Geophagia clay soil as a source of mineral nutrients and toxicants

Abstract

Geophagia, which involves ingestion of non-food lithospheric substances, is the major form of pica in many African cultures. A common lithospheric pica substance ingested in the Cape Three Point region of West Africa, particularly Ghana and Togo, is a white loamy clay soil. This clay soil is usually ingested by women of reproductive age. Some of the reasons assigned to clay geophagia include appealing flavour, to alleviate nausea during pregnancy, and for absorption of toxins in the gastrointestinal tract. Some speculation indicates that geophagia may be an attempt to replenish mineral nutrients in undernourished persons. The study of the acid extractable mineral contents of this white clay soil was done to provide information on the mineral contents that could potentially be absorbed in the gastrointestinal tract. Results showed that the clay soil was very dry with mean moisture content of 0.19±0.01%. On dry weight basis, the geophagia clay soil contained (mg/100 g) aluminium, 1,239.6; iron, 962.9; lead, 2.4; magnesium, 64.3; and zinc, 54.6. The extractable mineral contents of this clay soil, on dry weight basis, were (mg/100 g): zinc, 1.40±0.05; iron, 14.19±0.13; magnesium, 23.83±0.31; and aluminium, 37.91±2.94. Compared to the total minerals contents of the clay soil, the acid extractable fractions represented 2.6% of zinc, 1.5% of iron, 36.4% of magnesium, and 3.2% of aluminium. Even though lead was not detected in the acid extracts, a small amount was detected in the dry clay soil. Arsenic was not detected in any clay sample or extracts. It was concluded that the main mineral nutrient potentially contributed by this clay pica substance was iron. The clay soil liberated a substantial amount of iron (14.2 mg/100g), which constituted 78.9% of the 18 mg/d iron RDA for women of reproductive age and 53.0% of the 27 mg/day iron RDA for pregnant women. The potentially undesirable effect of ingesting this clay soil is the high level of aluminium (37.9 mg/100g). Key words : Geophagia, pica, pregnancy, clay, iron