Optical parameters extraction of soil and its microplastics contamination using terahertz spectroscopy

The primary focus of this study investigates the potential of continuous-wave terahertz frequency-domain spectroscopy(CW-THz-FDS) as a rapid, non-destructive technique for detecting microplastic contamination in soil. Focusing on low-density polyethylene (LDPE) as a model microplastic, we prepared soil mixtures with varying LDPE concentrations (1 %,5 %,10 %,15 % by weight). We used a THz-FDS system operating between 0.1 and 0.7 THz to analyze the optical properties (transmission coefficient, attenuation and refractive index) of these mixtures and LDPE samples separately. Notably both soil and LDPE particles were of micrometer scale. Our results revealed distinct, concentration-dependent variations in these properties. The refractive index for the higher concentration (15 %) ranged from 2.2 to 2.3, while the attenuation coefficient varies between 10 and 14 cm^-1. Crucially, we identified polylactic acid [PLA] as a suitable sample holder material due to its high transmission in the THz range. Consequently, this study suggests that terahertz spectroscopy can be a promising technique for detecting microplastic contamination in soil, offering a non-destructive and sensitive method for environmental monitoring.