Heavy Metal Contamination Of Ologe Lagoon, Nigeria And Biomarkers Of Oxidative Stress In Pachymelania Aurita

ABSTRACT

The physico-chemical characterization, macrobenthic invertebrates and biomarkers of oxidative stress as indicators of heavy metal (Cu, Fe, Pb, Mn and Zn) contamination in Ologe Lagoon, Nigeria were investigated from January, 2007 - December, 2008. Biomarkers of oxidative stress [Catalase (CAT), Glutathione S- transferase (GST), Superoxide Dismutase (SOD), Reduced Glutathione (GSH) and Malondialdehyde (MDA)] activities were evaluated in Pachymelania aurita exposed to sublethal concentrations (1 /10th, 1 /50th and 1 /100th) of the 96h LC50 of heavy metals in laboratory bioassays. The water and air temperatures showed seasonal changes that are indicative of the rainfall pattern in South-Western, Nigeria. The water depth, turbidity, total suspended solid (TSS) and dissolved oxygen (DO) were higher in the wet season than in the dry season while transparency, total dissolved solid and salinity were higher during the dry season than in the wet season. There were no seasonal variations in the nutrient levels, chemical oxygen demand (COD) and biological oxygen demand (BOD) values. The observed levels of Cu, Fe, Zn, Mn and Pb were higher than the World Health Organization (WHO) limits for drinking water. The temporal variations in the level of the heavy metals were characterized by irregular fluctuations. The bottom deposits of most of the sampled stations were muddy (silt/clay). The total organic content (TOC) of sediment ranged from 0.20 - 66.80 % while sand and mud ranged from 11.00 - 96.84 % and 3.16 - 89.00 % respectively. The level of observed heavy metals in sediment was Fe ˃ Mn ˃ Zn ˃ Cu ˃ Pb. A total of 1671 individuals comprising 3 phyla, 7 classes, 17 families and 19 species were recorded in this study with Phylum Mollusca being the dominant. Pachymelania fusca quadriseriata accounted for the highest density while Tubifex tubifex and Chironomus sp. were the most widely distributed.