The relationship between the interfacial properties of surfactants and their toxicity to aquatic organisms

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 extende d to include the toxicity of the cationic surfactant class (homologues of a lkyl trimethylammonium chloride and alkyl hydroxyethyl dimethylammonium chl oride) to green algae (Selenastrum capricornutum) and the bioconcentration of linear alkylbenzene sulfonate (LAS) isomers and homologues by fish (Pime phales promelas and Ictalurus punctatus). In each case, the interfacial act ivity is expressed by the physicochemical parameter, DeltaG(ad)(0)/A(min), where DeltaG(ad)(0) is the standard free energy of adsorption of the surfac tant at the air/solution interface and A(min) is the minim um cross section al area of the surfactant, or the analogous parameter, Delta (I)(s)G(ad)(0) /(I)(s)A(min), at the solid/liquid interface, where the solid is an immobil ized artificial membrane (IAM) that mimics a biological cell membrane. The general nature of the relationship between interfacial activity of surfacta nts and their biological effects in aquatic systems indicates that sorption to biological membranes is a critical parameter for predicting and underst anding environmental effects. While specific interactions probably occur on ce a surfactant has penetrated a membrane bilayer, nonspecific hydrophobic interactions appear to be driving the sorption process.