抄録
Dioxin concentrations in water sampled from a drainage ditch flowing into the Furuayase River (southeast Saitama Prefecture, Japan) were monitored during a 3-h rainfall event. The dioxin concentrations in toxic equivalent (TEQ) ranged between 3.5 and 17 pg-TEQ/L. The concentrations in all 12 samples exceeded the Japanese environmental standard (ES) for water (1 pg-TEQ/L), and the concentrations in 5 samples exceeded even the Japanese wastewater standard (10 pg- TEQ/L). Excellent correlation between TEQ and SS in the water samples was observed. The amount of precipitation during the observation period was 8.7 mm. Discharges of suspended solids (SS) and dioxins from the ditch to the river during the event were estimated at 570 kg and 68 μg-TEQ, respectively. The average concentration of dioxins in SS was 120 pg-TEQ/g, which is lower than the Japanese ES for sediment. Because the dioxin concentrations and SS in the ditch water varied with rainfall conditions, it was difficult to determine whether the presence of dioxins in the SS was the sole reason that dioxin concentrations of the riverbed exceeded the ES for sediment. The ratio of 1,3,7,8-/1,3,7,9-TeCDF to TeCDFs in the ditch water was extremely high. This typical pattern in the ratio was similar to the reported value of sediment in the Furuayase River, indicating that the discharge from the ditch into the river still continued.
