Risk of human exposure to metals in some household hygienic products in Nigeria

Overview

An Elsevier Toxicology Reports open-access study quantifying nine metals (Cd, lead (Pb), chromium (Cr), Cu, Co, nickel (Ni), Mn, Zn, Fe) in twenty-seven brands of household hygienic products (HHPs) purchased in Abraka, Sapele and Warri (Delta State, southern Nigeria). The sample mix spans powdered laundry detergents (n=10), bar soaps (n=8), liquid dish-washing soaps (n=3), hand sanitizers (n=2), spot-removing creams (n=2) and hand/body creams (n=2). Three to five sub-samples per brand were analysed to capture intra-brand variation across manufacturing dates and batch numbers. Digestion was a triacid attack on a 0.5 g aliquot using HNO₃, HCl and HClO₄ in a 1:3:1 volume ratio (3 mL HNO₃, 9 mL HCl, 3 mL HClO₄) with a pre-digest at room temperature and heating to 110 °C; quantification was on a PerkinElmer Analyst 200 atomic absorption spectrophotometer. Spike-recovery validation gave 84.9-101.8 % across three concentration levels in the absence of a matrix-matched certified reference material. The authors then converted the metal concentrations into Systemic Exposure Dosages (SEDs) using the SCCS body-weight-normalised equation with the standard daily-application, skin-surface-area, frequency-of-application and retention-factor inputs for each product type, applied a 50 % (midpoint) and 100 % (worst-case) bioaccessibility assumption, and compared the SEDs against the (now withdrawn but still used as indicative) FAO/WHO Provisional Tolerable Daily Intake of 3.6 µg Pb kg⁻¹ bw day⁻¹ and the EFSA 0.35 µg cadmium (Cd) kg⁻¹ bw day⁻¹ tolerable weekly-intake-derived daily comparator. The authors’ Margin-of-Safety values for every product-metal combination exceeded the 100 SCCS minimum-acceptable threshold; their public-health conclusion is that the HHPs in this market basket are “reasonably safe for the investigated metals” despite the presence of significant Cd and Pb levels.

Key numbers

Pooled ranges across all 27 brands (abstract and Section 3, units µg g⁻¹ of finished product on an as-purchased, dry-digest basis):

Per-product-category ranges (Table 3, p. 917; brand columns suppressed per Part 12; ranges computed across the per-brand mean values within each category):

Within-brand standard deviations (3-5 replicate sub-samples per brand) ranged from approximately ± 0.1 to ± 28.6 µg g⁻¹ across the analyte-product combinations and are tabulated brand-by-brand in Table 3 of the source; they are not reproduced here because the brand-attribution layer is suppressed.

Authors’ headline category-level findings (Section 3, pp. 916-917):

• The order of mean Cd contamination across product categories was reported as: detergents > bar soaps > liquid soaps > hand sanitizers > hand creams. The highest single-brand Cd value (5.4 µg g⁻¹) occurred in a powdered detergent.
• The Pb concentration range was driven by a single exceptionally high powdered-detergent brand (47.0 µg g⁻¹). On average, the Pb level in detergents was reported as surpassing that in the other product categories.
• Cr was detected in 11 of the 27 brands and below the LOD in the remaining 16. Where detected, the highest Cr was in a bar soap (43.7 µg g⁻¹), with three powdered detergents in the 31-32 µg g⁻¹ range.
• Cu, Co and Ni were detected in most brands; the authors note that the levels of Cr in five brands, Co in fifteen brands and Ni in twenty-two brands of the twenty-seven examined surpassed the 5 µg g⁻¹ Basketter-et-al.-derived sensitization-safety threshold cited for pre-sensitized subjects.
• The Pb levels in eight brands surpassed the Health Canada 10.0 µg g⁻¹ cosmetics limit (cited from reference [13]).
• The Pb levels in two brands of detergents exceeded the US FDA 20.0 µg g⁻¹ limit for Pb as an impurity in colour additives in cosmetics (cited from reference [21]).
• Zn in a single bar soap was reported as 675 µg g⁻¹, the highest single-brand value across all metals and product categories.
• Fe was the most prominent element overall, with the detergents and bar soaps containing higher Fe than the liquid soaps; the highest Fe value (434 µg g⁻¹) was in a bar soap.

Systemic Exposure Dosage and Margin-of-Safety summary (Tables 4 and 5, pp. 918-921):

The authors computed SED (µg kg⁻¹ bw day⁻¹) for each metal × brand combination under both 50 % (Table 4) and 100 % (Table 5) bioaccessibility, and the corresponding MoS = NOAEL / SED. The MoS values for every product × metal combination exceeded the SCCS-mandated 100 minimum-acceptable threshold under both bioaccessibility assumptions. The authors’ qualitative summary:

• At 100 % systemic availability (worst case), the calculated Cd SED summed across the HHPs accounted for approximately 31 % of the EFSA-derived 0.35 µg Cd kg⁻¹ bw day⁻¹ daily comparator.
• At 100 % systemic availability, the calculated Pb SED summed across the HHPs accounted for approximately 32 % of the FAO/WHO 3.6 µg Pb kg⁻¹ bw day⁻¹ indicative PTDI (the PTWI/PTDI was formally withdrawn in 2011 by FAO/WHO but is retained here as an indicative comparator).
• The SED values for Fe, Mn and Zn at 100 % systemic availability were less than 24 % of their respective Recommended Dietary Allowances.
• The descending order of SED across the metals investigated was Fe > Zn > Pb > Ni > Co > Cu > Cd > Mn > Cr.

The authors’ overall conclusion (Section 4, p. 922) is that the HHPs investigated can be considered safe for human use without causing deleterious effects on the basis of the MoS values exceeding 100, but that the presence of significant Cd and Pb (toxic), Ni and Cr (allergenic) and Mn / Zn / Fe (low-toxicity) levels remains a potential environmental concern via wash-water effluent.

Methods (brief)

Sample acquisition. Twenty-seven brands of household hygienic products were purchased from sale outlets in Abraka, Sapele and Warri (Delta State, southern Nigeria). Brands were selected to reflect market popularity, pricing and use across different income groups. Three to five sub-samples per brand of different manufacturing dates and batch numbers were purchased to evaluate intra-brand variation. Country-of-origin information (Nigeria, Indonesia, USA, Italy) and product colour are reported brand-by-brand in Table 1 of the source.

Sample preparation and digestion. A 0.5 g aliquot of each sample was weighed into a 150 mL Teflon beaker. A triacid digestion mixture of 9 mL HCl (37 % v/v; BDH, Poole, UK), 3 mL HNO₃ (69 % v/v; BDH) and 3 mL HClO₄ (70 % v/v; Riedel-de-Haën, Seelze, Germany) was added — a 1:3:1 HNO₃:HCl:HClO₄ volume ratio per the source abstract phrasing (Section 2.3, p. 915). The sample was pre-digested at room temperature for at least 3-4 hours, then heated to 110 °C on a regulated heating block for 1 hour. The cooled, clear digest was filtered through Whatman No. 1 filter paper and diluted to 25 mL with 0.25 mol L⁻¹ HNO₃. Reagent blanks (n = 3) were prepared in parallel by omitting the sample.

Reagents. Acids were analytical grade; deionised water was supplied by a Millipore Elix UV5 water purification system (Millipore, USA). Working standards were prepared in 0.25 mol L⁻¹ HNO₃ by serial dilution of 1000 mg L⁻¹ commercial standards.

Instrumentation. Quantification was by atomic absorption spectrophotometry on a PerkinElmer Analyst 200 (Norwalk, CT, USA). Calibration was at three concentration levels with R² values between 0.9995 and 0.9999.

Quality assurance and quality control. Glassware and sample containers were washed with metal-free detergent and soaked in 10 % HNO₃ for 24 h, then rinsed with double-distilled and deionised water. No certified reference material was available for these product matrices; method validation relied on a spike-recovery approach at three concentration levels. Average percentage recoveries reported by analyte (Section 2.4):

All analyses were performed in triplicate with relative standard deviations between 2 % and 10 %. Instrumental and method limits of detection (LOD, 3:1 S/N) and quantification (LOQ, 10:1 S/N) reported by analyte (µg g⁻¹):

Replicates. Three to five sub-samples per brand (different manufacturing dates and batch numbers) were analysed, and each was measured in triplicate at the instrument stage.

Statistical analysis. ANOVA was used to evaluate intra- and inter-brand differences; Tukey’s test was used to evaluate differences across product categories. Software: SPSS version 24 (SPSS Inc., Illinois, USA).

Speciation. Total metals only. The paper measures total chromium and does not distinguish hexavalent chromium (Cr-VI) from Cr-III. No arsenic or mercury speciation issues arise because neither analyte is measured.

Basis. Concentrations are reported as µg of metal per g of finished product on an as-purchased, triacid-digested basis (i.e., per gram of product as placed on market).

Exposure-risk evaluation. The Margin of Safety (MoS) was computed as MoS = NOAEL / SED, where SED (µg kg⁻¹ bw day⁻¹) = (Cs × AA × SSA × F × RF × BF / BW) × 10⁻³ × DF, with Cs the measured metal concentration (mg kg⁻¹), AA the amount of product applied per day (g; SCCS defaults: 20.0 for detergents, liquid soaps, bar soaps and hand sanitizers; 1.54 for spot-removing creams; 2.16 for hand/body creams), SSA the skin surface area in contact (cm²; 860 for most products; 565 for spot-removing creams), F the frequency of application per day (2 for detergents, liquid soaps, bar soaps and hand/body creams; 10 for hand sanitizers; 2.14 for spot-removing creams), RF the retention factor (0.01 for detergents, liquid soaps, bar soaps and hand sanitizers; 1 for spot-removing creams and hand/body creams), BF the bioaccessibility factor (50 % midpoint scenario in Table 4; 100 % worst-case scenario in Table 5), BW the human body weight (60 kg), and DF a dilution factor (0.2 for detergents and soaps assuming approximately 5 L of water during reconstitution; 1 for hand sanitizers, spot-removers and hand/body creams which do not require water dilution). NOAEL values were derived from oral reference doses (mg kg⁻¹ day⁻¹): Pb 4 × 10⁻³, Cd 1 × 10⁻³, Cu 4.0 × 10⁻², Co 3 × 10⁻⁴, Cr 3 × 10⁻³, Fe 7.0 × 10⁻¹, Ni 1.4 × 10⁻², Zn 3.0 × 10⁻¹ — each multiplied by an uncertainty factor (UF, default 100) and a modifying factor (MF, default 1) per the SCCS framework.

Implications

• The dataset adds a fully populated nine-metal × twenty-seven-brand market-basket from Delta State (Abraka, Sapele, Warri), southern Nigeria, to the broader corpus on metals in household hygienic products. Six metals on the HMTc certification analyte panel are quantified here as totals (Pb, Cd, Ni, aluminum (Al) — though Al is not measured — Cr though as total Cr not Cr-VI, and tin (Sn) is not measured); the remaining analytes (Cu, Co, Mn, Zn, Fe) are reported for environmental and sensitization-allergen context. Speciation discipline restrictions apply: the chromium values inform the broader chromium literature but do not bind Cr-VI threshold-setting.
• The single exceptional Pb value (47.0 µg g⁻¹ in a powdered detergent) and the two-brand exceedance of the US FDA 20.0 µg g⁻¹ Pb limit for colour additives in cosmetics together establish that the upper tail of the Nigerian detergent Pb distribution penetrates a recognised cosmetics-impurity ceiling. The eight-brand exceedance of the Health Canada 10.0 µg g⁻¹ cosmetics Pb limit broadens this conclusion across the wider product set.
• The MoS-based safety conclusion is the authors’ interpretation under the SCCS-default exposure scenario (60 kg adult, 50-100 % bioaccessibility, 0.01 retention factor for wash-off products). Direct application to threshold work would require re-running the calculation under HMTc-relevant body-weight and bioaccessibility assumptions and is deferred to a Part 9 synthesis pass.
• The category-level Cd, Ni and Cr sensitization-threshold exceedances (five brands for Cr, fifteen for Co, twenty-two for Ni over the 5 µg g⁻¹ pre-sensitized-subject reference) are relevant occurrence data for the dermal-sensitization-via-household-products exposure pathway; these are not heavy-metal-by-ingestion findings.
• The paper does not propose HMTc-relevant threshold values. No threshold values are proposed by this source page.

Limitations

• No certified reference material. The authors note that “since there is no available certified reference material for these product types, a spike recovery method was adopted to validate the analytical method.” Spike recoveries are 84.9-101.8 % across analytes, which is within the conventional acceptable range, but matrix-matched CRM validation is absent. Pb recovery (84.9 %) is the lowest and is just inside the conventional 80-120 % acceptance window.
• Total Cr only. Cr-VI vs Cr-III speciation is not performed. The chromium values cannot be applied directly to Cr-VI threshold-setting.
• No arsenic (As), mercury (Hg), Sn, Al on the analyte panel. The HMTc certification panel (Pb, total arsenic (tAs), Cd, methylmercury (MeHg), total mercury (tHg), inorganic arsenic (iAs), Ni, Al, Cr-VI, Sn) overlaps with this study only on Pb, Cd, Ni. Cr is measured as total Cr (not Cr-VI). As, Hg, Sn, Al are not measured at all.
• Sample size per brand is modest (3-5 sub-samples). The 3-5 sub-samples per brand support an estimate of within-brand variation across manufacturing dates and batches, but the n = 27 brand-level sample is too small to anchor a robust market-distribution percentile for the Nigerian HHP market as a whole. Per-category n is smaller still (n = 2 for hand sanitizers, spot-removing creams and hand/body creams).
• Geographic scope is Delta State only. Abraka, Sapele and Warri are all in Delta State in the Niger Delta region of southern Nigeria. The findings do not generalize without caveat to other Nigerian regions or to other West African markets.
• Exposure model uses SCCS adult-default body weight of 60 kg. Direct application to child-relevant exposure scenarios or to HMTc-specific use scenarios would require recomputation under different defaults.
• Indicative-rather-than-binding PTDI. The FAO/WHO 3.6 µg Pb kg⁻¹ bw day⁻¹ PTDI was formally withdrawn by JECFA in 2011 on the grounds that “it could no longer be considered health protective”; the authors retain it as an indicative comparator. The 31-32 % “fraction of comparator” framing should be read in that light.
• Brand-by-brand reporting in source tables. Tables 1, 3, 4 and 5 list brand-coded data (HD1-HD10, HBS14-HBS21, HLS11-HLS13, HS22-HS23, SRC24-SRC25, HBC26-HBC27) tied to brand names in Table 1. The wiki strips brand attribution per Part 12 and reports only per-category ranges and pooled distribution statistics; the underlying per-brand values remain in the source PDF for those auditing the wiki against the original.
• Folder-vs-content mismatch. The source PDF was filed in the archived source file, but the paper is about household hygienic products (detergents, soaps, hand sanitizers, spot-removers, hand creams), not toilet-bowl / bathroom descalers. The folder-level mis-categorisation is a manual-fetch-tracker note, not a content defect.

Provenance

• Source PDF: the archived source file
• SHA-256: cb021c19592c3bad44e0b5063599989645fc74288103620bdd2e3183857f2d5e
• File size: 504 KB; 10 pages (cover + nine body pages including five tables and references).
• Journal: Toxicology Reports, Volume 6 (2019), pages 914-923 (Elsevier; ISSN 2214-7500).
• Publication dates: received 20 Aug 2018; revised 22 Aug 2019; accepted 23 Aug 2019; available online 24 Aug 2019.
• DOI: 10.1016/j.toxrep.2019.08.014.
• License: open-access under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0).
• Funding acknowledgement: BSM (Martincigh) thanks the Medical Research Council of South Africa for the award of a SIR grant.
• Access date: 2026-06-03.
• Acquisition path: included in source-retrieval Agent Download Corruption Issue (KADC) folder household_papers/02_Toilet_Bathroom_Descaler/. (Folder naming reflects raw-asset provenance, not topical fit — the paper is a household-hygienic-products study filed alongside toilet-and-bathroom-descaler literature in the KADC batch.)

Related evidence

• Lead
• Cadmium
• Chromium
• Nickel
• Cobalt
• Copper
• Manganese
• Zinc
• Iron
• Laundry detergents (liquid, powder, pods/sheets, delicates)
• Bathing soaps
• Dish soaps (manual dishwashing)
• Pre-treaters (spray/gel/stick) and stand-alone stain/spot removers
• Body/hand leave-on skin care

Update history

No substantive edit history is available in this build. The full commit record is available in git.