Linear low-dose extrapolation for noncancer heath effects is the exception, not the rule

Lorenz R. Rhomberg, Julie E. Goodman, Lynne T. Haber, Michael Dourson, Melvin E. Andersen, James E. Klaunig, Bette Meek, Paul S. Price, Roger O. McClellan, Samuel M. Cohen

Research output: Contribution to journalReview articlepeer-review

67 Scopus citations


The nature of the exposure-response relationship has a profound influence on risk analyses. Several arguments have been proffered as to why all exposure-response relationships for both cancer and noncarcinogenic endpoints should be assumed to be linear at low doses. We focused on three arguments that have been put forth for noncarcinogens. First, the general "additivity-to- background" argument proposes that if an agent enhances an already existing disease-causing process, then even small exposures increase disease incidence in a linear manner. This only holds if it is related to a specific mode of action that has nonuniversal propertiesproperties that would not be expected for most noncancer effects. Second, the "heterogeneity in the population" argument states that variations in sensitivity among members of the target population tend to "flatten out and linearize" the exposure-response curve, but this actually only tends to broaden, not linearize, the dose-response relationship. Third, it has been argued that a review of epidemiological evidence shows linear or no-threshold effects at low exposures in humans, despite nonlinear exposure-response in the experimental dose range in animal testing for similar endpoints. It is more likely that this is attributable to exposure measurement error rather than a true nonthreshold association. Assuming that every chemical is toxic at high exposures and linear at low exposures does not comport to modern-day scientific knowledge of biology. There is no compelling evidence-based justification for a general low-exposure linearity; rather, case-specific mechanistic arguments are needed.

Original languageEnglish (US)
Pages (from-to)1-19
Number of pages19
JournalCritical reviews in toxicology
Issue number1
StatePublished - Jan 2011


  • Additivity to background
  • dose-response
  • exposure measurement error
  • linear
  • nonlinear
  • population heterogeneity
  • threshold

ASJC Scopus subject areas

  • Toxicology


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