Trace metals in bulk freefall and roof intercepted rainwater at Ile-Ife, Southwest Nigeria

Abstract

Samples of bulk freefall and roof-intercepted rainwater collected over five roof types (viz: Iron–Zinc sheets, Aluminum sheets, Asbestos sheets, Slate tiles, and Thatch) at Ile-Ife (SW Nigeria) were analysed for nine trace metals (aluminum, cadmium, chromium, copper, iron, lead, manganese, nickel, and zinc) using atomic absorption spectrophotometry (AAS). The mass concentrations and percent detection of the trace metals were generally higher in roof-intercepted samples than in the freefall samples. The ranking order of the mean concentrations of the metals in freefall samples (Al > Cr > Fe > Zn > Pb > Mn > Ni > Cu > Cd) is indicative of an atmospheric environment greatly influenced by heavy vehicular emissions and remobilized suspended particulate matter of soil origin. Mean metal enrichment of samples over the different roofs was in the order of Iron–Zinc > Aluminum > Thatch > Asbestos > Slate roof. Each roof sample type (except Slate samples) was characterized by relatively high enrichment of one or two metals. These include the high enrichment of zinc and iron in Iron–Zinc roof samples, cadmium and manganese in Aluminum roof samples, copper and manganese in Thatch roof samples and cadmium in Asbestos roof samples. The metal concentrations of roof-intercepted rainwater were lower than those of neighboring surface water, packaged table water, and vegetation-intercepted rainwater in the same environment. The metal levels in all the rainwater sources occurred within the allowable guide levels for most public and domestic applications.

Keywords:

• Atmospheric precipitation
• Roof collected rainwater
• Public water supply
• Water quality
• Metal enrichment
• Dust remobilization
• Vehicular traffic