Heavy metal fractionation in roof run off in Ile-Ife, Nigeria

Runoff was collected from three different roofing materials that are commonly used for roofing in Ile-Ife, Nigeria, between the months of June to August, 2004. The samples were collected in four geographical locations in the town. The run offs were analysed for pH, Temp, TDS, CI^-, S0₄^2-, PO₄^3-, N0₃^2-, EC and some heavy metals both as regards total, dissolved and particulate fractions. Analysis of the heavy metals was done using flame Atomic Absorption Spectrophotometer. The quantity of these parameters varies with the different roofing materials. In terms of dissolved metals, Fe is the most predominant metal with mean values 0.59 ± 0.29, 0.82 ± 0.14, and 1.04 ± 0.27 mg/L for asbestos, ceramic tiles and metal sheets respectively. The tendency of the roofing materials to release dissolved metals is arranged as follows: Zn, Cr and Fe (metal sheet > Ceramic > asbestos); Cd and Pb (asbestos > ceramic > metal sheet). In terms of particulate metals, the concentration of Cd and Pb are higher in the asbestos than other roofing stuffs. The sequence of their predominance in asbestos is as follows: Pb (0.83±0.55 mg/L) > Cd (0.29 ± 0.07 mg/L). In all the roofs, both particulate and dissolved metals except Zn exceeded WHO permissible limits for drinking water. The high levels of the metals obtained in this study may likely result in consumer complaints since some of the metals are not only carcinogenic but are also liable of impacting bad taste in water.

Keywords
Runoff, heavy metals, roofing, flame atomic absorption spectrophotometry