Effect of different chitosan molecular weights on microplastic excretion

Introduction Microplastic (MP) ingestion poses a considerable health risk to organisms, including humans, and the environment. The previously established average molecular weight of chitosan that promotes MP excretion is approximately 800,000; however, the effects of chitosan with different molecular weights on MP excretion and the intestinal environment remain unclear. This study aimed to clarify the effects of different chitosan molecular weights on MP excretion and gut microbiota. Methods Sprague–Dawley rats were fed a diet containing MPs with an average particle size of 50 μm. Results Compared with the control group, fecal weight increased in all chitosan groups across different molecular weights (low: 83,000; medium: 673,000; high: 1,877,000). Furthermore, the medium and high molecular weight chitosan groups exhibited a significantly higher MP excretion rate and lower MP retention rate in the gastrointestinal tract. The 16S rRNA metagenomic analysis revealed a decrease in Firmicutes and an increase in Bacteroidota and Proteobacteria abundance in the high-molecular-weight chitosan group. Additionally, the abundance of beneficial bacterial genera, such as Akkermansia and Bacteroides , increased. These findings confirm that chitosan with ≥673,000 molecular weight promotes MP excretion. Additionally, chitosan intake may help protect the intestinal environment by improving gut microbiota.