Assessment of Contamination Status of Bomu and Oginigba Rivers, Rivers State, Nigeria, Using Some Trace Metals and Callinectes gladiator as Indices

Two Rivers: Bomu in Ogoniland and Oginigba in Port Harcourt all in Rivers State, Nigeria were strategically chosen to represent rivers in Rivers State that are prone to ecological degradation due to industrial activities. Their contamination status was assessed using trace metals in water, sediment and Callinectes gladiator (swimming crab). Water, sediment and crab samples were collected following standard procedures (APHA, 1975). They were prepared by acid digestion using 1:3:1 mixture of HCIO4, HNO3 and H2SO4 acids and Buck Scientific Atomic Absorption Spectrophotometer and air-acetylene flames were used for the trace metals analysis. The results of water analysis showed ranges of concentration (mgL-1) of trace metals as follows: Cu (1.089-3.327), Ni (2.997-3.897), Cd (<0.001), Cr (2.728-0.291), Zn (0.853-3.123) and Pb (0.369-1.198) in Bomu; Cu (0.692-2.019), Ni (3.389-4.693), Cd (<0.001), Cr (0.872-5.771), Zn (1.748-2.621) and Pb (0.642-0.999) in Oginigba. In the sediment, concentrations (ppm, dry weight) were: Cu (91.028-119.275), Ni (145.175-161.025), Cd (ND), Cr (119.725-144.275), Zn (143.200-243.350) and Pb (52.353-117.350) in Bomu; Cu (62.350-146.050), Ni (108.775-193.700), Cd (ND) Cr (92.350-162.575), Zn (182.725-285.775) and Pb (30.900-117.158) in Oginigba. Tissue analysis of C. gladiator gave concentrations (ppm, dry weight) for egg, exoskeleton and flesh as follows: Cu (45.215, 37.217 and 64.372), Ni (47.301,16.824 and 51.973), Cd (ND) Cr (64.222, 13.874 and 54.354), Zn (19.823, 13.801 and 56.421) and Pb (ND, 44.036, and 31.120) in Bomu; Cu (40.411, 15.203 and 66.580), Ni (33.402, 41.053 and 101.620), Cd (ND) Cr (28.131, 21.333 and 78.442), Zn (197.783, 17.680 and 87.510) and Pb (5.555, 3.055 and 7.658) in Oginigba. There were no significant (p>0.05) variations in the heavy metal concentrations between the two rivers with regard to water and sediment. However, concentrations of heavy metals in the two rivers columns seemed to have been much depleted by rapid sedimentation in the bottom sediment. The water and sediment analyses revealed largely anthropogenic trace metal enrichment that exceeded both national and international limits in most of the cases with exception of Pb in Oginigba River, and Cu and Pb in the sediment. The observed heavy metal concentrations of Cu, Ni and Zn in the tissues of C. gladiator also classified the organism as a good bio-indicator for monitoring trace metals pollution of these waterbodies.