全氟烷基酸类在土壤中的吸附解吸及淋溶行为研究

为探讨不同碳链长度全氟烷基酸(perfluoroalkyl acids,PFAAs)在土壤中的吸附解吸及淋溶行为,分别利用批量平衡法和土柱实验方法研究了8种PFAAs在潮土和黑土的吸附解吸及淋溶特性。结果表明,PFAAs在土壤中的吸附和解吸在24 h内均能达到平衡,解吸存在迟滞性,PFAAs在土壤中的吸附和解吸等温线符合Freundlich模型(R20.900),Kf在1.44~282之间;潮土对PFAAs的吸附能力强于黑土,土壤对全氟烷基磺酸的吸附能力优于全氟烷基羧酸,且碳链越长,越容易被吸附;土壤有机质含量、粒径分布及溶解性有机质共同影响土壤对PFAAs吸附能力。土柱实验表明,超过97%的短链PFAAs可被淋出;随着碳链延长,土壤对PFAAs截留能力增加,淋出时间延长,累积淋出率降低;PFAAs在潮土和黑土土柱中的淋溶行为具有明显的差异,黑土土柱淋出液中PFAAs浓度变化小于潮土土柱;溶解性有机质能够改变PFAAs的相对淋溶曲线的形状,对短链PFAAs的淋溶具有促进作用,同时抑制了全氟辛烷羧酸和全氟己烷磺酸在土层中的向下迁移。研究表明,目前广泛采纳的短链替代品在土壤中有较强的移动性,对地下水具有潜在的风险。

Sorption-desorption and leaching characteristics of perfluoroalkyl acids in soils

To elucidate the sorption-desorption and leaching of typical perfluoroalkyl acids (PFAAs) with different chain lengths and head groups on soils, batch experiments and soil-column experiments were conducted to investigate the sorption-desorption and leaching behaviors of seven kinds of PFAAs on fluvo-aquic soil and black soil, respectively. The sorption and desorption of PFAAs on the two soils reached an equilibrium within 24 h and desorption hysteresis was observed during the desorption process. The sorption and desorption isotherms of PFAAs were fitted well with the Freundlich model (R²>0.900), with K_f ranging from 1.44 to 282. The sorption capacities of PFAAs increased with carbon chain lengths. Perfluoroalkyl sulfonates held a higher affinity to soils than perfluoroalkyl carboxylic acids of the same chain length. Soil organic matter, particle size distribution, and dissolved organic matter might co-influence the sorption capacity of PFAAs. The column experiments revealed that the recovery of short-chain PFAAs from leachate generally exceeded 97%, whereas long-chain PFAAs showed comparatively lower recoveries, longer leaching time and lower cumulative leaching rates, because of their higher affinity to soils. The PFAAs showed quite different leaching behavior in the two soils, and the leachate concentrations of PFAAs changed more drastically in fluvo-aquic soil than in black soil. The level of dissolved organic matter altered the shape of the relative leaching curve and promoted the leaching of short-chain PFAAs. In contrast, it inhibited the vertical transport of perfluorooctanoic acid and perfluorohexane sulfonic acid in the soil column. Our results indicated the strong mobility of the short-chain PFAAs in soils, which may cause potential risk to groundwater.