Differences and Commonalities in Physical, Chemical and Mineralogical Properties of Zanzibari Geophagic Soils

Abstract

The function of human geophagy has long been questioned. We sought to test hypotheses concerning its potential physiological effects through analysis of soils and patterns in geophagy behavior. Eleven samples of geophagic soils consumed by pregnant women on Pemba Island, Zanzibar, Tanzania, were characterized according to their color, texture, major element chemistry, trace element chemistry, bulk mineralogy, and clay mineralogy. An epidemiological study (N = 2367) and ethnographic interviews (N = 57) on Pemba yielded information about geophagic behaviors and socio-demographic and biological characteristics of those who consumed earth. The soils varied widely in color, ranging from light red to white through various shades of brown and yellow, and texture ranged from clay to sand. Major element chemistry of the soils also varied greatly; most were low in Fe and Ca. Trace elements, whether of biological or non-biological significance, were uniformly low when compared with normal ranges of mineral soils. The sole commonality among the samples is that all clay fractions were dominated by a kaolin mineral: kaolinite, halloysite, or a mixture of both. Geophagy behavior also varied greatly, with one major exception: a greater proportion of pregnant women (7.1%) and young children (4.5%) consumed earth than non-pregnant women (0.2%) or men (0%). The presence of kaolin mineral in all samples, its palliative and detoxifying properties, and the highest prevalence of geophagy among those most biologically vulnerable suggest that geophagy may be a protective behavior.

Association of Pica with Anemia and Gastrointestinal Distress among Pregnant Women in Zanzibar, Tanzania

“…Furthermore, mineralogic analyses of 12 samples of Pemban geophagic earth indicated the presence of kaolin, which is consistent with this hypothesis. 29 Finally, the association between hookworm and both types of pica ( Table 3 ) could be interpreted as consistent with this hypothesis. It may be that pica is a response to parasitic infection, as is thought to be the case among various species of freeliving primates.…”

“…In Pemba, as in most parts of the world, earths are carefully selected and prepared by heating or cleaning before consumption. 15,29 Pica behaviors were asked about at multiple time points, including at any time during the current pregnancy, at the time of the baseline interview, and two weeks after delivery. Information on current pica practices was available for 2,367 of the 2,368 women enrolled, and on post-partum pica practices for 1,578 of the sample (66.7%).…”

“…Consideration of the physical and chemical structure of soils and starch provides some evidence that these dry, powdery substances may reduce micronutrient absorption by consumers. Pemban geophagic soils contain clay, 29 and clays often have a high cation exchange capacity, which means they are good at binding cations such as Fe 2+ . 56 However, the capacity of Pemban clays to bind heme or the binding capacity of raw rice for inorganic or heme iron have not yet been determined.…”

The past, present, and future of soils and human health studies

“…Phytoremediation of both heavy metals and organic chemicals has received attention (Tu et al, 2002;Cho et al, 2013;Ye et SOIL, 1, 35-46, 2015 www.soil-journal.net/1/35/2015/ E. C. Brevik and T. J. Sauer: The past, present, and future of soils and human health studies 39 al., 2014), as well as human exposures to contaminates obtained by plants through soils and passed up the food chain (Khan et al, 2008;Zhuang et al, 2009;Roy and McDonald, 2013). Work in geophagy frequently gets tied into these studies, because the deliberate ingestion of soil can lead to exposure to hazardous materials and soil organisms (e.g., Wilson, 2003;Abrahams, 2005;Shigova and Moturi, 2009;Young et al, 2010;Henry and Cring, 2013). The health effects of dust generated from soil sources has also seen recent interest.…”

Co-effect of Leached Metals and pH of Simulated Gastric Fluid on the Survival of Microorganisms in Geophagic Clays

“…Geophagia is the most encountered form of pica, which is defined as the deliberate consumption of soil and related materials [2]. It is a very extensive practice in all continents of the world, and has been reported in Africa, Asia, South America, North America [3,4]. Geophagia has been reported commonly in pregnant women and children [5].…”