114-11 Tracing Toxic Lead in Spices: Pb Isotope Systematics as a Provenance Tool

Session: Environmental Geochemistry and Health (Part I)

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Abstract:

Lead isotope ratios, particularly ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁶Pb, are established geochemical tools for distinguishing environmental lead sources. Because these ratios reflect the time-integrated evolution of uranium-thorium-lead systematics in source rocks, they yield distinct isotopic signatures tied directly to a deposit’s crustal age and geologic history. We apply this isotopic provenance framework to an urgent public health concern: toxic lead contamination in culinary spices, specifically turmeric and cinnamon, where lead chromate (PbCrO₄) is a known synthetic adulterant added for color enhancement. Such contamination has been linked to elevated blood lead levels in children and represents a persistent, difficult-to-regulate exposure pathway that isotopic fingerprinting can help address.

To evaluate potential source materials, we characterized the isotopic signatures of two commercial PbCrO₄ reagents using multi-collector inductively coupled plasma mass spectrometry, which affords the high-precision measurements required to resolve subtle isotopic differences between sources. The two reagents were clearly resolvable (²⁰⁶Pb/²⁰⁷Pb = 1.1219 vs. 1.1486), demonstrating that commercial lead chromate stocks do not represent a uniform, single-isotopic endmember. This observed heterogeneity reflects either distinct primary ore provenance or a blended signature inherited from recycled lead processing.

We subsequently analyzed three adulterated spice samples of concern: two severely adulterated cinnamon samples from Ecuador and one 25-ppm-lead turmeric sample packaged in the US (Brooklyn, NY). The first adulterated cinnamon sample contained 0.25% Pb with an isotopic ratio (²⁰⁶Pb/²⁰⁷Pb = 1.1489) indistinguishable from one of our commercial reagents. The second adulterated cinnamon sample contained 0.55% Pb and yielded a higher, unmatched ratio (²⁰⁶Pb/²⁰⁷Pb = 1.1695) plotting well outside the field defined by the reference materials, confirming a distinct lead origin. The turmeric sample (²⁰⁶Pb/²⁰⁷Pb = 1.1282) plotted close to, but significantly offset from, one reagent endmember, consistent with a related ore source or a two-component binary mixture.

This study establishes a robust analytical framework for identifying toxic lead additives in food products, with direct application to consumer protection, regulatory testing, and forensic tracing of contamination events back to specific manufacturing sources. An expanded suite of commercial reagents and culinary cinnamon and turmeric samples—complemented by trace-element signatures to help disentangle primary ore origins from recycled or blended lead sources—will be presented.

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