Calibration-free picosecond LIPS for quantifying heavy metals in soils near Egyptian industrial sites

Excessive fertilizer and chemical usage have led to soil contamination by toxic heavy metals near the Abu-Zaabal industrial complex in Egypt. We introduce a groundbreaking calibration-free methodology using ultrafast Picosecond Laser-Induced Plasma Spectroscopy (CF-Ps-LIPS) for quantifying contaminant elements (Cd, Zn, Fe, Ni) in soils near Egypt's Abu-Zaabal industrial complex. This study pioneers applying 170 ps laser pulses (Nd: YAG, 1064 nm) to achieve calibration-free analysis, eliminating matrix-matched standards and offering ± 1% agreement with ICP-OES. By integrating plasma diagnostics (electron density N_e = 1.2-1.5 × 10¹⁷ cm^{- 3} and temperature T_e = 8508-10,275 K), we establish CF-Ps-LIPS as a rapid, minimally invasive tool for on-site environmental monitoring, validated through spatial contamination gradients linked to wind patterns. Concentrations of Cd (25.1-136.5 mg/kg), Zn (19.8-146.9 mg/kg), Fe (59.7-62 mg/kg), and Ni (119.4-157.8 mg/kg) were analyzed across seven sampling sites. The seventh site was used as a test sample of unknown concentration to validate CF-Ps-LIPS. Utilizing the Boltzmann distribution with plotting techniques enables precise plasma electron density and temperature determination under local thermodynamic equilibrium (LTE) conditions. The CF-Ps-LIPS study revealed significant concentration variations dependent on trace metal type, sampling location, and facility orientation. The CF-Ps-LIPS method provides calibration-free, rapid, and accurate detection of metal contaminants in Egyptian soils for the first time. This methodology significantly advances environmental monitoring and soil contamination analysis, allowing on-site assessments with higher efficiency and reliability.