Degradation, pyrethroids

Tyler, C.R., Beresford, N., and van der Woning, M. et al. (2000). Metabolism and environmental degradation of pyrethroid insecticides produce compounds with endocrine activities. Environmental Toxicology and Chemistry 19, 801-809. 

Synthetic pyrethroids now account for at least 30% of the world insecticide market and are rapidly replacing other agricultural chemicals for control of insect pests. Fenvalerate is one of the more widely used synthetic pyrethroid insecticides. It is derived from a combination of a-cyano-3-phenoxybenzyl alcohol and a-isopropyl phenylacetate ester. Technical fenvalerate is a mixture of four optical isomers, each occurring in equal amounts but with different efficacies against insect pests. Fenvalerate does not usually persist in the environment for >10 weeks, and it does not accumulate readily in the biosphere. Time for 50% loss (Tb 1/2) in fenvalerate-exposed amphibians, birds, and mammals was 6 to 14 h for reptiles, terrestrial insects, aquatic snails, and fish it was >14 h to <2 days and for various species of crop plants, it was 2 to 28 days. Fenvalerate degradation in water is due primarily to photoactivity, and in soils to microbial activity. Half-time persistence in nonbiological materials is variable, but may range up to 6 days in freshwater, 34 days in seawater, 6 weeks in estuarine sediments, and 9 weeks in soils. 

Miyamoto J (1976) Degradation, metabolism and toxicity of synthetic pyrethroids. Environ Health Perspect 14 15-28... 

The second difference between the laboratory tests and exposure under realistic environmental conditions is that in the laboratory exposure concentrations are maintained, or the ecotoxicological endpoints are adjusted to account for any decline. Under natural conditions a combination of the pyrethroids tendency to partition rapidly and extensively to organic matter, coupled with their susceptibility to degradation in aquatic systems where algae and macrophytes are present [13,14], means their overall dissipation rate from the water phase is generally relatively rapid. Water column dissipation half-lives tend to be around 1 day (see Sect. 5). This behavior means that it is unlikely that aquatic organisms will be exposed to pyrethroids in the water phase for prolonged periods in natural water bodies. 

Similarly, the reductions in toxicity observed in laboratory toxicity tests where exposure is modified (either through the addition of sediment or by removal to clean water) are also apparent in the field. Field effect concentrations are generally observed to occur at concentrations around three to ten times above those based on standard laboratory data. Dissipation and degradation are therefore clearly the critical factors in mitigating effects of pyrethroids under field conditions. This provides reassurance that preliminary ecological risk assessments based on... 

In contrast to hydrolysis and photolysis, an enantioselective and/or regioselective degradation of pyrethroids is expected since various kinds of enzymes in microbes participate in their metabolism in soil and sediment. The diastereomers should be separated by using a chiral GC or HPLC to examine the fate of each isomer [85]. Sakata et al. [86] have conducted the first extensive aerobic soil metabolism study... 

Sakata S, Mikami N, Yamada H (1992) Degradation of pyrethroid optical isomers in soils. J Pestic Sci 17 169-180... 

Qin S, Budd R, Bondarenko S, Liu W, Gan J (2006) Enantioselective degradation and chiral stability of pyrethroids in soil and sediment. J Agric Food Chem 54 5040-5045... 

Grant RJ, Daniell TJ, Betts WB (2002) Isolation and identification of synthetic pyrethroid-degrading bacteria. J Appl Microbiol 92 534—540... 

Grant RJ, Betts WB (2004) Mineral and carbon usage of two synthetic pyrethroid degrading bacterial isolates. J Appl Microbiol 97 656-662... 

Leahey JP (1985) Metabolism and environmental degradation. In Leahey JP (ed) The pyrethroid insecticides, Chap 5. Taylor Francis, London, pp 263-342... 

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