Sediment pollutant fractionation and controlling factors of bioaccumulation and ecological risks in coastal benthic ecosystems around Kaohsiung Harbor

To understand pollutant fate, transport, and impacts in benthic ecosystems around Kaohsiung Harbor, a highly polluted international commercial harbor, this study evaluated sediment pollution status, fractionated sediment metals for bioavailability, illustrated benthic ecology and trophic status, and modeled the relationship of accumulated metals and their trophic transfer in different benthic organisms. As expected, grain size influenced sediment metal distribution, with fine sediments areas exhibiting higher anthropogenic metal inputs. Due to the impacts of pollution, benthic organisms (n = 1956) showed lower densities near the harbor entrances and metal distribution with high MPI near the harbor entrance (10.4) and marine outfall (5.43), decreasing offshore (2.27–4.25). Metal bioaccumulation significantly differs among benthic organism groups, with mollusks accumulating more due to their trophic position and feeding habits. Lower trophic levels accumulated higher levels of Cu, Cr, Cd, Ni, and Pb, leading to biodilution, while As and Hg biomagnified (TMF > 1, p < 0.05), exceeding safety thresholds and posing ecological and human health risks. PCA exemplified the relationship of sediment available metals with biota, supporting their role as a major driver of bioaccumulation. This study provides comprehensive evidence of pollutant impacts in benthic ecosystems, crucial for accurately estimating ecological risks, bioaccumulation indices, and pollution management.