Salinity and the persistence of parathion in flooded soils

The persistence of parathion in five coastal saline soils of varying electrical conductivity and in one nonsaline soil sample was studied under flooded conditions. Parathion was decomposed faster in nonsaline soil than in saline soils and its stability increased with increasing electrical conductivity. The addition of salts to the nonsaline soil at 4, 8 and 16 dS^?1 increased the persistence of parathion. Nitro-group reduction, and not hydrolysis, was the major route of parathion degradation in saline and nonsaline soils. The accumulation of aminoparathion was less pronounced in saline soils than in nonsaline soil concomitant with slow degradation of parathion in saline soils. The inhibition of nitro-group reduction in saline soils was related to low microbial activities as reflected in decreased dehydrogenase activity and slow iron reduction.