Soil heavy metals across land uses on Zhoushan Island, China: Spatial patterns, risks, and potential sources

Heavy metal accumulation in island soils is a critical environmental issue because spatially constrained coastal systems receive overlapping inputs from urbanization, tourism-supporting infrastructure, shipping, industry, and agriculture. In this study, 43 surface-soil samples from 42 locations on Zhoushan Island, China, were analyzed for As, Cd, Cr, Cu, Ni, Pb, and Zn using contamination indices, health-risk assessment, multivariate statistics, and positive matrix factorization (PMF). Mean concentrations of all seven metals exceeded the Zhoushan background values, with Zn showing the greatest variability and exceeding the national soil risk-screening value at 6/43 sites (13.95%). Cd dominated ecological risk, with 21/43 sites (48.84%) exceeding the low-risk category under the primary Zhoushan background. Screening-level health assessment showed that children had higher estimated risks than adults, with HI > 1 at 6/43 sites (13.95%), while Cr and As were the principal contributors to carcinogenic risk. The five-factor PMF solution was interpreted as exploratory, with complementary concentration-based evidence supporting broad geogenic, Cu-associated anthropogenic, Pb-associated urban-deposition, and CdZn mixed anthropogenic profiles. Background sensitivity further showed that 10/43 RI classifications changed between reference datasets, particularly affecting Cd-related risk estimates. This study provides an uncertainty-explicit island-scale screening baseline for confirmatory monitoring, hotspot verification, and precautionary soil management in densely inhabited coastal environments.