Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:5:p3
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 5 (pt 3/18)
Character Range: 2973679–2979788

averaging intakes over the period of exposure (essentially the exposure duration multiplied by 365 days in a year). It is noted that the exposure duration cancels out in the exposure equations for threshold compounds.

For non-threshold toxicants, intakes are calculated by averaging the total cumulative dose over a lifetime. This approach for carcinogens is based on the assumption that a high dose received over a short period of time is equivalent to a corresponding low dose spread over a lifetime (US EPA 1989). The convention is almost universally to use an averaging time of a 70-year lifetime, expressed as days, resulting in an estimate of exposure as an annual average daily rate. Hence, for non-threshold contaminants, the averaging time is important.

At birth, the average male in Australia has a life expectancy of 79 years and the average female has an expectancy of 84 years (enHealth 2012b). In fact, according to the 20062008 life tables from the Australia Bureau of Statistics, 88% of females and 81% of males are still alive at age 70. By age 85, these numbers have almost been halved with 40% of males and 56% of females still alive, and these numbers drop rapidly for the next 10 years. Cancer is a disease that can take many years to form, with estimates ranging from 1020 years total. Thus, exposures in the environment that occur into old age are unlikely to have impacts on cancer rates later in life due to the rapid increase in mortality after age 85. Allowing for 1015 years of cancer development, considering lifetime exposure to age 70 would cover the average lifespan for men and women and it would cover most exposure periods where cancers are likely to be initiated. On this basis, the averaging time of 70 years has been retained for carcinogens.

Table 5. Exposure parameters*
                                                                                                                                                                                                                                                                   HIL A                             HIL B         HIL C
Parameter                                                                                                                                                                                                                Symbol (refer to Appendix B)  Units       residential                       residential   Open space  HIL D Commercial/industrial scenario
                                                                                                                                                                                                                                                                   scenario                          scenario      scenario
                                                                                                                                                                                                                                                                   Adult                             Child         Adult       Child                                 Adult   Child  Adult
Body weight                                                                                                                                                                                                              BWA or BWC                    kg          70                                15            70          15                                    70      15     70
Exposure duration                                                                                                                                                                                                        EDA or EDC                    years       29                                6             29          6                                     29      6      30
Exposure frequency                                                                                                                                                                                                       EF                            days        365                               365           365         365                                   365     365    240
Soil/dust ingestion rate1                                                                                                                                                                                                IRSA or IRSC                  mg/day      50 2                              100 2         12.5 3      25 3                                  25 4    50 4   25 5
Soil/dust to skin adherence factor                                                                                                                                                                                       AF                            mg/cm2/day  0.5                               0.5           0.5         0.5                                   0.5     0.5    0.5
Skin surface area                                                                                                                                                                                                        SAA or SAC                    cm2         20 000                            6100          20 000      6100                                  20 000  6100   20 000
Fraction of skin exposed                                                                                                                                                                                                 Fs                            %           31.5                              44.3          31.5        44.3                                  31.5    44.3   19
Dermal absorption factor                                                                                                                                                                                                 DAF                           %           Chemical specific values applied
Time