Interplay of natural and anthropogenic factors in source and distribution of heavy metals in Pingtan coastal area, Fujian Province

The coastal area of Pingtan in Fujian Province holds strategic importance in the development of the Western Taiwan Strait Free Trade Zone, yet the issue of heavy metal pollution has come to the fore in recent years. This study focuses on the Pingtan coastal area of Fujian Province, China, employing field surveys, sample collection, and laboratory analyses integrated with multivariate statistical and spatial analysis techniques to investigate the interplay of natural and anthropogenic factors in the sources and distribution of heavy metals. The results indicate that the concentrations of Cu, Pb, Zn, Cr, Cd, As, and Hg in surface sediments all comply with the Class I standards of China’s Marine Sediment Quality Criteria. Hg exhibits the highest coefficient of variation, reflecting significant spatial heterogeneity, while the remaining elements demonstrate moderate CVs and relatively uniform distributions. Compared with Xiamen, Meizhou, and Xinghua Bays, Pingtan shows lower mean concentrations for most heavy metals. Spatial distribution patterns reveal distinct regional heterogeneity in heavy metals, with the formation of high- and low-concentration zones influenced by both natural and anthropogenic factors. The geoaccumulation index indicates that Cd exhibits relatively higher pollution levels, with mild to moderate contamination in some areas, while As shows slight pollution in two stations. The pollution load index suggests that the study area remains uncontaminated overall. Ecological risk assessment demonstrates that, apart from Cd, all other heavy metals pose low ecological risks. Cd presents moderate to high ecological risk, serving as the primary contributor to overall risk, followed by Hg, resulting in a moderate comprehensive ecological risk level for the region. Pearson correlation analysis reveals significant correlations among certain heavy metals, indicating shared sources or similar migration and transformation patterns, while other elements exhibit weak or negative correlations, suggesting divergent origins or environmental behaviors. Principal component analysis extracts four principal components, representing natural sources, anthropogenic sources (primarily industrial emissions and traffic pollution), mixed sources, and agricultural/phosphorus fertilizer inputs, respectively. This highlights the complexity of heavy metal sources and the intricate interactions between natural and anthropogenic factors in governing their distribution and accumulation patterns.