Mirex By: Peta Walker

Structure Molecular formula : C 10 Cl 12 Chemical name : 1,1a,2,2,3,3a,4,5,5,5a,5b,6-dodeca- chloroocta-hydro-1,3,4-metheno-1H- cyclobuta[ cd]pentalene

Physical and Chemical Properties Molecular Weight : g/mol Mirex is a white crystalline, odorless solid. Melting point : 485 degrees C Solubility : WATER - 0.6mg/L (practically insoluble) ORGANIC SOLVENTS – Dioxane (15.3%), xylene (14.3%), benzene (12.2%), CCl 4 (7.2%), methyl ethyl ketone (5.6%) Partition Coefficient : Log K ow = 5.28 h, Log K oc = f Vapor 25 degrees C : 3x10 -7 mm Hg It is an extremely stable compound that does not react with sulfuric, nitric, hydrochloric or other common acids and is unreactive with bases, chlorine or ozone.

Uses and Application Mirex was mainly used as a flame-retardant and as a stomach insecticide. It was formulated into baits for the control of fire ants and harvester ants. Most of the bait was in the form of 4X mirex bait and was applied by aircraft, helicopter, or tractor. To combat the problem, approximately 250,000 kg of mirex was applied to fields from 1962 to It is still used under the name Dechlorane as a flame retardant in plastics, rubbers, and paints.

Production History First synthesized in 1946 by Prins but was not used in pesticide formulations until Made by the dimerization of hexachlorocyclopentadiene in the presence of aluminum chloride. In 1976 the EPA ordered a phasing out of the use of mirex for pest control and brought in a ban with exemptions on June 30, 1978.

Mode of Entry in Aquatic Environment Waste waters discharged from manufacturing and formulation plants. Activities associated with the disposition of residual pesticides. Direct use as a pesticide. Most likely to enter surface waters as a result of soil runoff. Strongly adsorbed on sediments in aquatic systems.

Chemical Reactivity with Water, Chemical Speciation, and Physical Half-Life Lipophilic – Insoluble in water Half life in sediment: t ½ = 10yrs The half-life of mirex in rainbow trout was found to be greater than 1,000 days in fish exposed for 96 days to a mean concentration of 4.1 ng/L. Half-life of mirex after oral administration to rats was more than 100 days.

Toxicity to Aquatic Life Mirex is moderately toxic in single-dose animal studies (oral LD50 values range from mg/kg body weight) Moderately acutely toxic. Chronic toxicity is a better indicator of the true toxicity of mirex and is uniformly high. Mirex is also toxic to fish and can affect their behavior (LC50 (96 hr) from 0.2 to 30 mg/L for rainbow trout and bluegill. Crustaceans are very sensitive to Mirex. Crayfish immersed in nominal concentrations of 0.1 to 5.0 ppb mirex for periods of 6 to 144 h died 5 to 10 days after initial exposure. It accumulates in adipose tissue and biomagnifies in food chains.

Toxic Effects Delayed mortality and numerous birth defects in aquatic and terrestrial fauna Tumor formation The toxic effects of mirex in short-term studies are generally characterized by a decrease in body weight, hepatomegaly, induction of mixed-function oxidases, morphological changes in liver cells, and sometimes death. Wildlife population alterations Early growth and development Degradation into toxic metabolites Disrupted mammalian energy metabolism and detection of residues in human milk and adipose tissues. The most sensitive effects of repeated exposure in experimental animals are principally associated with the liver, and these have been observed with doses as low as 1.0 mg/kg diet (0.05 mg/kg body weight per day). Mirex administered to fish resulted in kidney lesions and gill damage. At higher dose levels, it is fetotoxic (25 mg/kg in diet) and teratogenic (6.0 mg/kg per day). There is evidence of its potential for endocrine disruption and possibly carcinogenic risk to humans.

Biomagnification of Mirex Biomagnification of mirex is supported by a study of various aquatic organisms that comprise an aquatic food chain in Lake Ontario (Oliver and Niimi 1988). The following concentrations (+ standard deviation) of mirex were found:

Mode of Entry into Organisms Enters the body via inhalation, ingestion, and via the skin. Ingestion of contaminated food rather than absorption across the gills, is the primary exposure route for trout.

Molecular Mode of Toxic Interaction Mirex is a neurotoxic compound. It disrupts the normal transmission of impulses along nerves and across synapses. Mirex is a GABA (gamma- aminobutyric acid) antagonist. It binds to GABA receptors, reducing the flow of Cl - ions. Results in convulsions. Toxicity increases with increasing ambient temperature.

Biochemical Metabolism and Breakdown Mirex is one of the most stable and persistent organochlorine compounds known. It is resistant to chemical, photolytic, microbial, metabolic, and thermal degradation processes. Degradation products include hexachlorobenzene, hexachlorocyclopentadiene, and kepone.

Biochemical metabolism and Breakdown When exposed to sunlight mirex is converted to the 8-monohydro derivative (photomirex). Photomirex is even more poisonous than mirex. Photolytic dechlorination occurs in some organic solvents when mirex is exposed to UV radiation. The half-life of mirex dispersed in water under intense UV radiation at °C was 48.4 h. The photodegradation products are 10-monohydromirex, 8- monohydromirex, 5,10-dihydromirex, chlordecone and 2,8- dihydromirex Mirex is very resistant to microbiological degradation and is only slowly dechlorinated to a monohydro derivative by anaerobic microbial action in sewage sludge. Mirex does not appear to be metabolized to any significant extent in any animal species so far investigated (mice, rats, rabbits, monkeys).

Excretion A study done using rats that were fed mirex showed that 12-25% of the dose was eliminated in the feces after 1 week.

Defense Strategies Mobile organisms can move and feed away from areas where there is high concentration of mirex. Shelled invertebrates can seal off their internal environment. However, mirex is very persistent.

Bibliography InChem - ( Agency for Toxic Substances and Disease Registry - ( ( ml ml