Iron-fortified biochar cuts “forever chemical” uptake in food crops

In controlled soil–plant experiments, the iron-modified biochar lowered total PFAS accumulation in radish by nearly half and reduced PFAS levels in the edible bulb by more than 25%.

PFAS are widely used synthetic chemicals found in firefighting foams, industrial applications, and consumer products. Their strong carbon–fluorine bonds make them extremely persistent in soil, water, and living organisms. Studies show that PFAS can be taken up by crops and transferred through the food chain, even at low soil concentrations, with short-chain PFAS being especially mobile and prone to plant accumulation. Because removing PFAS from soil is costly and technically challenging, immobilization strategies that reduce their bioavailability have gained attention. Carbon-based sorbents such as biochar are promising options due to their low cost, agricultural compatibility, and tunable properties through feedstock choice and production conditions.

A study (DOI: 10.48130/ebp-0025-0010) published in Environmental and Biogeochemical Processes on 27 November 2025 by Jason C. White’s team, The Connecticut Agricultural Experiment Station, demonstrates that iron-fortified, low-temperature biochar can effectively immobilize PFAS in contaminated soils, significantly reducing their bioavailability and accumulation in food crops while remaining compatible with agricultural production.

Using a stepwise workflow combining contaminated-soil profiling, biochar sorbent characterization, leachate screening, and replicated soil–plant uptake experiments, researchers evaluated whether hemp-derived biochar (BC) produced at 500–800 °C, with or without ~8 wt.% iron fortification, could immobilize PFAS and reduce crop bioaccumulation. The field soil, a sandy loam (pH 5.6) impacted by legacy firefighting foams, contained 576 ± 117 ng/g total PFAS, with 20 of 24 target compounds detected and PFOS dominating (~60.7%), followed by PFUnA, PFNA, and PFHxS. To link biochar production conditions with sorbent performance, FTIR spectroscopy, BET surface area and pore analysis, and mineralogical characterization (supported by XRD) were applied. Biochar produced at 500 °C exhibited strong FTIR signals (2,400–1,000 cm⁻¹) associated with oxygen-containing functional groups, whereas higher pyrolysis temperatures progressively reduced these features, indicating loss of surface functionality and greater aromatic condensation. In parallel, macro-element contents (Ca, K, Mg, P) increased with temperature. Structurally, BET surface area and pore volume declined sharply from ~233 to 17.7 m²/g and from 0.054 to 0.006 cm³/g as temperature increased, consistent with pore collapse and mineral pore-blocking at ≥700 °C. In contrast, iron fortification markedly increased surface area and pore volume (≈300–343 m²/g; 0.072–0.089 cm³/g), introducing iron oxide/hydroxide sites expected to enhance electrostatic and ligand-exchange interactions with anionic PFAS. A leachate screening assay identified 500 °C materials (BC500 and iron-fortified FBC500) as the most effective for PFAS retention, leading to their selection for radish trials (2 or 5 wt.% amendments). Radish showed no phytotoxic effects and often increased biomass, while PFAS uptake remained chain-length dependent, with short-chain compounds accumulating most strongly. Notably, BC500 slightly increased whole-plant PFAS, whereas FBC500 reduced whole-plant PFAS to 2,630 ± 367 ng/g and lowered bulb PFAS by 25.7%, demonstrating that iron addition transforms biochar into a more effective PFAS immobilization sorbent.

These findings highlight iron-fortified biochar as a practical tool for managing PFAS-contaminated agricultural soils. By immobilizing PFAS, farmers and land managers could reduce contaminant transfer into crops and lower human exposure through food. Because biochar can be produced from agricultural residues such as hemp and applied using standard soil-amendment practices, this approach aligns well with sustainable and circular-economy principles.

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References

DOI

10.48130/ebp-0025-0010

Original Source URL

https://doi.org/10.48130/ebp-0025-0010

Funding Information

This project was funded by the US HHS FDA award 5U19FD007094.

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Environmental and Biogeochemical Processes is a multidisciplinary platform for communicating advances in fundamental and applied research on the interactions and processes involving the cycling of elements and compounds between the biological, geological, and chemical components of the environment.