Heavy metals in surface water, sediments, fish and perwinkles of Lagos lagoon.

Abstract

Lagos Lagoon, covering 700 km , is a brackish coastal lagoon, on the Western part of Nigeria (6°26'2 37'N; 3°23'-4°20'E) and the largest along the West African coast. The sampling and processes of analyzed samples was carried out as described by American Public Health Association (APHA) and samplings were done between January and June, 2008. The results showed that the concentration of Arsenic (As) (.010±.000) mg/L, Cu (0.197±.144) mg/L, Mn (0.087± .040) mg/L and Zn (0.53± .363) mg/L in surface water were generally low when compared to WHO standard of 2004.On the other hand, Cd, Cr, Pb and Ni were generally high with mean values of 0.354±.297, 0.060±.028, 0.263±.118 and 0.140±.075 mg/L, respectively recommended for marine waters: World Health Organization, 2004. ANOVA test showed that arsenic, nickel and iron are significant at (P< 0.05). This is an indication that they have tendency to bioaccumulate and affect aquatic life. In the sediments however, the mean values were generally low when compared with WHO and FEPA standards. The mean levels of heavy metals in the sediments of Lagos lagoon were generally low and fell within the acceptable limits described by World Health Organization, 2004 and FEPA.The average concentrations for the heavy metals were As, Cd, Ni, Cr, Cu, Fe, Pb, Mn, Zn are 0.083±0.035; 1.150±0.090; 0.867±0.075; 0.618 ±0.193; 0.600±0.272; 19.393±6.649; 0.450±0.598; 2.040±1.049; 0.730±0.337 mg/kg, respectively. Iron, Manganese and Nickel were not defined. When these values are compared with ones recorded for surface water, there is clear evidence that sediments recorded higher values and indication that most of metals were adsorbed to the sediment. In the organisms (Oreochromis niloticus and Tympanotonus fuscatus Radula) the shell fish tend to bioaccumulate heavy metals more than the fin fish. The shell fish bioaccumulate these metals namely, Cd (0.555±0.742), Cr (0.066±0.091), Pb (0.675±0.940), Mn (1.4300±1.711) Ni (0.230±0.311) and Zn (1.066±1.1.449) mg/kg, respectively. While the finfish bioaccumulated arsenic, Fe (3.583±0.711) and Cu (0.517±0.004) mg/kg, respectively. There was significant (p=0.05) variation in the elemental concentrations between and within groups.