The reliability of measures of amphibole fiber concentration in water

Our plain-English summary of The reliability of measures of amphibole fiber concentration in water, by A.L. Brown, W.F. Taylor, R.E. Carter (Environmental Research, 1976).

The study

• Authors: A.L. Brown, W.F. Taylor, R.E. Carter
• Journal: Environmental Research
• Published: 1976;12(2):150-60
• Cited by: 8 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Water samples from four communities whose source of drinking water is Lake Superior and from one site in the lake itself were examined in eight laboratories by electron microscopy to determine the concentration of amphibole fibers. The number of sites and samples from each site were unknown to the laboratories. Laboratories differed widely, both between and among themselves, in the concentrations reported when aliquots from the same sample of water were examined. Some laboratories varied much more than others. However, the relative variability among laboratories was reasonably uniform. There was general agreement that water from some sites was consistently high in concentrations of amphibole fibers, while other sites were consistently low. We conclude that comparisons of water concentrations of amphiboles at two sites or under two different sets of circumstances as determined by electron microscopy can be done if at least two provisions are fulfilled: (1) all concentration measurements must be made in the same laboratory using the same equipment and the same technician and (2) several aliquots of each sample of water must be examined independently.

PubMed has no abstract for this study. This is the authors' abstract, copied from the article.

In plain English

This study was requested by a federal judge in Minnesota hearing a case about the Reserve Mining Company. It tested how consistently laboratories measure amphibole fiber concentrations in water by electron microscopy. Water was taken at five sites: two in Duluth, one in Two Harbors, a tap in Beaver Bay, and Lake Superior itself off the tailings delta of the taconite plant at Silver Bay. Each site's water was split into portions, randomly numbered and sent to laboratories that did not know how many sites there were. Eight laboratories completed the study. Results for the same water varied widely, for example from 1.3 to 575 million amphibole fibers per liter for the Beaver Bay sample. Differences among laboratories and among sites were highly significant statistically. In the authors' analysis, the lake site was always low and Beaver Bay always high. The authors concluded that the data did not measure the true concentration. They said two sites could be compared only if one laboratory, using the same equipment and technician, examined several portions of each sample independently.

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: Interlaboratory comparison of the reliability of electron microscope counts of amphibole fibers in water, made by court-appointed consultants. Laboratories were not told the sample sources.
• Who was studied: Water samples from five sites. Sites 1 and 2 were in Duluth (the main pumping station and a firehall tap 15 miles from the intake). Site 3 was the Two Harbors main pumping station, site 4 a tap in Beaver Bay, and site 5 Lake Superior off the tailings delta at Silver Bay. Eight laboratories each received 19 water samples from the five sites plus one standard sample. Four other laboratories received samples but did not provide usable measurements.
• Exposure: Amphibole fibers in drinking water and lake water, counted by electron microscopy. Fibers were defined as particles with an aspect ratio greater than 3 and an electron diffraction pattern consistent with amphibole. A cummingtonite-grunerite standard sample was also included.
• Main results:
  • Concentrations reported for portions of the same site 4 (Beaver Bay) water sample ranged from 1.3 to 575 million amphibole fibers per liter.
  • Differences among the five sites and among the eight laboratories were highly significant statistically. Site 5 (the lake) was much lower and site 4 much higher than sites 1, 2 and 3. Laboratory 6 reported higher, and laboratory 9 lower, than the rest.
  • Relative variability (coefficient of variation) was similar for four of the five laboratories with fairly complete reporting. Laboratory 2 had a considerably smaller coefficient of variation.
  • After a logarithmic transformation, analysis of variance found statistically significant variation among the five sites in every laboratory except laboratory 1. The site ranking was consistent from laboratory to laboratory.
  • At the variability found in this study, comparing two sites whose true concentrations differ by a ratio of 3 would need 18 portions from each site (significance level 0.05, power 0.90). If variability were halved, five portions would be needed.
  • For the cummingtonite-grunerite standard sample, the expected concentration was estimated at 7 million fibers per liter. Laboratories reported from 0 to 9 million fibers per liter for it. The correlation between laboratories' results on the standard and their five-site means (r = 0.37) was not significantly greater than 0.
• The authors' conclusion: The authors concluded that the data did not measure the true amphibole fiber concentration. In their view, concentrations at two sites can be compared in a relative sense only if two conditions are met. All measurements must be made in the same laboratory with the same equipment and technician. Several portions of each water sample must be examined independently.
• Limitations the authors state:
  • The authors lacked sufficient data to assume fibers were randomly distributed on the microscope grids, so they did not use Poisson-based statistics.
  • Counting and chemical analysis methods were not standardized across laboratories.
  • Replying to a laboratory's comment, the authors acknowledged that a Duluth sample and a Two Harbors sample may have been transposed.
  • The authors had no independent measure of how well the large containers were mixed before the water was divided.
  • The comparison using the standard sample involved a small sample size.
  • The paper had a limited purpose: it looked only at variation in reported concentrations, not at differences in fiber shape or mineral mix.

Topics

Medical terms in this study, explained in our Lexicon: Amphibole Group.

Related studies

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• Cancer morbidity investigations: lessons from the Duluth study of possible effects of asbestos in drinking water — E.E. Sigurdson, B.S. Levy, et al. (1981)
• Cancer incidence in relation to asbestos in drinking water in the Puget Sound region — L. Polissar, R.K. Severson, et al. (1982)
• A case-control study of asbestos in drinking water and cancer risk — L. Polissar, R.K. Severson, et al. (1984)
• Asbestos-contaminated drinking water: its impact on household air — J.S. Webber, S. Syrotynski, et al. (1988)

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