Cancer incidence and mortality associated with non-occupational and low dose exposure to Libby vermiculite in Minnesota

Our plain-English summary of Cancer incidence and mortality associated with non-occupational and low dose exposure to Libby vermiculite in Minnesota, by T. Konen, J.E. Johnson, P. Lindgren, et al (Environmental Research, 2019).

The study

• Authors: T. Konen, J.E. Johnson, P. Lindgren, A. Williams
• Journal: Environmental Research
• Published: 2019;175:449-456
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: A vermiculite processing plant in a Minneapolis, Minnesota neighborhood utilized asbestos-containing ore from Libby, Montana from the late 1930's until 1989. Multiple pathways of exposure to Libby asbestos were characterized in a cohort of over 6000 plant workers and residents living near the plant.

Objective: We conducted a cohort linkage study to assess the impact of cumulative low dose exposure and the role of occupational history on asbestos-related mortality and cancer morbidity among cohort members residing near a vermiculite plant.

Methods: Cohort members alive in 1988 (n = 5848) were linked to the Minnesota Cancer Surveillance System to identify incident cases of mesothelioma, lung cancer, and all-cancer diagnosed from 1988 to 2010. Proportional incidence ratios (PIRs) were calculated for mesothelioma and lung cancer. Vital status and cause of death were ascertained from Minnesota vital records and the National Death Index (1988-2011). Mortality rates of the cohort (2001-2011) for asbestos-related outcomes were compared to the Minnesota population to estimate standardized mortality ratios (SMRs) and stratified by gender, exposure, and occupational history categories.

Results: We identified seven cases of mesothelioma, with elevated incidence only in females (PIR = 11.76, 95% CI: 3.17, 30.12). Lung cancer was elevated in both genders: PIR = 1.54 (95% CI: 1.19, 2.0) in males and 1.62 (95% CI: 1.21, 2.12) in females. We found elevated mortality from COPD, lung cancer, and mesothelioma among females (SMR for mesothelioma in females = 18.97, CI: 3.91, 55.45), among the 546 deaths identified. All four deaths from mesothelioma occurred in the >75th percentile of exposure (>0.0156 fiber/cc x months). The SMR for lung cancer and all respiratory cancer was elevated even after controlling for occupation.

Conclusions: Community exposure to Libby amphibole asbestos from a vermiculite processing plant is associated with increased risk of COPD, lung cancer and mesothelioma incidence and mortality, most notably among females, and is likely to remain a public health issue for years to come.

Published by Elsevier Inc.

In plain English

The authors followed 5,848 people alive in 1988 who had lived near, worked at, lived with workers of, or handled waste from a Minneapolis vermiculite plant that processed Libby, Montana ore contaminated with amphibole asbestos from about 1938 to 1989. They compared cancer and death records with the Minnesota population. There were seven mesotheliomas; incidence was elevated in females (proportional incidence ratio 11.76; 95% CI 3.17 to 30.12) but not significantly in males or both sexes. Lung cancer proportional incidence ratios were elevated in males (1.54; 95% CI 1.19 to 2.00) and females (1.62; 95% CI 1.21 to 2.12). Among 526 deaths in 2001 to 2011, female deaths from mesothelioma (standardized mortality ratio 18.97; 95% CI 3.91 to 55.45), lung cancer and COPD were elevated, but not significantly in males. Death rates did not rise with modeled exposure, but all four mesothelioma deaths were in the top exposure group. The authors noted that smoking may largely explain the lung cancer excess and that cases were few. They concluded that low-dose community exposure was associated with increased asbestos-related disease and mortality.

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: Cohort record-linkage study. An existing community and worker cohort was linked to the state cancer registry and to death records and compared with the Minnesota population, using proportional incidence ratios and standardized mortality ratios.
• Who was studied: 5848 members of the Northeast Minneapolis Community Vermiculite Investigation (NMCVI) cohort who were alive on January 1, 1988 and consented to record linkage. The cohort included residents within about one-half mile of the plant, people who lived on a contaminated property or had direct contact with the waste rock, former plant workers, and workers' household members. Some had no history of living in the study area. Members were interviewed 2001 to 2004. Cancer follow-up ran 1988 to 2010, and the mortality analysis covered 2001 to 2011.
• Exposure: Libby amphibole asbestos (actinolite-tremolite-winchite-richterite series) from a vermiculite processing plant. Pathways included plant emissions to ambient air, work at the plant, household contact with workers, moving or using waste rock, installing insulation, and children playing on waste piles. Modeled cumulative ambient exposure was calculated for 5161 people. The geometric mean for the whole cohort was 0.0005 fibers/cc x months.
• Main results:
  • From 1988 to 2010 there were 636 incident cancers in the cohort. These included seven mesotheliomas (three in males, four in females) and 118 lung cancers (66 in males, 52 in females).
  • Mesothelioma incidence was significantly elevated in females: PIR 11.76 (95% CI 3.17, 30.12), and 11.11 (95% CI 2.99, 28.45) after adjusting for the area's overall cancer deficit. It was not significantly elevated in males (PIR 2.38) or in both sexes combined.
  • Lung cancer incidence was significantly elevated in males (PIR 1.54; 95% CI 1.19, 2.00) and in females (PIR 1.62; 95% CI 1.21, 2.12). It remained elevated after adjustment: males 1.48 (1.14, 1.88), females 1.54 (1.15, 2.02).
  • Among 526 cohort deaths from 2001 to 2011, the whole cohort had elevated all-cause mortality (SMR 1.11; 95% CI 1.02 to 1.21) and elevated cancer mortality (SMR 1.25; 95% CI 1.06 to 1.46).
  • In the whole cohort, there were 4 mesothelioma deaths (SMR 5.37; 95% CI 1.46 to 13.76) and 55 lung cancer deaths (SMR 1.67; 95% CI 1.26, 2.17).
  • Several causes of death were significantly elevated in females but not in males. These were mesothelioma (3 deaths, SMR 18.97; 95% CI 3.91, 55.45), lung cancer (SMR 1.91; 1.27, 2.76), COPD (SMR 1.71; 1.04, 2.64) and all cancers. Deaths from all respiratory cancers combined were elevated in both males (SMR 1.53) and females (SMR 1.88).
  • Two mesothelioma deaths occurred among females with no history of occupational asbestos exposure (SMR 13.56; 95% CI 1.64, 48.98).
  • SMRs did not increase with increasing cumulative ambient exposure for any outcome. However, all four mesothelioma deaths were in the highest category, above the 75th percentile (SMR 10.35; 95% CI 2.82, 26.50).
  • In sensitivity analyses, mesothelioma and lung cancer SMRs remained significant after plant workers were removed. They also remained significant after people who had played on the waste piles were removed.
• The authors' conclusion: The authors concluded that low-dose community exposure to Libby amphibole asbestos from a neighborhood vermiculite plant is associated with increased asbestos-related disease and mortality. They noted excess mesothelioma and lung cancer deaths in females even when accounting for possible occupational exposure. They stated that continued clinical follow-up and surveillance are warranted.
• Limitations the authors state:
  • Smoking was common (57% ever smokers, more than the state average), and the excess of lung cancer may be largely due to smoking rather than asbestos.
  • The authors could not rule out that lung cancer rates were raised by combined effects of smoking and asbestos.
  • Mesothelioma numbers were very small: seven incident cases and four deaths.
  • Restricting the mortality analysis to 2001 to 2011 removed older long-term residents and former workers, and may have underestimated death rates.
  • The PIR can be biased if the cohort's overall cancer rate differs from the reference population. The authors adjusted for an estimated overall cancer deficit in the area.

Topics

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

Medical terms in this study, explained in our Lexicon: Libby Vermiculite, vermiculite, Occupational History, Mesothelioma, Lung Cancer, standardized mortality ratio (SMR), COPD, Libby amphiboles.

Related studies

• Radiographic evidence of nonoccupational asbestos exposure from processing Libby vermiculite in Minneapolis, Minnesota — B.H. Alexander, K.K. Raleigh, et al. (2012)
• Select mortality and cancer incidence among residents in various U.S. communities that received asbestos-contaminated vermiculite ore from Libby, Montana — D.K. Horton, F. Bove, et al. (2008)
• Vermiculite worker mortality: estimated effects of occupational exposure to Libby amphibole — T.C. Larson, V.C. Antao, et al. (2010)
• Vermiculite, respiratory disease, and asbestos exposure in Libby, Montana: update of a cohort mortality study — P.A. Sullivan (2007)
• Mortality in a cohort of vermiculite miners exposed to fibrous amphibole in Libby, Montana — J.C. McDonald, J. Harris, et al. (2004)
• Low-level fiber-induced radiographic changes caused by Libby vermiculite: a 25-year follow-up study — A.M. Rohs, J.E. Lockey, et al. (2008)

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