Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:14:p2
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 14 (pt 2/9)
Character Range: 2336064–2338978

14.2          Previous HIL
The derivation of the previous HIL (HIL A = 250 mg/kg) for cyanide is presented by Turczynowicz (1993) and NEPC (1999). In summary, the HIL was derived on the basis of the following:
    * Background intakes of cyanide were not estimated due to a lack of data, hence it has been assumed that 25% of the adopted acceptable intake is relevant for exposures from soil.
    * A tolerable daily intake (TDI) of 12 µg/kg/day referenced from WHO was considered for free cyanide.
    * Ingestion of both soil and dust has been considered assuming 100% is bioavailable and is absorbed.
    * Dermal absorption has been considered, with a dermal absorption rate of 5% assumed.
    * Inhalation of cyanide in dust has been considered both outdoors and indoors.

14.3          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.

    14.3.1     Oral Bioavailability
Insufficient data is available to adequately define the bioavailability of free cyanide. On this basis, a default approach of assuming 100% oral (and inhalation) bioavailability has been adopted in the derivation of an HIL. It is noted that a site-specific assessment of bioavailability can be undertaken where required and relevant.

    14.3.2     Dermal absorption
Turczynowicz (1993) noted that cyanides are moderately lipid soluble, which allows them to penetrate the epidermis. Some cyanide compounds, such as potassium cyanide, have a corrosive effect on the skin that increases the rate of absorption. In addition, hydrogen cyanide and soluble cyanide salts can be absorbed by the skin. The value of 5% adopted by Turczynowicz (1993) was estimated.

Limited information is available on dermal absorption of free cyanide, however DTSC (2005) has listed a dermal absorption of 0.1 for free cyanide in soil.  Limited information is available to support the value of 0.1, though, as data is lacking, the value has been adopted in the derivation of HILs.

    14.3.3     Inhalation of Dust
Inhalation exposures associated with particulates outdoors and indoors are expected to be of less significance than ingestion of soil. While likely to be negligible, potential inhalation exposures associated with dust have been considered in the HIL derived.

    14.3.4     Inhalation of HCN Gas
The fate and partitioning of free cyanide in soil to hydrogen cyanide gas has been reviewed. Cyanide behaves somewhat differently in soil with respect to phase partitioning from volatile organics. Phase partitioning (and speciation) depends on the soil pH, ionic strength, complexation and the presence of sunlight (Larsen 2005). As noted by RIVM (2001), little HCN gas has been reported at sites where