### UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON D.C., 20460

OFFICE OF PREVENTION, PESTICIDES AND
TOXIC SUBSTANCES



### PC Code: 128825

DP Barcode:D342574

MEMORANDUM

DATE: October 16, 2007

SUBJECT: Section 24C (Special Local Need) for Use of Bifenthrin (CAPTURE 2EC) to control larval dragonflies in commercially operated freshwater bait and ornamental fish ponds in the State of Arkansas.

TO: George Larocca, RM13 BeWanda Alexander, RM Reviewer Emergency Exemption Section (S7913)

FROM: José Luis Meléndez, Chemist N.E. Federoff, Wildlife Biologist, Team Leader

Environmental Risk Branch V Environmental Fate and Effects Division (7507P)

THROUGH: Mah Shamim, Chief

Environmental Risk Branch V Environmental Fate and Effects Division (7507P)

I. INTRODUCTION

The Arkansas State Plant Board is requesting a Section 24C (Special Local Need) for use of the synthetic pyrethroid Bifenthrin (CAPTURE 2EC insecticide/miticide) to control larval dragonflies in commercially operated freshwater bait and ornamental fish ponds in the State of Arkansas. Dragonfly nymphs are very efficient predators of small fish. A maximum of 1 application at the rate of 1-2 ppb may be made using ground equipment (no aerial applications). This use would be in non-watershed ponds that are not subject to significant outflow into adjacent waters.

Based on available effects data and the solubility limit of bifenthrin in water (0.014 ppb), estimated risk quotient (RQ) values exceeded th e endangered acute LOC for freshwater fish (RQ = 0.09) and chronic risk for freshwater invertebrates (RQ = 10.77).

Currently, EFED does not assess risk to non-target insects. Results of acceptable studies are

### used for recommending appropriate label precautions. Based on the results of a single study in honey bees (LD 50 

### of 0.015 μ g a.i./bee), bifenthrin is classified as highly toxic on an acute contact basis. This study suggests that the acute toxicity to non- target beneficial endangered insects may also be of concern should exposure actually occur.

Toxicity data are not available for terrestrial and semi-aquatic plants; thus, risks associated with bifenthrin exposure to terrestrial plants ca nnot be assessed. Furthermore, a review of bifenthrin’s mode of action (neural toxin) suggests that direct toxicity to plants should not be an

issue of concern.

II. ENVIRONMENTAL FATE CHARACTERIZATION

Bifenthrin is a synthetic pyrethroid. Its struct ure has three rings, two phenyl rings attached to each other by a single bond, and a cyclopropyl ring. The molecule has some chiral centers, and a double bond that bring isomer possibilities. According to the Capture 2EC Insecticide/Miticide label, a minimum of 97% consists of cis isomers (see figure above).

Studies conducted on bifenthrin indicate that it is persistent under most conditions and bioaccumulative. It appears that a route of degradation for the chemical is aerobic metabolism. Bifenthrin is relatively stable to hydrolysis at all pH’s. It is relatively stable to aqueous and soil photolysis and degrades slowly under both aerobic and anaerobic soil metabolism conditions (half-life range 97-250 days in 3 soils, and relatively stable, respectively). Bifenthrin is immobile in four soils tested (K OC 

### range 131,000 to 275,000; FAO mobility classification). Field studies show a pattern consistent with the laboratory studies, with relatively high persistence (half-lives ranging from 78 to 345 days in 10 field trials) and low mobility of the chemical in soil. In aquatic environments, it appears that residues of bifenthrin persist in pond sediments (and in the water column) for extended periods (at least 12 months of monitoring). No

### major metabolites were observed (>10% of the applied) in any of the laboratory studies. The high octanol/ water partition coefficient suggests that bifenthrin will bioconcentrate in aquatic organisms. Bifenthrin was highly bioaccumulative in fish with slow depuration. The very low water solubility and hydrophobic nature of bifenthrin leads to strong soil adsorption and a tendency to partition to sediment in aquatic systems.

Bifenthrin has a vapor pressure of 1.8x10 –7 

### mmHg, water solubility of 0.0140 ppb, and an estimated Henry’s law constant of 7.2x10 -3 

### atm-m 3 

### /mol. Based upon its Henry’s law constant and vapor pressure, bifenthrin is expected to have a moderate to low potential for volatilization from soil and water surfaces. Bifenthrin’s potential for volatilization is reduced significantly because it adsorbs strongly to soils, suspended solids, sediment and organic matter in the water column. A laboratory volatility study showed a maximum volatility at 40°C of 5.07x10 -4 

### μ g/cm 2


### hr (average at 14 days), a relatively low value.

Bifenthrin can be spray applied by ground or aerially on agricultural settings. A buffer region is label recommended; however, under a high end drift scenario, substantial amounts of the chemical can reach adjacent bodies of water via spray drift. Furthermore, substantial fractions of the applied bifenthrin should be available for runoff from several weeks to several months. Due to its low solubility (0.014 ppb) and high level of binding it appears that bifenthrin would remain bound to the soils during run-off events, and that the chemical would reach surface waters if the run-off event is accompanied by erosion. Once bifenthrin reaches surface water, the fate of the chemical is of concern since bifenthrin is very toxic to fish and aquatic invertebrates. Due to its high level of binding, bifenthrin would remain bound to the sediments and would dissolve only very slowly into the water column. Organisms that live near the sediments may be particularly at risk. The sediments may serve as reservoirs of bifenthrin, where it will persist.

A supplemental aquatic field dissipation study employing a site in Alabama showed that bifenthrin in aquatic environments (a pond) persists for extended periods of time. It was found throughout the 12 months of monitoring after the last pesticide application, that residues were observed in the water column and in the sediment, with no clear pattern of decline.

On the other hand, bifenthrin is not likely to reach subsurface soil environments or ground waters. Various terrestrial field dissipation studies confirm that bifenthrin remains mostly in the upper soil level.

Due to the slow dissipation pathways for bifent hrin, no transformation products were observed to be higher than 10% of the applied in any of the laboratory studies.

The major uncertainties with respect to the environmental fate studies on bifenthrin are related to the extremely low solubility of bifenthrin and the problems found when the registrant performed these studies. The hydrolysis, aqueous photolysis, and batch equilibrium studies were performed in unusually high concentrations of acetonitrile. The cosolvent may have had an effect on the results. Furthermore, the batch equilibrium studies were performed at a single concentration (a Freundlich isotherm was not developed). The EFED had to rely on a single point result.

### III. EFFECTS CHARACTERIZATION

Terrestrial

Birds, Acute and Subacute

An acute oral toxicity study using the technical grade of the active ingredient (TGAI) is required to establish the toxicity of bifenthrin to birds. The preferred test species is either mallard duck (a waterfowl) or bobwhite quail (an upland gamebird). Results of this test are

tabulated below.

Avian Acute Oral Toxicity

Species % ai LD50 (mg/kg) Toxicity Category MRID No.

Author/Year Study

Classification

Mallard duck (Anas platyrhynchos) 88.3 > 2,150 Practically nontoxic ACC251727

Fletcher/1984 Core

Northern Bobwhite quail (Colinus virginianus) 88.3 1,800 Slightly toxic ACC251727

Fletcher/1984 Core



### Since the LD50 falls in the range of 1,800 - 2,150 mg/kg, bifenthrin is categorized as slightly to practically nontoxic to avian species on an acute oral basis.

Two subacute dietary studies using the TGAI are required to establish the toxicity of bifenthrin to birds. The preferred test species are mallard duck and Bobwhite quail. Results of

these tests are tabulated below.

Avian Subacute Dietary Studies

Species % ai 5-Day LC 50 (ppm) Toxicity Category MRID No.

Author/Year Study

Classification

Northern Bobwhite quail (Colinus virginianus) 99.3 4,450 Slightly toxic ACC251727

Fletcher/1984 Core

Mallard duck (Anas platyrhynchos) 88.3 1,280 Slightly toxic ACC251727

Fletcher/1984 Core



### Since the LC 50 

### falls in the range of 1,280 and 4,450 ppm, bifenthrin is categorized as slightly to practically non toxic to avian species on a subacute dietary basis.

Birds, Chronic

Avian reproduction studies using the TGAI are required for bifenthrin because birds may be subject to repeated or continuous exposure to the pesticide, especially preceding or during the breeding season. Bifenthrin is stable in the environment ( half-life of 129-250 days aerobic soil metabolism) to the extent that potentially toxic amounts may persist in animal feed. The preferred test species are mallard duck and bobwhite quail. Results of these tests are tabulated

below.

### Avian Reproduction

Species % ai NOAEC/LOAEC (ppm) LOAEC Endpoints Mrid. No.

Author/Year Study

Classification

Northern Bobwhite quail (Colinus virginianus) 88.3 75/> 75 no adverse reproductive

effect 264644 Huntington/

1987 Core

Mallard duck (Anas platyrhynchos) 88.3 75/>75 no adverse reproductive

effect 264644 Huntington/

1987 Core



### Bifenthrin exposure of >75 ppm to Bobwhite quail or mallard duck did not produce chronic effects during reproduction studies.

Mammals, Acute and Chronic

Wild mammal testing is required on a case-by-case basis, depending on the results of lower tier laboratory mammalian studies, intended use pattern and pertinent environmental fate characteristics. In most cases, rat or mouse toxicity values obtained from the Agency's Health Effects Division (HED) substitute for wild mammal testing. These toxicity values are reported

below.

Mammalian Acute and Chronic Toxicity

Species % ai Test Type Toxicity

Value MRID No.

Laboratory rat (Rattus norvegicus) 91.4 Acute oral LD 50 = 53.8 - 70.1 mg/kg 00132519

Laboratory rat (Rattus norvegicus) 25.1 Acute

Inhalation LC 50 = 1.9 mg/L/4hrs 00144256

2-Generation reproduction laboratory rat (Rattus norvegicus) 88.35 Chronic NOAEL/LOAEL 30/60 ppm 005336



### An analysis of the results indicate that bifenthrin is categorized as moderately toxic to small mammals on an acute oral basis ( LD 50 

### = 53.8 - 70.1 mg/kg). Chronic reproductive effects are expected to occur at > 30 ppm (maternal weight decrease).

Insects

A honey bee acute contact study using the TGAI is required for bifenthrin because of its use may result in honey bee exposure. Results of this test are tabulated below.

### Nontarget Insect Acute Contact Toxicity

Species % ai LD50 (μg/bee) Toxicity Category MRID No.

Author/Year Study

Classification

Honey bee (Apis mellifera ) 2 EC < 1.0 Highly toxic VAOTALO1

Atkins/1981 Core

Honey bee (Apis mellifera ) 0.8 EC 0.015 Highly toxic VAOTALO1

Atkins/1981 Core



### An analysis of the results indicate that bifenthrin appears to be very toxic to honey bees on an acute contact basis (LD 50 

### = 0.0146 ug/bee).

Aquatic Freshwater Fish, Acute Two freshwater fish toxicity studies using the TGAI are required to establish the acute toxicity of bifenthrin to fish. The preferred test species are rainbow trout (a coldwater fish) and bluegill sunfish (a warmwater fish). Results of these tests are tabulated below.

Freshwater Fish Acute Toxicity

Species % ai 96-hour LC 50 (ppb) Toxicity Category MRID No.

Author/Year Study

Classification

Rainbow trout (Oncorhynchus mykiss) 88.3 0.15 Highly toxic ACC251727 Hoberg/1983 Core

Bluegill sunfish (Lepomis macrochirus) 88.3 0.35 Highly toxic ACC251727 Hoberg/1983 Core



### Acute toxicity values for bifenthrin to fres hwater fish show that the compound is highly toxic (0.15 - 0.35 ppb). EFED will use the worst case value (LC50 =0.15 ppb) for evaluating acute toxic exposure to freshwater fish.

Freshwater Fish, Chronic

A freshwater fish early life-stage test using the TGAI is required for bifenthrin because the end-use product may be applied directly to water or is expected to be transported to water from the intended use site (i.e cotton), and the following conditions are met: (1) the bifenthrin is intended for use such that its presence in water is likely to be continuous or recurrent regardless of toxicity, studies on aquatic invertebrates showed reproductive effects (daphnid 21-day LOEC = 0.003 ppb), pesticide is persistent in water (e.g. half-life of 129-250 days aerobic soil metabolism). Results of this test are tabulated below.

Freshwater Fish Early Life-Stage Toxi city Under Flow-Through Conditions

Species % ai NOAEC/LOAEC (ppb) Toxicity
category Endpoints

Affected MRID No.

Author/Year Study

Classification

Fathead minnow

(Pimephales promelas) 70 0.04/0.096 Very highly

toxic Growth 40791301

1988 Core

### Chronic exposure of 0.096 ppb bifenthrin, has th e potential for toxicity concerns to fish early life stages (i.e fathead minnow).

Freshwater Invertebrates, Acute

A freshwater aquatic invertebrate toxicity test using the TGAI is required to establish the toxicity of bifenthrin to aquatic invertebrates. The preferred test species is Daphnia magna

. Results of this test are tabulated below.

Freshwater Invertebrate Acute Toxicity

Species % ai 48-hour EC 50 (ppb) Toxicity
category MRID No.

Author/Year Study

Classification

Waterflea ( Daphnia

magna ) 88.3 1.6 Very highly

toxic 41156501 Surprenant/

1989 Core



### The resulting acute 48-hour EC 50 

### value of 1.6 ppb shows that bifenthrin is very highly toxic to aquatic invertebrates (daphnids) on an acute basis.

Freshwater Invertebrate, Chronic

A freshwater aquatic invertebrate life-cycle te st using the TGAI is required for bifenthrin since the end-use product may be applied directly to water or is expected to be transported to water from the intended use site, and the following conditions are met: (1) bifenthrin presence in water is likely to be continuous or recurrent, (2) aquatic acute LC 50 

### or EC 50 

### are less than 1 mg/L (i.e.1.6 ppb), or, (3) the EEC in water is equal to or greater than 0.01 of any acute EC 50 

### or LC 50 

### value. Physicochemical properties indicate cumulative effects, and bifenthrin is persistent in water ( i.e. , half-life of 129-250 days aerobic soil metabolism). The preferred test species is Daphnia magna . Results of this test are tabulated below.

Freshwater Aquatic Invertebrate Chronic Toxicity

Species/Static

Renewal % ai 21-day

NOAEC/LOAEC (ppb) Endpoints

Affected MRID No.

Author/Year Study

Classification

Waterflea (Daphnia magna) 70 0.0013/0.003 Reduced growth

and # young/female 41156501

Battelle/1989 Core



### This compound has the potential for chronic toxicity to daphnids and possibly other freshwater invertebrates. Exposure to > 0.0013 ppb can result in reproductive effects that include reduced neonate growth and reduced number of young produced per female.

Estuarine and Marine Fish, Acute

Acute toxicity testing with estuarine/marine fi sh using the TGAI is required for bifenthrin because the end-use product is intended for direct application to the marine/estuarine environment or the active ingredient is expected to reach this environment because of its use in

### coastal counties. The preferred test species is sheepshead minnow. Results of these tests are

tabulated below.

Estuarine/Marine Fish Acute Toxicity

Species/Static % ai 96-hour LC50 (ppb) Toxicity Category MRID No.

Author/Year Study

Classification

Sheepshead minnow (Cyprinodon variegatus) 88.3 17.5 Very highly

toxic 264646

Battelle/1987 Core



### Since the LC 50 

### = 17.5 ppb, bifenthrin is categorized as highly toxic to estuarine/marine

fish on an acute basis.

Estuarine and Marine Fish, Chronic

An estuarine/marine early life-stage toxicity te st using the TGAI is required for bifenthrin because the end-use product is expected to transport to the estuarine/marine environment from the intended use site, and the pesticide is intended for use such that its presence in water is likely to be continuous or recurrent regardless of toxicity. The preferred test species sheepshead

minnow.

Estuarine and Marine Invertebrates, Acute

Acute toxicity testing with estuarine/marine invertebrates using the TGAI is required for bifenthrin because the end-use product is intended for direct application to the marine/estuarine environment or the active ingredient is expected to reach this environment because of its use in coastal counties (i.e.cotton). The preferred test species are mysid shrimp and eastern oyster.

Results of these tests are tabulated below.

Estuarine/Marine Invertebrate Acute Toxicity

Species % ai. 48-hour

EC50 (ppb) Toxicity Category MRID No.

Author/Year Study

Classification

Eastern oyster ( Crassostrea virginica ) 88.3 285 (embryos)

> 2.15 (spat) Very highly toxic 40383501

Ward and

Dose/1988 Core

Mysid (Americamysis bahia) 88.3 0.0040 Very highly toxic 264647

Battelle/1987 Core



### The data show that bifenthrin significantly reduced survival of oysters and mysid shrimp at concentrations that range from 0.004 - 285 ppb. This categorizes the compound as very highly

toxic to estuarine/marine invertebrates.

Estuarine and Marine Invertebrate, Chronic An estuarine/marine invertebrate life-cycle toxicity test using the TGAI is required for

### bifenthrin because the end-use product may be applied directly to the estuarine/marine environment or is expected to be transported to this environment from the intended use site (i.e. cotton), and the following conditions are met: (1) the pesticide is intended for use such that its presence in water is likely to be continuous or recurrent regardless of toxicity, (2) any aquatic

acute LC 50 

### or EC 50 

### is less than 1 mg/L (e.g.mysid EC 50 

### = 0.004 ppb), (3) the EEC in water is equal to or greater than 0.01 of any acute LC 50 

### or EC 50 

### value, or, (4) studies of other organisms indicate that the reproductive physiology of fish and/or invertebrates may be affected, physicochemical properties indicate cumulative effects, or the pesticide is persistent in water ( e.g. , half-life of 129-250 days aerobic soil metabolism). The preferred test species is mysid shrimp.

Toxicity to Plants

Terrestrial Plants Currently, terrestrial plant testing is not required for pesticides other than herbicides except on a case-by-case basis (e.g., labeling bears phytotoxicity warnings incident data or literature that demonstrate phytotoxicity). Therefore, EFED does not require terrestrial plant testing for

bifenthrin.

No data were identified on terrestrial plant testing with bifenthrin.

Aquatic Plants Aquatic plant testing (EC 50 

### Aquatic Plant Test: Guideline 122-2 (Tier I) is required for bifenthrin for the following reasons: (1) It has outdoor non-residential terrestrial uses. It is unlikely to move off-site by run-off (low solubility in water) however it may be applied to aquatic sites through leaching. The Tier I study as defined in the Pesticide Registration Rejection Rate Analysis (EPA 738-R-94-085 SD December 1994) requires the EC50 aquatic plant test for Lemna gibba and Selenastrum carpicornutum

.

No data were identified on aquatic plant testing with bifenthrin.

IV. RISK CHARACTERIZATION

Risk Estimation To evaluate the potential risk to non-target orga nisms from the proposed use of Bifenthrin, risk quotients (RQs) would normally be calculated from the ratio of estimated environmental concentrations (EECs) to toxicity values. RQs would then be compared to levels of concern (LOCs) used by the Office of Pesticide Programs to indicate potential risk to non-target organisms and the need to consider regulatory action. However, under the conditions of this use pattern, it is assumed that neither avian nor mammalian species should be exposed, so no assessment was needed. Also, since the proposed use is only in freshwater ponds, no assessment was needed for estuarine/marine organisms.

### Aquatic organisms acute and chronic RQ’s for bifenthrin. RQ values are based on the solubility limit of 0.014 ppb.

Organisms Exposure Species Toxicity value (ppb) EEC (ppb) RQ

Acute Rainbow trout LC 50 = 0.15 0.014 0.09 Freshwater

Fish Chronic Fathead

minnow NOAEC =0.04 0.014 0.35

Acute Daphnia magna EC 50 = 1.6 0.014 0.01 Freshwater

Invertebrates Chronic Daphnia

magna NOAEC =

0.0013 0.014 10.77



### Based on available effects data and the solubility limit of bifenthrin in water (0.014 ppb), estimated risk quotient (RQ) values exceeded the endangered acute LOC for freshwater fish (RQ = 0.09) and chronic risk for freshwater invertebrates (RQ = 10.77).

Currently, EFED does not assess risk to non-target insects. Results of acceptable studies are used for recommending appropriate label precautions. Based on the results of a single study in honey bees (LD 50 

### of 0.015 μ g a.i./bee), bifenthrin is classified as highly toxic on an acute contact basis. This study suggests that the acute toxicity to non- target beneficial endangered insects may also be of concern should exposure actually occur.

Toxicity data are not available for terrestrial and semi-aquatic plants; thus, risks associated with bifenthrin exposure to terrestrial plants ca nnot be assessed. Furthermore, a review of bifenthrin’s mode of action (neural toxin) suggests that direct toxicity to plants should not be an

issue of concern.

Risk Discussion Bifenthrin is a second generation synthetic pyrethroid that is persistent in the environment, readily binds to soils (Koc ≥ 131,000), and is stable to breakdown from sunlight. Generally there are no major breakdown products from the slow biode gradation of bifenthrin. The chemical also shows high bioccumulation potential and slow depur ation. Furthermore, it is highly toxic to aquatic animals. It is persistent and bioaccumulative.

EFED has completed a screening level risk assessment that suggests the potential for toxic environmental exposure that could present risk s to freshwater aquatic organisms (e.g., fish, crustacean, amphibians, etc.) and beneficial insect species. This screening level assessment shows that there is the potential for acute and chronic risk to aquatic life from exposure to bifenthrin in the water column, as well as from bifenthrin bound to the sediment (once bifenthrin reaches a water body it quickly partitions to particulate and settles onto the sediment where it can persist for several months).

Once in aquatic environment, the chemical may pose risk to non-target aquatic organisms (including benthic and epibenthic dwellers) because bifenthrin is very highly toxic to most fish and invertebrates. The Agency believes, however, that due to its high level of binding,

### bifenthrin is likely to remain bound to the sediments and would dissolve only very slowly into the water column. Organisms that live near or in the sediment may be particularly at risk if exposure should occur. Sediments may serve as reservoirs of bifenthrin, where it will persist. This was also shown in an aquatic field dissi pation study where residues of bifenthrin were observed during the 12 months monitoring period (with no discernable pattern of decline).

Bifenthrin is a neural toxic insecticide acti ng through direct contact and ingestion, having a slight repellent effect. The primary biological effects of bifenthrin and other pyrethroids on insects and vertebrates reflect inhibition of the correct firing of neurotransmitter delivery signals from one cell to another via nerve membrane inhibition of the voltage-gated Ca 2+ 

### channels coupled with a stimulatory effect on the voltage-gated Na + 

### channels (sodium ion channels). The pyrethroids (including bifenthrin) 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 sympto ms 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). Advancedelectrophysiological experiments using voltage clamp and patch clamp, together with ligandbinding 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, permethrin) and Type II (e.g., cypermethrin, 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).

Review of Incident Data There have been incidents reported for bifenthrin. Two aquatic incidents (I004439-076 and I003351-028) were reported as being probable for bi fenthrin. One involved a restricted use aerial application which killed an unknown number of organisms in NC. The second incident involved an unknown application method that killed 25 Catf ish in Imperial county in CA. A probable incident involving leafcutter bee mortality after an application to seed alfalfa was also reported but was catagorized as a misuse of the chemical. These incidents do show that aquatic organisms and bees may be adversely affected if exposed.

Endangered Species Based on available effects data and the solubility limit of bifenthrin in water (0.014 ppb), estimated risk quotient (RQ) values exceeded the endangered acute LOC for freshwater fish (RQ = 0.09) and chronic risk for freshwater invertebrates (RQ = 10.77).

Analysis of raw data from the aquatic acute toxi city studies for bifenthrin estimate slopes of 3.5 (95% C.I. 2.08 and 4.99) for freshwater fish, 1.69 (95% C.I. 1.35 and 2.03) for freshwater invertebrates, and a 4.5 default slope for estuarine/marine fish and for estuarine/marine invertebrates. Based on these slopes, the corresponding estimate chance of individual mortality

### following bifenthrin exposure is 1 in 3.79 x 10 5 

### for freshwater fish, 1 in 10 x 7.17 for freshwater invertebrates, and 1 in 4.17 x 10 8 

### for estuarine/marine fish and invertebrates.

To explore possible bounds to such estimates, the upper and lower values for the mean slope estimate can be used to calculate upper and lower estimates of the effects probability associated with the listed species LOC. These values are 1 in 2.94 x 10 2 

### to 1 in 2.35x10 for freshwater fish

and 1 in 2.53 to 1 in 2.42 x 10 2 

### for freshwater invertebrates.

Currently, EFED does not assess risk to non-target insects. Results of acceptable studies are used for recommending appropriate label precautions. Based on the results of a single study in honey bees (LD 50 

### of 0.015 μ g a.i./bee), bifenthrin is classified as highly toxic on an acute contact basis. This study suggests that the acute toxicity to non- target beneficial endangered insects may also be of concern should exposure actually occur.

Toxicity data are not available for terrestrial and semi-aquatic plants; thus, risks associated with bifenthrin exposure to terrestrial plants ca nnot be assessed. Furthermore, a review of bifenthrin’s mode of action (neural toxin) suggests that direct toxicity to plants should not be an

issue of concern.

### Endangered Species Listing: Freshwater Fish, Freshwater Invertebrates, Insects and Amphibians

An endangered species listing for the current use could not be generated because it is not associated with any crop.