A New Perspective on the Apparent Solubility of Dissolved Black Carbon
A New Perspective on the Apparent Solubility of Dissolved Black Carbon
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DOI：
10.3389/feart.2017.00075
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发表时间：
2017-09-26
影响因子：
2.9
通讯作者：
Jaffe, Rudolf
中科院分区：
文献类型：
--
作者：
Wagner, Sasha;Ding, Yan;Jaffe, Rudolf
黑碳（BC）是生物质不完全燃烧产生的热解有机物，在环境中无处不在。组成 BC 化合物库的分子结构由其被含 O 官能团（例如羧基）多取代的稠合芳香族核心结构定义。尽管BC分子具有明显的疏水性，但相当一部分BC以溶解BC（DBC）的形式从陆地转移到水生系统。然而，控制黑碳从陆地转移到水中的具体生物地球化学机制仍然难以捉摸。在当前的研究中，DBC 的表观溶解度是根据辛醇-水分配系数 (K-ow) 推断的，该系数为具有不同缩聚程度和极性官能度的 DBC 结构建模。模拟 K-ow 值表明，具有小芳环系统和高亲水官能度的 DBC 分子可能真正溶解在水相中。然而，大型且高度浓缩的 DBC 结构产生了高 K-ow 值，这表明在水生环境中量化的 DBC 库中有相当一部分并未真正溶解。我们假设其他 DOM 组分可能在稠合芳香族分子的增溶过程中充当介体，并通过疏水性分子间缔合来增加 DBC 的溶解度。通过受控浸出实验检验了这一假设，以确定在 DOM 存在的情况下，DBC 从颗粒土壤和炭中的动员是否得到增强。然而，我们观察到每种样品类型固有的特性对 DBC 表观溶解度的影响比添加的 DOM 更大。此外，对从同一组土壤和炭中获得的渗滤液进行的分子标记（苯多羧酸）和超高分辨率质谱数据（FT-ICR/MS）的直接比较并未显示出两种分析方法在 DBC 定量或表征方面存在明显重叠。 FT-ICR/MS 结果与 BPCA 之间的相关性不显着，可能是由于方法学窗口和/或样本量较小的差异。我们的结果无法提供证据支持 DOM 和 DBC 之间提出的疏水相互作用，这表明其他物理/化学机制在 BC 溶解中发挥着重要作用。
Black carbon (BC), pyrogenic organic matter generated from the incomplete combustion of biomass, is ubiquitous in the environment. The molecular structures which comprise the BC pool of compounds are defined by their condensed aromatic core structures polysubstituted with O-containing functionalities (e.g., carboxyl groups). Despite the apparent hydrophobicity of BC molecules, a considerable portion of BC is translocated from terrestrial to aquatic systems in the form of dissolved BC (DBC). However, the specific biogeochemical mechanisms which control the transfer of BC from the land to the water remain elusive. In the current study, the apparent solubility of DBC was inferred from octanol-water partition coefficients (K-ow) modeled for proposed DBC structures with varying degrees of polycondensation and polar functionality. Modeled K-ow values indicated that DBC molecules with small aromatic ring systems and high degrees of hydrophilic functionality may be truly solubilized in the aqueous phase. However, large and highly condensed DBC structures yielded high K-ow values, which suggested that a considerable portion of the DBC pool which has been quantified in aquatic environments is not truly dissolved. We hypothesized that other DOM components may act as mediators in the solubilization of condensed aromatic molecules and serve to increase the solubility of DBC via hydrophobic, intermolecular associations. This hypothesis was tested through controlled leaching experiments to determine whether the mobilization of DBC from particulate soils and chars became enhanced in the presence of DOM. However, we observed that characteristics inherent to each sample type had a greater influence than added DOM on the apparent solubility of DBC. In addition, the direct comparison of molecular marker (benzenepolycarboxylic acids) and ultrahigh resolution mass spectral data (FT-ICR/MS) on leachates obtained from the same set of soils and char did not show a clear overlap in DBC quantification or characterization between the two analytical methods. Correlations between FT-ICR/MS results and BPCA were not significant possibly due to differences in the methodological windows and/or small sample size. Our results were unable to provide evidence in support of proposed hydrophobic interactions between DOM and DBC, suggesting that other physical/chemical mechanisms play important roles in the dissolution of BC.