RADIOGENIC ISOTOPES AS POTENTIAL TRACERS OF WINE ORIGIN

This investigation is a case study to test the use of radiogenic isotopes of Pb and Sr as potential tracers of wine origin. Vineyard samples including soil, grapes, leaves, and airborne particulate matter as well as winery samples including grape juice, a wine collected at different stages of production, four other bottled wines, water, yeast and a wine stabilizer were analyzed from a single American vineyard located within a mixed agricultural, industrial, suburban environment. Lead and Sr isotopic compositions were determined by thermal ionization mass spectrometry. Among the soil samples, a large ⁸⁷Sr/⁸⁶Sr variation is observed, becoming less radiogenic with depth but a limited variation is observed in ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb. Wine, juice, grape leaf and grape samples display a restricted variation in Sr isotopic signatures and are similar to that of the deepest soil sample taken at 90 cm depth. However, these samples show significant variations in Pb isotopes, and are distinctly less radiogenic than any soil samples. The variation in Sr isotopic signatures among the soil samples could be attributed to the preferential weathering of Rb-rich minerals within the loess at the upper horizons and carbonate bedrock having a greater relative contribution to the ⁸⁷Sr/⁸⁶Sr ratios in the lower horizons. However, the Sr isotopic compositions of the lowermost soil sample, and the grapes and leaves display a restricted variation and remains essentially constant throughout the wine making process from fermentation to bottling. In contrast, a significant difference between the Pb isotope signature of the soil versus the grapes and leaves, with the latter significantly less radiogenic, may be attributed to a contribution from less radiogenic atmospheric particulate matter, which impacts the Pb isotopic signature of the grape plants. Additional variation in Pb and Sr isotope signatures between the grapes and leaves, the juice, and among the wines, suggests that the winemaking process itself can impart further modification of the isotopic signature inherited from the grapes. Results from this study illustrate that Sr isotopes may not always serve as robust geochemical tracers of the geographic provenance of wine, and the utility of Pb isotopes as tracers of a wine’s origin may present even more limitations.