Studies on the Fate of Nonionic Surfactant in the Soil Environment

为了弄清烷基乙氧基酸盐、烷基酚乙氧基酸盐等非离子表面活性剂在土壤环境中的归宿，采用土壤灌注法进行了生物降解试验。在生物降解试验中，用总有机碳（TOC）法分析了灌注液中残留的表面活性剂。结果表明，由于TOC在土壤上的吸附作用，在开始灌注后TOC立即急剧下降，滞后约40 d后发生生物降解。这些结果表明，非离子表面活性剂在土壤上的吸附在土壤环境中的消失现象中起着重要作用。然后，考察了壬基酚聚氧乙酸酯（NPE,n=10、15、18、20）在土壤和土壤粘土水溶液中的吸附行为。NPE对高岭土、铈土、钙膨润土等黏土矿物的吸附等温线在临界胶束浓度以下可分为两个不同的阶段，在此阶段吸附量接近于恒定值。等温线在较低浓度范围内表现为langmuir型，随后吸附量随浓度的增加而增加。随着环氧乙烷(n)与壬基酚吸附量的增加，吸附量减小。这些结果表明，在较低浓度范围内，NPE分子在粘土表面的排列方式是亲水成分环氧乙烷与表面平行，而在较高浓度范围内，通过疏水相互作用在表面形成二维或三维胶束的聚集体。NPE对黏土矿物的吸附行为与对黏土矿物的吸附行为相似。另一方面，当浓度低于CMC时，腐殖质土壤的吸附等温线服从Freundrich方程。本实验继续阐明非离子型表面活性剂对腐殖质的吸附特性。

In order to clarify the fate of such nonionic surfactants as alkyl ethoxylates,alkylphenol ethoxylates in the soil environment,the biodegradation test with soil perfusion method was carried out.In the biodegradation test, residual surfactants in the perfused fluid were analysed by total organic carban (TOC).It was observed that TOC decreased sharply immediately after the initiation of perfusion because of the adsorption onto soil,and biodegradation occured after lag time about 40 days.These results show that the adsorption of nonionic surfactants on the soil plays an inportant role in the disappearance phenomena in the soil environment.Then,the adsorption behavior of nonylphenol ethoxylate(NPE,n=10,15,18,20)on soil and soil clays in aqueous solution was examined.Adsorption isotherms of NPE on such clay minerals as Kaolin,Cericite and Ca-bentonite could be divided into two distinct stages below CMC (critical micelle concentration),at which adsorption amount attained nearly constant values. Isotherms showed a Langmuir-type in a lower concentration range,and then adsorption amount increased with an increase in concentration.The adsorption amounts decreased with increasing number of ethylene oxides,n, attached to nonylphenol.These results suggest that in a lower concentration range molecules of NPE arrange themselves on the clay surface in such a way that the hydrophilic constituents,ethylene oxides,are parrallel to the surface,while in a higher concentration range aggregates of two or three dimentional micelles are formed on the surface by the hydrophobic interaction.The adsorption behavior of NPE on soil clay was similer to that on clay minerals.On the other hand,adsorption isotherms on humic soil obeyed the Freundrich equation at concentration lower than CMC.This experiment is continued to clarify the adsorption properties of nonionic surfactants on humic substances.