Occurrence and fate of 6 neonicotinoid insecticides belonging to different chemical classes were investigated in the aqueous phase of surface water at 16 sampling locations along the Romanian side of the Danube River and its three main tributaries (Jiu, Olt, Arges). This is the first report on the neonicotinoid occurrence in the Danube River and three tributaries. It was observed a contamination of Danube River and its tributaries, higher in planting period than pre-or post- planting period, with the next compounds (detection frequency and the concentration range): thiamethoxam (68.7%, 0.9-3.8ng/L), clothianidin (64.6%, 0.84-9.6ng/L), nitenpyram (52.08%, 0.39-11.1ng/L), imidacloprid (31.2%, 0.5-8.2ng/L), acetamiprid (16.6%, 0.84-12.7ng/L). The four main neonicotinoids (clothianidin, thiamethoxam, imidacloprid, nitenpyram) follow the classic pattern in which concentrations and frequency increase during the planting period and that is correlated with seed crop treatment. Total neonicotinoid levels present in investigated Rivers, reaching up to 31.6 ng/L, may affect aquatic invertebrates that are most susceptible to these insecticides. For clothianidin and nitenpyram were obtained positive correlations between the percentage of the area planted with cereals and concentrations of this compound (r= 0.574, r =0.665) which indicate their use in agricultural area. For imidacloprid were obtained positive correlations between percent of permanent cultivated crop in urban land and concentrations of this compound (r =0.264, r =0.877).
Radiocarbon and Stable Isotopes as Groundwater Tracers in the Danube River Basin of SW Slovakia
