Global variability in dissolved organic matter: implications for metal bioavailability and risk assessment

溶解有机物（DOM）是地球表面天然沃茨中普遍存在的物质。溶解有机物在全球碳平衡中至关重要，对养分循环和气候变化具有影响/控制作用。碳显然是生命过程中的重要元素，DOM代表了地球上碳的潜在动态成分。除了DOM在影响生产力和气候方面的作用外，DOM的第二个作用是结合污染物并影响其生物有效性和运输。生物配体模型（BLM）等毒性预测模型隐含地考虑了DOM，因为它有可能络合金属并减轻其毒性。溶解有机物通常以溶解有机碳（DOC）的形式定量表示，并以毫克碳/升为单位报告。DOC是一个有用的代理，因为它可以很容易地测量，使用碳分析仪，但它仍然是一个悬而未决的问题，如果DOM的分子差异需要考虑到了解碳/营养循环，气候变化，以及污染物的命运和运输？已知DOM是小的低分子量羧酸沿着与大分子组分的混合物。DOM的来源影响了组合。我的实验室和其他人已经证明，所有DOM在光学性质方面都不相同，或者在对金属和质子的反应性方面（酸碱和金属滴定），甚至在毒性缓解方面（深色有机物往往比浅色有机物更具保护性）。尚未评估这些差异在广泛地理范围内的重要性，也未评估其对依赖DOM的建模和风险评估的具体影响。我实验室的工作主要集中在加拿大南部安大略的样品（以前的NSERC发现补助金）和北美沿海的海洋/河口有机物（以前的NSERC CRD补助金）。有必要将这一早期工作扩大到更广泛的样品，并使用日益复杂的分析技术。 利用发现基金，将从北美收集一组南北样本，并利用合作者和补充资金来源，还将从加拿大西北地区、巴西亚马逊盆地和中国重庆三峡地区收集样本。分子光谱学将作为一种“指纹”技术应用于所有样品。为了评估金属结合滴定法，将使用游离离子测量作为重点。DOM绑定到一套金属的特性将允许统一的模型来解释物种形成。在全球范围内，随着监管机构转向北美和欧洲开发的类似BLM的方法，重要的是要确保DOC在分子水平上“驱动”这些模型。

Dissolved organic matter (DOM) is a ubiquitous substance in natural waters on the earth's surface. Dissolved organic matter is crucial in global carbon balance with implications/controls on nutrient cycling as well as climate change. Carbon is obviously a significant element in life processes and DOM represents a potentially dynamic component of carbon on earth. In addition to DOM's role in influencing productivity and climate, a secondary role of DOM is to bind pollutants and influence their bioavailablity and transport. Toxicity prediction models such as the Biotic Ligand Model (BLM) implicitly take DOM into account due to its potential to complex metals and mitigate their toxicity.******Dissolved organic matter is often represented quantitatively as dissolved organic carbon (DOC) and reported in milligrams carbon per litre. DOC is a useful proxy because it can be readily measured, using a carbon analyzer, but it remains an open question if molecular differences in DOM need to be taken into account in understanding carbon/nutrient cycling, climate change, as well as pollutant fate and transport? DOM is known to be a mixture of small low molecular weight carboxylic acids along with macromolecular components. The source of DOM influences the composition. It has been shown by my lab, and others, that all DOM is not created equal in terms of optical properties, or in terms of reactivity towards metal and protons (acid-base and metal titrations), or even in terms of toxicity mitigation (darker organic matter tends to be more protective than lighter coloured organic matter). The significance of these differences on a wide geographic scale has not been assessed nor has the specific implications for DOM dependent modelling and risk assessment.******Work in my lab has focused on samples from Southern Ontario Canada (previous NSERC Discovery Grant) and marine/estuarine organic matter from coastal North America (previous NSERC CRD grant). It is necessary to expand this earlier work to a much wider range of samples and also using increasingly sophisticated analytical techniques. Using Discovery funds a North-South set of samples will be collected from North America and using collaborators and complementary funding sources, samples will also be collected from the Northwest Territories in Canada, the Amazon Basin in Brazil and the three gorges region of Chongqing province in China.******Molecular spectroscopy will be used as a "fingerprint'' technique applied on all samples. To assess metal binding titrimetry will be utilized with an emphasis on free ion measurement. Characterization of DOM binding to a suite of metals will allow for unified models to account for speciation. Globally, as regulators move towards the BLM-like approaches developed in North America and Europe it is important to make sure that the DOC that "drives" these models in the same at a molecular level.