Effect of Combined Exposure to Microplastics and Cadmium on Neurobehavior of Juji ( <scp> <i>Gobiocypris rarus</i> </scp> )

Microplastic pollution is pervasive in the aquatic environments. Given their adsorption capacity, the combined toxicity of microplastics and other contaminants is a key concern, but the neurobehavioral effects of microplastics combined with cadmium exposure are rarely reported. In this study, we conducted a 96-h experiment of individual and combined exposure of polystyrene microplastics (MPs, 200 and 1000 μg/L) and cadmium (Cd, 12 mg/L) to Juji (Gobiocypris rarus). After exposure, anxiety-like behaviors were evaluated using a light-dark tank test and an open-field test, and physiological indicators (cortisol, 5-HT, DA, thyroid hormone (TH), 5-HIAA and DOPAC level) were measured. Results showed that MPs and Cd significantly reduced the latency to enter the light area, and increased the number of entries into the light area, time spent in the light area, large movement counts, total movement counts, and the number of crossings of the central area. Combined exposure to MPs and Cd synergistically affected these anxiety-like behavioral indicators and the swimming ability of Juji. Biochemically, the levels of cortisol, 5-HT, and DOPAC increased significantly, while the levels of THs, DA, and 5-HIAA decreased significantly, indicating neuroendocrine disruption. Overall, our findings demonstrate that MPs could enhance the accumulation and toxicity of Cd, and the observed behavioral alterations are closely associated with neurological and hormonal imbalances. This study highlights the potential indirect and cumulative ecological risks of microplastics and combined pollution may pose to aquatic ecosystems, calling for further research into the underlying mechanisms.