Carbon Nanomaterials Boost Alfalfa's Ability to Degrade Plastic

Researchers at University College London (UCL), Department of Civil, Environmental and Geomatic Engineering, have published a 90-day soil-plant study in Environmental Science and Ecotechnology showing that carbon nanomaterials can prime alfalfa rhizospheres to accelerate polyethylene (PE) biodegradation. The team tested multi-walled carbon nanotubes (MWCNTs) and graphene oxide (GO) at different doses and two soil depths, tracking PE mass loss, surface chemistry, mechanical strength, plant growth, and microbial communities. PE accounts for about 60% of global plastic waste and persists due to its chemical inertness; conventional remediation is energy-intensive, and plant-based approaches alone degrade PE very slowly. 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 nanomaterials showed no detectable degradation. 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 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. FT-IR and 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.

The study also identified microbial taxa and predicted metabolic functions linked to enhanced breakdown. MWCNTs enriched early degraders such as Pseudolabrys and Oleiharenicola and predicted 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%; nanomaterials alleviated this phytotoxicity. The authors said the key advance was separating rapid surface chemistry from slower root-driven processes, with MWCNTs acting almost like an early catalyst at the surface and GO supporting a more sustained microbial response deeper in the soil. They stressed that the plant was essential: without alfalfa, no measurable PE degradation occurred even with nanomaterials. The findings suggest a tunable route for nanomaterial-assisted rhizoremediation, with MWCNTs potentially suited for short-term, intensive cleanup of surface hotspots and GO for longer, deeper soil restoration. 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 require further study. The work was supported by Artesc Bioscience and UCL Civil, Environmental and Geomatic Engineering.