Effects of carbon amendment on in situ atrazine degradation and total microbial biomass

This study elucidates the effects of carbon amendment on metabolic degradation of atrazine (6-chloro-N-2-ethyl-N-4-isopropyl-1,3,5-triazine-2,4-diamine) and total microbial biomass in soil. Degradation of C-14-ring-labelled atrazine was monitored in laboratory incubations of soils supplemented with 0, 10, 100 and 1000 mu g g(-1) sucrose concentrations. An experiment to determine the effect of carbon amendment on total microbial biomass and soil respiration was carried out with different concentrations of sucrose and non-labelled atrazine. The soils were incubated at a constant temperature and constant soil moisture at water potential of -15 kPa and a soil density of 1.3 g cm(-3). Mineralization of C-14-ring-labelled atrazine was monitored continuously over a period of 59 d in the first experiment. The CO2 production was monitored for 62 d in the second experiment and microbial biomass determined at the end of the incubation period. The addition of 1000 mu g g(-1) sucrose reduced atrazine mineralization to 43.5% compared to 51.7% of the applied amount for the treatment without sucrose. The addition of 1000 mu g g(-1) sucrose modified the transformation products to 1.08 mu g g(-1) deisopropylatrazine (DIA), 0.32 mu g g(-1) desethylatrazine (DEA) and 0.18 mu g g(-1) deisopropyl-2-hydroxyatrazine (OH-DIA). Treatment without sucrose resulted in formation of 0.64 mu g g(-1) hydroxyatrazine (HA), 0.28 mu g g(-1) DIA and 0.20 mu g g(-1) OH-DIA. Atrazine dealkylation was enhanced in treatments with 100 and 1000 mu g g(-1) of sucrose added. HA metabolite was formed in the control (no sucrose) and in the presence of 10 mu g g(-1) of sucrose, whereas DEA was only detected in treatment with 1000 mu g g(-1) sucrose. Results indicate that total microbial biomass increased significantly (P < 0.001) with the addition of 1000 mu g g(-1) sucrose.