Microplastics and plastic additives as contaminants of emerging concern: A multi-biomarker approach using Rhinella arenarum tadpoles

Abstract

Polyethylene microplastics (PE-MPs), a whitish thermoplastic polymer with numerous applications, is one of the materials most widely used in the industrial sector, whereas tetrabromobisphenol A (TBBPA) is a brominated flame retardant. The aim of this study was to analyze the effects of PE-MPs and TBBPA on Rhinella arenarum tadpoles at the laboratory scale. Tadpoles were chronically exposed (30 days) to four treatments: PE-MPs (60 mg L−1), TBBPA (10 µg L−1), their mixture (PE-MPs + TBBPA), and dechlorinated water as negative control (CO). Biomarkers of enzymatic activity (acetylcholinesterase, AChE; carboxylesterase, CbE; glutathione reductase, GR; and glutathione-S-transferase, GST), hepatic physiological alteration (alkaline phosphatase; ALP activity, and cholesterol; CHOL level), and endocrine disruption through thyroid hormone (T4) levels were assessed. In addition, intestine and liver were histomorphologically evaluated. AChE activity in tadpoles was significantly inhibited after exposure to PE-MPs and TBBPA with respect to CO. In addition, CbE, GR, and ALP activities showed higher values in the mixture of PE-MPs+ TBBPA treatment than in CO, whereas CHOL level was higher in TBBPA and PE-MPs+ TBBPA treatments than in CO. GST activity did not show significant differences between treatments and CO. T4 levels increased significantly in all treatments with respect to CO. The intestinal structure of tadpoles exposed to PE-MPs and PE-MPs+ TBBPA showed signs of mechanical damage. The intestinal wall of tadpoles under PE-MPs, TBBPA and PE-MPs+ TBBPA treatments was thicker than that of CO individuals. The analysis of liver histology demonstrated the hepatotoxicity caused by PE-MPs+ TBBPA. This study provides quantitative evidence of the harmful effects of PE-MPs, TBBPA and their mixture on enzymatic and hormonal activities, and histological evidence of intestinal wall hypertrophy and liver damage of R. arenarum tadpoles.