Mercury and lead concentrations in six cartilaginous fish species from the Lagos Lagoon and its coast

Abstract

Mercury and lead concentrations in cartilaginous fishes from Lagos Lagoon and coastal waters of South-West Nigeria were investigated between May and August 2013. There are obvious discharges of toxic heavy metal substances into these waters and which can get to man by bioaccumulation and biomagnifications in fish consumed. Range of total length of 54 specimens collected by species were as follows : Brown ray (Raja miraletus), 12.1-43.4 cm (total weight 50.00-400.00 g); Sting ray (Dasyatis margarita), 38.0-86.5 cm (total weight 85.00-876.00 g); Dog fish shark (Squalus megalops), 33.5-85.3 cm (total weight 100.0 -3200.0 g); Hammer head shark (Sphyrna couardi), 48.0 -59.5 cm (total weight 500.00-1000.00 g); White spotted guitar fish (Rhinobatos albomaculatus), 64.5- 64.8 cm (total weight 900.00-1000.00 g) and thornback guitar fish (Zanobatus scholeinii), 35.0 cm (total weight 291.00 g). Mercury and lead levels (mg/kg) respectively were: R. miraletus (0.04±0.001 and 0.17±0.01), S. couardi (0.002±0.001 and 0.37±0.46), S. megalops (0.004±0.001 and 0.6±0.43), D. margarita (0.01±0.001) Z. scholeinii (0.007±0.001) and R. albomaculatus (0.003±0.001 and 0.13±0.01). The study showed that these fishes from Lagos Lagoon and its coast have concentrations below the permissible FAO/WHO standards for toxic metals in consumable fish products.

Keywords: Bioaccumulation, heavy metals, level, fish, Lagos Lagoon