LAUSR

Simple Summary This study looked at the effects of exposure to small plastic particles (polyethylene microplastics) and a flame retardant (tetrabromobisphenol A) on the freshwater shrimp Palaemonetes argentinus. We used biomarkers such as enzymes and thyroid hormones to assess the sublethal effects after 96 h of exposure. Results showed that the mixture of microplastics and TBBPA at environmentally realistic concentrations led to a decrease in enzyme activities and an increase in T4 hormone levels. These findings suggest that microplastics and plastic additives together could disrupt physiological processes in freshwater crustaceans and ultimately affect upper levels of the food chain. Abstract The biochemical effects of sublethal exposure to polyethylene microplastics (PEM) of 40–48 µm particle size and the flame retardant tetrabromobisphenol A (TBBPA), a plastic additive, on the freshwater shrimp Palaemonetes argentinus were assessed. Here, we postulate that the use of enzyme and thyroid hormones as biomarkers contributes to the knowledge of the effects of microplastics and plastic additives on freshwater crustaceans. To address this, we evaluated the activities of acetylcholinesterase (AChE), glutathione S-transferase (GST), and carboxilesterase (CbE, using 1-naphthyl acetate (NA) as substrate) and levels of the thyroid hormones thyroxine (T4) and triiodothyronine (T3) after shrimp were exposed (for 96 h) to these xenobiotics at environmentally realistic concentrations. The results showed that the mixture of both xenobiotics led to a decrease in AChE and GST activities and increased T4 levels. We suggest that physiological processes could be compromised in freshwater organisms when exposed to microplastics and TBBPA together, and this could ultimately affect upper levels of the food web.