COMPARISON OF THE LEACHING PROPERTIES OF ALACHLOR, METOLACHLOR, TRIAZINES AND SOME OF THEIR METABOLITES IN AN EXPERIMENTAL FIELD

Alachlor, metolachlor, atrazine, cyanazine, simazine and terbuthylazin e were applied to plots containing a drainage system in order to deter mine the concentrations of parent compounds and their metabolites in s oil and in leachate samples. The results indicated that all these herb icides disappeared substancially in the soil surface layer following f irst order kinetics. In the surface soil, the disappearance times of 5 0% of the concentration (DT50s) for terbuthylazine, atrazine, metolach lor, cyanazine, simazine and alachlor were 44, 35, 34, 28, 28 and 20 d ays, respectively. All pesticides leached to a depth of about 90 cm in the soil. After application at agricultural doses, leachate concentra tions of herbicides ranged from 24 mu g/l for metolachlor to 128 mu g/ l for cyanazine. The recoveries of the initial amount of compounds add ed ranged from 0.03% for metolachlor to 0.3% for simazine and its meta bolite, deisopropylatrazine (DIA). Of particular interest was the high rate of formation of DIA from simazine and of desethylterbuthylazine (DET) from terbuthylazine. In the leachate, DIA occurred at concentrat ions much higher than simazine. (C) 1998 Elsevier Science Ltd.