ATRAZINE DEGRADATION IN SUBSURFACE SOIL BY INDIGENOUS AND INTRODUCED MICROORGANISMS

Significant atrazine degradation (50%) but only 1% mineralization was detected in samples taken from the upper soil layer (0-25 cm), but not in samples taken from deeper horizons. Thin layer chromatography anal ysis of noninoculated soil indicated dealkylation to be a major degrad ation pathway with deethylatrazine favoring deisopropylatrazine. Inocu lation with Pseudomonas sp. strain ADP (P.ADP) resulted in 90-100% min eralization of [C-14]atrazine in all samples after 15 days. Atrazine w as degraded in the soil via dechlorination as the first mineralization step. C-source competition was not responsible for differences in ini tial mineralization rates. Higher organic matter content in the upper soil level did not result in a sorption-related decrease in degradatio n rates. It is concluded that the limiting factor for atrazine mineral ization in the tested soil profiles was the absence of atrazine-minera lizing microorganisms. Therefore, bioaugmentation may be preferable to enhancement of intrinsic atrazine-degrading activity when complete at razine mineralization is the goal of bioremediation activity.