Air-drying of soil samples - A crucial step in the determination of leachable concentrations of per- and polyfluoroalkyl substances

Batch leaching tests at a liquid to solid ratio of 2 L/kg are a valuable tool for the assessment of low PFAS levels in soils. Data from different monitoring programs comprising samples without known local source of PFAS contamination showed that soil-sample drying at ambient temperature or at 40 degrees C prior to the leaching process leads to higher PFAS leachate levels compared to non-dried samples. The effect was greater for perfluoroalkyl carboxylic acids (PFCAs) than for perfluoroalkyl sulfonic acids (PFSAs). In a controlled field study comparing field-fresh (frozen to -18 degrees C and thawed) samples with air-dried (room temperature) samples median levels after drying increased to 140%-470% for C4 to C10 PFCAs and to 130%-200% for C4, C6, and C8 PFSAs, respectively. Thus, using field-fresh samples for batch leaching tests might underestimate the leachable fraction of PFAA in the field, where drying and leaching periods alternate. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

Batch leaching tests are valuable for assessing low PFAS levels in soils. Drying soil samples at ambient temperature or at 40 degrees C before the leaching process leads to higher PFAS leachate levels. The effect is greater for PFCAs than for PFSAs.