The Fate of Endosulfan in Water

Although the use of endosulfan to control cotton pests has declined, this insecticide
still has widespread application in agriculture and can contaminate riverine systems as
runoff from soil or by aerial deposition. The degradation of endosulfan in pure water at
different pH values of 5, 7 and 9 and in river water from the Namoi and the Hawkesbury
rivers of New South Wales (NSW), Australia, was studied in the laboratory. Endosulfan
transformation into endosulfan sulfate in river water using artificial mesocosms was
also investigated. The results show endosulfan is stable at pH 5, with increasing rates
of disappearance at pH 7 and pH 9 by chemical hydrolysis. Incubation of endosulfan with
river water at pH 8.3 resulted in the disappearance of endosulfan and the formation of
endosulfan diol due to the alkaline pH as well as formation of endosulfan sulfate. Although
the degradation of endosulfan by Anabaena, a blue-green alga, did not result in
the transformation of endosulfan to endosulfan sulfate, we conclude that other microorganisms
catalyzed the formation of the sulfate. Significant conversions of endosulfan
into endosulfan sulfate were also reported from associated field studies using artificial
mesocoms containing irrigation water from rivers inhabitated by micro-macro fauna.
From these results, we conclude that the presence of endosulfan sulfate in river water
cannot be used to distinguish contamination by runoff from soil from contamination by
aerial drift or redeposition.