Copper, zinc, lead and cadmium in roof and road runoff can be considered as major sources of heavy metals in urban drainage systems. Depending on the drainage system, they cause different environmental problems. In a combined sewer system heavy metals reach the wastewater treatment plant (WWTP) or can be discharged directly into a river as consequence of intense rainfall events. In the WWTP, heavy metals are transferred into the sewage sludge, to the receiving waters and into aquatic sediments [1]. If the sludge is used for land spreading in agriculture, heavy metals are distributed diffusely in agricultural soils where they accumulate slowly and may affect soil fertility [2].
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