Biodegradation and mineralization of atrazine in shallow subsurface sediments from Illinois

Agricultural chemical dealerships represent potential point sources of contamination by the corn (Zea mays L.) herbicide atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine), which is frequently detected in ground water in the Midwestern USA. The objective of this study was to investigate the potential for atrazine to biodegrade under imposed N-limited conditions in subsurface sediments collected from a contaminated former dealership in Illinois. Ten cores, 4.9 to 6.1 m deep, were obtained from four locations within the 3-ha dealership. Forty-four selected samples were screened in duplicate for the ability to biodegrade 21 mg L-1 atrazine in the presence of 21 g L-1 each of the C sources citrate and succinate. Although the shallow stratigraphy was fairly uniform across the site, the biodegradation of atrazine occurred predominantly in samples obtained from the southeastern corner of the site. In most of these samples atrazine was biodegraded to concentrations below detectable levels within 40 to 80 d with no detectable metabolites. In one sample from this location, indigenous bacteria mineralized 80% of applied [C-ring(14)C]atrazine in 100 d. Sediment N and atrazine residue concentrations were not good primary predictors of the samples' ability to biodegrade atrazine. These results indicate that without knowledge of the distribution of atrazine-degrading microorganisms, comparisons of bulk sediment parameters are useless for predicting biodegradation potential.