Liquid crystal monomers as emerging e-waste contaminants: a source-to-sink framework for multimedia fate, exposure, risk, and sustainable management

Liquid crystal monomers (LCMs) are proprietary mixtures of synthetic organics used in liquid crystal displays (LCDs). Growing evidence indicates that LCMs can behave as persistent, bioaccumulative and toxic (PBT-like) contaminants released across the LCD life cycle (manufacturing, in-use emissions, dismantling/recycling and disposal), yet current knowledge remains fragmented across matrices, study designs and analytical target lists. Here we move beyond a descriptive compilation by proposing a source-to-sink framework that links (i) structural motifs and physicochemical properties (e.g., polarity/halogenation-driven partitioning and persistence) to (ii) dominant release scenarios and (iii) multimedia transport, bioaccumulation, and human exposure. By critically comparing available measurements and workflows, we highlight consistent enrichment of LCMs in particle-associated media (indoor/outdoor dust and airborne particulate matter) and waste-derived sinks (sewage sludge, sediments, and landfill leachate), whereas systematic monitoring in surface water/groundwater and food matrices remains sparse and method-limited. Although current toxicological evidence remains limited, it indicates potential bioaccumulation and organ-specific distribution in biota, with implications for metabolic, endocrine, and developmental disruption. However, variability in QA/QC protocols, reliance on short-term assays, and the absence of standardized reference materials constrain cross-study comparability and hinder the establishment of quantitative risk thresholds. We close with a prioritized research and policy agenda: (1) harmonize targeted and suspect-screening methods and expand authentic/isotope-labeled standards; (2) establish longitudinal monitoring in sentinel matrices and populations (especially e-waste workers, pregnant women, and infants); (3) elucidate transformation products, mixture effects, and toxicokinetics; (4) integrate exposure modeling with probabilistic risk assessment; and (5) translate evidence into extended producer responsibility, safer-by-design material selection and engineered controls during formal recycling and disposal.