Improved toxicity models for aquatic environment
Biotic ligand models (BLMs) are widely used to predict the effects of water chemistry on the bioavailability and toxicity of metals. However, at present, these computer models are developed for single metals and do not take into account interactions between metals at the gill surface, which affects their accumulation. In the real environment, metals are rarely found in isolation and the links between metal accumulation and toxicity are complex. The METALTRANSP (Characterization of the trace metals transport and interaction mechanisms in zebrafish Danio rerio using molecular and stable isotope approaches) project was established to investigate interactions between toxic and essential metals. The project's overall objective was to identify shared cellular transporters in zebrafish gills, which are involved in the uptake of metals from their complex environment, using stable isotopes and molecular techniques. Researchers began by identifying the metal transporting proteins in zebrafish (Danio rerio). These transporters were responsible for essential (copper (Cu), iron, zinc) and non-essential (cadmium and lead (Pb)) trace metal transport during multi-metal exposure. Scientists also assessed the effect of multi-metal interactions on compartmentalisation of individual metals in tissues by correlating gene expression patterns to metal uptake. Results showed that addition of Pb significantly increased Cu uptake rates. The uptake of Pb is associated with the DMT1 transporter, and there was an increase in its expression levels only in combination with Cu at the later stage of exposure. This supported the idea of an alternative non-specific uptake pathway that was activated by multiple double-charged ions. It was also shown that the zinc transporting system plays a role in the Pb uptake process in a concentration-dependent manner due to activation of different transporting proteins. These findings showed that in the real world, where metals are rarely found in isolation, the accumulation process in an organism cannot be accurately predicted based on a single-metal exposure model. Essential and non-essential metals were found to share the same uptake pathways, which are activated depending on the concentrations of the metals present. METALTRANSP will provide fresh data for the development of metal mixture BLM models. The models can be used by environmental regulators to more accurately measure toxicity levels in aquatic environments.
