Effect of cresol isomers on reproduction and gene expression in Daphnia magna

Cresols are frequently detected in freshwater systems due to their wide use as disinfectants. However, there is limited knowledge regarding their adverse long-term toxicity effects on reproduction and gene expression patterns of aquatic species. Therefore, this study aimed to investigate the chronic toxic effects on reproduction and gene expression using D. magna. In addition, the bioconcentration behaviour of cresol isomers was also investigated. Based on the 48 h EC₅₀ value, p-cresol's toxicity unit (TU) (13.77 TU, very toxic) was higher than o-cresol (8.05 TU, toxic) and m-cresol (5.52 TU, toxic). Regarding population-level effects, cresols resulted in a decrease in offspring and a delay in reproduction. However, cresols did not significantly affect daphnia's body weight throughout the course of the exposure period of 21 day, while third brood neonates' average body length (m-cresol and p-cresol) was significantly affected in sub-lethal concentrations. In addition, the gene transcription did not vary significantly across treatments. For bioconcentration exposure experiments, D. magna quickly eliminated all cresols from their body, suggesting that cresol isomers are unlikely to bioaccumulate in aquatic species.