The EU Water Framework Directive1 requires Member States to take actions to achieve good chemical and ecological status of surface and ground water by 2015. It has identified 33 priority substances plus 8 other pollutants that are harmful to ecosystems and aquatic systems and include cadmium, mercury, lead and nickel. As a starting point, Member States are required to identify all sources of emissions affecting water quality in river basins.
The study identified and assessed the main human sources of metallic substances in receiving waters and summarised research findings in this area.
The effects of stormwater on metal levels in water have increased with urbanisation. Levels of cadmium, lead, copper and zinc in stormwater can be as high as those found in raw sewage and wastewater treatment plant (WWTP) effluent. The atmosphere, traffic and building materials are the most significant sources of metals in stormwater. Traffic wastes from sources, such as brake linings and road dust, generate substantial metal levels in water run-off from roads, particularly zinc but also lead and cadmium. Building materials used in roof coverings affect concentrations of mainly copper, lead and zinc in roof run-off.
The influence of metals due to effluents from industry will vary with country because each Member State implements its own regulations on treatment before discharge into receiving waters.
Effluents from WWTPs contribute significantly to a wide range of metal concentrations. The source of these can be household products, commercial effluents (especially car washing) and drinking water. Although WWTPs reduce total levels of metals, a proportion of dissolved metals remains untreated, particularly nickel. Metal levels in drinking water are influenced by geological conditions, plumbing systems and purification processes. The sewage system itself gives rise to metal inputs due to copper sewage pipes and, if left for a long time, the sewage sediments can cause metals to remix in the water.
Agriculture is another source of metals. Phosphate fertilisers release both cadmium and zinc, whilst sewage sludge used as a fertiliser may be a source of nickel, cadmium and zinc.
The research listed several additional factors that can increase metal concentrations. Sediments are an integral part of water systems but also a potential source of metal pollutants. The contribution of sediments to metal concentrations in waters has been estimated to be 20 per cent for cadmium, 30 per cent for copper and 10 per cent for zinc. The mining industry can also emit metals into water from mine waste, such as tailings and mine water. Landfills contribute to metal concentrations due to rainwater flowing through waste that contains metals. Lastly, sporting activities such as boating, fishing and shooting, also contribute to metal concentrations.
The study has outlined several important sources of metallic pollutants. Further research is needed to evaluate the relative contributions of each source on a case-by-case basis and to investigate the influence of societal and environmental conditions, for example, by collecting data on household practices and rainfall specific to catchment areas.
Source: Chon, H., Ohandja, D. & Voulvoulis, N. (2010). Implementation of E.U. Water Framework Directive: source assessment of metallic substances at catchment levels. Journal of Environmental Monitoring. 12: 36-47.