Stimulated Raman Scattering Microscopy Reveals Bioaccumulation of Small Microplastics in Protozoa from Natural Waters

Area of Science:

• Environmental Science
• Microbiology
• Analytical Chemistry

Background:

• Microplastics (MPs) are pervasive global pollutants, with bioaccumulation dictating their ecological impact.
• Microorganisms, vital to ecosystems, have had their MP accumulation unconfirmed in natural environments due to detection tool limitations (>10 μm).

Purpose of the Study:

• To develop and validate a method for detecting and quantifying small microplastics (<10 μm) in microorganisms.
• To investigate the presence and extent of microplastic bioaccumulation in protozoa from various natural water bodies.

Main Methods:

• Utilized stimulated Raman scattering (SRS) microscopy, a label-free technique, for imaging and spectral identification of microplastics.
• Applied SRS microscopy to quantify microplastic accumulation in protozoa, comparing its efficacy to flow cytometry.
• Analyzed water samples from the Yangtze River, Xianlin Wastewater Treatment Plant, Lake Taihu, and the Pearl River Estuary.

Main Results:

• Successfully imaged and quantified small microplastics (<10 μm) of various polymer types (e.g., polyethylene, polystyrene) within protozoa using SRS microscopy.
• Demonstrated SRS microscopy's quantitative capability for cellular microplastic accumulation, comparable to flow cytometry.
• Detected microplastic accumulation (<10 μm) in protozoa from all sampled locations, though MP-containing cells were infrequent (∼2-5%).

Conclusions:

• SRS microscopy provides a novel, effective tool for detecting and quantifying small microplastics in microorganisms.
• The presence of small microplastics in protozoa suggests a potential pathway for entry into aquatic food webs.
• Further research is warranted to assess the environmental and health risks associated with small microplastic transfer through the food chain.