Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:9:p2
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 9 (pt 2/7)
Character Range: 2221898–2224892

water.

9.3              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.

    9.3.1         Oral Bioavailability
Bioavailability has not been considered in the previous HIL, as insufficient data is available to adequately define the bioavailability of copper 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 a site-specific assessment of bioavailability can be undertaken where required.

    9.3.2         Dermal absorption
Limited data is available on the dermal absorption of manganese. Absorption of inorganic manganese is not considered to occur to any great extent (Lindon & Sabordo 1996). While no studies relating to dermal absorption of inorganic manganese by ATSDR (2008) are available, the review noted that for inorganic manganese compounds, dermal exposure is not a typical pathway of exposure because manganese does not penetrate the skin readily. However, for organic manganese, dermal exposure is a possibility. The HIL derived relates to inorganic manganese and hence organic compounds have not been considered further.

On the basis of the above, there is no data available to suggest that dermal absorption of manganese is significant and hence it has been assumed to be negligible in the derivation of HILs.

    9.3.3         Inhalation of Dust
Manganese is not volatile however WHO (1999) notes the following: 'Little is known about the relative toxicity of different manganese compounds. Inhaled manganese compounds tend to produce more severe toxicity than ingested manganese compounds. This is probably attributable to the difference in route-specific uptake of manganese from the lung (often assumed at 100%) compared with the gastrointestinal tract (35%). Studies have shown that a greater proportion of a manganese dose appears in the blood and brain of rats exposed via inhalation or intranasal instillation than when the same dose is given orally.'

Inhalation exposures associated with particulates outdoors and indoors are expected to be of less significance than ingestion of soil, however, due to the toxicity of inhaled manganese, it is relevant to include this pathway in the derivation of soil HILs.

    9.3.4         Plant Uptake
Manganese is a micronutrient required by plants for metabolism. Plant growth is affected by manganese deficiency as well as toxicity associated with excess levels of manganese. In general, natural levels of manganese in soil are sufficiently high to address deficiencies but where plant deficiencies occur it is typically due to manganese being present in a form not available for plant uptake. Hence the potential for plant uptake and toxicity will be dependent on