The PAHs loadings on river discharge was estimated based on consecutive measurements during rainfall and non-rainfall periods at a river in a suburban area in Hiroshima Prefecture, Japan. The PAH concentrations ranged from 12 to 58 ng L -1 for dissolved PAHs, and from 8 to 105 ng L -1 for particulate PAHs on rainy periods. In non-rainy periods, they ranged from 10 to 58 ng L -1 for dissolved PAHs, and from 4 to 418 ng L -1 for particulate PAHs. PAH concentrations on non-rainy periods were stable for diurnal and seasonal terms. The dissolved PAH concentration was negatively correlated with EC and the particulate PAH concentration was negatively correlated with SS concentration. The yearly loading amount of PAHs was calculated with the data of river flow rate and PAH concentration, and the calculated yearly PAHs specific loading in the River on rainy days was 37 µg m -2 year -1 and the loading in non-rainy days was 29 µg m -2 year -1 . The total loading was 66 µg m -2 year -1 . From these estimations and our previous studies, the atmospheric loadings and river discharge were compared. From the comparison, the order of the loading from river basin area was comparable to this from atmospheric loadings.Keywords: atmospheric deposition, PAHs, rainfall, river discharge. INTRODUCTIONPAHs are a group of organic compounds consisting of two or more fused benzene rings, and they are noticed due to carcinogenicity and mutagen city (Dipple 1985;Vinggaard et al, 2000;Xue and Warshawsky, 2005). PAHs are mostly produced in the combustion process of fossil fuels and are emitted into the atmosphere. After dispersion, PAHs accumulate on ground surfaces and discharge into water bodies with rain. The behavior of PAHs has been extensively studied in atmospheric and aquatic environments (Takada et al, 1990;Baek et al, 1991;Sharma et al, 1994;Lee et al, 1995;Wan et al, 2006;Kumata et al, 2006). Still, the relation of the source and environmental fate has not been well clarified yet. In our previous study (Ozaki, 2006;Ozaki et al (2006Ozaki et al ( , 2007), the behavior of PAHs in Hiroshima Bay area was quantitatively investigated, and it was found that there was a major difference in PAHs loadings between the road traffic emission and the atmospheric deposition or the particle sedimentation on seabed. In order to consider the gap in PAHs loadings between road traffic loadings and environmental discharges, PAHs river discharges were investigated in this study. At a river in suburban areas in Hiroshima Prefecture, PAH concentrations were measured in rainy days and non-rainy days to examine the short-or long-term variations in PAH concentrations. Flow rate and other basic water qualities were also measured in the river, and their dependencies on PAH concentrations were investigated. From the measurements, the factors affecting the discharges were modeled for daily basis, and the total loadings were summed for one year. Further, from the comparison of the loadings

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