Australian freshwater bivalves: Their applications in metal pollution studies

ABSTRACT: Australian freshwater bivalves possess a variety of attributes which make them particularly useful in both fundamental and applied studies of metal and radionuclide pollution. This paper focuses on the capacity of several species of freshwater bivalves (lile.sunio angasi, lilesunio amb£guuJ and HyrideOa depTeJfa) to bioaccumulate a variety of metals, in the context ofa mechanistic and predictive model of metal kinetics, which has demonstrated that (a) many metals are absorbed from the aquatic medium as metabolic analogues of Ca, to be deposited in extracellular calcium phosphate granules, and (b) that their differential rates ofloss from the soft tissue are controlled by their solubilities in the granules .. Several environmental applications that follow from these findings are that: (a) Ca water concentration is a major variable controlling the bioavailability of many metals in the aquatic medium. The implication of these results, which are also consistent with those for a variety of metals and freshwater phyla, is that the water quality criteria for the protection of freshwater life should employ Ca water concentration, rather than total water hardness, as the major variable that can ameliorate the toxicity of many metals in freshwater environments; and (b) Ca tissue concentration can be used to explain up to 98% of the variability between individuals in their tissue concentrations of a variety of metals .. This permits the establishment of background or preoperational metal levels, against which future increases can be readily discerned. Investigations that have commenced on the use of the shell micro laminations (i .. e .. nacre tablets) of two species offreshwater bivalves (Micrvanodonta anodontaiform£s and H. depwsa) as archival monitors of metal concentrations in water have shown