Dependence of accelerated degradation of atrazine on soil pH in French andCanadian soils

A series of agricultural soils varying in their atrazine treatment history were sampled from 12 sites in France and two sites in Canada. The soils var ied widely with respect to soil chemical, physical and microbiological (tot al microbial biomass, kinetics of C and N mineralization) properties. Soils treated with as few as two successive atrazine field applications minerali zed [U-ring-C-14]atrazine significantly more rapidly in 35 d laboratory inc ubations than did soils which had never received atrazine. Longer treatment history tended to favour more rapid mineralization in the so-called "adapt ed" soils. Up to 80% of the initially applied C-14-atrazine was mineralized at the end of the incubations in these adapted soils. Of the properties te sted, soil pH was the most significantly related to atrazine mineralized. I n soils with pH lower than 6.5, less than 25% of the initial C-14-atrazine was mineralized even after repeated application in field conditions. Atrazi ne retention in soil did not influence its mineralization rate. Both hydrox ylated and dealkylated atrazine metabolites were detected, but no clear pat tern of metabolite production could be determined. Large amounts of bound r esidues were formed in soils that mineralized little atrazine. (C) 2000 Els evier Science Ltd. All rights reserved.