Heavy Metals and their Effects on Macroinvertebrates Present in the Ojo River, Lagos, Nigeria

Aim: To provide information regarding the presence of heavy metals in the tissues of crab (Potamon fluviatile), prawn (Macrobrachium rosenbergii), and crayfish (Metanephrops australiensis) obtained from the Ojo river of Lagos State, Nigeria.

Study Design: Commercially sold marine crustacean samples (crab, prawn, and crayfish) obtained from the Ojo river of Lagos, Nigeria, were assessed for the presence of heavy metals, and also the potential health risks for local consumers.

Place and Duration of Study: Ojo river, located close to Ojo local government secretariat, Ojo, Lagos State, Nigeria.

Methodology: Live samples of macroinvertebrates such as Metanephrops australiensis, Potamon fluviatile, and Macrobrachium rosenbergii were purchased from the fishermen at the riverside in Ojo and immediately transferred to the laboratory. The samples were oven-dried and ground into a fine powder, then subjected to sample digestion and finally atomic absorption spectrophotometer (AAS), to obtain the various heavy metal concentrations present in each sample.

Results: The result indicated variations in the metal body load among species. All the metals were below the FAO/WHO permissible limit for food consumption except for Cd in crayfish which was slightly beyond the set limit. The highest concentration examined were found in crayfish, followed by crab and prawn. Zinc and iron were of higher concentrations in the tissues of the macroinvertebrates while lead was the least concentrated metal present only in the tissues of crayfish and absent in the tissues of both crab and prawn.

Conclusion: The human health risk evaluation for the marine organisms indicated that both the crab and the prawn samples examined were safe for consumption, while crayfish may not be considered safe for consumption. Also, the potential health risk from consuming seafood exposed to these metals should not be ignored.