Heavy Metal Contamination of Ologe Lagoon, Nigeria and Biomakers of Oxidative Stress in Pachymelania Aurita

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Samuel, O.B
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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. The organic pollution indicators encountered were Capitella capitata, Chironomus sp., Tubifex tubifex, Macoma cumana Samuel, O.B. (2012) xx and Alitta succinea. Species richness and evenness was slightly higher in the dry season than in the wet season while wet season showed higher species dominance. The Jaccard index of similarities showed faunal similarities among stations 1, 2, 8 and 9 while it showed dissimilarities between station 11 and other stations except station 10. The number of species correlated positively with DO, salinity, TSS, nitrate, phosphate, Cu, Zn and Fe while it correlated negatively with Pb and BOD. With the exception of percentage sand, number of species exhibited a negative correlation with sediment percentage mud, TOC, Cu, Mn, Zn, Fe and Pb. Based on canonical correspondence analysis (CCA) ordination, Chironomus sp. was found to be associated with transparent, deep and less turbid stations 1 and 2 and waters characterized by high sediment Cu. The mean concentration of metals in P. aurita and sediment collected from Ologe Lagoon was in the order; Fe > Mn > Zn > Cu > Pb while the mean concentration in the water column of the site of P. aurita collection was in the order; Fe > Zn > Cu > Mn > Pb. Based on the bio-sediment accumulation factor (BSAF) and bio-water accumulation factor (BWAF), the amount of heavy metals accumulated by P. aurita was higher than the level detected in the sediment and surface water. However, the level of Mn in P. aurita was less than the level detected in the sediment. Based on the probit analysis of concentration – mortality data, the 96hLC50 of Cu, Fe, Pb, Mn and Zn against P. aurita was 22.48, 125.28, 275.76, >1000.00 and 123.42 mg/l respectively. The susceptibility of P. aurita to heavy metals was in the order; Cu > Zn > Fe > Pb > Mn. The MDA level increased as the concentration and exposure period increased while CAT, GST, SOD and GSH activities decreased in most cases as the concentration and exposure period increased. In this study, the prevalence of organic pollution indicators was evidence that Ologe Lagoon is a stressed ecosystem. The study also reflected the sensitivity of biomarkers of oxidative stress activities as indicators of metal pollution.
A Thesis Submitted to the School of Postgraduate Studies, University of Lagos
physico-chemical characterization , Oxidation Stress , macrobenthic invertebrates , Seasonal changes , Research Subject Categories::NATURAL SCIENCES::Biology::Organism biology
Samuel, O.B (2012). Heavy Metal Contamination of Ologe Lagoon, Nigeria and Biomakers of Oxidative Stress in Pachymelania Aurita. A Thesis Submitted to University of Lagos School of Postgraduate Studies Phd Thesis and Dissertation, 381pp.