Linkage between human population and trace elements in soils of the Pearl River Delta: Implications for source...

The human population is both an emitter and receptor of metals. This study aims to clarify how the relationship of metals and metalloids to human populations influences their source characterization and health risk, based on metal concentrations in 298 soil samples in the Pearl River Delta (PRD) and the corresponding zip-code level population. Nickel (Ni), copper (Cu), zinc (Zn), cadmium (Cd), mercury (Hg), and lead (Pb), but not chromium (Cr) and arsenic (As), were significantly correlated with population (p<0.01), suggesting potential anthropogenic sources. A principal component analysis (PCA) revealed three factors (i.e., F1, F2, and F3) contributing to metal levels in the PRD: (1) metal transport from rivers (F1), which explained the high levels of Cr, Ni, Cu, Zn, As, and Cd in downstream areas; (2) industrial sources (F2), mainly contributing to Ni, Cu, Zn, Cd, Hg, and Pb; and (3) natural and agricultural sources (F3), mainly contributing to As and Pb. F2 was significantly correlated with population, while F3 was not, indicating that an analysis of the correlation with population could be used to identify industrial sources of metals. Compared with directly calculated risks, the population-weighted non-carcinogenic and carcinogenic risks were increased by 4.2-4.9% and 7.7-9.2%, respectively. A unit increase in the concentration of industrial metals led to higher extra risks than a corresponding increase in natural metals due to the proximity to human populations.