Assessing phytotoxicity of microplastics on aquatic plants using fluorescent microplastics

Although studies on microplastics are increasing every year, still very little is known about their toxicity. Especially for plant species, even studies of uptake of microplastics are only few, not to mention phytotoxicity of microplastics. Therefore, we conducted a pilot study on the phytotoxicity of 1-mu m-sized fluorescent microplastics (FMPs) on the free-floating aquatic plants Spirodela polyrhiza and Salvinia natans and the emergent aquatic plant Phragmites australis using 0.1% and 0.01% FMP treatment. Furthermore, uptake of FMPs by plants was verified by detecting fluorescence of FMPs by laser. A free-floating aquatic plant S. polyrhiza and emergent aquatic plant P. australis showed significantly decreased harvested biomass after 3 weeks indicating phytotoxicity of FMPs, but S. natans did not show any differences of harvested biomass or chlorophyll contents among treatments. Detection of fluorescence from plant leaves provided evidence of active FMPs uptake by plants. The emission spectra of plant leaves in 0.1% FMP treatment showed similar peaks to those of free fluorescent microplastics, providing a firm evidence of FMPs uptake by plants. This study is one of the pioneering studies to explore fluorescent microplastic uptake and toxicity in aquatic plants and therefore provides a baseline for further studies.

Automated summary

Although knowledge about the toxicity of microplastics is still limited, this study investigates the phytotoxicity of 1-μm-sized fluorescent microplastics on free-floating aquatic plants Spirodela polyrhiza and Salvinia natans, as well as emergent aquatic plant Phragmites australis. The study confirms the uptake of microplastics by plants through detection of fluorescence, and demonstrates the phytotoxicity effect on S. polyrhiza and P. australis but not S. natans. This pioneering study provides a baseline for further research on fluorescent microplastic uptake and toxicity in aquatic plants.