Dioxin concentrations and estimation of sources in four major rivers in Miyagi Prefecture, Japan

We determined the concentrations of dioxins and suspended solids in river water samples collected from four major rivers in Miyagi Prefecture, Japan to estimate the sources of dioxins in the water. We also clarified the relationship among dioxins, suspended solids, and river flow rates. The major dioxin congeners in the river water were 1,3,6,8-TeCDD, 1,3,7,9-TeCDD, and OCDD. Principal components analysis (PCA) showed that two major components together accounted for 90.8% of the total variance in PCDD/F concentrations. Chemical mass balance model results suggested that chloronitrophen (CNP) and pentachlorophenol (PCP), which are impurities in chlorinated pesticides used in paddy fields, accounted for >90% of PCDD/F contributions, and exhaust gases for <10%. PCA results suggested that PCB products were the major sources of Co-PCBs, although total Co-PCB concentrations were lower than total PCDD/F concentrations. Concentrations of 1,3,6,8- and 1,3,7,9-TeCDD and suspended solids in river water increased with increasing flow rates. During periods of high flow, dioxin concentrations may have increased because of resuspension of bottom sediments that had adsorbed dioxins.