Atrazine degradation in boreal nonagricultural subsoil and tropical agricultural soil

Purpose The purpose of this study was to determine the natural atrazine degradation activity and the genetic potential in a soil profile spanning down to the groundwater zone, collected in Finland at a site where past use of atrazine has contaminated the groundwater, and in Indian agricultural top-soils having different histories of atrazine use. Materials and methods Atrazine degradation potential was assessed by quantifying the atrazine degradation genes atzA, trzN, and atzB by quantitative PCR reaction. Atrazine mineralization was studied by radiorespirometry in order to find out if these genes were expressed. Results and discussion Indian soils contained a large number up to 10(4)-10(5) copies (g(-1) dry weight (dw) soil) of atrazine degradation genes after the first treatment with atrazine. These genes were also expressed, as up to 55 % of atrazine mineralized. Some unspecific binding of primers required thorough investigation and confirmation by sequencing of the qPCR products in the agricultural soil samples. The degradation capability of the nonagricultural boreal soil profile was much lower: atrazine degradation genes were present at detection limit (10(2) copies g(-1) soil), but mineralization studies indicated that these genes were not transcribed, since no or very little atrazine mineralization was observed. Conclusions Our results indicate that when atrazine was applied in agricultural practice, the soil atrazine degradation capacity was high. The organisms responsible for the degradation were effectively degrading atrazine already 3 months after the first treatment with atrazine. However, in boreal soil, decades after atrazine use had been discontinued, residual atrazine was not degraded even though a small number of degradation genes could still be detected in soil. There is a need for more specific primers for qPCR in tropical soils.