Algal Degradation of a Known Endocrine Disrupting Insecticide, α-Endosulfan, and Its Metabolite, Endosulfan Sulfate, in Liquid Medium and Soil

The role of algae in the persistence, transformation, and bioremediation of two endocrine disrupting chemicals, α-endosulfan (a cyclodiene insecticide) and its oxidation product endosulfan sulfate, in soil (incubated under light or in darkness) and a liquid medium was examined. Incubation of soil under light dramatically decreased the persistence of α-endosulfan and enhanced its transformation to endosulfan sulfate, over that of dark-incubated soil samples, under both nonflooded and flooded conditions. This enhanced degradation of soil-applied α-endosulfan was associated with profuse growth of indigenous phototrophic organisms such as algae in soil incubated under light. Inoculation of soil with green algae, Chlorococcum sp. or Scenedesmus sp., further enhanced the degradation of α-endosulfan. The role of algae in α-endosulfan degradation was convincingly demonstrated when these algae degraded α-endosulfan to endosulfan sulfate, the major metabolite, and endosulfan ether, a minor metabolite, in a defined liquid medium. When a high density of the algal inoculum was used, both metabolites appeared to undergo further degradation as evident from their accumulation only in small amounts and the appearance of an endosulfan-derived aldehyde. Interestingly, β-endosulfan was detected during degradation of α-endosulfan by high density algal cultures. These algae were also capable of degrading endosulfan sulfate but to a lesser extent than α-endosulfan. Evidence suggested that both α-endosulfan and endosulfan sulfate were immediately sorbed by the algae from the medium, which then effected their degradation. Biosorption, coupled with their biotransformation ability, especially at a high inoculum density, makes algae effective candidates for remediation of α-endosulfan-polluted environments. Keywords: Endosulfan; endosulfan sulfate; algae; endocrine disruptor; biodegradation; soil