Overview
This Toxicology Reports paper measures copper, cadmium, mercury, lead, manganese, and nickel in 11 commercial black hair dye products on the Khartoum market using FAAS, then conducts exploratory biomonitoring in 19 women (10 FAAS plasma samples, 9 GFAAS whole-blood samples for lead (Pb), cadmium (Cd), Cu, As), and applies a dermal risk assessment framework using EDI, HQ, HI, and LCR. Manganese and lead were the predominant contaminants; two European-regulated cream products contained no detectable metals, contrasting with Asian-origin powdered and stone-based formulations. All three products with detectable lead exceeded the EU technically avoidable limit of 2 ppm. The source is not directly relevant to children’s makeup; it was included in this deposit as broad cosmetic heavy metal context.
Key numbers
All product concentrations are in finished hair dye as placed on market, measured by FAAS after acid digestion (HCl/HNO3 3:1 or HNO3/HClO4 1:1 for mercury). Units are ppm (mg/kg).
Method validation parameters
LOD (mg/L): Cd 0.125, highest LOD for nickel (Ni) 4.01.
LOQ (mg/L): 0.378 to 12.16.
Linearity (R squared): 0.9676 to 0.9995.
Precision (RSD): below 2%.
Recovery: 97.6 to 99.2%.
Product concentrations (Table 2; ppm = mg/kg)
Manganese: HD-J (Indian powder) 294.8 ppm; HD-C (Indian powder) 163.4 ppm; HD-I (Indian powder) 155.2 ppm. The other eight products had lower or non-detectable manganese; Table 2 values not fully tabulated in available text.
Lead: detected in three products only. HD-E: 29.5 ppm; HD-J: 17.5 ppm; HD-L: 7.99 ppm. All three exceeded the EU technically avoidable limit of 2 ppm for lead in cosmetics. The remaining eight products had lead below the LOQ.
Mercury: HD-H 0.929 ppm; HD-E 0.136 ppm; HD-A 0.008 ppm. The remaining eight products had mercury below the LOQ.
Cadmium: HD-D 0.853 ppm; HD-L 0.123 ppm. Remaining nine products below LOQ.
Nickel: HD-C 6.10 ppm; HD-B 2.30 ppm; HD-A 1.70 ppm; HD-J 0.79 ppm. Remaining seven products below LOQ.
The two European-regulated cream products (HD-F and HD-G) contained no detectable metals across all six measured elements, contrasting sharply with Asian-origin powdered formulations.
Biomonitoring (pilot, exploratory)
Nineteen women (occupational hair dye practitioners and consumers) recruited in Khartoum. FAAS measured plasma lead, cadmium, copper, and arsenic in 10 participants; GFAAS measured whole-blood lead in 9 participants. Detectable blood lead occurred only among participants with at least 20 years of occupational exposure. The source characterizes this as an exploratory finding requiring confirmation in a larger study.
Risk assessment
Non-carcinogenic risk (HQ) remained below 1 for individual products for consumer exposure. Occupational exposure approached HQ = 1 for high-lead products. Cadmium produced the clearest carcinogenic risk signal (LCR above conventionally accepted range for occupational workers under the modeled assumptions).
Methods (brief)
Sample collection. 11 black hair dye products from Khartoum retail outlets, March to August 2021. Formulation types: powdered (Indian and local), stone-based (locally unbranded), cream.
Sample preparation. Cu, Cd, Pb, Mn, Ni: 5.0 g digested in 40 mL HCl/HNO3 (3:1) on sand bath at 220 degrees C for 30 min, diluted to 200 mL. Mercury: separate aliquot in HNO3/HClO4 (1:1).
Analytical method. FAAS (Varian 220) at characteristic wavelengths. GFAAS (Varian 7000) for biomonitoring metals. Validation parameters: linearity (R squared), LOD, LOQ, RSD, and accuracy.
Questionnaire. 42-item Arabic-language questionnaire administered to 312 women for exposure characterization; Cronbach’s alpha 0.860.
Implications
Certification. Provides A-tier occurrence data for black hair dyes on the Sudanese market. The finding that lead in three of eleven products exceeded the EU technically avoidable limit of 2 ppm, and that manganese reached 294.8 ppm in powdered Indian-origin dyes, is relevant to the HMTc Cat 13 hair-dye product rows. This paper does not provide evidence relevant to the children’s makeup product page.
Courses. Useful as a case study for the contrast between EU-GMP-compliant cream formulations (no detectable metals) and poorly regulated powdered or stone-based dyes from Asian origin, illustrating how the same product category can span several orders of magnitude in contamination depending on market of origin and formulation type.
Related evidence
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