Persistence of endosulfan and endosulfan sulfate in soil as affected by moisture regime and organic matter addition

摘要

Endosulfan [(1,4,5,6,7,7-hexachloro-8,9,10-trinorborn-5-en-2,3-ylene-bis-methylene) sulfite], a mixture of two stereoisomers alpha and beta at around 2:1 ratio, has been widely used as a broadspectrum cyclodiene insecticide on a wide range of cropsincluding upland cotton and wetland rice systems. It persists in soil and water environments for 3 to 6 months or more (Rao and Murty 1980; Kathpal et al. 1997; Awasthi et al. 2000). However, it is generally less persistent in the environment than othercyclodienes. Endosulfan can undergo degradation to non-toxic or less toxic endosulfan diol or oxidation to equally or more toxic endosulfan sulfate in plants, microbial cultures and soils (Goebel et al. 1982). Formation of endosulfan sulfate is mediatedessentially by microorganisms while hydrolysis of endosulfan to endosulfan diol can be chemical, especially under alkaline conditions, and/or microbial. Off-farm transport of endosulfan and toxic and recalcitrant endosulfan sulfate especially from cottonand rice fields to surface and groundwater has caused problems of their toxicity to aquatic life, particularly fish and invertebrates (Leonard et al. 2001). Endosulfan sulfate appears to be the most persistent metabolite of endosulfan in soils, but undergoes rapid degradation in cotton foliage (Kennedy et al. 1998). Almost all studies on soil persistence hitherto were on the fate of endosulfan, and not that of endosulfan sulfate, although the latter has been detected in groundwater in significant amounts in Australia and elsewhere (Kennedy et al. 2001). Despite its off-farm transport to water resources and toxicity to aquatic ecosystem, endosulfan will continue to be used in Australia and other countries on an interim basis under guidelines designed to reduce its inappropriate use and to reduce its off-farm transport to creeks and rivers.