Ingested mineral fibers: elimination in human urine

Our plain-English summary of Ingested mineral fibers: elimination in human urine, by P.M. Cook, G.F. Olson (Science, 1979).

The study

• Authors: P.M. Cook, G.F. Olson
• Journal: Science
• Published: 1979;204(4389):195-8
• Cited by: 72 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Sediment in human urine examined by transmission electron microscopy contains amphibole fibers which originate from the ingestion of drinking water contaminated with these mineral fibers. The ingestion of filtered water results in the eventual disappearance of amphibole fibers from urine. These observations provide the first direct evidence for the passage of mineral fibers through the human gastro-intestinal mucosa under normal conditions of the alimentary canal.

In plain English

The authors used transmission electron microscopy to examine 16 urine samples from 14 healthy Minnesota volunteers aged 25 to 83. None reported kidney disease or occupational asbestos exposure. Drinking water in the prior month was coded as unfiltered Lake Superior water, carrying amphibole fibers (mostly cummingtonite-grunerite), filtered Lake Superior water, or well water; several subjects drank more than one, and two never drank Lake Superior water. Urine from the four people drinking only unfiltered water had estimates from 310 (95 percent confidence interval 194 to 469) to 1170 (562 to 2152) amphibole fibers per milliliter. The two who never drank Lake Superior water had none above detection limits. Two subjects retested after switching to filtered water had under one-tenth of their earlier levels. Fiber chemistry in urine closely matched the drinking water, and blank samples did not explain the counts. The authors concluded that the urine amphibole fibers could be attributed only to ingestion. They said the data suggest some ingested fibers accumulate in tissue but cannot predict permanent retention. They noted the method undercounted fibers by 29 percent in one test.

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 examination by transmission electron microscopy of urine samples from a small group of volunteers. Each sample was compared with a blank sample of filtered distilled water.
• Who was studied: 14 volunteer Minnesota residents (8 male, 6 female, ages 25 to 83), giving 16 urine samples. Two subjects (A and G) gave second samples about 1 year and about 2 months, respectively, after filtered tap water began in January 1977. All were in good health, with no reported kidney disease or occupational asbestos exposure. Two had never drunk Lake Superior water.
• Exposure: The exposure was amphibole fibers in drinking water drawn from western Lake Superior. The fibers were a mixture of approximately 75 percent cummingtonite-grunerite, 20 percent actinolite and 5 percent other amphibole minerals. Unfiltered Duluth water drunk by subjects A, B and G was estimated at approximately 50 x 10^6 amphibole fibers per liter. Filtered water generally contained less than 1 percent of the unfiltered concentration. Each subject's drinking water in the month before sampling was coded as unfiltered Lake Superior water, filtered Lake Superior water, well water, or never Lake Superior water. Several subjects had combinations of these, such as unfiltered plus filtered plus well water.
• Main results:
  • Urine amphibole fiber concentrations were associated with the type of drinking water. Only the subjects who drank unfiltered water had urine with more than ten times the detection limits (10 to 40 fibers per milliliter). The four subjects drinking only unfiltered water had the following estimates, with 95 percent confidence intervals: subject A, 310 (194 to 469); subject G, 590 (370 to 893); subject I, 580 (289 to 1038); and subject J, 1170 (562 to 2152) fibers per milliliter.
  • The two subjects who had never drunk Lake Superior water (M and N) had urine fiber levels below detection limits (less than 20 and less than 30 fibers per milliliter).
  • After months of drinking only filtered water, subjects A and G had less than one-tenth of the urine amphibole fiber concentrations measured when they drank only unfiltered water. Subject G fell from 590 to 40 fibers per milliliter after 2 months, a 90 percent reduction. Subject A fell from 310 to 13 fibers per milliliter after 13 months.
  • Blank samples contained either no detectable amphibole fibers or much lower concentrations than the matching urine samples. The authors concluded the fibers in urine were not contamination from sample preparation.
  • The chemical makeup of amphibole fibers in urine was almost identical to that of fibers in the drinking water.
  • In urine from subjects who drank unfiltered Duluth water, amphibole fibers averaged 0.96 micrometers long and 0.17 micrometers wide. Fibers in 1976 Duluth water samples averaged 1.42 micrometers long and 0.20 micrometers wide. The authors suggested that shorter fibers may pass into urine preferentially, although fibers up to 10 micrometers long were seen in urine.
  • Amphibole fibers eliminated in urine amounted to approximately one-thousandth (printed as 10-3) of the number of fibers ingested with drinking water. After a single day's ingestion, fibers were detectable in urine at least 10 days later.
  • Chrysotile fibers were abundant in most urine samples but were also present in blank samples. The membrane filters were identified as the main source of the chrysotile found in the blanks.
• The authors' conclusion: The authors concluded that the amphibole fibers seen in urine could be attributed only to ingestion. They said the data suggest some ingested mineral fibers accumulate in body tissue, but do not allow a prediction of whether fibers are permanently retained. They suggested that electron microscope analysis of urine could serve as an index of past exposure.
• Limitations the authors state:
  • A test sample with a measured addition of amphibole fibers showed a 29 percent underestimate of amphibole fibers by the method.
  • Daily variations in kidney function were not accounted for, because only one 24-hour specimen (subject A) was analyzed.
  • The extent of differences between people in how permeable the gut, kidney and other tissues are to particles is unknown.
  • The ratio of urine fibers to ingested fibers seemed remarkably large to the authors and may change with further measurements.

Topics

Medical terms in this study, explained in our Lexicon: Mineral Fiber, Transmission Electron Microscopy (TEM), Amphibole Group.

Related studies

• Epidemiological studies on ingested asbestos — J. Hopkins (1984)
• The contamination of Lake Superior with amphibole gangue minerals — A.M. Langer, C.M. Maggiore, et al. (1979)
• Review of published studies on gut penetration by ingested asbestos fibers — P.M. Cook (1983)
• Asbestos-contaminated drinking water: its impact on household air — J.S. Webber, S. Syrotynski, et al. (1988)
• Distribution of chemical carcinogens in aquatic environments — H.F. Kraybill (1976)
• Asbestos in public water supplies: discussion of future problems — J.P. Hills (1979)

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