Nkosi and Thembane characterized red and white clays bought at Durban Berea Market, where the material was sold for topical sun protection and cultural uses. X-ray fluorescence of the dried, ground samples reported lead at 27 and 16 ppm and total chromium at 130 and 560 ppm in red and white clay, respectively. These are measurements of two market clay samples, with analytical sensitivity and chromium speciation unreported; they do not establish exposure, clinical effects, or metal concentrations in formulated cosmetics.
Key numbers
Table 6 (PDF p. 6) reports the following elemental concentrations in ppm. Both samples originated from uMzinyathi, KwaZulu-Natal, reported at 29°30′0″ S, 30°56′0″ E, and were purchased in Durban. Values refer to material oven-dried at 40°C for approximately 48 hours, ground, and passed through a 50 µm sieve. They are preserved on that preparation basis; the paper gives no moisture correction for conversion back to market material.
Section 3.1.9 states that Mn and nickel (Ni) were detected only in red clay, supporting interpretation of the white-clay dashes as nondetections. No detection or quantification limits are reported, so these entries cannot be assigned a numerical upper bound or treated as zero. The same section describes arsenic (As), mercury (Hg), cadmium (Cd) and Se as absent, and describes Th and uranium (U) as absent at detectable levels (pp. 6–7), without tabulated measurements or analytical limits. Those statements are qualitative observations, not quantified nondetection results.
The abstract identifies two samples. Table 6 gives one result per clay and element without a metal-specific replicate count, standard deviation, or uncertainty. Table 7 (p. 7) identifies different mineral mixtures: red clay contains illite 56.7%, quartz 31.3%, albite 9.9% and vermiculite 2.0%; white clay contains illite 34.5%, albite 33.8% and montmorillonite 31.7%. The two clays therefore provide a local material comparison, not an estimated geographic distribution. Sampling dates, seasonal comparisons and historical trends are not reported.
Methods (brief)
The authors describe market-purchased hardened clay balls, reported as harvested from uMzinyathi. After oven drying, grinding and sieving, metals were measured with a Vanta handheld C Series XRF analyzer using a 50 keV rhodium-anode tube and silicon drift detector (Section 2.2, p. 2). XRF results are elemental totals; no Cr(III)/Cr(VI), inorganic arsenic, methylmercury, extraction-based bioaccessibility or skin-release analysis was performed. The paper does not report XRF calibration materials, recoveries, LODs, LOQs or replicate precision. Descriptions of triplicate spectrophotometry and duplicate microbiology do not establish an XRF replicate count.
Other characterization used XRD, FTIR, scanning electron microscopy, physicochemical measurements, in vitro UV absorbance and antimicrobial disk diffusion. These assays characterize the sampled clays; they do not measure dermal absorption, absorbed dose, or adverse effects in people. The authors explicitly identify metal binding and exchangeability as questions for further study.
Implications
Evidence Fitness: direct occurrence evidence for prepared cosmetic clay from one South African sourcing location, with a narrow sampling frame and incomplete analytical validation. It supports keeping red and white material separate when reporting lead (Pb), total chromium (Cr), Ni and the other measured elements. It does not support total-Cr substitution for Cr(VI), a general South African market prevalence estimate, or transfer of these concentrations to foods, dietary clay supplements or infant sunscreen formulations.
The material was marketed for direct topical use and also considered as a cosmetic ingredient. Its preparation and unreported detection limits matter when comparing it with other clay studies. Concentration alone cannot show how much metal transfers from mineral structures to skin or becomes absorbed. The paper’s discussion of permissible concentrations and health consequences is not an independently verified legal or clinical assessment of these samples.
Related evidence
- Cosmetic clay
- Sun/suntan products (including spray, self-tan, airbrush)
- Lead
- Chromium
- Nickel
- Titanium
- Vanadium
- Manganese
- Iron
- Zinc
Update history
The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git.
| Commit | Date | Change | Description |
|---|---|---|---|
| e626490c3e | 2026-09-10 | correction | 6 sections added; narrative text revised |