Atmospheric Fate and Risk Investigation of Typical Liquid Crystal Monomers

Liquid crystal monomers (LCMs), widely used in liquid crystal displays, have been recognized as a class of potential emerging pollutants in the environment. However, their atmospheric fate and toxicity involved in the atmospheric transformation have been rarely investigated. Herein, we employed quantum chemical calculation and computational toxicology to systematically investigate the •OH-initiated oxidation kinetics and mechanism of three LCMs (4-cyanophenyl 4-ethylbenzoate (CEB), 4-cyano-3-fluorophenyl 4-ethylbenzoate (CEB-F), and 4-cyano-3,5-difluorophenyl 4-ethylbenzoate (CEB-2F)) in the atmosphere, and the toxicity of CEB-2F (as an example) during transformation. The calculated gaseous rate constants and half-lives for CEB, CEB-F, and CEB-2F at 298 K were in the range of (0.9–1.4) × 10–12 cm3 molecule–1 s–1 and 5.7–8.9 days, respectively, suggesting that these LCMs had atmospheric persistence and long-range transport potential. The transformation products (TPs) of CEB-2F were found to be similar to those experimentally determined in •OH oxidation of particulate LCMs. Furthermore, some TPs were predicted to exhibit enhanced toxicity compared with the parent LCM, indicating that much attention should be also paid to their risks besides the original LCMs. These results would be helpful for the LCM regulation and provide guidance on their development and safe application.