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EXTOXNET primary files maintained and archived at Oregon State
Revised June 1996
Trade and Other Names:
Abamectin is also known as Avermectin B1a. Trade names include
Affirm, Agri-Mek, Avermectin, Avid, MK 936, Vertimec, and Zephyr.
Abamectin is a General Use Pesticide (GUP). It is classified as
toxicity class IV - practically nontoxic, and has no
precautionary statement on its label.
Abamectin is a mixture of avermectins containing about 80%
avermectin B1a and 20% avermectin B1b. These two components, B1a
and B1b, have very similar biological and toxicological
properties. The avermectins are insecticidal/miticidal compounds derived from
the soil bacterium Streptomyces avermitilis. Abamectin is a
natural fermentation product of this bacterium. It acts as an
insecticide by affecting the nervous system of and paralyzing
insects. Abamectin is used to control insect and mite pests of
citrus, pear, and nut tree crops, and it is used by homeowners
for control of fire ants.
- Acute toxicity: Abamectin is highly
toxic to insects and may be highly toxic to mammals as
well . Emulsifiable concentrate formulations may
cause slight to moderate eye irritation and mild skin
irritation . Symptoms of poisoning observed in
laboratory animals include pupil dilation, vomiting,
convulsions and/or tremors, and coma [141,142]. Abamectin
acts on insects by interfering with the nervous system.
At very high doses, it can affect mammals, causing
symptoms of nervous system depression such as
incoordination, tremors, lethargy, excitation, and pupil
dilation. Very high doses have caused death from
respiratory failure . Abamectin is not readily
absorbed through skin. Tests with monkeys show that less
than 1% of dermally applied abamectin was absorbed into
the bloodstream through the skin . Abamectin does
not cause allergic skin reactions . The oral LD50
for abamectin in rats is 10 mg/kg, and in mice ranges
from 14 mg/kg to greater than 80 mg/kg [141,142]. The
oral LD50 for the product Avid EC in rats is 650 mg/kg
. The dermal LD50 for technical abamectin in rats and
rabbits is greater than 330 mg/kg .
- Chronic toxicity: In a 1-year study with
dogs given oral doses of abamectin, dogs at the 0.5 and 1
mg/kg/day doses exhibited pupil dilation, weight loss,
lethargy, tremors, and recumbency . Similar results
were seen in a 2-year study with rats fed 0.75, 1.5, or 2
mg/kg/day. Rats at all the dosage levels exhibited body
weight gains significantly higher than the controls. A
few individuals in the high dose group exhibited tremors
. When mice were fed 8 mg/kg/day for 94 weeks, the
males developed dermatitis and changes in blood formation
in the spleen, while females exhibited tremors and weight
- Reproductive effects: Rats given 0.40
mg/kg/day of abamectin had increased stillbirths,
decreased pup viability, decreased lactation, and
decreased pup weights . These data suggest that
abamectin may have the protential to cause reproductive
effects at high enough doses.
- Teratogenic effects: Abamectin produced
cleft palate in the offspring of treated mice and
rabbits, but only at doses that were also toxic to the
mothers . There were no birth defects in the
offspring of rats given up to 1 mg/kg/day .
Abamectin is unlikely to cause teratogenic effects except
at doses toxic to the mother.
- Mutagenic effects: Abamectin does not
appear to be mutagenic. Mutagenicity tests in live rats
and mice were negative. Abamectin was shown to be
nonmutagenic in the Ames test .
- Carcinogenic effects: Abamectin is not
carcinogenic in rats or mice. The rats were fed dietary
doses of up to 2 mg/kg/day for 24 months, and the mice
were up to 8 mg/kg/day for 22 months . These
represent the maximum tolerated doses.
- Organ toxicity: Animal studies indicate
that abamectin may affect the nervous system.
- Fate in humans and animals: Tests with
laboratory animals show that ingested avermectin B1a is
not readily absorbed into the bloodstream by mammals and
that it is rapidly eliminated from the body within 2 days
via the feces . Rats given single oral doses of
avermectin B1a excreted 69 to 82% of the dose unchanged
in the feces. The average half-life of avermectin B1a in
rat tissue is 1.2 days . Lactating goats given daily
oral doses for 10 days excreted 89% of the administered
avermectin, mainly in the feces. Less than 1% was
recovered in the urine .
- Effects on birds: Abamectin is
practically nontoxic to birds . The LD50 for
abamectin in bobwhite quail is >2000 mg/kg. The
dietary LC50 is 3102 ppm in bobwhite quail . There
were no adverse effects on reproduction when mallard
ducks were fed dietary doses of 3, 6, or 12 ppm for 18
- Effects on aquatic organisms: Abamectin
is highly toxic to fish and extremely toxic to aquatic
invertebrates . Its LC50 (96-hour) is 0.003 mg/L in
rainbow trout, 0.0096 mg/L in bluegill sunfish, 0.015
mg/L in sheepshead minnows, 0.024 mg/L in channel
catfish, and 0.042 mg/L in carp. Its 48-hour LC50 in
Daphnia magna, a small freshwater crustacean, is 0.003
mg/L. The 96-hour LC50 for abamectin is 0.0016 mg/L in
pink shrimp, 430 mg/L in eastern oysters, and 153 mg/L in
blue crab . While highly toxic to aquatic organisms,
actual concentrations of abamectin in surface waters
adjacent to treated areas are expected to be low.
Abamectin did not bioaccumulate in bluegill sunfish
exposed to 0.099 ug/L for 28 days in a flow-through tank.
The levels in fish were from 52 to 69 times the ambient
water concentration, indicating that abamectin does not
accumulate or persist in fish .
- Effects on other organisms: Abamectin is
highly toxic to bees, with a 24-hour contact LC50 of
0.002 ug/bee and an oral LD50 of 0.009 ug/bee .
- Breakdown in soil and groundwater:
Abamectin is rapidly degraded in soil. At the soil
surface, it is subject to rapid photodegradation, with
half-lives of 8 hours to 1 day reported [142,145]. When
applied to the soil surface and not shaded, its soil
half-life is about 1 week. Under dark, aerobic
conditions, the soil half-life was 2 weeks to 2 months
. Loss of abamectin from soils is thought to be due
to microbial degradation. The rate of degradation was
significantly decreased under anaerobic conditions .
Because abamectin is nearly insoluble in water and has a
strong tendency to bind to soil particles, it is immobile
in soil and unlikely to leach or contaminate groundwater
. Compounds produced by the degradation of abamectin
are also immobile and unlikely to contaminate groundwater
- Breakdown in water: Abamectin is rapidly
degraded in water. After initial distribution, its
half-life in artificial pond water was 4 days. Its
half-life in pond sediment was 2 to 4 weeks . It
undergoes rapid photodegradation, with a half-life of 12
hours in water . When tested at pH levels common to
surface and groundwater (pH 5, 7, and 9), abamectin did
not hydrolyze .
- Breakdown in vegetation: Plants do not
absorb abamectin from the soil . Abamectin is
subject to rapid degradation when present as a thin film,
as on treated leaf surfaces. Under laboratory conditions
and in the presence of light, its half-life as a thin
film was 4 to 6 hours .
- Appearance: Abamectin is a colorless to
yellowish crystalline powder .
- Chemical Name: avermectin B1
- CAS Number: 71751-41-2 (avermectin B1a
and avermectin B1b) 
- Molecular Weight: 873.11
- Water Solubility: Insoluble 
- Solubility in Other Solvents: v.s. in
acetone, methanol, toluene, chloroform, and ethanol 
- Melting Point: 150-155 C 
- Vapor Pressure: Negligible 
- Partition Coefficient: Not Available
- Adsorption Coefficient: 5000 (estimated)
- ADI: 0.0001 mg/kg/day 
- MCL: Not Available
- RfD: 0.0004 mg/kg/day 
- PEL: Not Available
- HA: Not Available
- TLV: Not Available
Division of Merck and Co., Inc.
P.O. Box 2000
Rahway, NJ 07065
- Phone: 908-855-4277
- Emergency: Not Available
References for the information in this PIP can be found in
Reference List Number 10
information in this profile does not in any way replace or
supersede the information on the pesticide product labeling or
other regulatory requirements. Please refer to the pesticide