Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:8:p2
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 8 (pt 2/8)
Character Range: 2202272–2205240

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 of 15 µg/dL with a 2-fold safety factor)

                      o Based on a US EPA coefficient relating blood lead to exposure, a soil guideline of 1800 mg/kg was derived.

             + Use of US EPA Uptake/Biokinetic Model

                      o Using the US EPA model, with an air concentration of 1.5 µg/m3, soil lead levels of 8001300 mg/kg can be expected.

Based on review of the available approaches a soil guideline of 300 mg/kg for HIL A was determined.

8.3              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.

    8.3.1         Oral Bioavailability
A significant amount of data is available in relation to the bioavailability of lead. In addition, a number of international agencies have considered bioavailability in the derivation of soil guideline values. The available approaches include (MfE 2011):
    * RIVM (2001) use a relative bioavailability (the bioavailability from a soil matrix with respect to the bioavailability from the matrix in toxicity studies used to assess tolerable intakes) for lead of 0.6 (60%) in the derivation of serious (human health) risk concentrations.
    * UK and US agencies have developed models based on the relationship between exposure and blood lead concentrations to derive soil guideline values.
    * The IEUBK model was developed to describe the exposure of children to lead from multiple sources, and incorporates data on the toxicokinetics of lead – five exposure pathways are considered (air, water, diet, soil and dust). Using the various generic default parameters, including absorption factors of 0.3 for soil and dust, and 0.5 for food and water, a soil guideline value of 400 mg/kg is derived, and is considered appropriate for use in a residential scenario.
    * In contrast, the UK model considers the background exposure to lead from sources other than soil and dust, and the slope or response of the blood lead concentration versus soil and dust lead relationship.
    * WHO (2000) indicates that absorption of lead can range from 3 to 80% with typical absorption rates in adults and infants considered to be 10 and 50% respectively.
It is 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