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The information in this profile may be out-of-date. It was last revised in 1996. EXTOXNET no longer updates this information, but it may be useful as a reference or resource.

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E X T O X N E T

Extension Toxicology Network

Pesticide Information Profiles

A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Oregon State University, the University of Idaho, and the University of California at Davis and the Institute for Environmental Toxicology, Michigan State University. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.

EXTOXNET primary files maintained and archived at Oregon State University

Revised June 1996

Abamectin

Trade and Other Names: Abamectin is also known as Avermectin B1a. Trade names include Affirm, Agri-Mek, Avermectin, Avid, MK 936, Vertimec, and Zephyr.

Regulatory Status: Abamectin is a General Use Pesticide (GUP). It is classified as toxicity class IV - practically nontoxic, and has no precautionary statement on its label.

Chemical Class: Insecticide/miticide

Introduction: 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.

Formulation: Not Available

Toxicological Effects:

• Acute toxicity: Abamectin is highly toxic to insects and may be highly toxic to mammals as well [141]. Emulsifiable concentrate formulations may cause slight to moderate eye irritation and mild skin irritation [8]. 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 [143]. 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 [141]. Abamectin does not cause allergic skin reactions [142]. 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 [8]. The dermal LD50 for technical abamectin in rats and rabbits is greater than 330 mg/kg [144].
• 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 [141]. 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 [141]. 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 loss [142].
• Reproductive effects: Rats given 0.40 mg/kg/day of abamectin had increased stillbirths, decreased pup viability, decreased lactation, and decreased pup weights [142]. 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 [141]. There were no birth defects in the offspring of rats given up to 1 mg/kg/day [142]. 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 [1].
• 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 [141]. 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 [142]. 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 [144]. 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 [144].

Ecological Effects:

• Effects on birds: Abamectin is practically nontoxic to birds [142]. The LD50 for abamectin in bobwhite quail is >2000 mg/kg. The dietary LC50 is 3102 ppm in bobwhite quail [145]. There were no adverse effects on reproduction when mallard ducks were fed dietary doses of 3, 6, or 12 ppm for 18 weeks [145].
• Effects on aquatic organisms: Abamectin is highly toxic to fish and extremely toxic to aquatic invertebrates [142]. 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 [145]. 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 [145].
• 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 [145].

Environmental Fate:

• 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 [142]. Loss of abamectin from soils is thought to be due to microbial degradation. The rate of degradation was significantly decreased under anaerobic conditions [145]. 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 [145]. Compounds produced by the degradation of abamectin are also immobile and unlikely to contaminate groundwater [145].
• 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 [145]. It undergoes rapid photodegradation, with a half-life of 12 hours in water [142]. When tested at pH levels common to surface and groundwater (pH 5, 7, and 9), abamectin did not hydrolyze [145].
• Breakdown in vegetation: Plants do not absorb abamectin from the soil [145]. 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 [145].

Physical Properties:

• Appearance: Abamectin is a colorless to yellowish crystalline powder [1].
• Chemical Name: avermectin B1
• CAS Number: 71751-41-2 (avermectin B1a and avermectin B1b) [1]
• Molecular Weight: 873.11
• Water Solubility: Insoluble [1]
• Solubility in Other Solvents: v.s. in acetone, methanol, toluene, chloroform, and ethanol [1]
• Melting Point: 150-155 C [1]
• Vapor Pressure: Negligible [1]
• Partition Coefficient: Not Available
• Adsorption Coefficient: 5000 (estimated) [53]

Exposure Guidelines:

• ADI: 0.0001 mg/kg/day [12]
• MCL: Not Available
• RfD: 0.0004 mg/kg/day [13]
• PEL: Not Available
• HA: Not Available
• TLV: Not Available

Basic Manufacturer:

Merck Agvet
Division of Merck and Co., Inc.
P.O. Box 2000
Rahway, NJ 07065

• Phone: 908-855-4277
• Emergency: Not Available

References:

References for the information in this PIP can be found in Reference List Number 10

DISCLAIMER: The 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 product labeling.