Microplastics in the lower Volta Basin, Ghana - Quantitation and fish dietary exposure assessment using advanced...

Despite recent surge in microplastics (MPs) research, there is a paucity of information on freshwaters in Ghana. For the first time, MPs in cage and wild sites of the lower Volta Basin were evaluated, and polymer type characterized using LDIR and ATR-FTIR. Seasonal variations and mode of fish production significantly influenced MPs abundance. In fish, MPs concentration of 387 ± 33.85 (wet season) contrasted with 288 ± 21.4 items individual^-1 (dry season). Benthopelagics consumed 63% MPs; cage benthopelagics- Oreochromis niloticus consumed 58.5% MPs. Statistically significant differences in mean MPs were observed in fishes. MPs extracted from grower feed for cage fish was ≥24 items (kg feed)^-1. The high metabolic rates of smaller-weighted fishes induced a higher consumption of MPs. From fish health assessment, a positive growth coefficient was observed for Oreochromis niloticus; negative allometric growth was observed for some wild fishes. Spatially, MPs decreased in fish along Basin sites- Asikuma (365 ± 36.58 items individual^-1) > Kpong (209 ± 19.71 items individual^-1) > Sogakope (71.3 ± 20.86 items individual^-1). The Basin sediment was significantly polluted (1950 ± 80 MP items (kg dw)^-1), contrary to the freshwater (111.0 ± 11 MP items (L water)^-1). 12.3% of MPs polymers characterized had aged and 54% of particles were unknown. MP shapes detected were fibre (97.9%), fragment (2.1%) and film (0.06%). Dominant particle sizes (0.50-2.50 mm, 85%) were black- and blue-coloured. Major polymers were acrylates-polyurethane-varnish (45.7%) and PVC (39%). Lower contributions were obtained from PET, PA, PP, PE, and PE-Cl. An estimated freshwater-fish annual intake (cage: 2561; wild: 4785 MP items (person year)^-1) exceeded the recommended EUMOFA/NOAA guidelines (518-3078 particles (year capita)^-1). From this study, plastic aquaculture infrastructure from fish cages, effluents, and fishmeal contributed to MPs consumed by fish. This study provides baseline data on MPs distribution within the Volta Basin, Ghana.