College of Environmental Science and Engineering, Beijing Forestry University, Beijing 100083, China.
College of Urban and Environmental Science, Peking University, Beijing 100871, China.
Int J Environ Res Public Health. 2022 Feb 24;19(5):2600. doi: 10.3390/ijerph19052600.
Humic substances as an electron shuttle play an essential role in the biogeochemistry processes. However, the influence of total organic carbon (TOC) concentrations of humic substances on microbial Cr(VI) reduction remains unclear. In this study, the rates and extents of Cr(VI) reduction by MR-1 in the presence of Leonardite humic acids (LHA) and Pahokee peat humic acids (PPHA) with different TOC concentrations were evaluated. We found that the enhanced reduction in Cr(VI) was associated with TOC concentrations of 2.5-50 mg C/L of HA samples. The result shows that HA as an electron shuttle impacted both rates and extents of microbial Cr (VI) reduction, which delivered differently in terms of low TOC concentration range of 2.5 to 15 mg C/L and high concentration range of 15-50 mg C/L. The rates of Cr(VI) reduction significantly enhanced in the low TOC concentration range of HA compared to a high concentration range. The highest acceleration rate of Cr(VI) reduction was achieved at 15 mg C/L of HA. The quinone-like fluorophore was responsible for the main redox-active functional groups of HA by the three-dimensional excitation-emission spectroscopy. The fluorescence intensity of quinone-like fluorophore of HA in the low TOC concentration range was positively correlated with its acceleration coefficient, corresponding to the highest microbial Cr(VI) reduction rate obtained in 15 mg C/L of HA. These findings highlighted the effect of the TOC concentration of HA on microbial Cr(VI) reduction processes. It emphasized that the low TOC concentration of HA contributed to the high rates of Cr(VI) reduction, which is critical for better understanding the fate of Cr(VI) and evaluating the effectiveness of Cr(VI) restoration strategies in the future.
腐殖质作为电子穿梭体在生物地球化学过程中起着至关重要的作用。然而，腐殖质总有机碳（TOC）浓度对微生物 Cr(VI)还原的影响尚不清楚。在这项研究中，评估了不同 TOC 浓度的莱奥尼德特腐殖酸（LHA）和帕霍基泥炭腐殖酸（PPHA）对 MR-1 还原 Cr(VI)的速率和程度的影响。我们发现，增强的 Cr(VI)还原与 HA 样品 TOC 浓度为 2.5-50mgC/L 有关。结果表明，腐殖质作为电子穿梭体影响微生物 Cr(VI)还原的速率和程度，这在 TOC 浓度范围为 2.5-15mgC/L 的低浓度范围和 15-50mgC/L 的高浓度范围有不同的表现。与高浓度范围相比，HA 在低 TOC 浓度范围内 Cr(VI)还原的速率显著提高。HA 的最高 Cr(VI)还原加速率在 15mgC/L 时达到。三维激发-发射光谱表明，醌类荧光团是腐殖质主要的氧化还原活性官能团。HA 在低 TOC 浓度范围内醌类荧光团的荧光强度与其加速系数呈正相关，这与在 15mgC/L 的 HA 中获得的最高微生物 Cr(VI)还原速率相对应。这些发现强调了 HA 的 TOC 浓度对微生物 Cr(VI)还原过程的影响。这表明低 TOC 浓度的 HA 有助于提高 Cr(VI)还原的速率，这对于更好地了解 Cr(VI)的归宿以及未来评估 Cr(VI)修复策略的有效性至关重要。
