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 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 (LD50 of 0.015 μg 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 cannot 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 structure 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 (KOC 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-m3

/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

μg/cm2

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 bifenthrin, 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 LC50

(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 LC50 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 LD50 = 53.8 - 70.1 

mg/kg 

00132519 

Laboratory rat 

(Rattus norvegicus)

25.1 Acute 

Inhalation 

LC50 = 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 ( LD50 = 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 (LD50 = 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 LC50

(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 freshwater 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 Toxicity 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 the 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 EC50

(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 EC50 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 test 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 LC50 or EC50 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 EC50 or LC50 

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 fish 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 LC50 = 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 test 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 LC50 or EC50 is less than 1 mg/L (e.g.mysid EC50 = 0.004 ppb), (3) the EEC in water is 

equal to or greater than 0.01 of any acute LC50 or EC50 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 (EC50 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 organisms 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 LC50 = 0.15 0.014 0.09 Freshwater 

Fish 

Chronic Fathead 

minnow 

NOAEC =0.04 0.014 0.35 

Acute Daphnia magna EC50 = 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 (LD50 of 0.015 μg 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 cannot 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 biodegradation of bifenthrin. The chemical also 

shows high bioccumulation potential and slow depuration. 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 risks 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 dissipation 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 acting 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 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). Advanced 

electrophysiological 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 bifenthrin. 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 Catfish 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 toxicity 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 105

 for freshwater fish, 1 in 10 x 7.17 for freshwater 

invertebrates, and 1 in 4.17 x 108

 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 102 to 1 in 2.35x10 for freshwater fish 

and 1 in 2.53 to 1 in 2.42 x 102

 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 (LD50 of 0.015 μg 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 cannot 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.