Concentrations, characteristics, and human health exposure assessment of microplastics and heavy metals in freshwater fish in a potable water supply reservoire

Microplastic pollution in the environment is a global concern because it exposes the ecosystem and biota to microplastics and other contaminants that adsorp to their surfaces. Fish are regularly consumed by humans, exposing people to microplastics through their consumption. In this study, we investigated microplastics and heavy metals in catfish (Clarias gariepinus) and tilapia (Oreochromis niloticus) in a portable water supply reservoir in Ghana. We quantified microplastics (MPs) and polymer composition in the guts and muscles of the fish using microscopic identification and Fourier Transform Infrared Spectroscopy (FTIR). The Atomic Absorption Spectroscopy (AAS) was used to quantified the levels of zinc (Zn), copper (Cu), and lead (Pb) in the muscles and gills. The results indicated that the mean number of MPs in the guts for tilapia and catfish were 9.17 ± 1.47 MPs/individual and 7.655 ± 0.93 MPs/individual respectively. The mean number of MPs in the muscles for tilapia and catfish were 0.86 ± 0.41MPs/g and 1.21 ± 0.61MPs/g respectively. In terms of abundance, fibers were the most common type of microplastic in both species, accounting for 92% in tilapia and 76.5% in catfish. The identified polymers were polyethylene (PE), polypropylene (PP), polystyrene (PS), polyester (PES), and cellophane (CP). PE was the most abundant polymer found in the fish, while CP was the least abundant, accounting for 40% and 8%, respectively. The exposure assessment suggests that consuming catfish exposes people to more microplastics than consuming tilapia. Heavy metals were found to accumulate more in the gills than in the muscles of the fish. The heavy metal levels in the muscles were higher in tilapia than in the catfish, however, the levels of metals detected in both species were within recommended limits, posing no risk to consumers. For tilapia, the concentrations of Zn, Pb, and Cu in the gills were 24.59 ± 1.88 mg/kg, 1.99 ± 0.28 mg/kg, and 1.51 ± 0.12 mg/kg respectively. The concentrations of Zn, Pb and Cu in the muscles of tilapia were 10.67 ± 2.09 mg/kg, 0.31 ± 0.06 mg/kg and 0.18 ± 0.04 mg/kg respectively. The concentrations of Zn, Cu and Pb in the gills of catfish were 8.08 ± 1.31 mg/kg, 1.38 ± 0.14 mg/kg, and 1.18 ± 0.15 mg/kg respectively. In the muscles of catfish, the concentrations of Pb and Cu were below detection, and the concentration of Zn was 3.51 ± 1.39 mg/kg. The study also showed a moderate positive relationship between lead (Pb) levels in gills and muscles and microplastics in the muscle of tilapia. Overall, the study shows the occurrence of MPs and heavy metals in both species, with higher heavy metal concentrations in the gills than in the muscles. The findings suggest that microplastics could potentially act as vectors for heavy metals in fish.