Biotransformation of atrazine and metolachlor within soil profile and changes in microbial communities

Abstract

Biotransformation studies of atrazine, metolachlor and evolution of their metabolites were carried out in soils and subsoils of Northern Greece. Trace atrazine, its metabolites and metolachlor residues were detected in field soil samples 1year after their application. The biotransformation rates of atrazine were higher in soils and subsoils of field previously exposed to atrazine (maize field sites) than in respective layers of the field margin. The DT50 values of atrazine ranged from 5 to 18d in the surface layers of the adapted soils. DT50 values of atrazine increased as the soil depth increased reaching the value of 43d in the 80–110cm depth layer of adapted soils. Metolachlor degraded at slower rates than atrazine in surface soils, subsoils of field and field margins with the respective DT50 values ranging from 56 to 72d in surface soils and from 165 to 186d in subsoils. Hydroxyatrazine was the most frequently detected metabolite of atrazine. The maximum concentrations of metolachlor-OXA and metolachlor-ESA were detected in the soil layers of 20–40cm depth after 90d of incubation. Principal Component Analysis (PCA) of soil Phospholipid Fatty Acids (PLFAs), fungal/bacterial and Gram-negative/Gram-positive ratios of the PLFA profiles revealed that the higher biotransformation rates of atrazine were simultaneously observed with the abundance of Gram-negative bacteria while the respective rates of metolachlor were observed in soil samples with abundance of fungi.