Dioxins, furans, and dioxin-like PCBs can be assessed individually, or as an entire class of chemicals. To determine their combined toxicity, toxicity equivalency factors (TEFs) are applied to each congener's concentration, resulting in a toxicity equivalent concentration (TEQ). The summation of the congener's TEQs results in a Total TEQ that can be used for screening against the 2,3,7,8-TCDD (also TCDD or TCDD, 2,3,7,8-) PRG or for calculating cancer risk and hazard index. Section 2.3.5 of the RAIS Chemical PRG and Risk Calculator's User's Guides provides detail on the use of TEFs and TEQs for risk assessment. For the PRG and Risk Calculators, the dioxins, furans, and dioxin-like PCBs are assessed individually only when toxicity values are available from sources in the hierarchy, otherwise, the TEF/TEQ approach is recommended.

This tool will simultaneously calculate the dioxin TEQ in soil, water, and biota as well as oral cancer slope factor (CSFo), inhalation unit risk (IUR), chronic oral reference dose (RfD), and chronic inhalation reference concentration (RfC) toxicity values. Enter the exposure point concentration for each congener, and the form will automatically generate the dioxin TEQ. 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. If you have multiple samples, the EPA's 2014 dioxin TEF calculator spreadsheet can handle multiple samples and calculate exposure point concentrations.

Select the desired source of TEF values from the drop-down menu. If a TEF needs to be changed to recreate old dioxin equivalent concentration calculations or to use a TEF specific to your program, enter the value in the "User-Entered TEF" column. Since this tool screens against TCDD, 2,3,7,8-, changes to the TEF value of TCDD, 2,3,7,8- are not permitted. An orange outlined cell will appear if a TEF value is changed. At the end of the form there is a button to reset the TEFs, media concentrations, and units for the source selected. When switching between TEF sources, the TEFs, media concentrations, and units will reset. The 1998 and 2005 WHO TEFs can be found here and the 2022 BEF and WHO TEFS can be found here. The 2005 WHO TEFs are currently set as the defaults and used in the RAIS calculators.