Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:4:p5
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 4 (pt 5/5)
Character Range: 2967017–2968301

HIL that represents several contaminants. Where this has been done, directions for application of the HIL are given. The toxicity profile for the group of substances provides details of the assumptions that are inherent in the HIL for the group.

The TEF approach involves the approximation of the properties of a group of similar substances by those of a single member of the group. The components of the mixture are assumed to contribute to the toxicity in a similar way, and their relative effect is calculated in proportion to their concentration in the mixture by adjustment using a relative potency factor. This approach has been applied in the derivation of the HIL for carcinogenic PAHs using benzo(a)pyrene (BaP) as the reference substance.

The toxicity surrogate approach involves the generation of a risk level for a single 'indicator' chemical and the application of this information directly to the assessment of other similar chemicals within a group. The sum of all the chemicals in the group is compared to the HIL, assuming that their effect (if more than one of the group is present) is similar and additive. This approach is taken for cresols, PCBs, PBDEs and several groups of pesticides. The approach taken for each substance or group is described in Appendix A.