ABSTRACT
This study was conducted to examine the physical, chemical, mineralogical, geotechnical and phytochemical properties of seven samples of edible clay from Aforwa, Ubiaja, Uzalla (Benin Area), Ohordua Area, (Edo State) and Achalla Area (Anambra State) in order to determine potential human health risk as well as beneficial effect associated with their consumption and cosmetic use. From the geochemical data obtained by XRF, SiO2 (54.64, 55.70, 45.70, 46.88 and 54.95%), and Al2O3 (27.90, 29.20, 35.20, 36.56 and 26.40%) are the dominant oxides indicating that the samples are basically hydrous alumino-silicates. Calculated chemical index of alteration (CIA) of the clay samples ranges from 89.61 % (Achalla) and 95.18% (Ohordua) while the chemical index of weathering (CIW) ranges from 92.63% (Achalla) and 99.32% (Ohordua) which indicates a high degree of weathering of the clay samples. The clay minerals present from XRD are Aforwa (Illite-Smectite, Illite-Muscovite), Ubiaja (Illite-Muscovite and Kaolinite), Uzalla (Chlorite, Illite-Smectite and Illite-Muscovite), Ohordua (Smectite, Illite-Mica, Kaolinite and other clay minerals) and Achalla (Illite-Smectite, and Kaolinite). Most of the clays are interlayered clays. Mineral impurities in the clays are; quartz, jarosite, albite, anatase, orthoclase, microcline, hematite, calcite, pyrite, and gypsum. Apart from Ohordua and Ubiaja samples that has 2% and 5% sand respectively; the clay samples in terms of grain size are more of silt and clay which makes them texturally fine grained. Liquid limit range is 41% in Aforwa to 54% in Uzalla, plastic limit of 16.56% in Ubiaja to 19.51% in Uzalla, plasticity index of 21.96% in Aforwa to 36.44% in Ubiaja, Moisture content of 4.71% in Ubiaja to 35.24% in Uzalla, specific gravity of 2.00 in Ubiaja to 2.47 in Uzalla and swell of 0.00 in Aforwa to 50% in Uzalla. Also, raw and smoked samples of Achalla and Uzalla were compared to others that were not processed, results shows that pH range from 4.57 to 5.50, Organic matter of 0.78 to 5.66, CEC of 1.78 to 3.76, EC 2.65 to 7.23 and water retention of 19.23 to 62.05. Colour ranges from light gray to brown in Achalla raw and smoked and white to strong brown in Uzalla raw and smoked respectively. Ohordua and Aforwa were gray and light gray respectively. Naphthalene(NA), Acenaphthene (AC), Acenaphthylene (ACN), Fluorene (FL), Phenanthrene (PHE), Anthracene (AN), Fluoranthene (FA), Pyrene (PY), Benz[a]anthracene (B[a]A) were the polycyclic aromatic hydrocarbon (PAH) detected in the samples. Total PAH (mg/kg) range from 0.00 in Achalla and Uzalla smoked to 0.81 in Ubiaja. For the phytochemicals Glycosides, Alkaloids and Phenolics were detected in all the clay samples, while Achalla raw had Eugenols. Bioavailable nutrients range: Na (4.64 to 9.92), Ca (2.57 to28.54), Mg (0.02 to 0.40), Fe (2.50 to10.01), Mn (0.13 to 0.52), Cu (0.07 to 0.73), Pb (0.02 to 0.08), Cr (0.32 to 1.26), V (0.10 to 0.38) and Ni (0.20 to 0.80) mg/kg respectively. From the data, the various clay samples meet the standard use for cosmetic and consumption but smoking tend to be beneficial for the reduction of the PAH and hence should be applied apart from its impact on taste.
