In May 2021, the United States Environmental Protection Agency (EPA) updated the Integrated Exposure Uptake Biokinetic (IEUBK) model, which is used to evaluate childhood exposure to lead and develop Preliminary Remediation Goals (PRGs) at lead-contaminated sites. Lead is a common chemical of interest when evaluating impacted sites due to its historic use and widespread distribution in the environment.
The May 2021 IEUBK model update changed several model input parameters, including dietary lead exposure, drinking water consumption, baseline maternal blood lead concentration, inhalation rates, and soil/dust ingestion rates. These changes are important in the model calculations of soil lead PRGs because lead PRGs are based on total lead exposure, including from the site and other sources.
The most significant change incorporates a blood lead target of 5 micrograms per deciliter (µg/dL); the previous model’s default was 10 µg/dL. The new default brings the model in line with the Centers for Disease Control and Prevention (CDC) reference level released in 2012. Previously, EPA had issued updated default parameters for the Adult Lead Model using the 5 µg/dL target, but had not modified the blood lead target in the IEUBK model until now. The overall result is that the IEUBK model now calculates a PRG of 200 milligrams per kilogram (mg/kg), protective of child exposure for residential use, using the default parameters.
What’s next?
The change in lead thresholds has not yet been incorporated into the Regional Screening Levels (RSLs). The May 2021 RSLs still list an RSL of 400 mg/kg for a residential scenario, which is based on outdated IEUBK model input parameters (ca. 1994). The RSL User’s Guide still describes lead screening compared to a target blood lead concentration of 10 ug/dl. However, because the RSL stands at odds with CDC recommendations and EPA’s own model parameters, Trihydro anticipates a change to the RSLs may be forthcoming.
At least one state (i.e. Montana) has already incorporated the PRG of 200 mg/kg into its programs. However, it is worth noting that these changes are not likely to impact projects in California where lead is evaluated using a different model (LEADSPREAD), and the blood lead target is an incremental increase of 1 ug/dl rather than a total blood lead target, resulting in a PRG of 80 mg/kg.
What does a lower default soil screening level mean for projects?
Because lower default soil screening levels can impact remediation plans, those who have sites with lead are advised to follow this topic closely for updates as changes may result in the need to re-evaluate remedial strategies.
Any additional news to consider?
Recently, EPA conducted studies of urban background concentrations of lead, finding that concentrations can exceed 200 mg/kg. With studies demonstrating that background concentrations of lead can exceed the new IEUBK model thresholds, urban sites with lead may experience more complex remediation planning challenges.
Questions?
If you have questions about how the May 2021 IEUBK model update or understanding of anthropogenic background concentrations of lead in urban soils affects your organization, contact us today.
