Physicochemical insights into the environmental risks of metals

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Assessments of the ecological risk (ERA) of organic chemicals typically include determinations of their persistence, bioaccumulation and toxicity. For inorganic chemicals such as metals and nanomaterials, this approach is clearly an oversimplification. For example, trace metal speciation measurements, including the dynamics of complexation reactions are often critical in environmental systems. Similarly, for emerging contaminants such as nanoparticles, the stability of the colloidal systems (with respect to agglomeration) and the (often non-equilibrium) reactions leading to particle dissolution are certain to strongly influence their bioavailability. Therefore, the overall goal of this research program is to increase our understanding of the molecular underpinnings of environmental risk by carefully examining the mechanisms leading to the biological uptake or mobility of several emerging contaminants. Experiments are designed to lead to insights that will help improve existing models of environmental fate. Research will be focused on three key areas of importance that are required to better quantify the metal exposures in the environment: (i) determining the aging of novel metal containing materials (roughly persistence); (ii) developing better insight into the bioaccumulation of metal complexes and metallic nanoparticles and (iii) evaluating the mass transport of some emerging contaminants. Insights into metal toxicity (hazard), although not a main focus of this research programme, will nonetheless be acquired during transcriptome sequencing studies of metal bioavailability. Discovery grant funding will be used to gain fundamental insight into key biophysicochemical processes affecting ecological risk. For the trace metals, our focus will be on determining the role of chemical speciation on trace metal bioavailability with a particular emphasis on the contribution of metal complexes. Projects will be focused on the interesting and economically important lanthanide series of metals. We anticipate that their (primarily) trivalent nature and their strong capacity to bind organic matter will lead to the discovery of important exceptions to predictive models such as the Biotic Ligand Model. Analytical techniques will be optimized so that chemical speciation can be accurately measured. The biouptake of the hydrophilic metal complexes, generally neglected in predictive models such as the Biotic ligand model, will be studied thoroughly. In some cases, the bioavailability of toxic chemicals may be limited by the transfer of the compound from the water, soil or sediment to the surface of the biological organism (mass transport limitation). This implies that it is often just as important to understand the physical properties of chemicals as it is to understand their intrinsic chemical reactivity. We anticipate that for certain chemicals (larger, slowly diffusing chemicals such as nanomaterials) and in certain environments (biofilms, soils, sediments), mass transport will be limiting with the implication that dynamic models will be necessary in order to obtain accurate predictions of bioavailability. For contaminants such as nanomaterials, our work will be designed to carefully quantify dynamic and often non-equilibrium processes such as particle agglomeration and dissolution. Novel nanoparticle characterization techniques such single particle ICP-MS or analytical ultracentrifugation will be explored with the goal of measuring particle/agglomerate at their predicted low concentrations. Emphasis will be placed on improving our mechanistic understanding of these problems of environmental function so that as new (metal-based) contaminants of economic interest are identified, their ERA can be readily prioritized.