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Instructions,
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Acute Inhalation Toxicity Data Using Benchmark Concentration Methodology The benchmark dose or benchmark concentration (BMC) provides an estimate of a toxicological concentration which replaces, or refines, the no observed adverse effect level (NOAEL) currently used in health risk assessment. A BMC usually lies somewhere between the NOAEL and the lowest observed adverse effect level (LOAEL). The derivation of the inhalation reference concentration (RfC) has historically used the NOAEL and uncertainty factors in order to estimate a daily [allowable] exposure that is intended to protect the human population against harmful effects of a substance over a lifetime. Uncertainty factors account for (a) extrapolation from animals to humans, (b) more sensitive human populations, and (c) provide for extrapolation for duration of exposure. Over the last few years, there is increasing support for incorporation of the BMC instead of the NOAEL in the development of the RfC. An analysis of acute lethality data from 120 studies demonstratetd that BMCs for either 1% or 5% response incidence yielded results that were consistently close to the limit of experimentally detectable effects, did not exceed the NOAEL, and the results contained a smaller degree of uncertainty as determined by statistical confidence limits (Fowles et al. 1999). The BMC has distinct advantages over the NOAEL. First, the BMC reflects the shape of the dose response curve. BMC also takes into account the study sample size, thereby reducing the variability and thus having a reduced range in the confidence limits. This yields a reduced uncertainty in the dose estimate. Furthermore, with preliminary studies, it is no longer necessary to find a NOAEL in order to determine an exposure levels from a BMC. By: Arlene Weiss, M.S., D.A.B.T. email: pharmtoxic@aol.com
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