Researchers have developed a new method to measure the amount of microplastic pollution in soil

Affected by human activities, nano - and micron microplastics (N/MP) pollution widely exists in soil, ocean, air and even human body, and its harm is becoming more and more serious. Researchers in Japan have recently developed a new method that uses spectroscopy to measure N/MP content in different soil types at two wavelengths.

A large proportion of nano - and micron scale microplastics (N/MP) in the environment are found in soil, and understanding the distribution and migration of N/MP in soil is crucial to tackling its threat, Xinhua reported. At present, to measure the content of N/MP in soil, it is necessary to separate the N/MP in soil and organic matter, and then detect it by Raman spectroscopy and other methods. However, the existing methods have high technical requirements and limited resolution, in addition, part of N/MP is often lost in the process of soil separation, resulting in inaccurate measurement.

Researchers at Waseda University and other institutions in Japan have developed a new spectral method that can measure the N/MP content in soil without separating organic matter from the soil. The principle is to pass a specific wavelength of light through the sample, using N/MP and soil particle absorption spectrum differences to quantify N/MP. Therefore, finding the right wavelength to distinguish between N/MP and soil particles is critical.

In January, a new study published in the Proceedings of the National Academy of Sciences reported that each liter of bottled water contains between 110,000 and 370,000 particles, of which 90 percent are nanoplastics and the rest are microplastics. Residents pour water into a rubbish-strewn street in the town of Atcube in Abidjan, West Africa. (AFP)

The researchers made suspensions of six dry soil samples with different characteristics in terms of particle size distribution and organic matter content, and mixed them with polystyrene (a common microplastic component) nanoparticles to form six different soil suspensions that simulated N/ MP-containing pollutants. N/MP levels were maintained at five milligrams per litre. A spectrophotometer was then used to measure the absorption spectra of these soil suspensions in the wavelength range of 200 nm to 500 nm, and the N/MP content in the dry soil was determined accordingly. Then find the best combination of the two wavelengths for measuring N/MP.

The study showed that the six samples had the lowest error when using a combination of 220 nm to 260 nm and 280 nm to 340 nm wavelengths, making them suitable for measuring N/MP content in different soil types. The researchers also created a calibration curve between the N/MP content in the soil suspension and the N/MP content added to the dry soil sample, allowing accurate estimates of the N/MP content in the dry soil.

The results were recently published in the journal Ecotoxicology and Environmental Security. The researchers show that the method can be used as a preliminary assessment tool for N/MP content in soil to help people further understand the distribution and migration of N/MP in soil.

Nano-plastics have certain toxicity, which can cause reproductive abnormalities and stomach diseases. A study by a research team at Waseda University in Japan last September found that in addition to plastic pollutants in the ocean, microplastics are also present in clouds, and they may affect the climate in ways that humans do not fully understand. (AFP)