Beyond consumption: a multi-pathway human health exposure risk assessment of potentially toxic elements in geophagic soils of Botswana

Geophagy, the deliberate consumption of earth materials, is a practice widely reported throughout human history; however, its potential health risks are poorly documented in Botswana. This research aimed to characterize geophagic soils based on their geochemical and mineralogical properties and to assess the potential human health risks associated with exposure via multiple pathways. Samples from six geophagic hotspots were analysed for macro elements (K, Ca, Mg, and P), microelements (Cu, Cr, Ni, Fe, Zn), and potentially toxic elements (PTEs) (As, Pb, Cd, Hg). Geochemical ratios from the United States Environmental Protection Agency (USEPA) were used to compute human health risk indices (HRIs), including carcinogenic risk (CR) and non-carcinogenic risks (hazard quotient (HQ) and hazard index (HI)). Mineralogy of the clay-sized fractions indicates the presence of kaolinite, goethite, illite, calcite, and muscovite. The average concentrations of macro elements followed the order: K (1.43%) > Ca (0.88%) > Mg (0.47%) > P (0.012%), while the average contents for microelements were Fe > Cu > Cr > Ni > Zn, and PTEs ranged as follows: Pb > As > Hg > Cd with Pb having a mean concentration of 15.16 mg kg⁻¹ and As 1.92 mg kg⁻¹ respectively. The HIs of the PTEs for all three exposure pathways are below 1 for both adults and children. Ni, Cr, and As have the highest mean CR values, which fall within the acceptable range of 1.00E−06 to 1.00E−04 for both adults and children for exposure through oral consumption and dermal contact, while the mean CR values for exposure through inhalation are all below 1.00E−06. Thus, exposure to PTEs in the soil is unlikely to pose health risks. Nevertheless, caution is necessary as cumulative exposure from other sources could significantly increase the overall health risk to practitioners.