A review of chemical speciation techniques used for predicting dissolved copper bioavailability in seawater

Abstract

Copper (Cu) is an essential metal, but it is also toxic at concentrations reached in polluted coastal areas. In seawater, the speciation of this metal is largely controlled by the presence of dissolved organic matter (DOM), which binds Cu ions decreasing the concentration of inorganic and free forms of the metal. This is important to aquatic life, given that the bioavailability of dissolved metals is generally expected to be determined by the free ion concentration according to bioavailability models such as the free ion activity model and biotic ligand model (FIAM/BLM). The analytical determination of free metal concentrations in seawater is a challenging task that is needed (in combination with toxicity tests or other means of testing bioavailability) in order to test the applicability of the FIAM/BLM in particular systems and also for its application in monitoring and risk assessment of metals. This review summarises the studies that combine a biological measure of Cu bioavailability with the use of a chemical speciation technique for the measurement of Cu speciation in seawater, and it presents a critical examination of the results of those studies in order to determine which techniques are more suitable for the prediction of Cu bioavailability in seawater and to highlight research needs in the field. The technique showing the highest level of agreement with bioavailability data is anodic stripping voltammetry (ASV). Cathodic stripping voltammetry (CSV), aluminium hydroxide coated exchange resin (ALSA), and diffusion gradients in thin films (DGT) are also promising in this regard, although DGT slightly overestimates bioavailable Cu. More research is needed comparing the performance of different chemical speciation techniques with Cu bioavailability in seawater, especially at environmentally relevant concentrations of Cu.