Variability, transport, and fate of riverine perfluorooctanoic acid (PFOA) in a heavily PFOA-impacted coastal sea

The rivers around the Seto Inland Sea (SIS) have high perfluorooctanoic acid (PFOA) concentrations, and the SIS is expected to be a PFOA source for the Pacific Ocean. To investigate variability, transport, and fate of riverine PFOA in this sea, we use a hydrodynamic-ecosystem-PFOA model to simulate the behaviors of its dissolved and biogenic particle phases in the SIS. The sum of dissolved and particulate PFOA presents a mean concentration of 468.5 ng m -3 in the eastern part of SIS, which is much higher than that in the western part (11.5 ng m -3 ). The partitioning between particulate and dissolved phases is higher in nearshore than in offshore areas. The inputs from the Yodo and Yamato Rivers dominate the PFOA levels in the ESIS. After entering Osaka Bay, 25% of the PFOA is transported to Harima Nada, while 63% is transported to the Kii Channel. The latter is transported farther to the Pacific Ocean through the upper 20 m of the Kii Channel, which is the dominant fate of PFOA in the SIS. We use the proportions of PFOA outflow to the Pacific Ocean from the rivers discharging into Osaka Bay (88%) and Suo Nada (57%) as upper and lower limits, respectively, to estimate the amount of PFOA from the rivers along the coast south of Japan entering the Pacific Ocean. The annual amount is 328.0–348.9 kg, to which the SIS contributes the largest part. • Osaka Bay is one of the coastal regions worldwide with relatively high PFOA levels. • The Yodo River input dominates the PFOA in the eastern part of SIS. • PFOA export to the Pacific along Japan’s coast is 328-349 kg/yr, mainly from the SIS.