Mirex

Synonyms and Trade Names (partial list): Dechlorane, Ferriamicide, GC 1283.
Appearance: White crystalline, odourless solid.

Overview

Mirex is a stomach insecticide with little contact activity. It's main use was against fire ants in the southeastern United States, but it has also been used to combat leaf cutters in South America, harvester termites in South Africa, Western Harvester ants in the US, mealybug of pineapple in Hawaii and has been investigated for possible use against Yellow Jacket Wasps in the US. It has also been used as a fire retardant in plastics, rubber, paint paper, and electrical goods.

Mirex is very resistant to breakdown, is very insoluble in water, and has been shown to bioaccumulate and biomagnify. Due to its insolubility, Mirex binds strongly to aquatic sediments.

Usage in South East Asia

 

Used or Found in Country?

Years of Usage

Regulatory Controls

Cambodia

   

Restricted

Lao PDR

   

Banned

Malaysia

   

Banned

Thailand

   

Banned in 1995

Indonesia

   

Banned

Philippines

   

Restricted

Viet Nam

     

(table references)

Human Exposure

There are no reports of injuries to humans resulting from exposure to Mirex. Mirex residues in human adipose have been reported. A range of 0.16 - 5.94 ppm was reported in 6 of 1,400 samples collected in 1971-1972 in the southern US. Samples from 8 southeastern US states were collected, and residues detected in 10.2 percent of those tested, with a geometric mean of 0.286 ppm in lipids.

IARC has concluded that while there is inadequate evidence for the carcinogenicity of Mirex in humans, there is sufficient evidence in experimental animals. IARC has classified Mirex as a possible human carcinogen (Group 2B).

Animal Exposure

In acute studies, the oral LD50 of Mirex to rats ranges from 600 to >3,000 mg/kg, depending on the sex of the test animal and the nature of the formulation tested. Short term effects included decreased body weight, hepatomegaly, induction of mixed function oxidases, and morphological changes in liver cells.

Rats which were fed 5 ppm Mirex in their diets for 30 days prior to mating and for 90 days after, showed reduced litter size and increased parental mortality. Reduced litter sizes, and viability of neonates, along with formation of cataracts were observed in rats fed 25 ppm Mirex in the diet.

Plant Exposure

Contamination of plants is primarily a surface phenomenon resulting from aerial deposition of emissions or deposition of compound that has volatilized from the surface of the soil.

A reduction in germination and emergence in several plant species was observed, which increased as the concentrations of Mirex increased.

Uptake, accumulation and translocation of Mirex by a variety of plant species has also been seen. These results are questionable, however, as lipophilic compounds such as Mirex are generally not known to be taken up and translocated by plants.

Aquatic Organism Exposure

Crustaceans are the most sensitive aquatic organisms, with larval and juvenile stages being the most sensitive. Delayed mortality is typical of Mirex poisoning in crustaceans. Larval crabs exposed to 0.1 and 10 µg/L did not exhibit any adverse effects on survival for 5 days after hatching. Delayed mortality then occurred at the 1 and 10 µg/L exposure levels. Mirex is also toxic to fish and can affect fish behaviour. Mirex has a low short term toxicity to birds with acute oral LD50 values in the range of 1,400 mg/kg body weight in pheasant to 10,000 mg/kg in quail.

BioAccumulation

Mirex is considered to be one of the most stable and persistent pesticides, with a half life of up to 10 years. This persistence, combined with lipophilicity, provides the conditions necessary for Mirex to bioconcentrate in organisms. Bioconcentration factors of 2,600 and 51,400 value have been observed in pink shrimp and fathead minnows, respectively.

The chemical properties of Mirex (low water solubility, high lipid solubility, high stability, and semi-volatility) favour its long range transport, and Mirex has been detected in Arctic freshwater and terrestrial organisms.

The main route of exposure of Mirex to the general population is through food, especially meat, fish and wild game, and intake is generally below established residue tolerances.

Mirex residues were found in only one of 806 milk sample composites collected in a survey of US pasteurized milk.

No residues of Mirex were detected in any samples of fish in Egypt nor in any samples from the fat of domestic farm animals in Ontario, Canada.

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References:

Adapted from Persistent Organic Pollutants: Information on POPs, their alternatives and alternative approaches (United Nations Environmental Programme (UNEP) 1995).

Chemical structure of Mirex
Source: UNEP
Hatfield Consultants The World Bank funded by the Canadian POPs Trust Fund through the      
Canadian International Development Agency
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