水飽和的土壤中，土壤無機質的吸附被大量的水所抑制，因此非離子有機污染物的吸附主要為有機質的分佈作用（Partition），其吸附等溫線呈現線性。近期不少文獻中指出，非離子有機污染物在極低濃度時，土壤對其呈現非線性的吸附作用；存在其他共同吸附質時，這種非線性吸附作用會被抑制。造成這種現象的原因可能與土壤有機質中存在一些特殊組成有關，進而推測土壤有機質對非離子有機污染物的作用機制應不只一種。 本研究以三種原始土壤和兩種淋洗土壤對二種有機污染物（三氯乙烯、四氯乙烯）在極低濃度下進行一系列單一和雙重吸附質之等溫吸附實驗。實驗結果顯示，土壤對低濃度非離子有機污染物的吸附等溫線呈非線性，這種非線性的吸附等溫線以泰山森林土最明顯，其次為紗帽山土和IFP，大部分在平衡濃度等於0.05mg/L時即呈現向下凹之曲線；在雙重吸附質的系統中，非線性吸附效應會被共同吸附質所抑制，抑制的能力則決定於共同吸附質的分子量，土壤淋洗對不同土壤的組成有不同的效應。實驗結果較符合HSACM-SI Model （High-Surface-Area Carbonaceous Material-Specific Interactions Model）假說：土壤對非離子有機污染物之非線性吸附來自於土壤中之微量且具高吸附力之HSACM。 In aqueous solution, the sorption of nonionic organic compounds (NOCs) on soil/sediment occurs mainly by partition into the soil organic matter (SOM) because the adsorption on soil mineral fraction is strongly suppressed by water. Recently, many researchers have been speculated that the sorption of NOCs on some soils displays a nonlinear sorption isotherm at relatively low concentration. The nonlinear uptake of a solute by soils at low NOCs concentration may be suppressed by other solutes (i.e., cosolutes) in multiple-solute systems. These observations indicate that more than one mechanism are required to account for the sorption of SOM. A series of single-solute and binary-solute sorption experiments were conducted for the sorption of nonionic organic compounds on three soil samples and two washed soil samples. The data were extended to relatively low solute concentrations (Ce/Sw) where Ce and Sw are the equilibrium concentration and solubility in water, respectively. At about Ce/Sw＝10-4, the nonionic organic solutes exhibit nonlinear sorption isotherm (of a concave-downward shape). The nonlinear uptake of a solute at low Ce/Sw is suppressed to different extents by other cosolutes in binary-solute system. The abilities of different cosolutes to suppress the nonlinear magnitudes depend on the molecular weight. The washed soils show different curvature on each adsorbate. These results in agreement with the hypothesis that adsorption on a small amount of strongly adsorbing HSACM is largely responsible for the nonlinear sorption of nonionic organic solutes on soils.
