Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1 (pt 1/16)
Character Range: 2052452–2055349

1                   Arsenic

1.1              General
Several comprehensive reviews of arsenic in the environment and its toxicity to humans are available and should be consulted for more detailed information not presented in this summary (ATSDR 2007; NRC 2001; WHO 2001; and EA 2009a). The following provides a summary of the key aspects of arsenic that are relevant to the derivation of a soil health investigation level (HIL).

Arsenic is a metalloid that can exist in four valence states (-3, 0, +3 and +5) and forms a steel grey, brittle solid in elemental form (ATSDR 2007). Under reducing conditions, arsenite (As III) is the dominant form and, in well oxygenated environments, arsenate (As V) predominates (WHO 2000). Arsenic is the 20th most commonly occurring element in the Earth's crust, occurring at an average concentration of 3.4 ppm (ATSDR 2007).

1.2              Previous HIL
The derivation of the HIL (HIL A = 100 mg/kg) for arsenic is presented by Langley (1991). In summary, the previous HIL was derived on the basis of the following:
    * Intakes of arsenic from other sources were estimated, with dietary intakes considered most significant for the general population. Intakes based on data from the 1987 and 1990 Australian Market Basket Surveys were estimated to be 6.7 µg/kg/week for a 2-year-old child. This was approximated to contribute up to 50% of the provisional tolerable weekly intake (PTWI) considered.
    * A PTWI of 15 µg/kg/week referenced from the World Health Organization (WHO) was adopted as the toxicity reference value.
    * Ingestion of both soil and dust was considered assuming 100% is bioavailable and is absorbed.
    * Dermal absorption was considered to be low with 1% of arsenic compounds absorbed in 24 hours;
    * Inhalation of arsenic in dust, both outdoors and indoors, has been considered.
    * The total absorption of arsenic, based on 100 mg/kg in soil, for a young child was calculated to be 11.4 µg/day, approximately 40% of the adopted toxicity reference value.

1.3              Significance of Exposure Pathways
Ingestion of soil and dust is considered the most significant pathway of exposure for inorganics in soil. The consideration of bioavailability and inclusion of other exposure pathways in the derivation of a soil HIL has been further reviewed, as noted below.

    1.3.1         Oral Bioavailability
Most international jurisdictions have adopted a default value of 100% oral bioavailability in the derivation of investigation levels, allowing site-specific bioavailability to then be considered in further assessment. It is also understood that review of arsenic bioavailability in 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