A study published in Environmental and Biogeochemical Processes determined that iron-fortified, low-temperature biochar can immobilize per- and polyfluoroalkyl substances (PFAS) in contaminated soils. The controlled soil–plant experiments indicated that iron-modified biochar reduced total PFAS accumulation in radish by approximately half and decreased PFAS levels in the edible radish bulb by more than 25%. This study demonstrated that this process can significantly reduce PFAS bioavailability and accumulation in food crops.
PFAS are synthetic chemicals commonly used in consumer products and industrial applications. They have strong carbon–fluorine bonds, which make them persistent in soil, water, and living organisms. Previous studies found that PFAS can be absorbed by crops and transferred through the food chain, posing a significant health risk to humans. Biochar is a carbon-based sorbent that offers a more efficient and less expensive soil remediation strategy than other methods.
The researchers used a stepwise workflow involving contaminated-soil profiling, biochar sorbent characterization, leachate screening, and replicated soil–plant uptake experiments. The research team assessed whether hemp-derived biochar produced at 500–800°C (with or without ~8 wt.% iron fortification) could immobilize PFAS and minimize bioaccumulation in crops. They used a sandy loam field soil (pH 5.6) tainted by legacy firefighting foams, which contained 576 ± 117 ng/g total PFAS. They detected 20 of 24 target compounds. The research team used Fourier Transform Infrared Spectroscopy (FTIR), BET surface area and pore analysis, and XRD-supported mineralogical characterization (supported by XRD) to link biochar production conditions with sorbent performance.
The study found that biochar produced at 500°C exhibited strong FTIR signals (2,400–1,000 cm⁻¹) associated with oxygen-containing functional groups. In contrast, higher pyrolysis temperatures reduced these features, leading to a loss of surface functionality and increased aromatic condensation. Macro-element contents (Ca, K, Mg, P) increased with temperature. Surface area and pore volume decreased significantly from ~233 to 17.7 m²/g and from 0.054 to 0.006 cm³/g as temperature increased. Another finding showed that iron fortification increased surface area and pore volume. The researchers used a leachate screening assay to determine biochar produced at 500°C was most effective for PFAS retention. Radish did not show phytotoxic effects and increased biomass.
The findings suggest that iron-fortified biochar can be an effective tool for treating agricultural soils contaminated by PFAS. This approach could significantly limit contaminant transfer into crops and subsequent human exposure through food intake.
Sources: Environmental and Biogeochemical Processes, Eureka News Alert
