Assessing Seasonal and Spatial Variations of Heavy Metal Concentrations in Microplastics, a case study of Otuoke River, Southern Nigeria

This study assessed the seasonal and spatial variations of heavy metal concentrations in microplastics present in water (MCPW) within the Otuoke River, Southern Nigeria, employing an integrated analytical approach. A dissecting microscope was used to visually identify microplastics, and a Flame Atomic Absorption Spectrophotometer (FAAS) was employed to evaluate heavy metals in accordance with US EPA 3050B procedure. Investigated metals included Cr, Fe, Hg, Mn, Ni, Cu, Pb, and Cd. The findings showed that in every sampling location and season, the amounts of Cd, Pb, and Hg were below detection thresholds. Conversely, during the dry season, elevated concentrations of Cu (41.06 ± 6.67 mg/kg), Mn (133.22 ± 2.71 mg/kg), Ni (33.23 ± 0.72 mg/kg), Cr (15.96 ± 0.67 mg/kg), and Fe (14,072.18 ± 1402.27 mg/kg) were recorded. These concentrations significantly exceeded the permissible limits and chronic hazard rating (CHR) recommendations set by the Federal Environmental Protection Agency (FEPA). Seasonal analysis showed that the concentrations of these metals declined sharply during the wet season. Principal Component Analysis (PCA) showed two major components with 85% of total variance, indicating common sources and intermetallic associations. This study is a pointer to the potential health and ecological risks posed by heavy metal-laden microplastics, indicating the need for stringent pollution control measures. The findings contribute to understanding the interaction between microplastics and toxic metals in river systems, suggesting a platform for environmental management cum policy framework in the Niger Delta regions and other regions with similar contamination profiles.