"Earth eaters": Ancient and modern perspectives on human geophagy

Abstract

Every person reading this chapter has eaten soil. For many, especially the wellto- do and those residing in a developed country, this statement may come as a surprise, but such people will have ingested soil if only accidentally. This involuntary consumption may arise, for example, through the transfer of fine (i.e., typically >250 ?m) soil particles that adhere to fingers into the mouth. Young children up to the age of about 4 years are especially prone to this route of exposure, since they use their mouths as a means of exploration (Fig. 23.1) that includes so-called hand-to-mouth activity. Professional judgment suggests that such behaviour leads to toddlers ingesting more soil than children of other ages, who in turn consume more than adults (Calabrese and Stanek 1994). How much soil is ingested involuntarily depends on a variety of factors such as the effectiveness of food preparation procedures in removing adhering soil particles from vegetables and other foodstuffs, personal hygiene, and professions that can bring some people into close contact with soil. Much further research needs to be undertaken on quantifying the rates of involuntary soil ingestion, but investigations on young children to date has indicated a range from less than one to the low hundreds of milligrams per day (e.g., Binder et al. 1986; Calabrese et al. 1997; Davis and Mirick 2006; Van Wijnen et al. 1990). Studies on adults are even more limited than those investigating children, but occupational exposure to soil may result in more variable rates of daily ingestion (Davis and Mirick 2006). An investigation on just 10 subjects indicated that the "average adult" ingested 10 mg/day (Stanek et al. 1997). Considerable surprise is expressed by many when they learn that some humans also deliberately consume soil. This practice, known as geophagy or geophagia-the name is derived from two Greek words, ge- (earth) and phag (eat)-is the most reported form of pica, defined here as a craving for oral ingestion of a given substance that is unusual in kind and/or in quantity (Lacey 1990). Soil-pica involves the recurrent ingestion of unusually high amounts of soil, on the order of 1000-5000 mg/day according to the U.S. Agency for Toxic Substances and Disease Registry (ATSDR 2000), although many geophagists consume significantly more than this. Considering that even the involuntary ingestion of soil has important health implications to humans, being a potentially significant pathway of exposure to environmental pollutants for example, it can be appreciated that the higher rates of soil consumption by geophagists has important consequences. Such implications to health are discussed in a later section of this chapter, along with an assessment on the causes of geophagy. Initially, to appreciate the fact that the deliberate ingestion of soil is more common than many people suspect, the following section considers the geophagical practices of humans from both a historical and geographical perspective.