Some chemicals are members of the same family and exhibit similar toxicological properties; however, they differ in the degree of toxicity. A relative potency factor (RPF) may be applied to adjust the concentration based on the relative potency to the primary compound. Polycyclic Aromatic hydrocarbons (PAHs) are one of these chemical families. To determine their combined toxicity, relative potency factors (RPFs) are applied to each congener's concentration, resulting in a relative potency concentration (RPQ). The summation of the congener's RPQs results in a Total RPQ that can be used for screening against a benzo[a]pyrene (BaP) PRG or for calculating cancer risk. Section 2.3.6 of the RAIS Chemical PRG and Risk Calculator's User's Guides provides detail on the use of RPFs and RPQs for risk assessment.

For the PRG and Risk Calculators, a few PAHs are assessed individually by applying the RPFs to the toxicity values. Although this is not in complete agreement with the intent of RPFs, this approach was used so that toxicity values could be generated for each PAH. Computationally it makes little difference whether the RPFs are applied to the concentrations of PAHs found in environmental samples or to the toxicity values as long as the RPFs are not applied to both.

This tool will simultaneously calculate the PAH RPQ in soil, water, and biota. Enter the exposure point concentration for each congener, and the form will automatically generate the PAH RPQ. It is important to consider the number of significant digits and round appropriately. For non-detected values consider using one-half of the detection limit if no guidance is offered by your regulatory agency.

Select the desired source of RPF values from the drop-down menu. If a RPF needs to be changed to recreate old PAH RPQs or to use a RPH specific to your program, enter the value in the "User-Entered RPF" column. Since this tool screens against BaP changes to the RPF value of BaP are not permitted. An orange outlined cell will appear if a RPF value is changed. At the end of the form there is a button to reset the RPFs, media concentrations, and units for the source selected. When switching between RPF sources, the RPFs, media concentrations, and units will reset. The 1993 RPFs can be found here and the 2010 and 2006 RPFs can be found here. The 1993 RPFs are currently set as the defaults and used in the RAIS calculators.