Risks of microplastics on germination and growth of pepper (Capsicum annuum L.) depending on the type, concentration, and particle size

Microplastics (MPs) accumulation is a growing concern and poses potential risks to cultivated vegetables. An accurate assessment of the risks associated with microplastics on seedling germination and growth is essential, particularly considering factors such as concentration, species, and particle size. Therefore, a cultivation experiment was conducted to investigate the risks of MPs on pepper with varying concentrations and particle sizes of polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET). Our results indicated that germination of pepper seeds was inhibited in most cases, with the inhibition ranging from 6.28 % to 15.99 %. The addition of PP and PET-MPs resulted in a significant reduction in root weight and length in pepper seedlings. Generally, the growth of pepper seedlings was more significantly affected by PET than by PE or PP. Furthermore, MPs induced oxidative stress in peppers, which varied with particle sizes. The effects of small-size (25 μm) treatments were ranked as PET > PP > PE, and the average values of the integrated biomarker response index (IBRv2) were 4.02, 3.67, and 3.66, respectively. In contrast, the IBRv2 values for the large-size (300 μm) treatments were ranked as PE > PP > PET, with average IBRv2 values of 7.68, 7.36, and 6.86, respectively. This suggests that an increase in particle size of MPs enhances oxidative stress. These findings allowed a more comprehensive assessment of the mechanisms of phytotoxicity of MPs to pepper plants. • PE, PP and PET-MPs had inhibitory effects on pepper seed germination and seedling growth. • MPs affected pepper antioxidant enzyme activity and organic matter content. • Increased particle size of MPs enhances oxidative stress.