The U.S. Environmental Protection Agency (EPA) in June 2013 released the updated Regional Screening Levels (RSLs), dated May 2013, 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.
EHS Support offers the following overview of these EPA updates. Our team of environmental scientists, geologists and engineers, with local and national perspectives, specialize in managing complex sites. We are able to recommend and implement a wide range of approaches and look forward to discussing the needs of your project or facility based on these recently released updates.
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), Agency for Toxic Substances and Disease Registry (ATSDR), and California Environmental Protection Agency (CalEPA). The PPRTV are considered a second tier source of human health toxicity values by the EPA in the hierarchy of toxicological sources, and the ATSDR and CalEPA are considered a third and fourth source, respectively. The changes include the reference dose (RfD), reference concentration (RfC), and slope factor (SF).
The following are the changes based on updates to the PPRTV:
- Toluene-2,5-diamine, RfD decreased, SF added
- Butylbenzene, tert-, new, RfD added
- Butylbenzene, sec-, new, RfD added
- Octyl Phthalate, di-N-, RfD decreased,
- Thiocyanic Acid, new, previously Thiocyanate
- Dinitrotoluene, 2,6-, RfD decreased, SF added
- Methyl-1,4-benzenediamine dihydrochloride, 2-, RfD increased
- Methylbenzene-1,4-diamine sulfate, 2-, RfD increased, SF added
- Benzenediamine-2-methyl sulfate, 1,4-, RfD increased, SF added
- Dinitrotoluene, Technical grade, new, RfD added, SF added.
The following are the changes based on updates to the ASTDR:
- Uranium (Soluble Salts), RfC added
- 1,4-Dioxane, RfC decreased
- Tricresyl Phosphate (TCP), new, RfD added
- Cadmium (diet and water), RfC decreased
- Vanadium and Compounds, RfC added
- Tris(1,3-Dichloro-2-propyl) Phosphate, mutagen classification removed.
The following are the changes based on updates to the Cal EPA:
- Nickel Refinery Dust, RfD and RfC decreased
- Nickel Carbonyl, RfD and RfC decreased
- Nickel Oxide, RfD and RfC decreased
- Nickel Subsulfide, RfD and RfC decreased.
The change of toxicological values for the 20 constituents listed above will result in changes to the RSLs for these constituents. If you have a project where one of these constituents may be present, the change in the RSLs may 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 added, more stringent RSLs may be developed. If the RfD or RfC increased, less stringent RSLs may result.
What were the other changes that were made to RSL chemicals?
New Tables are now provided with target hazard quotients (THQ) of 1.0 and 0.1. If you are unclear about which set of tables (THQ=1.0 or THQ=0.1) to use at your site, EHS Support is able to provide guidance for your project or facility. The rationale for using THQ of 0.1 for screening is that if 10 chemicals were at a site and all narrowly passed a screening at THQ=1.0, the resulting total HI could actually be 10. Many EPA regions and States routinely require the use of a THQ = 0.1 when selecting constituents of concern (COCs) in the risk assessment process.
In addition, chemical-specific changes include:
- The RfDs for the numbered, dioxin-like PCBs are now based on the 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) RfD from the EPA Integrated Risk Information System (IRIS) and the toxicity equivalence factors (TEFs) presented in RSL User Guide.
- The high aliphatic and high aromatic total petroleum hydrocarbons (TPHs) were classified as semi-volatile organic compounds (SVOCs), and all the TPHs were given chemical-specific parameters. Chemical-specific parameter assignment was based on the representative compound identified in the PPRTV paper when available. The medium aliphatic TPH did have a surrogate listed in the PPRTV paper; therefore n-nonane was assigned. The TPHs are currently available in the calculator only.
- Glyphosate Koc was updated.
- Thiocyanic Acid was given the CAS number 463-56-9. This number was previously assigned to Thiocyanate.
- Vanadium and Compounds was given the CAS number 7440-62-2. Previously it did not have a CAS number. This results in the database matching an RfC from ATSDR (see above).
- The arsenic screening levels for ingestion of soil are now calculated with the relative bioavailability factor (RBA) of 0.6. The RBA can be adjusted using the calculator in site-specific/user-provided mode the same way toxicity values can be changed. The RBA for soil ingestion is shown in the calculator output. See Section 5.10 of the User Guide for more information.
The RSL calculator, if operated in site-specific mode, now gives the option to substitute the Csat for the inhalation route screening level as well as giving the opportunity to substitute the theoretical concentration limit of 1E+05 mg/kg for the total screening level. These two options, combined with the ability to change the target risk and the target hazard quotient, should provide users with enough flexibility to generate screening levels applicable to many site-specific situations.
The following is a clarification to the November 2012 Update for the third to the last bullet that identifies the updates to the recreator landuse scenario:
- The calculator-based recreator landuse scenario shares the following identical default exposure parameters with the residential landuse scenario: body surface area, ingestion rates, body weight, and soil adherence factors. Default recreational exposure parameters are not provided for exposure frequency, exposure time, and events per day because recreational activities vary greatly and should be derived on a site-specific basis. Please see the User’s Guide for the exposure equations and a conceptual model of quantified pathways.
Where can my company obtain more information?
EPA RSLs can be found at http://www.epa.gov/reg3hwmd/risk/human/rb-concentration_table/index.htm. For more information on the updated EPA RSLs or recommendations on how to apply these changes to your daily operations, please contact Tom Biksey at 724-884-6724 and firstname.lastname@example.org, or Chrissy Peterson at 412-925-1385 and email@example.com. Also, visit our website at www.ehs-support.com to learn more about the services that EHS Support can offer to your team or facility.