Zinc and copper in roof runoff
The zinc and copper content of roof runoff could originate from different sources such as dry and wet deposition and the corrosion of the material. The zinc runoff rate from a galvanized surface depends on the corrosion products formed during the dry days, the rain intensity and roof slope, which determinates the contact time. In the present study the contact time dependence of zinc rate and the re-dissolution of the zinc were investigated with steeping tests and a pilot study. The average zinc runoff measured in the first 2.8 l of runoff was 3.8 mg m–2 (1.1–8.4 mg m–2), while in the following samples 1.2 mg m–2 were detected. These results are in accordance with the 5–10 min, and 40–60 s contact time laboratory steeping test, respectively, which are realistic. The estimated specific yearly zinc runoff rate was 0.7 g m–2y–1, while the dry and wet deposition rate of copper was 0.009 mg m–2d–1 and 0.053 mg m–2storm–1 respectively. The re-dissolution of the zinc from the evaporated then re-filled samples of leaching tests with high initial zinc content was just 60% after 60 min.