In previous work, the toxicity of several anionic and nonionic surfactants to rotifer (Brachionus calyciflorus) was shown to be highly correlated with interfacial activity. In this study, the relationship between interfacial properties of surfactants and their effects on aquatic organisms is extended to include the toxicity of the cationic surfactant class (homologues of alkyl trimethylammonium chloride and alkyl hydroxyethyl dimethylammonium chloride) to green algae (Selenastrum capricornutum) and the bioconcentration of linear alkylbenzene sulfonate (LAS) isomers and homologues by fish (Pimephales promelas and Ictalurus punctatus). In each case, the interfacial activity is expressed by the physicochemical parameter, delta G0ad/Amin, where delta G0ad is the standard free energy of adsorption of the surfactant at the air/solution interface and Amin is the minimum cross sectional area of the surfactant, or the analogous parameter, delta 1sG0ad/1sAmin, at the solid/liquid interface, where the solid is an immobilized artificial membrane (IAM) that mimics a biological cell membrane. The general nature of the relationship between interfacial activity of surfactants and their biological effects in aquatic systems indicates that sorption to biological membranes is a critical parameter for predicting and understanding environmental effects. While specific interactions probably occur once a surfactant has penetrated a membrane bilayer, nonspecific hydrophobic interactions appear to be driving the sorption process.

The combination of biomarkers examined appears to be a good overall descriptor of the health of the scalp in dandruff, and changes in these biomarkers track with tissue-level events that underlie clinical efficacy in the treatment of dandruff by ZPT shampoo. For the first time, we demonstrate a set of tools that extend beyond flaking scores to provide insight into specific biological changes occurring on the scalp to enable an objective assessment of scalp health.

A new LC/MS method has been developed for the simultaneous measurement, in water and wastewater samples, of all species contained in commercial samples of linear type of alcohol ethoxylate (AE) surfactants including fatty alcohols. The method requires derivatization of the terminal hydroxyl of each surfactant species with 2-fluoro-N-methylpyridinium p-toluenesulfonate, which imparts a permanent cationic charge, allowing all species including the fatty alcohols and those with only one ethoxylate to be effectively detected by electrospray MS. Detection limits of typically <10 ppt for each individual species were attained in treated wastewater, in which total AE concentrations (combination of up to 114 individual species) are not expected to exceed 10 ppb. The method was validated for clean water as well as sewage influent and effluent samples.

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