Estimation of Cu, Cd and Hg transported by plankton from a contaminated area (Ria de Aveiro)

Abstract

The efficiency of plankton to sorb/incorporate anthropogenic metals discharged in a contaminated area of the Ria de Aveiro and the amount exported to the rest of the lagoon were examined. Suspended particulate matter and material collected in 63 and 200 μm plankton nets were sampled hourly on a semi-diurnal spring tidal cycle. The collected material was analysed for total Cu, Cd, Hg and Pb. Higher metal concentrations were registered in material collected during the ebb period, which indicates their incorporation into the plankton biomass previously transported into the area during the flood period. On the basis of the water volume variation, plankton biomass associated to the 63 and 200 μm nets and metal concentrations, mass balances were calculated for Cu, Cd and Hg. Clearly, metals associated with plankton were exported from the contaminated area to the rest of the lagoon. The net exported metals (63 μm net) were 223–336% of the imported metals corresponding to 2.4 g of Cd, 67 g of Cu, and 11 g of Hg, over the spring tidal cycle.