Cinosulfuron: chemical and biological degradability, adsorption and dissipation in flooded paddy field sediment.
Cinosulfuron is a sulfonylurea herbicide largely used in the extensive cultures of flooded rice in North Italy. The degradation of cinosulfuron has been investigated in sterile aqueous solutions at 30 degrees C at different pH values. It was rapidly degraded at acidic pH (half-lives 3, 9 and 43 days at pH 4, 5 and 6, respectively) while the half-life was > 1 year at pH 7 and 9. Two degradation products formed by cleavage of the sulfonylurea bridge were identified by LC-MS. Degradation by selected mixed microbial cultures tested in aerobic and anaerobic conditions was very slow and attributable to chemical hydrolysis due to the acidic pH of the cultural broths. Degradation took place in freshly collected rice field water treated for two years with cinosulfuron but, in this case also, chemical hydrolysis prevailed over microbial degradation. In contrast, in flooded sediment simulating the paddy field environment, the dissipation rate of cinosulfuron was higher than expected from chemical hydrolysis according to the pH of the system, indicating the involvement of soil microflora. Although the herbicide exhibited a reduced affinity for the sediment surfaces demonstrated by the low value of the K(f) Freundlich coefficient (0.87 on a micromolar basis), the rapid dissipation observed in the simulated paddy field should prevent its leaching to ground water.
Nègre
Michèle
M
Dipartimento di Valorizzazione e Protezione delle Risorse Agroforestali (DI VA PRA), Settore Chimica Agraria, Università di Torino, Via Leonardo da Vinci 44, 10095 Grugliasco (TO), Italy. michele.negre@unito.it
Baiocchi
Claudio
C
Gennari
Mara
M
D000327:Adsorption; D001673:Biodegradation, Environmental; D004785:Environmental Pollutants; D019015:Geologic Sediments / Q000737:chemistry*; D006540:Herbicides / Q000737:chemistry*; D015394:Molecular Structure; D013453:Sulfonylurea Compounds / Q000737:chemistry*; D013997:Time Factors; D014867:Water / Q000737:chemistry; D000096926:Benzenesulfonamides
D004785:Environmental Pollutants; D006540:Herbicides; D013453:Sulfonylurea Compounds; D014867:Water; C469574:cinosulfuron; D000096926:Benzenesulfonamides