The importance of gathering more knowledge on metal transport mechanisms to predict the uptake and toxicity of dissolved metals by phytoplankton: new insights and challenges for the development of the biotic ligand model
The accumulation and (acute) toxicity of dissolved metals in many aquatic organisms are normally well predicted with the biotic ligand model (BLM), although some exceptions have been reported. In long-term chronic metal exposures, complex physiological interactions with essential and non-essential metals may modulate metal uptake rates and toxicity. The present literature review discusses recent advances in environmental chemistry, molecular biology, and physiology related to the regulatory mechanisms of membrane transport of essential metals in eukaryotic phytoplankton and to their impacts on the accumulation and toxicity of cadmium, a usually non-essential metal. This literature review finally evaluates the possibility of including elements of algal physiology in the current version of the BLM in order to enhance the potential of this model to predict metal uptake and toxicity in chronic exposures. The available results in the literature suggest that the inclusion of negative and positive feedback interactions of metals on the kinetic parameters (Vmax: maximal uptake rate; KM: metal affinity of the transport sites) of multiple metal transport systems shows promise for better predicting the long-term accumulation and toxicity of metals in phytoplankton. The development of a BLM able to predict the chronic toxicity of metals under various physicochemical conditions representative of those found in the environment will benefit from recent and future advances in toxicology, biology and environmental chemistry. The knowledge gained will aid in achieving the ambitious goal of developing an extended BLM that reliably predicts metal toxicity in complex natural aquatic environments.