Toxicity of Data-Poor Metals in Soil-Plant Systems

拟议的工作将涉及稀土元素（REEs）和铂族元素（PGEs），这些元素在生态学上“数据贫乏”。铂族元素如钯（Pd）和铂（Pt）从汽车催化转化器以及开采贱金属和贵金属中共同排放到环境中，从而沉积到土壤中。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营养素;稀土元素的开采量从1990年的50千吨/年增加到2010年的150千吨/年。激效是对应激的反应，其是双相的，即取决于浓度的测量终点的刺激和抑制。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毒物兴奋效应的低暴露浓度。如果毒物兴奋效应在毒性阈值的数据中没有被识别出来，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获得性取决于土壤的物理和化学特性，并且已经证明，当归一化为土壤特性（例如eCEC、pH、%粘土和OM）时，土壤[金属]总量的毒性阈值更加协调。其目标是：确定植物暴露于土壤中稀土元素铈（Ce）、钕（Nd）、镧（La）和钇（Y）的毒性阈值，无论是单一的还是全部混合物;确定植物暴露于土壤中铂族元素钯（Pd）和铂（Pt）的毒性阈值，无论是单一的还是全部混合物;确定土壤中铂族元素和稀土元素的生物可获得性，以及如何加以控制;并量化反应终点的RE和PGE的兴奋效应。有人说，“接受生态毒理学中的毒物兴奋效应和必要性需要重大的概念变化和大量的新数据”。拟议的研究将通过确定对这些数据贫乏的金属的兴奋效应剂量反应来应对这一挑战，没有这些金属，关于如何以及是否应该在ERA框架中容纳兴奋效应的辩论就无法推进。物种或基因型之间毒性阈值的差异是种群或群落改变结构以应对环境污染物的原因，特别是对于亚致死性的暴露。植物对污染物的激素反应在物种之间可能存在差异，几乎肯定是对环境毒素敏感性变化的一部分，如果不能充分描述对环境污染物的激素剂量反应，可能导致NOEC高于“真实NOEC”，这将是激素反应的峰值。鉴于加拿大新矿产资源的开发（如火环）以及加拿大矿业公司在海外的开发，加拿大填补这些数据不足的金属的数据空白对于其自身的环境保护至关重要，同时也是采矿可持续性的全球领导者。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损失;过度保护则会造成不必要的减少和补救，从而产生生产力成本。这项工作的第二个影响将是为可能出现在受污染场地的所有混合物确定毒性阈值-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很可能是“否”，为二元和第三金属混合物的全部因子确定毒性阈值是资源限制性的，因此，“全混合物”毒性阈值填补了环境保护方面的一个重要数据空白。

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.