Abstract: BACKGROUND: Plastic as a durable, inexpensive, easy to manufacture organic synthetic polymer materials are widely used. At the same time, plastic resistance to high temperatures, acid and alkali resistance, corrosion-resistant properties make it difficult to degrade in nature, and ultimately forming a huge number of microplastic pollution threatening human health. 
OBJECTIVE: To investigate the effects of microplastic exposure on growth and development and hepatic lipid metabolism in mice. 
METHODS: Twenty C57BL/6J male mice were adaptively fed for one week, and then randomly divided into normal and microplastic groups (n=10 per group). Mice in the normal group were given a normal diet and water, for 4 weeks. Mice in the microplastic group were given a normal diet and free drinking of microplastic (polystyrene) water with a concentration of 1 000 μg/L, for 4 weeks. At 2 and 4 weeks of drinking, body mass and grip strength, blood lipids and liver and kidney function, ultrasonic morphology and pathological morphology of liver and lipid deposition were detected.
RESULTS AND CONCLUSION: (1) With the extension of time, the body mass of mice in the two groups gradually increased, and the body mass of mice in the microplastic group was greater than that in the normal group after 2, 4 weeks of drinking water (P < 0.05). With the extension of time, the grip strength of mice in the normal group gradually increased, and the grip strength of mice in the microplastic group first decreased and then increased, and the grip strength of mice in the microplastic group was lower than that in the normal group after drinking water for 4 weeks (P < 0.05). (2) Liver ultrasound examination showed that compared with the normal group, the ultrasonic echo signal of the liver in the microplastic group was enhanced after 2 and 4 weeks of drinking water. (3) Hematoxylin-eosin staining showed that the morphology of liver cells in the microplastic group did not change significantly after 2 and 4 weeks of drinking water, but inflammatory cell infiltration could be seen. Oil red O staining showed that obvious lipid deposition was observed in the liver of microplastic group after 2 and 4 weeks of drinking water. (4) Compared with the normal group, the levels of serum high density lipoprotein cholesterol, triacylglycerol, and aspartate aminotransferase in the microplastic group were decreased after 2 weeks of drinking water (P < 0.05), and the serum triacylglycerol concentration was decreased after 4 weeks of drinking water (P < 0.05). (5) These findings confirm that microplastics may cause weight gain, loss of physical strength, and abnormal hepatic lipid metabolism in mice.

Key words: polystyrene, microplastics, growth and development of mice, lipid metabolism, liver and kidney function