September 18, 2024
US EPA provides guidance and recommendations for using a simple time-weighted average approach to assess cumulative lead risks that consider intermittent or variable exposures at secondary non-residential locations.
In August 2024, the US Environmental Protection Agency (US EPA) released new guidance and recommendations for the assessment of cumulative lead risks when exposures occur at multiple sites, including primary residences (for children), non-residential sites (for adults), and secondary non-residential sites (for both children and adults). US EPA also provided guidance for deriving Preliminary Remediation Goals (PRGs) and simulating intermittent air lead exposure pathways using a time-weighted average (TWA) approach. According to the guidance, secondary lead exposure sites may include recreational areas (i.e., neighboring parks or playgrounds) or contaminated worksites and should be incorporated into modeling when media lead concentrations at secondary sites differ from primary sites. Figure 1 below, from the US EPA guidance document, summarizes when intermittent or variable lead exposures should be incorporated into lead exposure modeling under the new guidance:
US EPA stated that this new methodology is not intended to replace the typical residential approach of the Integrated Exposure Uptake Biokinetic (IEUBK) model (i.e., for children 12-72 months) and non-residential approach of the Adult Lead Methodology (ALM); rather, this new guidance is intended to supplement existing guidance. Previously, US EPA’s lead models focused on simulating lead exposures at a single location. US EPA recommends incorporating secondary exposure scenarios only if receptors are exposed at a secondary site for at least three months, with exposures occurring at least once every seven days. According to US EPA, the reliability of models in predicting blood lead concentrations has not been assessed when exposures occur less than once every seven days for at least three months.
According to the new guidance, there are several factors that could contribute to either an overestimation or underestimation of blood lead concentrations when time-weighted exposures to media concentrations are used as inputs to the IEUBK model and ALM, including:
In combination with recently lowered guidance levels for lead-contaminated soil in residential areas, US EPA’s new TWA approach may impact its cleanup recommendations. Further, PRGs derived using this new approach could prompt remediation efforts at both primary and secondary exposure sites. Earlier this year, US EPA released the final version of the All Ages Lead Model (AALM), which can simulate the impact of intermittent exposures on lead concentrations in children and adults. US EPA’s new TWA approach did not discuss the AALM or how the new guidance intersects with evaluating intermittent lead exposures using the AALM.
For more information, refer to US EPA’s website and/or contact Gradient.
Contact:
Steven R. Boomhower, Ph.D.
Senior Toxicologist
Steven.Boomhower@gradientcorp.com
Kyle J. Colonna, Ph.D., M.P.H.
Epidemiologist
Kyle.Colonna@gradientcorp.com
Rosemary L. Mattuck, M.S.
Senior Environmental Engineer
Rosemary.Mattuck@gradientcorp.com