An estimate of diffuse sources of heavy metals (Hg, Cd, Cu, Zn, Pb, Cr, Ni) in the Rhine catchment stressed the urban storm water discharges in the German part and drainage flow in the Dutch part as the most important pathways. Additional sources are erosion and, to a far lesser extent, atmospheric deposition on open water areas. All other pathways were of minor importance. Meanwhile, after reduction of the point sources by between 72-95%, the diffuse sources dominate the total emissions. For several metals the anthropogenic diffuse sources amounted to 40-80%, the point sources to 15-40% and the geogeneous sources to 5-40%. The estimated inputs sufficiently agreed with the loads of the river Rhine. For the estimation, mean values were used for the water masses and the substance concentrations of the different hydrological pathways. It is recommended to undertake further studies on diffuse sources of heavy metals in urban areas and on the possibilities to improve urban storm water management. The calculation methods and the recommendations of the International Commission for the Protection of the Rhine (ICPR) are explained in detail.

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