Seasonal transport of herbicides (triazines and phenylureas) in a small stream draining an agricultural basin: Mélarchez (France)
The transportation of triazines (atrazine, simazine, ametryne and cyanazine) 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 (isoproturon, linuron, diuron and chlortoluron) were studied in the surface waters from January 1992 to December 1993. So as to assess the evolution of water contamination by triazines and phenylureas during the survey period, the herbicide concentrations were considered together with the characteristic parameters of the catchment basin: types of cultivations, flows and precipitations. The main herbicides found in the stream of Fossé Rognon during our study were the atrazine (30–2450 ng/l), the simazine (10–1880 ng/l) and the isoproturon (10–1800 ng/l). The results, obtained from the stream, show that the contamination overstepped the application periods. The precipitations play a major part in the herbicide leaching after their application. In the groundwaters, the atrazine concentration (5–1700 ng/l) and the simazine concentration (5–1120 ng/l) were higher than those found in 1977, despite a reduction of the corn cultivated areas. The only degradation product of atrazine found in both the surface and the groundwaters was desethylatrazine (10–850 ng/l). It appears that the groundwaters were the main incoming sources of desethylatrazine to surface waters. The exportation balances by the stream of Fossé 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.