Involvement of hydrogen sulphide in the degradation of parathion in flooded acid sulphate soil

Abstract

There is increasing evidence that certain pesticides, resistant to degradation in aerobic systems, undergo fairly rapid degradation in anaerobic ecosystems such as flooded soil^1,2. After flooding, the soil components NO₃⁻, Fe³⁺, Mn⁴⁺ and SO₄²⁻ are reduced almost in a thermodynamic sequence with a corresponding shift in favour of anaerobic microorganisms³. Although anaerobic microorganisms have been implicated directly in the degradation of some pesticides in anaerobic environments^1,2, there is circumstantial evidence for chemically catalysed reactions, involving, for example, the iron redox system⁴ or reduced iron porphyrins⁵. However, the importance of this and other dominant redox reactions in the behaviour of pesticides in a flooded soil is not well understood. We report here the involvement of hydrogen sulphide, the end product of sulphate reduction, in the degradation of parathion in a flooded acid sulphate soil.