Xu et al. 2025 — Cola beverage reduces Pb bioaccessibility from contaminated soil via pyromorphite formation
This Nature Communications study demonstrates that cola beverages (containing phosphoric acid) dramatically reduce lead bioaccessibility from contaminated soil particles when co-ingested, through a geochemical mechanism: phosphoric acid in cola reacts with soil Pb to form pyromorphite (Pb5(PO4)3Cl), an insoluble Pb mineral with very low bioaccessibility. The study tested 22 contaminated soils using in-vitro PBET (physiologically based extraction test) and validated the finding in vivo using rat and swine models. The work directly addresses the exposure pathway by which soil-contaminated food environments or pica behavior in children leads to Pb ingestion.
Key numbers
- In-vitro PBET: cola reduced Pb bioaccessibility by 32.6–98.8% across 22 contaminated soils (IQR approximately 60–90% reduction depending on soil Pb speciation).
- Rat model (blood Pb reduction): 32.9–96.0% reduction in blood Pb compared to contaminated soil ingestion without cola; effect size strongly correlated with Pb bioaccessibility reduction in PBET.
- Swine model (blood Pb reduction): 31.5–81.5% reduction in blood Pb; swine physiology more closely approximates human gastrointestinal conditions.
- Pyromorphite formation confirmed by XRD and XANES spectroscopy in post-digestion gastric residues.
- Effect is phosphate-mediated: the phosphoric acid content of cola (~8.5 mM in Coca-Cola) drives the Pb5(PO4)3Cl precipitation in the acidic gastric phase (pH ~2–3).
- Soils tested: US shooting ranges (Pb >10,000 mg/kg), Florida battery recycling site soils (Pb ~5,000 mg/kg), and Chinese contaminated urban soils; results hold across wide range of initial Pb concentrations and Pb speciation forms.
- Lowest bioaccessibility reduction (~32%) was observed for soils where Pb was already largely in insoluble mineral form; highest reductions were observed for soils with high dissolved or carbonate-bound Pb.
Methods (brief)
In-vitro: PBET (Ruby et al. 1996 protocol) simulating gastric-phase extraction (pH 1.8, 1 hour, 37°C); cola added at beverage:soil ratios reflecting co-ingestion scenarios. In-vivo rat: oral gavage of contaminated soil slurry ± cola; blood Pb measured at 0, 6, 24, 72 h by ICP-MS. In-vivo swine: same design; blood Pb over 72 h. Mineralogy: XRD and XANES to characterize Pb speciation changes. Published in Nature Communications (IF > 16), received 10 October 2023, accepted 8 January 2025.
Implications
Certification: Pyromorphite formation mechanism is directly relevant to the mitigation page for Pb exposure from contaminated soil/food environments; this is a high-quality primary study documenting a specific, mechanistic, and large-magnitude intervention. Relevant to lead-soil-bioaccessibility. Courses: Excellent case study for modules on Pb exposure from non-food sources (soil ingestion, dust) and the role of diet-contaminant interactions in bioaccessibility; the phosphate mechanism generalizes to phosphate-rich foods (dairy, legumes) as potential co-ingestion moderators. App: Does not directly inform food contamination_profile values. Potentially relevant to app exposure estimation where soil contamination near food production sites is a variable. Microbiome: Not applicable.