Effect of pesticides on microbial biomass of flooded soil

Application of 2,4–13 and its analog 2,4,5-T at 0.75 μg g−1 soil led to a distinct increase in microbial biomass carbon content over that of untreated soil samples both under flooded and nonflooded conditions. 2,4-D was inhibitory to microorganisms at 7.5 and 15.0 μg g−1 soil. Repeated applications of a commercial formulation (an isomeric mixture) of hexachlorocyclohexane (HCH) to flooded soil caused a marked increase in microbial biomass content. Technical grade γ-HCH was also stimulatory to microbial biomass content. Suspensions of soil treated even once with commercial HCH formulation effected rapid aerobic degradation of α- and γ-HCH, but not β- and δ-HCH in a mineral salts medium supplemented individually with these isomers as a single carbon source.