Distribution and partitioning of metals in surface sediments of a coastal river dominated ecosystem: Insights to geochemical fractionation, sources and ecological risk

Riverine is the most vital ecosystem, which serves numerous important benefits to their locality, and it undergoes various chemical reactions that influence coastal water composition, nutrient cycling and broader geochemical processes. In this research, geochemical fractionation of metals with respect to the spatial distribution in the Miri River was examined. Initially, pXRF survey was conducted to understand the spatial variability of metal concentrations in the river sediments. Subsequently, selected sediment samples in the vulnerable zones (upstream, mid-stream and downstream) were collected and extracted into different geochemical phases via sequential extraction method, and analysed for metal concentrations. From the pXRF results, the order of dominance of metals are as follows: Fe > Zn > Pb > Cr > Ni > Cu > Mn > Cd, in which the higher concentration of metals was observed in the downstream and upstream sections of the river. From the sequential extraction, most of the metals are associated with residual, Fe-Mn oxides and organic matter fractions, as absorbed phases with less mobile and less readily available condition. Factor analysis also confirms that Fe-Mn oxyhydroxides was the major geochemical phase to absorb metals from various sources including anthropogenic activities and chemical weathering. Various pollution indices have been used to assess the potential ecological risk of the river sediments. All the indices revealed the contamination level of river sediments, particularly the elevated concentration of Cd and Ni. From this study, sequential extraction offers insights into the fractionation, availability, and mobility of metals, which can aid in evaluating environmental contamination in the river.