Long-Term Exposure to Polystyrene Nanoplastics Impairs the Liver Health of Medaka

Abstract

Highlights: What are the main findings? The hepatotoxic effects of nanoplastics (NPs) are evaluated in medaka fish. What is the implication of the main finding? Digestive, innate immune, and antioxidant enzyme activities are affected by NP exposure. Histopathology confirmed direct liver tissue damage by NP exposure. We conclude that NPs at as low as 10 items/L can be toxic to medaka in long term. Nanoplastic (NP) has become a global environmental concern due to its potentially wide distribution and unknown impacts on organisms. Many laboratory studies have reported the short-term toxicity of NPs but their long-term effects are unclear. Here, the chronic hepatoxic effects of NPs (diameter 100 nm; 0, 10, and 104 items/L) in medaka (Oryzias latipes) were evaluated after three-month exposure by investigating the alterations in enzymatic biomarkers (digestion, oxidative status, and immunity) and histopathology in the liver. The trypsin and chymotrypsin activities of digestive enzymes were induced at a low concentration of NPs (10 items/L) but inhibited at high concentration (104 items/L); only the amylase activity was significantly decreased in all NP-treated medaka. Oxidative stress was also induced by NP exposure, which was indicated by the responsive superoxide dismutase and catalase. Lysozyme was significantly reduced after exposure to a high concentration of NPs, while alkaline phosphatase was significantly induced at a low concentration. Exposure to NPs also caused liver damage (e.g., congestion and dilated sinusoids). Taken together, our findings show that chronic exposure to NPs at low particle concentrations can impair the liver health of medaka by affecting liver enzymatic functions and causing histological damage. This implies potentially long-term threats of NPs to aquatic organisms, which call for more long-term aquatic toxicological studies on various species using low environmental concentrations.