Cinosulfuron is a sulfonylurea herbicide used to control a wide range of broadleaf weeds in rice. A 2-yr field study was conducted in northwest Italy to determine the effect of cinosulfuron on surface and subsoil waters in rice paddies. Cinosulfuron was applied at 70 g a.i. ha-1 on 35 ha of flooded rice. After the treatment, the change in herbicide concentration over time was studied by analysing water and sediment samples in a test paddy field (2.16 ha, located in the treated area), water in a spring and a pond (both located near the test paddy), two wells (up- and down-hill to the treated area), and two piezometers (along the test paddy levee). To better understand some of the field study results, cinosulfuron degradation was also evaluated in the laboratory in solutions buffered to different pH values. Two weeks after the treatment, the cinosulfuron concentration in the paddy water decreased by about 60%. No cinosulfuron was detected at about 2.5 months after the treatment. The concentration in the sediment gradually increased after the treatment, reaching the highest value (13.53 micro g kg-1) 3 weeks later. The maximum cinosulfuron content in the spring and pond were 0.91 and 0.29 micro g L-1, respectively, and these were detected 60 to 90 days after treatment (DAT). The water collected in the piezometers reached the highest concentration (0.99 micro g L-1) 29 DAT. Cinosulfuron was never detected in the wells. In the degradation study at different pH values, cinosulfuron degraded rapidly at low pH values.
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