Evaluation of Loads and Sources of Heavy Metals in Tama River, Tokyo

The loads and sources of heavy metals (Cd, Co, Cu, Mn, Mo, Ni, Pb, V, and Zn) in the midstream of Tama River were evaluated on the basis of their chemical analyses in ordinary and stormwater runoff from July 2007 to November 2008. Tama River is one of the three major rivers flowing into Tokyo Bay. The total annual water discharges differed largely for 2007 and 2008, depending on the scales of typhoon rainfalls and other heavy rainfalls in each year. The concentrations of the metals other than Mo in the river did not change markedly at a flow rate of less than approximately 200 m(3) s(-1), but at higher flow rates, the concentrations of all the metals increased linearly with the increase in the log of flow rate (r (2) = 0.94-0.99). The annual loads of heavy metals for 2007 and 2008 were estimated using regression equations between the above parameters and the hourly flow rate data for each year. For the metals other than Mo, the contribution of the loads at higher flow rates (> 200 m(3) s(-1)) was much larger than that at lower flow rates (< 200 m(3) s(-1)), showing the importance of the particulate loads (primarily crustal materials) during storm runoff following typhoon rainfalls and other heavy rainfalls. In contrast, the loads of Mo at lower flow rates accounted for major portions (56-78%) of the total loads, because of a relatively small contribution of particulate load during storm runoff. The contribution of the loads of Mo, Zn, Cd, Cu, and Ni at lower flow rates to the annual loads was larger than that of other metals. It was found that the concentrations of these metals in ordinary runoff are strongly affected by the discharge of treated water from sewage treatment plants which are located along the catchment. Thus, treated water from sewage treatment plants may be the primary source contributing to the present pollution of Mo, Zn, Cd, Cu, and Ni in Tokyo Bay.