Effect of Sample Storage on the Quantitative Determination of 29 PFAS: Observation of Analyte Interconversions during Storage

Abstract

In this study, we measured the effects of sample type and storage temperature on the stability of 29 per- and polyfluorinated alkyl substances (PFAS) in water. Spiked bottled water, surface water, and two types of effluent samples were stored in HDPE containers at +20, 4, and −20 °C over a period of up to 180 days. The analytes studied included C4 through C14 perfluorinated carboxylates (PFCAs); C4 through C10 and C12 perfluorinated sulfonates (PFSAs); 4:2, 6:2, and 8:2 fluorotelomer sulfonates (FTS); three perfluorooctane sulfonamides (PFOSA, N-MeFOSA, and N-EtFOSA); two perfluorooctane sulfonamide ethanols (N-MeFOSE and N-EtFOSE); and two perfluorooctane sulfonamide acetic acids (N-MeFOSAA and EtFOSAA). Overall, 10 analytes, PFOA, PFNA, 8:2 FTS, PFOSA, N-MeFOSA, NEtFOSA, N-MeFOSAA, N-EtFOSAA, N-MeFOSE, and N-EtFOSE, showed increasing or decreasing concentration trends under at least one of the experimental conditions investigated. Increases in concentrations of N-MeFOSAA and N-EtFOSAA in surface water and effluent samples at +20 and 4 °C correlated with the decreases in the concentrations of N-MeFOSE and N-EtFOSE, respectively, suggesting analyte interconversion during sample storage. This is the first time such analyte conversion is reported in samples under storage, and this work demonstrates the importance of assessing stability of PFAS in environmentally relevant matrices. The significance of this study extends beyond sample storage for analysis, as toxicological and exposure studies conducted at room temperature also need to consider the significance of analyte degradation through the exposure process.

Field Sampling Materials Unlikely Source of Contamination for Perfluoroalkyl and Polyfluoroalkyl Substances in Field Samples

“…The MIP membrane, which is constructed of PTFE material, gave total fluorine that was above the calibration range (Table ) but no quantifiable individual PFAS (Table ). Of the materials included in Group 3, only the MIP is a prohibited material in PFAS sampling guidance documents. ,− ,, However, none of the materials in Group 3 have concentrations for the commonly measured PFAS that are greater than LOQ. Thus, while the materials potentially come in direct contact with field samples, they are unlikely to impact measured PFAS concentrations in field samples.…”

“…All five cold packs were either ND or less than LOQ for PFAS even though they are listed as prohibited items in PFAS sampling guidance documents. ,,, As an exercise, a concentration equivalent to one-half of the LOQ (0.23 μg/m 2 ) for a cold pack (15 cm × 15 cm × 2 cm or 0.045 m 2 ), which was actually ND for PFOS and PFOA (Table ), was used to estimate the number of cold packs that would have to completely desorb inside a 1 L sample bottle to reach the EPA HAL and the LOQ for individual PFAS. A total of 6.7 ice packs would be needed to reach the EPA HAL, and 1.0 ice packs would be needed to reach a water concentration of 10 ng/L (Table ) if PFOA was present at one-half the LOQ.…”

“…Coolers for shipping samples were not evaluated because if ice packs are used to ship samples in coolers, there is no transfer medium (e.g., water) present. Moreover, samples in coolers are known to leak, but PFAS sampling guidance documents indicate that sample containers should be shipped in secondary containment (e.g., plastic bag) before being placed in coolers. ,,, …”

“…However, given that the EPA HAL concentrations are very low (ng/L), combined with the ubiquitous nature of PFAS, it is imperative to avoid creating artifacts (e.g., false positives) when collecting field samples, since detection of PFAS potentially has significant consequences for facility owners, the public, and other stakeholders. As a result, potential laboratory and instrumental contamination and the impact of sample storage time and temperature on measured PFAS concentrations have received attention …”

Longitudinal assessment of point‐of‐use carbon filters for removal of per‐ and polyfluoroalkyl substances from private well water

“…Due to laboratory shutdowns caused by Covid-19, samples were stored for seven up to 15 months prior to extraction. Although PFAS losses in water samples have been shown to be negligible for up to 70 days of holding time at room temperature (Sun et al, 2016), changes in PFAS levels may occur in some samples during extended storage times as a result of PFAS transformations (Woudneh et al, 2019). To evaluate the effect of the long holding time, 13 baseline, raw well water samples that were initially collected to determine each household's eligibility to participate in the study in July 2019 were analyzed twice, once after 2 months of holding time (September 2019) and again after approximately 18 months of holding time (January 2020) at room temperature.…”