Zn and Pb emissions from roofing materials--modelling and mass balance attempt at the scale of a small urban catchment.

Many studies have shown that roofing materials are an important source of metals in urban runoff. Today, in the context of the European Water Directive (2000/60 CE), the quantification of these emissions is necessary, and thus the development of assessment tools is needed. This study focuses on a small urban catchment (drained by a separative sewer system). Atmospheric fallout, road runoff, roof runoff and total runoff at the outlet of the catchment were sampled. The aim is (1) to verify the contribution of roofing materials to metallic flows of Zn and Pb at the catchment scale and (2) to try to model emissions using some models previously developed at the test-bed scale. These models have to be tested at different spatial scales. Results obtained confirm the strong contribution of roofing materials to Zn and Pb flows at the catchment scale. For Zn, models tested were successfully transposed and validated at the roof and the catchment scales, permitting a good quantification of Zn emissions. For Pb, the use of the models highlights some difficulties, especially concerning the identification and the quantification of lead surface areas implemented.