Ultrafast Picosecond Laser Spectroscopy and ICP-OES Assisted Calibration-free of Toxic Metal Concentrations in Contaminated Agricultural Soils

Abstract Excess fertilizer and chemical use have contaminated soil with harmful heavy metals near the Abu-Zaabal facility in Egypt. This study pioneers an approach using picosecond laser-induced plasma spectroscopy (Ps-LIPS) and inductively coupled plasma optical emission spectrometry (ICP-OES) to quantify toxic metal levels without calibration constraints. A 100 mJ Nd: YAG laser with 170 picosecond pulses has been employed for the Ps-LIPS. Systematic soil sampling at six sites near the facility enabled Ps-LIPS to formulate unrestricted calibration-free curves for lead, cadmium, cobalt, zinc, iron, and nickel. Applying the Boltzmann distribution and plot methods anchored to calcium spectral lines determined plasma electron density and temperature under local thermodynamic equilibrium. Models were validated against ICP-OES, affirming Ps-LIPS with under 8% average relative error. Results revealed notable concentration variations contingent on the metal, sampling site, and orientation to the facility. This pioneering Ps-LIPS study demonstrates precise quantification of toxic metals in soils without prior calibration. It provides a pragmatic tool for contamination assessment, representing a seminal advance in environmental analytical methodology.