Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1:p11
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1 (pt 11/16)
Character Range: 2079243–2082204

a single TRV for the assessment of arsenic exposures, the oral TRV used for the derivation of the soil HIL has not been considered to be a definitive value (refer to the calculations presented below). In addition, the approach adopted is based on developing science that should be reviewed in line with further developments in both science and policy.

    1.4.4         Inhalation Values
Less data is available with respect to inhalation exposures to arsenic, though trivalent arsenic has been shown to be carcinogenic via inhalation exposures (with lung cancer as the end point). Review of the relevant mechanisms for carcinogenicity by RIVM (2001) suggests that the mechanism for arsenic carcinogenicity is the same regardless of the route of exposure. Hence a threshold is also considered relevant for the assessment of inhalation exposures. This is consistent with the approach adopted in the derivation of the previous arsenic HIL (Langley 1991) and in the review undertaken by APVMA (2005). While NEPC and APVMA adopted the oral PTWI as relevant for all routes of exposure, RIVM (2001) has derived an inhalation-specific threshold value. The RIVM (2001) review identified that the critical effect associated with chronic inhalation exposures in humans is lung cancer. The lowest observable adverse effect concentration (LOAEC) for trivalent arsenic associated with these effects is 10 μg/m3 (based on the review by ATSDR 2007). Applying an uncertainty factor of 10 to address variability in human susceptibility, a tolerable concentration (TC) in air of 1 μg/m3 was derived.

Given the above, there is some basis for the assessment of inhalation exposures to arsenic to adopt an appropriate threshold value but the available epidemiological studies associated with exposures in copper smelters suggest a linear or non-threshold approach may be relevant. The WHO (2000) review of arsenic also suggested the use of a linear (non-threshold) approach to the assessment of inhalation exposures to arsenic. The assessment presented is limited and essentially adopts the US approach with no discussion or consideration of the relevance of the linear model adopted. The review by WHO (2001) with respect to inhalation exposures and lung cancer provides a more comprehensive review and assessment. The review presented identified that a linear doseresponse relationship is supported by the occupational and epidemiological studies. The three key studies associated with copper smelters in Tacoma, Washington (USA), Anaconda, Montana (USA) and Ronnskar (Sweden) (as summarised by WHO 2001) demonstrate a statistically significant excess risk of lung cancer at cumulative exposure levels of approximately 0.75 mg/m3 per year.

The relevance of inhalation values derived from studies near smelters to the assessment of contaminated arsenic in soil in areas away from smelters is not well founded. Hence it is recommended that a threshold approach is considered for