Sorptive constraints on the biodegradation of atrazine in surface and subsurface environments

To effectively evaluate the risk of herbicides on water resources it is necessary to understand the processes which affect their environmental fate. Perhaps the two most critical processes affecting the mobility and persistence of these chemicals are sorption and biodegradation. The effect of sorption on the biodegradation of atrazine was investigated in agricultural soil, vadose zone and aquifer sediments, and earthworm burrow-lining material collected from agricultural site under long-term no-till management. A pure atrazine-degrading bacterial culture was isolated from pesticide contaminated soil and was used as a biological probe to investigate atrazine bioavailability in inoculated soil microcosms. The organism (designated M91-3) was able to utilize atrazine as a sole source of both C and N under aerobic conditions. The isolate also degraded atrazine anaerobically. The degradation of binary and ternary mixtures of atrazine, simazine, and cyanazine was also investigated. Atrazine degradation by M91-3 resulted in cleavage of the s-triazine ring, an ability not previously reported for other s-triazine-degrading fungi or bacteria. In sterile and non-sterile subsurface sediments, inoculated with M91-3, variations in atrazine mineralization rate constants were partially explained by sorption of atrazine in these materials.;Atrazine bioavailability decreased with increasing soil residence time (aging) in atrazine amended soils that were allowed to age for various times ranging from 1 d to 90 d. Decreases in mineralization rate constants from sterile, inoculated soil were associated with reductions in aqueous phase atrazine concentrations. The data strongly suggested that M91-3 primarily utilized the aqueous pool of atrazine, and that extremely slow desorption rates controlled atrazine biodegradation. Decreases in the extent of atrazine mineralization with aging suggested the potential for bound residue formation.;Atrazine mineralization from inoculated earthworm burrow lining material (BLM) was generally greater than or equal to that observed in the corresponding bulk soil sampled at several depths along a vertical earthworm burrow. Atrazine mineralization in inoculated BLM was not correlated to pH, atrazine sorption or desorption, total organic carbon, water soluble organic carbon, or clay content. Enhanced sorption did not decrease atrazine mineralization, possibly because of an opposing, stimulatory effect by organic carbon on microbial activity. The enhanced sorption and biodegradation of atrazine in the BLM suggested that atrazine leaching through macropores in no-till managed soils would be retarded.