Accumulation of heavy metals from single and mixed metal solutions by the gastropod mollusc Tympanotonus fuscatus linnaeus from a Niger Delta estuary:: Implications for biomonitoring

The usefulness of the intertidal gastropod Tympanotonus fuscatus L as a biomonitor of heavy metals in tropical estuaries was assessed. The periwinkles were collected from a site in the upper Bonny Estuary, Southern Nigeria and exposed in a series of experiments either singly or binary mixtures to copper, zinc and cadmium. The accumulation of Cd was monotonic with increase in exposure concentration with a highly significant linear regression ( r(2) = 0.999, p < 0.001). However, no significant regressions were obtained in the accumulation of Zn ( r(2) = 0.018, p= 0.828) and Cu ( r(2) = 0.436, p= 0.125); in the case of Cu a negative relationship was apparent. Bioaccumulation factors followed the order Cu > Zn > Cd but those for Cu and Zn showed reduction as the exposure concentration increased suggesting regulation of these metals. In accumulation from binary mixtures, Cu was synergistic to Cd accumulation in combinations involving 0.05 mg/L Cu but antagonistic for 0.5 and 1.0 mg/L Cu combinations. Zn was antagonistic to Cd accumulation in mixtures with 0.05 and 1.0 mg/L Zn. Cd did not show any effect on Zn accumulation in any of the mixtures but it was antagonistic to Cu accumulation in some combinations ( 1.0 mg/L Cu + 0.05, 1.0 mg/L Cd). It is concluded that T. fuscatus is a good candidate for the biomonitoring of Cd but not for Zn and Cu. The ambient concentrations of Cu and Zn may affect the accumulation of Cd, and need to be considered in the interpretation of Cd data in T. fuscatus.