Yashim et al. 2020 - metals in hair dyes sold at Samaru market, Nigeria

Yashim and colleagues measured Pb, total Cr, Cd, Ni, and Cu in hair-dye products sold at Samaru market in Zaria, Nigeria. The paper reports mg/kg concentrations for four product-form composites: pure mineral dye, henna dye, black shampoo oil, and black shampoo jelly. The study is useful as C-tier finished-product occurrence evidence because the sampling frame is small and composited, no DOI is printed, and the source contains several figure/prose inconsistencies.

Key numbers

• Article identity: Nigerian Research Journal of Chemical Sciences 8(2):241-251; no DOI printed in extracted text.
• Sample frame: 25 samples of each hair-dye product form were purchased from different locations in Samaru market, Zaria, Nigeria. Solid pure mineral dye and henna samples were separately mixed/ground into composites; viscous black shampoo oil and black shampoo jelly samples were separately drained/mixed into composites.
• Analytical concentration basis: all occurrence values below are source-reported mg/kg; no conversion to ppm was performed even though the paper compares its values with ppm limits and literature.

Abstract concentration summary (mean ± reported error, mg/kg):

• Lead, Results/Figure 1: the narrative gives pure mineral dye 97.1 ± 0.013 mg/kg, henna dye 19.50±0.003 mg/kg, black shampoo oil 5.52±0.007 mg/kg, and black shampoo jelly 6.67±0.007 mg/kg; the abstract gives black shampoo oil 5.52±0.003 mg/kg and black shampoo jelly 6.76±0.007 mg/kg.
• Chromium, Results/Figure 3: pure mineral dye has the highest total-Cr value 42.45±0.001 mg/kg, followed by black shampoo jelly 7.36±0.004 mg/kg, henna dye 7.20±0.000 mg/kg, and black shampoo oil 3.92±0.004 mg/kg. The abstract gives pure mineral total Cr as 42.45±0.002 mg/kg.
• Nickel, Results/Figure 4: pure mineral dye 7.40±0.008 mg/kg, henna dye 6.60±0.005 mg/kg, black shampoo jelly 5.76±0.004 mg/kg, and black shampoo oil 5.68±0.010 mg/kg.
• Cadmium, Results/Figure 5: henna dye 5.40±0.002 mg/kg, pure mineral dye 3.80±0.005 mg/kg, black shampoo oil 1.50±0.013 mg/kg, and black shampoo jelly 1.20±0.002 mg/kg.
• Copper, Results/Figure 2: pure mineral dye 65.10±0.003 mg/kg, black shampoo oil 33.60±0.001 mg/kg, black shampoo jelly 30.50±0.029 mg/kg, and henna dye 22.00±0.001 mg/kg; the abstract instead prints black shampoo jelly Cu as 3.50±0.029 mg/kg.
• Source-side Health Canada comparators quoted by the paper: Pb 10 ppm, Ni 5 ppm, and Cd 3 ppm. The paper states that Pb and Cd in the synthetic dye products were below the comparator, while pure mineral and henna dyes carried higher heavy-metal concentrations and greater source-side health concern. These are source-side comparators, not HMTc thresholds.
• Statistical test: the paper reports one-way ANOVA with Tukey post hoc comparison at 95% confidence and states that metal levels differed significantly across studied samples (p < 0.05).

Methods (brief)

The authors bought hair-dye samples from different locations in Samaru market in Zaria, Nigeria. A total of 25 samples was collected for each of four product forms. The solid pure mineral dye and henna dye samples were separately mixed and ground to form composite powdered samples; the viscous black shampoo oil and black shampoo jelly products were separately drained into a 150 cm3 beaker and mixed to form composite samples.

For the solid products, 1 g of powdered hair dye was digested with 20 cm3 of concentrated HNO3 and HCl in a 3:1 ratio. For viscous products, 1 g was digested with 15 cm3 of concentrated H2SO4 and H2O2 in a 2:1 ratio. Digests were cooled, filtered through ashless Whatman No. 42 paper into 100 cm3 volumetric flasks, and diluted to volume with distilled water. Pb, Cd, total Cr, Ni, and Cu were measured by atomic absorption spectrophotometry using a model AAS-HP MY14470001; analysis was done in triplicate.

Speciation: the paper reports elemental Pb, Cd, Ni, Cu, and total Cr only. It discusses Cr(VI) toxicity in background text, but the analytical results are total Cr and should not be interpreted as Cr(VI).

Implications

Certification (HMTc): This is direct finished-product occurrence evidence for hair-dye and dye-shampoo product forms sold in the Nigerian market, but it is C-tier because the measured rows are composites rather than individual samples and because QA/QC details are sparse. The values should be used as occurrence context, not as a representative distribution.

Courses: The source is a compact example of preserving units and speciation while handling inconsistent source reporting. It also shows why sample-size notes matter: the study purchased 25 samples per product form but reports only four composited analytical rows.

App: If adult hair-product profiles are expanded, this source can support a Nigeria-market context card for hair dyes and dye shampoos. It should not be used to claim Cr(VI) occurrence or to rank named brands; the product forms are generic.

Wiki pages this source may touch

• permanent-hair-dyes-tints
• hair-dye-rinse-off
• shampoo-adult
• lead
• chromium
• cadmium
• nickel
• copper

Verification notes

• PDF text was extracted with pdftotext -layout to /tmp/mfk_june8_hair_dyes_risk.txt. The title/byline, abstract, sample collection/preparation text, digestion/AAS methods, Results/Figures 1-5, conclusion, and references were checked against this page.
• No DOI is printed in the extracted text. Title text, raw handle MFK_evaluation-of-heavy-metals-level-in-hair-dyes, raw SHA-256 f0e4e10d9950ecc9f49a408c447249afcb1489f2835754a2a99633fadd2e99fa, and candidate cite-key yashim2020-hair-dyes-metals-nigeria were searched before creation; no existing source page was found.
• Units are copied exactly as mg/kg; no conversion to ppm, µg/g, or ppb was performed.
• Speciation: chromium is recorded as total Cr. The paper discusses hexavalent chromium in toxicology background text, but it does not measure or report Cr(VI).
• Source-side inconsistencies retained rather than corrected: black shampoo jelly Cu is 3.50±0.029 mg/kg in the abstract but 30.50±0.029 mg/kg in the Results/Figure 2 text; black shampoo jelly Pb is 6.76±0.007 mg/kg in the abstract but 6.67±0.007 mg/kg in Results; black shampoo oil Pb has the same mean but different reported error (±0.003 in the abstract, ±0.007 in Results); and pure mineral total Cr has ±0.002 in the abstract but ±0.001 in Results.
• Brand firewall: the source describes generic product forms rather than named brands, so no brand-linked contamination values were present to suppress.
• Evidence tier: C because the study is a small peer-reviewed market survey with primary AAS measurements, but no DOI, no sampling year, no LOD/LOQ, no CRM/recovery, limited QC reporting, four composited analytical rows, and several source-side inconsistencies.
• Routing: all product slugs used in frontmatter appear in docs/gpt-collaboration/taxonomy-snapshot.md. The taxonomy lacks a precise adult dye-shampoo product slug, so the source routes broadly through hair-dye-rinse-off, permanent-hair-dyes-tints, and shampoo-adult.

Page history

The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.