Abstract

<p>Microplastics (MPs) have emerged as significant carriers of heavy metals in aquatic ecosystems, raising concerns over their ecological and public health implications. This study investigates the concentrations of cadmium (Cd), copper (Cu), chromium (Cr), iron (Fe), manganese (Mn), nickel (Ni), lead (Pb), and mercury (Hg) adsorbed onto microplastics collected from surface waters of the Otuoke River, South-South Nigeria, during both dry and wet seasons. Microplastic-bound water samples (MCPWs) were processed using the US EPA 3050B digestion protocol and analyzed with Flame Atomic Absorption Spectrophotometry (FAAS).</p>
<p>Results revealed marked seasonal differences in metal concentrations, with significantly higher levels recorded during the dry season (p &lt; 0.05). Among the findings, the highest copper (41.06 ± 6.67 mg/kg) and manganese (133.22 ± 2.71 mg/kg) concentrations were observed at sampling site STA-, while iron peaked at STA-3 with 13,932.68 ± 489.70 mg/kg. These variations suggest that hydrological changes influence metal adsorption dynamics in MPs.</p>
<p>Health risk assessments were conducted using Hazard Quotient (HQ) and Hazard Index (HI) models for both adults and children. Dry season HI values exceeded the safety threshold (&gt;1) for adults and indicated significant risk for children (&gt;10), reflecting heightened exposure due to increased metal bioaccumulation. In contrast, wet season assessments showed lower metal concentrations and reduced health risks, with HI values generally falling below critical levels for adults at several locations. Nonetheless, children remained more vulnerable, with potential risk levels persisting across both seasons.</p>
<p>The study highlights the dual threat of microplastics and heavy metals in freshwater systems and their compounded risks to vulnerable populations, particularly children. It underscores the urgent need for targeted pollution control strategies, including improved waste management, environmental monitoring, and stricter regulatory enforcement. These findings contribute to the growing body of knowledge on microplastics as contaminant vectors and support the development of proactive public health and environmental policies in Nigeria and similar contexts</p>