Source apportionment and health risks of the bioavailable and residual fractions of heavy metals in the park soils in a coastal city of China using a receptor model combined with Pb isotopes

The differences in the characteristics and sources of heavy metals in the park soils between bioavailable and residual fractions remain insufficiently demonstrated. In this study, 52 park soil samples were collected in Xiamen, southeast China. A modified sequential extraction method recommended by the European Community Bureau of Reference (BCR) was used to determine the speciations of V, Cr, Co, Mn, Ni, Cu, Zn, As, Cd, Ba, and Pb. Differences between different fractions in the sources and risks of heavy metals were determined using the Pb isotopes, multivariate statistical analysis, and a human health risk model. Based on enrichment factors (EFs) and comparison with a previous record, the contents of Cu, Zn, As, Cd, and Pb in the park soils were significantly influenced by anthropogenic sources, while those of Mn, Ba, V, Cr, Ni and Co were partially impacted by human activities. The bioavailable fraction constitutes important proportions of Cd (82.0%), Cu (58.5%), Mn (58.4%), Zn (57.6%), Co (55.4%), and Pb (50.3%), but 68.6-85.4% of V, Cr, Ni, As, and Ba are mainly present in the residual fraction. Principal component analysis and multiple linear regression (PCA-MLR) revealed that anthropogenic sources are the dominant contributors to the bioavailable fractions of most heavy metals, excluding Cr and Ni. However, 55.1-100% of the anthropogenic sources still contribute to the residual fractions of Cd, Ba, Pb, As, and Mn, which was confirmed by Pb speciation isotopes. These results imply that anthropogenic sources influence both the bioavailable and residual fractions, but more significantly impact the bioavailable fraction. The major contributing elements of Cr, Pb, and As as health risks mainly originate from soil parent materials, coal combustion, pesticides, and fertilizers. This study provides an example of source appointment between bioavailable and residual fractions to identify actual source-specific health risks of heavy metals in the park soil.