PhD student Alexandra Andersson Wikström studies the sources of stormwater pollution. She has examined what kind of pollutants come from different types of roofing materials when snowmelt and rainwater runs off roofs and via stormwater sewers is carried out into lakes and streams.
'We prepared synthetic rainwater and then poured it in beakers together with small pieces of 16 different roofing materials', she says. Analysis of the water showed that asphalt shingles released the highest number of pollutants.
The study included conventional roofing materials such as clay and concrete tiles that are common on houses, copper and zinc sheets, which occur, for example, in churches and roofing felt that is used on houses and large buildings.
Both dissolved metals and the total concentrations of metals in stormwater, as well as organic pollutants such as PAHs formed during combustion and also present in oil products, nonylphenol which is an industrial chemical used for example in manufacturing of plastics and paints as well as herbicides which can be added to prevent fouling on roofs, have been analyzed.
Pollution from roof runoff in stormwater systems come from both atmospheric deposition on the roofs and substances that are released directly from the roofing materials. The study shows that a surface treatment on the material can reduce release. It also shows that large differences may occur in the release from different materials that seemingly have a similar composition. The results from the study attracted big interest when presented on conferences in Berlin and Stockholm last autumn.