Novel method for measuring nano/microplastic concentrations in soil


Current techniques for measuring nano/microplastic (N/MP) concentrations in soil require the soil organic matter content to be separated and have limited resolution for analysing N/MPs sized less than one micrometer (µm).

Researchers have developed a simple method to measure nano/microplastic concentration in different soil types using spectroscopy at two wavelengths. This method does not require the soil to be separated to detect the N/MPs and can accurately quantify N/MPs regardless of their size.

Nano and microplastics are a well-known menace, found practically everywhere in nature, including soil, oceans, drinking water, air, and even the human body. Studies show that soils in particular hold a significant portion of N/MPs. The problem with these N/MPs is their microscopic size, which allows them to easily migrate through soil into the ground or freshwater bodies due to rainwater leaching. From there, they enter the human body. Hence, it is imperative to understand the distribution and movement of the soil’s N/MPs to gauge their threat and mitigate it.

Current techniques for measuring N/MP concentrations in soil require separating the soil organic matter content through chemical and physical processes. Subsequently, the isolated N/MPs are analyised using a microscope, Fourier-transform infrared spectroscopy, Pyrolysis–gas chromatography/mass spectrometry, or Raman spectrometry.

However, these techniques require advanced skills and have limited resolution for analyzing N/MPs smaller than one micrometer. Often some of the N/MPs in the soil are lost during the separation process, leading to inaccurate measurements.

A team of researchers, led by Kyouhei Tsuchida from Waseda University and National Institute of Advanced Industrial Science and Technology, along with Dr Yukari Imoto, Dr Takeshi Saito, and Dr Junko Hara from the National Institute of Advanced Industrial Science and Technology and Dr Yoshishige Kawabe, also from Waseda University, devised a simple method to measure N/MP concentrations in soil using spectroscopy without separating the soil organic matter.

Spectroscopy can determine the concentration of N/MPs in soils based on how much light of a particular wavelength passes through the sample and how much gets absorbed. In this way, spectroscopy can potentially detect N/MPs regardless of size, provided the correct wavelengths are used to distinguish between the N/MPs and soil.

Accordingly, the researchers developed a method to use the difference between the absorbance spectra of N/MPs and soil particles to quantify the N/MPs.

Their findings were published in Ecotoxicology and Environmental Safety journal on 28 May 2024.

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