Comparative study of mercury accumulation in some brackish water fishes in a tropical lagoon and its adjacent creek in south western Nigeria

Abstract

The Hg content of some brackish water fishes, water and sediment in Lagos lagoon and Abule - Agege creek were investigated from February to September, 2004. The pH of the lagoon was neutral however the creek was mildly acidic (6.75) in the dry season. The Hg content of the lagoon ranged from 0.27 - 0.40 mg/l for water and 0.46 - 0.56 μg/g dry wt for sediment lower than the creek range (0.41 - 0.42 mg/l and 0.71 - 0.72 μg/g) for the dry season. For the rainy season high Hg levels were recorded in lagoon water ranged from 0.41 - 0.48 mg/l more than the creek ranged from 0.42 - 0.44 mg/l. However, more mercury was recorded in the creek sediment 0.95 μg/g than that in lagoon sediment 0.71 - 0.81 μg/g. Surface water temperature for the creek was lower than the lagoon. Generally, higher mercury values were recorded in sediment than in the water in both the lagoon and the creek. For the fish species 0.72 ± 0.05 μg/g of Hg was detected in Sarotherodon melanotheron, more than in both Tilapia guineensis and Hemichromis fasciatus, this is related mainly to the mode of feeding. Hg content of the examined fish was below maximum permissible levels (0.5 - 1.5 μg/g) in the food chemical codex.

Key words: Biomagnifications, Hg, brackish water, fish, chemical codex.