The relationship of the environmental effect of surfactants to their interfacial properties

In an investigation of possible relationships between interfacial propertie s of surfactants and their environmental effect, using several anionic and nonionic surfactants, a linear correlation was found between the parameters , Delta G(ad)(0)/A(min ') and rotifer toxicity. Delta G(ad)(0) is a standar d free energy of adsorption at the air/aqueous solution interface, and A(mi n) is the minimal hydrated cross-sectional area of the surfactant molecule. Both quantities were evaluated from surface tension data. This correlation is much better than attempted correlations of the toxicity with the negati ve logarithm of the critical micelle concentration (-log CMC) or with Delta G(ad)(0) or A(min) alone. The Delta G(ad)(0)/A(min) correlation with rotif er toxicity is also better than the correlation with the analogous paramete r, Delta(s)(1)G(ad)(0)/(1)(s)A(min ') obtained from adsorption isotherms of the surfactants on a solid immobilized membrane simulating a cell membrane . The data support our hypothesis that toxicity is determined both by adsor ption tendency and ease of cell membrane penetration.