The anaerobic degradation of endosulfan by indigenous microorganisms from low-oxygen soils and sediments

Indigenous mixed populations of anaerobic microorganisms from an irrigation tailwater drain and submerged agricultural chemical waste pit readily biodegraded the major isomer of endosulfan (endosulfan I). Endosulfan I was biodegraded to endosulfan diol, a low toxicity degradation product, in the presence of organic carbon sources under anaerobic, methanogenic conditions. While there was extensive degradation (>85%) over the 30 days, there was no significant enhancement of degradation from enriched inocula. This study demonstrates that endosulfan I has the potential to be biodegraded in sediments, in the absence of enriched microorganisms. This is of particular importance since such sediments are prevalent in cotton-growing areas and are typically contaminated with endosulfan residues. The importance of minimizing non-biological losses has also been highlighted as a critical issue in determining anaerobic biodegradation potential. Seals for such incubation vessels must be both oxygen and pollutant impermeable. Teflon-lined butyl rubber provides such a seal because of its resistance to the absorption of volatiles and in preventing volatilization. Moreover, including a 100 mM phosphate buffer in the anaerobic media has reduced non-biological losses from chemical hydrolysis, allowing biodegradation to be assessed.