Micro-pollutants in urban residential roof runoff: Environmental and health implications.

Abstract

This study assessed concentration of micro-pollutants (heavy metals-Cd, Cu, Fe, Mn, Pb, and Zn; organic compound-PAHs, pathogenic microorganisms) in ambient and harvested rainwater under urban residential rooftops. Samples were analysed using standard analytical procedures. Rainwater harvested from the rooftops were alkaline (8.5-9.6) compared to pH of 5.94 for the ambient rainwater. Conductivity ranged from 95.2-150.4 μS/cm due to the dissolution of deposited aerosols and leaching of roofing materials. Turbidity, Cu, and microbial counts (HPC, E. coli, TC and FC) exceeded the allowable limits for drinking water with inputs from the rooftops. Concentration of Cu and Pb in harvested rainwater was higher than the WHO standards. Relative abundance of metals is as follows: Fe > Zn > Cu > Mn > Pb > Cd. Water quality from asbestos was the worst among the rooftops examined. Total PAHs was low ranging from 0.04 found in ambient rainwater to 0.18 in rusted galvanized iron sheet. All samples contain high amount of microbiological contaminants with the asbestos roofing sheet having TC and E. coli of 14000 and 12000 cfu/mL respectively. These can result in illnesses such as diarrhoea, urinary tract infections, respiratory illness and pneumonia. The study had shown that rooftops contributed significantly to contamination of harvested rainwater due to composition of roofing materials and age of the roof.