UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C., 20460

 OFFICE OF 

 PREVENTION, PESTICIDES AND

 TOXIC SUBSTANCES

February 16, 2006

PC Code 069001; Case No. 2580

DP Barcode: D324663

MEMORANDUM

SUBJECT: Revised Pyrethrins RED Chapter After Additional 60-Day Comment

Period, Phase 5

FROM: Miachel Rexrode, Ph.D., Senior Aquatic Biologist

José Luis Meléndez, Chemist

Environmental Risk Branch V

Environmental Fate and Effects Division (7507C)

THROUGH: Jean Holmes, DVM, Acting Chief

Environmental Risk Branch V

Environmental Fate and Effects Division (7507C)

TO: Cathryn O’Connell, Risk Manager Reviewer

Tom Myers, Review Manager #52

Special Review and Reregistration Division (7508C)

This memo summarizes the revised Environmental Fate and Effects Division’s (EFED) screening-level

Environmental Risk Assessment for the Reregistration Eligibility Decision of Pyrethrins. The

Pyrethrins are a broad-spectrum insecticide used in four major sectors: agricultural settings,

commercial/industrial/institutional/food & non-food/mosquito abatement, domestic home and garden,

and pet care. Pyrethrins are a mixture of naturally occurring insecticides derived from the flowers

of Chrysanthemum cinerariaefolium and Chrysanthemum cineum. The six individual pyrethrins are

pyrethrin 1, pyrethrin 2, cinerin 1, cinerin 2, jasmolin 1, and jasmolin 2. The technical grade active

ingredient (FEK-99) is commonly referred to as pyrethrum extract, which is the sum of Pyrethrins

I (the esters of chrysanthemic acid - pyrethrin 1, cinerin 2 and jasmolin 1) and Pyrethrins II (the esters

of pyrethric acid - pyrethrin 2, cinerin 2, and jasmolin 2), also called "the pyrethrins", and this mixture

constitutes 45 to 55% of pyrethrum extract. The product pyrenone crop spray, a formulation that

contains pyrethrins, piperonyl butoxide and inert ingredients, was used as a test material in many of

the ecological effects laboratory studies. There are many other formulation types, such as aerosol,

combustible coil, dust, emulsifiable concentrate, ready to use liquid, shampoo, and wettable powder.

All six pyrethrins have the same backbone molecular structure with different substituents at two sites.

Since all the structures at the two sites are similar, they are expected to have similar environmental

fate properties.
Risk to Aquatic and Terrestrial Organisms

The Agency evaluated potential pyrethrin exposure to aquatic and terrestrial organisms by considering

maximum and typical application rates. The conclusions from this risk assessment are as follows:

Agricultural Uses: 

Model generated exposure values suggests that maximum rates can result in acute risk to fish and aquatic

invertebrates (freshwater and estuarine/marine) with triggers that included restrictive use and endangered

species concern (although estuarine/ marine endangered invertebrate was triggered, EFED realizes that at this

time there are no listed species under this category). Evaluating chronic risk from this exposure scenario

showed that LOC triggers were exceeded for estuarine/marine invertebrates, while fish (freshwater and

estuarine/marine) and freshwater invertebrates may not be at chronic risk from pyrethrin exposure in the water

column.

Typical application rate appears to have the potential to reduce risk to aquatic systems. Evaluation of four crop

scenarios using the TGAI (ID potatoes, PA tomatoes, CA onions, OR snap beans) suggests that LOCs for

freshwater and estuarine/marine fish and invertebrates should not be exceeded if typical application rate is used.

The Agency also assessed the maximum and typical rates for a pyrethrin formulation with PBO but only

evaluated acute exposure to aquatic organisms. The calculated EECs show that acute risk from the maximum

formulation rate appeared to be higher than risk calculated only from the TGAI. This evaluation showed that

acute risk from the formulation was about 2-7X greater for freshwater and estuarine/marine fish and about

10X greater for estuarine/marine invertebrates. However, the typical formulation rate appears to reduce the

risk (freshwater and estuarine/marine fish and freshwater invertebrates), but this reduction in exposure still

presents the potential for acute high, acute restrictive, and chronic risk to estuarine/marine invertebrates

species. 

Mosquito Abatement:

The maximum rate showed that there did not appear to be the potential for acute risk to freshwater fish and

invertebrates or esrtuarine/marine fish but there was the potential for acute LOCs being exceeded for

estuarine/marine invertebrates. However, this risk to estuarine/marine invertebrates appeared to be eliminated

if the boom height is set at 150 ft and the droplet size at 40 um. 

The Agency also evaluated the typical rate and found that potential acute risk to estuarine/marine invertebrates

could be eliminated with a boom height of 75ft and a 50 um droplet size. 

Down-the-Drain

The Agency evaluated the pharmacological uses of pyrethrin in a Down-the-Drain model and found

that aquatic LOCs were not exceeded for freshwater or estuarine/marine organisms.

Risk to Terrestrial Organisms
In this screening-level risk assessment, the Agency did not find acute and chronic risks to listed or

non-listed mammalian and avian species. Although the Agency does not conduct a quantitative risk

assessment for beneficial insects, acute toxicity studies with honey bees show that pyrethrins are

highly toxic, both on a contact basis, and an acute oral basis. This also suggests that pyrethrins are

toxic to nontarget beneficial insects, as well as listed insect species.

Risks to Endangered Species

The acute level of concern (LOC) is exceeded for endangered and/or threatened species of freshwater

fish and invertebrates that live in the water column and are associated with the agricultural uses of

pyrethrins. Based on a probit slope analysis to calculate the chance of an individual event

corresponding to the freshwater fish, the estimated individual mortality associated with the calculated

RQ values (0.05 to 0.54) range from 1 in 3.34 x 1014 to 1 in 4.17 x 108 . For the freshwater

invertebrate, the estimated individual mortality associated with the calculated RQ values (0.05 - 0.24)

range from 1 in 1.0 x 1016 to 1 in 8.44 x 109

. 

The acute level of concern (LOC) is exceeded for endangered and/or threatened species of estuarine/

marine fish and invertebrates that live in the water column and are associated with the agricultural

and mosquito abatement uses of pyrethrins. For estuarine/marine fish, the estimated individual

mortality associated with the calculated RQ values (0.05 to 0.17) is 1.0 X 1016. For estuarine/ marine

invertebrates for agriculture and mosquito abatement uses, the probit slope analysis was completed

for both active ingredient and formulated product. Based on the default slope estimate of 4.5, the

corresponding chance of individual mortality for estuarine/ marine invertebrates following exposure

to the formulation is 1 in 4.17 x 108; and based on the slope estimate of 4.1, the corresponding

chance of individual mortality for estuarine/marine invertebrates following exposure to the technical

grade active ingredient is 1 in 2.08 x 107

. 

The listed species acute LOC is exceeded for sediment dwelling estuarine/marine invertebrates that

live near the agricultural areas. However, there are no listed estuarine/marine invertebrates, so this

risk concerns only applies to non-listed species.

The Agency is also concerned for endangered terrestrial invertebrates such as beneficial insects, as

well as listed species.

Outstanding Data Requirements and Data Gaps 

Environmental Fate:

The environmental fate database for the pyrethrins was completed with a representative pyrethrin:

pyrethrin 1. However, the toxicity testing was done with the mixture of compounds. As indicated

earlier, pyrethrin consists of a mixture of six compounds that are structurally related, which have the

same backbone molecular structure, but different substituents at two key sites of the molecule.

These different substituents are not expected to substantially change the fate and transport properties

of the chemicals. The general chemistry of the molecule is dictated by the ester link located near the

center of the structure. 
The environmental fate database is substantially complete, but it consists mostly of supplemental

studies. At this time, the database has been considered sufficient for a Tier I assessment; however,

should additional refinements be needed, additional data may be required.

Ecological Effects:

The ecological effects toxicity database is complete and adequate to conduct a Tier I risk assessment.

Most of the studies were classified as Core and were conducted with the technical grade active

ingredient (FEK-99) and a formulated product (pyrenone crop spray). Further ecological effects data

are needed on pyrethrin because of its phytotoxic effects on plants and potential risk to benthic

organisms.

There were no chronic studies with the technical grade active ingredient or the formulation for

estuarine / marine invertebrates or fish. Pyrethrins are acutely toxic to estuarine / marine invertebrates

and fish at levels below 1ppm (EC 50/LC50s are less than 1 ppm) and the chemical may be applied

directly to water for mosquito abatement use. These factors trigger a data requirement for submission

of chronic studies with estuarine / marine fish and invertebrates. However, using the acute to chronic

ratio estimation method, it does appear that chronic risk will be a concern to invertebrates in

estuarine/marine environments (water column and sediment). Under guideline §72-4 (a) and (b),

EFED is requesting submission of a life-cycle study with an estuarine/ marine invertebrate (e.g., mysid

shrimp) and fish early life-stage study with an estuarine/marine fish (e.g., sheepshead minnow).

No data were submitted to evaluate the effects of pyrethrin exposure to terrestrial or aquatic.

However the Agency does not consider pyrethrin or the other pyrethroids as being phytotoxic for the

following reasons: 1) the compound is used as a spray on agricultural crops with no phytotoxic

effects; 2) the neural toxic mode of action precludes phtotoxic concerns; 3) the Agency is not aware

of any incidents involving plants and cypyrethrin alone. The Agency is not requiring plant toxicity

data at this time.

Since pyrethrins can bind to particulate and sediment and are highly toxic to aquatic invertebrates,

EFED has a concern for acute and chronic risk to benthic organisms. Therefore, EFED is requesting

that a whole sediment acute test with the freshwater organism, Chironomus ripirians (Guideline

number 850.1735) and the marine water organism, Leptocheirus plumulosus (Guideline number

850.1740) be submitted to fully evaluate potential risk to benthic organisms.

Additionally, no chronic avian toxicity data were submitted, but the Agency is not requesting these

data at this time.

Uncertainties:

There is uncertainty with respect to the environmental fate studies that were deemed supplemental.

Some problems were found in these studies and there is uncertainty associated with the use of these

end points. Furthermore, the terrestrial field dissipation study was waived and the results of the

laboratory study could not be corroborated with real life situations in the field. The fact that a single

chemical (pyrethrin 1) was chosen as a surrogate compound or representative for the other six

pyrethrins may be a source of some uncertainty.
The uncertainties associated with pyrethrin exposure in the environment are mainly focused on the

possible impact to aquatic ecosystems. Since pyrethrin is highly toxic to fish and invertebrates, there

is a question of sustaining functional diversity in a system that has been exposed to toxic drift or

runoff. Proponents for the use of pyrethrin in agricultural settings argue that invertebrates are

resilient and affected populations will reintroduce themselves in time. EFED believes that the degree

of reintroduction of species that are keystone to an ecosystem is uncertain, and the impact of

diminished invertebrate diversity on ecosystem integrity has not yet been adequately evaluated. In

addition to a direct impact on invertebrate diversity, EFED is also concerned with the indirect effects

of food chain alterations that could influence fish populations that are dependent upon aquatic

invertebrates

Although pyrethrins bind and accumulate in sediments, EFED did not have sediment monitoring or

toxicity data to adequately evaluate this potential risk to benthic organisms. However, this uncertainty

was addressed by using model derived exposure values for sediment and pore water. The estimated

environmental concentrations (EECs) that were used to calculate RQ values were the pore water

output of the PRZM/EXAMS model, while the effects data were standard worst case water column

test (e.g., EC50 daphnia). Although the sediment systems is assumed to adsorbed a large portion of

the chemical over a short period of time, EFED chose to use the resulting concentrations in pore

water that are at equilibrium with sediment loads for the EECs. However, EFED also realizes that

there is uncertainty regarding the amount of sorbed pesticide that may contribute to the toxicity of

organisms that feed directly on the sediment itself. Therefore, the assumed risk to benthic organisms

has the potential to be greater than originally surmised.

EFED Label Recommendations

Manufacturing Use:

Do not discharge effluent containing this product into lakes, streams, ponds, estuaries, oceans or

other waters unless in accordance with the requirements of a National Pollutant Discharge

Elimination System (NPDES) permit and the permitting authority has been notified in writing prior

to discharge. Do not discharge effluent containing this product to sewer systems without previously

notifying the local sewage treatment plant authority. For guidance contact your State Water Board

or Regional Office of the EPA. Do not contaminate water when disposing of equipment washwaters.

End Use Products:

This product is toxic to fish and aquatic invertebrates. This product may contaminate water through

drift of spray in wind or via runoff events. Use care when applying in areas adjacent to any body of

water. Do not apply directly to water, to areas where surface water is present or to intertidal areas

below the mean high water mark. Do not apply when weather conditions favor drift from target area.

Do not contaminate water when disposing of equipment wash-waters or rinsate.

Label statements for spray drift management:

The Agency has been working with the Spray Drift Task Force, EPA Regional Offices and State Lead

Agencies for pesticide regulation and other parties to develop the best spray drift management

practices. The Agency is proposing interim mitigation measures for aerial applications that should
be placed on product labels/labeling. The Agency has completed its evaluation of the new data base

submitted by the Spray Drift Task Force, a membership of U.S. pesticide registrants, and is

developing a policy on how to appropriately apply the data and the AgDRIFT computer model to

its risk assessments for pesticides applied by air, orchard airblast and ground hydraulic methods. After

the policy is in place, the Agency may impose further refinements in spray drift management practices

to reduce off-target drift and risks associated with aerial as well as other application types where

appropriate.

The results of this risk assessment indicate that for many of the crop scenarios the level of spray drift

is an important component of the concentrations observed in adjacent bodies of water. Since

pyrethrin was found to be highly toxic to various aquatic animals, the risk managers have to pay

special attention to the labels statements placed to the pyrethrin products.

For mosquito abatement, application directions in the label are insufficient to accurately estimate

aquatic exposures that result from application of pyrethrin for controlling mosquitoes. Limitations

(as opposed to recommendations) on product labels for key parameters such as droplet size, wind

speed, release height, application interval, and number of applications allowed per year are not

specified. This exposure assessment represents the water concentrations expected from a typical,

low-level aerial application. Concentrations resulting from actual application of pyrethrin for

mosquito control could be significantly higher than modeled concentrations if applicators used

different application parameters.
Tables A and B show the Ecological Effects and Environmental Fate Data Requirements for

Pyrethrin

Table A. Ecological Effects Data Requirements for Pyrethrin.

Guideline

number Data requirement

Are further

data needed? Study ID #

Study

classificationa

71-1 Avian oral LD50 No 420109-01 Core

71-2 Avian dietary LC50 No 419688-01

419688-02

Core

71-4 Avian reproduction No No data No data

72-1 Freshwater fish LC50 No 430823-01

430823-02

430823-03

430823-04

Core

Core

Core

Core

Core

Core

72-2 Freshwater invertebrate acute LC50 No 430823-05

430823-06

Core

Core

72-3(a) Estuarine/marine fish LC50 No 430823-07

430823-08

Core

Core

72-3(b) Estuarine/marine mollusk LC50 No 430823-09

430823-10

Core

Core

72-3(c) Estuarine/marine shrimp LC50 No 430823-11

430823-12

Core

Core

72-4(a) Freshwater fish early life-stage No 432527-01 Core

72-4(a) Estuarine/marine fish early lifestageYes No data No data

72-4(b) Freshwater Aquatic invertebrate

life-cycle

No 432527-02 Core

72-4(b) Estuarine/marine invertebrate lifecycleYes No data No data

72-5 Freshwater fish full life-cycle No No data No data

122-1(a) Seed germination/seedling

emergence (Tier I)

No No data No data

122-1(b) Vegetative vigor (Tier I) No No data No data

122-2 Aquatic algal growth No No data No data

123-2 Duckweed (Lemna gibba) No No data No data
Table A. Ecological Effects Data Requirements for Pyrethrin.

Guideline

number Data requirement

Are further

data needed? Study ID #

Study

classificationa

123-1(a) Seed germination/seedling

emergence (Tier II)

No No data No data

123-1(b) Vegetative vigor 

(Tier II)

No No data No data

123-2 Aquatic plant growth No No data No data

144-1 Honey bee acute contact LD50 No 419688-03

Atkins et al., 1967

Stevenson, 1968

Stevenson, 1978

Core

Supplemental

Supplemental

Supplemental

141-2 Honey bee residue on foliage No N/A N/A

850.1735 Whole sediment acute, freshwater Yes N/A N/A

850.174 Whole sediment acute, marine Yes N/A N/A

a

Core: study satisfies guideline; Supplemental: study is scientifically sound, but does not satisfy guideline
Table B. Environmental Fate Data Requirements for Pyrethrin.

Guideline # Data

Requirement

Are

further

data

needed?

MRID #’s Study

Classification

161-1 835.2120 Hydrolysis no 43188201,

43567502

Core

161-2 835.2240 Photodegradation in Waterno 43096601,

43567601

Supplemental

161-3 835.2410 Photodegradation on Soilno 43096602 Supplemental

161-4 835.2370 Photodegradation in Airno NA Waived

162-1 835.4100 Aerobic Soil

Metabolism

no 43499803 Supplemental

162-2 835.4200 Anaerobic Soil

Metabolism

no 43499802 Supplemental

162-3

835.4400 Anaerobic 

Aquatic

Metabolism

no NA Not Required

162-4 835.4300 Aerobic

Aquatic

Metabolism

no 43499801 Supplemental

163-1 835.1240

835.1230

LeachingAdsorption/Des

orption

no 43096603 Core

163-2 835.1410 Laboratory

Volatility

no 43096604 Core

163-3 835.8100 Field Volatility no NA Waived

164-1 835.6100 Terrestrial

Field

Dissipation

no 42745501 Waived1

164-2 835.6200 Aquatic Field

Dissipation

no 43818501 Waived1

164-3 835.6300 Forestry

Dissipation

no NA Not Required

165-4 850.1730 Accumulation

in Fish

no 43302301,

43884102

Core
Table B. Environmental Fate Data Requirements for Pyrethrin.

Guideline # Data

Requirement

Are

further

data

needed?

MRID #’s Study

Classification

165-5 850.1950 Accumulation

– Aquatic Nontarget

Organisms

no NA Waived

166-1 835.7100 Groundwater –

Small

Prospective

no NA Waived1

201-1 840.1100 Droplet Size

Spectrum

no NA Not Required2

202-1 840.1200 Spray Drift

Field

Evaluation

no NA Not Required2

1. Waived based on its low persistence and mobility and other environmental fate characteristics.

2. The registrant is a member of the Spray Drift Task Force and the data requirement is covered by the data produced

by this coalition.
Preliminary Science Assessment for the Reregistration Eligibility Decision

(RED) Document for Case 2580:

PYRETHRIN

Prepared by:

Jerry L. Ellis, Jr., Biologist 

José L. Meléndez, Chemist

Miachel Rexrode, Ph.D., Fishery Biologist

United States Environmental Protection Agency

Office of Pesticide Programs

Environmental Fate and Effects Division

Environmental Risk Branch V

Ariel Rios Building

1200 Pennsylvania Ave., NW 

Mail Code 7507C

Washington, DC 20460

Reviewed by:

Jean Holmes, RAPL

Mah T. Shamim, Ph.D., Chief

Environmental Risk 

Branch V 
-1-

Table of Contents

Table of Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

I. Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

A. Risks to Non-target Organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

B. Nature of Chemical Stressor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

C. Conclusions - Exposure Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

D. Conclusions - Effects Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

II. Problem Formulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

A. Stressor Source and Distribution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1. Physical-Chemical and Fate and Transport Properties . . . . . . . . . . . . . . . . . . 6

2. Mode of Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3. Overview of Pesticide Usage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

B. Receptors: Ecological Effects .......................................... 8

C. Assessment Endpoints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

D. Conceptual Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

1. Risk Hypotheses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2. Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

E. Analysis Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

1. Develop Assessment Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2. Identification of Data Gaps and Methods for Conducting Assessment . . . . . 15

3. Measures to Evaluate Risk Hypotheses and Conceptual Model . . . . . . . . . . 16

a. Measures of Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

b. Measures of Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

III. Analysis .............................................................. 19

A. Use Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

B. Exposure Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

1. Environmental Fate and Transport Characterization . . . . . . . . . . . . . . . . . . . 23

2. Measures of Aquatic Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

a. Aquatic Exposure Modeling for Agricultural Crops . . . . . . . . . . . . . 33

b. Aquatic Exposure Modeling for Mosquito Abatement . . . . . . . . . . . 45

c. Aquatic Exposure “Down-the-Drain” Assessment . . . . . . . . . . . . . . 57

d. Aquatic Exposure Monitoring (Field Data) . . . . . . . . . . . . . . . . . . . . 59

3. Measures of Terrestrial Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

4. Non-Target Plant Exposures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

C. Ecological Effects Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

1. Aquatic Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

a. Aquatic Animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

b. Aquatic Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

2. Terrestrial Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
-2-

a. Terrestrial Animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

b. Terrestrial Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

IV. Risk Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

A. Risk Estimation - Integration of Exposure and Effects Data . . . . . . . . . . . . . . . . . . 60

1. Non-target Aquatic Animals and Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

a. Fish and Aquatic Invertebrates - Agricultural Uses and Mosquito

Abatement Uses and Down the Drain . . . . . . . . . . . . . . . . . . . . 70

b. Sediment Organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

2. Non-target Terrestrial Animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

a. Mammals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

b. Birds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

c. Insects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

3. Non-target Terrestrial and Semi-aquatic Plants . . . . . . . . . . . . . . . . . . . . . . 91

B. Risk Description - Interpretation of Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

1. Estimating Risks to Aquatic Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

2. Estimating Risks to Terrestrial Organisms (Mammals and Birds) . . . . . . . . . 95

3. Review of Incident Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

a. Incidents Involving Aquatic Organisms . . . . . . . . . . . . . . . . . . . . . . . 97

b. Incidents Involving Terrestrial Organisms . . . . . . . . . . . . . . . . . . . . . 97

4. Endocrine Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

5. Threatened and Endangered Species Concerns . . . . . . . . . . . . . . . . . . . . . . . 99

a. Taxonomic Groups Potentially at Risk . . . . . . . . . . . . . . . . . . . . . . 100

b. Action Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100

c. Indirect Effects Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

d. Critical Habitat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

C. Description of Assumptions, Uncertainties, Strengths, and Limitations . . . . . . . . . 103

1. Assumptions and Limitations Related to Exposure For All Taxa . . . . . . . . 103

2. Assumptions and Limitations Related to Exposure For Aquatic Species . . 103

3. Assumptions and Limitations Related to Exposure For Terrestrial Species . 103

4. Assumptions and Limitations Related to Effects Assessment . . . . . . . . . . . 105

5. Assumptions Associated With the Acute LOCs . . . . . . . . . . . . . . . . . . . . . 106

V. Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

ACKNOWLEDGMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

VI. Appendices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Appendices Page Number

APPENDIX A. Environmental Fate Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

APPENDIX B. Aquatic Exposure Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

APPENDIX C. T-REX Model and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

APPENDIX D. TerrPlant Model and Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

APPENDIX E. Ecological Effects Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

APPENDIX F. Risk Quotient Method and Levels of Concern . . . . . . . . . . . . . . . . . . 151
-3-

APPENDIX G. Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153

APPENDIX H. Summary of Endangered/Threatened Species . . . . . . . . . . . . . . . . . . 154

APPENDIX J. Data Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175

APPENDIX K. Ecotoxicity and Environmental Fate Bibliography . . . . . . . . . . . . . . . 182

APPENDIX L. Mosquito Abatement Modeling Using AGDISP v. 8.07 . . . . . . . . . . 189

APPENDIX N. T-REX Output File for Typical Application Rate..........................388

APPENDIX O. AgDRIFT® and PRZM/EXAMS Input and Output Files for Drift

and Buffer Zones Analysis..

........................................................392

APPENDIX P. Equilibrium Partitioning Model and Risk Estimation for Benthic

Organisms...........................

........................................................448

APPENDIX Q. EPIWIN Output Files and “Down-the-Drain” Output

Files.....................................

........................................................452
-1-

I. Executive Summary

A. Risks to Non-target Organisms

The Agency’s screening-level risk assessment for pyrethrin, is focused on maximum and typical

application rates for agricultural, and mosquito abatement uses. Consideration was also given for

pharmacological uses in a “Down-the-Drain” scenario.

For terrestrial organisms, the level of concern was not exceeded for acute or chronic risk to listed

or non-listed mammals or birds. Although EFED does not conduct risk assessments on non-target

terrestrial insects, toxicity studies show that pyrethrins are toxic to the honey bee on an acute contact

and oral basis.

Risk to Aquatic Organisms (Maximum and Typical Application Rates)

• Agricultural Uses: Maximum application of pyrethrin to various crops can result acute and

chronic risks to aquatic organisms: freshwater and estuarine/marine fish and invertebrates

(including sediment-dwelling organisms). This screening-level assessment shows the potential

for exceeding LOCs for acute risk, restricted use, and endangered species, as well as chronic

risk.

• The greatest risk (i.e., highest exceedance of LOCs) among aquatic receptors evaluated was

for aquatic invertebrates (both freshwater and estuarine/marine). 

• Typical application rates appear to reduce risk to aquatic organisms. The LOCs for freshwater

and estuarine/marine fish and invertebrates should not be exceeded under this exposure

scenario.

Mosquito abatement: In general maximum application showed that the major acute risk

concern was for estuarine/marine invertebrates. However, the acute risk to estuarine/marine

invertebrates appears to be eliminated if boom height is set at 150ft and the droplet size set

at 40 um. Acute risk to freshwater fish and invertebrates or estuarine/marine fish does not

appear to be an ecological concern from mosquito abatement use (maximum or typical

application rate).

• The typical application rate reduced residue exposure to aquatic areas by about 20 -50%. The

risk to the most vulnerable aquatic organisms (estuarine/marine invertebrates) could be

eliminated if boom height is set at a minimum boom height of 75ft and a corresponding

droplet size of 50 um.

• Down-the-Drain: The Agency evaluated the possible exposure to aquatic systems from the

pharmacological uses of pyrethrin. The Down-the-Drain assessment (various processing

scenarios of wastewater through treatment plants) showed that expected pyrethrin residues

should not exceed the LOCs for freshwater and estuarine/marine fish or invertebrates. 
-2-

•

Pyrethrins have generally effective “knockdown” potential but their toxicity is usually enhanced

through the use of synergist like piperonyl butoxide (PBO). In order to be inclusive, EFED has

addressed potential aquatic risk from the PBO formulation. Risk quotients were calculated using the

technical grade active ingredient for the agricultural uses and formulated product (PYRENONE®

Crop Spray, EPA Registration No. 432-1033 ) for the mosquito abatement uses. However, EFED

also calculated potential risk from PBO formulation use on agricultural crops, which showed that

acute risk to freshwater and estuarine/marine fish and invertebrates could increase up to 10X for all

crop scenarios. Piperonyl butoxide, as a synergist, is used to enhance the pesticidal properties of the

active ingredients by competitive inhibition of detoxifying enzymes (cytochrome P450).

• Acute and chronic risk estimates for birds and small mammals associated with the

agricultural uses

The acute and chronic levels of concern (LOCs) were not exceeded for listed or non-listed

mammals or birds.

• Toxicity and risk concerns about degradates of pyrethrins

Although toxicity studies on the degradates were not provided, an evaluation of the structures

indicate that they are the result of the rupture of the ester bridge of the parent, resulting in a

carboxylic acid (chrysanthemic acid), and an alcohol (that subsequently can be degraded to

an acid as well). The resulting molecules have lost their pyrethroid toxicological activity,

therefore, in this assessment, they were not considered of concern. Furthermore, the available

data indicated that chrysanthemic acid was formed at low levels except under hydrolytic

conditions at pH 9. 

B. Nature of Chemical Stressor

Pyrethrin is a mixture of naturally occurring insecticides derived from the flowers of Chrysanthemum

cinerariaefolium and Chrysanthemum cineum. The six individual pyrethrins are pyrethrin 1, pyrethrin

2, cinerin 1, cinerin 2, jasmolin 1, and jasmolin 2. These compounds are esters of a carboxylic acid

and a cyclopentenolone (chrysanthemic acid and pyrethric acid) and three cyclopentenolones

(pyrethrolone, cinerolone, and jasmolone). The technical grade active ingredient (FEK-99) is

commonly referred to as pyrethrum extract, which is the sum of Pyrethrins I (the esters of

chrysanthemic acid - pyrethrin 1, cinerin 1, and jasmolin 1) and Pyrethrins II (the esters of pyrethric

acid - pyrethrin 2, cinerin 2, and jasmolin 2), also called "the pyrethrins", and this mixture constitutes

45 to 55% of pyrethrum extract. In the US, the pyrethrum extract is standardized as 45-55% w/w

total pyrethrins, as indicated earlier. The typical proportion of Pyrethrins I to II is 1:14, while the

ratio of pyrethrin:cynerins:jasmolins is 71:21:7 (Tomlin 1997).

Pyrethrins are used as insecticides in agriculture, pet care, domestic home and garden, and

commercial/industrial/institutional settings, and for mosquito abatement. The final formulation and

application method depends upon the market sector for which pyrethrins are being used. Pyrethrins

are non-systemic insecticides that work by physical contact to the insect or by ingestion, and they

have a slight repellent effect. The toxicity of pyrethrins is due to their action on the sodium channel
-3-

of nerve cells. The formulated pyrethrins pesticide mixture usually contain a synergist, such as

piperonyl butoxide, piperonyl sulfoxide, or sesamex. These compounds enhance the insecticidal

activity of the pesticide by preventing some enzymes in the organism from breaking down the

pyrethrins.

According to the Master Label there are 19 formulation types and 45 application equipment types for

pyrethrin products for agricultural purposes. There are 17 formulation types for pet care, 16

formulation types for domestic/ home and garden, and 20 formulation types for commercial/

industrial/ institutional settings. Equipment types for agricultural crops include such examples as

fixed wing aircraft, and helicopter.

Since it is difficult to evaluate the environmental fate properties of a mixture, pyrethrin 1 was selected

as a surrogate for all the pyrethrins to generate the environmental fate data. As indicated earlier, the

six compounds have similar molecular structure, but with different substituents at two sites. The

individual chemical structures of all six pyrethrins are shown in Figure 1 of Appendix A. Since the

chemicals are structurally very similar, they are expected to have similar environmental fate

properties. However, the toxicity testing was done with the mixture of compounds. FEK-99 was

used to estimate risk to non-target organisms that are associated with the agricultural crop scenarios.

Toxicity data on the formulated product, PYRENONE® Crop Spray (EPA Registration No. 432-

1033), were used to evaluate risk to non-target organisms in the scenarios that involve direct

application to water (such as the mosquito abatement use).

C. Conclusions - Exposure Characterization

Based on the data obtained with pyrethrin 1, which was chosen as a surrogate for all the six

pyrethrins, the following conclusions were derived for these compounds: Pyrethrins are considered

to be persistent in certain environments and short lived in other environments. They are stable to

hydrolysis under neutral and acidic conditions (pH 5 & 7) but quickly photodegrade in shallow clear

water. Pyrethrins adsorb strongly to soil surfaces and are generally considered immobile in soils (Koc

range 12,400 to 37840); therefore, the potential to leach into groundwater is considered low. They

could reach surface water via spray drift or runoff events accompanied by erosion where they quickly

adsorb to suspended solids in the water column, and partition into the sediment. Sediments are likely

to be an environmental sink for any non-degraded pyrethrins since they appear to persist under

anaerobic conditions. Biodegradation under aerobic conditions occurs fairly rapidly with half-lives

of a few days Hydrolysis under alkaline conditions is also an important route of dissipation for

pyrethrins in water (half-life at pH 9 14-17 hours); however, this reaction appears to be relatively

slow under neutral or acidic conditions. Volatilization is not expected to be an important transport

process since pyrethrins tend to have relatively low vapor pressure and Henry’s Law constant. 

An evaluation of the structures of the degradation products of pyrethrins, indicate that they are the

result of the rupture of the ester bridge of the parent, resulting in a carboxylic acid (chrysanthemic

acid), and an alcohol (that could subsequently be degraded to an acid as well). The available data

indicated that chrysanthemic acid was formed in small amounts except under hydrolytic conditions

at pH 9 and the degradation products were deemed of low concern. In the majority of the studies
-4-

multiple degradates at very low concentrations were observed, but not characterized. The only other

significant isomer observed in the aqueous photolysis study was designated (E)-isomer of pyrethrin

1. 

The bioconcentration factor for 14C residues in edible tissues of fish was found to be 127X. The

predominant species present in the tissues were parent pyrethrin and chrysanthemic acid.

The effect of spray drift, and the use of buffer zones in reducing exposure to bodies of water adjacent

to treated areas was investigated. The first step was to determine if spray drift was the predominant

mode for transport of pyrethrins to surface water. Four crop scenarios were selected for this

evaluation which represented a wide range of geographical locations within the continental US.

PRZM/EXAMS model was run with the spray drift set to 0% and the results were compared to the

runs where the spray drift was set at 5%. For ID potato and CA grapes, the percent of the peak EEC

attributable to spray drift was very high (88.5 and 94.5%, respectively), for FL citrus and GA

peaches, the percent of the peak EEC related to spray drift appeared to be more moderate (44.9 and

47.6%, respectively). The next step was the buffer zone analysis, where the choice of crop scenarios

was narrowed down to GA peaches and ID potatoes. AgDRIFT® model was used to run a “high

end” (conservative) and a “low end” (best case) drift scenario. Two sets of spray drift values were

generated: using a spray volume of 10 gal./A for orchards and 2 gal./A for other crops, each with

buffer zones of 0, 50, 100, 150 ft. The resulting spray drift values were used as inputs in

PRZM/EXAMS for the two crop scenarios. As expected, the low end (best case) drift scenario

resulted in substantially lower EECs. Using the endpoint for the most sensitive species, RQs were

calculated for the GA peaches which also represented orchards. The magnitude of the exceedance

for the high end drift scenario with 50 ft. buffer zone was about 3.6 times higher compared to the low

end drift scenario with 150 ft. buffer zone. For the ID potatoes (representative of other crops), the

magnitude of the exceedance of the RQs was about 25 times higher for the high end scenario with

a 50 ft. buffer zone compared with the low end drift scenario with a 150 ft. buffer zone. The results

of the ground application and the low end drift scenario with a 150 ft. buffer zone yielded RQs of

similar order of magnitude. 

For the mosquito adulticide use, pyrethrins are applied as very small droplets to create a mist which

remains suspended over the field to more efficiently target the mosquitoes. Therefore, they are

susceptible to drift towards an adjacent body of water. To determine the deposition of the pesticide

to adjacent water bodies, the computer model AGDISP [AGricultural DISPersal (computer) model

(AGDISP)] was used. The results from AGDISP were subsequently used as input parameters in

PRZM/ EXAMS to model the degradation and partitioning in sediment for water bodies of various

depths (6 in, 1 ft., 1 m, and 2 m) that may be exposed to drift from the mosquito adulticide. It was

found that the shallow pond shows the lower concentration, possibly due to partitioning of the

chemical with the sediment. Variables that have a high impact on the aquatic EECs are the boom

height (the higher the boom height, the levels of deposition), the droplet size (the smaller droplets,

the lower the levels of deposition), the wind speed (too low wind speeds favor higher deposition),

and obviously the application rate (it appears that for many of the products the maximum application

rate is lower than the maximum application rate stated in the Master Label [0.0025 lb a.i./A vs 0.008

lb a.i./A]). The interval between applications and the number of applications are expected to have
-5-

also an effect on the EECs (similar to an agricultural application).

D. Conclusions - Effects Characterization

The ecological effects laboratory studies were conducted with the technical grade active ingredient

( FEK-99) for agricultural uses and the formulated product, PYRENONE® Crop Spray (EPA

Registration No. 432-1033) for mosquito abatement uses.

For aquatic species, pyrethrins are shown to be very highly toxic on an acute basis to both freshwater

and estuarine/marine fish and invertebrates (based on the TGAI and formulation). Acute studies,

conducted with the formulation, showed slightly more toxic endpoints compared to studies with the

TGAI. Chronic toxicity studies (using the TGAI) with freshwater organisms show that the most

sensitive endpoint for fish is growth (length and dry weight) and reproduction for invertebrates. The

chronic NOAEC for freshwater fish and invertebrates was 1.9 and 0.86 :g/L, respectively. No data

were submitted to evaluate the chronic risk to estuarine/marine fish or invertebrates. However, the

acute-to-chronic ratio method was used to estimate NOAECs for estuarine/marine fish (NOAEC

estimate of 5.9 ppb) and invertebrates (NOAEC estimate of 0.10 ppb). Since pyrethrins tend to

partition into the sediment compartment, toxicity data for the sediment dwelling organisms are

needed. 

The TGAI was the test substance used in the bird and laboratory rat toxicity tests. Pyrethrins appear

to be practically non-toxic to avian species on an acute oral and dietary basis. Chronic avian risk was

extrapolated by using surrogate data (pyrethrin Bobwhite quail NOAEC = 125 mg/kg/diet) and

suggest minimal chronic risk to avian species. Toxicity studies with rats suggest that pyrethrins can

be categorized as slightly toxic to small mammals on an acute oral basis. Acute toxicity studies with

honey bees show that pyrethrins are highly toxic on both a contact and an oral basis.

Although there were no aquatic or terrestrial plant data submitted to the Agency does not consider

pyrethrin or the other pyrethroids as being phytotoxic for the following reasons: 1) the compound is

used as a spray on agricultural crops with no phytotoxic effects; 2) the neural toxic mode of action

precludes phtotoxic concerns; 3) the Agency is not aware of any incidents involving plants and

pyrethrin alone (incidents that were reported for terrestrial ornamental plants were inconclusive and

suggest that inerts in the formulation or other circumstances related to application may have caused

the problem. The Agency is not aware of any reported incidents of pyrethrin phytotoxicity on

agricultural crops).

II. Problem Formulation

A. Stressor Source and Distribution

Pyrethrins are nonvolatile hydrocarbons produced by certain species of the chrysanthemum plant

(genus Chrysanthemum) and have been used as insecticides since the1800's. The plant species with

the most toxic content that can be efficiently used for industrial purposes are C. cinerariaefolium and

C. coccineum which are grown mainly in Australia and East Africa. The active insecticidal
-6-

components are collectively known as pyrethrins and consist of six esters. Although the ground

flowers can be used as a dust, a more concentrated and efficacious pyrethrin product is possible

through solvent extraction. Pyrethrin containing dusts and extracts usually have an active ingredient

content of about 30%. However, after filtration and reextraction the concentration can reach 90-

100% (Matsumura,1985). These compounds are contact poisons which can quickly penetrate the

neural system. Although the pyrethrins have an effective “knockdown” action (induction of temporary

paralysis) they do not necessarily have high killing properties by themselves. These compounds are

moderately persistent under certain environmental conditions but are quickly metabolized under other

conditions such as in the presence of sunlight (photolysis). However, in order to delay the metabolic

action (inhibition of microsomal enzymes) so that a lethal dose is assured, organophosphates,

carbamates, or synergists (such as piperonyl butoxide) may be added to the pyrethrins (Ecobichon

and Donald, 1991). Pyrethrin compounds have been used primarily to control human lice, mosquitoes,

cockroaches, beetles, and flies. Some pyrethrin compounds used to control insects in horticultural

crops, are only 0.3% to 0.5% pyrethrins, and are used at rates of up to 50 lb/A. Other pyrethrin

compounds may be used in grain storage and in poultry pens and on dogs and cats to control lice and

fleas. 

Natural pyrethrins have their limitations for use on a large scale for agricultural purposes because of

their cost and instability in sunlight. Therefore, in recent decades, many synthetic pyrethrin-like

compounds were developed and are referred to as synthetic pyrethroids. These compounds are stable

in sunlight (lower reactivity of side-chains) and are generally effective against most agricultural insect

pests when used at the very low rates. The synthetic pyrethroids have evolved over a period of time

and can be divided into four generations.

The formulated products of pyrethrin usually contain a synergist, such as pyperonyl butoxide,

pyperonyl sulfoxide, or sesamex. These compounds enhance the insecticidal activity of pyrethrin.

The Agency does not routinely include, in its screening risk assessments, an evaluation of more than

one active ingredient. In the case of product formulations of active ingredients, each active ingredient

is subject to an individual risk assessment for regulatory decision. It is noted, however, that some

formulations of pyrethrin contain up to 60% PBO, with only about 5 to 6% pyrethrin. It is not clear

if pyperonyl butoxide would have an effect in the solubility or on other physicochemical

characteristics of pyrethrin or on its environmental fate characteristics. This remains as an

uncertainty.

1. Physical-Chemical and Fate and Transport Properties

The pyrethrins are moderately persistent under certain environmental conditions and are very unstable

under other conditions. In soil and water, pyrethrins are degraded by a combination of abiotic and

biotic processes, and the rate of these reactions influences the amount of chemical that is ultimately

available to aquatic and terrestrial organisms. Pyrethrins are not highly volatile and inhalation is not

likely to be a major exposure pathway for mammals and birds. Pyrethrins are considered unstable in

the presence of sunlight and are quickly photodegraded. If released to water, photolysis in shallow

sunlit surface waters may occur rapidly, with a half-life on the order of several hours to about a day.

Biodegradation under aerobic conditions also occurs fairly rapidly with half-lives on the order of days.
-7-

On the other hand, pyrethrins are stabe to hydrolysis under acidic and neutral environments ( pH 5

& 7). Pyrethrins adsorb strongly to soil surfaces and are generally considered immobile in soils,

showing a low potential to leach into groundwater, but a high potential to reach surface water in

runoff events accompanied by erosion. Pyrethrins are expected to adsorb to suspended solids and

sediment in the water column, and sediment is likely to be an environmental sink for any non

degraded pyrethrins since they appear to persist under anaerobic conditions (half-life >80 days).

The degradation products of pyrethrin are the result of the rupture of the ester bridge of the parent,

resulting in a carboxylic acid and an alcohol. No data about possible degradates related to the

cyclopentene ring are available. The major degradate observed in many of the studies was

chrysanthemic acid which was observed at a maximum of 4.0% in the aerobic soil metabolism study,

7.0% in the sediment phase of the anaerobic aquatic metabolism study, 8.4% and 8.1% in the aqueous

and sediment phases respectively in the aerobic aquatic metabolism study. The only exception was

observance of this degradate at a maximum of 64.5% in a hydrolysis study at pH 9 which is an

unlikely environmental condition. Although, based on the octanol water coefficient, pyrethrins are

expected to bioaccumulate in the organic compartment, a fish bioaccumulation study showed low

bioaccumulation potential due to metabolism of the parent compound to chrysanthemic acid.

Pyrethrin is stable in the anaerobic aquatic environment, however, a relatively minor degradate,

chrysanthemum dicarboxylic acid, was detected at a maximum of 14.2% of the applied at 364 days.

In the majority of the studies multiple degradates at very low concentrations were observed, but not

characterized. The only other significant isomer observed in the aqueous photolysis study was

designated (E)-isomer of pyrethrin 1. 

 

2. Mode of Action

The pyrethroids (including pyrethrin) share similar modes of action, resembling that of DDT, and are

considered axonic poisons that affect both the peripheral and central nervous system. It is now well

established that severe neurological symptoms of poisoning with pyrethroids and DDT in mammals

and insects are the result of modification of Na+ channel activity (cellular pores through which

sodium ions are permitted to enter the axon to cause excitation) (Matsumura,1985). Advanced

electrophysiological experiments using voltage clamp and patch clamp, together with ligand-binding

and ionic flux experiments, have unveiled unique actions of pyrethroids of keeping the Na+ channel

in the open state for an extremely long period, sometimes as long as several seconds. This

modification of Na+ channel properties leads to hyperactivity of the nervous system. Pyrethroids have

also been shown to suppress GABA and glutamate receptor-channel complexes and voltage-activated

Ca 2+ channels, but the toxicological significance of these actions is uncertain. Relative to

physiological responses, researchers have designated two types of pyrethroids, Type I (e.g.,

pyrethrins, S-bioallethrin, resmethrin, pyrethrin)and Type II (e.g., cypyrethrin, deltamethrin,

fenvalerate). Type I pyrethroids’ action is mainly associated with compounds that cause nerve

excitation symptoms typified by the appearance of repetitive firing of axons in the peripheral nervous

system and a negatively correlated temperature reversible knockdown property (similar to DDT)

(Clark and Matsumura, 1987). Pyrethrins are non-systemic insecticides that work by physical contact

to the insect or by ingestion, and they have a slight repellent effect.
-8-

The paralyzing effects caused by pyrethrins usually cannot occur without a synergist. For example,

the synergist compound in PYRENONE® Crop Spray (EPA Reg. No. 432-1033) is piperonyl

butoxide, and it blocks the metabolic pathway that would breakdown pyrethrin before the toxic effect

occurs. Products that contain pyrethrins are primarily used as a knock-down agent on the insects and

the addition of a synergist does contribute to the killing efficiency of a formulation (Casida and

Quistad, 1995).

3. Overview of Pesticide Usage

Pyrethrins (CAS number 8003-34-7) are a group of naturally occurring insecticides effective against

a broad range of pests used in four major sectors: agricultural, commercial/industrial/institutional/food

& non-food/mosquito abatement, domestic home and garden, and pet care. Some of these sectors

are not currently assessed by EFED because they do not involve exposure to wildlife or to drinking

waters. There are six naturally occurring pyrethrins derived from the flowers of Chrysanthemum

cinerariaefolium and Chrysanthemum cineum: pyrethrin 1, pyrethrin 2, cinerin 1, cinerin 2, jasmolin

1 and jasmolin 2.

The final formulation type depends upon the end use, examples include aerosol, combustible coil,

dust, emulsifiable concentrate, ready to use liquid, shampoo, and wettable powder. Pyrethrins are

often mixed with other insecticides or used in conjunction with synergists such as piperonyl butoxide

or sesamex. Recent statistics on agricultural uses of numerous pesticides across the United States

during the 1990's are recorded in the National Center for Food and Agricultural Policy’s National

Pesticide Use Database available from USGS (2004; http://ca.water.usgs.gov/pnsp/use92/) and

NFCAP (2002; http://www.ncfap.org/database/default.htm); however, these databases do not include

data or maps on uses of pyrethrins [refer to Section III.A. for additional information about Use

Characterization]. As indicated earlier, natural pyrethrins have their limitations for use on a large

scale for agricultural purposes because of their cost and instability in sunlight.

B. Receptors: Ecological Effects

Table 1 gives examples of taxonomic groups and test species evaluated for ecological effects in

screening level risk assessments. Within each of these very broad taxonomic groups, an acute and/or

chronic endpoint is selected from the available toxicity data (see Section 2(C)). Additional ecological

effects data on honey bees (Apis mellifera) have been incorporated into the risk characterization as

an additional line of evidence.

A complete discussion of all toxicity data available for this risk assessment and the resulting

measurement endpoints selected for each taxonomic group are included in Appendix E. 
-9-

Table 1. Taxonomic groups and test species evaluated for ecological effects in screening

level risk assessments.

Taxonomic group Example(s) of representative species

Birdsa Mallard duck (Anus platyrhynchos)

Bobwhite quail (Colinus virginianus)

Mammals Laboratory rat

Freshwater fishb Bluegill sunfish (Leopomis macrochirus)

Rainbow trout (Oncorhynchus mykiss)

Freshwater invertebrates Water flea (Daphnia magna)

Estuarine/marine fish Sheepshead minnow (Cyprinodon variegatus)

Estuarine/marine

invertebrates

Eastern Oyster (Crassostrea virginica) 

Mysid Shrimp (Americamysis bahia)

Terrestrial plantsc Monocots – corn (Zea mays)

Dicots – soybean (Glycine max)

Aquatic plants and algae Duckweed (Lemna gibba) 

Green algae (Selenastrum capricornutum)

a

Birds may be surrogates for amphibians (terrestrial phase) and reptiles.

b

Freshwater fish may be surrogates for amphibians (aquatic phase).

c

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

dicot families, of which one is soybeans.

C. Assessment Endpoints

Assessment endpoints are defined as “explicit expressions of the actual environmental value that is

to be protected.” Defining an assessment endpoint involves two steps: 1) identifying the valued

attributes of the environment that are considered to be at risk; and 2) operationally defining the

assessment endpoint in terms of an ecological entity (i.e., a community of fish and aquatic

invertebrates) and its attributes (i.e., survival and reproduction). Therefore, selection of the

assessment endpoints is based on valued entities (i.e., ecological receptors), the migration pathways

of pesticides, and the routes by which ecological receptors are exposed to pesticide-related

contamination. The selection of clearly defined assessment endpoints is important because they

provide direction and boundaries in the risk assessment for addressing risk management issues of

concern.

A summary of the assessment and measurement endpoints selected to characterize potential

ecological risks associated with exposure to pyrethrins is provided in Table 2.
-10-

This ecological risk assessment considers maximum application rates on vulnerable soils, maximum

number of applications (as well as single applications), and minimum intervals between application

for uses on representative crops to estimate exposure concentrations. This assessment is not intended

to represent a site or time-specific analysis. Instead, this assessment is intended to represent high-end

exposures at a national level. Likewise, the most sensitive toxicity endpoints are used from surrogate

test species to estimate treatment-related direct effects on acute mortality and chronic reproductive,

growth and survival assessment endpoints. Toxicity tests are intended to determine effects of

pesticide exposure on birds, mammals, fish, terrestrial and aquatic invertebrates, and plants. These

tests include short-term acute, subacute, and reproduction studies and are typically arranged in a

hierarchical or tiered system that progresses from basic laboratory tests to applied field studies. The

toxicity studies are used to evaluate the potential of a pesticide to cause adverse effects, to determine

whether further testing is required, and to determine the need for precautionary label statements to

minimize the potential adverse effects to non-target animals and plants (40 CFR §158.202, 2002). 

Table 2. Summary of assessment and measurement endpoints.

Assessment Endpoint Measurement Endpoint

1. Abundance (i.e., survival, reproduction,

and growth) of birds.

1a. Bobwhite quail acute oral LD50.

1b. Bobwhite quail and mallard duck subacute dietary LD50.

1c. Bobwhite quail and mallard duck chronic reproduction

NOAEC and LOAEC.

2. Abundance (i.e., survival, reproduction,

and growth) of mammals.

2a. Laboratory rat acute oral LD50.

2b. Laboratory rat developmental and chronic NOAEC and

LOAEC.

3. Survival and reproduction of individuals

and communities of freshwater fish and

invertebrates.

3a. Rainbow trout and bluegill sunfish acute LC50.

3b. Rainbow trout chronic (early-life) NOAEC and LOAEC.

3c. Water flea (and other freshwater invertebrates) acute

EC50.

3d. Water flea chronic (life-cycle) NOAEC and LOAEC.

4. Survival and reproduction of individuals

and communities of estuarine/marine fish and

invertebrates.

4a. Sheepshead minnow acute LC50.

4b. Estimated chronic NOAEC and LOAEC values based on

the acute-to-chronic ratio for freshwater fish.

4c. Eastern oyster and mysid shrimp acute LC50.

4d. Mysid shrimp chronic (life-cycle) NOAEC and LOAEC.

4e. Estimated NOAEC and LOAEC values for mollusks

based on the acute-to-chronic ratio for mysids.

5. Perpetuation of individuals and populations

of non-target terrestrial and semi-aquatic

species (crops and non-crop plant species).

5a. Monocot and dicot seedling emergence and vegetative

vigor EC25 values.

6. Survival of beneficial insect populations. 6a. Honeybee acute contact LD50.

7. Abundance (i.e., survival, reproduction,

and growth) of earthworm populations.

7a. Acute and subchronic earthworm LC50 values.
Table 2. Summary of assessment and measurement endpoints.

Assessment Endpoint Measurement Endpoint

-11-

8. Maintenance and growth of individuals and

populations of aquatic plants from standing

crop or biomass.

8a. Algal and vascular plant (i.e., duckweed) EC50 values for

growth rate and biomass measurements.

LD50 = Lethal dose to 50% of the test population.

NOAEC = No-observed-adverse-effect concentration.

LOAEC = Lowest-observed-adverse-effect concentration.

LC50 = Lethal concentration to 50% of the test population.

EC50/EC25 = Effect concentration to 50/25% of the test population.

D. Conceptual Model

1. Risk Hypotheses

Risk hypotheses are specific assumptions about potential adverse effects (i.e., changes in assessment endpoints)

and may be based on theory and logic, empirical data, mathematical models, or probability models (EPA

1998a). For this assessment, the risk is stressor-initiated, where the stressor is the release of pyrethrin to the

environment. The following risk hypothesis is presumed for this screening level assessment:

The use of pyrethrins for agricultural purpuses and vector control (as a mosquito adulticide)

involve situations where terrestrial and/or aquatic animals may be exposed to the chemical.

Based on pyrethrins’ persistence, mode of action, direct toxicity and potential indirect

effects to trophic food webs, the Agency assumes that this compound has the potential to

cause reduced survival, and reproductive impairment to both terrestrial and aquatic

organisms.

Adequate protection is defined as protection of growth, reproduction, and survival of aquatic and terrestrial

ecological populations, and individuals of threatened and endangered species, as needed.

2. Diagram

The conceptual model (shown in Figure 1 for agricultural uses and 1b for mosquito abatement uses) is a

generic graphic depiction of the risk hypothesis. It includes the potential pesticide or stressor (pyrethrins), the

source of the pesticide and/or transport pathways, exposure media, exposure point, biological receptor types,

and attribute changes.

In the specific case of pyrethrin, the source and mechanism of release of pyrethrins may include ground or

aerial spray applications to agricultural crops, or ground or aerial applications of the chemical as a mosquito

adulticide. Note that in both cases, the conditions of applications are very different. Surface runoff from the

areas of application is assumed to depend on factors such as topography, irrigation, and rainfall events.

Additional transport mechanisms include spray drift and wind erosion, which may potentially transport

contaminants to the surrounding sites. In addition, direct deposition may result in contamination of food items

that may be consumed by terrestrial organisms.
-12-

The major point of exposure for aquatic organisms, is direct contact with contaminated water (gill/ integument

uptake), while for terrestrial animals, it is likely that they will eat certain food items contaminated with

pyrethrins, such as grass, foliage, and small insects. For plants, it is direct contact.

The representative aquatic receptors are certain freshwater and estuarine/ marine fish, invertebrates, and, in

certain cases, aquatic plants. The representative terrestrial receptors are certain mammals, birds, and, in

certain cases, terrestrial plants. It should be noted, that these species do not cover all the possible species in

the animal and plant kingdoms. For example, no reptiles are represented in this scheme.

The attribute changes depend on the type of test (eg. reduced survival, growth, or reproduction, and for plants,

seedling emergence and vegetative vigor).
-13-
-14-
-15-

E. Analysis Plan 

1. Develop Assessment Design

For aquatic receptors, the main pathway of exposure is through direct contact with surface water

contaminated with runoff from agricultural fields and spray drift. Risks to aquatic species were based

on estimated environmental concentrations (EECs) using the Tier 2 model PRZM/EXAMS, and for

adulticide uses, with the help of AGDISP. Residues in potential dietary sources for mammals and

birds (e.g., vegetation, insects, fruits/pods, and seeds) were estimated using the Tier 1 model T-REX.

2. Identification of Data Gaps and Methods for Conducting Assessment

The adequacy of the submitted data was evaluated relative to Agency guidelines. The following

identified data gaps for ecological fate and effects endpoints result in a degree of uncertainty in

evaluating the ecological risk of pyrethrins. 

• Chronic data for estuarine / marine fish and invertebrates were not submitted by the

registrant for pyrethrins. Therefore, chronic risks could not be calculated for these

particular taxa; however based on an acute to chronic ratio method done by EFED,

NOAECs were estimated for these species. In the absence of data, the estimated

NOAECs suggest that chronic risk quotients for estuarine/marine invertebrates exceed

the level of concern. However, pyrethrins do not pose a risk concern for

estuarine/marine fish. Chronic toxicity data for estuarine / marine fish and

invertebrates (fish early life cycle and invertebrate life cycle) are needed to fully

characterize effects to these animals. 

• No field study data were identified to estimate pyrethrin residues on plants and

provide estimates of foliar dissipation half-lives. Therefore, in the terrestrial exposure

assessment a half-life of 1- 14days was used to represent dissipation of pyrethrins on

plant surfaces.

• Risks to terrestrial and semi-aquatic plants were not evaluated because toxicity data

on these receptors were not available. However, there are significant incidence data

reported that provides evidence of possible phytotoxicity of the pyrethrin compounds

and formulated products. Toxicity data are needed for terrestrial and aquatic plants

to fully understand the extent of phytotoxicity of products that contain pyrethrins.

• Chronic risks to birds were not evaluated because toxicity data on avian species were

not available.

• Inhalation and dermal pathways for terrestrial mammals and birds were not evaluated

because these routes of exposure are considered to be minimal compared to the

dietary ingestion pathways. Uncertainties associated with exposure pathways for
-16-

terrestrial animals are discussed in Section 4(C)(3).

• Risks to semiaquatic wildlife via consumption of pesticide-contaminated fish were not

evaluated. However, given that bioaccumulation of pyrethrins is low, ingestion of fish

by piscivorous wildlife (such as bears) is not likely to be of concern.

C Exposure to birds and small mammals (up to 1000 g) via ingestion of grasses, plants,

fruits/pods, seeds, and insects was considered. Risk to mammals of large body

weights (such as wolves or bears) were not evaluated because the toxic endpoints

from laboratory tests with the surrogate mammal (laboratory rat) are based on small

body weight.

• In the absence of sediment toxicity and exposure data, a screening method developed

by the Office of Water (OW), that relies on equilibrium partitioning (EqP) of the

chemicals, was used to estimate the risk quotients for sediment dwelling organisms.

Pyrethrin degrades with an aerobic soil half-life of about 10 days; however, it is

relatively persistent under anaerobic conditions in the aquatic environments. Nondegraded pyrethrins are likely to bind to sediment and be available to sediment

dwelling organisms for extended periods of time. To estimate the exposure to

pyrethrins in sediment, EFED calculated the pore water concentrations using

PRZM/EXAMS. Furthermore, using the OW methodology, toxicity data for the water

column invertebrates were used to estimate the toxicity and associated risk to benthic

organisms. 

• Surrogates were used to predict potential risks for species on which the Agency does

not have data (e.g., birds as surrogates for reptiles and terrestrial phase amphibians

and fish as surrogate species for aquatic phase amphibians). It was assumed that use

of surrogate effects data is sufficiently conservative to apply the broad range of

species within taxonomic groups. If other species are more or less sensitive to

pyrethrins, and its associated degradates, risks may be under- or overestimated,

respectively.

• The pyrethrins label supports a minimum interval between applications of one day,

although a three day interval is recommended for typical uses. Most EECs were

estimated using the more protective assumption of a one day interval for each of 10

applications (high pest pressure). There were a few selected crops that were modeled

using the same number of applications, but with the three day interval to represent

exposure based on typical use (normal pest pressure). 

3. Measures to Evaluate Risk Hypotheses and Conceptual Model

a. Measures of Exposure

C The major routes of dissipation of pyrethrins in the environment are photolysis (both in water
-17-

and soil) and to a lesser degree, aerobic soil metabolism. The pyrethrins are relatively stable

under hydrolytic conditions at pH 5 and 7, and under anaerobic conditions. Pyrethrins adsorb

strongly to soil surfaces and are generally considered immobile in soils. The degradation

products of pyrethrin are considered of low concern. Pyrethrins are unlikely to reach ground

waters, but they can reach surface waters via spray drift and rainfall events that cause runoff

accompanied by erosion. Once in the water, they are expected to partition in the sediment

where they may persist for a long period of time.

C For agricultural uses, exposure concentrations for aquatic ecosystems assessments were

estimated based on EFED’s aquatic Tier 2 model PRZM/EXAMS. A graphical user interface

(pe4v01.pl), developed by the EPA (http://www.epa.gov/oppefed1/models/water), was used

to facilitate inputting chemical and use specific parameters into the appropriate PRZM input

files (inp) and EXAMS chemical files. This approach employs PRZM, which simulates runoff

and erosion from an agricultural field on a daily time step. The runoff and erosion flux output

data from PRZM are used as chemical loadings to EXAMS, which simulates surface water

in order to predict the EECs. Thirteen PRZM field scenarios were modeled: GA Peaches,

FL Citrus, CA Wheat, OR Snapbeans, IL corn, ME Potato, MS Cotton, PA Tomato, ND

Wheat, CA Onion, NC Apple, ID Potato, MN Alfalfa, and CA Grapes. These scenarios were

selected to represent a variety of crops and sites in the continental US. EECs for ecological

risk assessment were determined using a Mississippi Pond modeling scenario which describes

a generic scenario for the EXAMS component of the modeling exercise.

C For agricultural scenarios, a subset of the selected scenarios were analyzed with the typical

application rate and number of applications. Priority was provided to vegetable crops.

C For the mosquito adulticide use, pyrethrins are applied as very small droplets to create a mist

which remains suspended over the field to more efficiently target the mosquitoes. Therefore,

they are susceptible to drift towards an adjacent body of water. To determine the deposition

of the pesticide to adjacent water bodies, the computer model AGDISP [AGricultural

DISPersal (computer) model (AGDISP v. 8.08)] was used. The outputs of interest from

AGDISP are the application efficiency (fraction of the material that deposits in the target area

under the aircraft), and the downwind deposition (fraction of the material that deposits in the

designated area or the standard pond). These results were subsequently used as input

parameters in PRZM/ EXAMS to model the degradation and partitioning in sediment for

water bodies of various depths (6 in, 1 ft., 1 m, and 2 m) that may be exposed to drift from

the mosquito adulticide. Furthermore, the analysis was performed using boom height of 75

ft and 150 ft (which were found to by typical for adulticide applications), and droplet sizes

of 40 and 50 :m, and the maximum application rate supported by the PJV in the Master Label

(0.008 lb a.i./A), and a typical application rate (of 0.0025 lb a.i./A).

C Analysis of the most conservative scenario (1 day interval between applications, which is the

interval for high pest pressure) was performed for 13 crops; however, three crops were

selected and run with a less conservative scenario, which will be nominated typical scenario

(3 days interval, designated as the interval between applications for normal pest pressure).
-18-

A comparison of the results was provided. These crops represented the range of EECs that

were observed among the 13 crops run originally with 1 day interval between applications.

C The effect of spray drift and buffer zones on exposure to bodies of water adjacent to treated

areas was investigated using the AgDRIFT® model. As a first step, the evaluation of spray

drift as a possible predominant route of exposure for a number of crops scenarios was

performed using the PRZM/ EXAMS model. Representative crops were run in PRZM/

EXAMS with spray drift set to 0% (to detect the extent of spray drift for that crop scenario),

and 1% (to simulate ground application). EFED bracketed the spray drift options by running

a “high end” (conservative) and a “low end” (best case) drift scenarios. The simulations were

performed using AgDRIFT® with spray drift levels for buffer zones of 0, 50, 100, and 150

ft. at the “low” end and “high” end drift scenarios. The output values from AgDRIFT® were

used as input values in PRZM/ EXAMS.

C Screening level RQs for sediment dwelling organisms were estimated with an extrapolation

method recommended by the Office of Water (USEPA). This was based on the Agency

Equilibrium Partitioning Sediment Guidelines (ESG) under the Clean Water Act [CWA

Section 304(a)(2)]. After consultation with the OW, EFED adopted the equilibrium

partitioning (EqP) sediment method to be used when sediment toxicity and exposure data are

not available. This extrapolation method is useful for estimating potential sediment exposure

values, as well as sediment toxicity values that can be used in a screening level risk

assessment. The EqP theory holds that a nonionic chemical in sediment partitions between

sediment organic carbon, interstitial (pore) water and benthic organisms. At equilibrium, if

the concentration in any phase is known, then the concentration in the other phases can be

predicted through the organic/ carbon soil partition coefficient. The EECs are calculated

from the pore water concentration (an output from PRZM/ EXAMS) through the KOC. In

the absence of sediment toxicity data, the endpoints are extrapolated from the water column

invertebrate toxicity tests.

C Residues in potential dietary sources for mammals and birds (e.g., vegetation, insects) were

estimated using the conceptual approach given in the Tier 1 model T-REX Version 1.4 (TREX, 2004).

C To estimate exposure related to releases of pyrethrins to domestic wastewater treatment, the

Agency relied on the Office of Pollution Prevention and Toxics (OPPT) model, Exposure and

Fate Assessment Screening Tool (E-FAST) (USEPA, 1999). From this model, the Agency

used the “Down-the-Drain” module, which is designed for releases to domestic wastewater

treatment. It is suitable for all sources of pyrethrins that could potentially be exposed through

a “down-the-drain” scenario. The model provides screening level estimate concentrations of

chemicals in surface waters that may result from household uses and disposal of consumer

products into wastewater using a few simple input parameters (production volume and

fraction of the chemical removed during wastewater treatment).

b. Measures of Effect
-19-

Measures of effect are generally based on the results of a toxicity study, although monitoring data

may also be used to provide supporting lines of evidence for the risk characterization. A complete

summary of the measures of effect based on toxicity studies for different ecological receptors and

effect endpoints (acute/chronic) is given in Table 2. In the absence of chronic data for estuarine/

marine fish and invertebrates, the acute-to-chronic ratio method can be used to estimate NOAECs

for these animals. Examples of measures of acute effects (e.g., lethality) include an oral LD50 for

mammals and LC50 for fish and invertebrates. Examples of measures of chronic effects include a

NOAEL for birds or mammals based on reproduction or developmental endpoints, and an EC50 for

plants based on growth rate or biomass measurements.

III. Analysis

A. Use Characterization

Pyrethrins (CAS number 8003-34-7) are a group of naturally occurring insecticides effective against

a broad range of pests. There are no statistics regarding the use of pyrethrins in the National Center

for Food and Agricultural Policy pesticide database (NCFAP) (NCFAP, 2003). According to the

manufacturer label, there are four main sectors of use for pyrethrins:

1) agriculture

2) pet care

3) domestic home and garden; and

4) commercial, industrial, institutional, food & non food, mosquito abatement.

The major focus of this environmental assessment is on agricultural uses and mosquito abatement.

It is acknowledged that, as indicated earlier, natural pyrethrins have their limitations for use on a large

scale for agricultural purposes because of their cost and instability in sunlight. The agricultural preharvest applications to field crops are divided into several cropping groups which are summarized in

Table 3. It is noted that this does not include the greenhouse, domestic, or commercial uses.

According to the Master Label, the same use rate applies to all the crops. In 2000, more than

200,000 lb of pyrethrin were sold, of which around 6% was used for terrestrial non-food uses, and

around 1% was used for outdoor recreation (including mosquito abatement).

For uses on crops, the following assumptions were made: application rate of 0.05 lbs a.i.A, 10

applications, and a 1-day interval or 3-day interval. For mosquito abatement uses, the following

assumptions were made: application rate of 0.008 lbs a.i./A (from the label), 26 applications, and a

4-day interval. The mosquito abatement use covers a longer time period in order to approximate a

period when mosquito abatement would be warranted.
-20-

Table 3. The following crops appear in the master label for pyrethrin.a The maximum application

rate appears in the first row.

Maximum application rate: 0.050 lb a.i./A

Maximum seasonal application rate 0.500 lb a.i./A/season

Maximum number of applications: 10

Minimum application intervals: 1 day (under extreme pressure), 3 days (under normal pressure)

Crop Group 1: Root and Tuber Vegetables (root crop vegetables): arracacha, arrowroot,

Chinese artichoke, Jerusalem artichoke, fodder beet, garden beet, sugar beet, edible burdock,

edible canna, carrot, cassava, celeriac, chayote, turnip rooted chervil, chicory, chufa, dasheen,

ginger, ginseng, horseradish, leren, turnip rooted parsley, parsnip, potato, radish, oriental

radish, rutabaga, salsify, black salsify, Spanish salsify, skirret, sweet potato, tanier, taro,

turmeric, turnip, yam bean, and true yam.

Crop Group 2: Leaves of Root and Tuber Vegetables: fodder beet, garden beet, sugar beet,

edible burdock, carrot, cassava, turnip rooted chervil, chicory, dasheen, parsnip, radish, oriental

radish, rutabaga, salsify, black salsify, Spanish salsify, tanier, taro, turnip, and true yam.

Crop Group 3: Onion (root crop vegetables): green onions, scallion onions, spring onions,

shallot, garlic, leek, great headed garlic, dry bulb onion, potato onion, tree onion, and welsh

onion.

Crop Group 4: Leafy Vegetables (leafy and stem vegetables, except brassica vegetables): leafy

amaranth, arugula, cardoon, celery, Chinese celery, celtuce, chervil, edible-leaved

Chrysanthemum, garland Chrysanthemum, salad corn, garden cress, upland cress, dandelion,

dock, endive, Florence fennel, sea kale, head lettuce, leaf lettuce, orach, parsley, garden

purslane, winter purslane, radicchio, rhubarb, spinach, Chinese spinach, New Zealand spinach,

vine spinach, Swiss chard, and Tampala.

Crop Group 5: Cole Crops (leafy and stem vegetables, brassica leafy group): broccoli,

Chinese, broccoli, raab broccoli, cabbage, Chinese cabbage, bok choy, Chinese mustard

cabbage, Chinese napa cabbage, cauliflower, , collards, kale, kohlrabi, mustard greens, mustard

spinach, and rape greens.

Crop Group 6: Legume Vegetables (succulent or dried seed and pod vegetables): bean, adzuki

bean, broad bean, dry bean, kidney bean, lablab bean, lima bean, moth bean, mung bean, navy

bean, pink bean, pinto bean, rice bean, runner bean, snap bean, tepary bean, urd bean, wax

bean, yardlong bean, catjang, chickpea, cowpea, edible gum, jackbean, lentil, grain lupin, pea,

blackeyed pea, crowder pea, dry pea, dwarf pea, edible-pod pea, English pea, field pea, garden

pea, green pea, pigeon pea, snow pea, Southern pea, succulent pea, sugar snap pea, soybean,

swordbean.

Crop Group 7: Foliage of Legume Vegetables (seed and pod vegetables): dry bean, lima bean,

snap bean, cowpea, grain lupin, field pea, pigeon pea, soybean.
Table 3. The following crops appear in the master label for pyrethrin.a

 The maximum application

rate appears in the first row.

Maximum application rate: 0.050 lb a.i./A

Maximum seasonal application rate 0.500 lb a.i./A/season

Maximum number of applications: 10

Minimum application intervals: 1 day (under extreme pressure), 3 days (under normal pressure)

-21-

Crop Group 8: Fruiting Vegetables (except cucurbits): chili, eggplant, groundcherry, pepino,

pepper, bell pepper, nonbell pepper, nonbell sweet pepper, tomatillo, tomato.

Crop Group 9: Cucurbit Vegetables: balsam apple, balsam pear, cantaloupe, chayote,

cucumber, Chinese cucumber, West Indian gherkin, edible gourd, melon, citron melon,

muskmelon, pumpkin, squash, Summer squash, Winter squash, watermelon, Chinese

waxgourd.

Crop Group 10: Citrus Fruits: calamondin, citrus citron, citrus, citrus hybrids, grapefruit,

kumquat, lemon, lime, satsuma mandarin, sour orange, sweet orange, pummelo, tangelo,

tangerine.

Crop Group 11: Pome Fruits: apple, crabapple, loquat, mayhaw, pear, Oriental pear, quince.

Crop Group 12: Stone Fruits: apricot, sweet cherry, tart cherry, nectarine, peach, plum,

chickasaw plum, damson plum, Japanese plum, prune plum.

Crop Group 13: Berries: blackberry, blueberry, currant, elderberry, gooseberry, huckleberry,

loganberry, black and red raspberry, canaberry.

Crop Group 14: Tree Nuts: almond, beech nut, Brazil nut, butternut, cashew, chestnut,

chinquapin, filbert, hickory nut, macadamia nut, pecan, pistachio, walnut black, English walnut.

Crop Group 15: Cereal Grains: barley, buckwheat, corn, field corn, pod corn, pop corn, sweet

corn, millet, pearl millet, proso millet, oat, rice, wild rice, rye, grain sorghum, teosinte, tricale,

wheat, vavilovi wheat, wild einkorn wheat, wild emmer wheat.

Crop Group 16: Forage, Fodder and Straw of Cereal Grains: barley, field corn, pod corn, pop

corn, sweet corn, millet, pearl millet, proso millet, oat, rice, wild rice, rye, forage sorghum,

grain sorghum, teosinte, tricale, wheat, vavilovi wheat, wild einkorn wheat, wild emmer wheat.
Table 3. The following crops appear in the master label for pyrethrin.a

 The maximum application

rate appears in the first row.

Maximum application rate: 0.050 lb a.i./A

Maximum seasonal application rate 0.500 lb a.i./A/season

Maximum number of applications: 10

Minimum application intervals: 1 day (under extreme pressure), 3 days (under normal pressure)

-22-

Crop Group 17: Grass Forage, Fodder, and Hay: alkali sacaton, alkakigrass, Arizona

cottontop, bahiagrass, beachgrass, spike bentgrass, Bermudagrass, blowoutgrass, gluegrass,

silky bluegrass, Australian bluestern, big bluestern, caucasian bluestern, Díaz bluestern, little

bluestern, sand bluestern, silver bluestern, South African bluestern, yellow bluestern, plains

bristlegrass, bromegrass, broomsedge, Buffalograss, buffelgrass, annual Canarygrass, reed

Canarygrass, caribgrass, carpetgrass, broadleaf carpetgrass, centipedegrass, marshhay

cordgrass, crabgrass, curly mesquite, dallisgrass, pine dropseed, sand dropseed, tall dropseed,

fescue, feather fingergrass, creeping foxtail, meadow, Eastern gamagrass, grass, galleta grass,

grama grass, muhly grass, pasture grass, St. Augustine grass, wildrye grass, zoysia grass, tufted

hairgrass, hardinggrass, Indiangrass, junegrass, limpograss, lovegrass, maidencane, mannagrass,

foxtail millet, Japanese millet, molassesgrass, napiergrass, needlegrass, sand oat, slender oat,

wild oat, tall oat, oniongrass, pangolagrass, panicgrass, paspalum, polargrass, quackgrass,

redtop, reedgrass, rhodesgrass, multiflower false rhodesgrass, Indian ryegrass, Italian ryegrass,

perennial ryegrass, prairie sandreed, sixweeks threeawn, sloughgrass, smilograph, forage

sorghum, green sprangletop, Sudangrass, sunolgrass, tanglehead, Timothy, alpine Timothy,

spike trisetum, vaseygrass, perennial veldtgrass, velvetgrass, wheatgrass, bluebunch

wheatgrass, crested wheatgrass, fairway wheatgrass, intermediate wheatgrass, pubescent

wheatgrass, Siberian wheatgrass, slender wheatgrass, streambank wheatgrass, tall wheatgrass,

thickspice wheatgrass, Western wheatgrass, hooded windmillgrass.

Crop Group 18: Nongrass Animal Feeds: alfalfa, arrowleaf balsamroot, clover, alsike clover,

alyce clover, arrowleaf clover, ball clover, berseem clover, bigflower clover, crimson clover,

hop clover, lappa clover, Persian clover, red clover, rose clover, seaside clover, strawberry

clover, striate clover, sub clover, sweet clover, true clover, white clover, whitetip clover,

crownvetch, kudzu, lespedeza, lupine, forage lupine, sweet lupine, mustard, sainfoin, trefoil,

velvetbean, vetch, milk vetch.

Crop Group 19: Herbs and Spices: allspice, anise, anise hyssop (mint), star anise, annatto,

balm, basil, borage, burnet, camomile, caper, caraway, black caraway, cardamom, cardamom

amomum, cassia, catnip, celery seed, chervil, chive, Chinese chive, cinnamon, clary, clove,

coriander, costmary, culantro, cumin, curry, dill, dillweed, fennel, Florence fennel, fenugreek,

grains of paradise, horehound, hyssop, juniper berry, lavender, lemongrass, lovage, mace, pot

marigold, marjoram (oregano), mustard, nasturtium, nutmeg, parsley, pennyroyal, black

pepper, white pepper, poppy, rosemary, rue, saffron, sage, Summer savory, Winter savory,

sweet bay, tansy, tarragon, thyme, vanilla, wintergreen, woodruff, wormwood.
Table 3. The following crops appear in the master label for pyrethrin.a

 The maximum application

rate appears in the first row.

Maximum application rate: 0.050 lb a.i./A

Maximum seasonal application rate 0.500 lb a.i./A/season

Maximum number of applications: 10

Minimum application intervals: 1 day (under extreme pressure), 3 days (under normal pressure)

-23-

Subtropical Fruits: acerola, avocado, banana, carob bean, cherimoya, date, durian, feijoa, fig,

guava, kiwifruit, lychee, mango, papaya, passionfruit, pineapple, pomegranate.

Oriental Vegetable: acerola, Chinese artichoke, atemoya, balsam pear, mung bean, yardlong

bean, Chinese broccoli, Chinese cabbage, bok choy, napa, coriander (cilantro), dasheen, ginger,

ginseng, melon, citron, Oriental radish, rambutan, Chinese spinach, starfruit (carambola),

Chinese waxgourd.

Miscellaneous Crops: asparagus, coffee, tea, grapes, strawberry, cranberry, hops, sesame,

jojoba, safflower, sunflower, okra, sugarcane, cotton.

a

PHI = 0 days (“wait until the material applied is dry”); for cotton PHI is 14 days (of seed harvest); do not wet plants to point of

runoff or drip.

B. Exposure Characterization

1. Environmental Fate and Transport Characterization

The physical and chemical properties and some environmental fate properties of the pyrethrins are summarized

in Table 4 (certain references were obtained from the TOXNET database).

Table 4. Summary of environmental chemistry and fate properties of pyrethrins.

Parameter Value Reference/Commentsa

Selected Physical/Chemical Parameters

PC code 069001

CAS No. 8003-34-7 Pyrethrum,

121-21-1 pyrethrin 1,

121-29-9 pyrethrin 2,

25402-06-6 cinerin 1,

121-20-0 cinerin 2,

4466-14-2 jasmolin 1,

1172-63-0 jasmolin 2
Table 4. Summary of environmental chemistry and fate properties of pyrethrins.

Parameter Value Reference/Commentsa

-24-

Physical state Clear pale viscous liquid Budavari, S. (ed.). The

Merck Index – An

Encyclopedia of Chemicals,

Drugs, and Biologicals. 

Whitehouse Station, NJ:

Merck and Co., Inc., 1996,

1369.

Lewis, R.J., Sr. (Ed.). 

Hawley’s Condensed

Chemical Dictionary. 13th

Ed. New York, NY: John

Wiley & Sons, Inc. 1997. 

273, 942

Odor Faint: Dried flowers Reported by the registrant

Stability Stable at room temperatures

for over three years when

stored in the absence of light in

steel drums

Reported by the registrant.
Table 4. Summary of environmental chemistry and fate properties of pyrethrins.

Parameter Value Reference/Commentsa

-25-

Chemical name pyrethrin 1: (Z)-(S)-2-methyl4-oxo-3-(penta2,4-dienyl)cyclo pent-2-enyl

(1R)-trans-2,2-dimethyl3-(2-methylprop-1-enyl)cyclopropanecarboxylate

pyrethrin 2: (Z)-(S)-2-methyl4-oxo-3-(penta2,4-dienyl)cyclo pent-2-enyl

(E)-(1R)-trans-3-(methoxy

carbonylprp-enyl)-

2,2-dimethylcyclopropanecarboxylate

cinerin 1: (Z)-(S)-3-(but2-enyl)2-methyl4-oxocyclopent-2-enyl

(1R)-trans-2,2-di methyl3-(2-methyl prop-1-enyl)-

cyclopropanecarboxylate

cinerin 2: (Z)-(S)-3-(but2-enyl)-2-methyl4oxocyclopent-2-enyl

(E)-(1R)-trans-3-(2-methoxycarbonylprop 1-enyl)-

2,2-dimethyl cyclopropanecarboxylate

jasmolin 1: (Z)-(S)-2-methyl4-oxo-3-(pent-2-enyl)-

cyclopent-2-enyl (1R)-trans2,2-dimethyl-3(2-methylprop1enyl)-

cyclopropanecarboxylate

jasmolin 2: (Z)-(S)-2-methyl4-oxo-3-(pent-2-enyl)-

cyclopent-2-enyl (1R)-trans3-(2-methoxycarbonylprop1-enyl)-2,2-dimethylcyclopropanecarboxylate
Table 4. Summary of environmental chemistry and fate properties of pyrethrins.

Parameter Value Reference/Commentsa

-26-

Chemical formula C21H25O3, C21H25O5,

C20H25O3,C22H30O5, C21H28O3,

C22H28O5

Molecular weight 328.4 g/mol pyrethrin 1

372.4 g/mol pyrethrin 2

316.4 g/mol cinerin 1

360.4 g/mol cinerin 2

330.5 g/mol jasmolin 1

357.7 g/mol jasmolin 2

Water solubility pyrethrin 1: 0.2 ppm

pyrethrin 2: 9.0 ppm

cinerin 1: Insoluble

cinerin 2: Insoluble

jasmolin 1: 0.03 ppm

jasmolin 2: 0.09 ppma

Estimated values from

EPISUITE.a

Other values from HSDB

2001 (Hazardous Substances

Data Bank, as cited in

Pyrethrins and Pyrethroids,

Chapter 4. Chemical and

Physical Information)

Solubilities Soluble in alcohol, ether,

diethyl ether, kerosene, carbon

tetrachloride, nitromethane,

and ethylene dichloride

Budavari, S. (ed.). The

Merck Index – An

Encyclopedia of Chemicals,

Drugs, and Biologicals. 

Whitehouse Station, NJ:

Merck and Co., Inc., 1996,

1369

Density pyrethrin 1: 1.5192 g/cm3

 @

18 °C

Pyrethrum: 0.84–0.86 g/cm3

(25%

pale extract) 

0.975 g/cm3

, range 0.97–0.98

g/cm3

Lide, DR (ed.). CRC

Handbook of Chemistry and

Physics. 81st Edition. CRC

Press LLC, Boca Raton: FL

2000, p. 3–137.

Tomlin, C.D.S. (Ed.). The

Pesticide Manual – World

Compendium, 11th Ed.,

British Crop Protection

Council, Surrey, England

1997 1057.

Reported by the registrant.
Table 4. Summary of environmental chemistry and fate properties of pyrethrins.

Parameter Value Reference/Commentsa

-27-

Boiling point 146–148 °C at 2x10-3 mm Hg,

146–150 °C at 5x10-4 mm Hg,

and 170 °C at 0.1 mm Hg for

pyrethrin 1

196–198 °C at 7x10-3 mm Hg,

192–193 °C at 7x10-3 mm Hg,

200 °C at 0.1 mm Hg for

pyrethrin 2

136–138 °C at 8x10-3 mm Hg

for

cinerin 1

182–184 °C at 0.001 mm Hg

for

cinerin 2

Partially from: Budavari, S.

(ed.). The Merck Index – An

Encyclopedia of Chemicals,

Drugs, and Biologicals. 

Whitehouse Station, NJ:

Merck and Co., Inc., 1996,

1369.

Reported by the registrant.

Vapor pressure (25 °C) pyrethrin 1: 2.03x10-5 mm Hg

pyrethrin 2: 3.98x10-7 mm Hg

cinerin 1: 1.1x10-6 mm Hga

cinerin 2: 4.6x10-7 mm Hga

jasmolin 1: 4.8x10-7 mm Hga

jasmolin 2: 1.9x10-7 mm Hga.

Tomlin, C.D.S. (Ed.). The

Pesticide Manual – World

Compendium, 11th Ed.,

British Crop Protection

Council, Surrey, England

1997 1057, 1058

Estimated value from

EPISUITEa

Henry's Law constant pyrethrin 1: 7.7x10-7

Atm-m3/mola

pyrethrin 2: 7.4x10–10

Atm-m3/mola

cinerin 1: 9.6x10-7

Atm-m3/mola

cinerin 2: 9.2x10-10

Atm-m3/mola

jasmolin 1: 1.3x10-6

Atm-m3/mola

jasmolin 2: 1.2x10–9

Atm-m3/mola

Estimated value from

EPISUITEa
Table 4. Summary of environmental chemistry and fate properties of pyrethrins.

Parameter Value Reference/Commentsa

-28-

log KOW pyrethrin 1: 5.9

pyrethrin 2: 4.3

Tomlin, C.D.S. (Ed.). The

Pesticide Manual – World

Compendium, 11th Ed.,

British Crop Protection

Council, Surrey, England

1997 1057, 1058

Persistence

Hydrolysis t1/2

pH 5

pH 7

pH 9

Stable

Stable

14 days

MRID 43188201

pH 5

pH 7

pH 9

Stable

Stable

17 days

Major degradate chrysanthemic

acid (54–64%) at 21 days

MRID 43567502

Photolysis t1/2 in water 11.8 hours, for the combination

of pyrethrin and the (E)-Isomer

of pyrethrin 1 (@ 55.7% at 2

hours)

MRID 43567601

Photolysis t1/2 on soil <24 hours, numerous minor

degradation products

MRID 43096602

Soil metabolism aerobic t1/2

24–25 °C

9.5 days (total)

3.2 days (bi-phasic initial halflife)

MRID 43499803

Soil metabolism anaerobic

t1/2

NA N/A

Aquatic metabolism aerobic

t1/2

10.5 days MRID 43499802

Aquatic metabolism

anaerobic t1/2

86 days MRID 43499801

Mobility/Adsorption-Desorption
Table 4. Summary of environmental chemistry and fate properties of pyrethrins.

Parameter Value Reference/Commentsa

-29-

Batch equilibrium – unaged soil type

classification

Kads Koc MRID 43096603

S Immob 198 3784

7 

SL Immob 268 1247

2

Average KOC = 35,170

SiL Immob 430 7417

5

SiClL Immob 310 1619

0

Laboratory volatility Limited volatility, #0.002

:g/cm2•hour; after 30 days,

volatilized residues totaled a

maximum of ~16% of which

~9% was CO2, ~0.3% was

pyrethrin, ~10% chrysanthemic

acid, and ~#2.4 of two other

degradates.

MRID 43096604

Field Dissipation

Terrestrial field dissipation 1–2 days MRID 42745501

Aquatic field dissipation Study is not valid MRID 43818501

Bioaccumulation

Accumulation in fish,

maximum BCF

873X viscera

127X edible tissues

predominant species were

parent and chrysanthemic acid

MRID 43302301, 43884102

Pyrethrin is a naturally occurring substance that contains six esters that are biologically active. Pyrethrin 1

was chosen as a surrogate chemical to represent all six pyrethrin. All of the environmental fate studies were

performed with pyrethrin 1.
-30-

General Stereochemistry of the Pyrethrins

R = -CH3 (for cinerin), -CH2CH3 (for jasmolin) or -CH=CH2 (for pyrethrin)

R’= -CH3 (for pyrethrins I), -CO2CH3 (for the pyrethins II)

As noted, all the pyrethrins have the same backbone structure, with the exception of variations in the

substitutions in the external or outermost groups. Due to the fact that all the pyrethrins have very similar

structures, the environmental fate studies were conducted and well characterized with only one of the

pyrethrins: pyrethrin 1.

Except for the interaction with polarized light, enantiomers have identical physico/ chemical properties.

However, diastereoisomers could have somewhat different basic properties. In this case the differences are in

the substituents at two sites. The substituents at -R are expected to have low reactivity, with the ethene being

slightly more reactive. In any case, the driving fate reaction is the breaking of the ester bond which is away

from -R. On the other hand, in the case of -R’, we have two different moieties. The methyl moiety will be

relatively unreactive, while the acetyl group (ester bond) will be susceptible to hydrolysis, resulting in an acid

and an alcohol. It is noted from the Table 4 that the water solubility of the various pyrethrins varies due to

some structure variations among them, however, since the environmental fate of only pyrethrin 1 was

characterized, its solubility was used in the models. This may add some uncertainty to the assessment.

Nevertheless, we do not expect major differences in the overall biotic and abiotic degradation of the pyrethrins.

In general, the environmental fate and transport data base of pyrethrin 1 is adequate to characterize the

environmental fate, drinking water, and ecological exposure of the pyrethrins. It is unlikely that the submission

of additional data would change the environmental fate assessment substantially. There are no mobility and

little persistence data for the degradates of pyrethrin 1. In addition, studies using radiolabeling on the

cyclopentene side of the ester linkage were not conducted and cold analysis was not performed in the

cyclopropyl labeled studies. Consequently, there was no analysis of potential degradates containing the

cyclopentene ring originating from the cleavage of the carboxylate ester linkage.

Degradation and Metabolism

Cyclopropane ring-labeled [1-14C]pyrethrin [pyrethrin 1], at a nominal concentration of 0.4 ppm, was relatively

stable in sterile aqueous pH 5 and pH 7 buffer solutions that were incubated in the dark at 25 ± 1/C for 30

days. In pH 9 solutions, pyrethrin 1 hydrolyzed with a calculated half-life of 14 days and 17 days. The major

degradation product identified was chrysanthemic acid at up to 64% of the applied at 21 days.

In an aqueous photolysis experiment, pyrethrin 1 isomerized to the (E)-isomer of pyrethrin 1 (which reached

a maximum 50.7–55.7% of the applied amount at 2 hours post-treatment ) with an observed half-life of
-31-

approximately 1 hour in sterile aqueous 0.01 M buffer solutions (pH 7) that were irradiated with sunlight in

Irvine, California (33°41'N, 117°15'W) at 25 °C for 71 hours, between 11 AM on October 7 and 10 AM on

October 10, 1993. The overall calculated half-life of dissipation of pyrethrin 1 and its (E)-isomer was 11.8

hours. In a soil photolysis study, [14C]Pyrethrin [pyrethrin 1] photodegraded with an observed half-life of <24

hours (registrant reported 12.9 hours) in sandy loam soil that was treated at 9.0–9.6 ppm and irradiated with

natural sunlight in California at 24+2 °C for 24 hours in mid-November. In contrast, the dark control samples

degraded with a reported half-life of 82.9 hours.

The reported half-life of 14C-pyrethrin 1 applied at a nominal application rate of 1 ppm, in an aerobic sandy

loam soil adjusted to 75% of field capacity and incubated in the dark at 25±1 °C for up to 181 days was 9.5

days. The degradation was reported as biphasic [half-lives were 3.2 days (0–14 day data) and 23.5 days

(14–59 day data)]. Chrysanthemic acid was a minor identified metabolite. Another band (which appears to

consist of multiple peaks) could not be identified.

[

14C]pyrethrin 1 degraded with a half-life of 10.5 days (r2

 = 0.96) in flooded sandy loam soil incubated at

25±1 °C for up to 30 days in an aerobic aquatic dissipation study. In an anaerobic aquatic dissipation study

the half-life of pyrethrin 1 was 86 days.

It is noted that in all the studies, the material was radiolabeled in the cyclopropane ring. As a result, mostly

the degradate that would be observed is chrysanthemic acid. Material radiolabeled in the cyclopentenolone ring

would result in different degradation products; however, the first step in the degradation of pyrethrin 1 is the

rupture of the ester bridge, resulting in a carboxylic acid, and an alcohol. The resulting molecules have lost

their pyrethroid toxicological activity; therefore, in this assessment, they were not considered of concern.

Furthermore, the available data show that chrysanthemic acid does not reach high levels except upon hydrolysis

at pH 9. In the majority of the studies multiple degradates at very low concentrations were observed, but not

characterized. The only significant isomer observed in the aqueous photolysis study was the (E)-isomer of

pyrethrin 1; however, the half-life of pyrethrin 1 was reported for the photolysis of pyrethrin 1 plus the isomer

(as if it was parent) in the calculation (the resulting half-life was less than one day).

The figure that follows shows the structures of the expected degradation products of the various pyrethrins.

All six of them are expected to be more soluble and mobile than their respective parent compounds, specially

the acids. Based on the information from pyrethrin 1, chrysanthemic acid appeared to be short lived and

pyrethric acid and chrysanthemum dicarboxylic acid would be expected to behave similarly. The E-isomer of

pyrethrin 1 was shown in the photolysis on soil study to be short lived as well, therefore, it is of low concern.
-32-

Fig. 2. Structures of Degradation Products of the Pyrethrins

Soil Sorption and Mobility

Based on batch equilibrium experiments, [14C]pyrethrin 1 was determined to be immobile in sand, sandy loam,

silt loam, and silty clay loam soil:calcium chloride solution slurries (1:100, w:v). The respective Koc values

in were 37,847, 12,472, 74,175, and 16,190.

Field Dissipation

EFED has waived the Terrestrial Field Dissipation Study (§164-1) data requirement. EFED believes that a

new study will not substantially change the environmental fate assessment. The parent degrades rapidly and

the ultimate degradate is CO2, and bound residues in soil. It appears that formed metabolites are of no

significant environmental concern, as indicated earlier. The proposed use rate is low (single application rate

of 0.050 lb a.i./acre, seasonal application rate of 0.50 lbs a.i./acre). The degradates such as chrysanthemic

acid may not reach sufficiently high levels to pose a toxicological concern. Based on data from the laboratory

studies, at the current application rate, in field use conditions the peak degradates’ concentrations are likely

to be below 0.01 ppm.

A study, providing marginally supplemental data (bare ground soils in CA, GA, and MI) appears to indicate

that dissipation in the field is very rapid (~1-2 days). The test substance was pyrethrum extract (mixture of

pyrethrins I and pyrethrins II). The results appear to confirm what would be expected from the laboratory

studies.
-33-

2. Measures of Aquatic Exposure

Pyrethrins applied aerially could contaminate shallow surface water through spray drift, or runoff and erosion

events which might occur shortly after application. In shallow, sunlit, surface water bodies, the primary route

of dissipation could be aqueous photolysis (t1⁄2= 11.8 hours); however, pyrethrins are also expected to rapidly

adsorb to suspended solids and accumulate into the sediments. In aquatic environments, pyrethrins are

moderately persistent under aerobic metabolism (t1⁄2= 10.5 days), but more persistent under anaerobic conditions

(t1⁄2= 86.1 days); pyrethrins are hydrolytically stable at pH 5 and 7, but have a hydrolysis half-life of about 14

days at pH 9. Given the fate of this chemical, and assuming the sediments are relatively anoxic, there is

potential for pyrethrin to persist in the sediments where it might pose a risk to sediment-dwelling organisms.

Based on its octanol/water partition coefficient (KOW = 794,000), pyrethrin would be expected to bioaccumulate

substantially. However, pyrethrin 1 accumulated only moderately in fish (127x for the edible tissues, 873x for

the nonedible tissues, and 471x for whole fish). It appears that fish have the ability to metabolize low

concentrations of pyrethrin to water soluble degradates which are then excreted. Depuration was rapid; by day

1, 77% of the accumulated [14C]residues were eliminated from the edible tissues, 66% from the nonedible

tissues, and 68% from the whole fish.

Acute studies on aquatic organisms show that pyrethrins are very highly toxic to freshwater fish (96-hour

LC50= 3.2 :g/L) and aquatic invertebrates (daphnid 48-hour EC50 =6.7 :g/L) at levels well below the water

solubility of this chemical. 

a. Aquatic Exposure Modeling for Agricultural Crops

Modeling of Agricultural Crops:

To determine aquatic ecological risks associated with agricultural uses of pyrethrins, estimated environmental

concentrations (EECs) in surface water were modeled using the Tier II model PRZM (Pesticide Root Zone

Model, version 3.12 compiled May 24, 2001), and EXAMS (Exposure Analysis Modeling System, version

2.98.04 compiled November 12, 2002). PRZM simulates runoff and erosion from an agricultural field on a

daily time step. The runoff and erosion flux output data from PRZM are used as chemical loadings to the

EXAMS surface water program in order to predict the EECs. A graphical user interface (pe4v01.pl),

developed by the EPA (http://www.epa.gov/oppefed1/models/water), was used to facilitate inputting chemical

and use specific parameters into the appropriate PRZM input files (inp) and EXAMS chemical files. With

this aquatic model, it is assumed that the receiving body of water, the EXAMS standard pond, is adjacent to

the treated field, the direction of the spray drift is towards the pond and both the runoff and the spray drift mix

quickly in the pond, also, there is no flow in the pond. These assumptions of PRZM/EXAMS apply in all cases

in this report.

The following 13 PRZM field scenarios were modeled: ID potato, ME potato, CA onion, OR snapbeans, PA

tomato, FL citrus, NC apple, GA peaches, ND wheat, IL corn, MN alfalfa, CA grapes, MS cotton. The

Master Label provides all the crops on which pyrethrin can be applied. They are divided into crop groups

which agree with EPA’s classification procedures. There are 19 crop groups plus three additional special crop

groups (Suptropical Fruits, Oriental Vegetables, and Miscellaneous Crops), with crops that could not be

categorized along with the others. Probably hundreds of crops are listed in the Master Label (refer to Table

3 for a sinopsis of the agricultural crops listing). The 13 crop or field scenarios were selected with PRZM/

EXAMS to represent, not only this wide variety of crops, but the ample geographical regions of the continental

US. The 13 crop scenarios represent the Crop Groups 1, 3, 7, 8, 10, 11, 12, 15, 16, 18, and Miscellaneous
-34-

Crops (cotton).

EECs for ecological risk assessment were determined using a Mississippi Pond modeling scenario which

describes a generic scenario for the EXAMS component of the modeling exercise. Table 5 summarizes the

input parameter values used to run PRZM/EXAMS. The three critical application variables required for this

assessment are the (1) maximum application rate; (2) number of applications per year, and (3) interval between

applications. The maximum application rate of 0.05 lbs a.i./A, maximum number of applications (10), and

minimum interval between applications (1 day, which applies when there is extreme pest pressure) was used

for modeling all crop uses, based on the product label (Table 3). In addition, for selected crops, runs were

made with the interval between applications of 3 days (normal pest pressure). The variability in the EECs for

the different standard scenarios reflect effects of the environmental setting of the scenario including soil

properties and weather, rather than the agricultural characteristics and chemical properties which are consistent

across scenarios. For certain crop scenarios, additional special runs were performed in which the value of

spray drift was set at 0% to determine if spray drift is an important component of the EECs for those crops

(by comparison with the standard run).

Table 5. Input variables and parameter values for PRZM/EXAMS. 

Input Variable Parameter Value Source

Molecular weight Pyrethrin 1: 328.4 g/mol

Water solubility (20 °C) 2.0 ppm Maximum solubility, Tomlin, C.D.S.,

Pesticide manual (TOXNET)

10x available value as per EFED

Model Input Guidance, Version II

(2002)

Vapor pressure Pyrethrin 1: 

2.03 x 10-5 mm Hg

Tomlin, C.D.S., Pesticide manual

(TOXNET)

Henry’s Law constant Pyrethrin 1: 

7.7 x 10-7 atm-m3

/mol

Estimated value from EPISUITE

Hydrolysis t1⁄2, pH 7 (25 °C) pH 5: stable

pH 7: stable

pH 9: 17 days

MRID 43567502

Spray drift fraction 0.05 EFED Model Input Guidance, Version

II (2002)

Application efficiency 0.95 EFED Model Input Guidance, Version

II (2002)

Aerobic soil metabolism t1⁄2 (3-times

available value)

28.5 days MRID 43499803

Aerobic aquatic metabolism t1⁄2

(3-times available value)

31.5 days MRID 43499802

Anaerobic aquatic metabolism t1⁄2 86 days MRID 43499801
Table 5. Input variables and parameter values for PRZM/EXAMS. 

Input Variable Parameter Value Source

-35-

Direct aqueous photolysis t1⁄2 0.5 day MRID 43567601

Koc 35,170 Average Value. MRID 43096603,

EFED Model Input Guidance, Version

II (2002)

PLDKRT (foliage pesticide half-life) 0 days EFED Model Input Guidance, Version

II (2002)

FEXTRC (foliar extraction) 0.5 EFED Model Input Guidance, Version

II (2002)

FILTRA (filtration parameter;

required if CAM set to 3)

NA –

PLVKRT (pesticide decay rate on

plant foliage)

0/day EFED Model Input Guidance, Version

II (2002)

IPSCND (condition for disposition of

foliar pesticide after harvest)

3 PRZM Version 3.0 User’s Manual

(Carsel 1998) 

CAM (chemical application method) 2 PRZM Version 3.0 User’s Manual

(Carsel 1998) 

UPTKF (plant uptake factor) 0 EFED Model Input Guidance, Version

II (2002)

DAIR (diffusion coefficient for

pesticide in the air)

0 PRZM Version 3.0 User’s Manual

(Carsel 1998) 

ENPY (enthalpy of vaporization of

pesticide)

Not reported –

Benthic layer 5 cm EXAMS Default

CROP MANAGEMENT

Standard scenarios ID potato, ME potato, CA onion, OR snapbeans, PA tomato, FL

citrus, NC apple, GA peaches, ND wheat, IL corn, MN alfalfa, CA

grapes, MS cotton

Application rate

(kg a.i./ha/application) 

All scenarios: 0.056

For TYPICAL

APPLICATION RATE:

ID potato 0.0224

PA tomato 0.0067

CA onion 0.0146

OR snap beans 0.0235

Product label

-------

Typical data obtained from various

sources and provided to EFED by

BEAD,
Table 5. Input variables and parameter values for PRZM/EXAMS. 

Input Variable Parameter Value Source

-36-

Number of applications All scenarios: 10

For TYPICAL

APPLICATION RATE:

ID potato 1

PA tomato 2

CA onion 2

OR snap beans 5

Product label

------

No data were available on number of

applications for beans; therefore, the

EFED used a conservative value of 5.

Interval between applications 

(days)a

All scenarios: 1

For TYPICAL

APPLICATION RATE,

and selected crops, 3

Product label

Date of first application All scenarios: 1-June Pyrethrin can be applied at any time of

the year, when there is pest pressure.

Application type and depth of

incorporationa

(cm)

Aerial/0.0/1 day Interval between applications 

(days)a

The Agency has modeled the maximum and typical application rates for pyrethrin (Table 6). The range of peak

daily EECs (maximum rate) for all 13 scenarios is 0.35-2.77 :g/L, while for typical application rate can result

in peak daily EEC’s of 0.0017 - 0.056 ug/L. Special runs with 3-day intervals between applications were also

considered by the Agency and show that the standard scenario with the highest EECs is Illinois Corn. The

modeled values for maximum application rate show that the scenarios with the highest EEC’s were Maine

Potatoes, Pennsylvania Tomatoes, and the Mississippi Cotton. 

Table 6. Surface water EECs from PRZM/EXAMS (ppb) for ecological risk assessment based on

pyrethrins use on several crops.

Crop

App. rate

(kg/ha)

No. of

app./int

between

applicat.

(days)

Peak 96 Hour 21 Day 60 Day 90 Day Annual

IL corn 0.056 10/1 2.766 1.410 0.598 0.374 0.314 0.158

ME potato 0.056 10/1 1.353 0.817 0.387 0.284 0.250 0.146

MS cotton 0.056 10/1 1.906 0.982 0.411 0.279 0.232 0.087

PA tomato 0.056 10/1 1.514 0.742 0.336 0.204 0.181 0.089
Table 6. Surface water EECs from PRZM/EXAMS (ppb) for ecological risk assessment based on

pyrethrins use on several crops.

Crop

App. rate

(kg/ha)

No. of

app./int

between

applicat.

(days)

Peak 96 Hour 21 Day 60 Day 90 Day Annual

-37-

ND wheat 0.056 10/1 0.683 0.366 0.228 0.134 0.112 0.058

CA onion 0.056 10/1 0.777 0.462 0.248 0.125 0.097 0.038

NC apple 0.056 10/1 0.607 0.371 0.233 0.131 0.114 0.056

OR snapbeans 0.056 10/1 0.452 0.340 0.186 0.102 0.083 0.042

ID potato 0.056 10/1 0.366 0.293 0.165 0.085 0.067 0.033

MN alfalfa 0.056 10/1 0.362 0.292 0.163 0.083 0.066 0.032

FL citrus 0.056 10/1 0.401 0.296 0.175 0.092 0.073 0.028

GA peaches 0.056 10/1 0.656 0.424 0.189 0.096 0.073 0.031

CA grapes 0.056 10/1 0.348 0.279 0.149 0.071 0.055 0.021

SPECIAL RUNS WITH 3-DAY INTERVAL BETWEEN APPLICATIONS (3 days, normal pest pressure)

IL corn 0.056 10/3 2.402 1.168 0.501 0.334 0.285 0.151

ID potato 0.056 10/3 0.208 0.140 0.122 0.080 0.065 0.033

CA onion 0.056 10/3 0.392 0.229 0.156 0.092 0.071 0.028

TYPICAL APPLICATION RATE, NUMBER OF APPLICATIONS, AND INTERVAL BETWEEN APPLICATIONS

Crop App. Rate

(Kg a.i./ha)

No of app./

interval

between

app.

Peak 96 Hour 21 Day 60 Day 90 Day Annual

ID potato 0.0224 1/(N/A) 0.052 0.024 0.007 0.003 0.003 0.001
Table 6. Surface water EECs from PRZM/EXAMS (ppb) for ecological risk assessment based on

pyrethrins use on several crops.

Crop

App. rate

(kg/ha)

No. of

app./int

between

applicat.

(days)

Peak 96 Hour 21 Day 60 Day 90 Day Annual

1 Curry, K.K, and Brookman, D.J. “Pyrethrins Master Label” An unpublished document

sponsored by the Pyrethrin Joint Venture c/o Consumer Specialty Products Association, Inc.,

Report No. PJV-03-01, 84 p., no MRID.

2 AgDRIFT® is a computer program provided by the Agency’s OPP, as a product of the Cooperative

Research and Development Agreement (CRADA), between the EPA’s Office of Research and

Development, and the Spray Drift Task Force (SDTF, a coalition of pesticide registrants formed to develop

a comprehensive database of off-target drift information in support of pesticide registration requirements).

-38-

PA tomato 0.0067 2/3 0.033 0.017 0.008 0.005 0.004 0.002

CA onion 0.0146 2/3 0.042 0.022 0.008 0.004 0.003 0.001

OR snap beans 0.0235 5/3 0.094 0.056 0.038 0.021 0.017 0.009

Effect of Spray Drift and Buffer Zones:

The extent to which spray drift may be an important component of the concentration of pyrethrin reaching

bodies of water adjacent to treated areas after their application, was investigated. There are numerous

pyrethrin labels. The Pyrethrin Joint Venture, however, provided a document entitled “Pyrethrins Master

Label,”1

 which summarizes all the uses of pyrethrin, application types and equipment, specific restrictions, etc.

Pyrethrin can be used on hundreds of crops as shown in Table 3. According to the Master Label there are 19

formulation types, and 45 application equipment types for pyrethrin products used for agricultural purposes.

Equipment types include examples such as fixed wing aircraft, and helicopter.

The Master Label gives no indication that there are buffer zones established between the treated areas and

adjacent bodies of water to minimize the level of spray drift. The following restrictions are found:

C “Aerial applications: do not apply less than two gallons of diluted solution per acre to field crops or

less than 10 gallons of diluted solution per acre to orchard crops.”

C “Do not wet plants to point of runoff or drip.”

C “Do not apply directly to water, or to areas where surface water is present, or to intertidal areas below

the mean high water mark.”

The label does not establish a range of droplet sizes, boom height, or wind speed.

Traditionally, the EFED has used a default level of spray drift for aerial applications of 5%. It would be useful

to compare this value to the data from AgDRIFT®2

. A cursory review of the AgDRIFT® data indicates that

the “standard” level of 5% spray drift is adequate for ASAE Coarse to Very Coarse and ASAE Medium to
-39-

Coarse sprays, but the level may be an underestimation for ASAE Fine to Medium and ASAE Very Fine to

Fine sprays.

EFED selected two scenarios, GA peaches and ID potatoes. Both crops yielded relatively low EECs.

Furthermore, one crop scenario (GA peaches) is representative of orchards, and the other (ID potatoes) is

representative of other agricultural crops and these scenarios are located in opposite sides of the nation. First,

EFED ran PRZM/ EXAMS for these crops (plus two other selected crops) with the same standard input

parameters as the original runs, except that the spray drift level was set to 0% instead of 5%. It is noted that

of the 13 scenarios ran by EFED, some will be driven by runoff, while others will be driven by spray drift,

depending on weather conditions, soil type and porosity, site slope, interception, and other factors.

Table 7 provides the peak EECs for theoretical applications where spray drift is 0%. It is noted that for FL

citrus and GA peaches, the peak EECs decreased by almost a half, while for ID potato, and CA grapes, the

peak EECs decreased substantially more. For all these crop scenarios, spray drift is an important component

of the peak EEC. By comparison of the EECs generated with the standard run (5% drift) and the special run

(0%) drift, the percentage of the peak EEC attributable to spray drift can be calculated (see Table 6b). This

percentage is around 45% for FL citrus and GA peaches, and >88% for ID potato and CA grapes. Therefore,

drift is an important component of the peak EECs for the four selected crops. 

Table 7. Surface water EECs from PRZM/EXAMS (ppb) for ecological risk assessment

based on pyrethrins use on selected crops, compared to same crops with Spray Drift set to

0%. The regular runs are presented for comparison purposes only.

Crop Peak EEC

STANDARD RUNS, WITH SPRAY DRIFT SET TO 5%

ID potato 0.366

FL citrus 0.401

GA peaches 0.656

CA grapes 0.348

SPECIAL RUNS WITH SPRAY DRIFT SET TO 0%, Concentration / % attributable to spray drift

ID potato 0.042 / 88.5

FL citrus 0.221 / 44.9

GA peaches 0.344 / 47.6

CA grapes 0.021 / 94.0

Second, for the two selected scenarios, standard PRZM/EXAMS runs were performed simulating ground

applications, for comparative purposes. Then, since pyrethrin yielded RQs that exceeded the levels of concern

for certain aquatic organisms, a number of PRZM/ EXAMS models were run, to anticipate the possible effect

of buffer zones of up to 150 ft. The level of spray drift was determined with the help of AgDRIFT®. Since

the Master Label for pyrethrin does not indicate most of the conditions for the aerial applications (except for
-40-

spray volume), EFED bracketed the options by running a “high end” (worst case) and a “low end” (best case)

scenarios. Essentially, they are described as follows:

Table 8. Drift Scenarios

High End Drift Scenario Low End Drift Scenario

high release height, 15 ft low release height, 8 ft

high wind speed, 15 mph low wind speed, 3 mph

small droplets, ASAE Very Fine droplets (DV0.5 =

81.52 :m)

large droplets, ASAE Medium to Coarse droplets

(DV0.5 = 340.86 :m)

The estimation of the level of spray drift is considered a Tier II Aerial calculation in AgDRIFT®; however,

all possible AgDRIFT® parameters were kept at their default levels for simplicity. Two sets of values were

generated using a spray volume of 10 gal. (spray volume for orchards), and 2 gal. (spray volume for other

crops), with buffer zones of 0, 50, 100, 150 ft. The output value of concern is the spray drift fraction. These

results are summarized in Table 6c, and the inputs/outputs of AgDRIFT® and PRZM/ EXAMS appear in

Appendix O.

Table 9 presents the EECs for two selected crops with modeled standard ground and aerial applications,

theoretical aerial application with no spray drift (partial results also presented in Table 7), and modeled aerial

runs with buffer zones and high end (worst case) drift scenario and low end (best case) drift scenario. As

expected, the low end scenario resulted in substantially lower EECs. It was noted also that for both crops, the

levels of spray drift also decreased, in some cases substantially with the low end drift scenario. The results of

the ground application and the low end drift scenario with a large buffer zone yielded EECs of the same order

of magnitude. For example, the peak EEC of the low end (best case) drift scenario of the ID potato (0.087 ppb,

buffer zone 100 ft) was similar to the peak EEC of the same crop applied by ground methods (0.082 ppb).

Table 9. Surface water EECs (ppb) for ecological risk assessment based

on pyrethrin use on GA peaches and ID potatoes, and buffer zones of 50,

100, and 150 ft. Results using average KOC = 35,170

Crop

Peak

EEC

(ppb)

21 day

EEC

(ppb)

60 day

EEC

(ppb)

Standard Aerial Run, With Spray Drift Set To 5%

Georgia Peaches 0.656 0.189 0.096

Idaho Potatoes 0.366 0.165 0.085

Special Run, With Spray Drift Set To 1%, Ground Application

Georgia Peaches 0.421 0.078 0.042

Idaho Potatoes 0.082 0.038 0.020
Table 9. Surface water EECs (ppb) for ecological risk assessment based

on pyrethrin use on GA peaches and ID potatoes, and buffer zones of 50,

100, and 150 ft. Results using average KOC = 35,170

Crop

Peak

EEC

(ppb)

21 day

EEC

(ppb)

60 day

EEC

(ppb)

-41-

Special Run, With Spray Drift Set To 0%

Georgia Peaches 0.344 0.054 0.028

Idaho Potatoes 0.042 0.006 0.004

High end, release height 15 ft, wind speed 15 mph, very fine droplets

Buffer Zone 0 ft, 24.0% spray drift for GA peaches/ 31.2% spray drift for ID potatoes

Georgia peaches 1.681 0.747 0.359

Idaho Potatoes 2.259 1.002 0.514

Buffer Zone 50 ft, 16.8% spray drift for GA peaches/ 23.1% spray drift for ID potatoes

Georgia peaches 1.436 0.535 0.259

Idaho Potatoes 1.673 0.743 0.381

Buffer Zone 100 ft, 12.7% spray drift for GA peaches/ 18.4% spray drift for ID potatoes

Georgia Peaches 1.164 0.415 0.202

Idaho Potatoes 1.333 0.596 0.304

Buffer Zone 150 ft, 10.2% spray drift for GA peaches/ 15.4% spray drift for ID potatoes

Georgia Peaches 0.998 0.341 0.168

Idaho Potatoes 1.116 0.497 0.255

Low end, release heigh 8 ft, wind speed 3 mph, medium to coarse droplets

Buffer Zone 0 ft, 2.8% spray drift for GA peaches/ 3.0% spray drift for ID potatoes

Georgia peaches 0.519 0.126 0.065

Idaho Potatoes 0.223 0.101 0.052

Buffer Zone 50 ft, 1.4% spray drift for GA peaches/ 1.5% spray drift for ID potatoes

Georgia Peaches 0.431 0.087 0.046

Idaho Potatoes 0.115 0.053 0.028

Buffer Zone 100 ft, 1.1% spray drift for GA peaches/ 1.1% spray drift for ID potatoes
Table 9. Surface water EECs (ppb) for ecological risk assessment based

on pyrethrin use on GA peaches and ID potatoes, and buffer zones of 50,

100, and 150 ft. Results using average KOC = 35,170

Crop

Peak

EEC

(ppb)

21 day

EEC

(ppb)

60 day

EEC

(ppb)

-42-

Georgia Peaches 0.413 0.079 0.042

Idaho Potatoes 0.087 0.041 0.021

Buffer Zone 150 ft, 0.9% spray drift for GA peaches/ 0.8% spray drift for ID potatoes

Georgia Peaches 0.400 0.073 0.039

Idaho Potatoes 0.067 0.031 0.016

Based on 1-in-10 year exceedance probability (0.10). Peak EEC’s provided with three

decimal points for information only.

Equilibrium Partitioning and Concentration in the Sediment:

The pyrethrins are lipophilic compounds that can adsorb readily to particulate and sediment, thus possibly

limiting its exposure to aquatic life in the water column but increasing toxic exposure in the benthos. Sediment

can act as a reservoir for lipophilic persistent compounds. The sediment and particulate likely adsorb a high

percentage of pyrethrin, as indicated by its high KOC. Therefore, coupled with pyrethrin’s persistence in

anaerobic environments, sediment bound pyrethrin could present a toxicity risk for benthic aquatic life and

aquatic ecosystems in general. Exposure to this sediment can result in a direct impact to aquatic life through

respiration, ingestion, dermal contact, as well as indirect impact through alterations of the food chain. 

Under the Clean Water Act (CWA Section 304(a)(2) the Environmental Protection Agency (EPA) and the

States are expected to develop programs for protecting the chemical, physical, and biological integrity of the

nation’s waters. In order to meet the objectives of the CWA, EPA has periodically issued ambient water quality

criteria (WQC). However, toxic contaminants in bottom sediments of lakes, rivers, wetlands, and coastal

waters create potential for environmental degradation even if water column contamination values are low and

comply with EPA’s water quality criteria. In order to evaluate this possible concern the USEPA’s Office of

Water (OW) also calculates Equilibrium Partitioning Sediment Guidelines (ESG).

Pesticide compounds that bind readily to particulate and organic carbon in the water column can eventually

settle onto the benthos. This increase in particulate-bound pesticides can result in an accumulation of

compounds in or on the sediment that may have the potential for toxic impact to benthic and epibenthic aquatic

organisms (e.g., early life stage of many invertebrates and fish, as well as crabs and shrimp). However,

evaluating the risk to aquatic life from this exposure becomes problematic especially if there is a lack of

adequate sediment toxicity and exposure data. Therefore, in order to assess this potential for pesticide risk to

aquatic benthic systems, the Environmental Fate and Effects Division (EFED) of the Office of Pesticides

Program (OPP) has adopted the method used by the Office of Water that relies on equilibrium partitioning

(EqP) of chemicals. Th EqP theory is based on the hydrophobicity and concentrations of the chemical

normalized to organic carbon (OC) in sediment (De Toro et al. 1991) and holds that a nonionic chemical in

sediment partitions between sediment organic carbon, interstitial (pore) water and benthic organisms. At
-43-

equilibrium, if the concentration in any phase is known, then the concentration in the other phases can be

predicted. A key component to this theory is the chemicals organic carbon coefficient (Koc), which is constant

for every chemical and represents the ratio of the chemical concentration in water to the concentration in

organic carbon. The document, “ Technical Basis for the Derivation of Equilibrium Partitioning Sediment

Guidelines (ESGs) for the Protection of Benthic Organisms: Nonionic Organics” (USEPA, 2000a),

demonstrates that biological responses of benthic organisms to nonionic organic chemicals in sediments are

different when the sediment concentrations are expressed on a dry weight basis, but similar when expressed

on a ug chemical/g organic carbon basis (ug/goc). Similar responses were also observed across sediments when

interstitial water concentrations were used to normalize biological availability. The Technical Basis Document

further demonstrates that if the toxic effect concentration in water is known (e.g., LC50), the effect

concentration in sediment on a ug/goc basis can be predicted by multiplying the effect concentration in water

by the chemical Koc..

 (LC50 ug/L x Koc L/kgoc x 1 kgoc/1000goc = LC50 ug/goc)

Since, EFED uses a deterministic method for its screening level risk assessment, the calculation of risk quotient

values (RQ) is important for assessing possible risk. The RQ values are calculated by taking the ratio of the

estimated exposure concentrations (EEC) to the toxicity effect value (e.g., LC50, NOAEC). The EEC values

are model generated (e.g., PRZM/ EXAMS) and reflect peer evaluated and approved scenarios for assessing

pesticide exposure to an aquatic environment. However, the PRZM/ EXAMS output produces water column

EEC values, as well as sediment and pore water EEC values. Therefore, in order to assess possible toxic

pesticide exposure to aquatic organisms from sediments, EFED is using the PRZM/ EXAMS model which

incorporates the principles of the equilibrium partitioning theory, in order to generate EECs from sediment and

pore water. By relying on sediment and/or pore water output values, EFED has two ways for calculating RQ

values for sediments by using pore water exposure values and bulk sediment values. 

The calculations that rely on pore water can be calculated by dividing the PRZM/ EXAMS output value for

pore water concentrations by the dissolved concentrations in the water column that caused toxicity in bioassays

(e.g., LC50).

 EEC pore water ug/L / LC50 ugL

If sediment effects data are available (LC50 ug/kgoc), RQ can be produced by using the PRZM/ EXAMS

sediment output value for sediment. 

EEC sediment ug/ugoc / LC50 ug/kgoc

Assumptions of the equilibrium partitioning model:

Three principle observations that underlie the equilibrium partitioning (EqP) approach:

C The concentrations of nonionic organic chemicals in sediments (expressed on an organic carbon basis)

and in interstitial waters correlate with observed biological effects on sediment-dwelling organisms

across a range of sediments. 

C Partitioning models can relate sediment concentrations for nonionic organic chemicals on an organic

carbon basis to freely-dissolved concentrations in interstitial water.

C The distribution of sensitivities of benthic organisms is similar to that of water column species.

The EqP approach assumes that the partitioning of a chemical between sediment organic carbon and interstitial
-44-

water is at or near equilibrium. Another assumption is that the concentration in either phase can be predictive

using appropriate partition coefficient and the measured concentration in the other phase. Furthermore, it is

assumed that organisms receive equivalent exposure from water-only exposures or from any equilibrated phase

(interstitial water via respiration; from sediment via ingestion or other sediment integument exchange). The

final assumption is that for nonionic compounds, effect concentrations in sediments on an organic carbon basis

can be predicted using the organic carbon partition coefficient (KOC) and effects concentrations in the water.

The Agency evaluated maximum and typical application of pyrethin relative to expected sediment residues

(Table 10). Maximum application rate produced EEC estimates for benthic pore water (PRZM/ EXAMS) that

range from 0.029–0.209 :g/L, while the typical application rate resulted in lower EEC values of 0.002 - 0.010

ug/L (peak daily concentrations). The range of EECs follows the pattern exhibited by the surface water EECs

with the highest EECs estimated for the IL Corn standard scenario and the lowest EECs for the CA Grape

standard scenario. One of the key parameters in the PRZM/ EXAMS model is weather, especially the rainfall

pattern. The amount and frequency of rain for scenarios representing MN potato, IL corn, and PN tomato uses

created conditions for greater runoff of pyrethrins from the field and into the adjacent pond compared to the

warmer, drier climates of the CA grape, FL citrus, and GA peaches standard scenarios.

Table 10. PRZM/EXAMS output for benthic pore water EECs (ug/L) based on pyrethrins use on

several crops.

Crop

App. rate

(kg/ha)

No. of

app./

interval

(days)

Peak 96 Hour 21 Day 60 Day 90 Day Annual

IL corn 0.056 10/1 0.209 0.208 0.204 0.182 0.169 0.103

ME potato 0.056 10/1 0.159 0.158 0.154 0.145 0.138 0.098

MS cotton 0.056 10/1 0.137 0.137 0.132 0.125 0.115 0.051

PA tomato 0.056 10/1 0.117 0.116 0.111 0.098 0.092 0.055

ND wheat 0.056 10/1 0.068 0.068 0.065 0.058 0.054 0.037

CA onion 0.056 10/1 0.060 0.059 0.065 0.047 0.042 0.021

NC apple 0.056 10/1 0.060 0.060 0.058 0.054 0.052 0.035

OR snapbeans 0.056 10/1 0.047 0.047 0.046 0.042 0.040 0.026

ID potato 0.056 10/1 0.038 0.038 0.037 0.033 0.030 0.020
Table 10. PRZM/EXAMS output for benthic pore water EECs (ug/L) based on pyrethrins use on

several crops.

Crop

App. rate

(kg/ha)

No. of

app./

interval

(days)

Peak 96 Hour 21 Day 60 Day 90 Day Annual

-45-

MN alfalfa 0.056 10/1 0.036 0.036 0.035 0.032 0.030 0.019

FL citrus 0.056 10/1 0.036 0.036 0.035 0.032 0.029 0.015

GA peaches 0.056 10v 0.039 0.039 0.038 0.033 0.030 0.019

CA grapes 0.056 10/1 0.029 0.029 0.028 0.024 0.021 0.011

SPECIAL RUNS WITH TYPICAL INTERVAL BETWEEN APPLICATIONS (3 days, normal pest pressure)

IL corn 0.056 10/3 0.193 0.192 0.187 0.167 0.155 0.100

ID potato 0.056 10/3 0.036 0.036 0.034 0.031 0.029 0.020

CA grapes 0.056 10/3 0.040 0.039 0.037 0.032 0.029 0.015

TYPICAL APPLICATION RATE, NUMBER OF APPLICATIONS, AND INTERVAL BETWEEN APPLICATIONS

Crop App. Rate

(Kg a.i./ha)

No of app./

interval

between

app.

Peak 96 Hour 21 Day 60 Day 90 Day Annual

ID potato 0.0224 1/(N/A) 0.002 0.002 0.001 0.001 0.001 0.001

PA tomato 0.0067 2/3 0.003 0.003 0.002 0.002 0.002 0.001

CA onion 0.0146 2/3 0.002 0.002 0.001 0.001 0.001 0.001

OR snap beans 0.0235 5/3 0.010 0.010 0.009 0.009 0.008 0.006

b. Aquatic Exposure Modeling for Mosquito Abatement

In 2000, more than 200,000 lb of pyrethrin were sold, of which around 6% were used for terrestrial non-food

uses, and around 1% was used for outdoor recreation (including mosquito abatement). Pyrethrin can be used

in such places like residential, industrial, recreational, and agricultural areas as well as swamps, marshes,
-46-

overgrown waste areas, roadsides and pastures where adult mosquitoes occur. Some of these places could

involve direct or indirect exposure to aquatic environments.

Mosquito adulticides are more efficacious if they come into contact with insects in flight. For that reason,

mosquito abatement using pyrethrin (as well as other mosquito adulticides) is typically applied via aerial spray

methods with very fine droplets or mists, to prevent immediate deposition of the pesticide.

The modeling approach for this type of use included calculations of spray drift using the AGricultural

DISPersal model (AGDISP v. 8.08). This model/ computer program estimates the deposition of the pesticide

to the treated area, and, by means of its toolbox “deposition assessment,” to the adjacent bodies of water (i.e.

the standard pond). In other words, AGDISP estimates the application efficiency and downwind deposition

or spray block deposition (to the water body, equivalent to the level of spray drift). AGDISP provides a better

prediction of spray drift under the circumstances where a mosquito adulticide is used.

The ten labels for pyrethrins have few specifications about application methods. For example, the intervals

between applications are not specified, the maximum number of applications allowed per time period are not

specified, and the boom (or application release) height is not specified (except for one label). Labeling

statements dealing with the spray droplet size range, wind speed, and time of day to apply pyrethrin are

provided as recommendations but are not provided as requirements.

The output data from AGDISP files and PRZM/EXAMS are provided in Appendix L. Various of the labels

for pyrethrin recommended an optimum droplet size of Dv0.5=30 :m (half of the volume is contained in droplets

less than 30 :m and half of the volume is contained in droplets more than 30 :m; however, the product used

as an example to model pyrethrins in AGDISP, Pyrenone® 25-5 Public Health Insecticide, did not have

specifications for aerial applications. Therefore, the user defined droplet was Dv0.5~50 :m. The wind speed

in some of the labels was recommended as <5 mph in some labels and <10 mph in others; the one used in

modeling was the one in the label for Pyrenone® 25-5 Public Health Insecticide, that is, 10 mph. The master

label indicated that the wind speed would be <10 mph. The spray volume selected was 0.1 gal/A for the

maximum application rate. It was assumed that the product was diluted in an oil with specific gravity of 0.8.

The boom height was varied according to the table below, since the labels have no specifications. The

maximum application rate indicated in the Master Label is lower than that for agricultural settings: 0.008 lb

a.i./A It appears that a typical application rate is 0.0025 lb a.i./A. EFED selected a temperature and relative

humidity of 85°F and 90%, respectively, to simulate conditions where mosquitoes grow. For the most part,

the conditions selected were the default values in AGDISP.

Since the original pyrethrins assessment was issued, more refinements have been achieved in the way the EFED

conducts its adulticide assessment. In order to obtain the level of drift the EFED uses the toolbox “Deposition

Assessment.” This toolbox of the AGDISP model, can be utilized to obtain the levels of spray drift with buffer

zones (even though it does not apply to this chemical). The dimensions of the standard pond are entered in the

toolbox, and the return is the “effective” application rate on the standard pond. By dividing the output of the

toolbox by the application rate, the fraction of drift is obtained. This is the input value that should be used in

PRZM/EXAMS. The results obtained are summarized in the following table (compare to the default values

of 95% application efficiency and 5% spray drift, for agricultural applications). Note that variables such as

the boom height and the application rate will have an effect on the results obtained. The higher the boom

height, the lower the level of deposition and the application efficiency. A low application rate is expected to

result in lower EECs, despite the fact that the levels of deposition are similar. In addition, the droplet size is

an important factor that determines the level of deposition. Large droplets cause more deposition; they cannot
-47-

stay in the air as long as small droplets. It was observed that a buffer zone did not have a major effect on the

level of deposition, when the boom height is 75 ft. With a buffer zone of 0, 100 and 200 ft, the level of

deposition is around 21±1%. Therefore, only the 75 ft boom height with different buffer zones were modeled

for illustration; however, only the no buffer zone was calculated or modeled in PRZM/EXAMS.
-48-

Table 11. Results from AGDISP for PyrethrinsParameter ValueDroplet Size (:m) 50 50 50 50 40 40 50 50 50 5

Boom height (ft) 25 75 75 75 75 150 100 150 75 1Application Rate (lba.i./A)

0.0081 0.008 0.008 0.008 0.008 0.008 0.008 0.008 0.00252 0.0

Application Rate (Kga.i./ha)

0.009 0.009 0.009 0.009 0.009 0.009 0.009 0.009 0.0028 0.0

Buffer zone (ft) 0 0 100 200 0 0 0 0 0 Application efficiency(fraction)

0.393 0.015 0.015 0.015 0 0 0 0 0.015 

Downwind depositionor Spray Drift (fraction)

0.563 0.200 0.213 0.225 0.125 0.005 0.088 0.013 0.200 0.

10.008 lb a.i./A is the maximum application rate supported by the registrant, according to the Master Label. 20.0025 lb a.i

appears to be the typical maximum application rate in most labels of the pyrethrins. Furthermore, comments from theDistricts and other interested parties indicated that they use the product at an application rate of 0.0020 to 0.0025 lb a.i./A.The highlighted columns were modeled in PRZM/ EXAMS.
-49-

Using the results from AGDISP, the tier 2 aquatic model PRZM/ EXAMS (using the graphical user interface

pe4v01.pl) was used to model surface water EECs using the FL turf site scenario. This scenario appears to

be suitable to represent sites such as parks, golf courses, etc. Ponds of various depths (EXAMS standard

ecological Mississippi pond) were simulated. PRZM/ EXAMS runoff component was modified according to

the results of AGDISP (with an application efficiency according to the table above). Furthermore, selected

input parameters were modified to capture the depth of the pond (e.g. CHARL = characteristic length = this

is a measure of the depth of the pond). Pond depths were varied to examine the concentration of pyrethrin in

shallow (i.e., marshes) to deep water bodies (i.e., pond). PRZM/ EXAMS was implemented individually for

pond depths of 6 inches, 1 foot, 1 meter (3.3 feet), and 2 meters (6.6 feet). It should also be clarified that

EXAMS uniformly distributes pyrethrins in the water while in real life situations, pyrethrins could be present

in higher concentrations in the proximity of the treated site. This makes this analysis less conservative because

aquatic animals in the proximity to the field are at greatest risk than farther away.

AGDISP input parameters were those typical for a mosquito adulticide and that were in agreement with the

product labels. They are listed in the Table 12. Input parameters for the PRZM/ EXAMS-pe4 modeling are

listed in Table 13. AGDISP model file is provided in Appendix L. Detailed PRZM/ EXAMS output file, for

each pond depth, is also provided in Appendix L. The summary of the PRZM/ EXAMS results appear in

Tables 14 to 19. The pore water concentrations were provided in Tables 20 to 25.

Various trends were noted. Modeled EECs increased with increasing pond depth. The trend of increasing EECs

with increasing pond depth is noticeable because the EEC’s follow the opposite pattern expected by dilution

only. The results of these runs indicated that dilution effects are not as influential as other factors when

modeling pyrethrins. Other factors, such as sediment adsorption of the chemical appear to be also important

with a chemical like this, with a very high KOC.

The lower concentrations in shallow water bodies compared to deep water bodies in this simulation, may be

partially explained by three depth-dependent variables in the EXAMS model: Henry’s Law constant, KOC, and

aqueous photolysis half-life. The Henry’s Law constant suggests a potential for loss of pesticide from the pond

via volatilization. Second, with a very high KOC, the pyrethrin tends to partition towards the sediment. This

equilibrium will occur more rapidly in shallow waters than in deeper bodies of water. Finally, a third possible

explanation is the short aqueous photolysis half-life (0.5 days) for pyrethrin. According to the Beer-Lambert

law, light intensity decreases exponentially with increasing water depth (light is not expected to penetrate into

depths longer than about 1 ft.). When a chemical has a short half-life (as in this scenario) and it is concentrated

in shallow waters (i.e., six inches), it can be expected to photodegrade more readily than when it is spread

throughout a deeper water column.

Given other same conditions, a larger droplet size caused an increase in the exposure. The peak EECs observed

for the runs performed with the maximum application rate (0.008 lb a.i./A), a boom height of 75 ft, and a

droplet size of Dv0.5 ~ 40 :m were 0.51-0.59 ppb; with a droplet size of around 50 :m, the peak EECs were

0.81-0.95 ppb.

The boom height has an extraordinary effect on the level of exposure observed in the pond. With the same

application rate of 0.008 lb a.i./A, and droplet size of 50 :m, two boom height were explored: 75 and 150 ft.

The respective peak EECs were 0.81-0.95 ppb and 0.05-0.06 ppb. A higher boom height causes more

dispersion of the ULV aerosol, and a smaller amount of it reaches the soil and the water.
-50-

The last variable that was changed and studied was the application rate. In this case, the boom height was 75

ft, the droplet size was 50 :m and the application rates were the maximum: 0.008 lb a.i./A, and what appears

to be a typical application rate from comments obtained in the Phase 5 Comment Period.: 0.0025 lb a.i./A.

The peak EECs’ were respectively 0.114-0.133 ppb and 0.036-0.041 ppb.

Table 12. Input parameters for AGDISP for Pyrethrin.

Parameter Value

Aircraft type Air Tractor AT-401; fixed wing

Swath Width 60 ft

Wing semispan 24.5 ft.

Swath Displacement 0 ft.

propeller rpm 2000; propeller rad. 4.5 ft.; 1 engine

Fixed wing 1 engine

Flight lines 20

Flight speed 120 mph

Boom height Refer to Supplementary Table(1)

Number of nozzles 42

Vortex decay rate 1.25 mph

Aircraft drag coefficient 0.1

Propeller efficiency 0.8

Ambient pressure 29.91 in Hg

Planform area 294 ft2

Semispan 24.5 ft.

Nozzle spacing (even) 0.78 ft = 9.36 in.

Wind speed 10 mph

Wind direction -90°, Perpendicular to flight path

Surface roughness 0.0075

Stability Daylight (solar insolation) Overcast

Relative humidity 90%
Table 12. Input parameters for AGDISP for Pyrethrin.

Parameter Value

-51-

Temperature 85°F

Droplet type User defined

Dv0.1 13.7 :m 11.26 :m

Dv0.5 51.03 :m 41.17 :m

Dv0.9 117.41 :m 94.88 :m

Relative span 2.03 :m 2.03

< 141 : 94.9% 97.22%

Spray material Oil

Specific gravity, carrier 0.8(2)

Specific gravity, nonvolatile 0.8

Active rate 0.008 lb a.i./A =

0.009 Kg a.i./ha

Fraction = 0.012

0.0025 lb a.i./A =

0.0028 Kg a.i./ha

Fraction = 0.012

Nonvolatile rate Fraction = 1

Spray volume rate 0.1 gal/A 0.0312 gal/A

Evaporation rate 0 :m2

/°C/sec

Downwind water body width 208.7 ft

Ave. depth 0.5 ft = 6 in; 1 ft.; 3.3 ft ~ 1 m; 6.6 ft. ~ 2 m(3)

(1). Release height is not specified on product labels.

(2). Value selected from recommendations in the label.

(3). 2 m or standard pond scenario (208.7 ft. wide, 6.6 ft. deep, static water body receiving runoff from 10 hectares).

Table 13. Input parameters for PRZM/EXAMS.

Parameter Value & Units Source

Molecular Weight Pyrethrin 1: 328.4 g/mol
Table 13. Input parameters for PRZM/EXAMS.

Parameter Value & Units Source

-52-

Water Solubility (20oC) 2.0 ppm Max. Solubility, Tomlin, C.D.S.,

Pesticide manual (TOXNET)

10x available value (0.2 ppm) as

per EFED Model Input Guidance

(2002)

Vapor pressure Pyrethrin 1: 2.03 x 10-5

mm Hg

Tomlin, C.D.S., Pesticide manual

(TOXNET)

Henry’s Law Constant Pyrethrin 1: 7.7 x 10-7

atm-m3/mol

Estimated value from EPISUITE

Hydrolysis t1⁄2, pH 7 (25o

C) pH 5: stable

pH 7: stable

pH 9: 17 days

MRID 43567502

Spray Drift Fraction 0.076 Modeled with AGDISP v8.07

Application Efficiency 0.300 Modeled with AGDISP v8.07

Aerobic Soil Metabolism t1⁄2 (3X

available value of 9.5)

28.5 days MRID 43499803

Aerobic Aquatic Metabolism t1⁄2

(3X available value of 10.5)

31.5 days MRID 43499802

Anaerobic Aquatic Metabolism t1⁄2 86 days MRID 43499801

Direct Aqueous Photolysis t1⁄2 0.5 day MRID 43567601

Soil Water Partition Coefficient

(Kd)

N/A – – – – 

KOC 35,170 MRID 43096603; Average value,

EFED Model Input Guidance,

Version II (2002)

PLDKRT (foliage pesticide halflife)0 days EFED Model Input Guidance,

Version II (2002)

FEXTRC (foliar extraction) 0.5 EFED Model Input Guidance,

Version II (2002)

FILTRA (filtration parameter;

required if CAM set to 3)

NA -
Table 13. Input parameters for PRZM/EXAMS.

Parameter Value & Units Source

-53-

PLVKRT (pesticide decay rate on

plant foliage)

0/day EFED Model Input Guidance,

Version II (2002)

IPSCND( condition for disposition

of foliar pesticide after harvest)

3 PRZM Version 3.0 User’s Manual

(Carsel 1998) 

CAM (chemical application

method)

2 PRZM Version 3.0 User’s Manual

(Carsel 1998) 

UPTKF (plant uptake factor) 0 EFED Model Input Guidance,

Version II (2002)

DAIR (diffusion coefficient for

pesticide in the air)

0.0 PRZM Version 3.0 User’s Manual

(Carsel 1998) 

ENPY(enthalpy of vaporization of

pesticide)

 -(Not reported) -

Benthic Layer 5 cm EXAMS Default

CROP MANAGEMENT

Application Rate Florida Turf: 0.008 lb

a.i./A/application = 0.009

kg a.i./ha/application

or

0.0025 lb a.i./A = 0.0028

Kg a.i./ha for Typical

Application Rate

Master Label and

Product Label for

Pyronyl Mosquito Use

Number of Applications Florida Turf: 26 Product Label

Interval Between Applications 

(days)

Florida Turf: 4 Product Label

Date of First Application Florida Turf: 1-Jun Product Label and EFED PRZM

Crop Scenarios (US EPA)

Application Type and Depth of

Incorporation (cm)

Aerial Product Label

POND DEPTH SCENARIOSa

Scenario Pond Depth (m) CHARLb (m)

A 0.1524 (6") 0.101

B 0.3048 (12") 0.177
-54-

C 1 0.525

D 2 1.025

a

 Edit Exams Commands: set charl(1) to “x”; set dep(1) to “x”; rec env 4, where x is the corresponding value listed

in the pond depth scenarios table.

b

 Characteristic Length = 0.5 (Pond Layer) + 0.5 (Benthic Layer) = A measure of pond depth.

Table 14. Surface water EECs (ppb or :g/L) for ecological risk assessment based on pyrethrins

mosquito abatement applications calculated using PRZM/ EXAMS for various pond depths.a

Conditions as follows: Droplet size 50 :m; Boom height 75 ft; Application rate 0.008 lb a.i./A

FL Turf Scenario

Instantaneous

Peak (0 day) 21 day 60 day 90 day

2 m 0.133 0.078 0.074 0.069

1 m 0.122 0.059 0.054 0.050

1 ft 0.117 0.046 0.041 0.038

6 in 0.114 0.042 0.038 0.035

a Surface water EECs are referred to as water segment concentrations in the PRZM/EXAMS output. b Three decimal places are provided to compare ranges in PRZM/EXAMS output. 

Table 15. Surface water EECs (ppb or :g/L) for ecological risk assessment based on pyrethrins

mosquito abatement applications calculated using PRZM/ EXAMS for various pond depths.a

Conditions as follows: Droplet size 40 :m; Boom height 75 ft; Application rate 0.008 lb a.i./A

FL Turf Scenario

Instantaneous

Peak (0 day) 21 day 60 day 90 day

2 m 0.083 0.049 0.046 0.043

1 m 0.076 0.037 0.034 0.031

1 ft 0.073 0.029 0.026 0.024

6 in 0.071 0.027 0.024 0.022

a Surface water EECs are referred to as water segment concentrations in the PRZM/EXAMS output. b Three decimal places are provided to compare ranges in PRZM/EXAMS output. 
-55-

Table 16. Surface water EECs (ppb or :g/L) for ecological risk assessment based on pyrethrins

mosquito abatement applications calculated using PRZM/ EXAMS for various pond depths.a

Conditions as follows: Droplet size 50 :m; Boom height 150 ft; Application rate 0.008 lb a.i./A

FL Turf Scenario

Instantaneous

Peak (0 day) 21 day 60 day 90 day

2 m 0.009 0.005 0.005 0.005

1 m 0.008 0.004 0.004 0.003

1 ft 0.008 0.003 0.003 0.002

6 in 0.007 0.003 0.002 0.002

a Surface water EECs are referred to as water segment concentrations in the PRZM/EXAMS output. b Three decimal places are provided to compare ranges in PRZM/EXAMS output. 

Table 17. Surface water EECs (ppb or :g/L) for ecological risk assessment based on pyrethrins

mosquito abatement applications calculated using PRZM/ EXAMS for various pond depths.a

Conditions as follows: Droplet size 50 :m; Boom height 75 ft; Application rate 0.0025 lb a.i./A

FL Turf Scenario

Instantaneous

Peak (0 day) 21 day 60 day 90 day

2 m 0.041 0.025 0.023 0.022

1 m 0.038 0.018 0.017 0.016

1 ft 0.036 0.014 0.013 0.012

6 in 0.036 0.013 0.012 0.011

a Surface water EECs are referred to as water segment concentrations in the PRZM/EXAMS output. b Three decimal places are provided to compare ranges in PRZM/EXAMS output. 

Table 18. Surface water EECs (ppb or :g/L) for ecological risk assessment based on pyrethrins

mosquito abatement applications calculated using PRZM/ EXAMS for various pond depths.a

Conditions as follows: Droplet size 40 :m; Boom height 150 ft; Application rate 0.008 lb a.i./A

FL Turf Scenario

Instantaneous

Peak (0 day) 21 day 60 day 90 day

2 m 0.003 0.002 0.002 0.002

1 m 0.003 0.001 0.001 0.001

1 ft 0.003 0.001 0.001 0.001

6 in 0.003 0.001 0.001 0.001
Table 18. Surface water EECs (ppb or :g/L) for ecological risk assessment based on pyrethrins

mosquito abatement applications calculated using PRZM/ EXAMS for various pond depths.a

Conditions as follows: Droplet size 40 :m; Boom height 150 ft; Application rate 0.008 lb a.i./A

FL Turf Scenario

Instantaneous

Peak (0 day) 21 day 60 day 90 day

-56-

a Surface water EECs are referred to as water segment concentrations in the PRZM/EXAMS output. b Three decimal places are provided to compare ranges in PRZM/EXAMS output. 

Table 19. Surface water EECs (ppb or :g/L) for ecological risk assessment based on pyrethrins

mosquito abatement applications calculated using PRZM/ EXAMS for various pond depths.a

Conditions as follows: Droplet size 50 :m; Boom height 150 ft; Application rate 0.0025 lb a.i./A

FL Turf Scenario

Instantaneous

Peak (0 day) 21 day 60 day 90 day

2 m 0.003 0.002 0.002 0.002

1 m 0.003 0.001 0.001 0.001

1 ft 0.003 0.001 0.001 0.001

6 in 0.003 0.001 0.001 0.001

a Surface water EECs are referred to as water segment concentrations in the PRZM/EXAMS output. b Three decimal places are provided to compare ranges in PRZM/EXAMS output. 

Table 20. Pore water EECs (ppb or :g/L) for ecological risk assessment based on pyrethrins

mosquito abatement applications calculated using PRZM/ EXAMS for various pond depths.a

Conditions as follows: Droplet size 50 :m; Boom height 75 ft; Application rate 0.008 lb a.i./A

FL Turf Scenario

Instantaneous

Peak (0 day) 21 day 60 day 90 day

2 m 0.031 0.030 0.028 0.027

1 m 0.030 0.029 0.027 0.026

1 ft 0.028 0.027 0.025 0.024

6 in 0.026 0.025 0.023 0.021

a Surface water EECs are referred to as water segment concentrations in the PRZM/EXAMS output. b Three decimal places are provided to compare ranges in PRZM/EXAMS output. 
-57-

Table 21. Pore water EECs (ppb or :g/L) for ecological risk assessment based on pyrethrins

mosquito abatement applications calculated using PRZM/ EXAMS for various pond depths.a

Conditions as follows: Droplet size 40 :m; Boom height 75 ft; Application rate 0.008 lb a.i./A

FL Turf Scenario

Instantaneous

Peak (0 day) 21 day 60 day 90 day

2 m 0.020 0.019 0.018 0.017

1 m 0.019 0.018 0.017 0.016

1 ft 0.018 0.017 0.016 0.015

6 in 0.016 0.015 0.014 0.013

a Surface water EECs are referred to as water segment concentrations in the PRZM/EXAMS output. b Three decimal places are provided to compare ranges in PRZM/EXAMS output. 

Table 22. Pore water EECs (ppb or :g/L) for ecological risk assessment based on pyrethrins

mosquito abatement applications calculated using PRZM/ EXAMS for various pond depths.a

Conditions as follows: Droplet size 50 :m; Boom height 150 ft; Application rate 0.008 lb a.i./A

FL Turf Scenario

Instantaneous

Peak (0 day) 21 day 60 day 90 day

2 m 0.002 0.002 0.002 0.002

1 m 0.002 0.002 0.002 0.002

1 ft 0.002 0.002 0.002 0.002

6 in 0.002 0.002 0.001 0.001

a Surface water EECs are referred to as water segment concentrations in the PRZM/EXAMS output. b Three decimal places are provided to compare ranges in PRZM/EXAMS output. 

Table 23. Pore water EECs (ppb or :g/L) for ecological risk assessment based on pyrethrins

mosquito abatement applications calculated using PRZM/ EXAMS for various pond depths.a

Conditions as follows: Droplet size 50 :m; Boom height 75 ft; Application rate 0.0025 lb a.i./A

FL Turf Scenario

Instantaneous

Peak (0 day) 21 day 60 day 90 day

2 m 0.010 0.010 0.009 0.009

1 m 0.009 0.009 0.008 0.008

1 ft 0.009 0.008 0.008 0.007

6 in 0.008 0.008 0.007 0.007
Table 23. Pore water EECs (ppb or :g/L) for ecological risk assessment based on pyrethrins

mosquito abatement applications calculated using PRZM/ EXAMS for various pond depths.a

Conditions as follows: Droplet size 50 :m; Boom height 75 ft; Application rate 0.0025 lb a.i./A

FL Turf Scenario

Instantaneous

Peak (0 day) 21 day 60 day 90 day

-58-

a Surface water EECs are referred to as water segment concentrations in the PRZM/EXAMS output. b Three decimal places are provided to compare ranges in PRZM/EXAMS output. 

Table 24. Pore water EECs (ppb or :g/L) for ecological risk assessment based on pyrethrins

mosquito abatement applications calculated using PRZM/ EXAMS for various pond depths.a

Conditions as follows: Droplet size 40 :m; Boom height 150 ft; Application rate 0.008 lb a.i./A

FL Turf Scenario

Instantaneous

Peak (0 day) 21 day 60 day 90 day

2 m 0.001 0.001 0.001 0.001

1 m 0.001 0.001 0.001 0.001

1 ft 0.001 0.001 0.001 0.001

6 in 0.001 0.001 0.001 0.001

a Surface water EECs are referred to as water segment concentrations in the PRZM/EXAMS output. b Three decimal places are provided to compare ranges in PRZM/EXAMS output. 

Table 25. Pore water EECs (ppb or :g/L) for ecological risk assessment based on pyrethrins

mosquito abatement applications calculated using PRZM/ EXAMS for various pond depths.a

Conditions as follows: Droplet size 50 :m; Boom height 150 ft; Application rate 0.0025 lb a.i./A

FL Turf Scenario

Instantaneous

Peak (0 day) 21 day 60 day 90 day

2 m 0.001 0.001 0.001 0.001

1 m 0.001 0.001 0.001 0.001

1 ft 0.001 0.001 0.001 0.001

6 in 0.001 0.001 0.001 0.001

a Surface water EECs are referred to as water segment concentrations in the PRZM/EXAMS output. b Three decimal places are provided to compare ranges in PRZM/EXAMS output. 

c. Aquatic Exposure, “Down-the-Drain” Assessment

The USEPA has received various comments from interested parties during the 60 day comment period, requesting tto

address the fact that the pyrethrins are likely to drain and reach water treatment plants. They specifically had
-59-

mentioned the approach utilized by the Agency for pyrethrin with E-FAST (see below). The USEPA intends hereby

to address the issue.

In order to address this issue of pyrethrin release to domestic wastewater treatment, the Agency relied on the Office

of Pollution Prevention and Toxics (OPPT) consumer exposure model, Exposure and Fate Assessment Screening Tool

(E-FAST) (USEPA, 1999). This Down-the-Drain module of E-FAST is specifically designed to address all sources

of pyrethrins that could potentially be disposed to domestic wastewater from a “down-the-drain” application. This

model provides screening level estimate of chemical residues in surface water that may result from household uses and

the disposal of these consumer products into wastewater. The model uses input parameters that include annual

production volume of the pesticide and takes into account the fraction of the chemical removed during wastewater

treatment. The assumptions of the model state that in a given year, the entire production volume of the chemical in

question is parceled out on a daily per capita basis to the U.S. population and converted to a mass release per capita

(e.g., gm/person/day). This mass is diluted into the average daily volume of wastewater released per person per day

to arrive at an estimated concentration of target chemical in wastewater prior to entering a treatment facility. The

target chemical (pyrethrins) concentration in untreated wastewater is then reduced by the fraction removed during

wastewater treatment process before release into a river or stream. The remaining chemical is discharged into surface

water, where it is assumed that it is instantaneously diluted, with no further removal. A Stream Dilution Factor is the

volume of the receiving stream flow divided by the volume of the wastewater released from the Publicly Owned

Treatment Works (POTW). The resulting values are used for ecological effects: estimated environmental

concentrations (EECs)

The equations used are as follows:

Daily per capita release of a chemical in household wastewater

HR = ProdVol x 1000g/Kg x 1 year/365 days

 Pop

HR Daily per capita release of the chemical to a wastewater treatment facility

(grams/person/day)

ProdVol Production volume (Kg/year) [use information will be provided by SRRD]

Pop US population (persons) = 2.727x108

 persons (US Bureau of the Census, 1999)

Surface Water Concentrations

 HR x 1 x (1 - WWT) x CF1

CSM = _______QH___________________

 SDFM

 HR x 1 x (1 - WWT) x CF1

CSH = _______QH___________________

 SDFL

CSM Median time-averaged surface water concentration (:g/L)

CSH High end time averaged surface water concentration (:g/L)

HR Daily per capita release of chemical (i.e. pre-treatment release, g/person/day)

QH Daily per capita wastewater volume released (364 L/person/day, USEPA, 1990; Versar, 1992)

WWT Fraction of chemical removed during wastewater treatment [see alternative values below]

SDFM 50th percentile stream dilution factor for stream to which wastewater treatment facilities discharge

(980.69, Versar, 1992)
-60-

SDFL 10th percentile stream dilution factor for stream to which wastewater treatment facilities discharge

(75.44, Versar, 1992)

CF1 Conversion factor (1x106 :g/g)

Removal of Pyrethrins (WWT)

Information on the degree of removal of pyrethrins from wastewater at POTWs is unavailable. Therefore, the

EPA relied in modeling to obtain this value. The EPIWIN program was utilized. Two levels of removal are obtained

from EPIWIN, the most conservative (the lowest) was utilized in E-FAST modeling.

WWT value = 92.7%

Production Volume

The production volume of pyrethrins was chosen to be very conservative. The total volume of pyrethrins

produced for all uses in the United States was reported by BEAD to be approximately 200,000 lb a.i./A (Biological and

Economic Analysis Division, BEAD).

Substituting the previous values, the following is obtained:

HR = 0.000911 g/person/day

Surface Water Concentrations

Surface water concentrations were modeled using computer program E-FAST, and the results were as

indicated in the following Table (please, refer to Appendix Q for output files from EPIWIN and E-FAST).

Surface Water Concentrations Modeled By E-FAST

WWT\Concentration Acute/ ppb Chronic/ ppb

92.7% 0.00242 0.000186

d. Aquatic Exposure Monitoring (Field Data)

No data were identified to provide information on aquatic exposure monitoring. In addition, at this

time, there are limited surface water or groundwater monitoring data available for pyrethrins. The

U.S. Geological Survey’s National Water Quality Assessment program (NAWQA) did not have any

data regarding the detection of pyrethrins in streams or groundwater.

3. Measures of Terrestrial Exposure

A primary concern with pyrethrins is that birds and mammals may be exposed shortly after application

through oral or dietary exposure to vegetative plant material or insects when foraging in the treated

fields for nesting material or food. The EFED terrestrial exposure model, T-REX (T-REX, Version

1.2.3, dated August 8, 2005), is used to estimate exposures and risks to avian and mammalian

species. Input values on avian and mammalian toxicity as well as chemical application and foliar halflife data are required to run the model. The model provides estimates of both exposure

concentrations and risk quotients (RQs). Specifically, the model provides estimates of concentrations

(maximum and average) of chemical residues in different types of foliage that may be sources of

dietary exposure to avian, mammalian, reptilian, or terrestrial-phase amphibian receptors. The

exposure concentration (ppm) is estimated by multiplying the application rate (pounds active
-61-

ingredient per acre) by a value specific to each food item. These values (termed the Hoerger-Kenaga

estimates) along with a more detailed discussion of the methodology implemented by T-REX, are

presented in Appendix C (T-REX Model and Results). By comparing these estimated concentrations

to acute and chronic toxicity reference values, acute and chronic RQs are calculated. 

For this assessment, T-REX was run for a single crop use scenario that is considered generally

representative of the maximum uses of pyrethrins (see Table 26). The foliar half-life of 1-14 days

found for phenothrin and pyrethrin were used in the absence of foliar dissipation studies on pyrethrins.

To explore the importance of the foliar half-life assumption, multiple calculations were performed and

a plot is provided illustrating the relationship between foliar half-life and the most sensitive scenario -

acute RQs for the small mammal foraging on short grass. The EEC is determined for multiple

application scenarios (10 applications for pyrethrins) by adding the mass on the surface immediately

following the application to the mass of the chemical still present on the surfaces on the day of

application (determined based on first order kinetics using the foliar half-life as the rate constant). 

Table 26. Input parameters for T-REX.

Parameter Value Comment

Application rate (lbs a.i./A) 0.05 product label

Foliar half-life (days) 1 -14 Total and dislodgeable residues for phenothrin and

pyrethrin, respectively. 

Willis, G and L. McDowell. 1987. Pesticide

Persistance and Foliage. Review of Environmental

Contamination and Toxicology. Vol. 100. SpringerVerlag, new York, pp 24-73.

Frequency of application (days) 1 interpreted as the minimum interval between

applications; product label (high pest pressure)

Frequency of applications (days) 3 Typical application interval (low pest pressure)

Maximum applications per year 10 product label

4. Non-Target Plant Exposure

No data were submitted to evaluate the effects of pyrethrin exposure to plants. However the Agency

does not consider pyrethrin or the other pyrethroids as being phytotoxic for the following reasons:

1) the compound is used as a spray on agricultural crops with no direct phytotoxic effects; 2) the

neural toxic mode of action precludes phtotoxic concerns; 3) the Agency is not aware of any incidents

involving aquatic or terrestrial plants and pyrethrin alone. Therefore, EECs were not determined. 

C. Ecological Effects Characterization

1. Aquatic Effects

a. Aquatic Animals
-62-

The complete range of toxicity reference values available for aquatic organisms exposed to pyrethrins

is given in Appendix E. The most toxic of these reference values are summarized in Table 27a.

Toxicity testing was conducted with both pyrethrin extracts or technical grade active ingredient

(TGAI), FEK-99 (57.5% a.i.), as well as with a formulated end-use product, typically a Pyreonone

crop spray (6.02% a.i.). The results of the toxicity testing suggests that pyrethrins are very highly

toxic to freshwater fish (LC50 = 3.2–10 :g/L) and to invertebrates (EC50 = 6.7–11.6 :g/L), as well

as to estuarine/marine fish (LC50 = 3.8–16.0 :g/L) and to invertebrates (LC50/EC50 = 0.14–1.4 :g/L)

on an acute basis. Toxicity tests on the formulated product (60.25% piperonyl butoxide PBO, and

6.02% pyrethrin) show a relative increase in toxicity when compared to tests on pyrethrin alone.

Table 27b gives some indication as to the synergistic effects of PBO that help to increase the

effectiveness of the active ingredient. The synergist activity can be seen when data on the formulation

is compared to data on the TGAI. As shown in Table 27b, when animals are exposed to the

formulation, there is a major difference in acute toxicity that occurs. Across all aquatic species tested,

the formulation is more toxic to fish and invertebrates on an acute basis than the TGAI. The greatest

difference in toxicity is seen with the estuarine/marine invertebrates (e.g., shrimp). There is a 90%

difference between LC50s, when comparing the TGAI to the formulation.

Chronic toxicity studies were conducted with the TGAI only. Studies show that pyrethrins impair

growth (length and weight) of freshwater fish (LOAEC of 3.0 :g/L and reproduction of freshwater

invertebrates (LOAEC of 2.0 :g/L. The chronic NOAECs for freshwater fish and invertebrates were

reported as 1.9 and 0.86 :g/L, respectively. No data were submitted to evaluate the chronic risk to

estuarine/marine fish or invertebrates. However, as shown in Table 27c, based on the acute to

chronic ratio method, NOAECs were estimated for the sheepshead minnow and mysid shrimp. 

The Agency calculated RQ values for agricultural uses by looking at maximum and typical application

rates (TGAI and formulation). For maximum application there are differences in risk quotients

calculated for fish and invertebrates when exposure to the active ingredient alone is considered versus

the formulation. Shown in Tables 27d through 27g, exposure to the formulated product increases

the risk quotients, primarily because of the higher toxicity to fish and invertebrates. In this assessment,

the estuarine/marine invertebrates are most sensitive and have the highest risk estimates. In general,

the model shows that maximum application rate can result in acute risk to freshwater invertebrates

from exposure to the formulation was equal to or 2X greater than comparable acute risk for

freshwater fish. Typical application rate appeared to reduce residue exposure to an aquatic area by

about 40% resulting in no acute risk to fish and freshwater invertebrates. However, this same scenario

shows that typical use (formulation) still has the potential for acute risk to estuarine/marine

invertebrates. Four crop scenarios were also chosen to show the influence of drift to possible risk

to aquatic areas. The Agency modeled these scenarios by setting the drift component to zero from

the normal 5% drift default value. As shown in table 27h, when drift is set to zero, there is a

reduction in EECs from 45 - 89% depending upon the crop scenatio, suggesting that drift is a major

contributor to water concentrations for the GA peaches, ID potato, FL citrus, and CA grape crop

scenarios. 

Since pyrethrins tend to partition to the sediment compartment, data regarding the toxicity of

pyrethrins to sediment dwelling organisms are needed. For this risk assessment, the sediment toxicity
-63-

was estimated based on the aquatic toxicity to aquatic invertebrates multiplied by the Koc value for

pyrethrins.

Table 27a. Toxicity reference values for aquatic organisms exposed to the pyrethrin

formulation and to the pyrethrin technical grade active ingredient (TGAI).

Exposure

scenario Species 

Exposure

duration

Toxicity 

reference value Referencea

Freshwater Fish

Acute Rainbow trout

(Oncorhynchus mykiss)

96 hours LC50 = 3.2 :g/L MRID 43082304

Core, 6.02% a.i.

Acute Rainbow trout

(Oncorhynchus mykiss)

96 hours LC50 = 5.1 :g/L MRID 43082303

Core, 57.5% a.i.

Chronic Fathead minnow

(Pimephales promelas)

early life stage NOAEC = 1.9 :g/L MRID 43252701,

Core, 57.5% a.i.

Freshwater Invertebrates

Acute Waterflea

(Daphnia magna)

48 hours EC50 = 6.7 :g/L MRID 43082306,

Core, 6.02% a.i.

Acute Waterflea

(Daphnia magna)

48 hours EC50 =11.6 :g/L MRID 43082305,

Core, 57.5% a.i.

Chronic Waterflea

(Daphnia magna)

reproduction NOAEC = 0.86 :g/L MRID 43252702,

Core, 57.5% a.i.

Esutarine/Marine Fish

Acute Sheepshead minnow

(Cyprinodon variegatus)

96 hours LC50 = 3.8 :g/L MRID 43082308,

Core, 6.02% a.i.

Acute Sheepshead minnow

(Cyprinodon variegatus)

96 hours LC50 = 16.0 :g/L MRID 43082307,

Core,57.5% a.i.

Chronic: No data submitted; the acute-to-chronic ration method was used to estimate a NOAEC of 5.9 :g/L for

Sheepshead minnow 

Estuarine/Marine Invertebrates

Acute Mysid shrimp

(Mysidopsis bahia)

96 hours LC50 = 0.14 :g/L MRID 43082312,

Core, 6.02% a.i.

Acute Mysid shrimp

(Mysidopsis bahia)

96 hours LC50 = 1.4 :g/L MRID 43082311,

Core, 57.5% a.i.

Chronic: No data was submitted, however the acute-to-chronic ratio method was used to estimate a NOAEC of

0.10 :g/L for Mysid shrimp

Aquatic Plants
Table 27a. Toxicity reference values for aquatic organisms exposed to the pyrethrin

formulation and to the pyrethrin technical grade active ingredient (TGAI).

Exposure

scenario Species 

Exposure

duration

Toxicity 

reference value Referencea

-64-

Acute: No data

a

The technical grade active ingredient (TGAI) is 57.5% a.i, using a test substance called FEK-99. The

formulation is 6.02% a.i., using a product called PYRENONE® Crop Spray (EPA Reg. No. 432-1033) .

Table 27b. Comparison of acute toxicity of pyrethrin extract/ technical grade

active ingredient (FEK-99) to the formulated product (Pyrenone crop spray).

Test Species Exposure

duration 

LC50 (:g/L)

Percent Difference in

Toxicity TGAI Formulation

Freshwater Fish

Acute Rainbow

trout

(Oncorhynch

us mykiss)

96 hours 5.1 3.2 37%

Freshwater Invertebrates

Acute Waterflea

(Daphnia

magna)

48 hours 11.6 6.7 42%

Esutarine/Marine Fish

Acute Sheepshead

minnow

(Cyprinodon

variegatus)

96 hours 16.0 3.8 76%

Estuarine/Marine Invertebrates

Acute Mysid shrimp

(Mysidopsis

bahia)

96 hours 1.4 0.14 90%
-65-

Table 27c Acute to chronic ratio method calculations

Species Acute LC50 (:g/L) Chronic NOAEC (:g/L)

Rainbow Trout 5.1 No data

Fathead minnow No data 1.9

Sheepshead minnow 16.0 5.9 (estimated)a

Daphnia magna 11.6 0.86

Mysid shrimp 1.4 0.10 (estimated)b

a

The NOAEC estimated for the sheepshead minnow is based on the acute-to-chronic ratio method, determined

by the following mathematical relationship: Freshwater LC50 (5.1) / Freshwater NOAEC (1.9) =

Estuarine/marine LC50 (16.0 ppb)/ X (estimated value for estuarine/marine NOAEC). b

The NOAEC estimated for the Mysid shrimp is based on the acute-to-chronic ratio method, determined by the

following mathematical relationship: Freshwater LC50 (11.6 ppb)/ Freshwater NOAEC (0.86 ppb) =

Estuarine/marine LC50 (1.4 ppb)/ X (estimated value for estuarine/marine NOAEC).
-66-

Table 27d. Comparison of the Acute RQs calculated for the TGAI and PBO Formulation for freshwater and

estuarine/marine fish associated with agricultural uses of pyrethrins. Toxicity values are based on studies

with rainbow trout (Oncorhynchus mykiss) (LC50 = 3.2 :g/L for PBO formulated product; 5.1 :g/L for TGAI),

and sheepshead minnow(Cyprinodon variegatus) (LC50 = 3.8 :g/L for formulated product; 16 :g/L for TGAI).

 EEC values are generated from PRZM/EXAMS using maximum and typical rates.

EECs

(:g/L ) Freshwater fish Estuarine/marine fish

Scenario

(state/crop)

peak Acute RQ

Formulation 

Acute RQ

TGAI 

Acute RQ

Formulation

Acute RQ

TGAI

IL corn 2.77 0.87a,b,c 0.54a,b,c 0.73a,b,c 0.17a,b

MS cotton 1.91 0.60a,b,c 0.37a,b 0.50a,b,c 0.12a,b

PA tomato 1.51 0.47a,b 0.29a,b 0.40abc 0.10a,b

ME potato 1.35 0.42a,b 0.26a,b 0.36a,b 0.08a

CA onion 0.78 0.24a,b 0.15a,b 0.21a,b 0.05a

ND wheat 0.68 0.21a,b 0.13a,b 0.18a,b 0.04

NC apple 0.61 0.19a,b 0.12a,b 0.16a,b 0.04

FL citrus 0.40 0.13a,b 0.08 0.11a,b 0.03

OR snapbeans 0.45 0.14a,b 0.09 0.12a,b 0.03

GA peaches 0.66 0.21a,b 0.13a,b 0.17a,b 0.04

ID potato 0.37 0.12a,b 0.07 0.10a,b 0.02

MN alfalfa 0.36 0.11a,b 0.07 0.10a,b 0.02

CA grapes 0.35 0.11a,b 0.07 0.10a,b 0.02

SPECIAL RUNS USING 3-DAY INTERVAL BETWEEN APPLICATIONS, NORMAL PEST PRESSURE

IL corn 2.40 0.75a,b,c 0.47a,b 0.63a,b,c 0.15a,b

ID potato 0.21 0.07a 0.04 0.06a 0.01

CA onion 0.39 0.12a,b 0.08a 0.10a,b 0.02

TYPICAL APPLICATION RATE AND NUMBER OF APPLICATIONS

ID potato 0.05 0.02 0.01 <0.00 0.01

PA tomato 0.03 0.01 0.01 <0.00 0.01

CA onion 0.04 0.01 0.01 <0.00 0.01

OR snap beans 0.09 0.03 0.02 0.01 0.02
Table 27d. Comparison of the Acute RQs calculated for the TGAI and PBO Formulation for freshwater and

estuarine/marine fish associated with agricultural uses of pyrethrins. Toxicity values are based on studies

with rainbow trout (Oncorhynchus mykiss) (LC50 = 3.2 :g/L for PBO formulated product; 5.1 :g/L for TGAI),

and sheepshead minnow(Cyprinodon variegatus) (LC50 = 3.8 :g/L for formulated product; 16 :g/L for TGAI).

 EEC values are generated from PRZM/EXAMS using maximum and typical rates.

EECs

(:g/L ) Freshwater fish Estuarine/marine fish

Scenario

(state/crop)

peak Acute RQ

Formulation 

Acute RQ

TGAI 

Acute RQ

Formulation

Acute RQ

TGAI

-67-

a

RQ exceeds LOC for acute endangered species ($0.05). b

RQ exceeds LOC for acute restricted use ($0.1). c

RQ exceeds LOC for acute high risk ($0.5).

Table 27e. Comparison of the Acute RQs calculated for the TGAI and PBO Formulation for freshwater and

estuarine/marine invertebrates associated with agricultural uses of pyrethrins. Toxicity values are based

on studies with waterflea (Daphnia magna) (EC50 = 6.7 :g/L for PBO formulated product; EC50 = 11.6 :g/L

for TGAI) and mysid shrimp (Mysidopsis bahia) (LC50 = 0.14 :g/L for formulated product; LC50 = 1.4 :g/L

for TGAI). EEC values are generated from PRZM/EXAMS using maximum and typical rates. 

EECs (:g/L ) Freshwater invertebrates Estuarine/marine invertebrates

Scenario

(state/crop)

peak Acute RQ

Formulation

Acute RQ

TGAI 

Acute RQ

Formulation

Acute RQ

TGAI

IL corn 2.77 0.41a,b 0.23a,b 19.79a,b,c 1.98a,b,c

MS cotton 1.91 0.29a,b 0.16a,b 13.6a,b,c 1.36a,b,c

PA tomato 1.51 0.23v 0.13a,b 10.79a,b,c 1.08a,b,c

ME potato 1.35 0.20a,b 0.12a,b 9.64a,b,c 0.96a,b,c

CA onion 0.78 0.12a,b 0.07a 5.67a,b,c 0.56a,b,c

ND wheat 0.68 0.10a,b 0.06a 4.86a,b,c 0.49a,b 

NC apple 0.61 0.10a,b 0.05a 4.36a,b,c 0.44a,b

FL citrus 0.40 0.10a,b 0.03 2.86a,b,c 0.29a,b

OR snapbeans 0.45 0.10a,b 0.04 3.21a,b,c 0.32a,b

GA peaches 0.66 0.10a,b 0.06a 4.71a,b,c 0.47a,b

ID potato 0.37 0.10a,b 0.03 2.64a,b,c 0.26a,b
Table 27e. Comparison of the Acute RQs calculated for the TGAI and PBO Formulation for freshwater and

estuarine/marine invertebrates associated with agricultural uses of pyrethrins. Toxicity values are based

on studies with waterflea (Daphnia magna) (EC50 = 6.7 :g/L for PBO formulated product; EC50 = 11.6 :g/L

for TGAI) and mysid shrimp (Mysidopsis bahia) (LC50 = 0.14 :g/L for formulated product; LC50 = 1.4 :g/L

for TGAI). EEC values are generated from PRZM/EXAMS using maximum and typical rates. 

EECs (:g/L ) Freshwater invertebrates Estuarine/marine invertebrates

Scenario

(state/crop)

peak Acute RQ

Formulation

Acute RQ

TGAI 

Acute RQ

Formulation

Acute RQ

TGAI

-68-

MN alfalfa 0.36 0.10a,b 0.03 2.57a,b,c 0.26a,b

CA grapes 0.35 0.10a,b 0.03 2.50a,b,c 0.25a,b

SPECIAL RUNS USING 3- DAY INTERVAL BETWEEN APPLICATIONS, NORMAL PEST PRESSURE

IL corn 2.40 0.36a,b 0.20a,b 17.14a,b,c 1.71a,b,c

ID potato 0.21 0.03 0.02 1.50a,b,c 0.15a,b

CA onion 0.39 0.10a,b 0.03 2.79a,b,c 0.28a,b

TYPICAL APPLICATION RATE AND NUMBER OF APPLICATIONS

ID potato 0.05 0.01 <0.00 0.36a,b 0.04

PA tomato 0.03 <0.00 <0.00 0.21a,b 0.02

CA onion 0.04 0.01 <0.00 0.29a,b 0.03

OR snap beans 0.09 0.01 0.01 0.64a,b,c 0.06a

a

RQ exceeds LOC for acute endangered species ($0.05). b

RQ exceeds LOC for acute restricted use ($0.1). c

RQ exceeds LOC for acute high risk ($ 0.5).
-69-

Table 27f. Comparison of the Acute RQs calculated for the TGAI and PBO Formulation for freshwater and

estuarine/marine fish associated with mosquito abatement uses of pyrethrins. Toxicity values are based on

studies with rainbow trout (Oncorhynchus mykiss) (LC50 = 3.2 :g/L for formulated product; 5.1 :g/L for

TGAI), and sheepshead minnow (Cyprinodon variegatus) (LC50 = 3.8 :g/L for PBO formulated product; 16

:g/L for TGAI). EEC values are generated from AGDISP and PRZM/EXAMS for pyrethrins applied in a

Florida Turf scenario. 

EECs (:g/L) Freshwater fish Estuarine/marine fish

Depth of 

water body

peak Acute RQ 

Formulation

Acute RQ 

TGAI

Acute RQ 

Formulation

Acute RQ 

TGAI

6.0 inches 0.047 0.01 0.01 0.01 <0.01

12.0 inches 0.049 0.02 0.01 0.01 <0.01

3.3 feet (1 meter) 0.056 0.02 0.02 0.01 <0.01

6.6 feet (2 meters) 0.066 0.02 0.02 0.02 <0.01

Table 27g. Comparison of the Acute RQs calculated for the TGAI and PBO Formulation for freshwater and

estuarine/marine invertebrates associated with mosquito abatement uses of pyrethrins. Toxicity values are

based on studies with waterflea (Daphnia magna) (EC50 = 6.7 :g/L for formulated product; EC50 = 11.6 :g/L

for TGAI) and mysid shrimp (Mysidopsis bahia) (LC50 = 0.14 :g/L for PBO formulated product; LC50 = 1.4

:g/L for TGAI). EEC values are generated from AGDISP and PRZM/EXAMS for pyrethrins applied in a

Florida Turf scenario. 

EECs (:g/L ) Freshwater invertebrates

Estuarine/marine invertebrates

Depth of 

water body Peak

Acute RQ

Formulation

Acute RQ

TGAI Acute RQ

Formulation 

Acute RQ

TGAI

Surface Water 

6 inches 0.047 <0.01 <0.01 0.33a 0.03

12 inches 0.048 0.01 <0.01 0.34a 0.03

3.3 feet (1 meter) 0.050 0.01 <0.01 0.36a 0.04

6.6 feet (2 meters) 0.055 0.01 <0.01 0.39a 0.04

a

RQ exceeds LOC for acute restricted ($0.1) and acute endangered species ($0.05).
-70-

Table 27h. Evaluation of acute exposure (peak EECs) to fish and invertebrates for 4 selected crop scenarios

(GA peaches, ID potatoes, FL citrus, and CA grapes), when spray drift is set to 5% versus when spray drift

is set to zero.

EECs (:g/L )

Crop Scenario Peak EEC

Drift set to 5%

Peak EEC

Drift set to zero 

Percent reduction in exposure to fish

and invertebrates when spray drift

component is eliminated

GA peaches 0.66 0.344 48%

ID potato 0.37 0.042 89%

FL citrus 0.401 0.221 45%

CA grapes 0.348 0.021 94%

b. Aquatic Plants

No data were submitted to evaluate the effects of pyrethrin exposure to non-target plants. 

2. Terrestrial Effects

a. Terrestrial Animals

Toxicity reference values for terrestrial organisms exposed to pyrethrins are summarized in Table 28. Pyrethrins appear

to be practically non-toxic to avian species on a acute oral and dietary basis (oral LD50 >2,000 mg/kg bw; dietary LC50

>5,620 mg/kg diet). Reproductive toxicity data were not submitted, so chronic avian risk could not be evaluated. The

available toxicity data are listed in Appendix E. 

The technical grade active ingredient was used as the test substance in the acute and reproductive mammalian toxicity

data. Synergists, such as piperonyl butoxide, work as competitive alternative substrate that bind cytochrome P-450

mixed function oxidase system (MFO)enzymes, thus delaying the breakdown of toxins like the pyrethrins in both

insects and mammals. Since the mammalian MFO system is more active than that of insects, pyrethrins are

metabolized more efficiently in these organisms. Studies have suggested that piperonyl butoxide may enhance the

production of MFO enzymes in mammals.

Mammalian toxicity data suggest that pyrethrins are slightly toxic to small mammals on an acute oral basis (LD50 =

700 mg/kg body weight). In the 2nd generation rat reproduction study, parental male systemic and reproductive toxicity

were detected at 1000 ppm (65 mg/kg body weight per day) and parental female systemic toxicity was detected at 3000

ppm (196 mg/kg body weight per day). The NOAEL for parental systemic (male) and reproductive toxicity was 100

ppm (6.4 mg/kg body weight-day).

Acute toxicity studies with honey bees show that pyrethrins are highly toxic on both a contact and an oral basis (contact

LC50 = 0.022 :g a.i./bee and oral LD50 = 0.15 :g a.i./bee).
-71-

Table 28. Toxicity reference values for mammals and birds exposed to pyrethrins.

Exposure

Scenario Species

Exposure

Duration

Toxicity 

Reference Value Referencea

Mammals

Acute Rat 

(Rattus norvegicus)

Single dose LD50 = 700 mg/kg bwb MRID 42008101,

57.467 % a.i.

Chronic Rat 

(Rattus norvegicus)

2-generation

reproduction

NOAEL = 6.4 mg/kgdayMRID 41327501,

57.6% a.i.

Birds

Acute Bobwhite quail

(Colinus virginianus)

5 daysc LC50 >5,620 mg/kg diet MRID 41968801,

Core, 57.6% a.i.

Acute Mallard duck 

(Anas platyrhynchos)

5 daysc LC50 >5,620 mg/kg diet MRID 41968802,

Core, 57.6% a.i.

Chronic: No data However, chronic data from permethrin are used as surrogate information because of similar

mode of action NOAEC = 500 ppm.

a

Test material reported as FEK-99, 57.467% to 57.6% a.i. pyrethrins, is considered to be representative of technical grade

active ingredient (TGAI).

b

Female rats only; LD50 for males in the same study was 2,140 mg/kg bw. c

Referred to as a “subacute study”; 5-day dietary exposure followed by additional 3-day observation period.

b. Terrestrial Plants

No data were submitted to evaluate the effects of cypyrethrin exposure to terrestrial plants. However

the Agency does not consider pyrethrin or the other pyrethroids as being phytotoxic for the following

reasons: 1) the compound is used as a spray on agricultural crops with no phytotoxic effects; 2) the

neural toxic mode of action precludes phtotoxic concerns; 3) the Agency is not aware of any incidents

involving plants and pyrethrin alone (e.g., incident reports regarding terrestrial plant impact are

inconclusive with regard to direct effect from pyrethrin).

IV. Risk Characterization

A. Risk Estimation - Integration of Exposure and Effects Data

1. Non-target Aquatic Animals and Plants

Details regarding RQs and exceedances of levels of concern (LOCs) for each scenario are provided below.
-72-

a. Fish and Aquatic Invertebrates: Agricultural Uses

Table 29 shows that acute LOCs are exceeded for fish ( endangered species, restricted uses, and acute high

risk) that may be exposed to pyrethrin residues that are associated with agricultural uses and maximum

application rate. The risk categories and RQ ranges associated with the agricultural crop scenarios for

freshwater fish are: Acute high risk (RQ = 0.54 for IL corn); acute restricted use (RQ range = 0.13 to 0.54 for

GA peaches, OR snapbeans, FL citrus, NC apple, ND wheat, CA onions, ME potato, PA tomato, MS cotton,

and IL corn); and endangered species risk (RQ range = 0.07 to 0.54 for all crop scenarios- CA grapes, MN

alfalfa, ID potato, GA peaches, OR snapbeans, FL citrus, NC apple, ND wheat, CA onions, ME potato, PA

tomato, MS cotton, and IL corn). The risk categories and RQ ranges associated with the agricultural crop

scenarios for estuarine/marine fish are: Acute restricted use (RQ range = 0.12 to 0.17 for MS cotton and IL

corn); and endangered species risk (RQ range = 0.05 to 0.17 for CA onions, ME potato, PA tomato, MS

cotton, and IL corn). Typical application rates showed no acute or chronic risk (RQ <0.0) to fish

(estuarine/marine or freshwater).

Table 30 shows that acute LOCs for aquatic invertebrates (endangered species, restricted uses, and acute high

risk) were exceeded when the potential for acute exposure was calculated relative to several agricultural uses

of pyrethrins and maximum application use. The risk categories and RQ ranges associated with the

agricultural crop scenarios for freshwater invertebrates are: Acute restricted use risk (RQ range = 0.12 to 0.24;

crops IL corn, MS cotton, PA tomato, and ME potato); and acute endangered species risk (RQ range = 0.05

to 0.07 for NC apple, ND wheat, GA peaches and CA onion). The risk categories and RQ ranges associated

with the agricultural crop scenarios for estuarine/ marine invertebrates are: Acute high risk (RQ range = 0.56

to 1.98 for CA onion, ME potato, PA tomato, MS cotton, and IL corn); acute restricted use (RQ range 0.25

to 1.98 for all crop scenarios-CA grapes, MN alfalfa, ID potato, GA peaches, OR snapbeans, FL citrus, NC

apple, ND wheat, CA onion, MD potato, PA tomato, MS cotton, and IL corn); and acute endangered species

risk (RQ range = 0.25 to 1.98 for all crop scenarios-CA grapes, MN alfalfa, ID potato, GA peaches, OR

snapbeans, FL citrus, NC apple, ND wheat, CA onion, MD potato, PA tomato, MS cotton, and IL corn).

Typical application rates in general showed no acute or chronic risk (RQ <0.0) to aquatic invertebrates

(estuarine/marine or freshwater),(the OR snap beans scenario produced an endangered species RQ exceedance

for estuarine/marine invertebrates. However, at this time there are no endangered estuarine/marine

invertebrates).

As shown in Tables 29 and 30 there were no chronic risks found for freshwater fish or invertebrates associated

with the agricultural uses relative to maximum and typical application rates.. However, there are risk concerns

for estuarine/marine invertebrates that are associated with the agricultural uses. In the absence of chronic data

for Mysid shrimp, the NOAEC of 0.10 ppb was estimated and used in the risk assessment. When the 21-day

EECs were compared to this estimated NOAEC, chronic LOCs were exceeded for all crops (CA onion, ID

potato, IL corn, CA grapes, MN alfalfa, GA peaches, OR snapbeans, FL citrus, NC apple, ND wheat, MS

cotton, and PA tomato; RQ range = 1.5 to 6). A acute-to-chronic ratio NOAEC estimate of 5.9 ppb was also

calculated for the estuarine/marine fish (sheepshead minnow). All RQs for chronic risk of pyrethrins to

estuarine/marine fish are below the LOC..
-73-

Table 43 shows the peak EECs and the RQs for two selected crop scenarios that were run for aerial and ground

applications. The scenarios also included three buffer zones and two levels of spray drift (high end and low end

drift scenarios). Even though all the RQs are above the LOC, it is noted that the ground application and the

low end drift scenario, with the large buffer zone yield the lower EECs and the lower RQs. The GA peach crop

scenario had higher RQs, compared to the ID potato crop scenario. When the run with the drift set to 0% was

compared to the standard run with drift set to 5%, it was found that drift was an important component of the

peak EECs for both scenarios. It is also noted that even a small buffer zone of 50 ft reduces the RQs by more

than 20%, compared to the same conditions with no buffer zone (for both the high end and low end drift

scenarios).

• The acute endangered species LOC and chronic LOC were slightly exceeded for small mammals (RQ

= 0.15 for endangered species and RQ = 1.10 for chronic). Chronic risk to birds could not be

evaluated because no bird reproduction data were submitted. 

• Although toxicity studies on the degradates were not provided, an evaluation of the structures indicate

that they are the result of the rupture of the ester bridge of the parent, resulting in a carboxylic acid

(chrysanthemic acid), and an alcohol (that subsequently be degraded to an acid as well). The resulting

molecules have lost their pyrethroid toxicological activity, therefore, in this assessment, they were not

considered of concern. Furthermore, the available data indicated that chrysanthemic acid was formed

in small amounts except under hydrolytic conditions at pH 9. 

The Master Label provided by the registrant, indicates that 1 day is used when pest pressure is high, but the

normal interval between applications is 3 days. Three crop scenarios were selected and run with PRZM/

EXAMS with the same original input parameters, except that the interval between applications was set at 3

days instead of 1 day. The EEC’s obtained are summarized in Table 7, and the RQs appear in Tables 12 and

13. It was noted a reduction in the RQs approximately proportional to the EECs, which ranged from around

12-15% for IL corn, to about 45% for ID potato, to about a half for CA onion. The RQs for some of the crop

scenarios (i.e. alfalfa) may not be necessarily the most conservative because certain crops are grown more often

than once per year. This assessment assumed a single season per year. 
-74-

Table 29. Acute and chronic RQs for freshwater and estuarine/marine fish associated with

agricultural uses of pyrethrins based on rainbow trout LC50 = 5.1 ug/L, fathead minnow NOAEC =

1.9 ug/L, sheepshead minnow LC50 = 16.0 ug/L, and extraoplated NOAEC sheepshead minnow 5.9

ug/L. EEC values are generated from PRZM/EXAMS. 

EECs (:g/L )

Scenario

(state/

crop)

Peak 60-day

average

Freshwater

Fish

(Rainbow

Trout)

Acute RQ

TGAI 

Freshwater

Fish

(Fathead

Minnow)

Chronic RQ

TGAI

Estuarine/

marine Fish

(Sheepshea

d Minnow)

Acute RQ

TGAI

Estuarine/marine

Fish

(Sheepshead

Minnow)

Chronic RQ

TGAI

RUNS PERFORMED WITH MINIMUM INTERVAL BETWEEN APPLICATIONS, 1 DAY, HIGH PEST PRESSURE

IL corna 2.77 0.37 0.54ab 0.19 0.17ab 0.06

MS

cottona

1.91 0.28 0.37ab 0.15 0.12ab 0.05

PA

tomatoa

1.51 0.20 0.30ab 0.11 0.09a 0.03

ME

potatoa

1.35 0.28 0.26ab 0.15 0.08a 0.05

CA

oniona

0.78 0.13 0.15ab 0.07 0.05a 0.02

ND

wheata

0.68 0.13 0.13ab 0.07 0.04 0.02

NC applea 0.61 0.13 0.12ab 0.07 0.04 0.02

FL citrus 0.40 0.09 0.08ab 0.05 0.03 0.02

OR

snapbeans

a

0.45 0.10 0.09ab 0.05 0.03 0.02

GA

peaches

0.66 0.10 0.13ab 0.05 0.04 0.02

ID potatoa 0.37 0.09 0.07a 0.05 0.02 0.02

MN

alfalfaa

0.36 0.08 0.07a 0.04 0.02 0.01

CA

grapes

0.35 0.07 0.07a 0.04 0.02 0.01

SPECIAL RUNS USING A 3-DAY INTERVAL BETWEEN APPLICATIONS, NORMAL PEST PRESSURE

IL corn 2.40 0.33 0.47ab 0.17 0.15ab 0.06
Table 29. Acute and chronic RQs for freshwater and estuarine/marine fish associated with

agricultural uses of pyrethrins based on rainbow trout LC50 = 5.1 ug/L, fathead minnow NOAEC =

1.9 ug/L, sheepshead minnow LC50 = 16.0 ug/L, and extraoplated NOAEC sheepshead minnow 5.9

ug/L. EEC values are generated from PRZM/EXAMS. 

EECs (:g/L )

Scenario

(state/

crop)

Peak 60-day

average

Freshwater

Fish

(Rainbow

Trout)

Acute RQ

TGAI 

Freshwater

Fish

(Fathead

Minnow)

Chronic RQ

TGAI

Estuarine/

marine Fish

(Sheepshea

d Minnow)

Acute RQ

TGAI

Estuarine/marine

Fish

(Sheepshead

Minnow)

Chronic RQ

TGAI

-75-

ID potato 0.21 0.08 0.04 0.04 0.01 0.01

CA onion 0.39 0.09 0.08a 0.05 0.02 0.02

TYPICAL APPLICATION RATE AND NUMBER OF APPLICATIONSd

ID

potatoes

0.05 0.003 0.01 <0.00 <0.00 <0.00

PA

tomatoes

0.03 0.005 0.01 <0.00 <0.00 <0.00

CA

onions

0.04 0.004 0.01 <0.00 <0.00 <0.00

OR snap

beans

0.09 0.021 0.02 0.01 0.01 <0.00

a

RQ exceeds LOC for acute endangered species ($0.05). b

RQ exceeds LOC for acute restricted use ($0.1). C The NOAEC estimated for the sheepshead minnow is based on the acute-to-chronic ratio method, determined by the

following mathematical relationship: Freshwater LC50 (5.1) / Freshwater NOAEC (1.9) = Estuarine/marine LC50 (16.0 ppb)/ X

(estimated value for estuarine/marine NOAEC).

d For the 60-day values, three significant figures were shown.
-76-

Table 30. Acute and chronic RQs for freshwater and estuarine/marine invertebrates associated with

agricultural uses of pyrethrins based on Daphnia magna EC50 = 11.6 ug/L, Daphnia magna NOAEC =

0.86 ug/L, mysid shrimp EC50 = 1.4 ug/L, and extraoplated NOAEC mysid shrimp 0.10 ug/L. EEC values

are generated from PRZM/EXAMS.

EECs (:g/L )

Scenario

(state/

crop)

peak 21-day 

average

Freshwater

Invertebrate

(Daphnia

magna)

Acute RQ

TGAI 

Freshwater

Invertebrate

(Daphnia

magna)

Chronic RQ

TGAI

Estuarine/

marine

Invertebrate

(Mysid Shrimp)

Acute RQ

TGAI

Estuarine/

marine

Invertebrate

(Mysid

Shrimp)

Chronic RQ

TGAI

RUNS PERFORMED WITH MINIMUM INTERVAL BETWEEN APPLICATIONS, 1 DAY, HIGH PEST

PRESSURE

IL corna 2.77 0.60 0.24ab 0.70 1.98abc 6.0

MS cottona 1.91 0.41 0.16ab 0.48 1.36abc 4.1

PA tomatoa 1.51 0.34 0.13ab 0.40 1.08abc 3.4

ME potatoa 1.35 0.39 0.12ab 0.45 0.96abc 3.9

CA oniona 0.78 0.25 0.07a 0.29 0.56abc 2.5

ND wheata 0.68 0.23 0.06a 0.27 0.49ab 2.3

NC applea 0.61 0.23 0.05a 0.27 0.44ab 2.3

FL citrus 0.40 0.18 0.03 0.21 0.29ab 1.8

OR

snapbeansa

0.45 0.19 0.04 0.22 0.32ab 1.9

GA peaches 0.66 0.19 0.06a 0.22 0.47ab 1.9

ID potatoa 0.37 0.17 0.03 0.20 0.26ab 1.7
Table 30. Acute and chronic RQs for freshwater and estuarine/marine invertebrates associated with

agricultural uses of pyrethrins based on Daphnia magna EC50 = 11.6 ug/L, Daphnia magna NOAEC =

0.86 ug/L, mysid shrimp EC50 = 1.4 ug/L, and extraoplated NOAEC mysid shrimp 0.10 ug/L. EEC values

are generated from PRZM/EXAMS.

EECs (:g/L )

Scenario

(state/

crop)

peak 21-day 

average

Freshwater

Invertebrate

(Daphnia

magna)

Acute RQ

TGAI 

Freshwater

Invertebrate

(Daphnia

magna)

Chronic RQ

TGAI

Estuarine/

marine

Invertebrate

(Mysid Shrimp)

Acute RQ

TGAI

Estuarine/

marine

Invertebrate

(Mysid

Shrimp)

Chronic RQ

TGAI

-77-

MN alfalfaa 0.36 0.16 0.03 0.19 0.26ab 1.6

CA grapes 0.35 0.15 0.03 0.17 0.25ab 1.5

SPECIAL RUNS USING A 3-DAY INTERVAL BETWEEN APPLICATIONS, NORMAL PEST PRESSURE

IL corn 2.40 0.50 0.21ab 0.58 1.71abc 5

ID potato 0.21 0.12 0.02 0.14 0.15ab 1.2

CA onion 0.39 0.16 0.03 0.19 0.28ab 1.6

TYPICAL APPLICATION RATE AND NUMBER OF APPLICATIONSe

ID potatoes 0.05 0.007 <0.00 0.01 0.04 0.07

PA

tomatoes

0.03 0.008 <0.00 0.01 0.02 0.08

CA onion 0.04 0.008 <0.00 0.01 0.03 0.08

OR snap

beans

0.09 0.038 0.01 0.04 0.06a 0.38

a

RQ exceeds LOC for acute endangered species ($0.05). b

RQ exceeds LOC for acute restricted use ($0.1). c

RQ exceeds LOC for acute high risk ($ 0.5). d The NOAEC estimated for the Mysid shrimp is based on the acute-to-chronic ratio method, determined by the following

mathematical relationship: Freshwater LC50 (11.6 ppb)/ Freshwater NOAEC (0.86 ppb) = Estuarine/marine LC50 (1.4 ppb)/

X (estimated value for estuarine/marine NOAEC).

e

 For the 21-day values, three significant figures were shown, because the values were small in magnitude.
-78-

Mosquito Abatement

For mosquito control, application directions in the label are insufficient to accurately estimate aquatic

exposures that result from application of pyrethrin for controlling mosquitoes. Limitations (as opposed to

recommendations) on product labels for key parameters such as droplet size, wind speed, release height,

application interval, and number of applications allowed per year are not specified. The exposure assessment

conducted here represents the water concentrations expected from a typical, low-level aerial application.

Concentrations resulting from actual application of pyrethrin for mosquito control could be significantly higher

than modeled concentrations if applicators used different application parameters.

In order to evaluate mosquito abatement with various parameters (droplet size, boom height, maximum, and

typical rates), a different modeling approach was used as compared to agricultural uses. The mosquito

adulticides are applied as mists (very small droplet sizes) that do not deposit rapidly but are expected to drift.

Acute risk (RQs), relative to the level of this drift, were calculated for various water depths. Typically, the

FL turf scenario is used in PRZM/EXAMS (or decoupled EXAMS) to calculate the EEC’s. The toxicity data

endpoints used for the mosquito abatement assessment were based on the formulated product (pyrenone crop

spray) and maximum and typical rates. Tables 31 and 32 show that the maximum mosquito rate can result

in residues that exceed the acute restricted use and endangered species triggers for estuarine/marine

invertebrates (RQ range = 0.81 to 0.95) while the acute risk concerns for freshwater invertebrates or fish

appears to be low. Using the maximum rate and decreasing the droplet size from 50 um to 40 um resulted in

about a 37% reduction in residues but acute risk still exceeded the LOCs for these esturine/marine organisms

(Tables 32 and 34). Raising the boom height to 150 ft. also reduced the potential acute risk to estuarine/marine

invertebrates by about 90% ( although the endangered species trigger was exceeded this scenario appears to

present the lowest risk since there are no endangered estuarine/marine invertebrates listed at this time). Table

40 shows that maintaining droplet size at 40 um, boom height 150 ft, maximum application rate appears to

eliminate the potential for acute risk to estuarine/marine invertebrates. Table 38 shows that by using the typical

application rate (0.0025lbs ai/A) and keeping boom height at 75 ft and droplet size at 50 um, acute risk to

estuarine/marine invertebrates can also be decreased significantly. Since there was no chronic data on the

formulated product, chronic risk could not be estimated for the mosquito abatement uses. Although residues

may increase with depth, presumably because photodegradation is impeded in deeper water bodies, and the

level of adsorption of the chemical by the sediments is decreased as the depth of the water bodies increase, the

expected residue levels appear to be below the LOCs for freshwater organisms and estuarine/marine fish. 
-79-

Table 31. Acute RQs for freshwater and estuarine/marine fish associated with mosquito abatement uses

of pyrethrins. EEC values are generated from AGDISP and PRZM/EXAMS for pyrethrins applied in a

Florida Turf scenario. Effects values on the PBO formulation were rainbow trout LC50 = 3.2 ug/L and

sheepshead minnow LC50 = 3.8 ug/L. Droplet size 50 :m, Boom height 75 ft, Application Rate 0.008 lb

a.i./A

EECs (:g/L) Freshwater fish Estuarine/marine fish

Depth of 

water body

 peak Rainbow Trout

Acute RQ 

Formulation

Sheepshead Minnow

Acute RQ 

Formulation

Surface Water

6.0 inches 0.114 0.03 0.03

12.0 inches 0.117 0.04 0.03

3.3 feet (1 meter) 0.122 0.04 0.03

6.6 feet (2 meters) 0.133 0.04 0.04

Table 32. Acute RQs for freshwater and estuarine/marine invertebrates associated with mosquito

abatement uses of pyrethrins. EEC values are generated from AGDISP and PRZM/EXAMS for

pyrethrins applied in a Florida Turf scenario. Effects values on the PBO formulation were Daphnia

magnia EC50 = 6.7 ug/L and mysid shrimp LC50 = 0.14 ug/L. Droplet size 50 :m, Boom height 75 ft,

Application Rate 0.008 lb a.i./A

EECs (:g/L ) Freshwater

invertebrates

Estuarine/marine

invertebrates

Depth of 

water body

 peak Daphnia magna

Acute RQ

Formulation

Mysid Shrimp

Acute RQ

Formulation 

Surface Water 

6 inches 0.114 0.02 0.81a

12 inches 0.117 0.02 0.84a

3.3 feet (1 meter) 0.122 0.02 0.87a

6.6 feet (2 meters) 0.133 0.02 0.95a

a

RQ exceeds LOC for acute ($0.5), acute restricted ($0.1) and acute endangered species ($0.05).
-80-

Table 33. Acute RQs for freshwater and estuarine/marine fish associated with mosquito abatement uses

of pyrethrins. EEC values are generated from AGDISP and PRZM/EXAMS for pyrethrins applied in a

Florida Turf scenario. Effects values on the PBO formulation were rainbow trout LC50 = 3.2 ug/L and

sheepshead minnow LC50 = 3.8 ug/L. Droplet size 40 :m, Boom height 75 ft, Application Rate 0.008 lb

a.i./A

EECs (:g/L) Freshwater fish Estuarine/marine fish

Depth of 

water body

 peak Rainbow Trout

Acute RQ 

Formulation

Sheepshead Minnow

Acute RQ 

Formulation

Surface Water

6.0 inches 0.071 0.02 0.02

12.0 inches 0.073 0.02 0.02

3.3 feet (1 meter) 0.076 0.02 0.02

6.6 feet (2 meters) 0.083 0.03 0.02

Table 34. Acute RQs for freshwater and estuarine/marine invertebrates associated with mosquito

abatement uses of pyrethrins. EEC values are generated from AGDISP and PRZM/EXAMS for

pyrethrins applied in a Florida Turf scenario. Effects values on the PBO formulation were Daphnia

magnia EC50 = 6.7 ug/L and mysid shrimp LC50 = 0.14 ug/L. Droplet size 40 :m, Boom height 75 ft,

Application Rate 0.008 lb a.i./A

EECs (:g/L ) Freshwater

invertebrates

Estuarine/marine

invertebrates

Depth of 

water body

 peak Daphnia magna

Acute RQ

Formulation

Mysid Shrimp

Acute RQ

Formulation 

Surface Water 

6 inches 0.071 0.01 0.51a

12 inches 0.073 0.01 0.52a

3.3 feet (1 meter) 0.076 0.01 0.54a

6.6 feet (2 meters) 0.083 0.01 0.59a

a

RQ exceeds LOC for acute ($0.5), acute restricted ($0.1) and acute endangered species ($0.05).
-81-

Table 35. Acute RQs for freshwater and estuarine/marine fish associated with mosquito abatement uses

of pyrethrins. EEC values are generated from AGDISP and PRZM/EXAMS for pyrethrins applied in a

Florida Turf scenario. Effects values on the PBO formulation were rainbow trout LC50 = 3.2 ug/L and

sheepshead minnow LC50 = 3.8 ug/L. Droplet size 50 :m, Boom height 150 ft, Application Rate 0.008 lb

a.i./A

EECs (:g/L) Freshwater fish Estuarine/marine fish

Depth of 

water body

 peak Rainbow Trout

Acute RQ 

Formulation

Sheepshead Minnow

Acute RQ 

Formulation

Surface Water

6.0 inches 0.007 <0.00 <0.00

12.0 inches 0.008 <0.00 <0.00

3.3 feet (1 meter) 0.008 <0.00 <0.00

6.6 feet (2 meters) 0.009 <0.00 <0.00

Table 36. Acute RQs for freshwater and estuarine/marine invertebrates associated with mosquito

abatement uses of pyrethrins. EEC values are generated from AGDISP and PRZM/EXAMS for

pyrethrins applied in a Florida Turf scenario. Effects values on the PBO formulation were Daphnia

magnia EC50 = 6.7 ug/L and mysid shrimp LC50 = 0.14 ug/L. Droplet size 50 :m, Boom height 150 ft,

Application Rate 0.008 lb a.i./A

EECs (:g/L ) Freshwater

invertebrates

Estuarine/marine

invertebrates

Depth of 

water body

 peak Daphnia magna

Acute RQ

Formulation

Mysid Shrimp

Acute RQ

Formulation 

Surface Water 

6 inches 0.007 <0.00 0.05a

12 inches 0.008 <0.00 0.06a

3.3 feet (1 meter) 0.008 <0.00 0.06a

6.6 feet (2 meters) 0.009 <0.00 0.06a

a

RQ exceeds LOC for acute endangered species ($0.05).
-82-

Table 37. Acute RQs for freshwater and estuarine/marine fish associated with mosquito abatement uses

of pyrethrins. EEC values are generated from AGDISP and PRZM/EXAMS for pyrethrins applied in a

Florida Turf scenario. Effects values on the PBO formulation were rainbow trout LC50 = 3.2 ug/L and

sheepshead minnow LC50 = 3.8 ug/L. Droplet size 50 :m, Boom height 75 ft, Application Rate 0.0025 lb

a.i./A

EECs (:g/L) Freshwater fish Estuarine/marine fish

Depth of 

water body

 peak Rainbow Trout

Acute RQ 

Formulation

Sheepshead Minnow

Acute RQ 

Formulation

Surface Water

6.0 inches 0.036 0.01 0.01

12.0 inches 0.036 0.01 0.01

3.3 feet (1 meter) 0.038 0.01 0.01

6.6 feet (2 meters) 0.041 0.01 0.01

Table 38. Acute RQs for freshwater and estuarine/marine invertebrates associated with mosquito

abatement uses of pyrethrins. EEC values are generated from AGDISP and PRZM/EXAMS for

pyrethrins applied in a Florida Turf scenario. Effects values on the PBO formulation were Daphnia

magnia EC50 = 6.7 ug/L and mysid shrimp LC50 = 0.14 ug/L. Droplet size 50 :m, Boom height 75 ft,

Application Rate 0.0025 lb a.i./A

EECs (:g/L ) Freshwater

invertebrates

Estuarine/marine

invertebrates

Depth of 

water body

 peak Daphnia magna

Acute RQ

Formulation

Mysid Shrimp

Acute RQ

Formulation 

Surface Water 

6 inches 0.036 0.01 0.25a

12 inches 0.036 0.01 0.25a

3.3 feet (1 meter) 0.038 0.01 0.27a

6.6 feet (2 meters) 0.041 0.01 0.29a

a

RQ exceeds LOC for acute restricted ($0.1) and acute endangered species ($0.05).
-83-

Table 39. Acute RQs for freshwater and estuarine/marine fish associated with mosquito abatement uses

of pyrethrins. EEC values are generated from AGDISP and PRZM/EXAMS for pyrethrins applied in a

Florida Turf scenario. Effects values on the PBO formulation were rainbow trout LC50 = 3.2 ug/L and

sheepshead minnow LC50 = 3.8 ug/L. Droplet size 40 :m, Boom height 150 ft, Application Rate 0.008 lb

a.i./A

EECs (:g/L) Freshwater fish Estuarine/marine fish

Depth of 

water body

 peak Rainbow Trout

Acute RQ 

Formulation

Sheepshead Minnow

Acute RQ 

Formulation

Surface Water

6.0 inches 0.003 <0.00 <0.00

12.0 inches 0.003 <0.00 <0.00

3.3 feet (1 meter) 0.003 <0.00 <0.00

6.6 feet (2 meters) 0.003 <0.00 <0.00

Table 40. Acute RQs for freshwater and estuarine/marine invertebrates associated with mosquito

abatement uses of pyrethrins. EEC values are generated from AGDISP and PRZM/EXAMS for

pyrethrins applied in a Florida Turf scenario. Effects values on the PBO formulation were Daphnia

magnia EC50 = 6.7 ug/L and mysid shrimp LC50 = 0.14 ug/L. Droplet size 40 :m, Boom height 150 ft,

Application Rate 0.008 lb a.i./A

EECs (:g/L ) Freshwater

invertebrates

Estuarine/marine

invertebrates

Depth of 

water body

 peak Daphnia magna

Acute RQ

Formulation

Mysid Shrimp

Acute RQ

Formulation 

Surface Water 

6 inches 0.003 <0.00 0.02

12 inches 0.003 <0.00 0.02

3.3 feet (1 meter) 0.003 <0.00 0.02

6.6 feet (2 meters) 0.003 <0.00 0.02
-84-

Table 41. Acute RQs for freshwater and estuarine/marine fish associated with mosquito abatement uses

of pyrethrins. EEC values are generated from AGDISP and PRZM/EXAMS for pyrethrins applied in a

Florida Turf scenario. Effects values on the PBO formulation were rainbow trout LC50 = 3.2 ug/L and

sheepshead minnow LC50 = 3.8 ug/L. Droplet size 50 :m, Boom height 150 ft, Application Rate 0.0025 lb

a.i./A

EECs (:g/L) Freshwater fish Estuarine/marine fish

Depth of 

water body

 peak Rainbow Trout

Acute RQ 

Formulation

Sheepshead Minnow

Acute RQ 

Formulation

Surface Water

6.0 inches 0.003 <0.00 0.02

12.0 inches 0.003 <0.00 0.02

3.3 feet (1 meter) 0.003 <0.00 0.02

6.6 feet (2 meters) 0.003 <0.00 0.02

Table 42. Acute RQs for freshwater and estuarine/marine invertebrates associated with mosquito

abatement uses of pyrethrins. EEC values are generated from AGDISP and PRZM/EXAMS for

pyrethrins applied in a Florida Turf scenario. Effects values on the PBO formulation were Daphnia

magnia EC50 = 6.7 ug/L and mysid shrimp LC50 = 0.14 ug/L. Droplet size 50 :m, Boom height 150 ft,

Application Rate 0.0025 lb a.i./A

EECs (:g/L ) Freshwater

invertebrates

Estuarine/marine

invertebrates

Depth of 

water body

 peak Daphnia magna

Acute RQ

Formulation

Mysid Shrimp

Acute RQ

Formulation 

Surface Water 

6 inches 0.003 <0.00 0.02

12 inches 0.003 <0.00 0.02

3.3 feet (1 meter) 0.003 <0.00 0.02
Table 42. Acute RQs for freshwater and estuarine/marine invertebrates associated with mosquito

abatement uses of pyrethrins. EEC values are generated from AGDISP and PRZM/EXAMS for

pyrethrins applied in a Florida Turf scenario. Effects values on the PBO formulation were Daphnia

magnia EC50 = 6.7 ug/L and mysid shrimp LC50 = 0.14 ug/L. Droplet size 50 :m, Boom height 150 ft,

Application Rate 0.0025 lb a.i./A

EECs (:g/L ) Freshwater

invertebrates

Estuarine/marine

invertebrates

Depth of 

water body

 peak Daphnia magna

Acute RQ

Formulation

Mysid Shrimp

Acute RQ

Formulation 

Surface Water 

-85-

6.6 feet (2 meters) 0.003 <0.00 0.02

Table 43. Surface water EECs (ppb) and RQs for ecological risk assessment

based on pyrethrin use on Georgia peaches and California grapes, and

buffer zones of 50, 100, and 150 ft. Results using average KOC = 35,170

Crop

Peak

EEC

(ug/L)

Acute RQ for estuarine/marine

invertebrates exposed to pyrethrin,

based on an LC50 of 0.14 :g/L for

mysid shrimp*

Standard Aerial Run, With Spray Drift Set To 5%

Georgia Peaches 0.656 4.69a, b, c

Idaho Potatoes 0.366 2.61a, b, c

Special Run, With Spray Drift Set To 1%, Ground Application

Georgia Peaches 0.421 3.01a, b, c

Idaho Potatoes 0.082 0.58a, b, c

Special Run, With Spray Drift Set To 0%

Georgia Peaches 0.344 N/A

Idaho Potatoes 0.042 N/A

High end, release height 15 ft, wind speed 15 mph, very fine droplets

Buffer Zone 0 ft, 24.0% spray drift for GA peaches/ 31.2% spray drift for ID potatoes

Georgia peaches 1.681 12.01a, b, c
Table 43. Surface water EECs (ppb) and RQs for ecological risk assessment

based on pyrethrin use on Georgia peaches and California grapes, and

buffer zones of 50, 100, and 150 ft. Results using average KOC = 35,170

Crop

Peak

EEC

(ug/L)

Acute RQ for estuarine/marine

invertebrates exposed to pyrethrin,

based on an LC50 of 0.14 :g/L for

mysid shrimp*

-86-

Idaho Potatoes 2.259 16.14a, b, c

Buffer Zone 50 ft/ 16.8% spray drift for GA peaches/ 23.1% spray drift for ID potatoes

Georgia peaches 1.436 10.26a, b, c

Idaho Potatoes 1.673 11.95a, b, c

Buffer Zone 100 ft, 12.7% spray drift for GA peaches/ 18.4% spray drift for ID potatoes

Georgia Peaches 1.164 8.31a, b, c

Idaho Potatoes 1.333 9.52a, b, c

Buffer Zone 150 ft, 10.2% spray drift for GA peaches/ 15.4% spray drift for ID potatoes

Georgia Peaches 0.998 7.13a, b, c

Idaho Potatoes 1.116 7.97a, b, c

Low end, release heigh 8 ft, wind speed 3 mph, medium to coarse droplets

Buffer Zone 0 ft, 2.8% spray drift for GA peaches/ 3.0% spray drift for ID potatoes

Georgia Peaches 0.519 3.71a, b, c

Idaho Potatoes 0.223 1.59a, b, c

Buffer Zone 50 ft, 1.4% spray drift for GA peaches/ 1.5% spray drift for ID potatoes

Georgia Peaches 0.431 3.08a, b, c

Idaho Potatoes 0.115 0.82a, b, c

Buffer Zone 100 ft, 1.1% spray drift for GA peaches/ 1.1% spray drift for ID potatoes

Georgia Peaches 0.413 2.95a, b, c

Idaho Potatoes 0.087 0.62a, b, c

Buffer Zone 150 ft, 0.9% spray drift for GA peaches/ 0.8% spray drift for ID potatoes

Georgia Peaches 0.400 2.86a, b, c

Idaho Potatoes 0.067 0.48 b, c
Table 43. Surface water EECs (ppb) and RQs for ecological risk assessment

based on pyrethrin use on Georgia peaches and California grapes, and

buffer zones of 50, 100, and 150 ft. Results using average KOC = 35,170

Crop

Peak

EEC

(ug/L)

Acute RQ for estuarine/marine

invertebrates exposed to pyrethrin,

based on an LC50 of 0.14 :g/L for

mysid shrimp*

-87-

Based on 1-in-10 year exceedance probability (0.10). Peak EEC’s provided with three decimal

points for information only.

*Mysid shrimp was the most sensitive aquatic species.

a

RQ meets or exceeds LOC for acute high risk (LOC = 0.5)

b

RQ meets or exceeds LOC for acute restricted risk (LOC = 0.1)

c

RQ meets or exceeds LOC for acute endangered species risk (LOC = 0.05).

 “Down-the-Drain” Exposure: Acute and Chronic Risk

The Agency has assumed that many of the indoor uses of pyrethrin should not impact ecological systems

because of their reduction in exposure potential. Pyrethrin is used in various household products, such as

pyrethrin-containing prescription drugs, over the counter drugs, and pet products (like shampoo), available to

the US consumers. Potential release of pyrethrin in the domestic wastewater (referred to as “down-the-drain”

release) may occur from using these household products. The information on the amount of pyrethrin utilized

on each of these uses is considered Confidential Business Information and cannot be provided in this report,

but it is stressed that these uses are of concern and included in The Agency’s assessment. The risk to aquatic

systems from products that pass through wastewater treatment plants and the eventual potential exposure to

aquatic organisms was assessed. This assessment suggests that pyrethrin residues released to aquatic areas

from this process should not cause acute or chronic risk to freshwater or estuarine/ marine fish and

invertebrates (Tables 44 and 45).
-88-

Table 44. Acute and chronic RQs for freshwater and estuarine/marine fish associated with “downthe-drain” uses of pyrethrins based on rainbow trout LC50 = 5.1 ug/L, fathead minnow NOAEC =

1.9 ug/L, sheepshead minnow LC50 = 16.0 ug/L, and extraoplated NOAEC sheepshead minnow 5.9

ug/L. EEC values are generated from PRZM/EXAMS. 

EECs (:g/L )

Scenario

(state/

crop)

Peak Chronic Freshwater

Fish

(Rainbow

Trout)

Acute RQ

TGAI 

Freshwater

Fish

(Fathead

Minnow)

Chronic RQ

TGAI

Estuarine/

marine Fish

(Sheepshea

d Minnow)

Acute RQ

TGAI

Estuarine/marine

Fish

(Sheepshead

Minnow)

Chronic RQ

TGAI

“

downthe-drain”0.00242 0.000186 <0.00 <0.00 <0.00 <0.00

a

RQ exceeds LOC for acute endangered species ($0.05). b

RQ exceeds LOC for acute restricted use ($0.1). C The NOAEC estimated for the sheepshead minnow is based on the acute-to-chronic ratio method, determined by the

following mathematical relationship: Freshwater LC50 (5.1) / Freshwater NOAEC (1.9) = Estuarine/marine LC50 (16.0 ppb)/ X

(estimated value for estuarine/marine NOAEC).

Table 45. Acute and chronic RQs for freshwater and estuarine/marine invertebrates associated with

‘down-the-drain” uses of pyrethrins based on Daphnia magna EC50 = 11.6 ug/L, Daphnia magna NOAEC

= 0.86 ug/L, mysid shrimp EC50 = 1.4 ug/L, and extraoplated NOAEC mysid shrimp 0.10 ug/L. EEC

values are generated from PRZM/EXAMS.

EECs (:g/L )

Scenario

(state/

crop)

peak chronic Freshwater

Invertebrate

(Daphnia

magna)

Acute RQ

TGAI 

Freshwater

Invertebrate

(Daphnia

magna)

Chronic RQ

TGAI

Estuarine/

marine

Invertebrate

(Mysid Shrimp)

Acute RQ

TGAI

Estuarine/

marine

Invertebrate

(Mysid

Shrimp)

Chronic RQ

TGAI

“down-thedrain”0.00242 0.000186 <0.00 <0.00 <0.00 <0.00

a

RQ exceeds LOC for acute endangered species ($0.05). b

RQ exceeds LOC for acute restricted use ($0.1). c

RQ exceeds LOC for acute high risk ($ 0.5). d The NOAEC estimated for the Mysid shrimp is based on the acute-to-chronic ratio method, determined by the following

mathematical relationship: Freshwater LC50 (11.6 ppb)/ Freshwater NOAEC (0.86 ppb) = Estuarine/marine LC50 (1.4 ppb)/

X (estimated value for estuarine/marine NOAEC).
-89-

b. Sediment Organisms

The pyrethrins are lipophilic compounds that can adsorb readily to particulate and sediment, thus

possibly limiting its exposure to aquatic life in the water column but increasing toxic exposure in the

benthos. Sediment can act as a reservoir for lipophilic persistent compounds. Exposure to this sediment

can result in a direct impact to aquatic life through respiration, ingestion, dermal contact, as well as

indirect impact through alterations of the food chain. In order to evaluate this possible concern the

USEPA Office of Water (OW) has developed the Equilibrium Partitioning Sediment Guidelines (ESG).

The EFED used the Equilibrium Partitioning Guidelines, which are based on the hydrophobicity and

concentrations of the chemical normalized to organic carbon (OC) in sediment (De Toro et al. 1991),

to estimate sediment concentrations and sediment dwellers toxicity.

Since, EFED uses a deterministic method for its screening level risk assessment, the calculation of risk

quotient values (RQ) is important for assessing possible risk. The RQ values are calculated by taking

the ratio of the estimated exposure concentrations (EEC) to the toxicity effect value (e.g., LC50,

NOAEC). The EEC values are model generated (e.g. by PRZM/ EXAMS). However, the PRZM/

EXAMS output produces water column EEC values, as well as sediment and pore water EEC values.

Therefore, in order to assess possible toxic pesticide exposure to aquatic organisms from sediments,

EFED used the PRZM/ EXAMS model which incorporates the principles of the equilibrium partitioning

theory, in order to generate EECs from sediment and pore water. By relying on sediment and/or pore

water output values. 

The calculations that rely on pore water were calculated by dividing the PRZM/ EXAMS output value

for pore water concentrations by the dissolved concentrations in the water column that caused toxicity

in bioassays (e.g., LC50).

 EEC pore water ug/L / LC50 ugL

For the scenarios modeled in this assessment on pyrethrins, the benthic pore water concentrations

(EECpore) are, on average, estimated to be approximately 60% lower than the surface water

concentrations using PRZM/ EXAMS. Therefore, the RQsed value is generally 60% lower than the RQaq

value for the same scenario and effects endpoint. 

The Agency evaluated the potential for acute and chronic risk from sediments that could act as a

repository for pyrethrin residues. Table 46 shows that there are estimated acute risk concerns to

estuarine/marine invertebrates (restricted use, RQ range 0.10 to 0.15) as noted in the scenarios that

represent MS cotton, ME potato, and IL corn (endangered species risk concerns (RQ range 0.05 to 0.15

for ND wheat, PA tomato, MS cotton, ME potato, and IL corn were calculated but the Agency

acknowledges that currently there are no endangered estuarine/marine invertebrates listed). Table 47

shows the potential for chronic risks to estuarine/marine sediment dwelling invertebrates. In the absence

of chronic data for estuarine/marine invertebrates, the NOAEC estimated for estuarine/marine

invertebrates that was used to estimate risk to invertebrates in the water column was also used for

sediment. The chronic LOCs were exceeded for estuarine/marine organisms associated with the

agricultural uses (RQ range = 1.1 to 2, Crops: PA tomato, MS cotton, ME potato, and IL corn). There

are no chronic risks to freshwater sediment-dwelling invertebrates associated with the agricultural uses.
-90-

Table 46. Acute Risk Estimation to freshwater and estuarine/marine sediment-dwelling organisms

based on data from the surrogate species, Daphnia magna (EC50 = 11.6 :g/L ) and Mysid Shrimp

(LC50 = 1.4 :g/L). EEC values reflect pore water estimates that are in equilibrium with sediment

concentrations (KOC of 35,170 L/kg) as generated from PRZM/EXAMS for the agricultural crop

uses. 

Scenario

EEC Acute RQ

Pore water

peak

(:g/L)

Sediment

(:g/kgoc)

Freshwater

TGAI

Estuarine/marine

TGAI

IL corn 0.21 7350 0.02 0.15ab

ME potato 0.16 5590 0.01 0.11ab

MS cotton 0.14 4820 0.01 0.10ab

PA tomato 0.12 4110 0.01 0.09a

ND wheat 0.07 2390 0.01 0.05a

CA onion 0.06 2110 0.01 0.04

NC apple 0.06 2110 0.01 0.04

OR

snapbeans

0.05 1650 <0.01 0.04

ID potato 0.04 1350 <0.01 0.03

MN alfalfa 0.04 1270 <0.01 0.03

FL citrus 0.04 1270 <0.01 0.03

GA peaches 0.04 1370 <0.01 0.03

CA grapes 0.03 1020 <0.01 0.02

a

RQ exceeds LOC for acute endangered species ($0.05). b

RQ exceeds LOC for acute restricted ($0.1)
-91-

Table 47. Chronic Risk Estimation to freshwater and estuarine/marine sediment-dwelling organisms

based on data from the surrogate species, Daphnia magna (NOAEC = 0.86 :g/L ) and Mysid Shrimp

(NOAEC = 0.10 :g/L ). EEC values reflect pore water estimates that are in equilibrium with

sediment concentrations (KOC of 35,170 L/kg) as generated from PRZM/EXAMS for the agricultural

crop uses.

Scenarios

EECs Chronic RQ

Pore water

21-day

(:g/L)

Sediment

(:g/kg) Freshwater Estuarine/marine

IL corn 0.20 7170 0.23 2

ME potato 0.15 5420 0.17 1.5

MS cotton 0.13 4640 0.15 1.3

PA tomato 0.11 3900 0.13 1.1

ND wheat 0.07 2290 0.08 0.7

CA onion 0.07 2290 0.08 0.7

NC apple 0.06 2040 0.07 0.6

OR snapbeans 0.05 1620 0.06 0.5

ID potato 0.04 1300 0.05 0.4

MN alfalfa 0.04 1230 0.05 0.4

FL citrus 0.04 1230 0.05 0.4

GA peaches 0.04 1340 0.05 0.4

CA grapes 0.03 985 0.03 0.3

2. Non-target Terrestrial Animals

a. Mammals

Table 19 provides acute and chronic risk quotient (RQ) values for mammals of different body weight

size classes exposed to different forage items. Using the foliar half-life of 1 and 14 days, the acute RQs

are all mammals (listed and non-listed) are less than the LOC of 0.1. All chronic RQs for listed and nonlisted mammals exposed to pyrethrins in all dietary scenarios are below the LOCs. Both scenarios (1 -

3 day interval) using the typical application rate are depicted in Table 19.
-92-

Table 48. Acute and chronic RQ calculations for mammalian consumption of plant and insect

forage material. The RQs are based on acute LD50 of 700 mg/kg body weighta

 and an NOAEC

of 100 ppm diet in rats (Rattus norvegicus). RQ values were calculated for two foliar dissipation

residue half-lives as found in Willis and McDowell, (1987) for surrogate pyrethroids, phenothrin

and pyrethrin.

Crop

application rate

(lbs ai/A;

no. app.)

Forage item

Maximum

EEC

(ppm)

Acute RQsb Chronic

RQsb

15 g 35 g 1000 g

Various crops

0.050 (10),

interval between

applications 1 day

Short grass 23.98 - 97.01 0.06 0.05 0.03 0.97

Tall grass 10.99 - 44.46 0.03 0.02 0.01 0.44

Broadleaf/

forage plants and

small insects

13.49 - 55.57 0.03 0.03 0.02 0.55

Fruits/pods/seeds/

large insects

1.50 - 6.06 0.0 0.0 0.0 0.06

Various crops

0.050 (10),

typical interval

between

applications 3 day

Short grass 13.71 - 67.25 0.01 -

0.04

0.1 -

0.04

0.0 -

0.02

0.67

Tall grass 6.29 - 30.82 0.0 -

0.02

0.0 -

0.02

0.0 -

0.01

0.31

Broadleaf/

forage plants and

small insects

7.71 - 37.83 0.0 -

0.02

0.0 -

0.02

0.0 -

0.01

0.38

Fruits/pods/seeds/

large insects

0.86 - 4.20 0.0 0.0 0.0 0.04

a

The acute mammalian LD50 is based on female mortality of rats exposed to FEK-999; the LD50 for male rats

in the same study was reported as 2,140 mg/kg body weight, suggesting a gender-specific difference for acute

effects (mortality) of a factor of 3.

b

 RQ calculated for foliar dissipation residue half-lives of 1 and 14 days. respectively 

b. Birds

Table 20 provides acute and chronic risk quotient (RQ) values for avian food items following application

of pyrethrins under a maximum use pattern for various crop species. An analysis of the results indicates

that avian acute, restricted use, chronic and endangered species LOCs are not exceeded at registered

maximum application rates for pyrethrins. Chronic risk to avian species was estimated by using

pyrethrin avian NOAEC for Bobwhite quail.(NOAEC = 125 mg/kg/diet)..
-93-

Table 49. Acute RQ calculations for bird consumption of plant and insect forage material. 

The RQs are based on a dietary LC50 of 5,620 mg/kg diet with the bobwhite quail (Colinus

virginianus) and mallard duck (Anas platyrhynchos)

a

. RQ values were calculated for two

foliar dissipation residue half-lives as found in Willis and McDowell, (1987) for surrogate

pyrethroids, phenothrin and pyrethrin.

Crop application

rate (lbs ai/A; no.

appl.) Forage item

Maximum EEC

(ppm)

Acute

RQb

Chronic

RQbc

Various crops

0.050 (10), interval

between applications 1

day

Short grass 23.98 - 97.01 0.0- 0.02 0.02 - 0.78

Tall grass 10.99 - 44.46 0.0 - 0.01 0.09 - 0.36

Broadleaf/forage plants

and small insects

13.49 - 55.57 0.0 - 0.01 0.11- 0.44

Fruits/pods/seeds/large

insects

1.50 - 6.06 0.0 0.01- 0.05

Various crops

0.050 (10), typical

interval between

applications 3 days

Short grass 13.71 - 67.25 0.0 - 0.01 0.11 - 0.54

Tall grass 6.29 - 30.82 0.0 - 0.01 0.05 - 0.25

Broadleaf/forage plants

and small insects

7.71 - 37.83 0.0 - 0.01 0.06 - 0.30

Fruits/pods/seeds/large

insects

0.86 - 4.20 0.0 0.01 - 0.03

a

The acute toxicity is reported as LC50 > 5,620 mg/kg diet, suggesting that the actual LC50 was not determined by the dosing

regimen. Use of this toxicity value will likely overestimate acute risks.

b

 RQ calculated for foliar dissipation residue half-lives of 1 and 14 days. respectively 

c Avian chronic toxicity was substituted with a NOAEC from pyrethrin

c. Insects

Currently, EFED does not assess risk to non-target insects. Results of acceptable studies are used for

recommending appropriate label precautions. Pyrethrins are very toxic to honeybees. Therefore,

honeybees and other beneficial insects are expected to be at risk based on aerial applications that may

cause wind dispersal of pyrethrins to areas where these insects may pollinate and/or feed.

3. Non-target Terrestrial and Semi-aquatic Plants

Since toxicity data were unavailable for non-target plants, risks were not calculated.

B. Risk Description - Interpretation of Effects

Pyrethrins are the active insecticidal components of certain species of chrysanthemum plants that have

been used as insecticides for at least two centuries. These compound are moderately persistent, bind to

soils (Koc = 35,170) in the environment but are unstable to sunlight. The degradation products of
-94-

pyrethrin occur as a result of ester bond breakage resulting in carboxylic acid and an alcohol. Data on

the toxicity of the degradates were not available for this review, but because of the disruption of the

parent backbone structure during break-down, EFED assumes a decrease in effective toxicity. One of

the major insecticidal advantages of pyrethrin is their “knockdown” action that induces paralysis in target

organisms which is in contrast to their relatively lower killing potential (parent can be metabolized).

However, in order to delay this metabolic action (help inhibit microsomal enzyme breakdown) and

enhance lethality, pyrethrins are often used in combination with other pesticides and synergists (such

as piperonyl butoxide). However, for the purposes of this review only risk to the parent compound will

be assessed (exception is the evaluation for mosquito abatement where a formulation is used).

1. Estimating Risk to Aquatic Systems

EFED risk assessment of pyrethrin shows that a major risk of the chemical exposure in the environment

can be focused on aquatic systems. The evaluation of this risk to aquatic organisms was approached by

dividing aquatic systems into two very general parts or media; water column and the benthos. The first

portion is the water column, which is defined as the aquatic area between surface and benthos (6" above

the bottom). Organisms living in this area are free swimming and can feed and breed at the surface, mid

water and/ or on the benthos. Direct pesticidal contact (e.g., gill lamella, ingestion, and integument) to

these organisms is assumed to be from the water column and toxicity assessment points are the acute

LC50 and chronic NOAEC that are generated through standard water column toxicity tests. The second

aquatic compartment is the benthos which is composed of sediments and the area six inches above the

sediment (epibenthos). The benthos is composed of a diversity of aquatic invertebrates (e,g,, insect

larvae, crustaceans, mollusks), species of fish (e.g., catfish, loach), as well as certain critical life stages

of organisms that reside in the water column; the benthos is also the initial nursery area for several

species of fish especially commercial species such as salmonids. The benthos can also be a source of

food items for several species of fish (i.e., water column) actively feeding on the organisms in the

sediment and/or capturing organisms that are emerging from this area. 

In order to evaluate the potential for toxic risk from pyrethrin exposure in the water column, EFED used

the standard model generated EEC ratio to a most sensitive endpoint as defined from LC50, EC50, or

NOAEC. The evaluation of toxic risk to the benthos compartment was approached by assuming

equilibrium partitioning of high Koc compounds between the sediment and the interstitial water (i.e., this

is the pore water, the water found between particulate in the sediment). The EEC for pore water were

model generated (PRZM/ EXAMS) and used to calculate RQ values. Since, sediment toxicity data was

not available for this report, EFED relied on the most sensitive water column values. The RQ for

assessing potential risk to sediment reflects pore water EEC values/ most sensitive water column toxicity

value. EFED assumes that there is no difference in sensitivity between water column organisms and

comparable benthic organisms regarding toxicity to pyrethrin. These assumptions are supported by the

EPA Office of Water which uses a similar approach and assumption in developing sediment guidelines

(ESG) for the protection of benthic organisms (The ESG Technical Document, USEPA, 2000a). 

a. Estimating Risk to Aquatic Systems (Water Column Exposure)

In evaluating possible pyrethrin risk to aquatic systems from use on agricultural crops, the Agency chose

to evaluate maximum and typical application rates. Model generated exposure values suggests that

maximum rates can result in acute risk to fish and aquatic invertebrates (freshwater and

estuarine/marine) with triggers that included restrictive use and endangered species concern (although
-95-

estuarine/ marine endangered invertebrate was triggered, EFED realizes that at this time there are no

listed species under this category). Evaluating chronic risk from this exposure scenario showed that

LOC triggers were exceeded for estuarine/marine invertebrates, while fish (freshwater and

estuarine/marine) and freshwater invertebrates may not be at chronic risk from pyrethrin exposure in the

water column. This potential for acute and chronic risk reflects exposure from large acreage crops such

as corn, cotton, wheat and orchards (e.g., pome fruit and stone fruits). Concern from citrus use appears

to be reflected in possible acute risk to estuarine/marine fish and invertebrates, as well as chronic risk

to estuarine/ marine invertebrates. The risk quotients for some of the crop scenarios may not necessarily

be the most conservative because certain crop scenarios (i.e. alfalfa) are grown more than once per year.

This assessment assumed a single season per year.

The second scenario that depicts typical application rate appears to have the potential to reduce risk to

aquatic systems. Evaluation of four crop scenarios using the TGAI (ID potatoes, PA tomatoes, CA

onions, OR snap beans) suggests that LOCs for freshwater and estuarine/marine fish and invertebrates

should not be exceeded if typical application rate is used. The Agency also assessed the maximum and

typical rates for a pyrethrin formulation with PBO but only evaluated acute exposure to aquatic

organisms. The calculated EECs show that acute risk from the maximum formulation rate appeared to

be higher than risk calculated only from the TGAI. This evaluation showed that acute risk from the

formulation was about 2-7X greater for freshwater and estuarine/marine fish and about 10X greater for

estuarine/marine invertebrates. However, the typical formulation rate appears to reduce the risk

(freshwater and estuarine/marine fish and freshwater invertebrates), but this reduction in exposure still

presents the potential for acute high, acute restrictive, and chronic risk to estuarine/marine invertebrates

species. 

b. Estimating Risk to Aquatic Systems (Sediment Exposure)

The sediment scenario (high pest pressure application intervals, 1 day) modeled in this assessment

showed that the benthic pore water concentrations (EECpore) are about 60% lower than the water column

levels using the PRZM/ EXAMS model. This decrease in concentration levels suggests lower risk

potential. Acute risk to freshwater sediment dwelling invertebrates appears to be below our LOC for

all crop scenarios, while RQ values calculated for some crops (e.g., corn, potatoes, cotton, tomatoes, and

wheat) suggest acute risk to estuarine/marine benthic invertebrates. However, realistically the extent of

this acute risk depends on the proximity of these crops to estuatrine/ marine environments; wheat acreage

is not usually found in coastal areas, while tomatoes, cotton, potatoes and corn acreage may overlap this

area of concern in costal states. Although acute risk may appear to be low for freshwater and

estuarine/marine invertebrates, calculated chronic RQs for estuarine/marine sediments show LOC

exceedances for these crops (corn, potatoes, cotton, tomatoes) and suggest that there could be the

potential for chronic risk to estuarine/marine invertebrates that may be directly associated with these

sediments.

c. Estimating Risk to Aquatic Systems Through Mosquito Abatement

EFED used a different modeling approach to evaluate mosquito abatement (description of modeling

scenario in Section III.B.1.b). Mosquito adulticides are applied as mists (very small droplet sizes) with

the intent that the pesticide will linger in the air as a fog and that the eventual deposition onto the surface

will be relatively slow. Therefore, the level of drift can be substantial and has the potential for eventual

contact with adjacent bodies of water. Therefore, in order to estimate risk to aquatic systems, EFED
-96-

calculated the level of drift for such special circumstances (AGDISP), and the EEC values for bodies

of water of various depths using the FL turf scenario ( PRZM/ EXAMS). The toxicity data end points

used for this scenario were based on the formulated product (Pyrenone Crop spray). Calculated RQ

values for surface water EECs ranged in depth from 1⁄2 to 6.6 feet and suggest that this use pattern

should not cause acute risk to fish (freshwater and estuarine/marine) or invertebrates (freshwater).

However, there is the potential for acute risk to estuarine/ marine invertebrates like shrimp (restrictive

use category). 

The results of this assessment found lower concentrations in shallow water bodies compared to deep

water bodies. This may be partially explained by three reasons: The Henry’s Law constant suggests

a potential for loss of pesticide from the pond via volatilization. Second, with a very high KOC, the

pyrethrin tends to partition towards the sediment. This equilibrium will occur more rapidly in shallow

waters than in deeper bodies of water. Finally, a third possible explanation is the short aqueous

photolysis half-life (0.5 days) for pyrethrin. When a chemical has a short half-life (as in this scenario)

and it is concentrated in shallow waters (i.e., six inches), it can be expected to photodegrade more readily

than when it is spread throughout a deeper water column. Light is not expected to penetrate into depths

deeper than about 1 ft.

It was found that for mosquito control, application directions in the label are insufficient to accurately

estimate aquatic exposures that result from application of pyrethrin for controlling mosquitoes.

Limitations (as opposed to recommendations) on product labels for key parameters such as droplet size,

wind speed, release height, application interval, and number of applications allowed per year are not

specified. The exposure assessment conducted here represents the water concentrations expected from

a typical, low-level aerial application. Concentrations resulting from actual application of pyrethrin for

mosquito control could be significantly higher than modeled concentrations if applicators used different

application parameters.

It was also found that the shallow pond shows the lower concentration, possibly due to partitioning of

the chemical with particulate and the sediment. Variables that have a high impact on the aquatic EECs

are the boom height (higher boom height, the lower the level of deposition), the droplet size (the smaller

droplets, the lower the levels of deposition), the wind speed (too low wind speeds favor higher

deposition), and obviously the application rate (it appears that for many of the products the maximum

application rate is lower than the maximum application rate stated in the Master Label [0.0025 lb a.i./A

vs 0.008 lb a.i./A]). The interval between applications and the number of applications are expected to

also have an effect on the EECs (similar to an agricultural application). In general the Agency evaluation

of the adulticide scenario using maximum and typical application rates. The maximum rate showed that

there did not appear to be the potential for acute risk to freshwater fish and invertebrates or

esrtuarine/marine fish. However, the LOCs for estuarine/marine invertebrates were exceeded. This risk

to estuarine/marine invertebrates appeared to be eliminated if the boom height was set at 150 ft and the

droplet size was at 40 um. The Agency also evaluated the typical rate and found that potential acute risk

to estuarine/marine invertebrates could be eliminated with a boom height of 75ft and a 50 um droplet

size. 

d. Estimating Risk to Aquatic Systems Through “Down-the-Drain”

Consideration of Exposure from Pyrethrin Pharmacolsoticals.
-97-

Pyrethrin is used in various household products, such as pyrethrin-containing prescription drugs, over

the counter drugs, and pet products (like shampoo), available to the US consumers. Potential release

of pyrethrin in the domestic wastewater system (referred to as “down-the-drain” release) may occur from

using these household products. The information on the amount of pyrethrin utilized on each of these

uses is considered Confidential Business Information and cannot be provided in this report, but it is

stressed that these uses are of concern and included in The Agency’s assessment. The risk to aquatic

systems from products that pass through wastewater treatment plants and the eventual potential

exposure to aquatic organisms was assessed. This assessment suggests that pyrethrin residues released

to aquatic areas from this process should not cause acute or chronic risk to freshwater or estuarine/

marine fish and invertebrates.

e. Other Special Considerations for Evaluating Aquatic Risk (Buffer Zones)

The extent to which spray drift may be an important component of the concentrations of pyrethrins

reaching bodies of water adjacent to treated areas after their application, was investigated. EFED ran

four crop scenarios with spray drift set to 0% and compared the results to the corresponding runs with

spray drift set to 5%. The runs with drift set to 0% resulted in EECs lower than the standard runs.

When the results of the standard run (5% drift) with the special run (0% drift), it was found that the level

of the peak EEC attributable to spray drift for GA peach and for FL citrus was near 46%, while for ID

potato and CA grapes it was >88%. The selection of crop scenarios was then narrowed down to two.

These scenarios were run with standard input for ground applications and with various buffer zones.

This was done to see the possible affects of buffer zones in reducing risk from pyrethrin exposure to

aquatic systems. The level of spray drift simulated both a high end drift scenario (high boom, high wind

speed, small droplet size), and a low end drift scenario (low boom height, low wind speed, large droplet

size), to bracket the spectrum of possibilities. Calculated RQ values for buffer zones set at 0, 50, 100,

and 150 feet and spray drift set at 0,1 and 5% showed acute risk to estuarine/ marine invertebrates.

However, as expected, the low end drift scenario yielded lower levels of drift and consequently lower

EECs and RQs. Combined with large buffer zones (150 ft), the RQs were of similar order of magnitude

than those yielded by ground applications. It is also noted that even a small buffer zone of 50 ft reduces

the RQs by more than 20%, compared to the same conditions with no buffer zone (for both the high end

and low end drift scenarios).

2. Estimating Risk to Terrestrial Organisms (Mammals and Birds)

An evaluation of possible risk to terrestrial organisms was conducted using the T-REX model that

provides estimates of concentrations of chemical residues on different types of food items that may be

sources of dietary exposure to avian, mammalian, reptilian, or terrestrial-phase amphibian receptors.

Acute and chronic RQ values for pyrethrin exposure from various food items to mammals of different

weight classes were calculated using foliar dissipation values (1 - 14 days) found in Willis and

McDowell, (1987) for pyrethroids that have similar chemistry and mode of action as pyrethrin (pyrethrin

and phenothrin). The use of maximum and typical application rate produced acute and chronic RQ

values that were less than the Agency’s LOC for risks to non-listed and listed species mammalian

species for all scenarios.

Acute risk quotient (RQ) values for avian food items following application of pyrethrins under a

maximum use pattern for various crop species and foliar dissipation half-life of 1 - 14 days were also
-98-

calculated. An analysis of these results show that avian acute, restricted use and listed species LOCs

are not exceeded at registered maximum application rates for pyrethrins. Chronic risk to avian species

was estimated by using pyrethrin NOAEC = 500 mg/kg/diet for Bobwhite quail. Calculated RQ values

suggest no chronic risk to listed or non-listed birds or mammals.

3. Review of Incident Data

Incident reports submitted to EPA since approximately 1994 have been tracked by assignment of incident

numbers in an Incident Data System (IDS), microfiched, and then entered to a second database, the

Ecological Incident Information System (EIIS). This second database has some 85 fields for potential

data entry. An effort has also been made to enter information to EIIS on incident reports received prior

to establishment of current databases. Incident reports are not received in a consistent format (e.g.,

states and various labs usually have their own formats), may involve multiple incidents involving

multiple chemicals in one report, and may report on only part of a given incident investigation (e.g.,

residues). While some progress has been made in recent years, both in getting incident reports submitted

and entered, there has never been the level of resources assigned to incidents that there has been to the

tracking and review of laboratory toxicity studies, for example.

Incidents entered into EIIS are categorized into one of several certainty levels: highly probable, probable,

possible, unlikely, or unrelated. In brief, “highly probable” incidents usually require carcass residues,

substantial ChE inhibition in avian and/or mammalian species, and/or clear circumstances regarding the

exposure. “Probable” incidents include those where residues were not available and/or circumstances

were less clear than for “highly probable.” “Possible” incidents include those where multiple chemicals

may have been involved and it is not clear what the contribution was of a given chemical. The “unlikely”

category is used, for example, where a given chemical is practically nontoxic to the category of organism

killed and/or the chemical was tested for but not detected in samples. “Unrelated” incidents are those

that have been confirmed to be not pesticide-related.

Incidents entered into the EIIS are also categorized as to use/misuse. Unless specifically confirmed by

a state or federal agency to be misuse, or there was very clear misuse such as intentional baiting to kill

wildlife, incidents would not typically be considered misuse. Data entry personnel often do not have a

copy of the specific label used in a given application, and would not usually be able to detect a variety

of label-specific violations, for example.

Of the 11 reports in the database, all but one incident alleges that pyrethrins caused damage to non-target

terrestrial plants; one study (described below) associates pyrethrin use with effects in fish. No incidents

were assigned a certainty index of 4 (highly probable). In addition, most of these incidents involved

formulated products containing a very low concentration of pyrethrins and a high percentage of “inert”

ingredients. The Agency does not consider pyrethrin (or the synergist PBO) to have phytotoxic properties

and assumes that the reported toxicity to terrestrial plants after application of a formulation may be the

result of inerts or other circumstances associated with the application.

Although incidents associated with pyrethroid exposure to aquatic systems has resulted in kills to

aquatic organisms (e.g., pyrethrin, cypyrethrin) only one possible incident is recorded with the Agency

for pyrethrin (noted below). 

However, the number of documented kills in EIIS are believed to be a very small fraction of total
-99-

mortality caused by all pesticides. Mortality incidents must be seen, reported, investigated, and have

investigation reports submitted to EPA to have the potential for entry into the database. Incidents often

are not seen, due to scavenger removal of carcasses, decay in the field, or simply because carcasses may

be hard to see on many sites and/or few people are systematically looking. Poisoned birds may also

move off-site to less conspicuous areas before dying. Incidents seen may not get reported to appropriate

authorities capable of investigating the incident because the finder may not know of the importance of

reporting incidents, may not know who to call, may not feel they have the time or desire to call, may

hesitate to call because of their own involvement in the kill, or the call may be long-distance and

discourage callers, for example. Incidents reported may not get investigated if resources are limited or

may not get investigated thoroughly, with residue analyses, for example. Also, if kills are not reported

and investigated promptly, there will be little chance of documenting the cause, since tissues and residues

may deteriorate quickly. Reports of investigated incidents often do not get submitted to EPA, since

reporting by states is voluntary and some investigators may believe that they don't have the resources

to submit incident reports to EPA. An effort has also been made to enter information to EIIS on incident

reports received prior to establishment of current databases. Although many of these have been added,

the system is not yet a complete listing of all incident reports received by EPA. 

In addition, there are a number of uncertainties associated with the data that are reported. Incident

reports are not received in a consistent format (e.g., states and various labs usually have their own

formats), may involve multiple incidents involving multiple chemicals in one report, and may report on

only part of a given incident investigation (e.g., residues). While some progress has been made in recent

years, both in getting incident reports submitted and entered, there has never been the level of resources

assigned to incidents that there has been to the tracking and review of laboratory toxicity studies, for

example. This adds to the reasons cited above for why EPA believes the documented kills are but a

fraction of total mortality caused by pyrethrins.

a. Incidents Involving Aquatic Organisms

One incident involving several fish killed in a small pond was investigated in Stanly County, NC on May

5, 1994. A homeowner noticed that several fish in the pond were dead and asked the NC Department

of Agriculture to investigate. It was determined that there were several possible causes of the fish kill.

On April 30, 1994, the complainant’s dog, which had recently been treated with flea powder containing

pyrethrins, jumped into the pond, possibly releasing pyrethrins to the water and resulting in the fish kill.

While a mixture of herbicides (2,4-D, Weedone 638, and glyphosate) was applied to land adjacent to the

pond, the application date was reported as May 10, five days after the dead fish began to appear in the

pond. No information is available regarding applications prior to the incident and it is unlikely that the

herbicides were responsible for the fish kill. Three weeks after the herbicides were applied, analysis of

the pond water and surrounding vegetation gave negative results (presumably for the sprayed herbicides

and pyrethrins).

b. Incidents Involving Terrestrial Organisms

Although the Agency believes that the pyrethroid in general are non-phytotoxic, the incident (certainty

index score = 3) noted for pyrethrin occurred in Kootenai County, ID on August 25, 1999, and involved

damage to 12 of 14 rose bushes, sunflowers, and several other plants that were treated with an insecticide

containing pyrethrins and piperonyl butoxide. All other incidents of plant or crop damage associated

with pyrethrin uses were listed as possible (certainty index score = 2). The Agency assumes that toxicity
-100-

may have been related to inerts in the formulation or other circumstances related to application.

Table 38. Incident reports involving pyrethrins in chronological order.

Location 

and incident # Date

Organisms

involved

Certainty

indexa Descriptionb

NC 

I003826-024

5/4/1994 Aquatic

organisms

2 Fish from a pond died after possible

contamination with pyrethrins

WI 

I007155-181

5/9/1994 Terrestrial

plants

2 A complaint alleged the loss of

10,000 peppers as a result of

spraying with Pyrenone Crop Spray 

TN

I007340-671

5/13/1998 Terrestrial

plants

2 Damage to an edible crop may have

occurred following application of

Ortho Tomato and Vegetable Insect

Killer

TX

I007340-672

5/14/1998 Terrestrial

plants

2 Damage to ornamentals may have

occurred following application of

Ortho Tomato and Vegetable Insect

Killer

GA

I007340-700

5/26/1998 Terrestrial

plants

2 Damage to edible crops may have

occurred following application of

Ortho Tomato and Vegetable Insect

Killer

WI

I008693-046

4/29/1999 Terrestrial

plants

2 Damage to plants may have occurred

following application of Ortho

RosePride Rose and Flower Insect

Killer

CA

I008693-047

4/21/1999 Terrestrial

plants

2 Damage to about 12 bushes may

have occurred following 2

applications of Ortho RosePride

Rose and Flower Insect Killer

ID

I009262-095

8/24/1999 Terrestrial

plants

3 Damage to roses, snapdragons,

sunflowers, occurred following the

application of insecticide containing

pyrethrins.

No location

I009825-002

8/31/1999 Terrestrial

plants

2 Damage to unspecified plants,

occurred following the application of

insecticide containing pyrethrins.
Table 38. Incident reports involving pyrethrins in chronological order.

Location 

and incident # Date

Organisms

involved

Certainty

indexa Descriptionb

-101-

FL

I009916-023

2/1/2000 Terrestrial

plants

2 Damage to about 6 or 7 roses may

have occurred following applications

of Ortho RosePride Rose and Flower

Insect Killer

WI

I010017-017

3/7/2000 Terrestrial

plants

2 Damage to ornamentals occurred 2

weeks following the application of

Ortho RosePride Rose and Flower

Insect Killer

a

Certainty index scoring reflects the likelihood that the pesticide was responsible for the alleged

damage. Highly probable (4); Probable (3); Possible (2); Unlikely (1); Unrelated (0).

b

 All events are related to exposure from formulated products that contain pyrethrins + piperonyl

butoxide.

4. Endocrine Effects

There is no evidence to indicate that pyrethrin exposure results in endocrine toxicity in mammalian

species. Studies on the effects of pyrethrins on avian reproduction were not submitted to the Agency;

thus, no conclusion can be made regarding the potential for pyrethrins to cause endocrine disruption in

avian species. Regarding the potential for pyrethrins to produce endocrine toxicity in aquatic species,

reproductive effects were observed in full life-cycle studies in daphnids. Exposure to 2.0 ppb resulted

in reproductive effects, including the reduced number of offspring produced per adult. A chronic early

life stage study conducted using the fathead minnow showed that exposure to 3.0 ppb significantly

reduced hatching success, length and wet weight of freshwater fish. Although limited information is

available, based on the reproductive effects observed in freshwater fish and daphnia, pyrethrins exhibited

effects that may be indicative of endocrine disrupting activity.

Under the Federal Food, Drug and Cosmetic Act (FFDCA), as amended by the Food Quality Protection

Act (FQPA), EPA is required to develop a screening program to determine whether certain substances

(including all pesticide active and other ingredients) “may have an effect in humans that is similar to an

effect produced by a naturally-occurring estrogen, or other such endocrine effects as the Administrator

may designate.” Following the recommendations of its Endocrine Disruptor Screening and Testing

Advisory Committee (EDSTAC), EPA determined that there was scientific basis for including, as part

of the program, the androgen- and thyroid hormone systems, in addition to the estrogen hormone system.

EPA also adopted EDSTAC’s recommendation that the Program include evaluations of potential effects

in wildlife. For pesticide chemicals, EPA will use FIFRA and, to the extent that effects in wildlife may

help determine whether a substance may have an effect in humans, FFDCA authority to require the

wildlife evaluations. As the science develops and resources allow, screening of additional hormone

systems may be added to the Endocrine Disruptor Screening Program (EDSP). When the appropriate

screening and or testing protocols being considered under the Agency’s Endocrine Disruptor Screening

Program have been developed, pyrethrin may be subjected to additional screening and or testing to better

characterize effects related to endocrine disruption. 
-102-

5. Threatened and Endangered Species Concerns

The acute level of concern (LOCs) is exceeded for endangered and/or threatened species of freshwater

fish and invertebrates and are associated with the agricultural uses of pyrethrins. Based on a probit slope

analysis to calculate the chance of an individual event corresponding to the freshwater fish, the estimated

individual mortality associated with the calculated RQ values (0.24 to 1.10) range from 1 in 3.34 x 1014

to 1 in 4.17 x 108 . For the freshwater invertebrate, the estimated individual mortality associated with

the calculated RQ values (0.03 - 0.41) range from 1 in 1.0 x 1016 to 1 in 8.44 x 109

. 

The acute level of concern (LOCs) is exceeded for endangered and/or threatened (listed) species of

estuarine/ marine fish and invertebrates that live in the water column and are associated with the

agricultural and mosquito abatement uses of pyrethrins. For estuarine/marine fish, the estimated

individual mortality associated with the calculated RQ values (0.24 to 1.10 ) is 1.0 X 1016. For

estuarine/ marine invertebrates for agriculture and mosquito abatement uses, the probit slope analysis

was completed for both active ingredient and formulated product. Based on the default slope estimate

of 4.5, the corresponding chance of individual mortality for estuarine/ marine invertebrates following

exposure from the formulation is 1 in 4.17 x 108

; and based on the slope estimate of 4.1, the

corresponding chance of individual mortality for estuarine/marine invertebrates following exposure to

the technical grade active ingredient is 1 in 2.08 x 107

. 

In terrestrial environments, the Agency does not expect acute risk concerns for endangered mammals or

avian species.

Listed Species

a. Taxonomic Groups Potentially at Risk

For the aquatic species (fish and invertebrates) evaluated in this risk assessment, the acute RQs exceeded

the LOC for listed species for many of the crop uses and exposure scenarios considered. The registrant

must provide information on the proximity of Federally listed endangered species to the pyrethrins use

sites. This requirement may be satisfied in one of three ways: 1) having membership in the FIFRA

Endangered Species Task Force (Pesticide Registration Notice 2000-2); 2) citing FIFRA Endangered

Species Task Force data; or 3) independently producing these data, provided the information is of

sufficient quality to meet FIFRA requirements. The information will be used by the OPP Endangered

Species Protection Program to develop recommendations to avoid adverse effects to listed species. 

b. Action Area

For listed species assessment purposes, the action area is considered to be the area affected directly or

indirectly by the Federal action and not merely the immediate area involved in the action. At the initial

screening-level, the risk assessment considers broadly described taxonomic groups and so conservatively

assumes that listed species within those broad groups are collocated with the pesticide treatment area.

This means that terrestrial plants and wildlife are assumed to be located on or adjacent to the treated site

and aquatic organisms are assumed to be located in a surface water body adjacent to the treated site.

The assessment also assumes that the listed species are located within an assumed area which has the

relatively highest potential exposure to the pesticide, and that exposures are likely to decrease with
-103-

distance from the treatment area. Section III Analysis (A. Use Characterization) of this risk assessment

presents the pesticide use sites that are used to establish initial collocation of species with treatment

areas. 

If the assumptions associated with the screening-level action area result in RQs that are below the listed

species LOCs, a "no effect" determination conclusion is made with respect to listed species in that taxa,

and no further refinement of the action area is necessary. Furthermore, RQs below the listed species

LOCs for a given taxonomic group indicate no concern for indirect effects upon listed species that

depend upon the taxonomic group covered by the RQ as a resource. However, in situations where the

screening assumptions lead to RQs in excess of the listed species LOCs for a given taxonomic group,

a potential for a "may affect" conclusion exists and may be associated with direct effects on listed species

belonging to that taxonomic group or may extend to indirect effects upon listed species that depend upon

that taxonomic group as a resource. In such cases, additional information on the biology of listed

species, the locations of these species, and the locations of use sites could be considered to determine the

extent to which screening assumptions regarding an action area apply to a particular listed organism.

These subsequent refinement steps could consider how this information would impact the action area for

a particular listed organism and may potentially include areas of exposure that are downwind and

downstream of the pesticide use site.

c. Indirect Effects Analysis

The Agency acknowledges that pesticides have the potential to exert indirect effects upon the listed

organisms by, for example, perturbing forage or prey availability, altering the extent of nesting habitat,

and creating gaps in the food chain. In conducting a screen for indirect effects, direct effect LOCs for

each taxonomic group are used to make inferences concerning the potential for indirect effects upon

listed species that rely upon non-endangered organisms in these taxonomic groups as resources critical

to their life cycle.

Because screening-level acute RQs for mammals exceed the listed species acute LOCs, the Agency uses

the dose response relationship from the toxicity study used for calculating the RQ to estimate the

probability of acute effects associated with an exposure equivalent to the EEC (see Probit Analysis

below). This information serves as a guide to establish the need for and extent of additional analysis that

may be performed using Services-provided “species profiles” as well as evaluations of the geographical

and temporal nature of the exposure to ascertain if a “not likely to adversely affect” determination can

be made. The degree to which additional analyses are performed is commensurate with the predicted

probability of adverse effects from the comparison of the dose response information with the EECs. The

greater the probability that exposures will produce effects on a taxa, the greater the concern for potential

indirect effects for listed species dependent upon that taxa, and therefore, the more intensive the analysis

on the potential listed species of concern, their locations relative to the use site, and information

regarding the use scenario (e.g., timing, frequency, and geographical extent of pesticide application).

Probit Slope Analysis

The probit slope response relationship is evaluated to calculate the chance of an individual event

corresponding to the listed species acute LOCs. If information is unavailable to estimate a slope for a

particular study, a default slope assumption of 4.5 is used as per original Agency assumptions of typical

slope cited in Urban and Cook (1986). 
-104-

Freshwater fish

After an analysis of raw data from the acute toxicity studies (MRID 430823-03 and 430823-04) with

Rainbow Trout, one slope estimate was determined. A default slope of 4.5 was used for data from

MRID 430823-03 (FEK-99 as active ingredient) and a slope of 6 was used for data from MRID 430823-

04 (formulated product, pyrenone crop spray). Based on the default slope estimate of 4.5, the

corresponding estimate chance of individual mortality for freshwater fish following pyrethrins exposure

is 1 in 4.17 x 108

. The slope from the other study (MRID 430823-04) is 6 and the estimate of chance

of individual mortality following pyrethrins exposure is 1 in 3.34 X 1014. The lower and upper bound

estimate of the slope from MRID 430823-04 are -0.57 and 12.59, which provided an individual chance

mortality range of 1 in 13 and 1 in 1.0 X 1016, respectively. RQ exceedances that occurred for

freshwater fish, ranged from 0.07 to 0.5 compared to the LOC (0.05). The estimated individual

mortality associated with the calculated RQ values (0.07 to 0.5 ) range from 1 in 3.34 X 1014 to 1 in 4.17

x 108

.

Estuarine/ marine fish

After an analysis of raw data from the acute toxicity studies with Sheepshead Minnow (MRID 430823-

07 and 430823-08) two slope estimates were determined. The slope from the study done with the

technical grade active ingredient (MRID 430823-04) is 13.7 and the estimate of chance of individual

mortality following pyrethrins exposure is 1.0 X 1016. The lower and upper bound estimate of that

slope are 6.95 and 19.41, which provided an individual chance mortality range of 1 in 1.0 X 1016 for

both bounds. The slope from the study done with the formulated product (MRID 430823-08) is 8.35

and the estimate of chance of individual mortality following pyrethrins exposure is 1.0 X 1016. The

lower and upper bound estimate of that slope are 5.08 and 11.63, which provided an individual chance

mortality range of 1 in 2.56 X 1010 to 1 in 1.0 X 1016. RQ exceedances that occurred for estuarine/

marine fish, ranged from 0.05 to 0.17 compared to the LOC (0.05). The estimated individual mortality

associated with the calculated RQ values (0.05 to 0.17 ) is 1.0 X 1016.

Freshwater invertebrates 

After an analysis of raw data from the acute toxicity studies with daphnids (MRID 430823-05 and

430823-06) slope estimate were identified. A default slope of 10.3 was used from associated with the

technical grade active ingredient (MRID 430823-05) and a slope of 6.7 was taken from data with the

formulated product (MRID 430823-06). Based on the slope estimate of 10.3, the corresponding estimate

chance of individual mortality for freshwater invertebrates following pyrethrins exposure is 1 in 1.0 x

1016; and based on the slope estimate of 6.7, the corresponding chance of individual mortality for

freshwater invertebrates following exposure to the formulated product is 1 in 8.44 x 109

. The lower and

upper bound estimate of the slopes from MRID 430823-05 and MRID 430823-06 range from 14.2 to

9.8 and from 6.43 to 3.3 respectively. These slopes provided an individual chance mortality range of

1 in 1.0 x 1016 (technical grade active ingredient) to 1 in 1.0 X 1016 to 1 in 1.07 x 105

 (formulation). 

RQ exceedances that occurred for freshwater invertebrates, ranged from 0.05-0.24 (formulation) to 

0.03-0.24 (TGAI) compared to the LOC (0.05). The estimated individual mortality associated with the

calculated RQ values (0.03 - 0.41) range from 1 in 1.0 X 1016 to 1 in 8.44 x 109.

Estuarine/ marine invertebrates

After an analysis of raw data from the acute toxicity studies with Mysid shrimp (MRID 430823-11 and

430823-12) slope estimates were identified. A default slope of 4.5 was used for data associated with

the formulated product (MRID 430823-12) because there was no slope estimate from the study. A slope

of 4.1was taken from data with the technical grade active ingredient (MRID 430823-11). Based on the
-105-

default slope estimate of 4.5, the corresponding chance of individual mortality for estuarine/ marine

invertebrates following exposure from the formulation is 1 in 4.17 x 108

; and based on the slope

estimate of 4.1, the corresponding chance of individual mortality for estuarine/marine invertebrates

following exposure to the technical grade active ingredient is 1 in 2.08 x 107

. The lower and upper

bound estimate of the slopes from MRID 430823-11 range from 0.27 to 7.93. These slopes provided

an individual chance mortality range of 1 in 2.8 to 1 in 1.0 X 1016. RQ exceedances that occurred for

estuarine/ marine invertebrates, ranged from 19.79-2.50 (formulation) to 1.98-0.25 (TGAI) compared

to the LOC (0.05). The estimated individual mortality associated with the calculated RQ values (0.25

to 19.79) range from 1 in 4.17 x 108

 to 1 in 1 in 2.08 x 107.

d. Critical Habitat

In the evaluation of pesticide effects on designated critical habitat, consideration is given to the physical

and biological features (constituent elements) of a critical habitat identified by the U.S Fish and Wildlife

and National Marine Fisheries Services as essential to the conservation of a listed species and which may

require special management considerations or protection. The evaluation of impacts for a screening

level pesticide risk assessment focuses on the biological features that are constituent elements and is

accomplished using the screening-level taxonomic analysis (risk quotients, RQs) and listed species levels

of concern (LOCs) that are used to evaluate direct and indirect effects to listed organisms. This

screening-level risk assessment for critical habitat provides a listing of potential biological features that,

if they are constituent elements of one or more critical habitats, would be of potential concern. 

C. Description of Assumptions, Uncertainties, Strengths, and Limitations

1. Assumptions and Limitations Related to Exposure For All Taxa

There are a number of areas of uncertainty in the aquatic and terrestrial risk assessments. The toxicity

assessment for terrestrial and aquatic animals is limited by the number of species tested in the available

toxicity studies. Use of toxicity data on representative species does not provide information on the

potential variability in susceptibility to acute and chronic exposures. 

This screening-level risk assessment relies on labeled statements of the maximum rate of pyrethrins

application, the maximum number of applications, and the shortest interval between applications.

Together, these assumptions constitute a maximum use scenario. The frequency at which actual uses

approach these maximums is dependant on resistance to the insecticide, timing of applications, and

market forces.

2. Assumptions and Limitations Related to Exposure For Aquatic Species

For an acute risk assessment, there is no averaging time for exposure. An instantaneous peak

concentration, with a 1 in 10 year return frequency, is assumed. The use of the instantaneous peak

assumes that instantaneous exposure is of sufficient duration to elicit acute effects comparable to those

observed over more protracted exposure periods tested in the laboratory, typically 48 to 96 hours. In

the absence of data regarding time-to-toxic event analyses and latent responses to instantaneous

exposure, the degree to which risk is overestimated cannot be quantified. However, this constitutes a

conservative approach in the analysis of a relatively labile chemical that is used in multiple scenarios.

For PRZM/ EXAMS, thirteen scenarios were selected to represent a variety of uses, and use sites within

the Continental US. Furthermore, additional special runs were performed to represent typical application

interval, and to distinguish spray drift from runoff.
-106-

3. Assumptions and Limitations Related to Exposure For Terrestrial Species

The data available to support the exposure assessment for pyrethrins is substantially complete, with the

exception of a foliar dissipation study, which is an input variable for Tier 1 modeling of risks to birds

and mammals (i.e., T-REX). The terrestrial modeling was conducted with a foliar half-life of 1 - 14

days, which represent values calculated for phenothrin and pyrethrin, respectively, and may not be a

realistic foliar half-life for this compound. Photolysis data (both aqueous and soil) suggest that

pyrethrins undergo photolysis in the environment rapidly with half-lives of several hours to about a day.

Aerboic biodegradation also occurs rapidly with half-lives o the order of several days. Therefore, the

35 day half-life may be too high. 

For screening terrestrial risk assessments, a generic bird or mammal is assumed to occupy either the

treated field or adjacent areas receiving pesticide at a rate commensurate with the treatment rate on the

field. The actual habitat requirements of any particular terrestrial species are not considered, and it is

assumed that species occupy, exclusively and permanently, the treated area being modeled. This

assumption leads to a maximum level of exposure in the risk assessment. 

Screening-level risk assessments for spray applications of pesticides consider dietary exposure alone.

Other routes of exposure, not considered in this assessment, are discussed below:

Incidental soil ingestion exposure

This risk assessment does not consider incidental soil ingestion. Available data suggests that up to 15%

of the diet can consist of incidentally ingested soil depending on the species and feeding strategy. Since

pyrethrins may adsorb to soils, this may be an important exposure pathway. 

Inhalation exposure

The screening risk assessment does not consider inhalation exposure. Such exposure may occur through

three potential sources: (1) spray material in droplet form at the time of application (2) vapor phase

pesticide volatilizing from treated surfaces, and (3) airborne particulate (soil, vegetative material, and

pesticide dusts).

Available data suggest that inhalation exposure at the time of application is not an appreciable route of

exposure for birds. According to research on mallards and bobwhite quail, respirable particle size in

birds (particles reaching the lung) is limited to a maximum diameter of 2 to 5 microns. The spray droplet

spectra covering the majority of pesticide application situations (AgDrift model scenarios for very-fine

to coarse droplet applications) suggests that less than 1% of the applied material is within the respirable

particle size.

Theoretically, inhalation of pesticide active ingredient in the vapor phase may be another source of

exposure for some pesticides under some exposure situations. However, considering the low vapor

pressure value, it is very unlikely that pyrethrins will exist in the gaseous phase at levels high enough

to cause any adverse effects via inhalation.

The impact from exposure to dusts contaminated with the pesticide cannot be assessed generically as

partitioning issues related to application site soils and chemical properties render the exposure potential

from this route highly situation-specific.
-107-

Dermal Exposure

The screening assessment does not consider dermal exposure, except as it is indirectly included in

calculations of RQs based on lethal doses per unit of pesticide treated area. Dermal exposure may occur

through three potential sources: (1) direct application of spray to terrestrial wildlife in the treated area

or within the drift footprint, (2) incidental contact with contaminated vegetation, or (3) contact with

contaminated water or soil.

The available measured data related to wildlife dermal contact with pesticides are extremely limited. The

Agency is actively pursuing modeling techniques to account for dermal exposure via direct application

of spray and by incidental contact with vegetation.

Drinking Water Exposure

Drinking water exposure to a pesticide active ingredient may be the result of consumption of surface

water or consumption of the pesticide in dew or other water on the surfaces of treated vegetation. For

pesticide active ingredients with a potential to dissolve in runoff, puddles on the treated field may contain

the chemical. Given that pyrethrins are not soluble in water and do adsorb appreciably to suspended

solids and sediment in the water column, there exists the potential for exposure to pyrethrins from

drinking water.

Dietary Intake - The Differences Between Laboratory and Field Conditions

The acute and chronic characterization of risk rely on comparisons of wildlife dietary residues with LC50

or NOAEC values expressed in concentrations of pesticides in laboratory feed. These comparisons

assume that ingestion of food items in the field occurs at rates commensurate with those in the

laboratory. Although the screening assessment process adjusts dry-weight estimates of food intake to

reflect the increased mass in fresh-weight wildlife food intake estimates, it does not allow for gross

energy and assimilative efficiency differences between wildlife food items and laboratory feed.

On gross energy content alone, direct comparison of a laboratory dietary concentration- based effects

threshold to a fresh-weight pesticide residue estimate would result in an underestimation of field exposure

by food consumption by a factor of 1.25 - 2.5 for most food items. Only for seeds would the direct

comparison of dietary threshold to residue estimate lead to an overestimate of exposure.

Differences in assimilative efficiency between laboratory and wild diets suggest that current screening

assessment methods do not account for a potentially important aspect of food requirements. Depending

upon species and dietary matrix, bird assimilation of wild diet energy ranges from 23 - 80%, and

mammal's assimilation ranges from 41 - 85% (U.S. Environmental Protection Agency, 1993). If it is

assumed that laboratory chow is formulated to maximize assimilative efficiency (e.g., a value of 85%),

a potential for underestimation of exposure may exist by assuming that consumption of food in the wild

is comparable with consumption during laboratory testing. In the screening process, exposure may be

underestimated because metabolic rates are not related to food consumption.

Finally, the screening procedure does not account for situations where the feeding rate may be above or

below requirements to meet free living metabolic requirements. Gorging behavior is a possibility under

some specific wildlife scenarios (e.g., bird migration) where the food intake rate may be greatly

increased. Kirkwood (1983) has suggested that an upper-bound limit to this behavior might be the

typical intake rate multiplied by a factor of 5.
-108-

In contrast is the potential for avoidance, operationally defined as animals responding to the presence

of noxious chemicals in their food by reducing consumption of treated dietary elements. This response

is seen in nature where herbivores avoid plant secondary compounds.

4. Assumptions and Limitations Related to Effects Assessment

The data available to support the aquatic and terrestrial effects assessment is incomplete. Chronic

toxicity studies with freshwater organisms show that the most sensitive endpoint is growth (length and

dry weight) for fish and reproduction for invertebrates. No data were submitted to evaluate the chronic

risk to estuarine/marine fish or invertebrates. Since pyrethrins tend to partition to the sediment

compartment data regarding the toxicity of pyrethrins to sediment dwelling organisms is important.

Pyrethrins appear to be practically non-toxic to avian species on a subacute oral and dietary basis.

Chronic avian risk could not be evaluated because no reproductive toxicity data were submitted.

Toxicity studies with rats suggest that pyrethrins can be categorized as slightly toxic to small mammals

on an acute oral basis. Acute toxicity studies with honey bees show that pyrethrins are highly toxic on

both a contact and an oral basis.

Age class and sensitivity of effects thresholds

It is generally recognized that test organism age may have a significant impact on the observed sensitivity

to a toxicant. The screening risk assessment acute toxicity data for fish are collected on juvenile fish

between 0.1 and 5 grams. Aquatic invertebrate acute testing is performed on recommended immature

age classes (e.g., first instar for daphnids, second instar for amphipods, stoneflies and mayflies, and third

instar for midges). Similarly, acute dietary testing with birds is also performed on juveniles, with

mallard being 5-10 days old and quail 10-14 days old.

Testing of juveniles may overestimate toxicity at older age classes for pesticidal active ingredients, that

act directly (without metabolic transformation) because younger age classes may not have the enzymatic

systems associated with detoxifying xenobiotics. The screening risk assessment has no current

provisions for a generally applied method that accounts for this uncertainty. In so far as the available

toxicity data may provide ranges of sensitivity information with respect to age class, the risk assessment

uses the most sensitive life-stage information as the conservative screening endpoint.

Use of the Most Sensitive Species Tested

Although the screening risk assessment relies on a selected toxicity endpoint from the most sensitive

species tested, it does not necessarily mean that the selected toxicity endpoints reflect sensitivity of the

most sensitive species existing in a given environment. The relative position of the most sensitive species

tested in the distribution of all possible species is a function of the overall variability among species to

a particular chemical. In the case of listed species, there is uncertainty regarding the relationship of the

listed species' sensitivity and the most sensitive species tested.

The Agency is not limited to a base set of surrogate toxicity information in establishing risk assessment

conclusions. The Agency also considers toxicity data on non-standard test species when available. 

5. Assumptions Associated With the Acute LOCs

The risk characterization section of the assessment document includes an evaluation of the potential for
-109-

individual effects at an exposure level equivalent to the LOC. This evaluation is based on the median

lethal dose estimate and dose/response relationship established for the effects study corresponding to each

taxonomic group for which the LOCs are exceeded. 

V. Literature Cited

For list of literature cited, refer to Appendix K.

ACKNOWLEDGMENT

The Environmental Fate and Effects Division would like to thank Syracuse Environmental

Research Associates, Inc. (SERA), and Syracuse Research Corporation for their assistance in

developing this pyrethrins risk assessment. Thanks to the following persons for their

collaboration in making this product: Antonio Quiñones-Rivera, Mario Citra, Molly Ramsey,

Tim Negley, and Phil Goodrum.