Mirex is a very persistent compound in the environment and is highly resistant to both chemical and biological degradation. The primary process for the degradation of mirex is photolysis in water or on soil surfaces. The primary photoreduction product of mirex in water is photomirex, which can also cause harmful health effects is more poisonous than mirex it self.
Mirex has been detected in air, surface water, soil and sediment, aquatic organisms, and foodstuffs. Historically, mirex was released to the environment primarily during its production or formulation for use as a fire retardant and as a pesticide.
Because mirex is a very hydrophobic compound with a low vapour pressure, atmospheric transport is unlikely. Atmospheric releases of mirex could result from airborne dust from the production and processing of mirex, combustion of mirexcontaining products, or volatilization of mirex applied as a pesticide. Little information was found on the degradation of mirex in the atmosphere. Mirex is expected to be stable against photogenerated hydroxyl radicals in the atmosphere.
Based on a calculated soil sorption coefficient of 1,200 (5,800 experimental) for mirex, this compound will tightly bind to organic matter in soil and, therefore, will be highly immobile. Thus, mirex is most likely to enter surface waters as a result of soil runoff. In addition, most land applications of mirex to soils containing high organic content would result in very little leaching through soil to groundwater. However, leaching of mirex from some agricultural soils can occur as mirex has been detected in groundwater wells near agricultural areas.
In soil or sediments, anaerobic biodegradation is also a major removal mechanism whereby mirex is slowly dechlorinated to the lomonohydro derivative. Aerobic biodegradation on soil is a very slow and minor degradation process. Twelve years after the application of mirex to soil, 50% of the mirex and mirexrelated compounds remained on the soil. Between 6573% of the residues recovered were mirex and 36% were chlordecone, a transformation product.
Mirex has been released to surface waters via waste waters discharged from manufacturing and formulation plants, in activities associated with the disposition of residual pesticides, and as a result of its direct use as a pesticide, particularly in the fire ant eradication programs. Mirex insecticide baits were dispersed by aerial applications, and mirex could be released into surface water directly or could reach surface waters via runoff. Because mirex binds tightly to organicrich soils, leaching to groundwater is not generally expected to occur.