Mesothelioma Risk in the North Carolina Textile Cohort Quantified

By: Erin Therrian, Ray Harris

THE COHORT

EPA relied on the North Carolina textile cohort in its 2020 chrysotile risk evaluation for mesothelioma.1 The cohort comprised workers at four asbestos textile plants.2 The 2009 study relied on death certificates coded to pleural cancer before 1999 and to mesothelioma from 1999 to 2003. Plants 1 and 2 had no mesotheliomas or pleural cancers. There were three pleural cancers in plant 3. In plant 4, the authors reported four mesotheliomas and one pleural cancer.

THE DOSE-RESPONSE

The 2009 paper described the lung-cancer dose-response in the cohort and noted “[t]here were too few deaths from pleural cancer and mesothelioma for exposure–response analysis of those outcomes.”3 Nevertheless, without additional data, a 2019 paper by two of the same authors pooled the data from plants 1, 3, and 4 and quantified the risk of pleural cancer and mesothelioma.4

When the authors accounted for both cumulative exposure and time since first exposure, they reported no statistically significant association between cumulative exposure and pleural cancer or mesothelioma. With cumulative exposure alone, they reported a slight but significant increase in the risk of pleural cancer, including mesothelioma: a rate ratio of 1.15 for 100 fiber-yrs of exposure.5 But the risk was not doubled until 500 fiber-yrs of exposure.6 The 2019 authors also assessed the risk for the workers followed from 1999 to 2003. In that analysis, the risk was not statistically significant for 100 fiber-yrs of exposure.7

HOW EPA USED IT

EPA used this cohort to evaluate brake mechanics. For mesothelioma, it used the 1999–2003 subcohort.8 EPA’s estimate of a mechanic’s exposure, 0.006 f/cc over a 40-year career, or 0.24 fiber-yrs, exceeded its cancer-risk benchmark.9 The subcohort showed no significant risk at 100 fiber-yrs, more than 400 times the mechanic’s exposure. EPA projected from the subcohort’s exposures to the mechanic’s 0.24 fiber-yrs using a linear no-threshold model, which assumes a risk at every exposure above zero.

Notes

  1. U.S. Environmental Protection Agency, Risk Evaluation for Asbestos, Part I: Chrysotile Asbestos (Dec. 2020).
  2. Loomis, Dement, Wolf & Richardson, Lung Cancer Mortality and Fibre Exposures Among North Carolina Asbestos Textile Workers, 66 Occup. Envtl. Med. 535, 537, 539 (2009).
  3. Id. at 539.
  4. Loomis, Richardson & Elliott, Quantitative Relationships of Exposure to Chrysotile Asbestos and Mesothelioma Mortality, 62 Am. J. Indus. Med. 471, 472–73 & tbl. 1 (2019).
  5. Id. at 474 tbls. 2–3.
  6. 1.15 compounded five times, once for each 100 fiber-yrs, is 2.01.
  7. Loomis, Richardson & Elliott, supra note 4, at 474 tbl. 4.
  8. U.S. Environmental Protection Agency, supra note 1, at 164–65.
  9. Id. at 193 tbl. 4-23.