Studies on the Fate of Nonionic Surfactant in the Soil Environment

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We have studied on the fate of nonionic surfactants such as alkyl ethoxylates(alkylpoly(oxyethylene)ethers : AE)in the soil environment. Since it was already clarified that the fate of surfactants was caused by the adsorption on soil and biodegradation, adsorptivities of AE(C_<12>POE_n ; n=5, C_<12>E_5, n=8, C_<12>E_8)on such clay minerals as kaolin, cericite, and biodegradabilites of AE were examined in this study.Adsorption isotherms of C_<12>E_5 and C_<12>E_8on clay minerals could be divided into two stages or more below cmc (critical micelle concentration), at which adsorption amount attained nearly constant values. isotherms showed a Langmuir-type in a lower concentration range, and saturated adosorption amounts on both clays, kaolin and cericite, were the same values for C_<12>E_5, C_<12>E_8, respectively.The second stage of the isotherms started at a near concentration to saturated adsorption in the first stage, in the case where clay minerals came to contact with the initial solutions of, -AE at cmc. In the second stage of isotherms the saturated adsorption amount was twice as much as in the first stage. These results suggest that the adsorption of AE is probably the formation of a monomolecular layer over the clay surface below cmc, but is the formation of multimolecular layer in the case where the clay come to contact with a higher conceutration above cmc.Adsorption behaviors of nonionic surfactant and/or anionic surfactant onto clays in anionic-nonionic surfactant solutions were examined. Adsorption of anionic surfactant in mixed system was much higher than that in alone system. Biodegradation behaviors of AE in alone and AE-anionic surfactant solutions were tested by river die-away test. AE was easier decomposed to the extent of ultimate biodegradation than LAS (anionic surfactant). Biodegradability of AE was showing a tendency to decrease with increasing the number of EO-unit.