A team of researchers has introduced a groundbreaking method using spectroscopy to measure nano/microplastics in soil, eliminating the need for complex separation processes and offering unprecedented accuracy for sizes as small as ≤1 µm.
In a significant breakthrough, researchers from Waseda University and the National Institute of Advanced Industrial Science and Technology (AIST) have developed an innovative method using spectroscopy to measure the concentration of nano and microplastics (N/MPs) in soil. This new technique promises to simplify the detection process, eliminating the need for complex soil separation and offering remarkable accuracy for particles as small as ≤1 µm.
Nano and microplastics have become an omnipresent threat, contaminating soil, oceans, air and even the human body. Soil, in particular, retains a substantial portion of these particles, which can easily migrate into groundwater or freshwater bodies through rainwater leaching. Understanding their distribution and movement is critical to assessing and mitigating their threats.
Currently, techniques to measure N/MP concentrations involve separating soil organic matter through chemical and physical processes, followed by analysis using advanced tools like microscopes or spectrometers. These methods are technically demanding and often result in the loss of some N/MPs during the separation process, leading to inaccurate measurements. This underscores the need for a simpler and more reliable approach.
The research team, led by Kyouhei Tsuchida of Waseda University and AIST, devised a spectroscopy-based method to bypass the soil separation process entirely. Spectroscopy works by determining how much light at specific wavelengths passes through or is absorbed by a sample, allowing for the detection of N/MPs across various sizes.
“We measured the absorbance of these soil suspensions at various wavelengths ranging from 200 to 500 nm using a spectrophotometer and based on this, determined the N/MP concentrations in the soil. Then the best combination of two wavelengths was identified for measuring N/MPs, which helped negate the interference from soil particles and leached components in the suspension,” Tsuchida said in a statement.
The team experimented with six soil suspensions, simulating N/MP contamination using polystyrene nanoparticles. They discovered that using a combination of wavelengths between 220-260 nm and 280-340 nm minimized errors, making the method effective across different soil types.
Furthermore, they established a calibration curve reflecting the relationship between N/MP concentration in the soil suspensions and the added N/MPs in dry soil samples. This linear relationship took into account the adsorption of N/MPs on soil particles, enabling accurate estimation of concentrations.
“Our novel measurement approach can quantify different N/MPs, including polyethylene and polyethylene terephthalate, in a variety of soils and can easily be used as an initial assessment tool. Moreover, it can help further our understanding of the distribution and migration behavior of N/MPs in the geosphere environment,” added Tsuchida.
Published in the journal Ecotoxicology and Environmental Safety, this study marks a significant advancement in environmental science, offering a more accessible and accurate method to monitor a pervasive environmental issue.