Laser-induced breakdown spectroscopy for imaging and distribution analysis of heavy metal elements in soil

The accumulation of heavy metals (HMs) in soil due to industrial activities and sewage irrigation poses serious environmental and health risks. In this study, soil samples contaminated with copper (Cu), chromium (Cr), and lead (Pb) were selected for investigation. An experimental system based on laser-induced breakdown spectroscopy (LIBS) was developed to perform the elemental analysis and mapping of the contaminated soils. Based on the spectral line intensity, a 21 mm × 20.7 mm area was scanned via LIBS mapping with a resolution of 300 μm, enabling visualization of the spatial distribution of HM elements. The intensities of the selected emission lines were then converted into red, green, and blue (RGB) color channels to generate a composite image that visually highlights the HM-contaminated regions. To further classify contamination levels, the K-means clustering algorithm was applied to the spectral data, segmenting the soil surface into areas of severe, moderate, and slight contamination. Furthermore, principal component analysis (PCA) was employed for dimensionality reduction of the LIBS data, which facilitated the characterization of soil heterogeneity. Finally, the elemental mapping on the surface of the deep soil was carried out to investigate the distribution and migration characteristics of HM elements in three-dimensional space. The results demonstrate the feasibility of using LIBS technology for imaging and distribution analysis of HM elements in soils, offering valuable insights for environmental monitoring and soil remediation efforts.