Sowers et al. 2023 — Potassium jarosite soil remediation reducing Pb and As bioaccessibility
This study developed and tested a soil remediation method that converts soil lead and arsenic into jarosite-group minerals — plumbojarosite (PLJ) and beudantite — which have exceptionally low bioaccessibility at gastric pH (1.5–3). Treatment with potassium jarosite seeding reduced Pb and As bioaccessibility from approximately 70% and 60% (unamended) to less than 10% across all treatment conditions, representing a rare dual remediation option addressing both metals simultaneously. This is particularly significant because conventional phosphate-based Pb remediation can actually increase As bioaccessibility through competitive sorption effects.
Key numbers
- Unamended soil Pb bioaccessibility: approximately 70%
- Unamended soil As bioaccessibility: approximately 60%
- Post-treatment Pb bioaccessibility: < 10% across all K-jarosite treatments
- Post-treatment As bioaccessibility: < 10% across all K-jarosite treatments
- HPb-HAs soil: 2,393 mg Pb/kg, 369 mg As/kg (legacy Pb arsenate pesticide, orchard)
- MPb-LAs soil: 746 mg Pb/kg, 6 mg As/kg (zinc smelter contamination, residential)
- PLJ conversion at 40 °C for HPb-HAs: 71 ± 3.2%
- PLJ conversion at room temperature (22 °C) for MPb-LAs: 81 ± 2.1%
- Additional soils (200–500 mg Pb/kg): PLJ conversion ≥ 85% at room temperature
- US EPA soil Pb screening levels: 400 mg/kg (play areas), 1,200 mg/kg (other residential)
Bioaccessibility measured by EPA Method 1340 (glycine extraction at pH 1.5, 37 °C, 1 hour). Pb and As quantified by ICP-MS (iCAP RQ). Pb speciation by X-ray absorption near-edge structure (XANES) linear combination fitting.
Methods (brief)
Laboratory potted-soil experiments. K-jarosite synthesized per Baron and Palmer. Soils treated at various temperatures (room temperature, 40, 50, 60 °C) with and without K-jarosite seeding. 16-hour reaction time. Pb bioaccessibility by EPA Method 1340 (in vitro bioaccessibility assay). Pb and As speciation by bulk Pb L-III edge and As K-edge XAS at Argonne National Laboratory (MRCAT beamlines 10-ID and 10-BM). Fe⁵⁷ Mossbauer spectroscopy for jarosite-phase confirmation. NIST SRM 2710a (Montana I Soil) for method validation.
Implications
Certification: This is a supply-chain remediation paper, not a food-matrix measurement paper. It is relevant to the mitigation framework: when crops are grown in Pb/As-contaminated soil (legacy orchards, industrial sites, urban gardens), jarosite treatment is a potential in situ agronomic lever that can reduce dietary exposure via soil-to-plant transfer pathways. The bioaccessibility reduction from ~65% to < 10% is a meaningful magnitude for risk-reduction arguments.
Courses: Good case study for the interaction between Pb and As remediation — the conventional phosphate approach to Pb remediation worsens As exposure. The dual-remediation jarosite approach resolves this tradeoff.
App: Not directly applicable to ingredient-level contamination profiles, but informs the supply-chain screening module for legacy-orchard or smelter-adjacent agricultural sourcing.