Mirex
Encyclopedia
Mirex is a chlorinated hydrocarbon that was commercialized as an insecticide
and later banned because of its impact on the environment. This white crystalline odorless solid is a derivative of cyclopentadiene
. It was popularized to control fire ants but by virtue of its chemical robustness and lipophilicity it was recognized as a bioaccumulative
pollutant. Ironically, the spread of the red imported fire ant
was actually encouraged by the use of Mirex, which also kills native ants that are highly competitive with the fire ants. The United States Environmental Protection Agency
prohibited its use in 1976.
.
Mirex is a stomach insecticide. The insecticidal use was focused on Southeastern United States to control the imported fire ant
s Solenopsis saevissima richteri and Solenopsis invicta. Approximately 250,000 kg of mirex was applied to fields between 1962-75 (US NRC, 1978). Most of the mirex was in the form of "4X mirex bait," which consists of 0.3% mirex in 14.7% soybean oil
mixed with 85% corncob
grits. Application of the 4X bait was designed to give a coverage of 4.2 g mirex/ha and was delivered by aircraft, helicopter or tractor. 1x and 2x bait were also used. Use of mirex as a pesticide was banned in 1978. The Stockholm Convention
banned production and use of several persistent organic pollutant
and Mirex was one of the "dirty dozen."
, carbon monoxide
, hydrogen chloride
, chlorine
, phosgene
, and other organochlorine species. Slow oxidation produces chlordecone ("Kepone"), a related insecticide that is also banned in most of the western world. but more readily degraded. Sunlight degrades mirex to photomirex.
Mirex is highly resistant to microbiological degradation. It only slowly dechlorinates to a monohydro derivative by anaerobic microbial action in sewage sludge and by enteric bacteria. Degradation by soil microorganisms has not been described.
There is evidence of accumulation of mirex in aquatic and terrestrial food chains to harmful levels. After 6 applications of mirex bait at 1.4 kg/ha, high mirex levels were found in some species; turtle fat contained 24.8 mg mirex/kg, kingfishers, 1.9 mg/kg, coyote fat, 6 mg/kg, opossum fat, 9.5 mg/kg, and racoon fat, 73.9 mg/kg. In a model ecosystem with a terrestrial-aquatic interface, sorgum seedlings were treated with mirex at 1.1 kg/ha. Caterpillars fed on these seedlings and their faeces contaminated the water which contained algae, snails, Daphnia, mosquito larvae, and fish. After 33 days, the ecological magnification value was 219 for fish and 1165 for snails.
Although general environmental levels are low, it is widespread in the biotic and abiotic environment. Being lipophilic, Mirex is strongly adsorbed on sediments.
Mirex induces pervasive chronic physiological and biochemical disorders in various vertebrates. No acceptable daily intake (ADI) for Mirex has been advised by FAO/WHO. IARC (1979) evaluated the carcinogenic hazard resulting from exposure to mirex and concluded that "there is sufficient evidence for its carcinogenicity to mice and rats. In the absence of adequate data in humans, based on above result it can be said that it has carcinogenic risk to humans”. Data on human health effects do not exist.
Insecticide
An insecticide is a pesticide used against insects. They include ovicides and larvicides used against the eggs and larvae of insects respectively. Insecticides are used in agriculture, medicine, industry and the household. The use of insecticides is believed to be one of the major factors behind...
and later banned because of its impact on the environment. This white crystalline odorless solid is a derivative of cyclopentadiene
Cyclopentadiene
Cyclopentadiene is an organic compound with the formula C5H6. This colorless liquid has a strong and unpleasant odor. At room temperature, this cyclic diene dimerizes over the course of hours to give dicyclopentadiene via a Diels–Alder reaction...
. It was popularized to control fire ants but by virtue of its chemical robustness and lipophilicity it was recognized as a bioaccumulative
Bioaccumulation
Bioaccumulation refers to the accumulation of substances, such as pesticides, or other organic chemicals in an organism. Bioaccumulation occurs when an organism absorbs a toxic substance at a rate greater than that at which the substance is lost...
pollutant. Ironically, the spread of the red imported fire ant
Red imported fire ant
See main article Fire ant.The red imported fire ant , or simply RIFA, is one of over 280 species in the widespread genus Solenopsis...
was actually encouraged by the use of Mirex, which also kills native ants that are highly competitive with the fire ants. The United States Environmental Protection Agency
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
prohibited its use in 1976.
Production and applications
Mirex was first reported in 1946 by Prins but was not used in pesticide formulations until 1955. Mirex was produced by the dimerization of hexachlorocyclopentadiene in the presence of aluminium chlorideAluminium chloride
Aluminium chloride is the main compound of aluminium and chlorine. It is white, but samples are often contaminated with iron trichloride, giving it a yellow colour. The solid has a low melting and boiling point. It is mainly produced and consumed in the production of aluminium metal, but large...
.
Mirex is a stomach insecticide. The insecticidal use was focused on Southeastern United States to control the imported fire ant
Fire ant
Fire ants are a variety of stinging ants with over 285 species worldwide. They have several common names, including ginger ants, tropical fire ants and red ants.- Appearance :...
s Solenopsis saevissima richteri and Solenopsis invicta. Approximately 250,000 kg of mirex was applied to fields between 1962-75 (US NRC, 1978). Most of the mirex was in the form of "4X mirex bait," which consists of 0.3% mirex in 14.7% soybean oil
Soybean oil
Soybean oil is a vegetable oil extracted from the seeds of the soybean . It is one of the most widely consumed cooking oils. As a drying oil, processed soybean oil is also used as a base for printing inks and oil paints...
mixed with 85% corncob
Corncob
A corncob is the central core of a maize ear.The corn plant's ear is also considered a "cob" or "pole" but it is not fully a "pole" until the ear is shucked, or removed from the plant material around the ear...
grits. Application of the 4X bait was designed to give a coverage of 4.2 g mirex/ha and was delivered by aircraft, helicopter or tractor. 1x and 2x bait were also used. Use of mirex as a pesticide was banned in 1978. The Stockholm Convention
Stockholm Convention
Stockholm Convention on Persistent Organic Pollutants is an international environmental treaty, signed in 2001 and effective from May 2004, that aims to eliminate or restrict the production and use of persistent organic pollutants .- History :...
banned production and use of several persistent organic pollutant
Persistent organic pollutant
thumb|right|275px|State parties to the Stockholm Convention on Persistent Organic PollutantsPersistent organic pollutants are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes...
and Mirex was one of the "dirty dozen."
Degradation
Characteristic of chlorocarbons, mirex does not burn easily; combustion products are expected to include carbon dioxideCarbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
, carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...
, hydrogen chloride
Hydrogen chloride
The compound hydrogen chloride has the formula HCl. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry...
, chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
, phosgene
Phosgene
Phosgene is the chemical compound with the formula COCl2. This colorless gas gained infamy as a chemical weapon during World War I. It is also a valued industrial reagent and building block in synthesis of pharmaceuticals and other organic compounds. In low concentrations, its odor resembles...
, and other organochlorine species. Slow oxidation produces chlordecone ("Kepone"), a related insecticide that is also banned in most of the western world. but more readily degraded. Sunlight degrades mirex to photomirex.
Mirex is highly resistant to microbiological degradation. It only slowly dechlorinates to a monohydro derivative by anaerobic microbial action in sewage sludge and by enteric bacteria. Degradation by soil microorganisms has not been described.
Bioaccumulation and biomagnification
Mirex is highly cumulative and amount depends upon the concentration and duration of exposure.There is evidence of accumulation of mirex in aquatic and terrestrial food chains to harmful levels. After 6 applications of mirex bait at 1.4 kg/ha, high mirex levels were found in some species; turtle fat contained 24.8 mg mirex/kg, kingfishers, 1.9 mg/kg, coyote fat, 6 mg/kg, opossum fat, 9.5 mg/kg, and racoon fat, 73.9 mg/kg. In a model ecosystem with a terrestrial-aquatic interface, sorgum seedlings were treated with mirex at 1.1 kg/ha. Caterpillars fed on these seedlings and their faeces contaminated the water which contained algae, snails, Daphnia, mosquito larvae, and fish. After 33 days, the ecological magnification value was 219 for fish and 1165 for snails.
Although general environmental levels are low, it is widespread in the biotic and abiotic environment. Being lipophilic, Mirex is strongly adsorbed on sediments.
Safety
Mirex is only moderately toxic in single-dose animal studies (oral values range from 365–3000 mg/kg body weight). It can enter the body via inhalation, ingestion, and via the skin. The most sensitive effects of repeated exposure in animals are principally associated with the liver, and these effects have been observed with doses as low as 1.0 mg/kg diet (0.05 mg/kg body weight per day), the lowest dose tested. At higher dose levels, it is fetotoxic (25 mg/kg in diet) and teratogenic (6.0 mg/kg per day). Mirex was not generally active in short-term tests for genetic activity. There is sufficient evidence of its carcinogenicity in mice and rats. Delayed onset of toxic effects and mortality is typical of mirex poisoning. Mirex is toxic for a range of aquatic organisms, with crustacea being particularly sensitive.Mirex induces pervasive chronic physiological and biochemical disorders in various vertebrates. No acceptable daily intake (ADI) for Mirex has been advised by FAO/WHO. IARC (1979) evaluated the carcinogenic hazard resulting from exposure to mirex and concluded that "there is sufficient evidence for its carcinogenicity to mice and rats. In the absence of adequate data in humans, based on above result it can be said that it has carcinogenic risk to humans”. Data on human health effects do not exist.
See also
- International Organization for the Management of Chemicals (IOMC), 1995, POPs Assessment Report, December.1995.
- Lambrych KL, and JP Hassett. Wavelength-Dependent Photoreactivity of Mirex in Lake Ontario. Environ. Sci. Technol. 2006, 40, 858-863
- Mirex Health and Safety Guide. IPCS International Program on Chemical Safety. Health and Safety Guide No.39. 1990
- Toxicological Review of Mirex. In support of summary information on the Integrated Risk Information System (IRIS) 2003. U.S. Environmental Protection Agency, Washington DC.