Evaluating the Environmental Persistence of Liquid Crystal Monomers Indoors and Outdoors

Liquid crystal monomers (LCMs) exemplify a group of chemicals prevalent in indoor environments. However, current frameworks for assessing the environmental persistence of chemicals predominantly focus on outdoor environments, often overlooking indoor environments. Here, we model and compare the persistence of LCMs across indoor and outdoor multimedia environments. Our findings reveal that, when assessed in an outdoor context, <10% of the investigated LCMs exhibit overall persistence comparable to those of persistent organic pollutants regulated by the Stockholm Convention, and one-third to two-thirds of the investigated LCMs meet the Stockholm Convention's medium-specific half-life thresholds for persistence. However, we found a notable disparity between indoor and outdoor persistence: Approximately 90% of the investigated LCMs demonstrate substantially prolonged persistence indoors, 10 times longer on average, and up to ∼150 times longer in some cases, compared to outdoors. This long indoor persistence is mainly attributed to the low volatility of LCMs and their high affinity for indoor surface compartments. Our work highlights the indoor environment's role as both a continuous source of human exposure to LCMs and a potential reservoir for long-term regional contamination. Therefore, a tailored, fit-for-purpose assessment of "indoor persistence", focusing on chemicals predominantly found in indoor environments, carries profound implications for both human and ecological health.