Park_2026_Comp.Biochem.Physiol.C.Toxicol.Pharmacol__110594

Liquid crystal monomers (LCMs) are emerging contaminants in aquatic environments, but their compound-specific toxicity and sublethal effects in aquatic invertebrates remain insufficiently understood. In this study, we investigated and compared the toxic effects of three representative LCMs, EDPrB, tFPO-CF2-dF3B (tFPO), and BDPrB, using the freshwater water flea Daphnia magna. A 48-h acute toxicity test showed LC50 values of 55.9, 587.0, and 576.8 microg/L for EDPrB, tFPO, and BDPrB, respectively, indicating compound-dependent differences in acute toxicity. Based on these results, sublethal concentrations corresponding to 1/20 and 1/10 of each LC(50) were selected to evaluate chronic and molecular deleterious endpoints. During a 28-day exposure, reproduction was markedly reduced in the B60 group, while the time to first brood was delayed in the EDPrB- and BDPrB-exposed groups. To evaluate oxidative stress-related responses, intracellular reactive oxygen species (ROS) levels, superoxide dismutase (SOD) and catalase (CAT) activities, and the expression of antioxidant-related genes were measured. EDPrB and BDPrB exposure increased several oxidative stress-responses, particularly in the B30 and B60 groups. Behavioral analysis showed that T60 exposure altered swimming distance and was accompanied by alterations in acetylcholinesterase (AChE) activity and AChE gene expression. In addition, P-glycoprotein (P-gp) and Multidrug resistance protein (MRP) activities were assessed to examine potential changes in multixenobiotic resistance (MXR)-mediated detoxification capacity following LCM exposure. Overall, these findings suggest that representative LCMs can affect reproduction, oxidative stress-related responses, behavior, and MXR-related deteoxification capacity in D. magna. This study provides integrated toxicity information for LCMs in a freshwater invertebrate model and supports the need for further ecological risk assessment of LCM contamination in aquatic environment.