Effects of biodegradable and conventional microplastics on the intestine, intestinal community composition, and metabolic levels in tilapia (Oreochromis mossambicus)

Despite growing interest in conventional microplastics (CMPs) and their toxicological effects on aquatic species, little is known about biodegradable microplastics (BMPs) and their corresponding implications for aquatic life. Here, tilapia (Oreochromis mossambicus) were semi-statically exposed for 14 days to the bio-based plastic polylactic acid (PLA, 100 μg/L, 2.52 ± 0.46 μm) and the petroleum-based plastic polyvinyl chloride (PVC, 100 μg/L, 1.58 ± 0.36 μm). The results showed that ingesting the above two types of microplastics (MPs) led to oxidative stress in the fish gut, and damage to gut tissues and organelles, and PLA resulted in more obvious gut tissue edema than PVC. Furthermore, PLA caused increased levels of gut microbiota dysbiosis and a decrease in the abundance of the genus Cetobacterium, which is linked to vitamin B-12 synthesis, whereas an opposite relationship was observed on PVC. Metabolomic analysis indicated that PVC caused a significant down-regulation of orotic acid, co-metabolite of folic acid with vitamin B-12, while PLA did not affect orotic acid, which may lead to the accumulation of folic acid in fish. The joint analysis found that MPs disturbed gut metabolism homeostasis, implying that abnormal gut microbiota metabolites may be a key mechanism for MPs to induce tissue damage and oxidative stress in the gut. Overall, this study systematically illustrates the differential toxic effects of BMPs and CMPs on tilapia through gut microbiota and metabolite interactions, which will contribute to assessing the risks of BMPs to organismal health.