Abiological loss of endosulfan and related chlorinated organic compounds from aqueous systems in the presence and absence of oxygen

Endosulfan is a cyclodiene organochlorine currently widely used as an insec ticide throughout the world. This study reports that the endosulfan isomers can be readily dissipated from aqueous systems at neutral pH in the absenc e of biological material or chemical catalysts, in the presence or absence of oxygen. The study showed that aldrin, dieldrin, and endosulfan exhibit b i-phasic loss from water in unsealed and butyl rubber sealed vessels. Half- lives are substantially increased for endosulfan I when oxygen is removed f rom the incubation vessel. The study conditions, where PTFE was used, were such that loss due to volatilization and alkaline chemical hydrolysis was e liminated. Half-lives determined from these data indicate that the parent i somers are much less persistent than the related cyclodienes, aldrin and di eldrin, confirming the findings of previous studies. The major oxidation pr oduct of endosulfans I and II, endosulfan sulfate, is less volatile and can persist longer than either of the parent isomers. Endosulfan sulfate was n ot formed in any of the treatments suggesting that it would not be formed i n aerated waters in the absence of microbial activity or strong chemical ox idants. Since endosulfan sulfate is formed in many environments through bio logical oxidation, and is only slowly degraded (both chemically in sterile media and biologically), it represents a predominant residue of technical g rade endosulfan, which finds its way into aerobic and anaerobic aquatic env ironments. The data obtained contributes to and confirms the existing body of half-life data on endosulfan I and II and its major oxidation product, e ndosulfan sulfate. The half-life data generated from the current study can be used in models for predicting the loss of chlorinated cyclodiene compoun ds from aqueous systems. The findings also highlight the importance of crit ically reviewing half-life data, to determine what the predominant processe s are that are acting on the compounds under study. (C) 2001 Elsevier Scien ce Ltd. All rights reserved.