Trace metal and nutrient constitution of rain water and sediment/sludge harvested in various storage tanks from galvanized iron roof tops in Kampala City, Uganda

Abstract

Domestic rainwater harvesting (DRWH) provides an innovative solution to meeting water needs. However, problems of implementation, concerns about water quality and health remain unattended to especially in developing countries. In this study, rainwater and sediment/sludge samples were harvested from various storage tanks including concrete, metallic and plastic tanks whose house roofs are galvanized iron sheets. The samples were collected in four geographical locations in Kampala City, Uganda. Both rainwater and sediment/sludge samples collected were analysed for temperature, pH, EC, TDS, DO, hardness (Ca and Mg), nutrients (TN and TP) and some trace metals including Zn, Cu, Pb and Cd. Unlike sediment/sludge samples, the rainwater parameters such as temperature, pH, EC, TDS, DO were analysed on site using portable meters. Analysis of total dissolved trace metals was done using Atomic Absorption Spectrophotometer. The quality of rainwater varied slightly with different storage tanks. In terms of dissolved trace metals, Zn was the most predominant trace metal in rainwater samples with mean concentration values 0.389±0.186 mg/l, 0.920±0.629 mg/l and 1.119±1.039 mg/l for concrete, metallic and plastic tanks respectively. On the other hand, Cu was not detected in rainwater but had mean concentration values 0.498±0.193 mg/kg in the sediment/sludge samples. However, Pb exceeded WHO permissible limits for drinking water in all sampled tanks. The high levels of these trace metals, nutrients and other physico-chemical parameters obtained in this study may likely result in consumer complaints. This is because some of the parameters are not only liable to impacting bad taste in rainwater but are also carcinogenic.