Modeling community asbestos exposure near a vermiculite processing facility: Impact of human activities on cumulative exposure

Our plain-English summary of Modeling community asbestos exposure near a vermiculite processing facility: Impact of human activities on cumulative exposure, by J.L. Adgate, S.J. Cho, B.H. Alexander, et al (Journal of Exposure Science & Environmental Epidemiology, 2011).

The study

• Authors: J.L. Adgate, S.J. Cho, B.H. Alexander, G. Ramachandran, K.K. Raleigh, J. Johnson, R.B. Messing, A.L. Williams, J. Kelly, G.C. Pratt
• Journal: Journal of Exposure Science & Environmental Epidemiology
• Published: 2011;21(5):529-35
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Contaminated vermiculite ore from Libby, Montana was processed in northeast Minneapolis from 1936 to 1989 in a densely populated urban residential neighborhood, resulting in non-occupational exposure scenarios from plant stack and fugitive emissions as well as from activity-based scenarios associated with use of the waste rock in the surrounding community. The objective of this analysis was to estimate potential cumulative asbestos exposure for all non-occupationally exposed members of this community. Questionnaire data from a neighborhood-exposure assessment ascertained frequency of potential contact with vermiculite processing waste. Monte Carlo simulation was used to develop exposure estimates based on activity-based concentration estimates and contact durations for four scenarios: S1, moved asbestos-contaminated waste; S2, used waste at home, on lawn or garden; S3, installed/removed vermiculite insulation; S4, played in or around waste piles at the plant. The simulation outputs were combined with air-dispersion model results to provide total cumulative asbestos exposure estimates for the cohort. Fiber emissions from the plant were the largest source of exposure for the majority of the cohort, with geometric mean cumulative exposures of 0.02 fibers/cc × month. The addition of S1, S2 and S3 did not significantly increase total cumulative exposure above background exposure estimates obtained from dispersion modeling. Activity-based exposures were a substantial contributor to the upper end of the exposure distribution: 90th percentile S4 exposure estimates are ∼10 times higher than exposures from plant emissions. Pile playing is the strongest source of asbestos exposure in this cohort, with other activity scenarios contributing less than from plant emissions.

In plain English

This modeling study estimated non-work asbestos exposure near a northeast Minneapolis plant that processed contaminated vermiculite ore from Libby, Montana, from 1936 to 1989. The researchers selected 2222 members of a Minnesota Department of Health cohort who never worked at the plant, never lived with a plant worker, and were first at risk of exposure before 1981. Using air dispersion modeling and residential histories, they estimated background exposure from plant emissions for 2146 of them; 76 had invalid addresses. They estimated exposure from four questionnaire-reported activities using Monte Carlo computer simulation and air measurements from Libby: moving plant waste, using waste at home, installing or removing vermiculite insulation, and playing on waste piles at the plant. Typical (geometric mean) background exposure was about 0.02 fibers/cc-months. At the 90th percentile, exposure from pile playing was 9.6 times higher than background. Adding the other three activities to background did not significantly change total exposure. The authors concluded that use of waste rock likely added substantial exposure for a large subgroup. They noted uncertainties likely of an order of magnitude or more.

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: Exposure modeling study: air dispersion modeling of plant emissions combined with Monte Carlo simulation of activity-based exposures, using questionnaire data from a community cohort
• Who was studied: 2222 people from a Minnesota Department of Health/ATSDR cohort of 6724 living near the Western Minerals/W.R. Grace vermiculite plant in northeast Minneapolis. All had never worked at the plant, never lived with a plant employee, and were first at risk before 1981. Background estimates were available for 2146 of them; 76 had an invalid address.
• Exposure: Asbestos from Libby, Montana vermiculite ore processed at the plant. Two kinds of exposure were modeled: (1) plant stack and fugitive emissions (background), and (2) four activities: moving plant waste (S1), using waste at home, on lawn or garden (S2), installing or removing vermiculite insulation (S3), and playing in or around waste piles at the plant (S4).
• Main results:
  • Background exposure from plant emissions could not be estimated for 76 of the 2222 selected people because of invalid addresses.
  • For the whole group, the geometric mean cumulative background exposure from plant emissions was about 0.02 f/cc-month, with a geometric standard deviation of 6.5.
  • Median exposures from moving waste (S1), using waste (S2), insulation work (S3) and pile playing (S4) were 9%, 12%, 30% and 750%, respectively, of median background exposure.
  • At the 90th percentile, exposures from S1, S2 and S3 were 11%, 36% and 57%, respectively, of 90th percentile background exposure.
  • At the 90th percentile, exposure from playing on waste piles (S4) was 9.6 times higher than background exposure.
  • Total exposure combining background with S1, S2 and S3, without pile playing (Case III), was not significantly different from background.
  • Males and females had similar exposures up to the median. At the upper quartile and decile, males' exposures were about 2 to 3 times higher than females'.
• The authors' conclusion: The authors concluded that median exposures in the cohort were driven by direct plant emissions, but that use of waste rock likely resulted in substantial additional exposures for a large subgroup.
• Limitations the authors state:
  • The background exposure estimates were means with wide, largely unquantifiable confidence intervals, because of uncertainties in input data and model structure.
  • Recall bias was possible: reported activity frequencies may have been affected by perceived health status or by the community investigation.
  • There were no Minneapolis-specific data on airborne concentrations during the activities. Concentrations were taken from measurements of surrogate activities.
  • The cumulative exposure estimates have uncertainties likely to range by an order of magnitude or more, and are not strictly comparable to other locations.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Libby vermiculite mine, Montana

All asbestos mines

Topics

The National Library of Medicine indexes this study under subjects our site covers: Talc and vermiculite.

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, vermiculite, Cumulative Exposure, Non-Occupational Exposure, Background Exposure.

Related studies

• Radiographic evidence of nonoccupational asbestos exposure from processing Libby vermiculite in Minneapolis, Minnesota — B.H. Alexander, K.K. Raleigh, et al. (2012)
• Community exposure to asbestos from a vermiculite exfoliation plant in NE Minneapolis — J. Kelly, G.C. Pratt, et al. (2006)
• Association between cumulative fiber exposure and respiratory outcomes among Libby vermiculite workers — T.C. Larson, V.C. Antao, et al. (2012)
• Asbestos-related radiographic findings among household contacts of workers exposed to Libby vermiculite: impact of workers' personal hygiene practices — T.J. Hilbert, A. Franzblau, et al. (2013)
• The traveling Libby legacy: Minnesota community exhibits nonoccupational health impacts consistent with asbestos damage — T. Tillett (2012)
• An evaluation of potential occupational exposure to asbestiform amphiboles near a former vermiculite mine — J.F. Hart, T.M. Spear, et al. (2009)

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