Organic compound distribution between nonionic surfactant solution and natural solids: Applicability of a solution property parameter

A solution property parameter φ was defined to examine the distribution characteristics of organic compounds between the solids and four nonionic surfactant solutions. The studied compounds consisted of BTEX (benzene, toluene, ethylbenzene, and p-xylene) and chlorinated pesticides (lindane, α-BHC, and heptachlor epoxide), which span several orders of magnitude in terms of water solubility (Sw). The solid samples were composed of a very low organic matter clay (Ca-montmorillonite), and a high organic matter natural soil (Shamou Mountain soil). The surfactants tested included two alkyl chain surfactants and two containing aromatic group surfactants with added concentrations both below and above their critical micelle concentration (CMC). By observing the Kom or Ksf variation, the result indicates, besides the Sw of the organic compounds, the distribution coefficient is regarded as a function of the soil organic matter (SOM) constituents, and the chemical structure of the organic compounds. Also, it can be found the greater φ values represent the higher releasing ratios of the organic compounds from the contaminated soil to groundwater. For the relatively higher Sw compounds, such as BTEX, all of the φ values are close to 1. The φ values for the relatively lower Sw compounds are far greater than 1, and increase with the increasing affinity of the compounds to the surfactants.