Study on the effect of microplastics on the growth of mung bean seedlings based on FTIR and 2D-COS spectroscopy

Microplastics (MPs) are emerging agroecosystem pollutants, and their effects on crop growth warrant attention. In this paper, we investigated the effects of polystyrene (PS) and polymethyl methacrylate (PMMA) microplastics on mung bean (Vigna radiata) seed germination and early growth under concentration gradients (10–1000 mg/L). The results showed that, for PS, germination rate (GR) showed no significant change at low concentrations but decreased at high concentrations. PS microplastics inhibited the growth of roots and stems of seedlings. PMMA did not exhibit a significant effect on GR and only had a slight effect on early growth. Fourier-transform infrared (FTIR) spectral curve fitting of mung bean seedling tissues in the protein amide I region showed that the proportion of random coils increased, and the effect of PS was more substantial than that of PMMA. Curve fitting of the polysaccharide region in mung bean seedling tissues showed that a high concentration of PS caused an increase in peak area at 1049 cm⁻¹ and a slight decrease in peak area at 1158 cm⁻¹, while PMMA treatment showed similar but weaker changes. Synchronous two-dimensional correlation spectroscopy (2D-COS) of mung bean seedling tissues showed that under high PS, the dominant auto-peak shifted from 890 to 910 cm⁻¹ with increasing germination days, accompanied by more and stronger positive cross-peaks; changes under PMMA were minor. Our results suggest spectroscopic changes consistent with alterations in protein conformation and cell-wall polysaccharide organization under microplastic exposure. This study provides spectroscopic insights into the early structural responses of mung bean seedlings to different microplastic exposures under controlled conditions.