Overview
Asowata sampled the layers of an artisanal clay pit near Benin City that miners dig for eating, plus the discarded upper layers, and measured mineralogy by XRD and 13 trace elements by ICP-MS after aqua regia digestion. Lead was found in every sample, at 13 to 18 mg/kg in the consumed clay. Intakes at an assumed 20 g a day were compared with ATSDR minimum risk levels and recommended intakes.
Key numbers
- Lead, consumed clay (n = 8): mean 14.4 mg/kg, SD 1.85, range 13.0 to 18.0 mg/kg (Table 2).
- Chromium, consumed clay: mean 24.3 mg/kg, range 17.0 to 29.0 mg/kg (Table 2).
- Nickel, consumed clay: mean 14.6 mg/kg, maximum 22.0 mg/kg (Table 2).
- Discarded upper-layer clay had similar lead (mean 14.25 mg/kg) but lower nickel (3.44 mg/kg) (Table 2).
Methods (brief)
Air-dried, pulverized clay (0.5 g) was digested in aqua regia at 95 °C and analyzed by ICP-MS (PerkinElmer Avio 200) under an ACME laboratory protocol with blanks, certified reference materials and 20 percent duplicates. Detection limits were 3.0 mg/kg for lead and 1.0 mg/kg for most other elements. Arsenic, cadmium and mercury were not measured.
Evidence Fitness
Eight consumed-clay samples from one pit, collected at the source rather than bought, so they show what enters local trade but not market variability. Lead is the only one of the four main toxic metals reported. A nickel minimum below the detection limit and a zinc maximum attributed to a nonconsumed sample are small reporting inconsistencies. Direct evidence for clay-geophagy.
Related evidence
- Clay and geophagy
- Assessment of Heavy Metals in Edible Clays Sold in Onitsha Metropolis of Anambra State, Nigeria
- Lead
- Chromium
- Nickel
Update history
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