EPA Releases November 2012 RSLs

The U.S. Environmental Protection Agency (EPA) in December 2012 released the updated Regional Screening Levels (RSLs) that were developed using risk assessment guidance from the EPA Superfund program. Although the RSLs are developed for the Superfund program, most Federal and State risk-based environmental cleanup programs reference the RSLs. The RSLs are used as risk-based screening tools to determine if there is a potential need for further investigation or whether a site-specific risk assessment is required for cleanup of a site. Based on the current revisions, changes to the RSLs were both chemical specific and based on individual chemical toxicities and risk drivers (i.e., carcinogenic versus noncarcinogenic), and incorporate changes in several major potential exposure pathways.

What are the significant changes?

Toxicological values were revised and/or added for several constituents based on updates to the Provisional Peer Reviewed Toxicity Values for Superfund (PPRTV). The PPRTV are considered a second tier source of human health toxicity values by the EPA in the hierarchy of toxicological sources. Oral reference doses (RfDos) were added to the PPRTV database for fifteen chemicals: boron trichloride, 2-chloroethanol, cyclohexane, diethanolamine, methyl acrylate, di-N-octyl phthalate, thallium acetate, thallium carbonate, thallium chloride, thallium (I) nitrate, thallium sulfate, p-toluidine, triacetin, tris(1-chloro2-propyl)phosphate, and zirconium. An inhalation reference concentration (RfCi) was also added to the database for boron trichloride; the oral slope factor (SFo) for p-toluidine decreased. The addition of toxicological values for the fifteen constituents listed above result in the ability to calculate risk-based screening levels for these constituents. If you have a project where one of these constituents may be present, RSLs are now available for screening purposes and may result in inclusion of the constituent in a quantitative risk assessment. Previously, the chemicals may have been evaluated qualitatively.

The RfCi for acetone cyanohydrin increased; the RfCi for methylacrylonitrile increased. The RfDo for ethylene cyanohydrin and toluene-2,5-diamine increased. Additional toxicological changes included the addition of an RfCi for cyanide using hydrogen cyanide as a toxicological surrogate; replacement of the mercuric chloride RfCi wth the elemental mercury RfCi. For those constituents with an increase in a RfDo or RfCi or a decrease in a SFo, more stringent RSLs were developed. If the RfCi decreased, less stringent RSLs result.

What were the other changes that were made to RSL chemicals?

Updates were also made to the RSL calculator, which allows for site-specific or default calculation of RSLs. The updates include the addition of individual total petroleum hydrocarbons to the calculator; the residential scenario site-specific option now requires separate entries for each age cohort for calculation of the RSL; and, the soil to groundwater scenario now includes Protection of Ground Water Soil Screening Levels (SSLs) for both cancer and non-cancer.

Parameters for dermal exposure to water were updated: the most recent log Kow values are now used to determine effective predictive domain (EPD) regarding dermal permeability. The RSLs now calculate their own Fraction Absorbed (FA) for dermal to tapwater route.

The melting point database was updated, and the SSL Guidance followed for soil saturation limit (Csat) calculations. If a melting point is less than 20 degrees Celsius (Co), a chemical is liquid and Csat is calculated; if a melting point is greater than 20Co, the chemical is a solid and Csat is not calculated.

Other additions and revisions include:

Updates to the hierarchy of water solubility sources

Thiocyanate was reclassified as an inorganic compound

  • Maximum Contaminant Levels (MCLs) were added for aldicarb, aldicarb sulfone, and adicarb sulfoxide
  • Recreator scenario was updated to include additional default exposure assumptions to match the residential scenario.

Where can I get more information?

For more information on the updated EPA RSLs, please contact Tom Biksey at 724-884-6724 and tom.biksey@ehs-support.com <mailto:tom.biksey@ehs-support.com> , or Chrissy Peterson at 412-925-1385 and chrissy.peterson@ehs-support.com <mailto:chrissy.peterson@ehs-support.com>

Where can I find the RSLs?

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