Liquid crystal monomers in human milk from China: Occurrence, spatial distribution, and health risk assessment for breastfeeding infants.

Liquid crystal monomers (LCMs) are essential components of liquid crystal displays (LCDs) and may possess potential risks of persistence, bioaccumulation, and toxicity. However, evidence on LCM exposure and health risks in the maternal-infant population remains limited. In this study, 38 LCMs were measured in pooled human milk samples collected from 24 provinces across China. Fifteen of the 38 LCMs showed relatively high detection frequencies of higher than 10%, and the median concentration of ∑15LCMs was 2490 pg/mL (range: 129-2.34 × 10⁴ pg/mL). 1-methoxy-4-(4-propylcyclohexyl)cyclohexane (MOPB), a commonly used bicyclohexyl-based LCM, showed the highest median concentration (1150 pg/mL) and accounted for 86% of the total LCMs. The concentration and distribution pattern of LCMs in human milk varied across provinces. However, significantly higher levels of LCMs were observed in samples from Southern China compared to those from northern regions. Integrating dietary LCM intake among the Chinese adults from the Sixth China Total Diet Study, significant positive correlations were observed between dietary intake of certain LCMs from foods and their occurrence in breast milk, suggesting that diet may be an important exposure pathway for lactating women. At a national level, the mean and median estimated daily intakes (EDIs) of LCMs via breastfeeding for infants were 488 and 311 ng/kg bw/day, respectively. The hazard quotient (HQ) calculation indicated that the intake of LCMs via breastfeeding is unlikely to pose a significant health risk to infants. This is the first comprehensive assessment of maternal-infant exposure to LCMs based on human milk measurement in China.