Analysis of geophagy soils in Kibale Forest, Uganda

Four soil samples from the Kibale Forest, Uganda, representative of material regularly ingested by chimpanzees, were studied for their mineral, chemical, and geochemical composition. These geophagy soils have a high content of metahalloysite, a partially hydrated clay mineral that may act much like the pharmaceutical Kaopectate™. Among the elements that may act as a stimulus or stimuli for geophagy behavior, only iron is very high (total iron ranges from 6% to 17%); other possibilities such as calcium, chromium, cobalt, bromine, and iodine are either relatively low or are below their detection limits. Chlorine is below detection limits which eliminates sodium chloride as a possible stimulus. Depending on relative availability in the gut, iron offers the most likely chemical stimulus for geophagy and given the mineral composition of the samples, metahalloysite is the most likely mineral stimulus. Iron may play a role in replenishing hemoglobin which would be important in chimpanzee physiology at high elevations near the flanks of the Ruwenzori Mountains. Metahalloysite, which in this case exists in a relatively pure crystalline form, may well act to quell symptoms of diarrhea and act similarly to Kaopectate™. Organic chemical analyses indicate only traces of organic matter and no humic acids in the K14-E14 sample.