Here, we investigated the photoreduction of Hg(II) (Hg(NO₃)₂) mediated by dissolved black carbon (DBC, <0.45 μm size fraction) collected from water extracts of biochar derived by pyrolyzing crop residues (rice, soybean, and peanut). Under simulated sunlight conditions, the presence of 5 mg C/L DBC significantly facilitated the production of Hg(0) from Hg(II) (initially at 10 nmol/L) with a reduction ratio of 73 ± 4% in 5.3 h. Inhibition of photolysis-induced reactive oxygen species by a quencher or removal of dissolved oxygen indicated that Hg(II) was mainly reduced by superoxide anion (O₂^•–). Reduction by electrons transferred from photoexcited DBC components or by organic free radicals produced from photo-Fenton-like reactions was also proposed to play a role. Contrary to dissolved humic substances, the DBC-mediated photoreduction of Hg(II) led to unique positive mass-independent isotopic fractionation (MIF) of Hg(0) (Δ¹⁹⁹Hg = 1.8 ± 0.3‰), which was attributed to the dominance of secondary Hg(II) reduction by O₂^•–. The leachate from soil amended with rice biochar at 1–5% mass ratios exhibited significantly higher photocatalytic efficiency than that from unamended soil (wherein the reduced Hg(0) increased from 27 ± 1 to 63 ± 2% in maximum), and the efficiency positively correlated with the percentage of amended biochar. Under natural illumination conditions, the total mercury and/or methylmercury uptake by roots, shoots, and leaves of lettuce (Lactuca sativa L.) grown in water extracts of rice biochar-amended soil was consistently lower (up to 70 ± 20%) than that without the biochar amendment. The findings highlight that DBC might play an important and previously unrecognized role in the biogeochemical cycle and the environmental impact of mercury.

中文翻译：

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溶解的黑碳有助于将Hg（II）光还原为Hg（0），并减少莴苣（Lactuca sativa L.）的汞吸收。

在这里，我们研究了通过热解作物残渣（大米，大豆和大豆）得到的生物炭水提取物中收集的溶解的黑碳（DBC，<0.45μm粒径分数）介导的Hg（II）（Hg（NO ₃）₂）的光还原。花生）。在模拟的阳光条件下，5 mg C / L DBC的存在显着促进了Hg（II）从Hg（II）生成Hg（0）（最初为10 nmol / L），在5.3小时内的还原率为73±4％。淬灭剂抑制光解诱导的活性氧或除去溶解的氧表明Hg（II）主要被超氧阴离子（O ₂ ^•–）。还提出了通过从光激发的DBC组分转移的电子或类似光芬顿反应产生的有机自由基的还原作用。相反，溶解腐殖物质，汞的DBC介导的光致还原（II）导致了独特的正质量无关的同位素分馏汞柱（MIF）（0）（Δ ¹⁹⁹汞柱= 1.8±0.3‰），其归因于主导地位O ₂减少二次汞（II）的比例^•–。以质量比为1–5％的水稻生物炭改良土壤中的渗滤液显示出比未经改良土壤中的渗滤液显着更高的光催化效率（其中，还原态Hg（0）的最大值从27±1增加到63±2％），并且效率与修正的生物炭的百分比呈正相关。在自然光照条件下，水稻生物炭改良后的土壤水提取物中生长的莴苣（莴苣）的根，茎和叶对汞和/或甲基汞的总吸收量始终低于（高达70±20％）没有生物炭的修改。研究结果表明，DBC可能在生物地球化学循环和汞对环境的影响中发挥了重要的作用，而以前却未被认识。