Understanding the contribution of plastic additive in microplastic toxicity from consumer products using fathead minnow (Pimephales promelas).

Microplastics are ubiquitous in the environment. Once in the environment, these particles are ingested by organisms. The ingestion of microplastics can lead to various adverse effects. Still, what is driving the toxicity of microplastics is not well understood. Microplastics are a diverse suite of contaminants composed of several shapes, polymers, and chemical additives. The chemical additives in plastics are not always considered in toxicity studies despite their widespread presence in plastic products. We exposed fathead minnows (Pimephales promelas) for 60 days to four treatments: polyethylene microplastics with chemical additives, polyethylene microplastics without chemical additives, chemical additive leachates, and a control (no plastic, no additives). The main objective of this experiment was to understand what is driving the toxicity: the plastic itself (particles), the chemical additives, or both. We took samples at 12, 30, and 60 days to measure the accumulation of plastic and their additives, as well as to look for adverse effects via gene expression and measurements of weight, length, and condition index. Fish exposed to plastic with or without additives had plastic in their gastro-intestinal tract. We did not observe accumulation of Bismuth, a pigment we targeted chemically in the polyethylene. We observed no significant differences in weight, length, or condition between treatments at 12, 30, and 60 days. We also observed no differences in survival. We observed a significant difference in the expression of the following genes among treatments: sod1, sod2, gstp1, and esr2b. Significant differences were generally due to a lower relative expression in fish exposed to the plastics with additives and the chemical additives alone. In conclusion, we observed effects at the molecular level that appeared to be driven by plastic additives. Future studies should continue to try to understand the effects of plastics driven by additives and consider them in risk assessment frameworks.