Environmental behavior, toxic potencies, and risks of liquid crystal monomers: A critical review

Liquid crystal monomers (LCMs), prized for their unique optical properties, are ubiquitous in a range of electronic products. However, their growing use and disposal have led to a continuous influx of LCMs into the environment as contaminants. This review synthesizes information on the sources, environmental distribution, migration, transformation, toxicity, and risks associated with LCMs. It also introduces predictions of adverse outcomes related to protein binding potential, grounded in the Adverse Outcome Pathway framework. It was pointed out for the first time that the fundamental causes of LCM contamination were informal recycling and dismantling patterns, coupled with obsolete liquid crystal processing technologies. The significant variability among different types of LCMs in distribution patterns, environmental persistence, bioaccumulation, mobility, and toxicity were emphasized. Notably, fluorinated LCMs, especially fluorobiphenyls, which posed the greatest comprehensive risk, were prone to accumulate in atmospheric dust. Our molecular docking results showed that monomers containing cyano groups, which had greater direct toxicity, carcinogenic, and mutagenic risk, also exhibited strong binding affinity, underscoring the need for priority control strategies. Additionally, this review delved into LCM exposure pathways and the heightened toxicity during degradation and metabolism. It emphasizes the importance of risk assessments for LCMs and identifies key scientific questions that require further investigation. The insights provided a scientific foundation for preventing environmental risks and promoting green chemical alternatives related to LCMs.