Norwegian Institute for Water Research , Gaustadalléen 21, 0349 Oslo, Norway.
Environ Sci Technol. 2015 Mar 3;49(5):3015-23. doi: 10.1021/es5061879. Epub 2015 Feb 10.
Near-surface biogeochemical systems can oscillate between oxic and anoxic conditions. Under such periodic changes many redox-sensitive inorganic contaminants undergo speciation, mobility and toxicity changes. We investigated the changes to chromium (Cr), arsenic (As), selenium (Se), antimony (Sb) and uranium (U) mobility during a series of laboratory experiments where argillaceous substrates were subjected to successive cycles of oxidizing and reducing conditions. The EH oscillated between -320 and +470 mV, induced via both abiotic and microbial forcings. Chemically induced cycles of oxidation and reduction were achieved via a combination of gas (N2:CO2 vs compressed air) and carbon (ethanol) addition, to stimulate the metabolism of a natively present microbial community. The contaminants were added either alone or as contaminant mixtures. Results show clear on-off switch mobility behavior for both major elements such as carbon (C), iron (Fe) and manganese (Mn) and for contaminants. Mn, Fe, and As were mobilized under anoxic conditions, whereas Sb, Se, and U were mobilized under oxic conditions. While As, Sb, and U were reversibly sorbed, Se and Cr were irreversibly sequestered via reductive precipitation. When present in aqueous solutions at high concentrations, Cr(VI) prevented the reduction of Mn and Fe, and inhibited the mobilization of elements with lower EH(o). To improve remediation strategies for multiple contaminants in redox-dynamic environments, we propose a mixed kinetic-equilibrium biogeochemical model that can be forced by oscillating boundary conditions and that uses literature rates and constants to capture the key processes responsible for the mobilization of contaminants in soils.
近地表生物地球化学系统可以在氧化和缺氧条件之间振荡。在这种周期性变化下，许多氧化还原敏感的无机污染物会发生形态、迁移性和毒性变化。我们研究了在一系列实验室实验中，在氧化和还原条件下交替进行时，铬（Cr）、砷（As）、硒（Se）、锑（Sb）和铀（U）的迁移率变化情况。Eh 通过非生物和微生物驱动力在-320 至+470 mV 之间振荡。通过气体（N2:CO2 与压缩空气）和碳（乙醇）的组合来实现化学诱导的氧化还原循环，以刺激天然存在的微生物群落的代谢。污染物单独添加或作为污染物混合物添加。结果表明，对于主要元素如碳（C）、铁（Fe）和锰（Mn）以及污染物，都存在明显的开/关开关迁移行为。在缺氧条件下，Mn、Fe 和 As 被迁移，而 Sb、Se 和 U 在有氧条件下被迁移。虽然 As、Sb 和 U 可以可逆地吸附，但 Se 和 Cr 通过还原沉淀不可逆地被固定。当以高浓度存在于水溶液中时，Cr(VI) 会阻止 Mn 和 Fe 的还原，并抑制 Eh(o) 较低的元素的迁移。为了改进在氧化还原动态环境中处理多种污染物的修复策略，我们提出了一种混合动力学-平衡生物地球化学模型，该模型可以通过振荡边界条件来驱动，并使用文献中的速率和常数来捕捉导致土壤中污染物迁移的关键过程。
