Geochemical fractionation, mobility of elements and environmental significance of surface sediments in a Tropical River, Borneo

Miri River is a tropical river in Borneo that drains on flat terrain and urbanised area and debauches into the South China Sea. This paper documents the environmental status of this river, and provides an insight into the prov- enance using bulk chemistry of the sediments, and brings out the geochemical mobility, bioavailability, and potential toxicity of some critical elements based on BCR sequential extraction. The sediments are intense to moderately weathered and recycled products of Neogene sedimentary rocks. The hydrodynamic characteristics of the river favoured an upstream section dominated by fine sand, while the downstream sediments are medium silt. Based on the bulk geochemistry, the Miri River sediments are moderate to considerably contaminated by Cu, Mo, and As in the upstream and by Sb, As and Cu in the downstream. The potential ecological risk values are low except Cu and a significant biological impact is expected in downstream due to Cu, As, Zn and Cr. The mobility, bioavailability and Risk Assessment Code values for Zn and Mn are higher and thus may pose moderate to very high risk to aquatic organisms. Though a high bulk concentration of Cu is observed, the association of Cu with the bioavailable fraction is low.

Automated summary

This paper examines the environmental status of the Miri River in Borneo and investigates the provenance of its sediments through bulk chemistry analysis. The study also assesses the geochemical mobility, bioavailability, and potential toxicity of critical elements using BCR sequential extraction. The findings show that the sediments are weathered and recycled products of Neogene sedimentary rocks. The river's hydrodynamic characteristics result in a dominance of fine sand in the upstream section and medium silt in the downstream. The sediments are moderately to considerably contaminated by certain elements, with a significant biological impact expected downstream.