Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:5:p4
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 5 (pt 4/7)
Character Range: 2825149–2828301

depends on age at exposure, with higher lifetime risks attributable to exposures at younger ages. This is also noted by WHO (2000; 2011). Consistent with US EPA guidance, the derivation of non-threshold values for vinyl chloride has incorporated factors that address early life susceptibility and hence, if the US EPA non-threshold values are adopted, (also considered in the WHO values) no additional adjustment is required in the quantification of exposure. It is noted, however, that the application of the US EPA values for exposures by adults only (such as workers) needs to adopt the most correct values that do not include early-life susceptibility.

The most sensitive end point for vinyl chloride (particularly inhalation, which will dominate the derivation of an HIL) is carcinogenicity (noting that in the derivation of the ADWG both carcinogenic and non-carcinogenic effects were considered as sensitive for the oral pathway). Hence, the selection of appropriate non-threshold values for the assessment of vinyl chloride exposure is relevant.

The following quantitative non-threshold values are available for vinyl chloride from Level 1 Australian and International sources:
Source             Value                                Basis/Comments
Australian
ADWG (NHMRC 2011)  Adopted WHO non-threshold approach.  Current guideline derived on the basis of the WHO non-threshold value and additional consideration of non-carcinogenic effects with a TDI of 0.00013 mg/kg/day associated with a no-effect level of 0.13 mg/kg/day from lifetime studies in rats, and 1000-fold uncertainty factor.
OCS (2012)         No evaluation available

International
WHO DWG (2011)        SF = 1.15 (mg/kg/day)-1 (for exposures from birth)    WHO (2011, last review in 2004) derived on the basis of linear extrapolation from dose response data for all liver tumours from an oral exposure study in rats and assuming a doubling of the risk of exposure from birth (incorporating the 2-fold uncertainty identified by the US EPA (2000) review to address early life sensitivity. Exposures by workers (only adults) can be calculated on the basis of a slope factor that is 2 times lower.
                      SF = 0.7 (mg/kg/day)-1 (for exposures as adults)
WHO (2000)            UR = 1x10-6 (g/m3)-1                                 Inhalation unit risk derived on the basis of occupational exposures studies associated with haemangiosarcoma and a linear multistage model.  The value derived is noted to be limited as it does not address early life sensitivity identified in newborn animals (relevant to exposures by children to 10 years).
Health Canada (1992)  SF = 0.26 (mg/kg/day)-1                               Slope factor based on the upper value from a free extrapolation method associated with hepatocellular angiosarcomas in female rats. The evaluation is older than that considered by WHO and US EPA and does not include any consideration of early life sensitivity.

RIVM (2001)           SF = 0.17 (mg/kg/day)-1                               Slope factor derived on the basis of hepatocellular carcinomas, angiosarcomas and neoplastic nodules in female