Co-Adsorption of Novobiocin and Three Common Surfactants on Polystyrene: Molecular Insights from Experiments and Simulations.

In several environments, including wastewater treatment plants (WWTPs), plastics encounter surface-active molecules such as antibiotics and surfactants, essential components of consumer products, detergents, and drugs. In these conditions, synergistic and antagonistic effects could affect how surfactants and antibiotics compete for access to plastic surfaces. Experimental and computational results are presented here to quantify the adsorption on polystyrene (PS) of the antibiotic Novobiocin (NVB) in combination with adsorption of three surfactants─the anionic docusate sodium salt, AOT; the cationic cetyltrimethylammonium bromide, CTAB; and the nonionic hexaethylene glycol monododecyl ether, C12E6. The experimental results obtained with a quartz crystal microbalance with dissipation monitoring (QCM-D) suggest that, rather than removing NVB, the three surfactants yield an adlayer on the NVB film pre-adsorbed on PS. On the contrary, an aqueous solution of NVB partially removes pre-adsorbed surfactant films, and co-adsorption at the PS surface likely occurs. To rationalize these observations, molecular simulations were conducted at low concentrations of NVB and surfactants, somewhat similar to those found in aquatic environments. The computational results show that the interactions between NVB and PS are stronger than those between surfactants and PS. Combined, the results show that NVB and these surfactants are likely to co-adsorb on the polystyrene surface. Although generalization is premature, the observed synergism might facilitate the environmental dispersion of both antibiotics and microplastics, suggesting that advanced technologies are required to properly handle plastics, microplastics, and antibiotics in WWTPs, towards preventing the spread of antibiotic-resistant microorganisms.