SEASONAL TRANSPORT OF HERBICIDES (TRIAZINES AND PHENYLUREAS) IN A SMALL STREAM DRAINING AN AGRICULTURAL BASIN - MELARCHEZ (FRANCE)

The transportation of triazines (atrazine, simazine, ametryne and cyan azine) was investigated in an experimental catchment basin situated in an agricultural area. It focused on the surface and groundwaters from March 1991 to December 1993. In addition, the phenylureas (isoproturo n, linuron, diuron and chlortoluron) were studied in the surface water s from January 1992 to December 1993. So as to assess the evolution of water contamination by triazines and phenylureas during the survey pe riod, the herbicide concentrations were considered together with the c haracteristic parameters of the catchment basin: types of cultivations , flows and precipitations. The main herbicides found in the stream of Fosse Rognon during our study were the atrazine (30-2450 ng/l), the s imazine (10-1880 ng/l) and the isoproturon (10-1800 ng/l). The results , obtained from the stream, show that the contamination overstepped th e application periods. The precipitations play a major part in the her bicide leaching after their application. In the groundwaters, the atra zine concentration (5-1700 ng/l) and the simazine concentration (5-112 0 ng/l) were higher than those found in 1977, despite a reduction of t he corn cultivated areas. The only degradation product of atrazine fou nd in both the surface and the groundwaters was desethylatrazine (10-8 50 ng/l). It appears that the groundwaters were the main incoming sour ces of desethylatrazine to surface waters. The exportation balances by the stream of Fosse Rognon, expressed as a percentage of the applied amounts, were for atrazine, simazine and isoproturon, in 1992: 0.085, 0.18 and 0.035, and in 1993: 0.28, 0.3 and 0.083, respectively. (C) 19 97 Elsevier Science Ltd.