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. 2016 Jun:77:167-74.
doi: 10.1016/j.yrtph.2016.01.021. Epub 2016 Feb 4.

The bottom-up approach to bounding potential low-dose cancer risks from formaldehyde: An update

Thomas B Starr  1 , James A Swenberg  2
Affiliations
Free article

The bottom-up approach to bounding potential low-dose cancer risks from formaldehyde: An update

Thomas B Starr et al. Regul Toxicol Pharmacol. 2016 Jun.
Free article

Abstract

In 2013, we proposed a novel bottom-up approach to bounding low-dose cancer risks that may result from small exogenous exposures to chemicals that are always present in the body as a result of normal biological processes. The approach utilizes the background cancer risk and the background (endogenous) concentration of a cancer-related exposure biomarker in specific target tissues. After allowing for statistical uncertainty in these two parameters, the ratio of the background risk to background exposure provides a conservative slope factor estimate that can be utilized to bound the added risk that may be associated with incremental exogenous exposures. Our original bottom-up estimates were markedly smaller than those obtained previously by the US Environmental Protection Agency (USEPA) with a conventional top-down approach to modeling nasopharyngeal cancer and leukemia mortality data from a US worker cohort. Herein we provide updated bottom-up estimates of risk for these two cancers that are smaller still, and rely upon more robust estimates of endogenous and exogenous formaldehyde-DNA adducts in monkeys and a more robust estimate of the DNA adduct elimination half-life in rats, both obtained very recently. We also re-examine the worker mortality data used by USEPA in developing its estimate of human leukemia incidence from lifetime exposure to 1 ppm airborne formaldehyde. Finally, we compare a new bottom-up slope estimate of the risk of rat nasal cancer with conventional top-down estimates obtained with empirical dose-response modeling of rat nasal cancer bioassay data.

Keywords: Bottom-up approach; Carcinogenic risk assessment; Endogenous formaldehyde; Exogenous formaldehyde; Formaldehyde-DNA adducts; Upper 95% confidence bound.

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