Assessment of heavy metal bioaccumulation in periwinkles and crabs along Okpoka River, Port Harcourt Metropolis, Nigeria

The Okpoka creek is a tributary of the upper Bonny Estuary. This study was aimed at assessing the bioaccumulation of heavy metals in periwinkle and crabs in these areas. Three stations were sampled for 6 months on a monthly basis at Marine Base, Abuloma and Kalio-Ama. Results from surface water analysis indicate as follows; Biochemical Oxygen Demand (BOD) (3.92-4.00 mg/l), pH (6.51–6.82), Redox potential(ORP) (86.76–109.45 mV), Dissolved Oxygen(DO) (6.38–6.47 mg/l), Electrical Conductivity(EC) (15487.26-17926.47 µS/cm), Total Dissolved Solids(TDS) (10.97-13.06 mg/l), Salinity (13.13-15.85 ppt), Turbidity (17.65-110.96 NTU), Temperature (28.10-30.90 0C). EC TDS and Salinty (p>0.05) showed positive significance both in location and time. BOD, ORP and DO showed significant differences in time while pH and turbidity showed significant differences in location. Temperature had no significant difference (p>0.05) both in location and time. Results of heavy metal analysis done for sediments such as Lead(Pb) (4.38-5.18 mg/kg), Zinc(Zn) (9.88-15.04 mg/kg) and Cadmium(Cd) (0.08-0.10 mg/kg) showed no significant variation in location and time. Copper(Cu) (0.73-1.18 mg/kg) and Iron(Fe) (22.40-50.00 mg/kg) showed significant variations both in time and location. The tissue of the crab (Uca tangeri) was analyzed for heavy metal and result gotten showed Zn (6.95-9.37 mg/kg) and Cd (>0.001-0.01 mg/kg) had no significant difference, while, Pb (2.57-3.24 mg/kg) and Cu (3.28-5.14 mg/kg) had significant differences in location and time. Periwinkle (Tympanotonus fuscatus) tissues were analysed for heavy metals and the results gotten showed no significant difference in Pb (0.66-1.03 mg/kg), Zn (6.95-9.37 mg/kg) and Cd (0.02-0.04 mg/kg). Cu (0.47-3-31 mg/kg) showed significant difference in location and no significance in time. The correlation of metals in crab and physicochemical parameters showed both positive and negative correlation. Turbidity and Pb had significant correlation, BOD showed a significant correlation with Cd, the presence of Cu had a positive significance with Zn and Cd, the correlation of metals in Periwinkle and physicochemical parameters showed both positive correlations. Cd had a positive correlation with Pb and Cu had a positive correlation with Pb and Cd. In crab, Pb had the highest Biota sediment accumulation factor (BSAF) in Kalio-Ama, Zn had the highest BSAF in Abuloma, Cd and Cu had the highest BSAF in Marine Base. The bioaccumulation factor for heavy metals in the tissues of Uca tangeri was observed to be higher in Marine base for three heavy metals evaluated out of the four metals. In periwinkle, Pb and Cu had the highest BSAF in Marine base, Zn and Cd had the highest BSAF in Kalio-Ama. The BSAF observed in the tissues of Periwinkle were higher in Marine base and Kalio-Ama respectively. In conclusion the amount of heavy metal in the tissues of Periwinkle (Tympanotonus fuscatus) and crab (Uca tangeri) was generally high in all sampling stations. This is evident by the high amount of heavy metal pollution in the sediment of the Okpoka creek region which is highly exposed to petrochemical waste.