Identification and detection of label-free polystyrene microplastics in maize seedlings by Raman spectroscopy

Microplastics are a new type of pollutants that have attracted attention recently. However, there is limited research on the uptake of environmental microplastics by plants. In this study, scanning electron microscopy (SEM), micro-Raman spectroscopy, and Raman mapping were employed to identify and detect label-free micron-sized polystyrene (PS) microplastics accumulated in the roots and stems of maize (Zea mays L.) seedlings. The results demonstrated that the Raman spectra of PS microplastics were predominantly concentrated in the xylem and ducts of seedlings, confirming the transfer behavior of microplastics in the plants. The Raman spectra of PS microplastics in seedlings exhibited distinctive peaks at 621, 1002, 1030, and 1604 cm^-1, and the matching scores of these spectra with the standard PS Raman spectrum ranged from 40.61 % to 86.93 %. Additionally, the Raman mapping facilitated the precise identification and visualization of microplastics within the roots and stems of seedlings. The smallest size of the detected PS microplastics was ∼2 μm. This study provides new insights into the use of Raman spectroscopy for the detection of microplastics in plants.