Analysis and Seasonal Distribution of Some Heavy Metals in Sediment of Lagos Lagoon Using Environmental Pollution Indices

Some heavy metals (Mn, Pb, Cr, As and Zn) analysis and their seasonal distribution between in the sediment samples of Lagos Lagoon were studied during the dry and wet seasons in November, 2012 to June, 2013 using Atomic Absorption Spectrophotometer (AAS). Contamination Factor (Cf), Degree of Contamination (Cd) and Pollution Load Index (PLI) were the pollution indices employed to ascertain whether the contamination is anthropogenic or natural. Six sampling stations (Iddo, Ijora, Five cowries’ creek, Apapa port, Tincan creek, Commodore channel) were identified due to some anthropogenic activities observed in each station. Pb concentrations in all stations were within the permissible limits of 40 mg/kg of USEPA and Department of Petroleum Resources (DPR) of Nigeria except in stations 4 and 6 in wet season. Mn levels in all the analyzed sediments were also exceeded USEPA and DPR values of 46 mg/kg during the two seasons. Cr and Zn are within the permissible limits in all the stations during the wet and dry season hence, reflecting their natural background levels in the sediment. The concentration of As in all the analyzed sediments were exceeded the USEPA value of 9.8 mg/kg. Comparison between the results obtained from the sediment analyzed during dry and wet seasons for metal concentration indicates that all the contaminants are significant at P< 0.05 level during the dry and wet seasons except for Pb and Cr that are significant at P< 0.01 level while As and Mn are not significantly correlated between the two seasons. The metals concentrations decrease in order of Mn > As > Pb> Zn > Cr in the study areas during dry and wet seasons. The mean concentration of metals in sediment for the two seasons is significantly correlated at P=0.05 and 0.01 which implied that the metals increase within the seasons in the sediment. Sediment contamination by heavy metal based on the above indices showed that the study area have very high degree of metal contaminations.