Combined effect of diazepam and polystyrene microplastics on the social behavior of medaka (Oryzias latipes)
Description
[Abstract] The combined effect of microplastics and pharmaceuticals on aquatic organisms is an issue of concern. In this laboratory study, we evaluated the combined effect of polystyrene microplastics (2-µm diameter) and diazepam on the social behavior of medaka (Oryzias latipes) by using the shoaling behavior test. Five treatment group was set for the experiment: solvent control, polystyrene microplastics exposure group (0.04 mg/L), low concentration diazepam exposure group (0.03 mg/L), high concentration diazepam exposure group (0.3 mg/L), and co-exposure group of polystyrene microplastics and low concentration diazepam. After 7 days of exposure to polystyrene microplastics and/or diazepam, the shoal-leaving behavior of the high concentration diazepam exposure group (8.9 ± 8.3 counts/medaka) and the co-exposure group (6.8 ± 6.7 counts/medaka) was significantly greater than that in the solvent control group (1.8 ± 2.6 counts/medaka). Even after a 5-day recovery period, medaka in the co-exposure group left the shoal more often (7.3 ± 5.0 counts/medaka) than the solvent control group did (2.6 ± 2.6 counts/medaka), while shoaling behavior of medaka in other exposure groups except for high concentration diazepam exposure group were restored. In the co-exposure group, polystyrene microplastics accumulated and remained in the medaka gastrointestinal tract (22.9 ± 1.8 particles/mg body weight) even after the 5-day recovery period. Thus, the desorption of diazepam from microplastics remaining in the gastrointestinal tract may have affected medaka social behavior. Our findings clearly showed that the combined effects of diazepam and polystyrene microplastics suppressed medaka social behavior, suggesting that the presence of microplastics can enhance the adverse effects of pollutants on the social behavior of aquatic organisms. [Data description] Medaka exposed to diazepam and/or PS-MP were used in the shoaling behavior test (Maierdiyali et al., 2020), which was slightly modified for medaka. Twelve medaka (6 males and 6 females) in each treatment group were used. Two glass tanks (19 cm × 19 cm × 19 cm) each containing 1 L of dechlorinated water were placed in contact next to each other. One glass tank contained 4 healthy medaka (not exposed to diazepam or PS-MP, maintained in the same tank as the test medaka until just before the beginning of the exposure test), and 1 test medaka was introduced into the other tank. The swimming behavior of the test medaka was recorded with a camera (C615, Logitech, Lausanne, Switzerland) for 10 min (30 frames/s). The coordinates of swimming medaka (csv file) were obtained in UMATracker software (release 14, Yamanaka and Takeuchi, 2018). SolCon: solvent control group, PSMP: PS-MP exposure group, LowDZP: low concentration diazepam exposure group, HighDZP: high concentration diazepam exposure group, CoExp: co-exposure group, exp: exposure period, rec: recovery period, 01-06: male medaka, 07-12: fenale medaka.