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Nowadays, heavy metals pollution is becoming a serious problem in agriculture. This paper reports a
preliminary work on a feasibility study of applying terahertz (THz) technology for heavy metal ions
detection in soil. This study was first conducted at Oklahoma State University, and then carried out at
China Agricultural University and Capital Normal University. Pure soil was collected in an
experimental field, which contains nearly no heavy metal ions from standard detection; in the
experiment, heavy metal ions were mainly Pb2+, Cr3+, Zn2+ and Cu2+ from chemical compounds. Based
on the National Standard for Heavy Metals Pollution, a set of soil samples with different polluted levels
were prepared in the lab. The metal ions concentration levels were selected as 50ppm, 300ppm and
700ppm. Each soil sample was pre-processed by collecting, weighing, mixing, drying, grinding and
labeling before measurements. The thickness of soil samples was selected as 1.5mm and 3mm. The
absorption spectra for the soil samples with different heavy metal ions were collected using THz
time-domain spectroscopy (THz-TDS) equipments separately at Oklahoma State University and
Capital Normal University. The test results showed that soil samples with Pb2+, Cr3+, Zn2+ and Cu2+ had
different absorption characteristics within the bandwidth of 0.1-1.1THz. A narrow bandwidth only up
to 1.1THz was got because the soil particles showed much absorption and scattering properties to the
THz spectroscopy. Different soil samples with different concentration of heavy metal ions also showed
much difference and it could be used to predict the heavy metal concentration in the future. The results
from the preliminary study show a potential of THz technology applied for heavy metal ions detection
in agricultural fields environment. However, since the high scattering features of samples and high cost
of equipments, the measurement methods and practical issues needs to be further investigated and
improved to make the THz technology a feasible tool for soil heavy metal ions detection.
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