Rapid meneralization of the s-triazine ring of atrazine in soils in relation to soil management

Mineralization of the triazine ring of atrazine was studied in soils with similar physicochemical properties, from experimental plots under different crop rotations located in Grignon, France. Rapid mineralization rates were found inplots under continuous maize receiving atrazine every year. On the contrary, low mineralization rates were measured in plots under continuous wheat or permanent grass that had never received atrazine. The rapid mineralization of the atrazine-ring was observed without any previous laboratory microbial enrichment. It was also related to the presence of a chloro-substituent on the ring: rapid mineralization was also observed with simazine, another chloro-s-triazine, but not with terbutry, a thiomethyltriazine. The characterization of the extractable metabolites during the incubation experiments did not allow determination of the degradation pathway. In these soils, two competitive dissipation processes are proposed: (1) rapid dissipation through ring cleavage and mineralization in soil from the plot receiving atrazine every year, (2) more progressive dissipation through formation of bound residues in the other soils. The rate of mineralization of the atrazine-ring varied during the year and was rather sensitive to soil storage conditions.