Dose- and size-dependent effects of polystyrene microplastic on antioxidant and immune genes of gold fish (Carasius auratus)

Nowadays, plastic pollution is regarded as one of the most threatening environmental pollution. In this regard, microplastics may enter the food web and produce some negative impacts in aquatics. The goal of the present study was to study effects of polystyrene microplastic on antioxidant and immune genes expressions in gold fish (Carasius aurata). For this, polystyrene microplastic was synthetized via suspension and emulsion polymerization method in two sizes of 0/25 and 8 µm. The fish were exposed to the microplastic with sizes of 0.25 and 8 µm and concentrations of 0.05, 0.5 and 5 mg/L during 28 days under 6 treatments. Based on the results, polystyrene microplastic induced gene expression of SOD, CAT and HSP70 that were dependent on the microplastic concentration and size. Smaller size of microplastic showed higher induction effect on the studied genes expressions so that in most cases, the highest level in the same concentrations was observed in the treatments exposed to 0.25 µm microplastic. With increase in microplastic concentration from 0.05 to 5 mg/L, a similar decreasing-increasing trend was observed in the investigated genes expressions but the CAT gene reaction was slightly different. Overall, more studies seem necessary to understand polystyrene microplastic effects on aquatics and its potential mechanisms. With respect to the results from the present study indicating the changes in antioxidant and immune genes expressions under microplastic exposure, establishing some strategies seem to be obligatory to manage the effluents entered to the aquatic ecosystems and prevent more microplastics increase in the environment. Totally, based on the results, it could be said that polystyrene microplastic as a pollutant can induce the antioxidant and immune system of gold fish.