Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1:p6
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1 (pt 6/10)
Character Range: 2750662–2753856

the basis of Leydig-cell tumours in the testes of rats and a linear multistage model. Inhalation unit risk from rat study is supported by a similar unit risk of 9 x10-7 (g/m3)-1 derived from increased incidence of hepatic tumours in a cohort study of occupationally exposed adults. The non-threshold approach was adopted by the WHO as TCE was considered genotoxic and carcinogenic.
EU (2004)                     SF = 0.0019 (mg/kg/day)-1      TCE gives rise to concern for humans owing to possible mutagenic and carcinogenic effects and because it is not possible to identify a threshold exposure level below which these effects would not be expressed. For non-carcinogenic effects, the most sensitive threshold effect evaluated was associated with CNS disturbance following repeated dose where a NOAEL of 38 mg/kg/day was considered.
                                                             The EU has presented a calculation of lifetime cancer risk based on the T25 method in relation to non-Hodgkin lymphoma. From an inhalation study in female mice a HT25 dose descriptor for humans was derived as 130 mg/kg/day. Following the approach presented, the EU calculated increased cancer risk for TCE for all groups using an equivalent slope factor of 0.0019 (mg/kg/day)-1. This value was used in the quantification of risk associated with exposure from oral, dermal and inhalation pathways for workers, consumers and environmental exposures.
Health Canada (2005)          SF = 0.000811 (mg/kg/day)-1    Oral slope factor derived on the basis of the same study noted in WHO (2011), however a slightly different value is quoted.
                              UR = 1.2x10-7 (g/m3)-1        Inhalation unit risk based on renal adenocarcinomas in rats following inhalation exposures for 104 weeks in males (a lower, less conservative value was derived for females).
                              TDI = 0.00146 mg/kg/day        Note that the derivation of drinking water guidelines has also considered the oral TDI noted in the WHO DWG which results in a lower guideline than is derived on the basis of the oral slope factor.
CCME (2007)                   SF = 0.000811 (mg/kg/day)-1    Slope factor based on same study noted by Health Canada (2005).
                              UR = 6.4x10-7 (g/m3)-1        Inhalation unit risk based on older evaluation from Health Canada where a TC05 (concentration expected to cause a 5% incidence in cancer) of 0.082 mg/m3 and extrapolation based on an excess lifetime cancer risk of 10-6.
                              TDI = 0.00146 mg/kg/day        TDI and TC values also presented for non-carcinogenic end points.
                              TC = 0.04 mg/m3                TDI as noted by WHO DWG
                                                             TC adopted from the former US EPA RfC (currently withdrawn pending finalisation of the 2009 draft) associated with effects on the CNS, kidney, liver and endocrine system in inhalation studies where a point of departure (POD) of 38 mg/m3 was identified, and an uncertainty factor of 1000 adopted.
RIVM (2001)                   PTDI = 0.05 mg/kg/day          Provision threshold values derived