Assessing the Bioavailability of some Trace and Major Elements in Geophagical Clays of South-Western and Eastern Nigeria: An Invitro Study

  • Collins O. Eigbike
  • Isaac O. Imasuen
  • Festus Obomese
  • Daniel Imariabe Omoruyi
Keywords: Geophagical clay, Bioavailability, Invitro bio-accessibility, Major element, Trace element


Geophagy is the deliberate ingestion of soil. This study aims to assess the bioavailability of some trace and major elements in the edible clays of southern parts of Nigeria; in order to ascertain the essential elements and possible potential harmful elements that is bioaccessible and bioavailable to the geophagists. Raw and roasted samples were collected at the mining sites and from market vendors in Aforwa, Ohordua, Uzalla and Nteje. Physiochemical, geochemical and mineralogical compositions were quantified using various analytical equipment. The bio-accessible contents of some trace and major elements were determined by invitro bio accessibility tests that mimic the conditions of the human gastrointestinal environments. The colour of the clays ranges from whitish, to grey; the materials are dominantly clayey size particles. The pH is acidic with moderate to low CEC in all the samples (2.84 meq/100g). A range of elements was identified. The geophagic materials are majorly kaolinite, with other range of minerals like quartz, goethite, hematite. The concentration of the bio accessible elements in the 2-part acidalkaline invitro physiologically based test at 5g dose shows low bio accessibility of most elements but at higher dose of 20 g, the concentrations of the bio-accessible elements in the roasted samples were increased supplying 0.07-80% (Fe>Cu>Zn>Mn>Ca>Mg>P>K) nutrients based on the reference nutrients intake required by the geophagists. The Nteje clays are the highest supplier while, the Ohordua is the least supplier of both the trace and major elements, hence the edible clays are a moderate source of mineral nutrients and potential source of potential harmful elements (V, Ni, Cr, and Pb), and if consumed in excess or even at lower concentration may pose toxic effects to the consumers. Moderate dose of this material that is within and/or below the Safe Upper levels should be consume since geophagy has become inherent to human.


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