EPA Releases November 2013 RSLs
In December 2013,the United States Environmental Protection Agency (USEPA) released the updated Regional Screening Levels (RSLs) that were developed using risk assessment guidance from the USEPA Superfund program. Although the RSLs were developed for the Superfund program, most federal and state risk-based environmental cleanup programs reference the RSLs. 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.
EHS Support routinely uses the RSLs in the risk assessment process 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. We have also incorporated the RSLs in state-led risk assessments where their guidance requires the use of the RSLs either in setting standards or as a source of toxicity criteria for a toxicity assessment. EHS Support also conducts a cost-benefit analysis before using RSLs as remedial standards by comparing remedial action costs versus the cost of a site-specific risk assessment.
What are the significant changes? Toxicological values were revised and/or added for several constituents based on updates to the Integrated Risk Information System (IRIS), Provisional Peer Reviewed Toxicity Values for Superfund (PPRTV), and California Environmental Protection Agency (CalEPA). The changes include the reference dose (RfD), reference concentration (RfC), slope factor (SF), and inhalation unit risk (IUR).
Changes based on PPRTV:
- dinitrotoluene, technical grade, RfD decreased
- Nonane, n-, RfC decreased
- Ethyl acetate, RfC added
- tert-amyl-alcohol, RfC added (not previously an RSL)
- Ethoxyethanol, 2-, RfD decreased
- Dimethoxybenzidine, 3,3′-, SF increased
- Butylated hydroxytoluene, RfD and SF added (not previously an RSL)
- Nitromethane, RfC decreased
- Dibenzothiophene, RfD added (not previously an RSL)
- Dichlorobenzotrifluoride, 3,4- (subchronic only) RfD added (not an RSL)
- Trinitrophenylmethylnitramine (Tertyl), RfD decreased
- Endosulfan sulfate (subchronic only), RfD added (not an RSL).
Changes based on IRIS:
- Methanol, RfD and RfC increased
- Biphenyl, RfD increased
- 1,4-Dioxane, RfC decreased and IUR decreased.
Changes based on Cal EPA:
- Butadine, 1,3-, Acute Reference Exposure Level revised
- Caprolactam, RfC added.
The change of toxicological values for the 17 constituents listed above will result in changes to the RSLs or their use in risk assessments for these constituents. If you have a project where one of these constituents may be present, EHS Support will evaluate whether the change in the RSLs could affect the characterization of potential risks in a quantitative risk assessment. For those constituents with a decrease in an RfD or RfC, or if a SF was increased or added, more stringent RSLs might be developed. If the RfD or RfC decreased,or if the IUR was decreased, less stringent RSLs could result.
What were the other changes that were made to RSL chemicals?
- Total petroleum hydrocarbons (TPH) have now been added to the RSLs tables (previously only included in the calculator). Representative compounds from each fraction were used for toxicity values and/or chemical-specific parameters.
- Updates to the online calculator include enter site concentrations, a construction worker scenario, and adult and child scenarios for evaluation of a wider range of adult only exposures.
- Phthalates are now grouped in their own chemical group (e.g., like dioxins, cyanides).
- “Ethyl chloride” is now listed as “ethyl chloride (chloroethane)”Where can I get more information?
Where can I find the RSLs and specific information on the updated sections? http://www.epa.gov/reg3hwmd/risk/human/rb-concentration_table/index.htm
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