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Phytoremediation of polyethylene terephthalate (PET) and polypropylene (PP) microplastics by alfalfa ( Medicago sativa L. )
Summary
Alfalfa — a common forage crop — was tested for its ability to break down PET and polypropylene microplastics in soil over the course of a year. The plants showed measurable ability to reduce the mass and alter the surface structure of both plastic types, with associated changes in root-zone soil chemistry and microbial activity. While phytoremediation of microplastics is still in early stages, plant-based strategies could eventually complement other methods for cleaning up contaminated agricultural soils.
Phytoremediation is a plant-based approach for effective biodegradation of environmental pollutants but its efficacy for MPs mainly remains unknown. In this context, in the present study, the biodegradation of polyethylene terephthalate (PET) and polypropylene (PP) microplastics by alfalfa (Medicago sativa L.) was investigated for one year. Treatment with different types and concentrations of MPs showed no significant effects on alfalfa germination rate and growth. Bacterial communities in the rhizosphere of alfalfa with MPs treatment increased significantly compared to untreated controls. Types of MPs showed no effects on bacterial counts. Dehydrogenase (DHO) enzyme activity in the rhizosphere of plants with MPs treatment was significantly higher than plants without MPs treatment but the concentration and types of MPs showed no significant effects on rhizosphere DHO activity. The mean degradation rate for PET-MPs and PP-MPs was 0.29% and 0.44%, respectively. The increase of MPs concentration in the soil from 2 to 10 g/kg elevated the mean degradation rate from 0.26% to 0.48%. Rhizodegradation of MPs is a consequence of complex interactions between MPs, root exudates and microbial activities in the rhizosphere. Therefore, phytoremediation using alfalfa could be considered as a potential method for in situ removal of MPs from the soil.