Physicochemical Descriptors for Developmentof Aquatic Toxicity QSARs for Surfactants

摘要

The development of quantitative structure-activity relationships (QSARs) for theaquatic toxicity of surfactants is limited by the use of chemical descriptors based solely on hy-drophobicity. The premise of this investigation is that surfactant toxicity is best predicted fromparameters that describe the surface-active nature of the class rather than by conventional par-titioning. The application of literature values for surface activity parameters is not appropriatein this case. Surfactant behavior is highly dependent on water composition, and publishedphysical chemical values are typically measured in systems that differ significantly from eithernatural or laboratory waters used in toxicity testing. To rectify this, a consistent dataset has beengenerated where both the physicochemical and biological measurements are obtained undersimilar conditions using well-characterized and purified surfactant homologues. Critical micelleconcentration (CMC), pC20, and surface excess concentration parameters, derived from concen-tration dependent air/water surface tension data, are evaluated for their ability to predict theaquatic toxicity of nonionic and anionic surfactants. The aqueous phase molar surfactant con-centration required to lower surface tension 20 mN/m (pC20) reflects the relative tendency ofthe surfactants to adsorb at the nonpolar, uncharged air/water interface. Consequently, thesedata provide a reasonable estimate of surfactant hydrophobicity but cannot be used to predictspecific interactions with biological interfaces. Incorporation of additional terms, such as thecross-sectional area of the surfactant at the interface (Amin), increases the degree of correlationbetween the physical and biological datasets.