Microplastic–Heavy Metal Interactions across Water, Sediment, and Biota in the Benue River, Nigeria

Abstract

Microplastic pollution in freshwater systems has become a global challenge with serious consequences for our environment. An effective management system remains a critical challenge due to poor control and monitoring systems arising from a lack of understanding of its dynamism, especially in data-limited regions. Therefore, this paper assessed the microplastic–heavy metal interactions among water, sediment, and biota in the Benue River, Nigeria using appropriate standard procedures. Microplastics were found in all sampled compartments, with concentrations ranging from 2,275 to 13,258 particles L⁻¹, placing the river among highly contaminated freshwater systems globally. The dominance of fragment-type particles points to active in situ degradation processes that increase surface reactivity. Heavy metal analysis showed elevated levels of Pb, Cr, Fe, and Mn, with clear spatial overlap between microplastics and metal hotspots, particularly in urban areas. Strong correlations (r = 0.64–0.86) and pollution indices (CF, PLI, MPII, MMII) further confirm that microplastics and metals are closely linked, with the water column serving as a transport pathway and sediments as long-term storage zones. Fish contamination patterns suggest that exposure is mainly driven by sediment interactions rather than by direct water uptake. Machine learning results (Random Forest, R² = 0.704) showed that microplastic characteristics—especially matrix type and particle form—can reliably predict metal burden. Overall, this study shows that microplastics are not just passive pollutants but active drivers of contaminant transport and bioavailability, and it offers a practical, data-driven framework for improving environmental monitoring and management in rapidly urbanising freshwater systems.