How to Calculate RfD From NOAEL

When conducting animal research to determine a chemical's impact on public health, the Environmental Protection Agency (EPA) uses the term "No-Observable-Adverse-Effect Level (NOAEL)" to refer to the dosage size at which adverse effects begin to appear. To predict the maximum safe level for humans, the NOAEL is then divided by several "uncertainty factors (UF)" that adjust for differences between humans and the test animals. This human-calibrated level is known as the "Reference Dose (RfD).

Instructions

• 1

  Divide the NOAEL by 10, which is the standard interspecies (humans vs. test animals) uncertainty factor.

• 2

  Divide the result from step 1 by 10, which is the standard intraspecies (individual human vs. population average) uncertainty factor.

• 3

  Visit the EPA's Integrated Risk Information System (IRIM). For a direct link, see "Resources" below.

• 4

  Type the name or chemical formula of the compound in the "Search" text field and click on the "Go" button.

• 5

  Locate the compound's name in the search results. If you cannot find the compound, use the result from step 2 as your RfD. If you can find the compound, scan across its row until you find the folder-shaped icon underneath the "Quick View" column. Click on this button. This will take you to the compiled EPA research results for the compound.

• 6

  Locate the section labeled "Reference Dose For Chronic Oral Exposure (RfD)."

• 7

  Click on the integer that appears in the column labeled "MF." This will take you to a page explaining why the researchers used that specific modification factor (MF) in the study. If the MF has to do with some innate physiological property of the compound (e.g., if humans have greater tolerance for a particular chemical if it is ingested with food versus plain water), write it down. If the MF has to do with the design of the researcher's study (e.g., the researchers were unable to arrive at a lowest-observed-adverse-effect level [LOAEL]), then ignore this MF and use the result from step 2 as the RfD. However, if your research study is also unable to establish a LOAEL, then you should write down the MF.

• 8

  Divide the result from step 2 by the MF you recorded (from step 7). This will give you the RfD for your study.