Assessment of Heavy Metal Contamination in Shrimp and Water from the Great Kwa River: Implications for Human Health and Aquatic Ecosystems

The aftermath of heavy metal pollution can be hazardous to humans, considering the level of consumption of shellfish in riverine areas - which is relatively high. There is a growing concern about the quality of aquatic food (e.g. periwinkle and shrimp) in several parts of the world. The determination of toxic elements in food has prompted studies on toxicological effects of heavy metals in foods. Due to man’s industrialization activities such as oil exploration, the levels of toxicants in marine environments have increased over the years. This study aimed at evaluating heavy metal contents (lead, cadmium, nickel, manganese, chromium and copper) in shrimp and water obtained from Great Kwa River, Calabar, Cross River State, Nigeria. Fresh shrimp and water samples were collected from the river in Calabar metropolis, Cross River State. In the sample preparation, the soft tissue (edible part) of the shrimps were extracted, dried in the oven (at 80°C) for 72hours then, after which the weights of the shrimps and water from each sampling point were measured. Digestion of the samples were carried out before an Atomic Absorption Spectrophotometer was used to determine the concentrations of the heavy metals. Graph pad Prism Version 7 was used for statistical analysis and Microsoft Excel Application. The results indicate contamination of both the shrimps and water from the Great Kwa River by some heavy metals, which also pose a health risk to aquatic ecosystem and humans. Among the heavy metals studied, chromium had the highest concentrations in both shrimps (30.07 ± 0.67ppm) and water (27.68 ± 0.34ppm). The heavy metals were found in higher concentrations in the shrimp than in water, except for manganese which had a significantly (p<0.05) higher concentration in water (15.05 ± 0.67ppm as against 14.02 ± 0.93ppm in shrimp). Certain minerals have biological uses, but concentrations above recommended levels become detrimental to consumers. The levels of some of these heavy metals in this study, call for more investigation and regulation of their anthropogenic sources in order to reduce risk of public health issues.