Detection and analysis of soil contaminants by terahertz time-domain spectroscopy

In this work, the optical properties of several inorganic contaminants and organic pollutants in soil were characterized by using terahertz time-domain spectroscopy, such as heavy metals and microplastics. The main purpose of the present investigation is to provide a new technical approach for assessing the degree of soil pollutions and remediation. Terahertz wave is a kind of non-ionizing radiation with unique features located between microwave and infrared band. It has been widely utilized in many fields, such as the identification of heavy metals in organic pollutants heptachlor, DDT and inorganic pollutants in environmental science. Terahertz spectrum of soil samples subjected to different drying time was measured at first to explore the duration of moisture effects elimination. Based on the processing and analysis of the time-domain signal, the spectral absorption of wide band pulsed terahertz wave can be modulated by soil, hexavalent chromium and microplastics. The positive experimental results show that the absorption coefficient and refractive index of various samples corresponding to different types and proportion blends. Meanwhile, different samples have various absorption peaks in the terahertz region, which can be used to distinguish different contaminants. At the same time, the content of hexavalent chromium and the number of microplastics in the soil can be judged according to the degree of absorption. The experimental verification confirms that terahertz spectroscopy is a feasible, effective and promising method for the detection of soil pollutants with broad application prospects.