Combined Effects Of Microplastics And Cadmium On Oxidative Stress, Dna Damage, And Embryonic Development In Zebrafish (Danio Rerio)

Abstract

Mixed pollution in the aquatic environment is a major challenge, in which microplastics (MPs) and heavy metals like cadmium (Cd) are pollutants of significant concern. This study aimed to assess the toxic impacts of co-exposure to polystyrene microplastics (PS-MPs) and Cd on zebrafish (Danio rerio) embryos and larvae. Zebrafish embryos from 2 hours post-fertilization (hpf) were exposed to the following treatments: control, PS-MPs (100 µg/L), Cd (10 µg/L), and a combination of PS-MPs + Cd until 120 hpf. The results showed that, compared to the single-exposure groups, the co-exposure group exhibited the most severe synergistic effects: the lowest survival and hatching rates (68.9% and 45.2%, respectively), the highest malformation rate (particularly spinal curvature) at 43%, an increased heart rate (185 bpm), and a decreased body length (2.98 mm). The cause was identified as PS-MPs acting as vectors, significantly enhancing the bioaccumulation of Cd in the larvae (1.49 times higher). The toxicity mechanism involved a strong induction of oxidative stress, demonstrated by the highest levels of ROS and MDA, along with the superior upregulation of defense genes (SOD1, SOD2, CAT, MT2). Concurrently, DNA damage and apoptosis were strongly activated, with a marked increase in GADD45G expression and a severe imbalance towards pro-apoptosis (the Bax/Bcl-2 ratio increased 28.33-fold). These molecular damages led to clear histopathological alterations in the intestine. In conclusion, PS-MPs significantly exacerbated Cd toxicity by enhancing its bioaccumulation, leading to synergistic oxidative stress, cellular damage, and developmental disruptions in zebrafish. This study highlights the necessity of considering the risks from pollutant mixtures in environmental assessments.