Comparison of the leaching properties of alachlor, metolachlor, triazines and some of their metabolites in an experimental field

Alachlor, metolachlor, atrazine, cyanazine, simazine and terbuthylazine were applied to plots containing a drainage system in order to determine the concentrations of parent compounds and their metabolites in soil and in leachate samples. The results indicated that all these herbicides disappeared substancially in the soil surface layer following first order kinetics. In the surface soil, the disappearance times of 50% of the concentration (DT50s) for terbuthylazine, atrazine, metolachlor, cyanazine, simazine and alachlor were 44, 35, 34, 28, 28 and 20 days, respectively. All pesticides leached to a depth of about 90 cm in the soil. After application at agricultural doses, leachate concentrations of herbicides ranged from 24 μg/l for metolachlor to 128 μg/l for cyanazine. The recoveries of the initial amount of compounds added ranged from 0.03% for metolachlor to 0.3% for simazine and its metabolite, deisopropylatrazine (DIA). Of particular interest was the high rate of formation of DIA from simazine and of desethylterbuthlazine (DET) from terbuthylazine. In the leachate, DIA occurred at concentrations much higher than simazine.