Integrated assessment of trace element enrichment and accumulation in estuarine sediments of southwestern Taiwan using Sr/Ba ratios and pollution indices

This study investigated 64 surface sediment samples from eight estuarine zones in southwestern Taiwan (2021–2024), collected during both dry and wet seasons. A central focus of the research was the evaluation of the strontium-to-barium (Sr/Ba) ratio as a diagnostic indicator of sedimentary environments to refine regional geochemical baselines. Samples exhibiting Sr/Ba > 1, indicative of marine influence and lower anthropogenic impact, were selected as reference conditions for pollution index calculations. In contrast, estuaries within ports exhibited higher mud and total organic carbon content and elevated concentrations of Zn, Pb, Cd, Hg, and Ag, reflecting anthropogenic inputs and pollutant accumulation. Pollution indices, enrichment factor (EF), geo-accumulation index (I geo ), and potential ecological risk index (PERI), were applied using samples with Sr/Ba > 1 as representative background values. Results showed that port estuaries are pollution hotspots, with mean EF values of 2.5–5.0 and PERI values reaching 542–1383, mainly due to Hg, Ag, and Cd. Principal component analysis identified four geochemical controls: anthropogenic sources, lithogenic background, grain size/organic matter effects, and redox-driven metal mobility. Overall, Sr/Ba ratios served as a complementary geochemical indicator for distinguishing marine and terrestrial environmental influences, improving the contextual interpretation of pollution assessments in dynamic estuarine environments. • Sr/Ba ratio distinguishes trace element accumulation and sedimentary environments in estuaries. • Semi-enclosed estuaries with weak hydrodynamic energy are major pollution hotspots. • Hg and Cd pose the highest ecological risks in Kaohsiung estuarine sediments. • Integrating Sr/Ba ratios with pollution indices improves pollution assessment accuracy. • Combined indicators improve interpretation of estuarine contamination and sources.