Effect of nonionic and anionic surfactant on ecotoxicity and micellization behaviors of dodecyl trimethyl ammonium bromide (DTAB)

Mixtures of surfactants are extensively present in industrial applications for better performance and lower cost. The toxicity of cationic dodecyl trimethyl ammonium bromide (DTAB) against Photobacterium phosphoreum was investigated in the presence of other common surfactants, such as nonionic fatty alcohol-polyoxyethlene ether (AEO), and anionic sodium dodecyl benzene sulfonate (SDBS) as well as sodium dodecyl sulfate (SDS). The mechanism of the combined toxicity was explored based on the micellization behaviors and the characteristics of mixed micelles in surfactant systems. The toxicity of cationic DTAB was significantly higher than that of anionic SDBS, SDS and nonionic AEO, and was not affected by the combination with AEO or SDBS. However, the toxicity of the DTAB/SDS mixture was remarkably lower than that of DTAB alone. Scanning electron microscopy (SEM) images verified that the mixing of DTAB and SDS indeed hindered their action against the bacteria. The micellization behavior of binary mixtures showed an antagonistic effect in DTAB/AEO and DTAB/SDBS systems, but a synergistic effect in DTAB/SDS systems. Thus, the synergism facilitated the formation of mixed micelles and greatly reduced the toxicity of DTAB/SDS mixtures. Furthermore, the formation of mixed micelles in DTAB/SDS systems not only decreased the electrostatic effect of DTAB with the bacteria but also inhibited the interaction of surfactant molecules with bioactive protein, resulting in the lowest toxicity of DTAB/SDS mixtures with mass ratios of 2:3 and 1:4. These results can provide a reference for the development of highly efficient and environmentally friendly composite surfactants.