Overview
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.
Related evidence
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