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PFAS occurrence and distribution in yard waste compost indicate potential volatile loss, downward migration, and transformation
Summary
Researchers discovered unexpectedly high concentrations of PFAS, commonly known as forever chemicals, in yard waste compost. The study found 17 different PFAS compounds, with concentrations increasing in plastic debris during the composting process, suggesting that plastics in yard waste may be a source. Evidence indicates that PFAS can migrate downward through compost piles and that short-chain compounds may be lost through evaporation at the surface.
We discovered high concentrations of PFAS (18.53 ± 1.5 μg kg-1) in yard waste compost, a compost type widely acceptable to the public. Seventeen out of forty targeted PFAS, belonging to six PFAS classes were detected in yard waste compost, with PFCAs (13.51 ± 0.99 μg kg-1) and PFSAs (4.13 ± 0.19 μg kg-1) being the dominant classes, comprising approximately 72.5% and 22.1% of the total measured PFAS. Both short-chain PFAS, such as PFBA, PFHxA, and PFBS, and long-chain PFAS, such as PFOA and PFOS, were prevalent in all the tested yard waste compost samples. We also discovered the co-occurrence of PFAS with low-density polyethylene (LDPE) and polyethylene terephthalate (PET) plastics. Total PFAS concentrations in LDPE and PET separated from incoming yard waste were 7.41 ± 0.41 μg kg-1 and 1.35 ± 0.1 μg kg-1, which increased to 8.66 ± 0.81 μg kg-1 in LDPE and 5.44 ± 0.56 μg kg-1 in PET separated from compost. An idle mature compost pile revealed a clear vertical distribution of PFAS, with the total PFAS concentrations at the surface level approximately 58.9-63.2% lower than the 2 ft level. This difference might be attributed to the volatile loss of short-chain PFCAs, PFAS's downward movement with moisture, and aerobic transformations of precursor PFAS at the surface.