What’s Up With PFAS Hold Times?
Dec. 7 2022
Our clients often ask:
‘If PFAS are forever chemicals, why are hold times so short?’
It is a very good question and the answer is, when we were first developing PFAS test methods, hold times for water and soil were based on our reference methods at the time: EPA537 and ASTM7968-14. However, at that time, no comprehensive study of PFAS stability had been conducted for different storage conditions in soil and water. That has changed with the recent US EPA Draft Method 1633 release for the analysis of a wide range of PFAS in several aqueous and solid matrices.
When the EPA was developing Method 1633, they oversaw an extensive hold time study specific to PFAS in the permitted matrices, the results of which are published on the EPA website with the other method documents. Thus the hold time specifications in Draft Method 1633 are based on sound PFAS-specific science.
What are the default PFAS hold times?
In 2023, Bureau Veritas will be harmonizing hold times for most PFAS testing according to Draft Method 1633. These hold times are specified in table 1 below.
Table 1: Default PFAS Hold Times Effective January 1, 2023
|Water||28 days for refrigerated storage|
|Water||90 days for frozen storage (may be implemented in select cases)|
|Soil||90 days for refrigerated storage|
Are there exceptions to default PFAS hold times?
- Where contracted hold time obligations are more stringent than the Draft Method 1633 specifications, the contracted obligations will be honoured.
- All drinking water samples that are submitted under one of the two EPA-approved drinking water test methods* (EPA 533 or EPA 537.1) will continue with the current 14 day refrigerated hold time. However, if drinking water samples are submitted for a non-drinking water test, default hold times will apply.
*Draft Method 1633 is not permitted for use for drinking water sample reporting to regulatory authorities.
Should I refrigerate or freeze PFAS water samples?
- In the EPA hold time study, some perfluorooctane sulfonamide ethanols (MeFOSE, EtFOSE) and perfluorooctane sulfonamidoacetic acids (MeFOSAA, EtFOSAA), were less stable in some of the water matrices tested. Due to precursor interconversions some levels went down and some went up during 28 day refrigerated storage at percentages just outside of the method acceptance criteria of ±30%. These interconversions were not seen during frozen storage.
- If these parameters are of particular importance for your project we can provide frozen storage by special request at the time of sample submission. Additional charges may apply.
For further information please contact your Customer Service Representative.