Soil heavy metal pollution and health risk assessment of a residential land in Hangzhou City

This study aims to investigate the status of heavy metal pollution in soil resulting from the conversion of industrial land to residential land, analyze the sources, and evaluate health risks. Using a residential area in Hangzhou as the research site, a total of 67 soil samples were collected at different depths. Various methods, including the potential ecological risk index, PMF model, and Monte Carlo simulation, were employed to analyze the distribution characteristics, pollution levels, and sources of six heavy metals (Cu, Ni, Pb, Cd, As, Hg) in the study area, as well as to assess human health risks.The results indicate that the concentration of heavy metals follows the order: silty clay layer > silt/silty clay layer > mixed fill/clean fill layer, all of which are significantly below the risk screening values for construction land. In the mixed fill/clean fill layer, the average Hg content is 2.78 times the background value, showing significant human activity influence. The Nemerow index reveals that 52%, 66.7%, and 94.4% of points in the three soil layers are classified as lightly polluted, with 16% of points in the mixed fill/clean fill layer categorized as heavily polluted. Potential ecological risk assessments indicate that the mixed fill/clean fill layer is at a moderate ecological risk level, while others are at a slight ecological risk level. Correlation analysis, principal component analysis, and PMF modeling suggest that the sources of heavy metals include industrial sources (35.55%), traffic sources (26.37%), and special process sources (17.06%). Health risk assessments reveal that the non-carcinogenic health risks of heavy metals for both adults and children are negligible, while Ni and As present a certain tolerable carcinogenic risk for both groups. Notably, children’s non-carcinogenic-carcinogenic risk is higher than that of adults. Sensitivity analyses show that As is the main contributor to non-carcinogenic risk, whereas soil ingestion rate (IngR) and Ni are the primary factors influencing carcinogenic risk for both adults and children. In summary, the study area is generally under light pollution, with Hg and Ni identified as key pollutants requiring control. The findings provide a theoretical basis for formulating pollution prevention measures in the region.