The Sources of Lead Pollution in a Tropical Soil Chronosequence Based on Lead Isotope

Soil is important contributor to global biogeochemical cycles and often receives anthropogenic Pb contamination. Hainan soil chronosequence developed on basalt had provided a good opportunity to identify and quantify the relative contributions of Pb sources in remote tropical areas. The results revealed that Pb concentrations and isotopic ratios of the soils were clearly affected by anthropogenic source. The Pb concentrations and percentage changes of Pb/Th ratios showed significantly Pb enrichment. The low 206 Pb/ 207 Pb values of upper soils indicated a significant addition of extraneous Pb, whereas deeper soils showed a dominantly basaltic source. The 208 Pb/ 206 Pb vs. 206 Pb/ 207 Pb diagram of soils clearly indicated inputs of parent material and anthropogenic Pb sources. We also calculated the mass fractions of anthropogenic-derived Pb (ƒ Pb anthropogenic) based on isotope mass balance. The ƒ Pb anthropogenic values showed a generally decreasing trend with soil depth, implying a significant addition of anthropogenic Pb in top soils. The contribution of anthropogenic Pb in Hainan soil chronosequence highlighted the significance of anthropogenic contamination to soils globally.