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 analysis of noninoculated soil indicated dealkylation to be a major degradation pathway with deethylatrazine favoring deisopropylatrazine. Inoculation with Pseudomonas sp. strain ADP (P.ADP) resulted in 90-100% mineralization of [C-14]atrazine in all samples after 15 days. Atrazine was degraded in the soil via dechlorination as the first mineralization step. C-source competition was not responsible for differences in initial mineralization rates. Higher organic matter content in the upper soil level did not result in a sorption-related decrease in degradation rates. It is concluded that the limiting factor for atrazine mineralization in the tested soil profiles was the absence of atrazine-mineralizing microorganisms. Therefore, bioaugmentation may be preferable to enhancement of intrinsic atrazine-degrading activity when complete atrazine mineralization is the goal of bioremediation activity.