PFAS and nitrate leaching from undisturbed soil columns receiving biosolids and mitigation potential of biochar

Land application of biosolids recycles nutrients and reduces the need for
commercial fertilizers. However, per- and polyfluoroalkyl substances
(PFAS) may leach from biosolids, resulting in groundwater contamination.
We measured PFAS leaching from land-applied biosolids through undisturbed
soil column trials and evaluated the treatment potential of amending
biosolids with biochar. Synthetic rainfall was applied weekly to
undisturbed soil columns from four regions in Wisconsin, including two
fields with a history of biosolids application, simulating annual
precipitation. The treatments consisted of a control (soil only), soil
amended with biosolids, and soil receiving a mixture of biosolids and
biochar. Concentrations of total PFAS in leachate were significantly
affected by soil location and site history, while only long chain PFAS
concentrations were significantly affected by biosolids/biochar
treatments. One-time application of biosolids may result in groundwater
contamination, as PFAS concentrations in leachate exceeded the local
groundwater standard (a combined perfluorooctanoic acid and
perflourooctanesulfonic acid groundwater concentration of 20 ng L-1) at
three locations. Legacy PFAS may pose a risk to human health years after
biosolid application, as a control column from a site with an intensive
history of biosolid application exceeded PFAS groundwater standards.
Incorporation of biochar with biosolids during application mitigated PFAS
(specifically from soils with elevated leaching potential) through
significant reductions of C7 – C10 perfluoroalkyl carboxylic acids and C4,
C6 – C8 perfluorosulfonic acids (40 to 64% reduction in measured Σ28
PFAS). Biochar may facilitate sustainable use of biosolids through
mitigation of long-chain PFAS leaching, pending long-term field
evaluation.