Mineralogical and chemical interactions of soils eaten by chimpanzees of the Mahale Mountains and Gombe Stream National Parks, Tanzania

Termite mound soils eaten by chimpanzees of the Mahale Mountains and Gombe National Parks, Tanzania, have mineralogical and geochemical compositions s imilar to many soils eaten by higher primates. but release very low levels of either toxic or nutritional inorganic elements to solution at acid pH. C omparison with control (uneaten) soils from the same areas showed lower lev els of carbon and nitrogen in the eaten soils, a relationship confirmed by surface analysis. Surface analysis also revealed lower levels of iron on pa rticle surfaces versus interiors. and higher levels of iron on ingested ver sus control soil particle surfaces. The soils can adsorb dietary toxins, pr esent in the plant diet or those produced by microorganisms. Taking the tox ic alkaloids quinine. atropine, sparteine, and lupanine as examples, it is evident that soils from Mahale have a very good adsorptive capacity. A new adaptive advantage of geophagy is proposed, based on the prevention of iron uptake. The behavior of the soils in vitro is consistent with the theory t hat geophagy has a therapeutic value for these chimpanzees.