Heavy metals in water, sediment and soft tissues of clams in the middle reaches of Forcados River, Delta State, Nigeria

Abstract

Freshwater ecosystems are among the most threatened on the planet, confronting unprecedented pressures that result in habitat loss and overexploitation of natural resources due to increasing human population and anthropogenic pressure. The purpose of the study is to determine and compare the level of some heavy metals (Cadmium (Cd), Chromium (Cr), Copper (Cu), Lead (Pb), and Zinc (Zn)) in water, sediment and soft tissue of clams with WHO limit along selected Forcados River banks. Heavy metals in the river water, sediment, and clams were determined using an atomic absorption spectrophotometer (AAS). The other physicochemical parameters such as temperature, pH, electrical conductivity, dissolved oxygen, biochemical oxygen demand and total dissolved solids were determined using standard procedures. Most heavy metals were found in more significant concentrations in sediment samples from all three sampling areas, which is the clam's natural habitat. For the physicochemical analysis, the average temperature of the water samples ranged from 27.63 to 28.25^oC, the average pH ranged from 6.85 to 7.18, the average DO ranged from 4.71 to 5.2 mg/l, the average EC ranged from 26.76 to 33.64 µS/cm, the average BOD ranged from 1.37 to 1.88 mg/l, and the average TDS ranged from 14.63 to 18.14 mg/l. This highlights the importance of monitoring potential contaminants in our aquatic environment. The concentrations of heavy metals in the tissues of clams were within regulatory limits. However, there was evidence of bioaccumulation of metals, especially chromium. The Distribution Coefficient (Kd) was computed. Cd and Zn were the most and least stable metals, respectively (Mean Log (K_d) = 3.87 and 1.43). Based on Log (K_d), metals were ranked as Pb>Cd>Cr>Cu>Zn.