Bioaccumulation of Heavy Metals in Fish Sourced from Environmentally Stressed Axis of River Niger: Threat to Ecosystem and Public Health

Abstract

Pollution of freshwater ecosystems is alarmingly becoming high in Nigeria with attendant public health effects on the dependent populations. Fish, a source of protein with pronounced placement on local food menu is now considered an important dietary threat of heavy metal toxicity via consumptions. Bioaccumulation of heavy metals (copper, zinc and lead) in Silver catfish (Schilbe intermedius) from River Niger was conducted. The Fish samples were collected from different sites of Onitsha axis of the River Niger owing to their environmental stresses. Samples were analyzed for heavy metal (copper- Cu, zinc- Zn, and lead- Pb) concentrations in muscle tissues using the Atomic Absorption Spectrophotometer (AAS) and compared with Food and Agriculture Organization safe limits. Margin of exposure (MOE) was estimated to measure the potential public health risk of consuming the contaminated fish. The concentrations of heavy metals (Cu- 8.92±4.748, Zn- 0.36±0.249, and Pb- 2.689±1.505) observed were significant (P Pb>Zn. Statistical Pearson moment correlation analysis showed that the concentrations of heavy metals detected were independent of the weight of sampled fish for zinc but was positively correlated for copper and lead. Relating the mean metal concentrations obtained in the study with Food and Agriculture Organization standard for fish muscles indicated that mean concentrations of copper, zinc and lead are far above safe margins for human consumption except the fish sourced from sites A4 and A9 for lead and zinc, respectively. Margin of exposure was below one and tentatively considered not to be of risk to public health. However, there is considerable contamination of the Silver catfish from the River Niger with heavy metals. It is recommended that substantial attention be paid to the heavy metal levels in freshwater fishes from the river. Measures should be put in place to regulate the indiscriminate dredging activities, discharge of raw sewage and industrial effluent into the river and regular public health check on the level of heavy metals among the populace in the communities that border the area should be employed.