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；如果每种金属的这一比率，称为危险商(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。混合物毒性的浓度相加(CA)理论是假定单个COC的效应是总和。这项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测试CA理论：(A)为三个不同的门类：微生物过程、无脊椎动物和植物制定添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预测的无效应浓度(PNEC)模型计算的单剂量反应进行比较，以及(C)比较这种对来自一套田间污染土壤的添加混合物的反应。简而言之，实验方法是从加拿大不同地点收集参考土壤和金属混合物污染的土壤，在参考土壤中添加单一金属和钴、铜、镍、铅和锌的金属混合物，由此确定土壤生物的剂量-毒性关系，并使用田间污染土壤进行“整体混合物”验证。多个毒性终点将被确定为一些门，真正的，实现的土壤金属对受体的剂量将用仿生学来确定。实现这些目标将检验土壤风险评估的CA假设的稳健性，并为具有复杂混合物的地点提供预测工具。如果成功，该项目将通过提供一个确定特定地点金属混合物毒性估计的可靠程序，减少确定特定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.