The Ups & Downs of USEPA Regional Screening Levels
USEPA Regional Screening Level Updates: The Ups and Downs
The United States Environmental Protection Agency (USEPA) has released November 2024 updates to the Regional Screening Levels (RSLs). The USEPA updates tables supporting the derivation of RSLs twice per year; these are technically not cleanup levels, but they are often used extensively by states to inform decision making, derive state-specific regulations, or are deferred to as de facto state regulatory levels. The underlying toxicity values are used by human health risk assessors and regulators to evaluate site-specific risk. Notable changes include:
- Addition of a screening value and toxicity criteria (Reference Dose and/or Cancer Slope Factor) for over ten new chemicals including perfluorodecanoic acid (PFDA), based on updates from USEPA’s Integrated Risk Information System (IRIS) and/or Provisional Peer-Reviewed Toxicity Values;
- A higher (less conservative) screening value for hexavalent chromium [Cr(VI)] based on updates from IRIS (e.g., a revision from 0.3 milligrams per kilogram [mg/kg] in residential soil to 0.95 mg/kg in residential soil, at TR=1E-06/THQ=1); and
- For lead, a lower (more conservative) action level; a change from 15 to 10 µg/L as outlined in the Lead and Copper Rule Improvements, which was finalized by the Biden-Harris Administration on October 8, 2024. This lower threshold requires communities to take action when lead levels exceed 10 µg/L and implement rigorous drinking water testing, and requires the identification and replacement of lead pipes in the next ten years. This change is consistent with Roux’s prior updates on lead.
In addition, numerous revisions were rolled out for chlorinated solvents, based on updates to a 2021 USEPA memo, which recommended using a lower subchronic value in place of the existing chronic values for the toxicity data of 19 chemicals. Toxicity values for 1,1-dichloroethylene (1,1-DCE) and vinyl chloride were revised to utilize toxicity values from the Agency for Toxic Substances and Disease Registry instead of IRIS. The change in the underlying toxicity values results in significantly lower screening levels (e.g., revision in the residential indoor air screening criteria from 210 micrograms per cubic meter [µg/m3] to 4.1 µg/m3 for 1,1,-DCE).
While screening levels are not cleanup levels, the screening level changes are indicative of changes to underlying toxicity values, which could impact risk-based cleanup levels, and ultimately site closures. Have questions about what these changes in screening levels mean for your site? Get in touch with a Roux toxicologist or human health risk assessor using the link below.
