Passive Sampling for the Monitoring of PFAS in Water

Importance of the Topic

Passive sampling of PFAS in water addresses the challenge of accurately monitoring persistent and ubiquitous per- and polyfluoroalkyl substances (PFAS) in aquatic systems. PFAS pose environmental concerns due to their stability, bioaccumulation and long-range transport. Time-integrated sampling methods like Diffusive Gradients in Thin Films (DGT) enhance detection of dissolved PFAS, supporting source identification and trend analysis.

Study Objectives and Overview

This article reports the expansion of ALS laboratories' PFAS monitoring portfolio by employing DGT passive samplers for watershed-scale assessment. The primary aims are:

• To describe the design and operation of PFAS-specific DGT samplers.
• To validate method performance, including diffusion coefficients and reporting limits for 14 PFAS compounds.
• To compare passive sampling with conventional spot sampling in diverse water matrices.

Methodology and Instrumentation

The PFAS DGT sampler (LSNW-AP) comprises a filter membrane, diffusive agarose gel and hydrogel binding layer. Samplers are deployed in flowing fresh, marine or wastewater environments for 3-21 days. After retrieval, the hydrogel is extracted in methanolic ammonium hydroxide, concentrated under nitrogen, filtered, and quantified by UHPLC-MS/MS. Validation parameters include:

• Target analytes: 14 PFAS species (e.g., PFBA, PFOS, PFOA, GenX).
• Diffusion coefficients supplied by manufacturer.
• Reporting limits (ng/L) as a function of deployment time and temperature.

Main Results and Discussion

Passive DGT sampling delivers time-weighted average concentrations of freely dissolved PFAS, reducing variability associated with spot sampling. Key findings:

• Reporting limits decrease with longer deployment periods (optimal 3-21 days).
• Diffusion coefficients ranged from 3.46e-6 to 6.46e-6 cm2/s, influencing uptake rates.
• Consistent performance across freshwater, seawater and wastewater matrices.

Benefits and Practical Applications

• Time-integrated sampling averages out temporal fluctuations, enhancing trend analysis.
• Equipment-free deployment simplifies field operations and reduces power requirements.
• Applicability across diverse aquatic systems supports regulatory compliance and ecological risk assessment.

Used Instrumentation

• DGT passive samplers (LSNW-AP series): PES filter membrane, agarose diffusive gel, hydrogel binding layer.
• Sample extraction: Methanol with 0.5% NH4OH, nitrogen evaporation.
• UHPLC-MS/MS for analyte separation and quantitation via internal standard calibration.

Future Trends and Applications

Advances may include novel binding phases targeting emerging PFAS, integration of in situ temperature logging for improved flux calculations and coupling passive samplers with high-resolution mass spectrometry for non-target screening. Expansion to field-deployable sensors and real-time monitoring platforms could further support rapid decision-making in water quality management.

Conclusion

DGT passive sampling offers a robust, time-integrated approach to measure dissolved PFAS in water. The validated method demonstrates low reporting limits, matrix versatility and operational simplicity, making it a valuable tool for environmental monitoring programs focused on persistent organic pollutants.

References

• Zhou Fang et al., Development and Applications of Novel DGT Passive Samplers for Measuring 12 Per- and Polyfluoroalkyl Substances in Natural Waters and Wastewaters, Environmental Science & Technology, 2021.
• Kees Booij et al., Passive Sampling in Regulatory Chemical Monitoring of Nonpolar Organic Compounds in the Aquatic Environment, Environmental Science & Technology, 2016.
• DGTS Research Organic Analytes.