Characterization of mineral population by index particle: implication for the Stanton hypothesis

Our plain-English summary of Characterization of mineral population by index particle: implication for the Stanton hypothesis, by A.G. Wylie, R.L. Virta, J.M. Segreti (Environmental Research, 1987).

The study

• Authors: A.G. Wylie, R.L. Virta, J.M. Segreti
• Journal: Environmental Research
• Published: 1987;43(2):427-39
• Cited by: 25 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Fibers from seven crocidolite samples used by M. F. Stanton et al. (J. Natl. Cancer Inst. 67, 965-975 (1981] were measured from STEM and optical images. Their masses were computed. From these data, the population was normalized to a sample mass of 1 micrograms, and the number of fibers in various size categories of a 1-microgram sample was compared to the tumor probability for each sample. The purposes of this study were (1) to evaluate errors in and the utility of population characterization by index number (log of the number of particles longer than 8 micron with widths equal to or less than 0.25 micron) and (2) to review the Stanton hypothesis in view of this analysis. The study found that in most cases the index number is a reliable population parameter. However, index numbers between 0 and 2.5 cannot be obtained. Therefore, populations of mineral fibers will fall into two groups: those without index particles, which have indeterminant index numbers, and those with index numbers between 2.5 and 6.0. Within Stanton's populations that contain index particles, where y equals logit tumor probability and x equals index number, r equals 0.307 (insignificant). Where y equals tumor probability and x equals index number, r equals 0.503 (significant). The correlation coefficients are low enough to suggest the possibility that factors other than size and shape play a role in mineral fiber carcinogenicity.

In plain English

This laboratory study re-measured seven crocidolite samples from animal implantation studies by Stanton and co-workers, published in 1981. That work linked pleural sarcoma to an index number: the logarithm of the number per microgram of fibers over 8 micrometers long and at most 0.25 micrometer wide. The authors measured fibers by electron and optical microscopy and tested the index number's reliability. Their electron microscope index numbers were similar to Stanton's except for crocidolite 7 and crocidolite 10. For crocidolite 10, Stanton had counted two index fibers; the authors found none among 664 particles. The authors reported that index numbers between 0 and 2.5 are unlikely in counts of up to 1000 particles, and considered the three below-2.5 populations in Stanton's data anomalous. In Stanton's samples containing index fibers, the correlation between index number and logit tumor probability was 0.307, not statistically significant. A linear correlation with untransformed tumor probability was 0.530, significant but lower than Stanton's 0.80 for logit tumor probability. The authors concluded that long, thin fibers alone were insufficient and that other factors must play a role.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory re-measurement of fiber sizes in archived crocidolite samples by transmission electron microscopy and optical microscopy, combined with statistical reanalysis of the tumor data published by Stanton et al. (1981); no new animal experiments
• Who was studied: Seven crocidolite samples from the Stanton et al. (1981) implantation studies (crocidolite 2, 3, 4, 6, 7, 10 and 13), obtained from NIH. The correlation analysis used Stanton's published data for the samples that contained index particles.
• Exposure: Crocidolite fibers, characterized by the index number: the logarithm of the number per microgram of particles longer than 8 micrometers and 0.25 micrometer or less in width. In the earlier Stanton studies, these samples were implanted in test animals and pleural sarcoma was recorded. The reported tumor probabilities were 93, 93, 86, 63, 56, 26 and 0 percent for the seven samples. The 26 percent figure was listed as 33 percent in the 1981 publication.
• Main results:
  • For crocidolite 4, the authors calculated an index number of 5.20, compared with Stanton's 5.13, which was a statistically insignificant difference. For crocidolite 7, the values were 3.7 (authors) and 2.65 (Stanton), a statistically significant difference that was small compared with Stanton's overall range of 1.65 to 6.0.
  • Duplicate grids for crocidolite 4 and 7 gave somewhat different index numbers. The authors concluded that imprecision in measurement could not explain the large gaps between predicted and actual tumor probabilities.
  • For crocidolite 10, Stanton measured only two index fibers in 1000 particles. The authors found no index particles among 664 particles measured.
  • The authors' electron microscope index numbers gave estimates similar to Stanton's, except for crocidolite 10 and crocidolite 7.
  • According to the authors, index numbers below 2.5 should not be expected if any long, thin fibers are present. Stanton's data contained three populations below 2.5 (alumina 6, glass 15 and glass 9). The authors considered these anomalous, and in the worst case inaccurately characterized. They framed the generalization for samples of 1000 particles or less.
  • Among Stanton's populations that contained index particles, the correlation of logit tumor probability with index number was 0.307 (r squared 0.094). This was not significant at the 95% level.
  • In the same populations, the linear correlation of untransformed tumor probability with index number was 0.530 (r squared 0.281). This was significant at the 95% level, but lower than the r of 0.80 that Stanton determined for logit of tumor probability with index number.
• The authors' conclusion: The authors concluded that long, thin fibers must be present for the pleural sarcoma Stanton reported to develop, but that their presence alone is insufficient. In their view, some factor or factors other than size, shape and abundance must play a role.
• Limitations the authors state:
  • The authors measured about 300 particles per sample, compared with Stanton's 1000, so they expected more variation in their own estimates.
  • Stanton's raw data were not available. The authors estimated his counts by working backward from the published data, assuming 1000 particles had been measured.
  • Mass was calculated with a cylindrical model, although amphibole particles are rectangular in cross section. The authors put the resulting error at about a factor of 2.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Crocidolite.

Medical terms in this study, explained in our Lexicon: Stanton Hypothesis, Crocidolite, STEM, Mineral Fiber.

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