Occurrence of Pesticide Residues in Han River Basin in 2012 and 2014

BACKGROUND: To investigate distribution and seasonal variation of concentration and flux of pesticides in Han river basin, water samples were examined at 24 sites in 2012 and 2014. METHODS AND RESULTS:Water samples were collected four times per year and subjected to liquid-liquid partition extraction followed by GC-ECD/NPD analysis.Of fifteen pesticides detected, iprobenfos, diazinon, isoprothiolane, endosulfan sulfate and oxadiazon were detected in a higher frequency, while fenoxanil, carbofuran, fenitrothion, butachlor and metolachlor were only detected in a sample.Pesticides with high occurrences, iprobenfos, diazinon, isoprothiolane, endosulfan sulfate and oxadiazon were detected in residue level of 0.01-0.46,0.01-0.24,0.03-0.85,0.02-0.06and 0.05-0.24μg/L, respectively.Carbofuran and acetanilide herbicides were found at lower frequencies, but their concentrations were one order of magnitude higher than those of the others.CONCLUSION: Discharge of pesticides in downstream area were mainly contributed from rice farming and suburban horticulture, while pesticide occurrences in upstream area, such as Donggang river basin were caused by highland agriculture for cabbage and potato production.Despite the influx of pesticides from tributaries through intensive agriculture areas, pesticide concentration in the main stream water was low due to the dilution effect from the upstream.Therefore, the water quality was considered to be good at the most downstream, the effluent of Paldang dam.