Surface and ground water monitoring for bensulfuron methyl and metsulfuronmethyl study in East and West sesia following annual applications of Sigma(R).

Bensulfuron methyl and metsulfuron methyl are the active ingredients contai ned in the rice herbicide Sigma. In 1997 and 1998 groundwater and surface w ater were monitored for bensulfuron methyl and metsulfuron methyl in the ri ce growing surrounding Vercelli, Italy. The surface water was monitored at six locations. Shallow groundwater was sampled using a series of six pizome ters adjacent to a rice paddy which was treated with Sigma. Samples of grou ndwater at depths varying from two to nineteen meters were collected. All w ater samples were analysed by LC-MS with an LOD of 0.01 mu g/l. Detentions of bensulfuron methyl and metsulfuron methyl in surface water were limited to a single sampling date close to the time when Sigma applications were ma de and following an intense rainfall event. There were no metsulfuron methy l detentions in groundwater and one detection (0.02 mu g/l) of bensulfuron methyl at 2 meters. The hydrological properties of the soil were introduced and a description of infiltration in the unsaturated zone was obtained usi ng the Green Ampt model. The monitoring and modelling results support the c onclusion that bensulfuron methyl and metsulfuron methyl when applied as Si gma herbicide will generally be found in surface and groundwater at concent ration far below 0.01 mu g/l.