Bifenthrin is a pyrethroid insecticide used primarily against the red imported fire ant
by influencing its nervous system. It has a high toxicity to aquatic organisms. Although
it is listed as a restricted use chemical in the United States, it is allowed to be
sold for daily use, provided the product sold has a low concentration of bifenthrin. The
chemical was discovered and developed by FMC Corporation. Products containing bifenthrin
include Talstar, Maxxthor, Capture, Brigade, Bifenthrine, Ortho Home Defense Max, Bifen
IT, Bifen L/P, Torant, Zipak, Scotts LawnPro Step 3, Wisdom TC Flowable, FMC 54800, and
OMS3024.
Chemical properties Bifenthrin is poorly soluble in water and
often remains in soil. Its residual half-life in soil is between 7 days and 8 months, depending
on the soil type, with a low mobility in most soil types. Bifenthrin has the longest known
residual time in soil of insecticides currently on the market. It is a white, waxy solid with
a faint sweet smell. It is chemically synthesized in various forms, including powder, granules
and pellets. However, it is not naturally occurring.
Like other pyrethroids, bifenthrin is chiral; it has different enantiomers which can have
completely different effects on the human body, which is a chiral environment. Bifenthrin
is found in two enantiomers: 1S-cis-bifenthrin and 1R-cis-bifenthrin. 1S-cis-Bifenthrin is
3-4 times more toxic to humans than 1R-cis-bifenthrin, while the latter is more than 300 times more
effective as a pesticide. Toxicodynamics
The two types of pyrethroids are the ones with an α-cyanogroup and the ones without
an α-cyanogroup. The neurotoxicity of bifenthrin is based on the affinity with voltage-gated
sodium channels. The pyrethroids with an α-cyanogroup block the closing of the sodium-channel permanently,
causing the membrane to be permanently depolarized. The resting potential will not be restored,
and no further action potential can be generated. The pyrethroids without an α-cyanogroup,
to which bifenthrin belongs, are only able to bind to the sodium channel transiently.
This will result in so-called after potentials and eventual continuous firing of axons. The
resting potential is not affected by these pyrethroids.
Bifenthrin will open the sodium channel for a shorter period than other pyrethroids. The
mechanism in mammals and invertebrates is not different, but the effect on mammals is
much less due to higher body temperature, higher body volume, and lower affinity of
bifenthrin to sodium channels. Toxicokinetics
Numerous studies have been conducted on the half life of bifenthrin in soil, water, and
air under different conditions, such as aerobic or anaerobic, and at different temperatures
and pH. It is more likely to remain in the soil and not so much in water, nor in the
air. Because of the water-insolubility of bifenthrin, it will not rapidly cause contamination
of ground water. However, some contamination might occur by soil-bound bifenthrin to surface
water through runoff. For an overview of the environmental degradation of bifenthrin, see
figure below. The main path of degradation results in 4’-hydroxy bifenthrin.
Biotransformation Pyrethroids are much less toxic in mammals
than they are in insects and fish, because mammals have the ability to rapidly break
the ester bond in bifenthrin and break the substance into its inactive acid and alcohol
components: In humans and rats, bifenthrin is degraded by the cytochrome p450-family.
Use On a large scale, bifenthrin is often used
against red imported fire ants. It is also effective against aphids, worms, ants, gnats,
moths, beetles, grasshoppers, mites, midges, spiders, ticks, yellow jackets, maggots, thrips,
caterpillars, flies, and fleas. It is mostly used in orchards, nurseries, and homes. In
the agricultural sector, it is used in great amounts on certain crops, such as corn. About
70% of all hops and raspberries cultured in the United States are treated with bifenthrin.
Bifenthrin is not at all toxic to plants. Though it does not have a large toxicological
risk towards mammals or birds, bifenthrin is able to accumulate in food, so it might
be dangerous to mammals or birds in some scenarios. Toxicology
Toxicity in animals Mosquitoes
Bifenthrin is an effective pesticide to use against malaria and filaria vector mosquitoes.
It is still effective when a resistance to other pyrethroids is found. Mosquito nets
and indoor walls can be treated with bifenthrin to keep more mosquitoes away. Bifenthrin is
an effectively used insecticide, but the risk is high of it working only for a short time.
Mosquitoes can develop a resistance to it, as well.
Aquatic life Bifenthrin is hardly soluble in water, so
nearly all bifenthrin will stay in the sediment, but it is very harmful for the aquatic life.
Even in small concentrations, fish and other aquatic animals are affected by bifenthrin.
One of the reasons for the high sensitivity of fish is fish have a slow metabolism. Bifenthrin
will stay longer in the system of the fish. Another reason for the high sensitivity of
fish is the effect of bifenthrin as ATPase-inhibitor. The gills need ATP to control the osmotic
balance of oxygen. If the fish is no longer capable of taking up oxygen because ATP can
no longer be used, the fish will die. In cold water, bifenthrin is even more dangerous.
pH and calcium concentration are also factors that influence the toxicity. Vertebrates are
less sensitive to the effects of bifenthrin as ATPase-inhibitor.
Bees In bees, the lethal concentration of bifenthrin
is about 17 mg/l. At sublethal concentrations, bifenthrin reduces the fecundity of bees,
decreases the rate at which bee larvae develop into adults, and increases their immature
periods. Table of LD50 values
Toxicity in mammals Chemical consequences
Bifenthrin and other synthetic pyrethroids are being used in agriculture in increasing
amounts because of the high efficiency of these substances in killing insects, the low
toxicity for mammals, and good biodegradability. However, because of its success, they are
being used more often and high exposure of bifenthrin to humans can occur.
Cytotoxicity Scientific tests in vitro have concluded that
cytotoxic damage like DNA-breakdown and gene-mutation can be caused by bifenthrin. Cytotoxic effects
are not seen directly, but are more long-term. These effects can differ in severity based
on to which enantiomer the body is exposed and the dose. Cytotoxic damage in humans results
from increased oxidative stress, which leads to single-strand-DNA-breaking and degrading
of lipids in the plasma membrane and F-actin. The exact mechanisms included in this path
are not completely known yet, though several groups have found matching results regarding
increased reactive oxygen species production which induces apoptosis. Bifenthrin also activates
the LFA-1/ICAM function of T-cells. This function is a marker for inflammation. This means T-cells
are recognized by the body as if they were inflamed. This can ultimately lead to autoimmune
diseases, such as asthma, bronchitis, and arthritis, and cancer.
Neurotoxicity for humans Exposure to bifenthrin can be achieved either
by skin contact or ingestion. Skin contact is not toxic, apart from a slight tingling
sensation on the specific location of contact. Ingestion is toxic, although only slightly.
Commercially available bifenthrin, however, can induce toxic effects in those concentrations,
because the added chemicals which improve the sustainability either potentiate bifenthrin
or are toxic of their own. Symptoms of excessive exposure are nausea, headaches, hypersensitivity
for touch and sound, and irritation of the skin and the eyes.
Regulation The U.S. Environmental Protection Agency monitors
and regulates the use of pesticides in the United States. Bifenthrin is classified as
a restricted-use pesticide, meaning it is allowed to be legally sold only by certified
pesticide applicators. For everyday use, it is allowed to be sold in lower concentrations.
Bifenthrin has been approved for use against the Rasberry crazy ant in the Houston, Texas,
area, under a special "crisis exemption" from the Texas Department of Agriculture and the
EPA. The chemical is only approved for use in Texas counties experiencing "confirmed
infestations" of the newly imported, invasive ant species.
The EPA has classified bifenthrin as a class C carcinogen, a possible human carcinogen
based on a test with mice, which showed increased development of certain tumors.
An acute and chronic reference dose for bifenthrin has been established, based on animal studies.
The reference dose resembles the estimated quantity of a chemical which a person could
be exposed to every day without any appreciable risk of adverse health effects. The acute
reference dose for bifenthrin is 0.328 mg/kg bodyweight/day. The chronic reference dose
for bifenthrin is 0.013 mg/kg bodyweight/day. Bifenthrin was included in a biocide ban proposed
by the Swedish Chemicals Agency, because of its carcinogenic effect. This was approved
by the European Parliament in 2009. Pesticides containing bifenthrin were withdrawn from
use in the European Union. They have since been reinstated.
References
External links Pyrethrins and Pyrethroids Fact Sheet - National
Pesticide Information Center Pesticide Properties Database record for Bifenthrin