Human Health Risk and Environmental Analysis

This site is maintained and operated through an Interagency Agreement between the EPA/Office of Superfund Remediation and Technology Innovation and DOE/ORNL/Environmental Sciences Division. For questions or comments please contact Linda Gaines in EPA/OSRTI.

PPRTV Assessments Electronic Library

Office of Superfund Remediation and Technology Innovation
U.S. Environmental Protection Agency
Washington, DC 20460

DISCLAIMERS

This electronic library of assessment was developed for the U.S. Environmental Protection Agency (EPA)/Office of Superfund Remediation and Technology Innovation (OSRTI or Superfund). The toxicity values presented in this electronic library were developed in accordance with current Agency guidance on deriving human health toxicity values for EPA's Superfund Program and were externally peer reviewed. This electronic library will be periodically updated with current values; therefore, users should ensure that the values are current at the time of use.

These assessments are prepared for use at Superfund sites. Parties considering using these assessments in other programs outside of the programs implemented or overseen by EPA's OSRTI should not assume that EPA resources would be used to defend their use of these assessments or values.

For the past several years, PPRTV assessments have been directly accessible only to EPA computers. Others, such as states, other federal agencies and contractors have been able to obtain PPRTV assessments only by being placed on the PPRTV Registered User List and then making specific requests for assessments. In February 2011, OSRTI began making PPRTV assessments electronic library available to all computers. By this action, EPA is simplifying the process for obtaining PPRTV assessments in order to be more transparent about the toxicity values used and recommended by OSRTI. As explained below, EPA is not promoting the use of PPRTV assessments on other than Superfund and hazardous waste sites.

INTRODUCTION

The Provisional Peer-Reviewed Toxicity Values (PPRTVs) currently represent the second tier of human health toxicity values for the EPA Superfund and Resource Conservation and Recovery Act (RCRA) hazardous waste programs. See a more complete discussion of the hierarchy below. Both the Superfund and RCRA programs accept the primacy of human health toxicity values contained in EPA's Integrated Risk Information System (IRIS). Values placed on IRIS have undergone internal and external peer review. The toxicity values in this electronic library (PPRTVs) have been developed specifically for EPA's Superfund program and have not undergone the multi-program review and consensus required for toxicity values to be placed in IRIS.

BACKGROUND / HIERARCHY OF HUMAN HEALTH TOXICITY VALUE SOURCES

On December 5, 2003 the EPA Office of Superfund Remediation and Technology Innovation (OSRTI) revised its hierarchy of human health toxicity values for Superfund risk assessments, establishing the following three tiers as the new hierarchy.

  1. Integrated Risk Information System (IRIS)
  2. Provisional Peer-Reviewed Toxicity Values (PPRTVs)
  3. Other (Peer Reviewed) Values, including
    • Agency for Toxic Substance and Disease Registry's (ATSDR) Minimal Risk Levels (MRLs)
    • California Environmental Protection Agency (CalEPA) values
    • EPA's Health Effects Assessment Summary Tables (HEAST)

Note: Additional tier 3 sources may be identified in the future.

PURPOSE OF PPRTVs

PPRTVs are developed for use in the EPA Superfund Program. Requests to try and derive a PPRTV are generally filtered through the EPA Regional Superfund Program, in which the site subject to the request is located. However, Regions typically request PPRTVs regardless of what party is considered the lead agency or is funding response actions on the (Superfund) site, including Fund-lead sites, potential responsible party (PRP) lead sites, State-lead sites, and sites where other Federal agencies may be identified as the lead agency.

DEFINITION OF A PPRTV

A PPRTV is a toxicity value derived for use in the Superfund Program when such value is not available in EPA's Integrated Risk Information System (IRIS, the first tier in the Superfund hierarchy of human health toxicity values). PPRTVs are derived after a review of the relevant scientific literature using the methods, sources of data and guidance for value derivation used by the EPA IRIS Program. All provisional peer-reviewed toxicity values receive internal review by EPA scientists and external peer review by independent scientific experts. PPRTVs differ in part from IRIS values in that PPRTVs do not receive the multi-program consensus review provided for IRIS values. This is because IRIS values are generally intended to be used in all EPA programs, while PPRTVs are developed specifically for the Superfund Program.

PPRTV assessments are eligible to be updated on a 5-year cycle to incorporate new data or methodologies that might impact the toxicity values or characterization of potential for adverse human health effects and are revised as appropriate. Questions regarding nomination of chemicals for update can be sent to the appropriate U.S. EPA Superfund and Technology Liaison (https://www.epa.gov/research/fact-sheets-regional-science). In general, the need for a PPRTV is eliminated once an analogous IRIS value becomes available. Once IRIS values become available, PPRTVs are removed from the PPRTV electronic library. It should also be noted that sometimes available information is not sufficient to derive a PPRTV. Some PPRTV Derivation Support Documents conclude that a PPRTV cannot be derived based upon the available information.

DEVELOPMENT AND ORGANIZATION OF THE PPRTV ELECTRONIC LIBRARY

Staff in regional Superfund and RCRA program offices are advised to carefully review the information provided on PPRTVs to ensure that any PPRTV used is appropriate for the types of exposures and circumstances at the Superfund site or RCRA facility in question. Contact the appropriate personnel in OSWER1 with questions about PPRTVs and their appropriate use.

This searchable electronic library contains toxicity information only on chemical contaminants. Cancer slope factors for radionuclides are still presented in HEAST Table 4 and on EPA's Office of Air and Radiation (OAR) website: http://www.epa.gov/radiation/heast/download.htm.

The PPRTV electronic library contains toxicity values from two origins, both of which have undergone internal and external peer review. EPA Regional risk assessors and toxicologists routinely consult with Headquarters and associated EPA sources of toxicological expertise when a potentially significant contaminant is identified at a Superfund site and IRIS does not provide a relevant toxicity value. An EPA toxicologist reviews the available scientific literature and determines whether a toxicity value could be developed in response to the regional request. If a toxicity value is developed, it is provided to the requesting region as a PPRTV assessment and placed in this electronic library for the benefit of other Regions.

PPRTVs are also derived as a result from reassessments of HEAST toxicity values for chemical contaminants. A review of HEAST toxicity values for chemical contaminants is being conducted. Beginning in 2002, as these reviews are completed, such toxicity values are removed from HEAST. Using the same procedures as for developing PPRTVs in response to Regional or Headquarters requests, an EPA toxicologist may determine that the HEAST toxicity value continues to be appropriate or a new toxicity value may be derived if sufficient information exists. In either instance, the value would be derived in a PPRTV assessment and placed in this electronic library.

PPRTV CHEMICAL NOMINATION AND SELECTION

Representatives from the STSC, OLEM and the OH2R2AF Toxicity Workgroup will form a PPRTV Scoping Team that will collaborate to seek nominations, select a candidate chemical list, and prioritize the chemicals for PPRTV development on an annual basis. The goals of selecting and prioritizing the chemicals requested for PPRTV development are twofold: (1) emphasize development of high-quality deliverables based on the most current OLEM and Regional priorities/needs; and (2) optimize the expenditure of fiscal resources and human capital for assessment activities related to priority chemicals.

The SOP and related documents are available here:

DERIVING PPRTVs

The development of PPRTVs complies with Agency methodologies and practices for the development of toxicity values [including oral reference doses (RfDs) and inhalation reference concentrations (RfCs) on noncancer toxicity and slope factors and inhalation unit risks for cancer risk] and is summarized in "PPRTV Derivation Support Documents", which are provided in the PPRTV electronic library for the toxicity values presented.

QUESTIONS

Chemical Toxicity and Carcinogenicity

Questions regarding the contents of the chemical toxicity and carcinogenicity summaries in the Provisional Peer-Reviewed Toxicity Values electronic library (e.g., contaminants not covered, contaminants with pending IRIS toxicity values) may be directed to EPA's Office of Superfund Remediation and Technology Information. Point of contact is Michele Burgess (e-mail: Burgess.Michele@epa.gov, Telephone: 703-603-9003). Michele Burgess may direct the inquiry to an EPA toxicologist deriving PPRTVs. If this point of contact changes, it will be indicated in this electronic library.

CAUTION

Users of this electronic library are referred to the IRIS electronic library (http://www.epa.gov/iris/) for Agency consensus values. When no IRIS value is available and a PPRTV from this electronic library is used, it is important to remember that the numbers alone (i.e., a PPRTV) tell very little about the adverse effects of a chemical or the quality of evidence on which risk assessment information is based. The PPRTV Derivation Support Document, prepared when the PPRTV was placed in the electronic library, should be consulted in order to fully appreciate and characterize the strengths and limitations of a given PPRTV. As noted elsewhere in this electronic library, the Provisional Peer-Reviewed Toxicity Values are developed for the Office of Superfund Remediation and Technology Innovation (OSRTI). Since the Superfund Program must maintain its ability to recover its costs from potentially responsible parties (PRPs) on Superfund sites, it is necessary that the Superfund Program ensure that its resources support addressing potential Superfund sites. Therefore, programs or parties who may chose of their own initiative to use the PPRTVs outside of the Superfund Program are advised that Superfund resources will not generally be used to respond to challenges of the PPRTVs outside the Superfund Program.

STRUCTURE OF THE PROVISIONAL PEER-REVIEWED TOXICITY VALUE (PPRTV) ELECTRONIC LIBRARY

The PPRTV electronic library provides human health risk assessment information for chemical contaminants. This information is divided into the following sections:

  1. The "PPRTV Homepage" provides general information about the PPRTVs and their use in the Superfund Program.
  2. "Quickview" contains an alphabetized electronic library of the contaminants addressed in the PPRTV electronic library. Click on a contaminant and available PPRTVs for that contaminant will be shown. When IRIS values exist for that contaminant, the PPRTV electronic library links to the IRIS electronic library. The PPRTV Derivation Support Documents, which provide a risk characterization for the contaminant and the types of exposure and risk assessed, can be accessed under "Quickview" by clicking on "PPRTV Derivation Support Document" once a contaminant is submitted on the Quickview function.
  3. "Users' Guide: Chemical Toxicity" provides information about the types of toxicity values and assessments contained in the electronic library and how the toxicity values are derived.
  4. "PPRTV Derivation Support Documents" contains an alphabetical compilation of all available PPRTV Derivation Support Documents and also shows the year of their preparation and the CASRN for that contaminant. Individual assessments can also be accessed from this page by clicking on the name of a contaminant.

ENDNOTES

1The EPA Office of Solid Waste and Emergency Response (OSWER) contains both the Superfund and RCRA hazardous waste programs.