The impact of climate change on the flux and fate of metals in freshwater systems: implications for metal exposures across different scales

Climate change and chemical pollution are two of the gravest environmental concerns, and it is becoming increasingly recognised that climate change and climate variability will alter the environmental distribution and toxicity of chemical pollutants. Trace metals are an established pollutant group where decades of research have been able to determine causal links between environmental concentrations and water chemistry, and accumulation and toxic effects. In the present paper, we assert that to fully comprehend the impact of climate change on metal bioavailability and exposures in freshwaters, three distinct scales need to be understood: (i) the global scale of metal biogeochemical cycling which will alter metal inputs from soil into freshwater; (ii) the environmental scale of fluctuating water chemistry parameters that will change metal complexation dynamics; and (iii) the organismal scale at which climate-induced physiological modifications at the site of uptake may alter the bioaccumulation of metals and climate-induced impairments of cellular function that will change toxicity. At each scale much is already known about the processes and pathways that govern metal input, bioavailability and impacts on biota, but the key impact of climate variability is to alter the frequency, intensity, and rates at which these processes occur with the underlying commonality throughout scales being a shift to a more dynamic system. In an increasingly dynamic environment, it is the kinetics of both chemical and biological reactions that become more important compared to predictions of metal bioavailability from currently utilised thermodynamic equilibrium-based models. Extending such models to include climate variability is not easy, but to begin such a process would ultimately lead to more accurate and realistic applications to policy guidance.