Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:5:p13
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 5 (pt 13/18)
Character Range: 3005515–3008417

that it is generally recognised that there may be no threshold for the neurotoxic action of lead (DEFRA 2002).

    5.4.1         Modelling adult exposures to lead
Adult exposures to lead have been estimated based upon the methodology developed by US EPA (2003) as provided in the US EPA adult lead model. This methodology is focused on estimating blood lead concentrations in female adults exposed to lead-contaminated media and the transfer of blood lead to the unborn foetus. The adult blood lead model incorporates lead exposure, uptake into the body and biokinetic transfer into the blood and developing foetus.
The adult lead intake rate (dominated by soil ingestion) is calculated. The estimated adult exposure is then converted to a blood lead concentration. The equation applied in the transfer of lead into adult blood and into the developing foetus is based on the methodology provided in US EPA (2003) and is given below.
PbBadult  =  PbBbackground  +  Pbintake x BKSF x EF
                               AT

where

PbBadult       = total adult blood lead concentration from all sources (µg/dL)
AT             = averaging time (days/year)
EF             = exposure frequency (days/year)
PbBbackground  = background adult blood lead concentration (µg/dL)
Pbintake       = total lead uptake from all media (g/day)
BKSF           = biokinetic slope factor (µg/dL per µg/day)

This approach allows for protection of the most sensitive receptor in the adult scenario, which is an unborn child carried by a pregnant mother.

    5.4.2         Modelling child exposures to lead
Child exposure to lead has been estimated using the integrated exposure uptake biokinetic model for lead in children (IEUBK model, version 1.1 Build9, released June 2009) developed by the US EPA in 2002 and described by US EPA (1998, 2007b).

The IEUBK model comprises separate components for exposure, absorption and the biokinetic transfer of lead to all tissues of the body and calculates age-specific blood lead concentrations for children aged between 0 and 7 years. The HILs are based on the age range 12 years, as this age is considered to be the most sensitive as a result of lowest body weight combined with high hand-to-mouth activity and crawling.

The components of the IEUBK model can be summarised as follows:
    * The exposure component estimates intake from soil, dust, water, air and food. The estimate is based on data input by the user. The model provides default estimates for circumstances where site-specific information is not available. Where Australian values are available (for example, lead concentration in drinking water, dietary lead ingestion rates) these have been adopted.
    * The uptake component models the process by which the lead intake is transferred to blood plasma. The amount of lead that is taken up is controlled by the bioavailability of the lead, which can be specified