HUMAN GEOPHAGY: MODELING INGESTION OF ELEMENTS FROM SOILS AND CLAYS

Mineralogical and geochemical studies of soils and clay occurrences in the eastern United States provide new and critical data for modeling essential (e.g., K, Fe, Mn, V, Se, Zn) and potentially harmful elements (e.g., As, Pb, Cd, Hg, Al) released due to human ingestion. Geophagy, the consumption of soils and clays, was first documented in Native American populations in the late 1400’s. In the southeastern United States, the practice persists today on a small scale, especially among pregnant African American women, and has the potential to increase due to immigration of populations that continue the custom (e.g., Guatemalan Indians). Geochemical availability by ingestion varies with source materials, bulk composition, and mineralogy. Mineralogical (XRD) and geochemical data (XRF, INAA, EMPA) for soils and clay types from the eastern United States (New England coastal soil, South Carolina kaolinitic clay, and Florida attapulgite clay-bearing soil) were used to calculate relative yields of all elements during ingestion. The amount of an element ingested was calculated as a function of the concentration of the element in the material, the rate of ingestion, and the duration of the meal. For all soils, ingestion resulted in release of elements in amounts which exceed the reference oral dose (RfD) for many elements (EPA-IRIS). For example, consumption of white clays (composed mostly of quartz, sericite, and kaolinite) yielded ingested amounts in the range 0.03-0.188 mg-As/day and 0.13-0.83 mg-Pb/day. Red clays (quartz, sericite, kaolinite, and goethite) and coastal soils (quartz, feldspar, sericite, chlorite, Fe-Mn-hydroxides) yielded ingested amounts in the range 0.2-1.25 mg-As/day, 0.26-1.62 mg-Pb/day, and 3.0-16.12 mg-Zn/day. Thus, ingestion resulted in As and Zn releases that exceed RfD values (As=3x10-4 mg/kg/day, Zn=0.3 mg/kg/day) for most body weights. The Pb data are being applied to help model the effects of digestion on labile metals (e.g., sorbed Pb) compared to metals structurally bound in minerals (e.g., feldspar Pb).