The Invisible Plastic Beneath Our Feet: Scientists Unearth Soil’s Nanoplastics — and Reveal How Much Slips Through the Net
Soil may be one of the planet’s great hidden reservoirs of plastic pollution, and its most elusive contaminants — nanoplastics, fragments smaller than a thousandth of a millimetre — have remained almost entirely beyond the reach of analytical science. Now a team led by Hannah Forsyth and Moritz Bigalke of the Technical University of Darmstadt, working with colleagues at ETH Zurich, the Polytechnic of Turin, and Ulsan National Institute of Science and Technology in South Korea, has accomplished what no group had managed before: it systematically optimised, step by step, a method for extracting nanoplastics from soil while keeping the particles intact, and measured exactly how many are lost along the way. The study, published in the open-access journal Microplastics and Nanoplastics and conducted under the European Union’s Horizon 2020 MINAGRIS project on micro- and nanoplastics in agricultural soils, offers both a sobering reality check and a genuine breakthrough — the first recovery-tested, particle-preserving protocol for soil nanoplastics, and remarkably pure samples of these particles freed from a soil matrix.
The urgency behind this work stems from what is already known about these particles. Nanoplastics — generally defined as plastic particles below 1000 nanometres — are generated ceaselessly as ever-larger amounts of plastic debris fragment in the environment, and because particle numbers rise steeply as size falls, their abundance in soil may well exceed that of microplastics in the 1-to-5000-micrometre range. Their minute dimensions make them far more available for uptake by living organisms, including into individual cells, and their colloidal behaviour governs how they travel through soil and water. Laboratory studies have linked nanoplastic exposure to molecular toxicity in soil nematodes, transcriptomic disruption in soybean, and intestinal disruption in earthworms, while wheat seedling roots have been shown to accumulate them. Yet despite these warnings, scientists know remarkably little about how many nanoplastics soils actually contain, which polymers they are made of, or what shapes they take — because detecting them in a matrix as complex as soil is extraordinarily difficult.
Every existing analytical tool falls short somewhere. Micro-Fourier-transform infrared spectroscopy, a workhorse of microplastic research, cannot reliably detect particles below roughly 10 micrometres, and micro-Raman spectroscopy bottoms out near 300 nanometres — leaving the smallest, most biologically relevant particles invisible to routine screening. Pyrolysis gas chromatography–mass spectrometry, or Py-GC-MS, can identify polymer chemistry and quantify mass, and it has already detected nanoplastics in soil, water, plants, and animal tissues, but it incinerates the sample, sacrificing all information about particle size and shape, and it demands large starting volumes because nanoplastic mass concentrations are expected to be vanishingly low. Advanced imaging techniques such as scanning electron microscopy, atomic force microscopy–infrared spectroscopy, and scanning transmission X-ray microscopy can resolve individual nanoparticles, but they cannot reliably distinguish plastic from mineral grains or organic debris unless the sample is exceptionally pure. The German-led team set out to build a single extraction workflow that preserved particle integrity, stayed compatible with both microscopy and mass-based analysis, and came with honest, quantified recovery data — something no previous soil method had offered.
The key to measuring losses that would normally go undetected was a clever piece of chemical engineering. Instead of relying on ordinary plastic particles, the researchers used palladium-doped nanoplastics: spheres with a polyacrylonitrile core loaded with palladium and wrapped in a polystyrene shell, synthesised using a method co-developed by study co-author Denise Mitrano of ETH Zurich. Because the embedded metal can be quantified with exquisite sensitivity by inductively coupled plasma mass spectrometry, the palladium serves as a faithful proxy for the plastic itself. The team spiked 50-gram samples of an agricultural soil from Wageningen in the Netherlands with roughly 150-nanometre doped particles at a concentration of 188 milligrams per kilogram of soil, then tested each stage of the purification chain in isolation before chaining the steps together. For the imaging experiments, they used fluorescent polystyrene spheres of 100 and 250 nanometres, whose smooth, uniform shape makes them easy to spot and measure under an electron microscope.
The first hurdle — simply liberating particles from soil aggregates — proved to be the deepest. The soil was mixed with a litre of 2.5 millimolar tetrasodium pyrophosphate, a dispersing agent, shaken for 30 minutes, ultrasonicated for two minutes at 35 kilohertz, and left undisturbed for 18 hours so that large mineral grains would sink. The top centimetre of the suspension was then collected on the assumption that nanoplastics behave like colloids and remain evenly distributed in the liquid. Recovery was just 38 percent, with a standard deviation of 7 percent, making this initial extraction the single largest bottleneck of the entire protocol. The approach was adapted from a method that had recovered 84 percent of silver nanoparticles from soil, but nanoplastics differ from metallic nanoparticles in surface charge, density, hydrophobicity, and chemical reactivity, and they likely bind to different soil components with different strengths. The authors note that more powerful ultrasonic probes and denser soil-to-liquid ratios could push this number higher in future iterations.
Purification began with density separation, deliberately adapted for accessibility: instead of an ultracentrifuge, the team layered samples over a sucrose cushion of 1.22 grams per cubic centimetre and spun them in an ordinary benchtop centrifuge at 4696 times gravity for eight hours. This step recovered 74 percent of the particles, with a standard deviation of 18 percent that reflects how sensitive the procedure is to collecting the supernatant just five millimetres into the sucrose layer. Only 7 percent of particles landed in the pellet and a negligible 0.1 percent clung to the pipette; the rest stuck to the tube walls or stayed behind in the sucrose. Electron microscopy confirmed the spinning did not clump particles together. The sucrose approach involves a trade-off: its density accommodates common polymers such as polyethylene, polypropylene, polystyrene, polyamide, and polycarbonate, but excludes denser PVC and PET. Filtration proved equally revealing — conventional PTFE membrane filters clogged and trapped sub-micron particles, recovering only 25 percent, whereas single-layer stainless steel mesh filters with evenly spaced one-micrometre pores reached 92 percent recovery when rinsed with ethanol afterwards.
Not every inherited step survived scrutiny. The protocol previously included oxidising organic matter with 5 percent hydrogen peroxide; the team tested a stronger 15 percent concentration and found it stripped neither the sucrose nor the dissolved organic carbon from the samples — non-purgeable organic carbon levels barely budged over three hours, and the solution’s temperature stayed flat, signalling no vigorous reaction. Notably, the peroxide did not damage the plastic particles themselves, with 100-nanometre polystyrene spheres unchanged in size even after two hours in 20 percent peroxide, but because the oxidation accomplished so little, it was dropped from the final workflow entirely. That made the last step, ultrafiltration through 10-kilodalton polyethersulfone membranes, doubly important for washing and concentrating the sample. Here the team discovered a subtle trap: stirring the device created a vortex that drove particles into the membrane, depressing recovery. Two gentle washes without stirring cut dissolved organic carbon from 136 milligrams per litre to 12 while retaining 74 percent of the particles.
Then came the moment of truth. When the optimised steps were chained end to end, the recovery predicted from the individual stages was about 19 percent. What the researchers actually measured was 1.4 percent, with a standard deviation of 0.4 percent. The gap points to losses that only emerge in a full soil-to-sample workflow: transfers through pipettes and intermediate vessels, membrane fouling by the real soil matrix, and the adsorption or agglomeration of particles onto residual soil surfaces. The team also cautions that its tests used freshly spiked, well-defined spheres, whereas nanoplastics that have weathered in the environment for years may carry eco-coronas of natural organic matter, sorb pollutants, and attach more stubbornly to soil — characteristics that could make them even harder to extract. This honest accounting, uncomfortable as the number is, is precisely what the researchers argue the field has been missing: without recovery data, no nanoplastic measurement from soil can be trusted or systematically improved.
The downstream feasibility tests produced a split verdict. For mass-based analysis, the team adapted a solvent-transfer protocol in which dried samples were dissolved at 150 degrees Celsius in a one-to-one mixture of 1,2,4-trichlorobenzene and p-xylene containing the antioxidant butylated hydroxytoluene — solvents chosen because they dissolve polyethylene, polypropylene, and polystyrene, the most common soil plastics. Aliquots dried in pyrolysis cups recovered 87 percent of the polymer, though with a wide standard deviation of 41 percent. The instrumental detection limits were competitive with the state of the art, but the method-scale arithmetic failed: because only 24 millilitres of the original one-litre extract can be processed, and the high-boiling solvent caps the injectable volume at 30 microlitres, the method’s detection limit sits near 3 micrograms of polymer per gram of soil even assuming perfect recovery — while measured polystyrene nanoplastic concentrations in real soils have been reported as low as 0.16 to 0.73 micrograms per gram. Quantitative Py-GC-MS of soil nanoplastics through this route is therefore not yet within reach.
Where mass quantification faltered, imaging triumphed. When soil spiked with the fluorescent polystyrene spheres was pushed through the full workflow, the extracted particles were deposited on silicon wafers, coated with a five-nanometre platinum-palladium film, and imaged by scanning electron microscopy. The 100- and 250-nanometre spheres appeared well separated, intact, and virtually free of contamination — the only interferences being thin, elongated organic filaments and a faint carbon- and oxygen-rich residue, likely sucrose, both easily distinguished from the smooth spherical targets. Blank samples showed negligible cross-contamination. The result establishes the protocol as the first recovery-tested, particle-preserving extraction method for soil nanoplastics that yields samples clean enough for advanced microscopy, opening the door to techniques such as STXM-NEXAFS and AFM-IR that can deliver size, shape, and polymer identity for individual particles. The team’s roadmap for improvement — more aggressive ultrasonic extraction, larger processed volumes, and validation across different soil types — now gives the field a quantified baseline. For the first time, scientists know not only where soil’s invisible plastic fraction is hiding, but exactly how much slips through the net each time anyone tries to catch it.
Subject of Research: Optimisation and recovery testing of a particle-preserving extraction and purification method for nanoplastics in soil, with evaluation for scanning electron microscopy and Py-GC-MS analysis.
Subject of Research: Technology and Engineering
Article Title: Unearthing nanoplastics in soil: optimising extraction and purification while preserving particle integrity
Article References: Forsyth, H., Gnoffo, C., Oh, S., Sakaguchi-Söder, K., Mitrano, D. M., Frache, A., & Bigalke, M. (2026). Unearthing nanoplastics in soil: optimising extraction and purification while preserving particle integrity. Microplastics and Nanoplastics, 6(1), Article 7. https://doi.org/10.1186/s43591-026-00172-x
Image Credits: AI Generated
DOI: 10.1186/s43591-026-00172-x
Keywords: nanoplastics, soil pollution, extraction methods, density separation, ultrafiltration, Py-GC-MS, scanning electron microscopy, microplastics, particle recovery, environmental pollution
Cite Scienmag News
APA
MLA
Chicago
Gideon R. (August 29, 2026). Optimized method extracts soil nanoplastics while preserving particle integrity. Scienmag. https://scienmag.com/optimized-method-extracts-soil-nanoplastics-while-preserving-particle-integrity/
Gideon R. “Optimized method extracts soil nanoplastics while preserving particle integrity.” Scienmag, 29 August 2026, https://scienmag.com/optimized-method-extracts-soil-nanoplastics-while-preserving-particle-integrity/. Accessed 29 August 2026.
Gideon R. “Optimized method extracts soil nanoplastics while preserving particle integrity.” Scienmag. August 29, 2026. https://scienmag.com/optimized-method-extracts-soil-nanoplastics-while-preserving-particle-integrity/
Copy citation
Download RIS
Tags: advancements in plastic pollution scienceanalytical science of nanoplasticsenvironmental impact of soil nanoplasticsEuropean Union Horizon 2020 environmental researchEuropean Union Horizon 2020 researchimpact of nanoplastics on soil healthmicroplastics and nanoplastics in agriculturenanoplastics detection methodsnanoplastics particle preservationnanoplastics recovery protocolparticle integrity preservationsoil contamination analysissoil nanoplastics extractionSoil nanoplastics extraction methodsoil nanoplastics measurementsoil nanoplastics measurement challengessoil particle integrity in nanoplastics extractionsoil plastic debris recoverysoil plastic pollutionsoil plastic pollution detectionsoil pollution analytical techniquessoil pollution remediation techniques
