Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:8:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 8 (pt 1/8)
Character Range: 2199628–2202595

8                   Lead

8.1              General
Several comprehensive reviews of lead in the environment and its toxicity to humans are available and should be consulted for more detailed information (ATSDR 2007; IARC 2006; WHO 1989; WHO 2000). The following provides a summary of the key aspects of lead that are relevant to the derivation of a soil HIL.

Lead (Pb) is a naturally occurring element found in the Earth's crust at an average concentration of approximately 15 to 20 mg/kg. It is most commonly found in ores such as galena (PbS), anglesite (PbSO4) and cerussite (PbCO3). Lead is a bluish-grey, soft, dense, malleable, corrosion-resistant metal that is solid at room temperature and has a low melting point. It exists in three oxidation states—Pb(0) (metallic lead), Pb(II) and Pb(IV). The most common oxidation state of lead is Pb(II) (ATSDR 2007).

Lead is of primary use in a wide range of materials including batteries, metal alloys, X-ray shielding materials, ammunition, chemical-resistant linings and pigments. Lead has been widely used historically as an additive in petrol and also in many paints (ATSDR 2007).

Health effects associated with exposure to inorganic lead and compounds include, but are not limited to, neurotoxicity, developmental delays, hypertension, impaired haemoglobin synthesis, and male reproductive impairment. The most sensitive targets for lead toxicity are the developing nervous system, the haematological and cardiovascular systems and the kidney. However, due to the multi-modes of action of lead in biological systems, lead could potentially affect any system or organ in the body. The effects of lead exposure have often been related to the blood lead content, which is generally considered to be the most accurate means of assessing exposure (MfE 2011).

8.2              Previous HIL
The derivation of the previous HIL (HIL A = 300 mg/kg) for lead is presented by Maynard (1991). In summary, the HIL was derived on the basis of the following:
    * Intakes of lead from other sources were estimated from air, water, food, dust and soil (background). Based on available data from Australia these were estimated to be 20.3 µg/day (absorbed). In the calculations undertaken using a PTWI, this comprised 48% of the PTWI, leaving the intake from soil to be 52% of the PTWI.
    * Three approaches were presented in relation to the derivation of a soil HIL:
             + Use of a PTWI

                      o A provisional tolerable weekly intake (PTWI) of 25 µg/kg/week referenced from the Joint FAO/WHO was adopted as the toxicity reference value

                      o Soil intake of 80 mg/day was assumed with 100% bioavailability

                      o Dermal absorption was considered negligible

                      o Guideline value calculated was 300 mg/kg.

             + Consideration of 'safe' blood lead

                      o A blood lead goal of 7.5 µg/dL was considered (based on a NOAEL