Tracking heavy metals reveals sustainability deficits of urban drainage systems

Heavy metals such as cadmium, copper, lead and zinc are the critical metals in domestic wastewaters. Based on mass flow studies, the runoff from roofs and streets contribute 50-80% of these metals to the total mass flow in domestic sewage. Depending on the sewerage concept, the metals accumulate in different environmental compartments. Witt the combined sewer system, most commonly applied, the major part of the metals is bound to the sludge during sewage treatment. If the sludge is used in agriculture, the metals are enriched slowly in the top soils. With separate sewer systems, the metal loads to the receiving waters are increased, finally leading to accumulation in the sediments. If the new concept for the infiltration of runoff waters is applied, rapid and concentrated accumulation at the infiltration sites will occur. As a short term measure, new adsorptive elements in infiltration facilities would allow us to control the accumulation. The deposition of heavy metals in the environment cannot be avoided as long as no further efforts are made to reduce metal emission at the source. New partnerships between environmental/sanitary engineers and other professional groups such as architects, plumbers, car engineers, material technologists have to be established in order to minimize diffuse longterm deposition of hazardous substances and to be able to realize sustainable small water cycles without negative side-effects.