Overview
Oyebanjo and colleagues sampled 13 kaolinitic clays that are eaten in Nigeria, six from the Cretaceous Lakiri deposit and seven from the Paleogene/Neogene Ubulu-Uku deposit, and measured vanadium, chromium, cobalt, nickel, copper, zinc and lead by laser ablation ICP-MS and iron by XRF. They then estimated hazard and cancer risk indices for children and adults. Lead is the only one of the four priority metals reported; arsenic, cadmium and mercury were not measured.
Key numbers
- Lead, Cretaceous clays (n = 6): mean 35.16 mg/kg, SD 23.65, range 18.93 to 80.69 mg/kg (Table 2; SD from Table 3).
- Lead, Paleogene/Neogene clays (n = 7): mean 30.96 mg/kg, SD 8.99, range 19.63 to 42.69 mg/kg (Table 2; Table 3).
- Highest single lead value: 80.69 mg/kg in sample LP2 4 m (Table 2).
- Chromium means 143.54 and 113.45 mg/kg; nickel means 62.42 and 21.68 mg/kg (Table 2).
Methods (brief)
Samples were air-dried and gently pulverised without sieving, so they were analysed in the form in which they are eaten (dry basis). Trace elements were measured by 193 nm laser ablation on an Agilent 7700 ICP-MS, with USGS BHVO basaltic glass and powder as reference standards; iron by XRF on fused beads. Stated lead LOD and LOQ were 0.004 and 0.06 mg/kg.
Evidence Fitness
Direct evidence for the clay-geophagy page: the clays are sampled from deposits used for geophagy, not bought at market, and the sample is small (13 samples from two sites). Results are total element content in dry clay, not bioaccessible fractions. Collection dates are not reported. The “other studies” rows in Table 2 are quotes from earlier work and are not part of this study’s data.
Related evidence
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