Toxicity of Data-Poor Metals in Soil-Plant Systems

拟议的工作将针对生态“数据贫乏”的稀土元素（ree）和铂族元素（PGEs）。钯（Pd）和铂（Pt）等pge从汽车催化转化器以及从开采碱金属和贵金属中共同排放到环境中，因此沉积在土壤中。稀土元素对数字电子设备和能源技术至关重要，它们是提高作物产量的微量元素；稀土矿开采量从1990年的5万吨/年增加到2010年的15万吨/年。激效是对压力的一种双相反应，即测量端点的刺激和抑制取决于浓度。这种反应在物种、反应和有毒物质中极为普遍，但毒性阈值的推导通常不包括足以引起激效的低暴露浓度。如果在导出毒性阈值的数据中没有确定致效效应，那么由此产生的土壤质量指南（sqg）就不能保护环境健康。土壤中金属的生物可及性取决于土壤的物理和化学特征，并且已经证明，当与土壤特征（如eCEC、pH、%粘土和OM）归一化时，总土壤[金属]的毒性阈值更加协调。目标是：确定植物暴露于土壤中稀土元素（铈）、钕（Nd）、镧（La）和钇(Y)的毒性阈值，包括单独和整体混合物；确定植物单独和整体暴露于土壤中钯（Pd）和铂（Pt）的毒性阈值；确定pge和ree在土壤中的生物可及性以及如何控制；并量化ree和PGEs对反应终点的激效。有人说，“接受生态毒理学中的激效和必要性需要重大的概念改变和大量的新数据”。拟议的研究将通过确定对这些缺乏数据的金属的激效剂量反应来应对这一挑战，如果没有这些数据，关于如何以及是否应将激效纳入ERA框架的争论就无法推进。物种或基因型之间毒性阈值的差异是种群或群落对环境污染物，特别是对亚致死暴露作出反应而改变结构的原因。植物对污染物的辐射反应在不同物种之间可能存在差异，这几乎肯定是对环境毒素敏感性差异的一部分，如果不能充分表征对环境污染物的辐射剂量反应，则可能导致NOEC高于“真实NOEC”，而“真实NOEC”将是辐射反应的峰值。鉴于加拿大新矿产资源的开发（例如环太平洋火山带）和加拿大矿业公司在国外的开发，加拿大填补这些数据贫乏金属的数据空白对其自身的环境保护至关重要，同时也是采矿可持续性方面明显的全球领导者。拟议的工作将填补这一空白。保护不足的代价是生态系统结构和功能的丧失；过度保护造成不必要的减少和补救，这有生产力成本。这项工作的第二个影响将是为可能发生在污染地点的整体混合物建立毒性阈值-单一金属毒性阈值是否足以保护环境免受金属混合物的影响的问题可能是“否”，为二元和三级金属混合物的全因子建立毒性阈值是资源禁止的，因此“整体混合物”毒性阈值填补了环境保护的重要数据空白。

The proposed work will work on Rare Earth Elements (REEs) and Platinum Group Elements (PGEs) which are ecologically ‘data-poor’. PGEs such as Palladium (Pd) and platinum (Pt) are co-emitted into the environment from automotive catalytic converters, as well as from mining both base- and precious metals, thus are deposited to soils. REEs are critical to digital electronic devices and energy technologies, and they are micronutrients that enhance crop production; mining extraction of REEs increased from 50 kt/year in 1990 to 150 kt/year in 2010. Hormesis is a response to a stress which is bi-phasic, i.e. both stimulation and inhibition of the measured endpoint depending on concentration. This response is extremely widespread across species, responses and toxic agents, but the derivation of toxicity thresholds typically doesn’t include low enough exposure concentrations to cause hormesis. If hormesis is not identified in the data from which toxicity thresholds are derived, then resulting soil quality guidelines (SQGs) are not protective of environmental health. Bioaccessibility of metals in soils depends on soil physical and chemical characteristics, and it has been demonstrated that toxicity thresholds for total soil [metal] were more harmonized when normalized to soil characteristics such as eCEC, pH, %clay and OM. The objectives are to: determine toxicity thresholds for plants exposed to the REEs Cerium (Ce), Neodymium (Nd), Lanthanum (La) and Yttrium (Y) in soil, singly and in whole mixtures; to determine toxicity thresholds for plants exposed to the PGEs Palladium (Pd) and Platinum (Pt) in soil, singly and in whole mixture; to identify the bioaccessibility of PGEs and REEs in soils and how that is controlled; and to quantify hormesis for REEs and PGEs for response endpoints. It has been said that “The acceptance of hormesis and essentiality in ecotoxicology requires major conceptual changes and considerable new data”. The proposed research will respond to that challenge by identifying hormetic dose-responses to these data-poor metals, without which the debate on how and if hormesis should be accommodated in the ERA framework as questioned can’t advance. Variation in toxicity thresholds among species or genotypes is the reason why populations or communities shift structure in response to environmental contaminants, particularly for exposures that are sub-lethal. Hormetic responses by plants to contaminants, which may be differential among species, are almost certainly part of variation in sensitivity to environmental toxins, and failure to adequately characterize hormetic dose responses to environmental contaminants could result in a NOEC higher than the “true NOEC”, which would be the peak of the hormetic response. Given the development of new mineral resources in Canada (e.g. The Ring of Fire) and by Canadian mining companies abroad, it is crucial that Canada fill the data gaps for these data poor metals for its own environmental protection, as well as being a demonstrable global leader in sustainability of mining. The proposed work will fill that gap. The cost of under-protection is loss of ecosystem structure and function; over-protection imposes needless reduction and remediation which have productivity costs. A second impact of the work will be the establishment of toxicity thresholds for the whole mixtures likely to occur at contaminated sites – the question of whether single-metal toxicity thresholds adequately protect the environment from metal mixtures is likely “no”, establishing toxicity thresholds for a full factorial of binary and tertiary metal mixtures is resource –prohibitive, so ‘whole mixture’ toxicity thresholds fill an important data gap for environmental protection.