Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:11:p2
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 11 (pt 2/9)
Character Range: 2269756–2272495

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.

    11.3.1     Oral Bioavailability
Bioavailability has not been considered in the previous HIL, as insufficient data is available to adequately define the bioavailability of the different forms of nickel from soil. 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 the rate of nickel absorption from the gastrointestinal tract is dependent on its chemical form. While soluble nickel compounds (e.g. NiSO4) are better absorbed than relatively insoluble ones, the contribution of the poorly soluble compounds to total nickel absorption may be more significant, since they are more soluble in the acidic gastric fluids. In human volunteers who ingested nickel sulfate in the drinking water or food, at doses of between 12 and 50 µg/kg body weight (one treatment), the amount of nickel absorbed averaged 27±17% of the dose ingested in water compared with 0.7±0.4% of the same dose ingested in food (WHO 1991). These issues should be addressed in a site-specific assessment.

    11.3.2     Dermal absorption
Nickel is a potent skin sensitiser, and as many as 1–4% of men and 8–20% of women in the general population may be nickel-sensitive. Both oral and dermal exposures to nickel can cause hypersensitivity reactions of the skin. There has been a limited number of studies on the dermal absorption of nickel through human skin and even fewer examining uptake from soil. The Environment Agency (EA 2009a) reviewed the available studies and recommended the use of a value of 0.005 (0.5%), based on a study by Moody et al. (2009).

Moody et al. (2009) measured in vitro dermal absorption of radioactive nickel chloride through human breast skin over a 24-hour period with and without a spiked commercial soil. It is noted that several studies have noted that most nickel applied as a soluble salt is bound within the skin and does not reach systemic circulation though, until this effect is better documented, the dermal absorption value from Moody et al. (2009) has been adopted in the derivation of a soil HIL.

It is noted that US EPA (2004) has recommended the use of a gastrointestinal absorption factor (GAF) of 4% for nickel based on a diet study in rats used in the derivation of the oral RfD. Little supporting information is available on the basis for the GAF recommended by US EPA. The recommended oral TRV is derived from WHO (2008) as used in the derivation of the guidelines for drinking water. The TRV is based