Heavy metals and organisms in the Lagos Lagoon

Levels of cadmium, cobalt, copper, chromium, iron, manganese, nickel, lead and zinc were determined in the water and in some fish and shellfish in the Lagos Lagoon. The levels in the water were 3-5 orders of magnitude lower than the values reported for the sediments. They were also very much below the maximum allowable levels in marine waters set by the United States Environmental Protection Agency (US. EPA). The implication is that waste assimilation capacity of the system is high, a phenomenon attributable to dilution, continuous water exchange and sedimentation. Except for lead levels in fish, the metals were at low levels in the organisms. However, when compared with levels determined in fish from a rural river, relative enrichment in the lagoon fish, ranging from about 2 for lead to 66 for copper was observed, implying that urban and industrial wastes discharged into the Lagos Lagoon have had a significant impact on the ecosystem. High-petrol lead is believed to make a substantial contribution towards the high lead levels in fish.