Tracking Lead in Environmental Media in the City of Onitsha, Southeast Nigeria

BACKGROUND. The enrichment of lead (Pb) in a rapidly expanding urban environment is largely caused by industrial and anthropogenic activities. However, very few studies have come from sub-Sahara Africa as a whole, in spite of the increased rate of population, industrialization and urbanization in this region. The city of Onitsha is the commercial heartland of southeast Nigeria. OBJECTIVES. To determine the concentration of Pb in soils and sediments in Onitsha and the surrounding area and to identify the possible sources of Pb content in the environmental media. METHODS. One hundred and sixty-two (162) samples (120 top and subsoils, and 42 stream and side drain sediments) were collected from the city of Onitsha, Nigeria to determine Pb concentrations, identify the main sources of Pb in this region, and determine its fate in soil and sediments using Pb isotopes. Thirty (30) 15 g clay fractions of soil and sediment samples, and a sample each of galena (from the Lower Benue Trough), coal and soot from vehicle exhaust and battery cells were collected from the city and analyzed for lead isotopes (Pb204, Pb206, Pb207 and Pb208) using ultra-trace inductively coupled plasma emission spectrometry. RESULTS. The distribution and concentration of Pb in the soil of Onitsha was observed to be influenced by land use patterns with very elevated concentrations of Pb observed for mechanic and metal workshop samples (1444.3, 1067.5, 1048.1, 1730.5 and 580.5 ppm); active waste dump samples (448.4 and 311.9 ppm); and farmland and garden samples (366.2 ppm). The concentration of Pb in the sediments also showed varying elevated concentrations across locations, ranging from 45.7–540.1 ppm. A comparison with the control samples revealed that the Pb concentrations measured in the environmental media were several folds higher than that of the control. The Pb isotope analysis indicated that most of the Pb in environmental media was anthropogenic in origin and had been predominantly contributed by unsustainable environmental practices such as indiscriminate waste dumps, hydrocarbonbased products emissions, by-products from mechanical workshops that have been haphazardly constructed in the city, and industrial plants located within urban areas. CONCLUSIONS. The relatively higher concentrations of Pb in soils and sediments were found to be influenced by land use, as also observed in the Pb isotope readings, which will, over time, adversely affect environmental media and biota. COMPETING INTERESTS. The authors declare no competing financial interests.