While perfluorinated carboxylates and sulfonates (PFAA) such as PFOA and PFOS are known to be stable under all storage/environmental conditions, it is well known that many other PFAS, including PFAA precursors can transform in the environment from biological and chemical processes. But little was known about their stability in environmental samples sent to laboratory and stored cold.
A team of SGS AXYS scientists including Drs. Million Woudneh, Bharat Chandramouli and Coreen Hamilton have recently published a timely and relevant study “Effect of Sample Storage on the Quantitative Determination of 29 PFAS: Observation of Analyte Interconversions during Storage” that expands the knowledge of PFAS storage and stability and provides an unqualified recommendation to ensure six months of stability. This study had several unique attributes:
- Tests in real environmental samples such as wastewater treatment plant (WWTP) effluents and surface water unlike previous studies performed in reagent water
- A comprehensive list of PFAS including multiple precursors of environmental relevance
- A half-year duration with 6 timepoints and 3 replicates for each sample/timepoint
- Multiple storage temperatures including laboratory standard 0-4°C, frozen at -20°C and room temperature
- Best practice PFAS analysis including isotope dilution, weak anion exchange (WAX), and more.
This study found that under standard laboratory storage conditions of refrigerator storage, precursors, MeFOSE, for example, transformed into other PFAS such as MeFOSAA within six days in effluent and surface water samples. We were able to link and correlate these transformations to previously observed biological mechanisms in the field. Samples that were frozen at -20°C remained stable through six months of testing. Based on this finding, we recommend freezing of all samples for PFAS analysis upon laboratory receipt until further study into chemical or other preservation techniques has been validated and published.
This study was recently published in the Environment Science and Technology Journal. Please contact us if you would like more information, or a presentation from one of the scientists involved in the study.