Rapid characterization of heavy metals in single microplastics by laser induced breakdown spectroscopy

Microplastics (MPs) in aquatic environment usually carry hazardous matters, including toxic heavy metals. Quantification of heavy metals in MPs is crucial for the comprehensive understanding of their ecotoxicology in field environment. However, conventional methods for heavy metal determination either are applicable only to bulk/collective samples or require strict operation environment. Here we demonstrated that laser induced breakdown spectroscopy (LIBS) is a robust tool for the characterization of heavy metals in single MPs. Single-particle LIBS selects individual MPs with specific sizes (down to tens of microns), shapes, and morphologies and analyzes simultaneously multiple elements in milliseconds without sample pretreatment. In addition to the elaborate optical design, we also used stretched thin polyethylene film as a substrate, which significantly suppress the matrix interference to the particles' spectra. The single particle LIBS was demonstrated to be a quantitative analytical method, and was applied to heavy metal analysis of the MPs collected in the seawaters of the Beibu Gulf of China. Positive correlation between the spectral intensities and the local marine pollutions as well as significant heterogeneity in the elemental compositions were observed. The results demonstrate that single-particle LIBS is a promising method for MPs characterization and is suitable for studying pollutant transportation by using MPs as vectors.