Mineral composition and heavy metal risk assesment of selected geophagic soils from Tanzania

Abstract

Geophagy or Pica is the unintentional traditional behavior of eating soil by indigenous people in different countries. practiced in many countries due to nausea among pregnant women and mineral deficiencies without knowing the associated health risks. In this study the mineral composition of geophagic soil and its associated health risk among consumers was determined. Dry soil sticks consumed by women were obtained from open markets in Morogoro, Njombe and Mwanza regions in Tanzania. The elemental concentration of geophagic soil was analyzed using Flame Atomic Absorption spectrophotometer. Health risk assessment methods were used to obtain health information after chronic exposure to geophagic soils. The tests used were Target Hazard Quotients (THQ), Total Target Hazard Quotients (TTHQ) and Cancer Risks (CR). The concentration range of metals in samples obtained from three different regions were 16,335.7-47,773.7 mg/kg for Fe, 46.2-1073.5 mg/kg for Ca, 155.3-514.9 mg/kg for K, 44.5-112.4 mg/kg for Zn, 40.7-95.1 mg/kg for Na, 2.4-66.7 mg/kg for Cu, 109.5-572.6 mg/kg for Mn, 3.8-6.85 mg/kg for Pb, 3.1-93 mg/kg for Ni, 62.7-638.6 mg/kg for Cr and 0.4 mg/kg for Cd. The Provisional Daily Intake (PDI), THQ, TTHQ and CR ranged between 3.0 × 10^-3 -34.12 mg/kg/day bw, 0.043-48.75, 34.52-77.36 and 2.55×10^-5- 0.23 respectively. The TTHQ>1 was evident for metals in all sampling sites which is indicative of non-carcinogenic health effects. Prolonged exposure to Pb at low concentrations in samples from all the sites can cause pathological effects. The cancer risk values for Pb, Ni, Cr and Cd were <1 in which the consumer is likely not to develop cancer in a life time. Essential minerals - Fe, Ca, Zn, Na, K and toxic metals Pb, Cr, Ni and Cu were detected in all the samples. Cd occurred only in samples from Mwanza region that was below the tolerable daily intake. According to WHO/FAO expert's joint committee any amount of Pb consumption is not permitted. Given the presence of essential minerals in the geophagic soils which are however accompanied by toxic minerals in some cases which might have carcinogenic effects, prolonged consumption should be discouraged to avoid risks of serious adverse effects to the health of the general population.

Keywords: Cancer Risk; Geophagy; Mineral composition; Tanzania; Target hazard quotients.

Graphical abstract

Fig. 1

Geophagic soil sampling sites in different parts of Tanzania”.