Accumulation of Heavy Metals in Tissues of Oreochromis Mossambicus from the uMgeni River and Human Health Risk Assessment

Metal enrichment in aquatic ecosystems has compromised the potential of fish to enhance food security. The uMgeni River drains urban and industrialized catchment and flows through economically disadvantaged rural communities that opt for fish to supplement their protein needs. However, there are uncertainties on the safety of consuming fish from the uMgeni River. The present study aims to explore metal distribution between the water, sediment, and tissues of the preferred Oreochromis mossambicus, and evaluate whether concentrations in the muscle are safe for human consumption. The water, sediment, and fish samples were collected from Inanda and Nagle dams, and metal concentrations were analysed using inductively coupled plasma mass spectrometry. Alkaline pH was observed at both dams and metals were below detectable level in the water column. Even though metal concentrations in the water column were below detectable levels, significant concentrations were found in the sediment. No consistent trend in metal concentrations was observed across tissues, but higher levels were generally found in the liver, followed by the gill, and then the muscle. Nickel (Ni) and lead (Pb) exhibited concentrations exceeding the permissible limit for human consumption. Similarly, the target hazard quotient exceeded the threshold of 1 for Pb, chromium (Cr), and antimony (Sb) at both dams with Inanda Dam showing higher indices for Sb and Pb. The carcinogenic risk for the three metals was also found to be higher than 10-6. These findings suggest that consumption of O. mossambicus from the uMgeni River should be limited to no more than 150 g per week.