A comprehensive analysis of tracing the sources and dynamics of pollutants in a tropical Miri River, NW Borneo

Abstract The fractionation and distribution of elemental composition in water (particulate and colloid) and sediments were assessed to understand the major geochemical processes that control the contaminant transport in the Miri River, NW Borneo. Further, the study also focused on determining the potential sources of geochemical elements and assessing the ecological risk. In this regard, 11 surface water and 35 river bed sediment samples were collected along the course of the Miri River and analyzed for various elemental compositions. Pollution indices such as geo-accumulation index (I geo ) and contamination factor (CF) were used to determine the pollution status of the river. Principal component analysis (PCA) was also used to identify the key geochemical processes that control the metal distribution and its sources. The interpretation of the results indicates that elemental distribution in size fractions showed an increasing concentration trend from the colloidal to the particulate fraction. Fe was observed to be the dominant metal in both water and sediments, indicating the weathering of river sediments. Cd, Pb and Zn are mostly derived from anthropogenic impacts and risk evaluation indicate the probability of adverse ecological threats to the riverine biota. Colloidal fractions (0.30 µm and 0.20 µm) were identified as the primary facilitators of contaminant transport, particularly in the upstream and midstream, whereas particulate (0.45 µm) dominates in the downstream due to the tidal influx of seawater. PCA analysis confirmed that the majority of pollutants were contributed by domestic and industrial discharge, seawater incursion, geogenic sources and agricultural inputs.