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.

Annual metallic flows in roof runoff from different materials: test-bed scale in Paris conurbation.

A substantial database of annual metal runoff loads, obtained from a 14-month field exposure campaign on 12 different metal roofing materials at two sites within Paris conurbation, is presented herein. Thirteen metallic species have been considered. A comparison among the various roofing materials yields a ranking of their runoff pollution potential, which highlights that aluminum, coated products, and stainless steel display the lower emission levels, before zinc and copper materials. Lead materials appear to release more metallic species, and tend to do so in quite large quantities. Whatever the material family considered, older materials apparently release more metallic species with higher levels of emission. In considering zinc emissions from zinc-based materials, it is clear that surface coatings significantly reduce zinc emissions (40% less for the Zn3(PO4)2 surface-treated Anthra zinc, compared to natural zinc; and 99% less for prepainted galvanized steel compared to standard galvanized steel). In the case of Anthra zinc however, surface treatment induces the release of Ni into the runoff, and Ni constitutes a priority pollutant in the European Water Framework Directive (2000/60 CE). A high level of consistency with literature data has been found for Zn runoff when considering runoff rates reported at the same inclination.