Bioconcentration and Behavioral Interference Effect of Diazepam on Adult Japanese Medaka (Oryzias latipes)

Abstract

As one of the most commonly detected polluting drugs in the environment, diazepam (DZP) has been widely detected in rivers, soil, and organisms. To better understand the bioconcentration of DZP in fish and its impact on fish behaviors, we exposed both female and male medaka to a DZP (120 µg/L) for 7 days, and then transformed them to clean dechlorinated water for 3 days of depuration. Regardless of gender, DZP can rapidly accumulate in the brain and liver tissue and reach a stable phase within 24 hours of exposure. When the fish was transferred to purified water for purification, the concentration of DZP in the tissue was rapidly discharged, decreasing by one order of magnitude within 24 hours. The bioconcentration factors (BCF) of DZP in the brain and liver of males were calculated to be 10.47 and 19.58 L/kg, respectively, and those in females were calculated to be 6.12 and 6.03 L/kg. Compared with females, DZP accumulated more in the tissue of male fish, which exhibited a higher mortality rate during exposure. In addition, DZP can be significantly enriched in the ovaries of females, with a BCF of 10.54 L/kg. Furthermore, DZP exposure could significantly interfere with the interactive behaviors between males and females during the courtship, as indicated by the reduced duration of body contact and increased inter-individual distance. These findings highlight the need to study the transgenerational toxicity of DZP in Japanese medaka to assess its potential risk to fish populations accurately.