BACKGROUND: Distribution and seasonal variation of concentration and flux of pesticides in Han river basin 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 (14), diazinon (13), isoprothiolane (12), endosulfan sulfate (11) and oxadiazon (10) showed the highest occurrences, 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∼0.06 and 0.05∼0.24 μg/L, respectively. Carbofuran and acetanilide herbicides were founded at lower frequencies, but their concentration were one order of magnitude higher than that of the others. If sufficient detection capabilities for them are secured, occurrences of them may increase.
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 area, pesticide concentration of the main stream was low due to the dilution effect from the upstream. Therefore, the water quality was considered to be good at the most downstream, in effluent of Paldang dam.