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What is an Exposure Guidance Value?
Exposure Guidance Values are estimates of the daily exposure to a chemical that are believed to be without appreciable health risks. Such values may be presented in terms of daily doses or air concentrations. These values are identified by regulatory agencies or other authoritative bodies through a risk assessment process, and are used as guidelines for making risk management decisions (e.g., estimating tolerable concentrations of a chemical in drinking water or identifying clean-up goals for a contaminated site). These values, based on chemical risk assessments, are used as the basis for BE derivation.
Several agencies set exposure guidance values that can be used as the basis for BE derivation. These values are designated by different names, including Reference Doses (RfDs), Tolerable Daily Intakes (TDIs), Reference Concentrations (RfCs), and Minimum Risk Levels (MRLs). These guidance values can refer to different routes of exposure (oral, inhalation, dermal), different health endpoints, and different exposure durations (e.g., chronic, acute). Such values are typically derived after consideration of toxicity data from animal or human studies. A “Point of Departure” (POD), usually the “no observed adverse effect level” (NOAEL) or its equivalent, is identified from the toxicity data. The POD is divided by a series of uncertainty or safety factors to produce an estimate of exposure that is unlikely to result in an adverse human health effect, resulting in the exposure guidance value.
The BE value for a particular exposure guidance value is derived by consideration of the same underlying toxicity data, and the biomarker concentration consistent with the POD as well as with the exposure guidance value itself is estimated.
The following web site provides summaries of existing exposure guidance values for many chemicals as well as links to the various agencies that derived these values:
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