Overview
Gnonsoro and colleagues at LANADA (Laboratoire National d’Appui au Développement Agricole) and Université Félix Houphouët Boigny measured lead, cadmium, and total mercury in 30 hydroalcoholic gels (alcohol-based hand sanitizers) collected from supermarkets in Abidjan during the first weeks of the COVID-19 pandemic in March 2020. The paper reports per-sample bar charts and pooled mean ± SD with min/max for each metal, then calculates dermal chronic daily intake (CDI), hazard quotients (HQ), hazard index (HI), and incremental lifetime cancer risk (ILCR) using standard US-EPA dermal-exposure equations parameterised for an adult (70 kg body weight, 420 cm² hand surface area, 350 days/year for 30 years). All three metals were quantifiable in most samples but all sample concentrations fell below the Health Canada cosmetic-skin limits for lead (Pb) (10 mg/kg) and cadmium (Cd) (3.0 mg/kg) and below the US FDA Pb-as-impurity-in-colour-additives limit (20 mg/kg); no jurisdiction-specific limit was cited for mercury (Hg) in this product class. The hazard index (∑HQ) was 7.10×10⁻⁵ — three orders of magnitude below the unit threshold — and the cumulative ILCR for Pb plus Cd was 3.07×10⁻⁸, two orders of magnitude below the 10⁻⁶ insignificance floor. The authors report the per-analyte contribution to non-carcinogenic health risk in the order mercury > cadmium > lead, with mercury the dominant driver in the Kp set used (0.001 cm/h for Cd and Hg vs 0.0001 for Pb).
Key numbers
All concentration values are mg/kg in the as-purchased hydroalcoholic gel (density 0.79–0.99 g/mL; pH 5.37–7.14). Multiply mg/kg by 1000 to convert to ppb / µg/kg.
Heavy-metal concentrations in 30 hydroalcoholic gels (Source Table 6)
| Analyte | Mean ± SD (mg/kg) | Min (mg/kg) | Max (mg/kg) |
|---|---|---|---|
| lead (Pb) | 0.248 ± 0.110 | 0.122 | 0.715 |
| cadmium (Cd) | 0.006 ± 0.007 | <LOD | 0.024 |
| mercury (Hg) (total) | 0.172 ± 0.134 | <LOD | 0.481 |
In ppb-equivalent units, Pb ranged 122–715 ppb (mean 248 ± 110 ppb), Cd ranged <LOD–24 ppb (mean 6 ± 7 ppb), and total Hg ranged <LOD–481 ppb (mean 172 ± 134 ppb).
Method performance (Source Table 4)
| Analyte | Recovery (%) | LOD (mg/kg) | LOQ (mg/kg) |
|---|---|---|---|
| lead (Pb) | 96.0 | 0.046 | 0.104 |
| cadmium (Cd) | 97.0 | 0.002 | 0.019 |
| mercury (Hg) | 93.4 | 0.051 | 0.115 |
Physicochemical characteristics (Source Table 5)
| Parameter | Mean ± SD | Min | Max | WHO formulation-guide range |
|---|---|---|---|---|
| pH | 6.44 ± 0.46 | 5.37 | 7.14 | 6.0–7.0 (WHO 2010) |
| Density (g/mL) | 0.91 ± 0.05 | 0.79 | 0.99 | 0.8–1.0 (WHO 2009) |
Dermal exposure outputs (Source Table 8)
CDIdermal values were computed using the US-EPA Risk-Assessment-Guidance-for-Superfund dermal equation: CDI = (Cw·HSA·Kp·ABS·ET·EF·EP·CF)/(BW·AT). Parameter values (Source Table 2): Cw in mg/kg; HSA 420 cm² (adult hand surface area, both hands); Kp 0.0001 cm/h for Pb, 0.001 cm/h for Cd, 0.001 cm/h for Hg; ABS 0.001 for all metals; ET 0.05 hour/event; EF 350 day/year; EP 30 year; CF 0.001 L/cm³; BW 70 kg; AT 25,550 days (70-year non-cancer averaging time).
| Metric | Pb | Cd | Hg (total) | Total |
|---|---|---|---|---|
| CDIdermal mean (mg/kg/day) | 3.057×10⁻⁹ ± 1.35×10⁻⁹ | 1.38×10⁻⁹ ± 0.79×10⁻⁹ | 2.55×10⁻⁸ ± 1.48×10⁻⁸ | — |
| CDIdermal range (mg/kg/day) | 1.50×10⁻⁹ – 8.81×10⁻⁶ | 0 – 2.95×10⁻⁹ | 0 – 5.93×10⁻⁸ | — |
| HQdermal mean | 7.28×10⁻⁹ ± 3.23×10⁻⁹ | 1.56×10⁻⁷ ± 1.82×10⁻⁷ | 7.08×10⁻⁵ ± 5.52×10⁻⁵ | HI = 7.10×10⁻⁵ ± 5.52×10⁻⁵ |
| HQdermal range | 3.58×10⁻⁹ – 2.09×10⁻⁹ (sic) | 0 – 5.91×10⁻⁷ | 0 – 1.97×10⁻⁴ | 5.72×10⁻⁹ – 1.97×10⁻⁴ |
| ILCR mean | 2.59×10⁻⁸ ± 1.15×10⁻⁸ | 4.78×10⁻⁹ ± 1.56×10⁻⁹ | n/a (no CSF assigned) | ∑ILCR = 3.07×10⁻⁸ ± 1.33×10⁻⁸ |
| ILCR range | 1.27×10⁻⁸ – 4.77×10⁻⁸ | 0 – 1.80×10⁻⁸ | n/a | 1.27×10⁻⁸ – 8.24×10⁻⁸ |
Reference doses (RfDdermal) and cancer-slope factors (CSF) used in HQ/ILCR (Source Table 3): Pb RfDdermal 0.42 mg/kg/day, CSF 8.5 (kg·day/mg); Cd RfDdermal 0.005 mg/kg/day, CSF 6.1 (kg·day/mg); Hg RfDdermal 0.03 mg/kg/day, CSF not assigned (Hg “is not considered to create cancer” in the framework the authors used).
Source-page typographic note on the HQdermal Pb range: source Table 8 prints “3.58×10⁻⁹ – 2.09×10⁻⁹” with the upper bound apparently smaller than the lower bound — likely a typographical error in either the exponent or one of the mantissa values (a plausible intended upper bound is 2.09×10⁻⁸, consistent with the Pb CDI range 1.50×10⁻⁹–8.81×10⁻⁹ divided by RfDdermal 0.42; alternatively a transcription error in the lower bound). This page reproduces the published values verbatim rather than silently correcting; the typo does not affect mean HQ or HI conclusions.
Pearson correlation matrix (Source Table 7)
| pH | Density | Pb | Cd | Hg | |
|---|---|---|---|---|---|
| pH | 1.00 | — | — | — | — |
| Density | 0.10 | 1.00 | — | — | — |
| lead (Pb) | −0.13 | −0.09 | 1.00 | — | — |
| cadmium (Cd) | −0.42 | −0.12 | 0.10 | 1.00 | — |
| mercury (Hg) | 0.19 | 0.11 | −0.14 | −0.10 | 1.00 |
No correlation reached statistical significance at p<0.05 for any pair (between heavy metals, between heavy metals and pH/density).
Regulatory benchmarks the source compares against
- Health Canada (Guidance on Heavy Metal Impurities in Cosmetics, 2016): Pb 10 mg/kg in cosmetic products applied to the skin; Cd 3.0 mg/kg as an impurity in cosmetic products.
- US FDA (21 CFR 74.1306, D&C Red No. 6 colour-additive listing): Pb 20 mg/kg as an impurity in colour additives used as ingredients in cosmetic products.
- BfR (Germany): Cd 5.0 mg/kg in cosmetics (BfR Stellungnahme 025/2006).
All measured Pb (max 0.715), Cd (max 0.024) and unstated-limit Hg (max 0.481) values were below all named cosmetic-product limits in this paper.
Methods (brief)
Thirty hydroalcoholic gels were collected from supermarkets across the district of Abidjan between 03 and 12 March 2020. The selection targeted “high-consumption brands” identified by prior interviews with cosmetics sellers (no statistical sampling frame; convenience sampling weighted toward popular Côte d’Ivoire-produced gels). Each sample (0.5 g aliquot) was digested in a Milestone Ethos microwave digester with 5 mL HNO₃ (65%, Merck) and 2 mL H₂O₂ (30%), then transferred to a 25-mL volumetric flask and brought to volume with ultrapure water before refrigerated storage.
Pb, Cd, and Hg were quantified by atomic absorption spectroscopy on a Spectra A100 Varian spectrophotometer (Australia) equipped with a GTA-110 graphite furnace, per AOAC Official Method 999.10. The source describes the analytical platform as graphite furnace atomic absorption spectroscopy (GFAAS) throughout. Instrument conditions (Source Table 1): nitrogen gas carrier at flow rate 4; Pb at 283.3 nm with atomisation temperature 2100 °C; Cd at 228.8 nm with atomisation temperature 1800 °C; Hg at 253.7 nm with “dosage temperature” 25 °C (the source does not specify a separate atomisation step or accessory for Hg). Number of readings per replicate = 1; number of replicates = 3 (Source Table 1). Calibration used standard solutions of lead and cadmium at 1 g/L (Normex) with five-point linear calibration. Spike recoveries were 96.0% (Pb), 97.0% (Cd), and 93.4% (Hg). Mercury speciation was not performed; the paper measures and reports total mercury.
Method validation followed ISO/TS 22176:2020 and AFNOR NF V 03-110:2010 (selective evaluation, working/linear ranges, repeatability, reproducibility). Values below LOD are reported as “not detected” (ND); values between LOD and LOQ are reported as “<LOQ”. Statistical analysis (mean, min, max, SD, Pearson correlation) used Statistica 7.1 (2006) and Microsoft Excel 2013; significance was reported at p<0.05.
Health-risk assessment used the US-EPA Risk-Assessment-Guidance-for-Superfund dermal pathway (Means 1989; Wu et al. 2009) with Côte d’Ivoire-specific exposure scenario parameters listed above. ILCR for Pb and Cd was computed against the 10⁻⁶ insignificance and 10⁻⁴ “troublesome” thresholds commonly used in EPA-derived cumulative-risk frameworks; the authors cite no Hg cancer slope factor.
Scope limitations the source itself acknowledges or that the wiki notes: The paper does not differentiate inorganic mercury from methylmercury and cannot support methylmercury (MeHg) routing. It does not report per-sample replicate variance or any inter-laboratory comparison. The convenience-sampling design across “high-consumption brands” precludes treating the 30-sample distribution as representative of the full Abidjan market; the mean and SD describe the sampled set only. The paper does not report manufacturer or country of ingredient origin for individual samples; bulk-water trace-metal contamination in the Abidjan groundwater supply (Pb 0.02–2.80 mg/L, Ahoussi et al. 2008; Pb <0.001–0.04 mg/L and Cd <0.001–0.027 mg/L, Ahoussi et al. 2012) is named as one plausible upstream source of the Pb, Cd, and Hg traces detected. Detection-frequency per analyte is implied by the “<LOD” entries in the min column but is not stated as a fraction.
Implications
Certification: This paper contributes a 30-sample West-African hydroalcoholic-gel (alcohol-based hand-sanitizer) finished-product occurrence dataset on Pb, Cd, and total Hg in the as-sold gel basis. Hydroalcoholic gels are not currently an HMT&C product-row in the locked taxonomy; if HMT&C scope expands to hand-sanitizer / leave-on dermal-disinfection products, this source supports a Côte d’Ivoire-market 2020 occurrence anchor. All values were below Health Canada and US FDA cosmetic-skin limits but the paper provides no comparison to a hand-sanitizer-specific limit because none was named. Mercury is the dominant dermal-exposure driver in this product class because of its higher Kp; certification work in this space should require Hg speciation that this study did not perform.
Courses: A clean compact example of how dermal-pathway exposure modelling (CDI / HQ / HI / ILCR) layers on finished-product heavy-metal measurements in a personal-care matrix. Useful when teaching the difference between “concentrations in the product” and “estimated systemic dose to the consumer” for educator audiences. Also illustrates the typographical-error failure mode in published risk tables (the Pb HQ range in source Table 8 prints as a decreasing interval, which a careful reader catches but a downstream synthesis pass would silently propagate).
App: No food-occurrence data; do not route into any contamination_profile ingredient block. The product-class slug for hydroalcoholic gels / alcohol-based hand sanitizers is not yet in the wiki taxonomy; if added via a future Step 0 Lock, this source becomes the West-Africa-market anchor for that row.
Microbiome: No microbiome data in this source.
Related evidence
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