Nyamukamba et al. 2023 — Heavy metals, formaldehyde and pH in baby diapers from the South African market
This study quantifies extractable heavy metals (Pb, Cu, As, Zn, Co, Ni, Cr, Cd, Mn, Se), formaldehyde, and pH in 20 disposable baby diapers (DBD) purchased from high-, medium-, and low-end retail stores in Cape Town. Extractable metals were determined via ICP-OES after separate extractions in ISO-3160/2 artificial sweat (24 h) and a modified Brian-and-Shmaefsky artificial urine (extraction time not stated). All measured metal concentrations fell below the Oeko-Tex Standard 100 limits except for nickel, which exceeded the 0.1 mg/kg ceiling in one high-end diaper (H2, sweat extract: 0.197 mg/kg) and one low-end diaper (L2, urine extract: 0.224 mg/kg). Formaldehyde exceeded the Oeko-Tex 16 mg/kg recommended limit in 10/20 diapers (50%), with the highest readings (17.617 mg/kg) concentrated in medium-end products (M2, M5, M8). All 20 diapers had alkaline pH (7.32-8.93); only 5/20 (25%) fell within the Oeko-Tex 4.0-7.5 range. The authors conclude that diaper rash among South African babies could be driven by high alkaline skin pH and formaldehyde exceedances rather than by the measured heavy-metal content.
Key numbers
Sample
- n = 20 DBD; tiers H1-H5 (high-end), M1-M10 (medium-end), L1-L5 (low-end) (Table 1, p. 3)
- Origin of manufacture: South Africa (most), China (H2), Poland (H1, H4), Malaysia (L1); not on packaging for several samples
- 2.0 g of cut diaper per extraction; extracts analysed neat by ICP-OES
Formaldehyde (Table 2, p. 6; mg/kg)
- Overall range: 10.438 (H1, minimum) - 17.617 (M2 = M5 = M8, maximum)
- Group means (text, p. 8): high-end 14.56; medium-end 16.16; low-end 14.25; all-samples mean 15.28
- Oeko-Tex limit: < 16 mg/kg
- Exceedances above 16 mg/kg: 1/5 high-end (H2 = 16.205), 7/10 medium-end (M1, M2, M3, M5, M6, M7, M8), 2/5 low-end (L1 = 16.205, L2 = 17.029) — total 10/20 = 50%
- Per-tier within-limit shares: high-end 4/5, medium-end 3/10, low-end 3/5
pH (Table 3, p. 7)
- Overall range: 7.32 (H1) - 8.93 (L1)
- Group means (text, p. 7-8): high-end 7.65; medium-end 7.64; low-end 7.99; all-samples mean 7.7
- Oeko-Tex range: 4.0-7.5
- Within-limit: H1 (7.32), M1 (7.46), M4 (7.44), M10 (7.49), L5 (7.34) — 5/20 = 25%
- Highest sample-tier max: high-end 7.81 (H4); medium-end 8.03 (M6); low-end 8.93 (L1)
- All samples alkaline (pH > 7); no sample below 4.0
Extractable metals — artificial sweat extraction (Table 4, p. 9; mg/kg, ISO 3160/2 sweat, 24 h shake)
| Metal | Min | Max (sample) | Oeko-Tex 100 limit | Within-limit |
|---|---|---|---|---|
| Pb | 0.002 | 0.094 (M2) | < 0.2 | 20/20 |
| Cu | 0.001 | 0.019 (M1) | < 25 | 20/20 |
| As | 0.001 | 0.013 (H2 = L2 = L5; n.d. in M2 and M4) | < 0.2 | 20/20 |
| Zn | 0.014 | 0.644 (H2) | < 750 | 20/20 |
| Co | 0.002 | 0.013 (most samples) | < 1.0 | 20/20 |
| Ni | 0.022 | 0.197 (H2) | < 0.1 | 19/20 (H2 over) |
| Cr | 0.013 | 0.119 (H4) | < 1.0 | 20/20 |
| Cd | 0.001 | 0.006 (most samples) | < 0.1 | 20/20 |
| Mn | 0.002 | 0.034 (M1) | < 90 | 20/20 |
| Se | 0.002 | 0.038 (H5) | < 100 | 20/20 |
- Abundance order in sweat (text, p. 8): Zn > Ni > Cr > Pb > Se > Mn > Cu > Co = As > Cd
Extractable metals — artificial urine extraction (Table 5, p. 10; mg/kg, modified Brian & Shmaefsky urine)
| Metal | Min | Max (sample) | Oeko-Tex 100 limit | Within-limit |
|---|---|---|---|---|
| Pb | 0.001 | 0.011 (multiple) | < 0.2 | 20/20 |
| Cu | 0.008 | 0.019 (M2) | < 25 | 20/20 |
| As | 0.001 | 0.031 (M6); n.d. in 5 samples (H2, H3, M1, M10, L4) | < 0.2 | 20/20 |
| Zn | 0.002 | 0.230 (L2) | < 750 | 20/20 |
| Co | 0.002 | 0.013 (multiple); n.d. in 5 samples (H1, H4, H5, M5, L3) | < 1.0 | 20/20 |
| Ni | 0.001 | 0.224 (L2) | < 0.1 | 19/20 (L2 over) |
| Cr | 0.001 | 0.078 (H4); n.d. in L3 | < 1.0 | 20/20 |
| Cd | 0.001 | 0.006 (multiple); n.d. in L3 | < 0.1 | 20/20 |
| Mn | 0.002 | 0.034 (M2) | < 90 | 20/20 |
| Se | 0.001 | 0.061 (L3) | < 100 | 20/20 |
- Abundance order in urine (text, p. 9): Zn > Ni > Cr > Se > Mn > As > Cu > Co > Pb > Cd
Nickel — the only Oeko-Tex exceedance
- Sweat: H2 = 0.197 mg/kg (high-end diaper, made in China; nearly 2× the 0.1 mg/kg limit)
- Urine: L2 = 0.224 mg/kg (low-end diaper, made in South Africa; > 2× the 0.1 mg/kg limit)
- The two Ni-exceeding diapers are different samples in different extractants; the paper notes the difference in metal solubility between the two synthetic body fluids explains why abundance orders and per-sample maxima diverge between Tables 4 and 5.
Methods (brief)
- Sampling. Twenty disposable baby diapers procured from low-, medium-, and high-end stores in Cape Town, South Africa. Diapers were locally manufactured or imported from China, Poland, and Malaysia (Table 1).
- pH determination. Modified ISO 3071:2005 (Nyamukamba et al. 2020 method): 2.0 g of cut diaper in 100 mL water (pH 7.0, 27 °C), shaken 2 h; supernatant measured by pH electrode in triplicate.
- Heavy metals — artificial sweat extraction. 2.0 g cut diaper in 50 mL ISO 3160/2 artificial sweat (20 g NaCl, 17.5 g NH₄Cl, 5 g glacial acetic acid, 15 g lactic acid per L deionized water; pH 4.7 with NaOH). Shaken 24 h, filtered, analyzed.
- Heavy metals — artificial urine extraction. 2.0 g cut diaper in 50 mL modified Brian & Shmaefsky artificial urine (24.27 g urea, 10 g NaCl, 6 g KCl, 6.4 g Na₂HPO₄ per L distilled water; pH 5-7; 2.67 g creatinine, 0.067 g albumin added). Shake time not stated.
- Instrument. Spectro Arcos ICP-OES (side-on plasma; four-channel peristaltic pump). Run conditions: plasma 1400 W; pump 30 rpm; coolant flow 14.00 L/min; auxiliary 2.10 L/min; nebulizer 0.80 L/min. 10 % HNO₃ wash between samples.
- FTIR. PerkinElmer FTIR-ATR Spectrum Two for SAP-polymer characterization of the absorbent cores (Figure 3, p. 5).
- Speciation. None — total elemental concentrations only. As is reported as total As (tAs); Cr is reported as total Cr (Cr, not Cr-VI); Hg was not measured.
Implications
Certification: For HMTc Cat 2 (children’s personal care) diaper coverage, this paper documents:
- Extractable Ni in synthetic body fluids is the heavy-metal failure mode. Both Ni exceedances are < 2.5× the Oeko-Tex 0.1 mg/kg ceiling, but both occur in mainstream retail product (one high-end imported, one low-end domestic). Dermal Ni from diapers is plausible given that 19/20 measurements were already in the 0.022-0.197 mg/kg range — a tight Oeko-Tex pass is not a comfortable margin.
- Pb, Cd, tAs are all an order of magnitude below ceilings in both extractants (Pb max 0.094 mg/kg vs 0.2; tAs max 0.031 mg/kg vs 0.2; Cd max 0.006 mg/kg vs 0.1). For HMI’s threshold work on dermal-contact products, this paper is occurrence data toward the lower percentiles of the Cat 2 disposable-diaper distribution for these three analytes.
- The extraction-fluid choice matters. The same diaper produces different abundance orders and per-metal maxima in artificial sweat vs artificial urine. Any HMTc Cat 2 method specification for diapers should fix the extractant (and shake time, where the paper itself is silent for the urine extract).
- Formaldehyde and pH are the actual public-health story in this dataset, but both are out of scope for HMI metals work. Half the diapers exceed the Oeko-Tex formaldehyde ceiling and three-quarters are above the 7.5 pH ceiling. The authors attribute South African diaper-dermatitis prevalence to these two factors, not to heavy metals.
Courses: Useful for a Cat 2 module on synthetic-body-fluid extraction methodology (ISO 3160/2 sweat vs Brian & Shmaefsky urine) and on why the choice of extractant changes apparent ranking.
App: For diapers, the consumer-facing signal from this paper is “Ni is the metal most likely to exceed a dermal-contact ceiling, and it does so intermittently across retail tiers and origin countries.” The app should not surface specific sample codes (H2, L2) because they are anonymous within the paper and have no consumer-facing brand mapping.
Microbiome: Not addressed.
Verification notes
- Paper-internal metal-list inconsistency. The abstract states 11 metals were measured: “Pb, As, Co, Cr, Ni, Cu, Zn, Mn, Sr, Fe, and Cd,” and that “all heavy metals were found in all diapers except Sr, which was not found in sample M7.” However, Tables 4 and 5 — the actual data tables — report 10 metals: Pb, Cu, As, Zn, Co, Ni, Cr, Cd, Mn, Se. Sr and Fe are absent from the tables and Se is absent from the abstract metal list. The Oeko-Tex limit row at the bottom of Table 4 reads “Se < 100,” confirming that the column labelled Se is selenium (not strontium). This page reports the metals actually tabulated (the 10 in Tables 4-5) and treats the abstract list as a textual error in the source. No values are altered.
- Paper-internal method inconsistency (ICP-OES vs ICP-MS). Section 2.4 is titled “Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) Analysis,” and Section 2.3.2 states the artificial-sweat filtrate “was analyzed by ICP-MS.” However, the section 2.4 body identifies the instrument as a “Spectro Arcos ICP-OES instrument” with side-on plasma interface, and the listed run conditions (plasma 1400 W, coolant 14.00 L/min, auxiliary 2.10 L/min, nebulizer 0.80 L/min) are characteristic ICP-OES parameters. Spectro Arcos is a commercial ICP-OES line. This page records the method as ICP-OES based on the explicit instrument identification, and flags the “ICP-MS” wording in the section title and Section 2.3.2 as inconsistent with the equipment described.
- Brand firewall. The paper does not name diaper brands; samples are anonymous codes (H1-H5, M1-M10, L1-L5) with retail-tier and country-of-manufacture descriptors only. No brand-firewall scrubbing was needed. The instrument vendor (Spectro Arcos), FTIR vendor (PerkinElmer), and reagent supplier (Merck) are scientific-method vendor names and are retained per the Part 12 Exception 2.
- Speciation. As is reported as total (tAs) — no inorganic-vs-total speciation. Cr is reported as total (Cr) — no hexavalent-vs-trivalent speciation. Hg is not in the analyte list. Metals frontmatter uses tAs, Cr, etc., reflecting the paper’s actual analytical scope.
- Extraction shake-time gap. The paper specifies a 24-h shake for the artificial-sweat extraction (Section 2.3.2) but does not state a shake time for the artificial-urine extraction (Section 2.3.1). The urine extraction time is therefore unknown and not back-fillable.
- Audit correction 2026-05-18 (fresh-context subagent). The first commit of this page reported “n.d. in 6 samples” for both urine-extract As and urine-extract Co. Re-counting Table 5 (PDF p. 10): As n.d. = 5 (H2, H3, M1, M10, L4); Co n.d. = 5 (H1, H4, H5, M5, L3). Corrected to “n.d. in 5 samples” with the sample codes named explicitly. The audit subagent flagged the As count as 4 (missed L4) and the Co count as 5; an independent re-read confirmed 5 for both, so the larger of the two flagged counts was adopted with explicit sample-code attribution.
Page history
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