What is meant by inhalation reference concentration (RfC)?
The inhalation reference concentration (RfC) is an estimate of the daily allowable exposure of a substance, below which the human population will not experience harmful effects over a lifetime.
For more about how it is established, see
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The Inhalation Reference Concentration (RfC) is an assessment developed by the U.S. Environmental Protection Agency (EPA) to estimate the potential health risks associated with inhaling a specific substance. RfC represents the concentration of a substance in air that, when continuously inhaled over a lifetime, is unlikely to cause adverse health effects.
To understand how RfC is determined, several steps are followed:
1. Identify the substance: First, the EPA identifies the specific substance for which the RfC is needed.
2. Gather toxicity data: Relevant toxicity data related to the substance is collected from various sources, including animal studies, human studies, and epidemiological studies.
3. Select critical effects: The EPA identifies and selects the critical health effects caused by exposure to the substance, such as respiratory irritation, carcinogenicity, or other specific adverse effects.
4. Calculate a reference dose: The EPA calculates a reference dose (RfD) based on the toxicological data. RfD represents the estimated daily oral exposure dose to the substance that is without appreciable risk of harmful health effects over a lifetime.
5. Convert RfD to RfC: The RfD is then converted into an inhalation reference concentration (RfC) by adjusting it to reflect the differences in the route of exposure (inhalation rather than oral).
6. Uncertainty factors: Uncertainty factors are applied to the RfC to account for potential variability in the population's sensitivity to the substance and to ensure adequate protection for susceptible individuals.
The RfC is typically expressed in units of milligrams per cubic meter (mg/m³) or parts per million (ppm) and is used by regulatory agencies to establish guidelines and standards for occupational exposures and environmental air quality. It provides a useful tool in assessing the potential health risks associated with inhaling specific substances over prolonged periods.