School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
Department of Plant and Soil Sciences, University of Delaware, Newark, DE 19716, USA; National Research Council Resident Research Associate, U.S. Environmental Protection Agency, Ada, OK 74820, USA.
Environ Pollut. 2017 Nov;230:540-549. doi: 10.1016/j.envpol.2017.06.101. Epub 2017 Jul 11.
Land application of biochar has been increasingly recommended as a powerful strategy for carbon sequestration and soil remediation. However, the biochar particles, especially those in the nanoscale range, may migrate or carry the inherent contaminants along the soil profile, posing a potential risk to the groundwater. This study investigated the transport and retention of wood chip-derived biochar nanoparticles (NPs) in water-saturated columns packed with a paddy soil. The environmentally-relevant soil solution chemistry including ionic strength (0.10-50 mM), electrolyte type (NaCl and CaCl), and natural organic matter (0-10 mg L humic acid) were tested to elucidate their effects on the biochar NPs transport. Higher mobility of biochar NPs was observed in the soil at lower ionic strengths, with CaCl electrolyte being more effective than NaCl in decreasing biochar NPs transport. The retained biochar NPs in NaCl was re-entrained (∼57.7%) upon lowering transient pore-water ionic strength, indicating that biochar NPs were reversibly retained in the secondary minimum. In contrast, negligible re-entrainment of biochar NPs occurred in CaCl due to the primary minimum and/or particle aggregation. Humic acid increased the mobility of biochar NPs, likely due to enhanced electrosteric repulsive interactions. The transport behaviors of biochar NPs can be well interpreted by a two-site kinetic retention model that assumes reversible retention for one site, and irreversible retention for the other site. Our findings indicated that the transport of wood chip biochar NPs is significant in the paddy soil, highlighting the importance of understanding the mobility of biochar NPs in natural soils for accurately assessing their environmental impacts.
土地施用生物炭作为碳固存和土壤修复的有力策略已日益受到推荐。然而，生物炭颗粒，尤其是纳米级范围内的颗粒，可能会沿土壤剖面迁移或携带固有的污染物，对地下水构成潜在风险。本研究调查了水饱和条件下填充稻田土壤的柱状物中木质素衍生生物炭纳米颗粒（NPs）的迁移和滞留。包括离子强度（0.10-50 mM）、电解质类型（NaCl 和 CaCl）和天然有机物（0-10 mg/L 腐殖酸）等环境相关土壤溶液化学性质，以阐明它们对生物炭 NPs 迁移的影响。在较低离子强度下，土壤中观察到生物炭 NPs 具有更高的迁移性，其中 CaCl 电解质在降低生物炭 NPs 迁移方面比 NaCl 更有效。当降低瞬态孔隙水离子强度时，在 NaCl 中保留的生物炭 NPs 被重新夹带（约 57.7%），表明生物炭 NPs 在二次最小值中是可逆保留的。相比之下，由于初级最小值和/或颗粒聚集，在 CaCl 中几乎没有生物炭 NPs 被重新夹带。腐殖酸增加了生物炭 NPs 的迁移性，这可能是由于增强了电动斥力相互作用。生物炭 NPs 的传输行为可以通过假设一个位点为可逆保留，另一个位点为不可逆保留的双位动力学保留模型很好地解释。我们的研究结果表明，木质素生物炭 NPs 在稻田土壤中的迁移性显著，这突出了在自然土壤中了解生物炭 NPs 的迁移性对准确评估其环境影响的重要性。
