Department of Biology, McMaster University, Hamilton, ON, Canada L8S 4K1.
Aquat Toxicol. 2011 Oct;105(3-4 Suppl):3-8. doi: 10.1016/j.aquatox.2011.03.007. Epub 2011 Mar 21.
Dissolved organic carbon (DOC), through its ability to complex metals and thereby reduce their bioavailability, plays a major role in ameliorating metal toxicity in natural waters. Indeed DOC is a key variable in the Biotic Ligand Model (BLM) for predicting metal toxicity on a site-specific basis. However, recent evidence indicates that all DOCs are not alike, but rather heterogeneous in their ability to protect organisms against metal toxicity, at least in fresh water. The degree of protection appears to correlate with optical properties, such that dark, aromatic-rich compounds of allochthonous origin, with greater humic acid content, are more effective in this regard, particularly against Cu, Ag, and Pb toxicity. The specific absorption coefficient of the DOC in the 300-350nm range (SAC(300-350)) has proven to be a simple and effective index of this protective ability. PARAFAC, a multivariate statistical technique for analysis of excitation-emission fluorescence spectroscopy data, also holds promise for quantifying the humic-like and fulvic-like fluorophores, which tend to be positively and negatively correlated with protective ability, respectively. However, what has been largely missing in the toxicological realm is any appreciation that DOC may also affect the physiology of target organisms, such that part of the protection may occur by a mechanism other than metal complexation. Recently published evidence demonstrates that DOC has effects on Na(+) transport, diffusive permeability, and electrical properties of the gills in fish and crustaceans in a manner which will promote Na(+) homeostasis. These actions could thereby protect against metal toxicity by physiological mechanisms. Future research should investigate potential direct interactions of DOC molecules with the branchial epithelium. Incorporation of optical properties of DOC could be used to improve the predictive capabilities of the BLM.
溶解有机碳（DOC）通过与金属络合从而降低其生物有效性，在改善天然水体中金属毒性方面起着重要作用。事实上，DOC 是生物配体模型（BLM）中预测金属毒性的关键变量，该模型是基于特定地点进行预测的。然而，最近的证据表明，并非所有的 DOC 都相同，而是在保护生物免受金属毒性方面具有异质性，至少在淡水环境中是如此。这种保护程度似乎与光学特性相关，即具有更大腐殖酸含量的异源深色、芳香富化合物，在这方面更为有效，特别是对 Cu、Ag 和 Pb 的毒性。DOC 在 300-350nm 范围内的特定吸收系数（SAC（300-350））已被证明是这种保护能力的简单有效指标。PARAFAC 是一种用于分析激发-发射荧光光谱数据的多元统计技术，也有望量化腐殖质样和富里酸样荧光团，它们分别与保护能力呈正相关和负相关。然而，在毒理学领域中，人们在很大程度上没有意识到 DOC 也可能影响目标生物的生理学，以至于部分保护可能是通过除金属络合以外的机制发生的。最近发表的证据表明，DOC 对鱼类和甲壳类动物的鳃钠离子转运、扩散通透性和电特性具有影响，从而促进钠离子的体内平衡。这些作用可以通过生理机制来保护生物免受金属毒性的影响。未来的研究应该调查 DOC 分子与鳃上皮之间的潜在直接相互作用。DOC 光学特性的纳入可以提高 BLM 的预测能力。
