Analysis of Toxic Chemical Substances Adsorbed on Microplastics

Importance of the Topic

Microplastics in the environment can adsorb toxic organic pollutants and act as vectors for chemical exposure in aquatic organisms and food chains. Understanding adsorption behavior of polycyclic aromatic hydrocarbons (PAHs) and per- and polyfluoroalkyl substances (PFAS) on microplastics is critical for assessing ecological risks and guiding remediation strategies.

Objectives and Overview of the Study

This study aimed to quantify adsorption of representative PAHs and PFAS on three common microplastic types: polypropylene (PP), polystyrene (PS) and polyethylene (PE). The adsorption tests involved spiking ultrapure water with PAHs or PFAS and evaluating uptake by microplastics using targeted mass spectrometric analysis.

Methodology

The adsorption procedure comprised:

• Preparation of microplastic particles (PP, PS, PE) sized below 5 mm.
• Immersion of microplastics in 300 mL ultrapure water spiked with 100 ng total PAHs or 8 ng total PFAS.
• Gentle stirring for 24 h to facilitate adsorption.
• Recovery and drying of microplastics.
• Pretreatment:
• PAHs—ultrasonic extraction with hexane.
• PFAS—ultrasonic extraction with methanol.
• Quantitative analysis by GC-MS/MS for PAHs and LC-MS/MS for PFAS.

Instrumentation Used

Key analytical instruments and tools:

• GC-MS/MS: Shimadzu GCMS-TQ8040 triple quadrupole mass spectrometer with DB-5ms column.
• LC-MS/MS: Shimadzu LCMS-8060 triple quadrupole mass spectrometer coupled to Nexera X2 chromatograph and Inertsil ODS-SP column.
• Stereoscopic microscope (STZ-171-TP) and digital camera system (Moticam 1080) for particle sizing.

Main Results and Discussion

Quantitative analysis revealed:

• All target PAHs adsorbed on all three plastics, with PP and PE showing higher uptake than PS.
• PFAS adsorption varied significantly by compound; some long-chain PFAS exhibited measurable adsorption while others were below detection limits.
• A strong positive correlation between compound hydrophobicity (Log Kow for PAHs and Log D for PFAS) and microplastic transfer ratios, independent of plastic type.

Benefits and Practical Applications

This methodology enables accurate quantification of organic pollutant adsorption on microplastics, supporting:

• Risk assessment of microplastic-mediated contaminant transport.
• Development of water quality monitoring protocols.
• Design of mitigation strategies to reduce chemical exposure via microplastics.

Future Trends and Potential Applications

Anticipated developments include:

• Expansion to a broader range of emerging contaminants and real environmental samples.
• Evaluation of aged and weathered microplastics to mimic environmental conditions.
• Integration with bioavailability and toxicokinetic studies in aquatic organisms.
• Standardization of testing methods for regulatory purposes.

Conclusion

This study demonstrates that adsorption of PAHs and PFAS on microplastics is governed primarily by hydrophobic interactions. The combined use of GC-MS/MS and LC-MS/MS provides a robust analytical framework for investigating contaminant–microplastic interactions and informs environmental risk evaluations.

References

• Makoto Yasojima et al., Adsorption Characteristics of Chemical Substances on Microplastics, Proceedings of the 22nd Symposium of the Japan Society on Water Environment, 2019.
• Makoto Yasojima et al., Existence of Unknown Chemical Substances Adsorbed on Microplastics Immersed in Rivers, Proceedings of the 56th Environmental Engineering Research Forum, 2019.