Exploring the combined toxic effects of tri-n-butyl phosphate and polystyrene micro/nano-plastics on Daphnia magna under environmentally relevant concentrations.

As emerging pollutants prevalent in environments and biota, tri-n-butyl phosphate (TnBP) and microplastics (MPs) are harmful to aquatic organisms. Nevertheless, the combined toxicity of TnBP and MPs to aquatic organisms at environmental concentrations is still unknown. In this study, the co-toxic effects of both TnBP and micro/nano-polystyrene (MNPS) in Daphnia magna (D. magna) at environmental relevant concentrations were investigated for the first time. The results suggested that after 21 days of exposure to TnBP (1 μg/L) and MNPS (1 mg/L) alone or in combination, the expression of genes associated with growth and reproduction significantly decreased compared to the control group (p < 0.05), suggesting that MNPS and TnBP exerted growth and reproductive toxicity to D. magna. Moreover, the co-exposure group had lower gene expression levels compared to the single exposure group, implying that combined exposure could exacerbate toxicity impacts on D. magna's development and reproduction. The activities of enzymes related to oxidative stress and MDA levels in co-exposed group were higher than those in TnBP group, indicating that the MNPS enhanced TnBP-induced oxidative damage to D. magna. In addition, NPS might have caused greater oxidative stress and damage to D. magna than MPS, as higher enzyme activities and MDA levels were observed in the NPS groups. This study provided important information for a comprehensive understanding of the combined aquatic toxicity of MNPS and TnBP at environmental concentrations.