The Benchmark Dose Concept

The concept of the Benchmark Dose (BMD), a benchmark is a point of reference for a measurement, in health risk assessment of chemicals was first mentioned by Crump (1984) as an alternative to the NOAEL and LOAEL for noncancer health effects in the derivation of the ADI/TDI these terms are addressed in detail in Chapter 5. The BMD approach provides a more quantitative alternative to the dose-response assessment than the NOAEL/LOAEL approach. The goal of the BMD approach is to define a starting point of depariure (POD) for the establishment of a tolerable exposure level (e.g., ADI/TDI) that is more independent of the study design. In this respect, the BMD approach is not 

Toxicological Risk Assessments of Chemicals A Practical Guide 

Since the first description of the BMD approach in health risk assessment of chemicals, the method has been modified and extended by many others. Central in this work was a workshop organized by the International Life Science Institute (ILSl) and reported in Barnes et al. (1995) and a workshop organized by the US-EPA Risk Assessment Eomm resulting in a US-EPA report (US-EPA 1995). No consensus was reached at these workshops on which variation and extension of the BMD approach is most appropriate for the use in human health risk assessment. 

In the BMD approach, a curve is fitted to discrete responses (binary, dichotomous/quantal data, i.e., yes/no) or to continuous mean effect values (a response such as weight that can assume any value in a range). The curve is usually fitted to data using the maximum likelihood approach. 

For discrete responses, the BMR is typically chosen at 10% above the control response, the BMD 10 as an excess risk of 10% is considered to be at or near the limit of sensitivity in most carcinogenicity studies and in some noncarcinogenicity studies as well. If a study has greater than usual sensitivity, then a lower BMR can be used, although the BMDio and BMDLio should always be presented for comparison purposes. 

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