Okwuegbuna 2025 - tampon metal-release thesis

Okwuegbuna’s University of Toronto MSc thesis tested whether Cd, Pb, and Cu could be detected in tampon digests or released from tampons into simulated vaginal fluid (SVF). The source is C-tier thesis evidence: it is useful method and negative/inconclusive release context, but it is not a confirmed tampon metal-occurrence concentration dataset. The thesis names four commercial products; this page reports only anonymized category-level results under the brand firewall.

Key numbers

The thesis abstract states that up to 86% of women in the U.S. use tampons and that the study used square wave voltammetry (SWV) with screen-printed electrodes (SPEs) to analyze four tampon brands incubated in SVF. Chapter 2 targeted Cd, Pb, and Cu because the SPEs could detect those metals and because Shearston et al. had reported tampon concentrations above the expected SPE detection limits. The Shearston values cited in this thesis are secondary context and should not be double-counted as Okwuegbuna primary occurrence data.

For ICP-AES acid digestion, the absorbent portion of each tampon was digested in 70% HNO3; the thesis used 0.5g tampon material in 20mL acid, heated at 60oC for 24 hours, then diluted the nitric-acid concentration to 2%. The method produced 9 samples per product label: undiluted, 10x, and 100x dilution sets with triplicate preparation/measurement.

Table 7 reports ICP-AES calibration performance for Cd at 228 nm, Pb at 217 nm, and Cu at 218 nm. The calibration R2 values were 1 for Cd, 1 for Pb, and 0.999 for Cu. The source’s signal-intensity LOD values were Cd 12.6, Pb 5.32, and Cu 29.1; signal-intensity LOQ values were Cd 89.7, Pb 7.84, and Cu 37.5.

Table 8 reports that all digested tampon sample signal intensities were below the corresponding LOD signal intensity. Across the anonymized product/dilution rows, Cd signal intensities ranged from 9.9 ± 1.0 to 11.5 ± 2.0, Pb from 2.0 ± 2.0 to 3.8 ± 1.0, and Cu from 3.4 ± 0.5 to 5.3 ± 1.0. The thesis states that converting these values to concentrations would have yielded negative concentrations, so no Cd, Pb, or Cu concentration is reported from the ICP-AES tampon digests.

For SWV calibration, Cd, Pb, and Cu standards were tested from 0.5 mg/L to 160 mg/L; the linear range used for analytical figures of merit was 0.5 mg/L to 40 mg/L. Table 9 reports multiplex SWV LOD concentrations of Cd 5.20 mg/L, Pb 0.40 mg/L, and Cu 0.47 mg/L, with LOQ concentrations of Cd 16.0 mg/L, Pb 1.10 mg/L, and Cu 12.0 mg/L. The source text around the LOQ sentence appears to label the Pb value as Cd once; the table values are used here.

Spike-and-recovery in SVF showed that the multiplex calibration behaved differently by analyte. At 5, 10, and 20 mg/L, Cd recovery was 41.0%, 90.1%, and 102%; Pb recovery was 104%, 110%, and 115%; and Cu recovery was 362%, 242%, and 204%. The thesis therefore rebuilt a Cu-only calibration curve; Table 11 reports Cu-only LOD concentration 2.86 mg/L and LOQ concentration 8.68 mg/L, and Table 12 reports Cu-only recovery of 81.0%, 84.0%, and 118% at 5, 10, and 20 mg/L.

For SVF release testing, the thesis incubated 1 tampon in 75 mL SVF and 10 tampons in 200 mL SVF, with hourly measurements for 6 hours. One regular-cotton product showed progressively increasing unidentified peaks at -1.05 V and -0.3 V in the one-tampon and ten-tampon SVF scans. The second regular-cotton product had no current peak in the one-tampon test and a slight -0.3 V peak only in the first hour of the ten-tampon test. One organic-cotton product showed no peaks in the first 3 hours of the one-tampon test, then a slight -0.3 V peak at hours 4, 5, and 6, with a consistent -0.3 V peak in the ten-tampon test. The second organic-cotton product showed no current peaks in either the one-tampon or ten-tampon SVF scans.

The conclusion states that SWV revealed reduction peaks in 3 of the 4 tested product labels, but none matched the target-metal reductive potentials for Cd, Pb, or Cu (-0.85v, -0.5 V, and -0.2 V, respectively). The author suggests the -1.05 V peak might correspond to Zn and the -0.3 V peak might correspond to redox-active organic compounds, but the thesis did not confirm those identities. No heavy-metal release concentration should be extracted from the unknown SWV peaks.

Methods (brief)

The thesis combined acid digestion/ICP-AES with SWV on SPEs. ICP-AES analyzed Cd, Pb, and Cu after nitric-acid digestion of tampon absorbent material. SWV used PalmSens ItalSens SPEs for heavy-metal detection with a mercury-film carbon working electrode, carbon counter electrode, and silver reference electrode. SVF followed the Owen and Katz formulation with glucose, urea, NaCl, lactic acid, KOH, acetic acid, calcium hydroxide, and glycerin in MilliQ water. For SVF testing, only the absorbent part of each tampon was immersed.

Implications

Certification: This source should not contribute positive Cd, Pb, Cu, Zn, or other metal concentration values to the tampon occurrence pool. Its useful signal is a negative/inconclusive release-method finding: the ICP-AES digest signals were below LOD, and the SWV release peaks were not identified as target metals.

Courses: The thesis is a good teaching example for the difference between total-content measurement, physiological leachate testing, and unidentified electrochemical activity. It also illustrates why unknown peaks cannot be promoted to metal species without confirmatory standards or orthogonal analysis.

App: The source can support a nuanced evidence-card note that one thesis attempted SVF release testing and found unidentified electroactive peaks, not confirmed heavy-metal release values.

Microbiome: Not directly addressed. Later thesis chapters develop menstrual-blood biomarker and self-sampling methods, but no vaginal microbiome endpoint is measured.

Wiki pages this source may touch

• menstrual-tampons
• cadmium
• lead
• copper

Verification notes

Identity checks before drafting found no existing wiki/sources/ hit for raw handle MFK_paper-23-okwuegbuna-2025-thesis-menstrual-metals, cite key okwuegbuna2025-tampon-metal-release-thesis, author/title strings, or local filename. The thesis has no DOI printed in the extracted text; doi: null and no_doi_assigned: true are retained. The PDF SHA-256 is ab95c759c5b503edcc3f19cbaa69d58d099787d3d8779a64a35a8e7a57618dbc. Tables 7-12 and Sections 2.2-2.4 were re-opened from /tmp/hmi-fem-015.txt; all values preserve the source’s reported units or signal-intensity labels, and no units were converted. Brand firewall: the source names four brands, but this page omits the names and reports only anonymized regular-cotton/organic-cotton product categories. Speciation firewall: Cd, Pb, and Cu are total elemental targets in digestion/SWV standards; no inorganic arsenic, methylmercury, Cr-VI, total tin, or organotin is reported. Zn is mentioned only as the author’s possible explanation for an unidentified peak and is not routed as a measured metal.

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.