Lead and lead isotopes as tracers of soil contamination in southwestern Nigeria

Abstract

The association of soil Pb levels has received considerable attention in recent times in developing countries like Nigeria due to its human health and environmental effect. Unfortunately, the sources of the pollutant has not been resolved for environmental health interest. Therefore, the aim of this study is to trace the sources of Pb contamination using the isotopic composition of Pb in the soil. Thirty (30) soil samples were collected at 0-20 cm depth in 3 different land-use zones, industrial area (IDA, n=10), municipal solid waste facility (MSW, n=10), and traffic section (TRS, n=10). In addition, 3 rock (gneisses) and 3 blacksmith dust samples were collected in the study area for comparison. Properties of the soil such as physico-chemical parameters (pH, organic content, and soil texture) and mineralogical composition were determined to understand the distribution of Pb in the soil of the study area. Similarly, the samples were analyzed for their Pb concentrations and Pb isotopic compositions using inductively coupled plasma mass spectrometry. The soil pH, organic matter, and texture were slightly acidic (4.9-6.9), average organic content (7.9-19.1%), and sandy clay loam in nature, respectively. Therefore, the Pb distribution was enhanced by the physico-chemical parameters. However, the mineral constituent of the soil in order of their abundance include quartz, feldspars, illite-muscovite, kaolinite, Biotite, goethite, and hematite. Consequently, there is no Pb-rich primary mineral in the soil. The environmental assessment of Pb in the study area showed that all the zones were contaminated on the basis of the average contamination factor and geoaccumulation index values. Similarly, the ecological risk factor estimation of Pb showed that the three zones had moderate potential ecological risk factors (41-54). The isotopic compositions of 208Pb/207Pb, and 206Pb/207Pb of the contaminated soil were lower than the corresponding component in gneisses, while the composition of 208Pb/206Pb was higher than the gneisses. Furthermore, the standard plot of (208Pb/207Pb) vs (206Pb/207Pb) showed clearly that the source of Pb in the contaminated soil was mainly from anthropogenic sources.Therefore, from the Pb concentration and isotopic composition acquired, the Pb contamination was mainly sourced from anthropogenic activities from the study area. These sources mainly include scrap metal recycling industry, vehicle emission and domestic and industrial waste. So, more effective remediation strategies need to be developed to reduce the contamination.