Overview
Ijeoma and colleagues bought two types of edible clay (a kaolin type and a bentonite type) at four Onitsha markets in 2013 and measured zinc, lead, cadmium, copper, mercury and cobalt by flame AAS after aqua regia digestion. Mercury was present in every sample and above the cited 0.3 ppm food limit in most, while lead was detected only in one bentonite-type sample from Ochanja market. Cadmium was detected in samples from two markets.
Key numbers
- Mercury: Ochanja market mean 2.335 ± 0.276 ppm, other markets 0.251 to 0.796 ppm (Table 6).
- Lead: 3.171 ± 0.064 ppm in the bentonite-type clay from Ochanja; not detected in all other samples (Table 3).
- Cadmium: kaolin-type clay from Ochanja 1.027 ± 0.442 ppm and Ose 0.282 ± 0.080 ppm; not detected at Relief and Okpoko (Table 4).
- Zinc was higher in the bentonite-type clay (10.332 ppm) than the kaolin type (2.737 ppm) (Table 2).
Methods (brief)
Clay was ground, sieved, oven-dried at 100 °C, digested in aqua regia and analyzed on an FS240 flame AAS (detection limit 0.001 ppm). Results are means ± SD of three replicate measurements on a dry basis. No reference material or recovery data are reported.
Evidence Fitness
A small single-city survey with no QA beyond calibration. Mercury by flame AAS is unusual and may be unreliable, and some printed means (copper) do not reconcile with their own cells. The DOI is not printed in the PDF; title, journal, volume and pages match the manifest. Direct evidence for clay-geophagy; only a proxy for cosmetic-clay, which is a non-food use and should not be read against food bands.