植物角质层的蜡质组分对甲萘酚的吸附作用

采用批量平衡法,比较研究了苹果角质结合蜡质、分离蜡质和重建蜡质对极性有机污染物甲萘酚的吸附作用,并探讨了不同负载量的重建蜡质的吸附性能,以期为准确预测有机污染物在不同状态蜡质组分上的吸附行为提供依据.结果表明,甲萘酚在苹果角质层、脱蜡角质层、分离蜡质(IW)、重建蜡质(BW)上的等温吸附线呈非线性,符合Freundlich方程.植物蜡质对甲萘酚的吸附作用与蜡质所处状态密切相关,吸附能力(Koc)大小顺序为:重建蜡质(321.2) > 分离蜡质(190.4) > 角质结合蜡质(128.4),表明植物角质层进入土壤后发生演化过程中,其中不易降解的蜡质的吸附能力逐渐增大.重建蜡质(BW)的吸附系数(Kd)与甲萘酚的浓度呈负相关,与蜡质的负载量呈正有关.在低浓度时,甲萘酚的有机碳标化吸附系数Koc值随有机碳含量(foc)增大先增大后减小,存在一些强的特殊作用;而高浓度时, Koc-基本为一常数,不随蜡质负载量而变化,主要吸附机理为分配作用.角质结合蜡质(CW)对角质层的总吸附作用的贡献较小,但随甲萘酚平衡浓度的增大而逐渐增大,并于高浓度时, CW的吸附能力与IW相当.

Sorption of 1-Naphthol to Plant Cuticular Waxes with Different States

Wax components are ubiquitous in natural environments (such as plant and soil) and play a significant role in sorption of organic contaminants. To elucidate their sorption characteristics, cuticular waxes were isolated from the fruits of apple by organic solvent extraction method, and then the isolated-wax was reconstructed on montmorillonite with different loadings. Sorption behaviors of one polar organic pollutant, 1-naphthol, to isolated-wax, reconstructed-wax, and cuticle-associated-wax samples were compared by batch sorption method. Sorption properties of wax-montmorillonite complexes dependent on different wax-loadings were also investigated. Isotherms of 1-naphthol to wax samples were nonlinear, and fitted well with Freundlich equation. Although sorption of wax in the plant cuticle was weakened by other components of cuticle, its contribution to whole sorption of the cuticle increased with solute aqueous equilibrium concentration. Sorption coefficients at three equilibrium concentrations (1, 10, 100 microg/mL) were calculated, depending on solute concentrations and wax-loadings. Sorption coefficients normalized organic carbon contents (Koc) decreased with the increase of solute aqueous concentration. At low solute aqueous concentration, Koc values increased with the wax-loading increasing, reached maximum, and then decreased. At high solute aqueous concentration, Koc values were almost independent on wax-loadings. These observations indicated that partition was the dominant mechanism at high solute concentration, while specific interactions were involved as additional mechanisms at low solute concentration. Koc values of wax components in different states were in the order of reconstructed-wax (321.2) > isolated-wax (190.4) > cuticular-attached-wax (128.4), suggested that the sorption capability of wax was promoted once they were input into soil environment and then coated on mineral surface.