In 2007 the California Office of Environmental Health Hazard Assessment (OEHHA) developed a 1 microgram per deciliter (µg/dL) benchmark for source-specific incremental change in blood lead levels for protection of school children and fetuses. In 2009 OEHHA commenced an effort to estimate lead concentrations in soil that would lead to an incremental increase in blood lead (PbB) of up to 1 µg/dL, in people exposed to that soil (Revised California Human Health Screening Levels for Lead, Note table 3). For the residential scenario for lead, OEHHA evaluated the exposure to a child resident. For the commercial/industrial scenario, OEHHA evaluated the exposure to a pregnant adult worker.

The Department of Toxic Substances Control’s (DTSC) Leadspread model was used to estimate blood lead concentrations in children. The Leadspread model considers exposure to lead in soil by three pathways: ingestion, re-suspension and inhalation, and dermal contact. The Leadspread model was queried for the soil lead concentration that would give rise to a 90th percentile estimate of increase in blood lead of 1 µg/dL, which resulted in a soil lead concentration of 80 milligrams per kilogram (mg/kg). This value is currently used by DTSC as a screening level for residential, or unrestricted, land use.  Soils with a total lead concentration of 80 mg/kg or less are usually considered acceptable for reuse without restriction.

U.S. EPA’s Adult Lead Model (ALM) was used to estimate the blood lead concentration in a fetus of an adult worker exposed to lead-contaminated soil. The model was queried directly for the soil lead concentrations that would give rise to the 90th percentile estimate of change in blood lead of 1 µg/dL, which resulted in a soil lead concentration of 500 mg/kg. This value is currently used by DTSC as a screening level for commercial/industrial land use. Soils with a total lead concentration of 500 mg/kg or less are usually considered acceptable for use at commercial/industrial properties with prior written approval from DTSC, but land use restrictions are required to prevent unacceptable risk by limiting the use of the property.

The application of these screening levels in determining appropriate actions for soils containing lead is further discussed in Human Health Risk Assessment (HHRA) Note 3 and in LeadSpread-9 which are issued by the Human and Ecological Risk Office (HERO) of DTSC.