Biodegradation of Malathion

Laboratory studies using bench-scale activated sludge units and a Warburg respirometer show that an aerated aqueous microbial system can rapidly remove the organo-phosphate insecticide, Malathion, from solution and that the major mechanism of removal is microbial action. Following shock loading, there is an immediate nonrecoverable uptake of the compound followed by a rapid removal rate. Microbial systems of 2,000 mg per 1 solids can assimilate loadings of 100 mg per 1 Malathion with no observable toxic effect. Daily loadings can be effectively assimilated for prolonged periods of time when sufficient nutrients are present; however, repeated exposure results in considerable destruction of the predator population. The toxicity of the compound to a mixed biota is a function of the number of organisms present and not on the volume of water in which they are dispersed. High Malathion-to-microorganism ratios inhibit microbial activity whereas low ratios stimulate respiration. Acclimated systems are more resistant to toxic effects and are more efficient in using Malathion as an energy source. Degradation of Malathion is not as rapid when other, more biologically soft substrates are available.