Metal mixtures - Is 'concentration addition' the correct model for terrestrial ecological risk assessment?

加拿大的采矿业是一个重要的经济驱动力-它雇用了30多万加拿大人，是加拿大土著居民最大的私人雇主，贡献了加拿大国内生产总值的3.5%。 在加拿大，对含有多种污染物的场址进行的风险评估是基于每种关注污染物（CoC）相对于其毒理学参考值（TRV）的浓度;如果每种金属的这一比率（称为危害商数（HQ））小于1，则预计不会产生不利影响。 未考虑金属混合物的预期毒性。混合物毒性的浓度加和（CA）理论是假设单个CoC的效应是总和。拟议的研究将评估CA是一个有效的理论模型，用于土壤中金属混合物的风险评估时，混合物中的金属浓度相对于CCME的土壤质量指南（SQG）升高。 我们将通过以下方式检验CA理论：（a）为三个不同的门开发掺加金属混合物的毒性阈值：（B）将对金属混合物的这种反应与通过欧盟的预测无效应浓度（PNEC）模型计算的单剂量反应进行比较，以及（c）将该响应与来自一套现场污染土壤的掺加混合物进行比较。 简而言之，实验方法是现场收集参考和金属混合物污染的土壤从不同的位置在加拿大，穗的参考土壤与单一金属和金属混合物的钴，铜，镍，铅和锌，从剂量-毒性关系将确定土壤生物，并使用现场污染的土壤的“全混合物”验证。 将确定多个门的多个毒性终点，并使用仿生学确定土壤金属对受体的真实实现剂量。 实现这些目标将测试土壤风险评估的CA假设的鲁棒性，并为具有复杂混合物的场地提供预测工具。 如果成功的话，该项目将通过提供一个确定金属混合物毒性的具体地点估计值的可靠程序，减少确定具体地点补救目标的需要。

Canada's mining industry an important economic driver - it employs over 300,000 Canadians and is the largest private employer of aboriginal Canadians, contributing 3.5% of Canada's GDP. In Canada, the risk assessment for a site with multiple contaminants is based on the concentration of each contaminant of concern (CoC) relative to its toxicological reference value (TRV); if this ratio for each metal, termed a hazard quotient (HQ), is less than 1, then no adverse effect is expected. The expected toxicity of metal mixtures is not considered. The concentration addition (CA) theory of mixtures toxicity is that the effect of individual CoC is assumed to sum. The proposed research will evaluate if CA is a valid theoretical model for the risk assessment of metal mixtures in soils when the concentration of metals in the mixture is elevated relative to the CCME's soil quality guidelines (SQGs). We will test the CA theory by: (a) developing toxicity thresholds for spiked metal mixtures for three different phyla: microbial processes, invertebrates and plants across a variety of landuses, (b) comparing this response to metal mixtures to single dose responses calculated through the European Union's Predicated No Effect Concentration (PNEC) model, and (c) comparing this response to spiked mixtures from a suite of field-contaminated soils. In brief, the experimental approach is to field-collect reference and metal-mixture-contaminated soils from a variety of locations in Canada, spike the reference soils with single metals and metal mixtures of Co, Cu, Ni, Pb and Zn, from which dose-toxicity relationships will be determined for soil organisms, and use the field-contaminated soils for the 'whole mixture' validation. Multiple toxicity endpoints will be determined for a number of phyla, and true, realized dose of soil metals to receptors will be determined using biomimetics. Achieving these objectives will test the robustness of the CA assumption for soil risk assessment and offer predictive tools for sites with complex mixtures. If successful, this project will reduce the need for determination of site specific remediation objectives by providing a robust process for determining site specific estimates of metal mixture toxicity.