Roof runoff contamination: a review on pollutant nature, material leaching and deposition

Roof runoff is generally perceived as a relatively clean source of water and is therefore often discharged or used without any treatment. Available data from literature however show that roof runoff can be contaminated by a wide range of (micro)pollutants, and in concentrations often exceeding surface water quality and/or drinking water standards. In this review, information on more than 100 contaminants, including trace metals, polycyclic aromatic hydrocarbons, pesticides, phthalates, alkylphenols and alkylphenolethoxylates, is summarized and a meta-analysis provides quantitative proof that roof runoff is a major contributor to stormwater quality deterioration. The two prime sources of roof runoff contamination are leaching from roofing materials and atmospheric deposition. A detailed discussion on material-pollutant relationships is given and a benchmarking method is presented which ranks roofing materials based on their runoff quality. Treated wood roofing and metallic rooftops (copper and zinc) were found to have the highest impact on water quality. Atmospheric deposition is also discussed in detail and includes a summary on the concentration levels in deposition for more than 400 pollutants such as trace metals, pesticides and polycyclic aromatic hydrocarbons. As a conclusion, it can be argued that the general perception on roof runoff quality is inaccurate and that its quality aspects should not be overlooked when roof runoff is used or discharged.