Pyrolysis-GC-MS analysis of ingested polystyrene microsphere content in individual Daphnia magna
Risa Nakano1, Rıdvan Kaan Gürses2, Yuji Tanaka2
1Department of Life Science and Applied Chemistry, Graduate School of Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan.
Abstract:
Microplastic (MP) pollution in the aquatic environment is a cause for increasing concern. However, analyzing MPs ingested by small organisms, such as zooplankton, is difficult because of the low content and small size of the ingested MPs. We attempted to determine the content of ingested MPs in individual zooplankton using pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). To establish zooplankton model of MP ingestion, individual Daphnia magna were cultivated separately in microplate cells with polystyrene (PS) microspheres (10 μm in diameter, 245,000 particles, 135 μg) under different conditions. To prepare calibration curves for determining ingested PS content, approximately 100-150 μg of commercially available Daphnia-based powdered fish food, roughly corresponding to the weight of a single D. magna organism, was mixed with PS microspheres (0.005-26 μg) and analyzed using Py-GC-MS at 600 °C. In the resulting pyrograms, peaks of the styrene monomer and trimer from PS were detected, and linear relationships were obtained between the relative peak area and the amount of added PS. Finally, the cultivated zooplankton were individually subjected to Py-GC-MS analysis, and the ingested PS content in each zooplankton was successfully determined. Individual zooplankton cultured with PS in the absence of food ingested 2.3-7.9 μg of PS particles, whereas that in the presence of food (Chlorella vulgaris) ingested only 0.1-0.2 μg of PS particles. This result suggests that zooplankton might preferentially ingest ordinary food when both food and MPs are present, although further systematic studies are necessary to validate this observation.
Insights
Researchers developed a method to measure microplastics (MPs) in individual zooplankton. Zooplankton ingested fewer MPs when food was available, suggesting selective feeding behaviors in aquatic environments.
Area of Science:
- Environmental Science
- Analytical Chemistry
- Ecotoxicology
Background:
- Microplastic (MP) pollution is a growing global concern, particularly in aquatic ecosystems.
- Quantifying MP ingestion by small aquatic organisms like zooplankton is challenging due to low MP quantities and small organism size.
Purpose of the Study:
- To develop and validate a method for determining the microplastic content in individual zooplankton using pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS).
- To investigate the effect of food availability on microplastic ingestion by Daphnia magna.
Main Methods:
- Individual Daphnia magna were exposed to polystyrene (PS) microspheres under varying conditions (with/without food).
- Calibration curves were established by analyzing mixtures of zooplankton food and known amounts of PS microspheres using Py-GC-MS at 600°C.
- Ingested PS content in individual zooplankton was quantified by analyzing their pyrograms for styrene monomer and trimer peaks.
Main Results:
- Py-GC-MS successfully detected PS markers (styrene monomer and trimer) and established linear calibration curves.
- Individual zooplankton without food ingested significantly more PS (2.3-7.9 μg) compared to those with food (0.1-0.2 μg).
Conclusions:
- The developed Py-GC-MS method enables accurate quantification of ingested microplastics in individual zooplankton.
- Zooplankton exhibit selective feeding, preferring natural food sources over microplastics when both are available, which has implications for understanding MP transfer in aquatic food webs.
