Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:8:p3
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 8 (pt 3/8)
Character Range: 2204965–2207891

noted that review by MfE (2011) considered there to be issues in the range of lead bioavailability/ bioaccessibility values, no agreed laboratory methods available and uncertainties with the doseresponse used for blood lead. Hence the MfE has considered 100% bioavailability in the derivation of a soil guideline value.

Bioavailability has been considered in the derivation of the previous HIL, with 50% adsorption considered for dietary and water intakes, 40% absorption from inhaled particulates and 30% from ingested soil/dust considered in the assessment of intakes from other sources (background) (Maynard 1991).

Review of bioavailability by IARC (2006) identified a range of values and factors that have the potential to affect absorption. Based on the range of bioavailability values presented by IARC, an oral bioavailability of 50% (from soil/dust, food and water) is considered to be sufficiently conservative. These values have been considered in the derivation of HILs.

    8.3.2         Dermal absorption
Studies relating to dermal absorption of lead are reviewed by ATSDR (2007) where low levels of inorganic lead (<1% and much lower (well below 0.1%)) were reported. IARC (2006) notes that in the limited number of studies available, dermal absorption of inorganic lead is negligible, although slightly enhanced by high perspiration rates. Based on the available data, dermal absorption of lead has been considered to be negligible, consistent with the approach adopted in New Zealand (MfE 2011) and the UK (DEFRA & EA 2002)

    8.3.3         Inhalation of Dust
Lead is not volatile and 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.

    8.3.4         Plant Uptake
IARC (2006) has noted that plant uptake of lead from soil is low due to the low bioavailability of lead in soil and its poor translocation from the root to the shoot. Of all the toxic heavy metals, lead is considered the least phytoavailable. While soil properties affect the potential for uptake and translocation, water soluble and exchangeable lead that is readily available for uptake by plants constitutes only 0.1% of the total lead in most soils. Hence a chelate (such as EDTA) is used to increase lead uptake and translocation where phytoremediation is required.

For the derivation of soil HILs it has been assumed that the small amount of lead that may be taken up into home-grown produce is essentially accounted for in the consideration of intakes from the diet. In areas where the form of lead in soil is more soluble and available for plant uptake a site-specific assessment (including the sampling of home-grown produce) should be considered.

    8.3.5         Intakes from Other Sources – Background
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