum, Anabaena flos-aquae and Selenastrum capricornutum) exposed to 

pyridaben for 5 d under static conditions. Reported concentrations were based on initial 

measured values. Pyridaben was not detected at the conclusion of the studies. Percent inhibiton 

of cell density at the test conclusions are provided in Table C3 (MRID 43680422). In a Tier II 

test with S. capricornutum, an EC50 was estimated as >665 μg a.i./L (MRID 43680421). 

Table C3. Observed inhibition of growth of non-vascular and vascular plants exposed to 

pyridaben in Tier 1 tests (MRID 43680422). 

% inhibition of treatment level 

compared to controls 

Species Common name Initial 

exposure 

concentration 

(μg a.i./L) 

Negative Solvent 

Navicula pelliculosa Freshwater diatom 13.6 0.5 none 

Skeletonema costatum Saltwater diatom 16.1 16 24 

Anabaena flos-aquae Blue-green algae 13.4 11 none 

Selenastrum capricornutum Green algae 17.3 none none 

Lemna gibba duckweed 16.2 7 none 

A 14-d Tier I toxicity test with duckweed (Lemna gibba) exposed to 16.2 μg a.i./L pyridaben 

resulted in a no decrease in frond production compared to the solvent control and a 7% decrease 

in frond production compared to the negative control (MRID 43680422; Table C3). Because this 

was a tier 1 test, no EC50 or NOAEC was established for duckweed exposed to pyridaben. The 

exposure concentration is based on the initial measured value. Pyridaben was not detected at the 

conclusion of the 14 d study. 

-45 of 62-
C.2. Effects to Terrestrial Organisms 

Acute toxicity to terrestrial animals is categorized using the definitions provided in Table C4 

(U.S. EPA, 2004). Toxicity categories for terrestrial plants have not been defined. 

Table C4. Categories of Acute Toxicity for Avian and Mammalian Studies. 

Toxicity Category Oral LD50 (mg/kg-bw) Dietary LC50 (mg/kg-diet) 

Very highly toxic < 10 < 50 

Highly toxic 10 - 50 50 - 500 

Moderately toxic 51 - 500 501 - 1000 

Slightly toxic 501 - 2000 1001 - 5000 

Practically non-toxic > 2000 > 5000 

The available acute and chronic toxicity data for terrestrial animals exposed to pyridaben are 

from registrant-submitted studies conducted in the laboratory. The data summarized below 

correspond to exposures involving the technical grade active ingredient (TGAI) pyridaben. 

Terrestrial plant studies involved exposures in the greenhouse to technical pyridaben. 

As of February 15, 2010, no additional acute or chronic toxicity data for mammals or birds 

exposed to pyridaben were identified in the scientific literature (based on a search of ECOTOX). 

Effects data are available in the scientific literature involving exposures of arthropods to 

pyridaben; however these studies do not generate the endpoints used by EFED for beneficial 

insects (i.e., 48-h LD50). No data have been identified in the scientific literature that involve 

exposures of plants to pyridaben. 

C.2.1. Birds 

Pyridaben is classified practically non-toxic to birds on an acute oral exposure basis. In an acute 

oral toxicity study with the Northern bobwhite quail (Colinus virginianus), the LD50 for technical 

pyridaben (98%) was >2250 mg/kg-bw (MRID 42680106). In an acute oral study with the 

mallard duck (Anas platyrhyncos), the LD50 was >2500 mb/kg-bw for technical pyridaben (98%) 

MRID 42680105). There were no mortalities in the treatment levels of either acute oral test. 

On a subacute dietary basis, pyridaben is classified slightly toxic to birds. Data are available 

from two registrant submitted studies where 8-d LC50 values for technical pyridaben (98%) were 

4688 mg/kg-diet for mallard duck (MRID 42680107) and >5620 mg/kg-diet for bobwhite quail 

(MRID 42680108). 

Reproductive toxicity studies are available for the bobwhite quail (MRID 43792102) and the 

mallard duck (MRID 43792101) exposed to technical pyridaben (99.7%). In the mallard study, 

reproductive (decreases in eggs laid, eggs set, viable embryos, live 3 week embryos, normal 

hatchlings and hatch survival) and parental effects (decrease in size of adult male testes and 

decrease in number of female ovaries) were observed in birds fed pyridaben at levels as low as 

500 mg/kg-diet (LOAEC). The resulting NOAEC for the mallard duck was 100 mg/kg-diet. In 

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the bobwhite quail study, no statistically significant reproductive or parental effects were 

observed at the highest test dose, resulting in a NOAEC of 1000 mg/kg-diet. 

C.2.2. Mammals 

Pyridaben is moderately toxic to mammals on an acute oral exposure basis. The acute oral LD50

for mice exposed to pyridaben was 383 (318-462) mg a.i./kg-bw for females and 424 (364-494) 

for males (MRID 42680120). The acute oral LD50 (95% confidence interval) for rats exposed to 

pyridaben was 570 (373-872) mg a.i./kg-bw for females and 1100 (510-2374) mg a.i./kg-bw for 

males (MRID 42680119). 

In a 2-generation reproduction study, the LOAEC for pyridaben parental toxicity was 80 mg/kgdiet (6.31 and 7.82 mg/kg-bw/day for males and females, respectively) based on decreased body 

weights, body weight gains and food efficiency. No reproductive effects were observed at any 

test level, resulting in a reproductive LOAEC >80 mg/kg-diet. The study NOAEC was 28 

mg/kg-diet (2.20 and 2.41 mg/kg-bw/day for males and females, respectively) (MRIDs 

42680143 and 42680144). 

C.2.3. Invertebrates 

In an acute contact study, adult worker honey bees were exposed to technical pyridaben (99.7%) 

for 44 hours. The resulting LD50 was 0.024 (0.016-0.031) μg a.i./bee (MRID 43680423), 

indicating that pyridaben is highly toxic to honey bees. 

The toxicity of pyridaben applied to foliage was evaluated for honey bees after application of a 

formulated product containing pyridaben (76.8%) at 0.5 lbs a.i./A. At 2, 8 and 24 h after the 

application, 71.3%, 42.9% and 20.3% mortality, respectively, was observed in exposed adult 

worker bees (MRID 43680424). 

In a literature study, caged bumble bees, honey bees, alkali bees and alfalfa leafcutter bees were 

exposed to alfalfa treated with 0.4 lb a.i./A pyridaben (formulated product). Table C5 displays 

the reported % mortality in these species after 24 h of exposure to residues aged 2 and 8 h. Field 

residues aged 2 h resulted in mortality as high as 48% in alfalfa leafcutter bees. Field residues 

aged 8 h resulted in mortality as high as 31% in honey bees exposed for 24 hours (Mayer et al. 

1997). 

Table C5. Percent mortality in bees exposed to alfalfa containing aged residues of 

pyridaben. 

Bee Percent mortality from 

residues aged 2 h

Percent mortality from residues 

aged 8 h 

bumble bees 0 10 

honey bees 23 31 

alkali bees 36 15 

alfalfa leafcutter bees 48 6 

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C.2.4. Plants 

Seedling emergence and vegetative vigor data are available for 6 species of dicots and 4 species 

of monocots exposed to technical pyridaben (MRIDs 436804-19 and -20) (Table C6). These 

data are from Tier I studies that were conducted at 0.5 lb a.i./A. 

Table C6. Percent reduction of dry weight in monocot and dicot species exposed to 

technical pyridaben in Tier I seedling emergence and vegetative vigor. 

% Reduction in dry weight observed in treatment level (0.5 

lb a.i./A) relative to control 

Species (common name) 

Monocot/ 

dicot Seedling emergence 

(MRID 43680419)

Vegetative vigor 

(MRID 43680420)

Zea mays (Corn) monocot 22 1 

Allium cepa (Onion) monocot none 1 

Lolium perenne (Ryegrass) monocot none 14 

Avena sativa (Oat) monocot none 8 

Glycine max (Soybean) dicot none 4 

Raphanus sativus (Radish) dicot none 11 

Solanum esculentum (Tomato) dicot 23 18 

Cucumis sativus (Cucumber) dicot none none 

Brassica oleracea (Cabbage) dicot none 1 

Lactuca sativa (Lettuce) dicot 13 11 

C.3. References Cited 

Mayer, D. F., Lunden, J. D., and Kovacs, G. (1997). Susceptibility of Four Bee Species (Hymenoptera: Apoidea) to 

Field Weathered Insecticide Residues. J.Entomol.Soc.BC 94: 27-30. 

Rand, G. M. and Clark, J. R. (2000). Hazard/Risk Assessment of Pyridaben: I. Aquatic Toxicity and Environmental 

Chemistry. Ecotoxicology 9: 157-168. 

Rand, G. M., Clark, J. R., and Holmes, C. M. (2000). Use of Outdoor Freshwater Pond Microcosms: II. Responses 

of Biota to Pyridaben. Environ.Toxicol.Chem. 19: 396. 

Rand, G. M., Clark, J. R., and Holmes, C. M. (2001). The Use of Outdoor Freshwater Pond Microcosms. III. 

Responses of Phytoplankton and Periphyton to Pyridaben. Environ.Toxicol. 16: 96-103. 

Rand, G. M. and Clark, J. R. (2000). Hazard/Risk Assessment of Pyridaben: II. Outdoor Aquatic Toxicity Studies 

and the Water-Effect Ratio. Ecotoxicology 9: 169-177. 

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APPENDIX D: QSAR estimates of toxicities of pyridaben, PB-7 and PB-9 to 

aquatic organisms

D.1. ECOSAR 

ECOSAR identifies three chemical classes for pyridaben, including hydrazines, vinyl/allyl 

halides and amides. For PB-7, the relevant classes are the acid forms for pyridaben’s chemical 

classes. For PB-9, ECOSAR identifies the same classes as pyridaben, as well as the benzyl 

alcohols. The ECOSAR estimated toxicities for pyridaben, PB-7 and PB-9 derived using the 

hydrazine, vinyl/allyl halide and amide classes are provided in Table D1. 

Table D1. Estimated (using ECOSAR v.1.0) Toxicities of Pyridaben and Its Degradates of 

Concern to Aquatic Organisms†

Taxa (endpoint) Measured Estimated toxicity 

toxicity of 

Pyridaben 1 Pyridaben PB-7 2,3 PB-9 4

Vinyl/allyl halides 

FW fish (96-h LC50) 0.72-3.43 89 45600 20900 

FW invertebrate – daphnid (48-h LC50) 0.53-1.02 37 66300 50000 

Green Algae (96-h EC50) >665 996 81700 451000 

SW fish (96-h LC50) 17.2 319 62000 19400 

SW invertebrate – mysid shrimp (96-h LC50) 0.67 33 67900 54000 

Hydrazines 

FW fish (96-h LC50) 0.72-3.43 49 3723 808 

FW invertebrate – daphnid (48-h LC50) 0.53-1.02 4950 84500 10200 

Green Algae (72-h EC50) No data 0.0684 0.661 0.0635 

Amides 

FW fish (96-h LC50) 0.72-3.43 85 33100 13600 

FW invertebrate – daphnid (48-h LC50) 0.53-1.02 159 307 9560 

Green Algae (96-h EC50) >665 87 3010 494 †

 Units in μg/L. measured toxicity values for pyridaben are provided for comparison purposes.

1 Study details in Appendix C. 

2

Smiles code: c1cc(C(O)=O)ccc1CSC2=C(Cl)C(=O)N(C(C)(C)C)N=C2 

3

ECOSAR multiplies all estimated values by 10 because of acid moiety. 

4

Smiles code: c1cc(CO)ccc1CSC2=C(Cl)C(=O)N(C(C)(C)C)N=C2 

All three chemical classes predict acute toxicity values for fish and invertebrates exposed to 

pyridaben that are 1-2 orders of magnitude less toxic when compared to empirical data. 

Comparison of estimated fish and invertebrate values for pyridaben and PB-7 and PB-9 indicate 

that pyridaben is 2 orders of magnitude more toxic when compared to its degradates of concern. 

For green algae exposed to pyridaben, the empirical EC50 is greater than 665 μg a.i./L. The 

estimated EC50 for the vinyl/allyl halide class is on the same order of magnitude (i.e., 996 μg/L) 

compared to the empirical data; however, the estimated value for the amide class is 1 order of 

magnitude more toxic. Comparison of estimated algae values for pyridaben and PB-7 and PB-9 

indicate that pyridaben is 1-3 orders of magnitude more toxic when compared to its degradates of 

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concern. Because no empirical 72-h EC50 data are available for green algae exposed to 

pyridaben, the estimated values generated using the hydrazine class are not considered. 

D.2. ASTER 

ASTER predicts acute toxicity values for fish and D. magna exposed to pyridaben that are 1-2 

orders of magnitude less toxic when compared to empirical data. Comparison of estimated fish 

values for pyridaben and PB-7 and PB-9 indicate that pyridaben is 1 order of magnitude more 

toxic to fish when compared to its degradates of concern. For D. magna, the estimated toxicity of 

PB-7 is on the same order of magnitude as the parent, and PB-9 is an order of magnitude less 

toxic. 

Table D2. Estimated (using ASTER) Acute Toxicities of Pyridaben and Its Degradates of 

Concern to Aquatic Organisms†

Taxa (endpoint) Measured Estimated toxicity 

toxicity of 

Pyridaben 1 Pyridaben PB-7 2,3 PB-9 4

Rainbow trout (96-h LC50) 0.72-3.2 963 5402 27325 

Bluegill sunfish (96-h LC50) 2.52-3.43 2176 11024 50669 

Fathead minnow (96-h LC50) 2.3 2598 13616 64618 

Daphnia magna (48-h LC50) 0.53-1.02 1660 7983 34918 †

 Units in μg/L. measured toxicity values for pyridaben are provided for comparison purposes.

1 Study details in Appendix C. 

2

Smiles code: c1cc(C(O)=O)ccc1CSC2=C(Cl)C(=O)N(C(C)(C)C)N=C2 

3

ECOSAR multiplies all estimated values by 10 because of acid moiety. 

4

Smiles code: c1cc(CO)ccc1CSC2=C(Cl)C(=O)N(C(C)(C)C)N=C2 

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APPENDIX E: PRZM/EXAMS Input Parameters 

Table D.1. Chemical-Specific PRZM/EXAMS Input Parameters Used in Aquatic Exposure 

Modeling for pyridaben.1 

Input Parameter Value Reference Comment

Molecular mass (g/mol) 364.9 42676103 

Vapor pressure (torr) 8.21 x 10-5 42676103 

Henry's law constant 

(atm-m3

/mol) 6.84 x 10-3 -- Estimated (VP/WSol) 

Water solubility (mg/L) 0.012 42676103 

Organic carbon 

partitioning coefficient 

(KOC, L·kg-1) 

66,525 42680155 Mean of four values (USEPA, 2009) 

Aerobic soil metabolism 

t1/2 (days) 330 42680154 3x aerobic soil t1/2 (110 days; USEPA, 

2009) 

Aerobic aquatic 

metabolism t1/2 (days) 660 No data 

No acceptable data, therefore 2x 

Aerobic soil t1/2 (330 days; USEPA, 

2009) 

Anaerobic aquatic 

metabolism t1/2 (days) 0 42680154 Compound is stable to anaerobic 

microbial degradation. 

Hydrolysis t1/2 (days) 0 42680153 Compound is stable to hydrolytic 

degradation. 

Aqueous photolysis t1/2

(days) 0.06 43680427 

Foliar extraction 0.5 USEPA, 2009 Default 

Decay rate on foliage 

(days) 0 USEPA, 2009 Assume stable (default) 

1

 Application information, and management practices are listed in Table 3.1. 

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APPENDIX F: Data Call-In Tables 

The Environmental Fate and Effects Division (EFED) has completed a Data Call-In (DCI) table 

for the pyridaben environmental fate and effects data gaps identified in this Registration Review 

Problem Formulation. The attached DCI tables, which include the guideline number and study 

title for required data, also provide a rationale for requiring the data, an explanation of how the 

data will be used, and a brief description of how the data could impact the Agency’s future 

decision-making. 

Guideline Number: 835.4100 

Study Title: Aerobic Soil Metabolism 

Rationale for Requiring the Data 

Acceptable data on the aerobic soil metabolism of pyridaben are required under 40 CFR Part 158, 

Subpart N (revised July 1, 2009) for labeling that terrestrial outdoor uses. The Agency has a limited 

understanding of how pyridaben behaves in soil once applied. Depending on how quickly, to what 

extent, and to which transformation products the compound degrades, pyridaben may or may not pose 

potential exposure concern. Because the submitted aerobic soil metabolism study (MRID 43680128) only 

reported acceptable data from one soil that analyzed pyridaben biodegradation, this degradation route is 

not well understood. Therefore, the Agency is requiring an aerobic soil metabolism study conducted on 

three additional relevant soils of different organic carbon content, pH, clay content, and microbial 

biomass. 

Practical Utility of the Data 

How will the data be used? 

Additional aerobic soil metabolism data will facilitate a better understanding of the fate of pyridaben 

residues in soil. If data indicate that degradation in aerobic soil occurs rapidly and produces nontoxic 

transformation products, then the Agency could potentially determine that pyridaben residues of concern 

do not persist in soil under aerobic conditions. If data indicate that degradation is not appreciable in soil 

or that the transformation products are of similar or higher toxicity than the parent compound, then the 

Agency could conclude that pyridaben residues of concern persist in soil under some aerobic conditions. 

How could the data change the Agency’s decision or impact the Agency’s future decision-making? 

In the absence of the required data, the half-life with be multiplied by three, per guidance, due to 

uncertainty from using a single value. If the required data indicate that pyridaben in aerobic soils is 

rapidly biodegraded to nontoxic transformation products, then risk assessment conclusions and associated 

labeled use precautions and/or restrictions could be made less restrictive. 

Guideline Number: 835.4300 

Study Title: Aerobic Aquatic Metabolism 

Rationale for Requiring the Data 

Acceptable data on the aerobic aquatic metabolism of pyridaben are required under 40 CFR Part 158, 

Subpart N (revised July 1, 2009) for labeling that includes terrestrial outdoor uses. The Agency has a 

limited understanding of how pyridaben behaves in aquatic environments once applied. Depending on 

how quickly, to what extent, and to which transformation products the compound degrades, pyridaben 

may or may not pose potential exposure concern in water. Because pyridaben biodegradation in aquatic 

environments is not well understood, the Agency is requiring an aerobic aquatic metabolism study 

conducted at different pH levels. 

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Practical Utility of the Data 

How will the data be used? 

Aerobic aquatic metabolism data will facilitate a better understanding of the fate of pyridaben residues in 

water. If data indicate that degradation in aerobic conditions occurs rapidly in water and produces 

nontoxic transformation products, then the Agency could potentially determine that pyridaben residues of 

concern do not persist in water under aerobic conditions. If data indicate that degradation is not 

appreciable in aquatic environments or that the transformation products are of similar or higher toxicity 

than the parent compound, then the Agency could conclude that pyridaben residues of concern persist in 

aerobic aqueous conditions. 

How could the data change the Agency’s decision or impact the Agency’s future decision-making? 

In the absence of the required data, pyridaben will be conservatively assumed stable to aerobic aquatic 

metabolism. If the required data indicate that pyridaben in aerobic, aqueous environments is rapidly 

biodegraded, then risk assessment conclusions and associated labeled use precautions and/or restrictions 

could be made less restrictive. 

Guideline Number: 835.4400 

Study Title: Anaerobic Aquatic Metabolism 

Rationale for Requiring the Data 

Acceptable data on the anaerobic aquatic metabolism of pyridaben are required under 40 CFR Part 158, 

Subpart N (revised July 1, 2009) for labeling that includes terrestrial outdoor uses. The Agency has a 

limited understanding of how pyridaben behaves in anaerobic aquatic environments following 

application. Depending on how quickly, to what extent, and to which transformation products the 

compound degrades, pyridaben may or may not pose potential exposure concern in water. Because 

pyridaben biodegradation in aquatic environments, particularly oxygen-limiting environments, is not well 

understood, the Agency is requiring an anaerobic aquatic metabolism study conducted at different pH 

levels. 

Practical Utility of the Data 

How will the data be used? 

Anaerobic aquatic metabolism data will facilitate a better understanding of the fate of pyridaben residues 

in water, particularly oxygen-limiting environments. If data indicate that degradation in anaerobic 

aqueous conditions occurs rapidly and produces nontoxic transformation products, then the Agency could 

potentially determine that pyridaben residues of concern do not persist in water under anaerobic 

conditions. If data indicate that degradation is not appreciable in water or that the transformation 

products are of similar or higher toxicity than the parent compound, then the Agency could conclude that 

pyridaben residues of concern persist in anaerobic aqueous conditions. 

How could the data change the Agency’s decision or impact the Agency’s future decision-making? 

In the absence of the required data, pyridaben will be conservatively assumed stable to anaerobic aquatic 

metabolism, since the default assumption is to use the anaerobic soil metabolism study, which is stable. 

If the required data indicate that pyridaben in anaerobic, aqueous environments is rapidly biodegraded, 

then risk assessment conclusions and associated labeled use precautions and/or restrictions could be made 

less restrictive. 

Guideline Number: 835.6100 

Study Title: Storage Stability 

Rationale for Requiring the Data 

The Agency has a limited understanding of how pyridaben behaves in frozen storage conditions between 

the time of sampling and the time of analysis. Submission of a storage stability study is essential in order 

to be confident that any degradation measured in the test system was due solely to the environment of that 

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test system, and not due to handling and storage. 

Practical Utility of the Data 

How will the data be used? 

Storage stability data will facilitate a better understanding of the fate of pyridaben residues during storage 

and handling between sampling and analysis. If data indicate that degradation of pyridaben or its 

degradates occur then the data from the field studies are no longer valid as it would not be feasible to 

determine if the degradation measured in the test system was due solely to the environment of that test 

system, and not due to handling and storage. 

How could the data change the Agency’s decision or impact the Agency’s future decision-making? 

In the absence of the required data, the field data for pyridaben will be qualitatively used in the risk 

assessment. These data are used for confirmatory data to ensure that any degradation observed in the test 

systems is due solely to the test environment and not handling or storage. 

Guideline Number: 835.6200 

Study Title: Analytical Method (and Associated Independent Laboratory Validation) for Residues 

in Water 

Rationale for Requiring the Data 

Independently validated analytical methods for residues in soil, water, sediment, and plant material 

(environmental chemistry methods) submitted by the registrant are used to evaluate analyses described in 

submitted environmental fate and ecological effects studies. Submitted analytical methods are also used 

by various Federal, State, Tribal, and local agencies to detect and monitor residues that are or are 

suspected to be in environmental compartments due to outdoor uses and accidental releases. Independent 

laboratory validations for submitted analytical methods are necessary to confirm that the methods are 

functional and to confirm the levels of detection and quantitation reported in registrant-prepared 

validations. 

Use of pyridaben may impact surface water quality due to runoff of rain water and drift of residues. This 

is especially true for poorly draining soils, erodible soils, and soils with shallow ground water. 

Therefore, outside agencies may request analytical methods with which to monitor for pyridaben residues 

in water. 

Practical Utility of the Data 

How will the data be used? 

In the absence of independently validated environmental chemistry methods, submitted environmental 

fate and ecological effects data may not be reviewable and entities outside the Agency may lack 

chemical-specific methods for analyses in environmental compartments. Independently validated 

environmental chemistry methods will be used to evaluate newly submitted environmental fate and 

ecological effects data and will be made available for enforcement and monitoring purposes at the 

federal, state, and local levels. 

How could the data change the Agency’s decision, or impact the Agency’s future decision-making? 

Risk assessment conclusions could be altered if they are not supported by either study data or 

environmental monitoring detections that are based on independently validated environmental chemistry 

methods. Furthermore, while not directly related to Agency decision-making, independently validated 

environmental chemistry methods are necessary to ensure the safety of those in proximity to releases of 

pyridaben residues in the environment. 

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Guideline Number: 835.6100 

Study Title: Analytical Method (and Associated Independent Laboratory Validation) for Residues 

in Soil 

Rationale for Requiring the Data 

Independently validated analytical methods for residues in soil, water, sediment, and plant material 

(environmental chemistry methods) submitted by the registrant are used to evaluate analyses described in 

submitted environmental fate and ecological effects studies. Submitted analytical methods are also used 

by various Federal, State, Tribal, and local agencies to detect and monitor residues that are or are 

suspected to be in environmental compartments due to outdoor uses and accidental releases. Independent 

laboratory validations for submitted analytical methods are necessary to confirm that the methods are 

functional and to confirm the levels of detection and quantitation reported in registrant-prepared 

validations. 

Practical Utility of the Data 

How will the data be used? 

In the absence of independently validated environmental chemistry methods, submitted environmental 

fate and ecological effects data may not be reviewable and entities outside the Agency may lack 

chemical-specific methods for analyses in environmental compartments. Independently validated 

environmental chemistry methods will be used to evaluate submitted environmental fate and ecological 

effects data and will be made available for enforcement and monitoring purposes at the federal, state, and 

local levels. 

How could the data change the Agency’s decision, or impact the Agency’s future decision-making? 

Risk assessment conclusions could be altered if they are not supported by either study data or 

environmental monitoring detections that are based on independently validated environmental chemistry 

methods. Furthermore, while not directly related to Agency decision-making, independently validated 

environmental chemistry methods are necessary to ensure the safety of those in proximity to releases of 

pyridaben residues in the environment. 

Guideline Number: 850.1710 

Study Title: Bioconcentration in oysters 

Rationale for Requiring the Data 

Empirical BCFs from two separate laboratory studies involving rainbow trout (MRID 43792113) were 

342 and 439. BCF values are also available from a life cycle test with fathead minnows, BCF values 

ranged 1168-3780 (MRID 43792106). KABAM was used to estimate a fish BCF that considers 

metabolism and steady state. When the metabolism rate is estimated from the empirical BCF studies with 

the rainbow trout, estimated BCF for fish is 5740. Although metabolism by fish reduces the 

bioconcentration potential of pyridaben, this estimated BCF value is still sufficient to indicate that 

pyridaben may bioaccumulate in aquatic ecosystems. At this time, no empirical data are available that 

consider bioconcentration of pyridaben in aquatic invertebrates. Therefore, bioconcentration data are 

required for oysters. 

Practical Utility of the Data 

How will the data be used? 

Bioconcentration data for oysters will increase the understanding of the bioaccumulation potential of 

pyridaben in aquatic ecosystems. Although empirical BCF data indicate that pyridaben is metabolized in 

fish, the ability of aquatic invertebrates to metabolize pyridaben is unknown. Metabolism is an important 

consideration in determining the bioaccumulation potential of a chemical because metabolism can 

decrease the bioaccumulation of that chemical. In the case of fish exposed to pyridaben, metabolism by 

fish decreases the bioaccumulation potential of pyridaben. BCF data for oysters will provide information 

on the potential of aquatic invertebrates to metabolize pyridaben. 

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How could the data change the Agency’s decision or impact the Agency’s future decision-making? 

In the absence of the required data, EFED will assume that pyridaben is not metabolized by aquatic 

invertebrates. This is a conservative assumption that could potentially overestimate bioaccumulation of 

pyridaben in aquatic organisms if this chemical is actually metabolized by aquatic invertebrates. 

Alternatively, if the BCF study with oysters indicates that pyridaben is not metabolized by oysters, these 

data will support the conservative assumption of no metabolism by aquatic invertebrates, thereby 

increasing the certainty in the model estimates bioaccumulation. 

Guideline Number: 850.1850 

Study Title: Aquatic food chain transfer 

Rationale for Requiring the Data 

Empirical BCFs from two separate laboratory studies involving rainbow trout (MRID 43792113) were 

342 and 439. BCF values are also available from a life cycle test with fathead minnows, BCF values 

ranged 1168-3780 (MRID 43792106). KABAM was used to estimate a fish BCF that considers 

metabolism and steady state. When the metabolism rate is estimated from the empirical BCF studies with 

the rainbow trout, estimated BCF for fish is 5740. Although metabolism by fish reduces the 

bioconcentration potential of pyridaben, this estimated BCF value is still sufficient to indicate that 

pyridaben may bioaccumulate in aquatic ecosystems. This study is required to determine the potential 

bioaccumulation of pyridaben. 

Pyridaben registrants must submit a study protocol for review by the Agency prior to initiation of 

the aquatic food chain transfer study.

Practical Utility of the Data 

How will the data be used? 

Empirical bioaccumulation data will increase the understanding of the bioaccumulation potential of 

pyridaben in aquatic ecosystems. 

How could the data change the Agency’s decision or impact the Agency’s future decision-making? 

In the absence of the required data, EFED will assess the bioaccumulation potential of pyridaben using 

models and will make conservative assumptions in the place of data to refute the conservative 

assumptions (e.g., no metabolism of pyridaben by aquatic invertebrates). These empirical data will 

supplement model estimates. 

Guideline Number: 850.3040 

Study Title: Field testing for pollinators 

Rationale for Requiring the Data 

According to 40 CFR Part 158, this study is required if any of the following are met: 1) data from other 

sources (Experimental Use Permit program, university research, registrant submittals, etc.) indicate 

potential adverse effects on colonies, especially effects other than acute mortality (reproductive, 

behavioral, etc.); 2) data from residual toxicity studies indicate extended residual toxicity; or 3) data 

derived from studies with terrestrial arthropods other than bees indicate potential chronic, reproductive or 

behavioral effects. In a foliar residue study MRID (43680424), pyridaben residues aged 24 h caused 

mortality (> 20%) in honey bees. Therefore, the second condition relevant to this data requirement is met 

and submission of a field study of the effects of pyridaben on pollinators is required (Guideline 

850.3040). Pyridaben registrants must submit a study protocol for review by the Agency prior to 

initiation of the field testing for pollinators study.

Practical Utility of the Data 

How will the data be used? 

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Field testing data for pollinators (i.e., honey bees) will be used to identify potential risks to non-target, 

terrestrial invertebrates, including native pollinators, from chronic exposure to pyridaben. In this case, 

pyridaben will be present in the field as it is intended to be applied according to labels. The data will 

reduce uncertainties associated with the current risk assessment for terrestrial insects and will improve 

the Agency’s understanding of the potential effects of pyridaben on terrestrial species. If field testing 

effects data are not submitted, than risk to terrestrial insects from chronic exposure to pyridaben will not 

be refuted. 

How could the data impact the Agency’s future decision-making? 

If future endangered species risk assessments are performed without these data, the Agency would have 

to assume that pyridaben “may affect” listed terrestrial insects directly (and listed species from other taxa 

that rely upon terrestrial insects indirectly [ecological services] through pollination), and use of pyridaben 

and its formulated products may need to be restricted in areas where listed species could be affected. The 

lack of these data will limit the flexibility the Agency and registrants have in coming into compliance 

with the Endangered Species Act and could result in use restrictions for pyridaben use that are 

unnecessarily severe. 

Guideline Number: 850.1075 

Study Title: Estuarine/Marine Fish Acute Toxicity Test 

Rationale for Requiring the Data 

Acute toxicity data are available for sheepshead minnow exposed to pyridaben (43680406). This study 

was classified supplemental because the highest test concentration resulted in 50% mortality, leading to 

uncertainty in the established LC50. Submission of acceptable acute toxicity data for estuarine/marine fish 

will reduce uncertainty associated with the acute endpoint and increase confidence in risk conclusions. 

Practical Utility of the Data 

How will the data be used? 

Estuarine/marine fish acute toxicity data will be used to determine the potential for pyridaben to affect 

fish species in estuarine/marine environments. The data will reduce uncertainties associated with the 

current risk assessment for estuarine/marine fish and will improve the Agency’s understanding of the 

potential effects of pyridaben on aquatic animals. In the absence of data specific for estuarine/marine 

fish, supplemental data from MRID 43680406 will be used. 

How could the data impact the Agency’s future decision-making? 

Using toxicity data from a supplemental study increases the uncertainty for assessing risks to 

estuarine/marine species in screening-level assessments. 

Guideline Number: 850.1400 

Study Title: Saltwater fish early-life stage test 

Rationale for Requiring the Data 

Chronic toxicity data are not available for estuarine/marine fish. The Part 158 data requirements, specify 

that an early life-stage study is required for estuarine/marine fish for chemicals that have the potential to 

enter estuarine/marine water. In addition, these data may be required when the acute LC50 for an 

estuarine/marine fish is <1 mg/L, and when reproductive effects are observed in other aquatic organisms. 

Because pyridaben use sites may overlap with watersheds of estuarine/marine environments, pyridaben 

pas the potential to enter estuarine/marine environments. In addition, the LC50 for sheepshead minnow 

exposed to pyridaben is <1 mg/L (MRID 43680406) and reproductive effects have been observed in 

freshwater fish (MRID 43792106) and invertebrates (MRIDs 43680408 and 43680410) exposed to 

pyridaben. Therefore, chronic fish toxicity data are required for pyridaben. 

Practical Utility of the Data 

How will the data be used? 

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Chronic estuarine/marine fish toxicity data will be used to determine the potential for pyridaben to affect 

fish species in estuarine/marine environments following prolonged exposure. The data will reduce 

uncertainties associated with the current risk assessment for estuarine/marine fish and will improve the 

Agency’s understanding of the potential effects of pyridaben on aquatic animals. In the absence of data 

specific for these fish, the Agency will use acute to chronic ratios available for freshwater fish exposed to 

pyridaben. 

How could the data impact the Agency’s future decision-making? 

Using acute to chronic ratios increases the uncertainty for assessing risks to estuarine/marine species in 

screening-level assessments. 

Guideline Number: 850.1350 

Study Title: Estuarine/Marine invertebrate life cycle test 

Rationale for Requiring the Data 

Supplemental chronic toxicity data are available for mysid shrimp exposed to pyridaben (43680409). 

This study was classified supplemental due to poor control performance and lack of observed effects at 

any treatment level. Submission of acceptable chronic toxicity data for estuarine/marine invertebrates 

will reduce uncertainty associated with the chronic endpoint and increase confidence in risk conclusions. 

Practical Utility of the Data 

How will the data be used? 

Estuarine/marine invertebrate chronic toxicity data will be used to determine the potential for pyridaben 

to affect invertebrates species in estuarine/marine environments. The data will reduce uncertainties 

associated with the current risk assessment for estuarine/marine invertebrates and will improve the 

Agency’s understanding of the potential effects of pyridaben on aquatic animals. In the absence of data 

specific for estuarine/marine invertebrates, supplemental data from MRID 43680409will be used. 

How could the data impact the Agency’s future decision-making? 

Using toxicity data from a supplemental study increases the uncertainty for assessing risks to 

estuarine/marine species in screening-level assessments. 

Guideline Number: 850.1735 

Study Title: Whole sediment: acute freshwater invertebrates 

Rationale for Requiring the Data 

No data are currently available to characterize the acute toxicity of pyridaben to sediment dwelling 

invertebrates. The Part 158 data requirements, specify that acute toxicity data for sediment invertebrates 

are conditionally required if the half-life of the pesticide in sediment >10 days in aerobic soil or aquatic 

metabolism studies and if any of the following conditions exist: a) the Kd is ≥50; b) the log Kow is ≥3 or 

c) the Koc is ≥1000. Since the half-live of pyridaben in soil under aerobic conditions is >10 days, the Log 

Kow is >3 and the Koc is >1000, acute toxicity data for one species of sediment-dwelling invertebrate are 

required for pyridaben. 

Practical Utility of the Data 

How will the data be used? 

Invertebrate acute toxicity data will be used to determine the potential for pyridaben to affect sedimentdwelling aquatic invertebrates. The data will reduce uncertainties associated with the current risk 

assessment for sediment-dwelling invertebrates and will improve the Agency’s understanding of the 

potential effects of pyridaben on aquatic animals. 

How could the data impact the Agency’s future decision-making? 

Using toxicity data from a species inhabiting the water column as a surrogate for sediment-dwelling 

species increases the uncertainty for assessing risks to aquatic species in screening-level assessments, 

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especially because pyridaben is likely to partition to sediments. Additionally, if future endangered 

species risk assessments are performed without these data, the Agency would have to presume risk to 

listed sediment dwelling invertebrate species (e.g., mollusks) in the absence of such data for pyridaben. 

Therefore, the use of pyridaben and its formulated products may need to be restricted in areas where 

listed species could be exposed. The lack of these data will limit the flexibility the Agency and registrants 

have in coming into compliance with the Endangered Species Act and could result in use restrictions for 

pyridaben that are unnecessarily severe. 

Guideline Number: no guideline 

Study Title: Whole sediment: chronic freshwater invertebrates 

Rationale for Requiring the Data 

No data are currently available to characterize the chronic toxicity of pyridaben to sediment-dwelling 

invertebrates. The Part 158 data requirements, specify that chronic toxicity data for sediment 

invertebrates are conditionally required if the EEC in sediment is >0.1 of the acute LC/EC50 values and 

the half-live of the pesticide in the sediment is >10 days in aerobic soil or aquatic metabolism studies and 

if any of the following conditions exist: a) the Kd is ≥50; b) the log Kow is ≥3 or c) the Koc is ≥1000. 

Since the acute toxicity of pyridaben to sediment-dwelling invertebrates is unknown due to a lack of 

effects data, the relationship between the EEC and the acute toxicity cannot be determined. However, the 

half-live of pyridaben in soil under aerobic conditions is >10 days, the Log Kow is >3 and the Koc is 

>1000. Therefore, chronic toxicity data for one species of sediment-dwelling invertebrate are required 

for pyridaben. Pyridaben registrants must submit a study protocol for review by the Agency prior 

to initiation of the chronic toxicity study with sediment dwelling invertebrates.

Practical Utility of the Data 

How will the data be used? 

Invertebrate chronic toxicity data will be used to determine the potential for pyridaben to affect sediment 

dwelling aquatic invertebrates. The data will reduce uncertainties associated with the current risk 

assessment for sediment dwelling invertebrates and will improve the Agency’s understanding of the 

potential effects of pyridaben on aquatic animals. 

How could the data impact the Agency’s future decision-making? 

Using toxicity data from a species inhabiting the water column as a surrogate for sediment dwelling 

species increases the uncertainty for assessing risks to aquatic species in screening-level assessments, 

especially because pyridaben is likely to partition to sediments. Additionally, if future endangered 

species risk assessments are performed without these data, the Agency would have to presume risk to 

listed sediment dwelling invertebrate species (e.g., mollusks) in the absence of such data for pyridaben. 

Therefore, the use of pyridaben and its formulated products may need to be restricted in areas where 

listed species could be exposed. The lack of these data will limit the flexibility the Agency and registrants 

have in coming into compliance with the Endangered Species Act and could result in use restrictions for 

pyridaben that are unnecessarily severe. 

Guideline Number: 850.4100 

Study Title: Terrestrial Plant Toxicity Test, Tier I (Seedling Emergence) 

Rationale for Requiring the Data 

According to the 850.4100 guideline, seedling emergence data are required for a total of 10 plant species, 

including 4 monocot and 6 dicot species. The 4 monocot species must be from at least 2 families. One 

species of monocots must be corn. The 6 dicot species must be from 4 different families, and must 

include soybean and a root crop. 

Tier 1 data must test up to the highest single application rate allowed for a pesticide. If the Tier I data 

result in significant decreases in endpoints compared to controls or >25% effects to any test species, Tier 

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II data should be submitted for that species. Both Tier I and Tier II seedling emergence studies must be 

conducted with a typical end use product. 

Tier 1 data were submitted for seedling emergence study were plants were exposed to 0.5 lb a.i./A 

technical pyridaben (MRID 43680419). There are 2 uses of pyridaben (SLN on Pears and ornamentals) 

that have single application rates that exceed 0.5 lb a.i./A. This study was not conducted with a typical 

end use product. Therefore, guideline 850.4100 represents a data gap. In order to fulfill these guidelines, 

additional Tier 1 seedling emergence and vegetative vigor studies are required. These studies must be 

conducted at the highest single application rate for pyridaben (1.0 lbs a.i./A on ornamentals) and with a 

typical end use product containing pyridaben. 

If the Tier I data result in >25% effects to any test species, Tier II data should be submitted for that 

species. 

Practical Utility of the Data 

How will the data be used? 

Seedling emergence data for terrestrial plants will be used to determine the potential for pyridaben to 

affect non-target plant species in the terrestrial environment. The data will reduce uncertainties associated 

with the current risk assessment for terrestrial plants and will improve the Agency’s understanding of the 

potential effects of pyridaben on terrestrial plants. In the absence of data specific for these plants, for 

uses with applications of 0.5 lb a.i./A, it will be assumed that <25% effects occur. For uses with 

applications >0.5 lb a.i./A, risk cannot be precluded. 

How could the data impact the Agency’s future decision-making? 

Because terrestrial plants form the basis of the food chain in many terrestrial habitats, a solid 

understanding of the potential risks to terrestrial plants is essential for sound environmental risk 

management decision-making. Submission of seedling emergence data conducted at the highest single 

application rate and with a typical end use product will increase the Agency’s certainty in the measures of 

pyridaben’s toxicity to plants. 

Guideline Number: 850.4150 

Study Title: Terrestrial Plant Toxicity Test, Tier I (Vegetative Vigor) 

Rationale for Requiring the Data 

According to the 850.4150 guideline, vegetative vigor data are required for a total of 10 plant species, 

including 4 monocot and 6 dicot species. The 4 monocot species must be from at least 2 families. One 

species of monocots must be corn. The 6 dicot species must be from 4 different families, and must 

include soybean and a root crop. 

Tier 1 data must test up to the highest single application rate allowed for a pesticide. If the Tier I data 

result in significant decreases in endpoints compared to controls or >25% effects to any test species, Tier 

II data should be submitted for that species. Both Tier I and Tier II vegetative vigor studies must be 

conducted with a typical end use product. 

Tier 1 data were submitted for vegetative vigor study were plants were exposed to 0.5 lb a.i./A technical 

pyridaben (MRID 43680420). There are 2 uses of pyridaben (SLN on Pears and ornamentals) that have 

single application rates that exceed 0.5 lb a.i./A. This study was not conducted with a typical end use 

product. Therefore, guideline 850.4150 represents a data gap. In order to fulfill these guidelines, 

additional Tier 1 seedling emergence and vegetative vigor studies are required. These studies must be 

conducted at the highest single application rate for pyridaben (1.0 lbs a.i./A on ornamentals) and with a 

typical end use product containing pyridaben. 

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If the Tier I data result in >25% effects to any test species, Tier II data should be submitted for that 

species. 

Practical Utility of the Data 

How will the data be used? 

Seedling emergence data for terrestrial plants will be used to determine the potential for pyridaben to 

affect non-target plant species in the terrestrial environment. The data will reduce uncertainties associated 

with the current risk assessment for terrestrial plants and will improve the Agency’s understanding of the 

potential effects of pyridaben on terrestrial plants. In the absence of data specific for these plants, for 

uses with applications of 0.5 lb a.i./A, it will be assumed that <25% effects occur. For uses with 

applications >0.5 lb a.i./A, risk cannot be precluded. 

How could the data impact the Agency’s future decision-making? 

Because terrestrial plants form the basis of the food chain in many terrestrial habitats, a solid 

understanding of the potential risks to terrestrial plants is essential for sound environmental risk 

management decision-making. Submission of vegetative vigor data conducted at the highest single 

application rate and with a typical end use product will increase the Agency’s certainty in the measures of 

pyridaben’s toxicity to plants. 

Guideline Number: 850.5400 

Study Title: Aquatic plant toxicity (Tier I): algae 

Rationale for Requiring the Data 

Supplemental Tier I data are available for 4 species of algae exposed to <20 μg a.i./L pyridaben (MIRD 

43680422). In addition, a supplemental Tier II study is available for green algae exposed to pyridaben 

(MRID 43680421). In order to fulfill the guideline requirement for algae, additional Tier I data must be 

submitted for 4 species of algae exposed to pyridaben at a concentration of 100 mg a.i./L (limit test). If 

the Tier I data result in >50% effects to any test species, Tier II data should be submitted for that species. 

Practical Utility of the Data 

How will the data be used? 

Data from Tier I aquatic plant toxicity studies will be used to estimate potential risks to aquatic nonvascular plants from pyridaben exposure. The data will reduce uncertainties associated with the current 

risk assessment for aquatic plants and will improve the Agency’s understanding of the potential effects of 

pyridaben on aquatic plants. In the absence of Tier I data, risks to non-vascular aquatic plants will be 

presumed. 

How could the data impact the Agency’s future decision-making?

Because aquatic non-vascular plants form the basis of the food chain for aquatic habitats and significantly 

contribute to overall water quality, a solid understanding of the potential risks to aquatic plants is 

essential for sound environmental risk management decision-making. Without aquatic plant data for 

pyridaben, the Agency cannot determine if the current application rates for pyridaben may result in direct 

adverse effects to aquatic plants and/or indirect effects resulting from reduction in the prey base and/or 

loss of habitat/cover. If future endangered species risk assessments are performed without these data, the 

Agency would have to assume that pyridaben “may affect” aquatic plants directly (and listed species 

from other taxa indirectly via reduction in prey base and/or habitat), and use of pyridaben may need to be 

restricted in areas where listed species could be exposed. The lack of these data will limit the flexibility 

the Agency and registrants have in coming into compliance with the Endangered Species Act and could 

result in use restrictions for pyridaben which are unnecessarily severe. 

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Guideline Number: 850.4400 

Study Title: Aquatic plant toxicity (Tier I): vascular plants 

Rationale for Requiring the Data 

Supplemental Tier I data are available for duckweed exposed to <20 μg a.i./L pyridaben (MIRD 

43680422). In order to fulfill the guideline requirement for aquatic vascular plants, additional Tier I data 

must be submitted for a vascular aquatic plant (i.e., duckweed) exposed to pyridaben at a concentration of 

100 mg a.i./L (limit test). If the Tier I data result in >50% effects to the test species, Tier II data should 

be submitted for that species. 

Practical Utility of the Data 

How will the data be used? 

Data from Tier I aquatic plant toxicity studies will be used to estimate potential risks to aquatic vascular 

plants from pyridaben exposure. The data will reduce uncertainties associated with the current risk 

assessment for aquatic plants and will improve the Agency’s understanding of the potential effects of 

pyridaben on aquatic plants. In the absence of Tier I data, risks to vascular aquatic plants will be 

presumed. 

How could the data impact the Agency’s future decision-making?

Because aquatic vascular plants form the basis of the food chain for aquatic habitats and significantly 

contribute to overall water quality, a solid understanding of the potential risks to aquatic plants is 

essential for sound environmental risk management decision-making. Without aquatic plant data for 

pyridaben, the Agency cannot determine if the current application rates for pyridaben may result in direct 

adverse effects to aquatic plants and/or indirect effects resulting from reduction in the prey base and/or 

loss of habitat/cover. If future endangered species risk assessments are performed without these data, the 

Agency would have to assume that pyridaben “may affect” aquatic plants directly (and listed species 

from other taxa indirectly via reduction in prey base and/or habitat), and use of pyridaben may need to be 

restricted in areas where listed species could be exposed. The lack of these data will limit the flexibility 

the Agency and registrants have in coming into compliance with the Endangered Species Act and could 

result in use restrictions for pyridaben which are unnecessarily severe. 

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