Trace Metal Contamination in Tropical Endemic Fish: Factorial Effect Interactions and In situ Quantitative Risk Assessment

Aim: Contamination of the Anambra River with heavy metals (arsenic, As; cadmium, Cd; chromium, Cr; copper, Cu; lead, Pb; nickel, Ni; and zinc, Zn) was examined in two preponderant fish species (Synodontis clarias and Tilapia nilotica) following earlier detection of the elements in water column. Methods: Levels of heavy metals were measured in both seasonal regimes (rainy and dry) at five selected locations with atomic absorption spectrophotometer. Factorial effects and interactions were explored on completely randomized block design. Quantitative risk of metal exposure through contaminated fish consumptions among the resident community population at the river was assessed to extrapolate the probable public health threat. Results: The result showed variations among heavy metal concentrations in fish and Zn and Cu recorded significant amounts with S. clarias recording higher concentrations than T. nilotica. Season, species of fish and location and their interactions had significant effects on the amounts of Cu and Zn accumulated in the fish tissues except season by species effect. Zinc recorded the highest concentrations at all locations measured, with Onono (location 5) producing the fish species with the highest amount of metals compared with other locations. The heavy metal concentrations were below the comparable international safe standards. Margin of exposure and exposure dose calculated for the heavy metals were all below reference standards and tentatively considered not to be of risk to public health. Conclusion: However, there is considerable concern of contamination of the fish species with heavy metals and recommended regular monitoring or examination of edible fish species.