Evaluation of geochemical characteristics and health effects of some geophagic clays southern Nigeria.

Abstract

The geochemical characteristics of geophagic clays from Calabar and Okon-Eket, southern Nigeria were evaluated to determine their quality and the possible health effects of their consumption. The study involved the measurement of the pH, electrical conductivity (EC) and total dissolved solids (TDS) of the slurried clay samples soaked in distilled water for 48 h using digital multi-parameters probe as well as the elemental and mineralogical analyses of twenty geophagic clay samples for elemental and mineralogical constituents using both the ICP-MS and XRD, respectively. Medical data were also mined from medical facilities within the area in addition to the administering of questionnaire to adults involved in the geophagic practices in order to determine their justification for the practice as well as their and clay preferences. Results of physicochemical measurement revealed that the pH range of the samples ranges from 3.9 to 6.9 and 6.5 to 7.0; EC 0.3-377.7 and 0.12-82.38 µS/cm; TDS 1.98-2,432.65 and 0.08-52.95 mg/L for consumed and non-consumed clay, respectively. The elemental analyses revealed that the concentration of some potential harmful elements, PHEs, exceeded the recommended dietary intake by humans. This is especially true for Cu (9.1-23 ppm), Pb (16.7-55.6 ppm), Zn (13-148 ppm), Ni (11.1-46.4 ppm), Co (1.8-21.7 ppm), Mn (16-338 ppm), As (BDL-15 ppm) and Cd (BDL-0.2 ppm). The predominant phases established in the clay samples are quartz and kaolinite, while the minor minerals were montmorillonite and muscovite in all the clay samples. Respondents revealed that capacity for relief from gastrointestinal problems believes in the curative power to cure skin infections and cultural reasons as main justification for the geophagic practices. This is, however, not in conformity with information gleaned from the medical records which still indicated that the prevalent diseases in the area still include gastrointestinal problems in addition to malaria, hypertension and cardiac failure with minor cases of respiratory tract infections. The high concentrations of the PHEs may be responsible for or contribute in part to the prevalence of hypertension, cardiac failures and gastrointestinal problems within the study areas. Though the kaolinite present in the geophagic clays makes them suitable for use as traditional antacids; however, the toxic trace element concentrations and significant quartz content will most likely mask the beneficial effects of such kaolinite.