A 90-day soil-plant experiment has demonstrated that carbon nanomaterials can prime alfalfa rhizospheres to accelerate the biodegradation of polyethylene (PE), according to research published on 23 September 2026 in Environmental Science and Ecotechnology. The study, conducted by researchers at University College London (UCL), Department of Civil, Environmental and Geomatic Engineering, compared multi-walled carbon nanotubes (MWCNTs) and graphene oxide (GO) at different doses and two soil depths, tracking plastic mass loss, surface chemistry, mechanical strength, plant growth, and microbial communities. The findings offer a proof-of-concept strategy for tackling recalcitrant plastic waste in contaminated soils while reducing PE phytotoxicity.
Polyethylene accounts for about 60% of global plastic waste and persists in soils due to its chemical inertness. Conventional remediation methods, such as incineration and landfilling, are energy-intensive and can create secondary pollution. Plant-based approaches are low-cost and ecologically compatible, but quantitative PE degradation remains slow: wheat-soil systems lost only 2.8% over 100 days, and soybean rhizospheres degraded about 8% of poly(butylene adipate-co-terephthalate) (PBAT) microplastics over 70 days. Carbon nanomaterials (NMs) can accelerate pollutant breakdown in simplified laboratory systems, yet their performance in complex soil-plant systems, over time, and across soil depths has been poorly understood. The new study addresses this gap.
In unamended planted controls, PE loss remained low: 0.6% at the surface and 1.2% at the bottom after 90 days. Without plants, PE plus NMs showed no detectable degradation, underscoring the essential role of alfalfa. MWCNTs produced the strongest surface effect, reaching 12.1% loss at 200 mg kg-1 after 90 days and 9.1% by day 30, while bottom-layer loss plateaued near 6%. GO was weaker overall but most effective at 150 mg kg-1, reaching 7.0% at the surface and 5.8% in the bottom layer by 90 days. Mechanical testing showed pristine PE at 782.8 ± 0.3 MPa; planted treatments reduced modulus to 23.2 MPa at the bottom and 19.6 MPa at the surface, with MWCNTs causing the greatest loss. Fourier-transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) indicated surface oxidation, with an O 1s/C 1s ratio of 0.49 in surface films from the plant–MWCNT treatment versus 0.17 for pristine PE.
Microbial analysis revealed that MWCNTs enriched early degraders such as Pseudolabrys and Oleiharenicola and predicted Kyoto Encyclopedia of Genes and Genomes (KEGG) ortholog K00799, whereas GO sustained Rhodanobacter and Gemmatimonas and K02003. PE alone reduced germination potential by 32–35% and germination rate by 16–18%; NMs alleviated this phytotoxicity. The authors said the key advance was separating rapid surface chemistry from slower root-driven processes. They said MWCNTs appeared to act almost like an early catalyst at the surface, while GO supported a more sustained microbial response deeper in the soil. They also emphasized that the plant was essential: without alfalfa, no measurable PE degradation occurred even with nanomaterials.
The findings point to two possible applications. MWCNTs may suit short-term, intensive cleanup of surface-contaminated hotspots, where rapid oxidation and mass loss are priorities. GO may be better explored for longer, deeper soil restoration in synergy with plant roots, especially at optimized doses. However, the study also found lower insect-trap counts in most nanomaterial treatments, signaling possible non-target effects. Dose optimization, worker-safety controls, cost reductions, and life-cycle assessment are needed before field use. Commercial PE films also contain additives such as carbon black, whose interactions with nanomaterials and degradation intermediates require further study. Together, these findings highlight the need to balance degradation efficiency with ecological safety. The research was published with DOI 10.1016/j.ese.2026.100772.
