Deciphering multi-media occurrence and anthropogenic drivers of potentially toxic elements in a rapidly urbanized estuary: A neural network-enhanced source apportionment

Estuaries and adjacent waters are the most important and vulnerable areas to human activities in coastal seawater, and potentially toxic elements (PTEs) pollution have long received global attention. This study presents a multi-media occurrence to assess the distribution, sources, and ecological risks of PTEs (Cu, Pb, Zn, Cd, Cr, Hg, and As) in the Modaomen Estuary, a rapidly urbanizing coastal zone in southern China. Results revealed that the most abundant elements in seawater, surface sediment, and marine organisms was Zn, while the element with the lowest concentration was Hg. The PTEs in seawater is at a low pollution level according to the comprehensive pollution index (CPI). Sediment analysis highlighted significant enrichment of Cd and Hg, with potential ecological risk index (PERI) identifying these elements as the primary contributors to ecological hazards. Zn in seawater is the most easily enriched element by marine organisms. By integrating advanced Self-organizing maps (SOM) and Positive matrix factorization (PMF) model, we conducted a comprehensive source analysis of PTEs. The SOM-PMF model successfully delineated three major anthropogenic sources-industrial wastewater discharge, fossil fuel combustion, and agricultural activities-accounting for 62.5 % of the total PTEs contributions. This study not only provides a robust framework for understanding PTE dynamics in estuarine environments but also introduces an innovative methodological approach for source apportionment and risk assessment.