Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:6:p3
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 6 (pt 3/12)
Character Range: 1057296–1060326

Where non-threshold TRVs are adopted (that is, assuming a linear low-dose relationship), risks are estimated as the incremental probability of an individual developing cancer over a lifetime as a result of exposure to the carcinogen. The estimated intake for each exposure pathway and non-threshold TRV are multiplied to produce pathway-specific estimates of increased lifetime cancer risks (ILCR).

However, for those carcinogens where appropriate benchmark dose data are available, the risk estimation method outlined above for threshold compounds applies.

ILCR  =  Intake (mg/kg-day) x TRV(mg/kg-day)-1
ILCR  =  exposure concentration (mg/m3) x TRV(mg/m3)-1

ILCR estimates from all pathways and all contaminants should be summed to produce a total increased lifetime cancer risk, unless evidence is available that suggests that this is not appropriate. When combining ILCR estimates, the US EPA (1989) identifies several limitations which may be considered.

These include:
    * As each non-threshold TRV is an upper 95th percentile estimate of potency, and because upper 95th percentiles of probability distributions are not strictly additive, the total cancer risk estimate might become artificially more conservative as risks from a number of different carcinogens are involved.
    * It will often be the case that substances with different weights of evidence for human carcinogenicity are included. The cancer risk equation for multiple substances sums all carcinogens equally, giving as much weight to class 2 as to class 1 carcinogens. In addition, non-threshold TRVs derived from animal data will be given the same weight as non-threshold TRVs derived from human data.
    * The action of two different carcinogens may not be independent.
In practice, it will often be the case that there is insufficient information to make a well-informed decision as to whether it is reasonable or not to sum ILCRs across either pathways or contaminants (see also Section 6.5 of this Schedule). It is recommended that a precautionary approach (set out below) should be followed under most circumstances. Where more information is available, a decision to assess contaminants or pathways as independent and non-additive should be supported with reference to the toxicology of the contaminants concerned by appropriately qualified toxicologists.
    * ICLR estimates should normally be summed across pathways unless specific evidence is provided that the cancer end-points and/or modes of action of the contaminant are clearly different for different pathways or that the same person cannot be exposed by the different pathways.
    * ICLR estimates should normally be summed across contaminants unless specific evidence is provided that the cancer end-points and/or modes of action of the contaminant are clearly different for different contaminants.
    * ILCR estimates should only be summed where they relate to an exposed population that could plausibly be exposed to all of the contaminants / pathways that are added.
    *