Response to comment on "Exposure-response modeling of non-cancer effects in humans exposed to Libby Amphibole Asbestos; update" by Benson et al. (2015) submitted by Goodman et al. (2016)

Our plain-English summary of Response to comment on "Exposure-response modeling of non-cancer effects in humans exposed to Libby Amphibole Asbestos; update" by Benson et al. (2015) submitted by Goodman et al. (2016), by R. Benson, D. Berry, J. Lockey, et al (Regulatory Toxicology and Pharmacology, 2016).

The study

• Authors: R. Benson, D. Berry, J. Lockey, W. Brattin, T. Hilbert, G. LeMasters
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2016;80:270-1
• Type of article: Letter, Comment
• Cited by: 1 article, as counted by NIH iCite
• Read it: PubMed · Publisher

In plain English

This is a reply letter, not a new study. The authors of a 2015 paper on non-cancer effects of Libby Amphibole asbestos answered criticisms by Goodman and colleagues. The critics said the outcome called LPT (not spelled out in the letter) was a poor basis for a regulatory limit. The authors replied that their 2015 paper did not set such a limit, and that EPA's IRIS Program chose that outcome. They called the wide range of follow-up times among subjects an advantage. In new analyses for this reply, results for the full cohort and the survivor cohort were similar: values labeled BMC(70) and BMCL(70), given without units, were 3.3E-03 and 1.5E-03 for the full cohort and 3.4E-03 and 1.8E-03 for the survivor cohort. A second method of choosing variables kept the same ones as before: the log of cumulative exposure and time since first exposure. Using time since last exposure instead gave what the authors called a very poor fit. The authors concluded that none of the criticisms challenged their updated results or conclusions.

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: Letter replying to a published comment on the authors' 2015 exposure-response modeling paper; includes some additional modeling done for the reply
• Who was studied: The letter does not describe the subjects in detail. It refers to a full cohort, a sub-cohort, and a survivor cohort (the cohort studied by Lockey et al. 2015), with data through 2011
• Exposure: Libby Amphibole asbestos, measured as cumulative exposure in fibers/cc-years, along with time since first exposure (TSFE) and time since last exposure (TSLE)
• Main results:
  • The authors stated that their 2015 paper did not derive a reference concentration (RfC) for Libby Amphibole asbestos. They said the choice of LPT as the endpoint was made by the EPA IRIS Program.
  • The authors considered the wide range of follow-up times in the cohort an advantage, not a limitation.
  • Modeling on the full cohort and the sub-cohort, using data through 2011, gave results that the authors said did not depend strongly on which cohort was used.
  • In new LPT modeling with the CNDH model, the full cohort had BMC(70) 3.3E-03 and BMCL(70) 1.5E-03. The survivor cohort had BMC(70) 3.4E-03 and BMCL(70) 1.8E-03. Units are not stated.
  • A backwards elimination procedure using the CNDH model kept the log of cumulative exposure, ln(CE), and TSFE, and excluded all other candidate variables. This matched the earlier logistic regression.
  • Across four models in the full cohort, using TSLE instead of TSFE gave a much poorer fit. For the CNDH model, the fit score (AIC) was 344.67 with TSFE and 397.58 with TSLE.
• The authors' conclusion: The authors concluded that none of the issues raised by Goodman et al. challenged the validity of their updated modeling results or their conclusions.
• Limitations the authors state:
  • The authors agreed with the critics that the 2015 screening of covariates had used only logistic regression and not the other models. They then ran an additional check using the CNDH model.

Topics

Medical terms in this study, explained in our Lexicon: Libby amphiboles.

Related studies

• Comment on "Exposure-response modeling of non-cancer effects in humans exposed to Libby Amphibole Asbestos; update" by Benson et al. (2015) — J.E. Goodman, K. Zu, et al. (2016)
• Comment on "HRCT/CT and Associated Spirometric Effects of Low Libby Amphibole Asbestos Exposure" by Lockey et al (2015) — G. Tao, K. Zu, et al. (2015)
• Influence of exposure assessment and parameterization on exposure response. Aspects of epidemiologic cohort analysis using the Libby Amphibole asbestos worker cohort — T.F. Bateson, L. Kopylev (2015)
• Pulmonary inflammatory and fibrotic responses in Fischer 344 rats after intratracheal instillation exposure to Libby amphibole — D.J. Padilla-Carlin, M.C. Schladweiler, et al. (2011)
• Long-term response of rats to single intratracheal exposure of Libby amphibole or amosite — J.M. Cyphert, D.J. Padilla-Carlin, et al. (2012)
• Where occupation and environment overlap: US Forest Service worker exposure to Libby Amphibole fibers — M. Harper, C. Butler, et al. (2015)

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