Triclosan-loaded aged microplastics exacerbate oxidative stress and neurotoxicity in Xenopus tropicalis tadpoles via increased bioaccumulation.

Microplastics and chlorine-containing triclosan (TCS) are widespread in aquatic environments and may pose health risks to organisms. However, studies on the combined toxicity of aged microplastics and TCS are limited. To investigate the toxic effects and potential mechanisms associated with co-exposure to TCS adsorbed on aged polyethylene microplastics (aPE-MPs) at environmentally relevant concentrations, a 7-day chronic exposure experiment was conducted using Xenopus tropicalis tadpoles. The results showed that the overall particle size of aPE-MPs decreased after 30 days of UV aging, whereas the increase in specific surface area improved the adsorption capacity of aPE-MPs for TCS, resulting in the bioaccumulation of TCS under dual-exposure conditions in the order of aPE-TCS > PE-TCS > TCS. Co-exposure to aPE-MPs and TCS exacerbated oxidative stress and neurotoxicity to a greater extent than a single exposure. Significant upregulation of pro-symptomatic factors (IL-ß and IL-6) and antioxidant enzyme activities (SOD and CAT) indicated that the aPE-TCS combination caused more severe oxidative stress and inflammation. Molecular docking revealed the molecular mechanism of the direct interaction between TCS and SOD, CAT, and AChE proteins, which explains why aPE-MPs promote the bioaccumulation of TCS, causing increased toxicity upon combined exposure. These results emphasize the need to be aware of the combined toxicity caused by the increased ability of aged microplastics to carry contaminants.

Study on toxicity responses and their mechanisms in Xenopus tropicalis long-term exposure to Shigella flexneri and ciprofloxacin.

The abuse and overuse of antibiotics increased not only the exposure of aquatic animals to antibiotics but also the development of resistance in pathogenic bacteria. To investigate the effects and mechanisms of exposure, a long-term experiment lasting 120 days was conducted in which Xenopus tropicalis was exposed to single and combined stress factors of multiresistant pathogenic Shigella flexneri and ciprofloxacin (CIP). The intestinal oxidative stress, immune factors and flora, as well as the brain-gut axis correlation factors of X. tropicalis, were tracked to account for the response of aquatic animals to the exogenous pollutants. SOD activity and MDA content were significantly increased in stressed X. tropicalis (p < 0.001), while the levels of proinflammatory factors (IL-1ß, IFN-γ) were significantly reduced (p < 0.01). The content of intestinal beneficial bacteria decreased and that of harmful bacteria increased in the intestinal flora of the stressed X. tropicalis (p < 0.001). These results suggested that S. flexneri and CIP disturbed the intestinal flora and caused oxidative damage in the host, and the body produced a series of responses, such as oxidative stress responses and regulation of the expression of immune factors, to maintain the balance of antioxidant inflammation. Significant changes in the expression of intestinal neurotransmitters (5-HT, CGRP) and brain peptides (BDNF, NCAM, NPY) (p < 0.05) also indicated that the brain-gut axis interaction was disrupted. In addition, although the coexisting CIP could reduce intestinal toxicity caused by S. flexneri, the amount of intestinal pathogenic bacteria Desulfovibrio increased significantly. Moreover, compared with the single exposure group, SOD activity, CAT activity and MDA content were significantly reduced in the dual exposure group. Therefore, the health risks of multiresistant pathogenic bacteria on the intestinal and brain-gut axis interaction should be given more attention, and the interaction of brain-gut axis is more important when antibiotics coexist.