Bioaccessibility of environmentally aged 14C-atrazine residues in an agriculturally used soil and its particle-size aggregates

After 22 years of aging under natural conditions in an outdoor lysimeter the bioaccessibility of 14C-labeled atrazine soil residues to bacteria was tested. Entire soil samples as well as sand-sized, silt-sized, and clay-sized aggregates (>20, 20-2, and <2microm aggregate size, respectively) were investigated under slurried conditions. The mineralization of residual radioactivity in the outdoor lysimeter soil reached up to 4.5% of the total 14C-activity after 16 days, inoculated with Pseudomonas sp. strain ADP. The control samples without inoculated bacteria showed a mineralization maximum of only about 1% after 44 days of incubation. Mineralization increased in the clay-sized aggregates up to 6.2% of the total residual 14C-activity within 23 days. With decreasing soil aggregate sizes, residual 14C-activity increased per unit of weight, but only minor differences of the mineralization in the soil and soil size aggregates using mineral-media for incubation was observed. Using additional Na-citrate in the incubation, the extent of mineralization increased to 6.7% in soil after 23 days following incubation with Pseudomonas sp. strain ADP. These results show that long-term aged 14C-atrazine residues are still partly accessible to the atrazine degrading microorganism Pseudomonas sp. strain ADP.