Combined developmental toxicity and endocrine disruption of diisobutyl phthalate and polyethylene microplastics in Zebrafish

Microplastics (MPs) are ubiquitous contaminants in aquatic ecosystems and frequently co-occur with plasticizers such as phthalate esters (PAEs). While the combined toxicity of pristine MPs and pollutants has been increasingly reported, the role of environmentally relevant aged MPs in modulating co-contaminant toxicity remains critically understudied. Here, zebrafish (Danio rerio) embryos were exposed for 7 days to diisobutyl phthalate (DIBP), pristine polyethylene MPs (PE-MPs; ~0.3 μm), artificially aged PE-MPs (via UV treatment), and their binary mixtures. Results showed that DIBP exposure induced developmental inhibition, oxidative stress, and disruption of thyroid hormone homeostasis, with the severity of these effects generally increasing with concentration over the tested range (1, 10 and 100 µg/L). Both pristine and aged PE-MPs independently triggered oxidative and endocrine disturbances, with aged particles exhibiting greater intrinsic toxicity. Crucially, co-exposure outcomes diverged dramatically based on MP aging status: pristine PE-MPs partially alleviated DIBP toxicity, an effect we infer to be associated with reduced contaminant bioavailability, a process commonly attributed to adsorption by pristine MPs; conversely, aged PE-MPs significantly exacerbated DIBP-induced adverse effects, particularly on thyroid hormones. These findings highlight that microplastics not only act as contaminants in their own right but also serve as dynamic vectors whose capacity to modulate the bioavailability and toxicity of coexisting pollutants is critically shaped by environmental aging. Rather than functioning as passive carriers, aged MPs become active toxicological participants, thereby amplifying the ecological risks of MP-pollutant mixtures in aquatic environments.