Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:5:p9
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 5 (pt 9/18)
Character Range: 2994259–2997175

is assumed to be derived from the contaminated site.

5.3.3.2         Indoor dust concentrations
For the purpose of deriving the HILs, soil-derived dust concentrations in indoor air have been generally calculated using the approach proposed by EA (2009e). Indoor dust concentrations are assumed to equilibrate with outdoor dust concentrations, as described by the PEF, through natural building ventilation. In addition, indoor air is considered to be enriched with dust compared to the outdoor environment, due to the movement of dust indoors on clothing, footwear, pets, etc. and the potential for the resuspension of dust particles in the indoor environment (EA 2009e). To address this issue, the indoor dust concentration (or dust loading factor) is assumed to be equal to the 95th percentile from Australian data (enHealth 2012a), which is 39 µg/m3.

A significant proportion of house dust can be attributed to soil particles that have been tracked into the indoor environment from outdoors. enHealth (2012a) consider that 50% of the indoor dust is derived from the site soil, in accordance with the recommendations made by US EPA (2008; 2011). This value is the 'indoor dust transport factor' (TF), and is the same for all scenarios. The TF is multiplied by an 'indoor dust loading factor' (DL) to represent the proportion of this indoor dust (which is largely on the floor) that is resuspended into air by people moving about the building.

5.3.3.3         Dust lung retention factor
Dust particulates are characterised by enHealth (2012a) according to the following particulate size distribution:
    * total suspended particulates (particles with a diameter of 50 µm or less)  estimates inspirable dust
    * PM10 (particulate matter less than 10 µm in diameter) – estimates respirable dust
    * PM2.5 (particulate matter less than 2.5 µm in diameter)  estimates the respirable fraction thought to be related to health effects associated with urban pollution.
The dust lung retention factor describes the percentage of respirable dust that is small enough to be retained in lungs and is associated with health effects. For both indoor and outdoor dust exposures, the respirable fraction is estimated at 37.5% of the inspirable fraction. This fraction is consistent with the fraction considered in the previous HILs (NEPC 1999) and enHealth guidance (enHealth 2004), where it was considered that 75% of the inhaled (inspirable) dust will be retained in the respiratory tract (25% exhaled) of which 50% is small enough to reach the pulmonary alveoli, resulting in a respirable fraction of 37.5%.

    5.3.4         Indoor and outdoor inhalation of vapours derived from soil
This exposure pathway considers exposure to chemical vapours released from soil into indoor and outdoor air. The indoor inhalation of soil-derived vapours is often the most critical exposure pathway for volatile contaminants. Further