Tokunaga Tetsu K, Wan Jiamin, Firestone Mary K, Hazen Terry C, Olson Keith R, Herman Donald J, Sutton Stephen R, Lanzirotti Antonio
Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
J Environ Qual. 2003 Sep-Oct;32(5):1641-9. doi: 10.2134/jeq2003.1641.
Chromium has become an important soil contaminant at many sites, and facilitating in situ reduction of toxic Cr(VI) to nontoxic Cr(III) is becoming an attractive remediation strategy. Acceleration of Cr(VI) reduction in soils by addition of organic carbon was tested in columns pretreated with solutions containing 1000 and 10 000 mg L(-1) Cr(VI) to evaluate potential in situ remediation of highly contaminated soils. Solutions containing 0,800, or 4000 mg L(-1) organic carbon in the form of tryptic soy broth or lactate were diffused into the Cr(VI)-contaminated soils. Changes in Cr oxidation state were monitored through periodic micro-XANES analyses of soil columns. Effective first-order reduction rate constants ranged from 1.4 x 10(-8) to 1.5 x 10(-7) s(-1), with higher values obtained for lower levels of initial Cr(VI) and higher levels of organic carbon. Comparisons with sterile soils showed that microbially dependent processes were largely responsible for Cr(VI) reduction, except in the soils initially exposed to 10 000 mg L(-1) Cr(VI) solutions that receive little (800 mg L(-1)) or no organic carbon. However, the microbial populations (< or = 2.1 x 10(5) g(-1)) in the viable soils are probably too low for direct enzymatic Cr(VI) reduction to be important. Thus, synergistic effects sustained in whole soil systems may have accounted for most of the observed reduction. These results show that acceleration of in situ Cr(VI) reduction with addition of organic carbon is possible in even heavily contaminated soils and suggest that microbially dependent reduction pathways can be dominant.
铬已成为许多场地重要的土壤污染物，促使有毒的六价铬原位还原为无毒的三价铬正成为一种有吸引力的修复策略。通过向用含1000和10000 mg L⁻¹六价铬溶液预处理的柱中添加有机碳来测试土壤中六价铬还原的加速情况，以评估对高污染土壤进行原位修复的潜力。含有0、800或4000 mg L⁻¹胰蛋白胨大豆肉汤或乳酸形式有机碳的溶液扩散到受六价铬污染的土壤中。通过对土柱进行定期的微X射线吸收近边结构分析来监测铬氧化态的变化。有效一级还原速率常数范围为1.4×10⁻⁸至1.5×10⁻⁷ s⁻¹，初始六价铬水平较低且有机碳水平较高时获得的值更高。与无菌土壤的比较表明，除了最初暴露于10000 mg L⁻¹六价铬溶液且几乎没有（800 mg L⁻¹）或没有有机碳的土壤外，微生物依赖过程在很大程度上导致了六价铬的还原。然而，活性土壤中的微生物数量（≤2.1×10⁵ g⁻¹）可能太低，以至于直接酶促还原六价铬并不重要。因此，整个土壤系统中维持的协同效应可能是观察到的大部分还原的原因。这些结果表明，即使在污染严重的土壤中，添加有机碳加速原位六价铬还原也是可能的，并表明微生物依赖的还原途径可能占主导地位。
