Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1:p2
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1 (pt 2/16)
Character Range: 2055114–2058091

Australia (Ng et al. 2009) has not identified a default value.

As a note, some default bioavailability values have been adopted in the USA (based on reviews of state-specific data) as follows:
    * Region 8 (US EPA 2009) recommends a default of 0.5 (50%), noting that where concentrations are near a level of concern, site-specific bioavailability data is recommended.
    * Region 10 (US EPA 2000) recommends a default of 0.8 (80%) for soil at smelter sites, 0.6 (60%) for soil at mine sites and 1 (100%) for all other sites.
    * Texas recommends a default of 0.78 (78%).
While it may not be sufficiently conservative to apply a low value as adopted by the Australian Pesticides and Veterinary Medicines Authority (APVMA) (25%), some consideration of a conservative default in Australia is presented. It is noted that bioavailability is complex; however, based on relative bioavailability data available for Australian sites (presented in Ng et al. 2009; Juhasz et al. 2003), upper values were in the range of approximately 5070% with most significantly lower than these values, and a few studies reporting upper limit values that are higher (up to 97%). Juhasz et al. (2003) suggested a worst-case value of 50% could be considered. When considering long-term exposures from soil it is overly conservative to consider the maximum bioavailability value from one particular study, as exposures will be averaged over accessible soil/dust. Hence it would be reasonable to consider a conservative value of 70% bioavailability as a reasonable upper estimate that adequately addresses arsenic that may be derived from mine sites, smelters, railway corridors and other areas where herbicides/pesticides have been used.

Roberts et al. (2002) showed monkey absorption of arsenic from pesticide-treated soil and cattle dip soil is 10.724.7%. In August 2001, the US EPA Health Effects Division's Hazard Identification Assessment Review Committee (HIARC) evaluated the toxicology database for inorganic arsenic and established toxicological end points for incidental residential and commercial/industrial exposure risk assessments (US EPA 2001). As a key component of that assessment, HIARC established the appropriate relative bioavailability of arsenic in soil versus arsenic in water. For purposes of health risk assessment, US EPA evaluated a number of studies of relative bioavailability of arsenic (US EPA 2001). After careful consideration of data reported in the various bioavailability studies, US EPA determined that the monkey was considered an appropriate study model for humans due to its similarity in excretion and gastrointestinal absorption characteristics (US EPA 2001). The US EPA identified the comprehensive monkey study conducted by Roberts et al. (2002) as the study of choice. This study was conducted on behalf of the Florida Department of Environmental Protection (DEP) in order to specifically establish a gastrointestinal absorption efficiency factor for