Degradation of an atrazine and metolachlor herbicide mixture in pesticide-contaminated soils from two agrochemical dealerships in Iowa

The fate of atrazine and metolachlor, applied as a mixture, in soil taken from two pesticide-contaminated sites in Iowa (denoted as Alpha or Bravo) were determined in laboratory studies. Atrazine and metolachlor degradation, as well as atrazine mineralization, were greater in soil collected from Kochia scoparia L. (Schrader) rhizosphere than in soils from unvegetated areas. The radiolabeled ¹⁴C-carbinol and ¹⁴C-morpholinone metabolites were identified in ¹⁴C-metolachlorapplied soil 60 d after treatment. The half-life for atrazine in Alpha soil was significantly less in the rhizosphere soil (50 d) than in unvegetated soil (193 d). Quantities of specific atrazine degraders were one to two orders of magnitude greater in Bravo soils than in Alpha soils. In an experiment with plants present, significantly more ¹⁴C-atrazine was taken up by K. scoparia (9.9% of the applied ¹⁴C) than by Brassica napus L. Significantly less atrazine was extractable from soils vegetated with K. scoparia than from soils vegetated with B. napus or unvegetated soils.