Potentially toxic elements across nearshore–beach sediment interfaces: Source apportionment and probabilistic risk assessment in the northern Beibu Gulf

Contamination by potentially toxic elements (PTEs) in coastal sediments poses increasing threats to marine ecosystems and human health. This study quantified eight potentially toxic elements (PTEs), including As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn, in nearshore and beach surface sediments collected from 18 and 24 sites in the northern waters of the Beibu Gulf, respectively. Principal component analysis, positive matrix factorization, and Monte Carlo simulation were integrated to resolve sources and probabilistic risks. In nearshore sediments, Cd and As concentrations exceeded regional background values by 29.91-fold and 2.18-fold, respectively. Bay-specific comparisons showed significantly higher Cd concentrations in beach sediments than in corresponding nearshore sediments in EB and BE, whereas the mean contamination factors of Hg and As were higher in beach sediments overall. Source apportionment indicated contributions from maritime transport and tourism, aquaculture and agriculture, and industrial activities. Cd dominated the ecological risk assessment, with a sensitivity exceeding 96%, resulting in a high overall ecological risk across the coastal zone. Under the adopted recreational exposure assumptions, non-carcinogenic health-risk estimates for beach-sediment exposure remained below the screening benchmark. These findings identify Cd and As as priority contaminants for source control, targeted beach monitoring, and risk management for sensitive populations.