Cold plasma can shred microplastics, but may create new risks

Microplastics have become one of the most stubborn pollution problems of our time, turning up everywhere from wastewater effluents to deep-sea sediments and even remote mountain lakes. Their tiny size, enormous surface area, and tendency to soak up other pollutants like pharmaceuticals and persistent organic chemicals make them notoriously hard to remove from water and soil. Now, a team of Portuguese researchers argues that one of the most hyped technologies for destroying these particles may be a double-edged sword. In a perspective article published in Frontiers in Ocean Sustainability, Joana Antunes, José Gonçalves, and João Pequeno of NOVA University of Lisbon contend that cold plasma, often celebrated as a futuristic cleanup tool, can transform microplastic-associated risk in ways that current research has barely begun to measure.

Cold plasma is often described as the fourth state of matter, a partially ionized gas containing free electrons, ions, reactive neutral species, and photons. Unlike the thermal plasmas used in arc welding, where electrons and heavier particles reach equilibrium at thousands of kelvin, cold or non-thermal plasma operates far from equilibrium. Energetic electrons with effective temperatures of several electron-volts drive ionization and dissociation reactions, while the heavier ions and gas molecules stay near ambient temperature. This non-equilibrium is precisely what allows cold plasma to generate a highly reactive chemical environment without substantially heating the treated medium. The resulting reactive oxygen and nitrogen species, including hydroxyl radicals, ozone, hydrogen peroxide, atomic oxygen, and reactive nitrogen oxides, together with ultraviolet photons, ions, and electrons, interact with polymer surfaces to drive oxidation, chain scission, surface functionalization, and, under sufficiently intensive treatment, mineralization of the carbon backbone to carbon dioxide and other carbon oxides.

Yet the emerging literature reveals that cold plasma interacts with microplastics in multiple, sometimes opposing ways. Some studies demonstrate partial degradation or high mass loss in soil or catalytic systems, others show mainly surface oxidation and agglomeration in water, and still others use cold plasma as an accelerated aging tool to probe degradation products and toxicity rather than as a remediation technology. The authors argue that plasma-induced transformation can either reduce or redistribute environmental risk depending on the balance between polymer abatement, by-product formation, mobility, and toxicity. Remediation, they insist, should not be used as a synonym for any detectable change in polymer properties. It is essential to distinguish between physical removal or separation, such as aggregation or flotation-enhanced capture; partial degradation, including surface oxidation, chain scission, and mass loss; fragmentation, which may reduce particle size without reducing particle number or risk; and mineralization, where polymer carbon is converted primarily to carbon dioxide or carbon oxides.

The evidence base remains fragmented across water, soil, aging, co-contaminant, and plastic-conversion studies, and reported performance metrics are not directly comparable. In one of the first explicit water-treatment studies, researchers treated polypropylene and low-density polyethylene microplastics suspended in water using atmospheric dielectric barrier discharge. In thirty minutes of treatment, they reported mass losses of 1.4 to 11.3 percent, with polypropylene showing greater weight reduction than polyethylene, and mixtures of oxygen and nitrogen as feed gases outperforming single-gas plasmas. Surface analysis revealed cracks, pits, and a marked increase in the carbonyl index of polypropylene, indicating surface oxidation and hydrolytic degradation pathways. This established atmospheric cold plasma as a proof-of-concept tool for affecting microplastics in aqueous suspension, but also highlighted that under realistic treatment times, degradation was partial and confined largely to the surface.

More recent work has pushed the boundaries further. One study used a custom cold plasma reactor to treat melamine resin microplastics of roughly two micrometers suspended in water, achieving a size reduction to about 119 nanometers and 43 percent mass loss after thirty minutes. Transmission electron microscopy showed smooth microspheres transforming into porous nanofragments between 68 and 119 nanometers, consistent with oxidative chain scission and surface etching by plasma-generated hydroxyl radicals, ozone, and hydrogen peroxide. However, because this process also generated nanometric fragments, it should not be interpreted as remediation solely on the basis of size reduction or mass loss unless residual particle number, nanoplastic formation, and post-treatment toxicity are also assessed. Another study applied atmospheric dielectric barrier discharge directly to polyvinyl chloride, polystyrene, and polypropylene microplastics suspended in water, using real-time carbon dioxide monitoring to quantify mineralization. Using oxygen instead of atmospheric air markedly enhanced degradation, with polyvinyl chloride showing the highest carbon dioxide release and polypropylene the lowest reactivity, while scanning electron microscopy, Fourier-transform infrared spectroscopy, and Raman analyses revealed polymer-specific surface oxidation and backbone damage.

Plasma-activated water has also been explored as an indirect route for microplastic degradation in aquatic systems. A 2026 study on polystyrene microplastics reported roughly 80 percent removal of particle counts within two hours, and mechanistic analysis combining in situ electron paramagnetic resonance, optical emission spectroscopy, and density functional theory identified hydroxyl radical attack at benzylic sites as the dominant initiation step for backbone scission. Supporting total organic carbon, molecular-weight, and gas chromatography-mass spectrometry data showed progressive surface roughening, chain scission, and formation of low-molecular-weight oxidation products. A life-cycle assessment indicated a lower carbon footprint than photocatalysis or activated carbon for comparable treatment, and time-resolved ecotoxicity tests revealed an initial increase in effluent toxicity followed by a decline as treatment proceeded, with some products acting as substrates for microbial growth. That initial toxicity spike is exactly the kind of hidden cost the Portuguese team warns about.

Studies in soil and solid matrices are even scarcer but more dramatic. A 2023 study treating landfill soil containing polyethylene, polypropylene, polystyrene, and polyvinyl chloride microplastics between 50 and 1,500 micrometers with a coaxial dielectric barrier discharge plasma system achieved up to 96.5 percent mass loss in thirty minutes using air, with an energy efficiency of 19.03 milligrams per kilojoule. Focusing on polystyrene microplastics in soil, the same group obtained 98 to 99 percent degradation in sixty minutes, with most carbon converted to carbon oxides, and later showed that adding a Hopcalite stage in a two-step plasma-assisted catalytic system yielded almost complete conversion to carbon dioxide, around 98 to 99 percent, over repeated cycles. These soil and gas-solid configurations indicate that cold plasma can approach total mineralization for certain polymers in highly controlled reactors, but the authors caution that such results should not be extrapolated to dilute aquatic, sedimentary, wastewater, or marine matrices.

Beyond direct degradation, cold plasma has also been explored as a pre-treatment to enhance subsequent biodegradation. One study showed that cold atmospheric plasma pre-treatment increased the surface hydrophilicity, roughness, and microbial colonization of high-density polyethylene and polystyrene samples during fungal incubation, with stronger effects for polyethylene. Plasma has also been used as an accelerated aging tool. Researchers who aged polypropylene and polyethylene terephthalate microplastics with cold plasma found surface yellowing, higher carbonyl index and crystallinity, and complex mixtures of ketones, esters, acids, alcohols, and aromatic hydrocarbons. Others showed that plasma-aged polystyrene and polyvinyl chloride particles became more hydrophilic and more negatively charged, developed additional oxygen- and nitrogen-containing functional groups, and consequently exhibited markedly higher mercury adsorption and even partial reduction of mercury ions. Another team showed that plasma-aged polystyrene, polyvinyl chloride, polypropylene, and polyethylene not only developed cracked, oxidized surfaces but also released 4 to 14 milligrams per liter of humic-like dissolved organic carbon and produced substantial chlorinated disinfection by-products, mainly haloacetic acids up to roughly 1.2 milligrams per liter.

To capture this duality, the authors propose evaluating plasma-microplastic configurations along four intertwined axes. The first is abatement, which should be expressed not only as percentage mass loss or particle count reduction, but also as absolute load removed per unit energy input and reactor footprint. Current works largely report relative reductions without energy-normalized metrics. The second axis is degradation products, spanning gas, liquid, and particle phases, including low-molecular-weight organics, dissolved organic carbon release, disinfection by-product formation, and plastic additives, since polymer identity alone may not capture the full transformation-product profile of real-world microplastics. The third axis is mobility, encompassing how plasma-induced changes in size, surface charge, and aggregation state affect microplastic transport through porous media, sediments, and engineered units. Existing work shows that plasma can both aggregate particles, facilitating separation in engineered systems, and increase their mobility in saturated porous media, and that plasma-aged microplastics can act as enhanced sorbents and vectors for metals such as mercury and cadmium. The fourth axis concerns ecotoxicological effects, which remain poorly characterized. Existing studies mostly stop at physicochemical characterization, product identification, or transport behavior, and do not track acute or chronic biological responses to plasma-treated microplastics across marine organisms, making ecological risk the least resolved dimension of the field.

Seen through this four-axis lens, the current literature is revealing precisely because of what it omits. Most studies score strongly on at most one or two axes, typically abatement and qualitative surface chemistry, while leaving degradation products, mobility, and ecotoxicology either unquantified or inferred from limited proxies. No study currently combines energy-normalized abatement data, multi-phase product characterization, mobility metrics, and biological endpoints in a single experimental design. Very few studies evaluate cold plasma-microplastic interactions in seawater or estuarine matrices, and this gap is consequential. High chloride and bromide concentrations in seawater scavenge hydroxyl radicals and ozone, likely lowering effective oxidant dose and altering abatement kinetics relative to freshwater. The same halides can react with plasma-generated reactive species to form reactive halogen species, raising the possibility of halogenated degradation products beyond those already reported in freshwater systems. Seawater’s high ionic strength is also expected to compress the electrical double layer around suspended particles, promoting aggregation differently than in freshwater and changing how treated microplastics partition between the water column, sediment, and biofilm-coated surfaces. Marine and estuarine organisms experience these transformations under co-occurring salinity stress, so ecotoxicological outcomes cannot be reliably extrapolated from freshwater or soil toxicity data.

The authors conclude that cold plasma could become relevant for targeted microplastic treatment scenarios, particularly as part of engineered treatment trains, but only if future research demonstrates net risk reduction under environmentally and operationally realistic conditions. In practical implementation, cold plasma is more plausible as a polishing or transformation-control step applied to pre-concentrated streams, retained solids, membrane concentrates, or reactor recirculation loops than as a stand-alone treatment for large volumes of dilute environmental water. Any future demonstration of microplastic remediation by cold plasma should report a minimum set of indicators spanning all four axes, and any claim of remediation should be supported by evidence of net risk reduction, not only by evidence of altered polymer morphology or reduced particle counts. Future studies should be designed so that a positive result on one axis cannot mask deterioration on another, for example high particle-count removal accompanied by nanoplastic formation, toxic by-products, or increased transport potential. Until such seawater- and estuary-specific testing is performed, claims of marine microplastic remediation by cold plasma should be considered preliminary, because the technology may alter particle form without ensuring a net reduction in environmental risk.

Subject of Research: The plasma-plastic paradox: breaking down plastics, building up risk?

Article Title: The plasma-plastic paradox: breaking down plastics, building up risk?

Article References: The plasma-plastic paradox: breaking down plastics, building up risk?. (n.d.). https://doi.org/10.3389/focsu.2026.1923882

Image Credits: AI Generated

DOI: 10.3389/focsu.2026.1923882

Keywords: plasma-plastic, paradox, breaking, down, plastics, building, risk, scientific research