NUTRITION AND GEOLOGY OF THE SOLIS VALLEY, MEXICO: STONTIUM ISOTOPES AND ELEMENTAL FRACTIONATION IN TORTILLA PRODUCTION

In the mid-1980s, a Mexican/US consortium conducted a longitudinal study of mild-to-moderate malnutrition in six villages in the Solis Valley, 160 km NW of Mexico City. Maize (corn) consumption (mainly tortillas) constitutes about 50-70% of dietary energy. We have investigated the Sr isotope chemistry and elemental fractionations involved in tortilla production, beginning with the volcanic bedrock, soil and groundwater through the maize and other ingredients that make up tortilla flour, and finally to the deciduous teeth of children (Goodman et al., this meeting). Dried maize and "cal" (a highly variable mixture of CaCO3, Ca(OH)2 and CaO) are boiled together to improve maize digestibility, tortilla flour workability and flavor. "Cal" strongly influences both the isotopic and elemental food chain. Bedrock, soil and groundwater 87Sr/86Sr including published data for the nearby Amealco caldera range from 0.70380 to 0.70567. "Cal", sintered limestone, (0.70748) and tortillas (0.70744 to 0.70802) do not match the local landscape. Deciduous teeth span the landscape-"cal" gap (0.70577 - 0.70766) apparently reflecting varying "cal"-Sr availability, and possibly variation in maternal maize/tortilla consumption. In a suite of Solis households, and in a controlled laboratory production of tortillas, Ca/Sr (a widely used ratio in archaeological foodweb reconstructions) in tortillas generally mismatches that in the "cal" used to make the tortilla due to a preference by the boiled corn for Sr uptake relative to Ca. Very little dietary Zn or Fe is supplied by "cal", but enters with the corn. Supported by NSF C-RUI #DBI-78793.