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，它雇佣了30多万加拿大人，是加拿大原住民最大的私人雇主，贡献了加拿大GDP的3.5%。在加拿大，对有多种污染物的场地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；如果每一种金属的这一比率（称为危险系数（HQ））小于1，则预计不会产生不良影响。没有考虑金属混合物的预期毒性。混合毒性的浓度加成（CA）理论是假定单个CoC的作用总和。拟议的研究将评估当混合物中的金属浓度相对于CCME的土壤质量指南（SQGs）升高时，CA是否为土壤中金属混合物风险评估的有效理论模型。我们将通过以下方式来测试CA理论：(a)为三种不同的门（微生物过程、无脊椎动物和各种土地用途的植物）开发加刺金属混合物的毒性阈值，(b)将这种对金属混合物的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)将这种对一套田间污染土壤的加刺混合物的反应进行比较。简而言之，实验方法是从加拿大的不同地点实地收集参考土壤和金属混合物污染土壤，在参考土壤中加入单一金属和Co， Cu, Ni， Pb和Zn的金属混合物，从中确定土壤生物的剂量-毒性关系，并使用现场污染土壤进行“整体混合物”验证。将确定许多门的多重毒性终点，并使用仿生学确定土壤金属对受体的真实，实现剂量。实现这些目标将检验CA假设在土壤风险评估中的稳健性，并为具有复杂混合物的地点提供预测工具。如果成功，该项目将提供一个确定特定地点金属混合物毒性评估的可靠过程，从而减少确定特定地点修复目标的需要。

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.