Perchlorate Questions and Answers Document

NOTE: THIS POLICY HAS BEEN SUPERSEDED BY THE JANUARY 2006 ASSESSMENT GUIDANCE FOR PERCHLORATE

This Questions & Answers document serves to clarify the January 22, 2003 Status of EPA's Interim Assessment Guidance for Perchlorate issued by OSWER.

What is intended by virtue of the memorandum issued on January 22, 2003?

This Memorandum to Assistant Administrators and Regional Administrators "provide(s) information concerning the status of the interim assessment guidance for perchlorate originally transmitted on June 18, 1999 (the ‘1999 Interim Guidance')." It was issued to provide an update as to the status of EPA's scientific review of perchlorate, as well as EPA's regulatory process for developing a new standard for drinking water and/or ground-water or surface-water remediation.

What is the "interim assessment guidance" for perchlorate?

The interim assessment guidance is a memorandum providing practical information and advice to EPA risk assessors and risk managers at both headquarters and regional offices regarding evaluation of risks for perchlorate, a first step to develop information to assist in making risk assessment decisions for a substance for which no regulatory standards now exist. States and EPA regional offices have sought advice as the number of sites identified as potentially contaminated with perchlorate has increased due to advancements in detection methodology.

Which EPA interim assessment guidance for perchlorate currently applies?

As stated in the Memorandum, "The 1999 Interim Guidance remains the applicable guidance until supplanted by new guidance based on a finalized risk assessment."

What does the 1999 Interim Guidance say about the provisional reference dose?

The 1999 Interim Guidance recommended that agency risk assessors and risk managers continue to use the provisional reference dose (RfD) range of 0.0001 to 0.0005 mg/kg-day "because of continued uncertainty with respect to the impact of the pending data and analysis on the final estimate" (italics in original). By stating that the 1999 Interim Guidance still applies, EPA is saying that this continued uncertainty has not been resolved.

What is a "reference dose" (RfD)?

EPA defines a RfD as "[a]n estimate (with uncertainty spanning perhaps an order of magnitude) of a daily oral exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime."

This definition does not mean that exposure levels above the RfD are unsafe. Rather, the RfD value is in the center of a range of uncertainty that surrounds the best estimate of a "safe" level. The scientific uncertainty spans from one-third of the RfD to three times the RfD. In the case of a range, the uncertainty spans from one-third of the lower bound to three times higher than the upper bound. In the case of perchlorate, where the reference range is 4-18 ppb, the uncertainty spans from 1.3 ppb to 54 ppb.

The uncertainty inherent in the RfD is only one of the many uncertainties considered by a risk manager when deciding upon site specific risk assessment conclusions and developing of preliminary remediation goals.

What is the history behind the "provisional reference dose"?

ORD's provisional RfD was first established in 1992 at 0.0001 mg/kg-day. In 1995, ORD replaced this point estimate with a range of 0.0001 to 0.0005 mg/kg-day.

What is EPA's schedule for finalizing the perchlorate risk assessment and RfD?

ORD has been aware for some time that there are many questions about the science underlying both the provisional RfD and its risk assessment. In an effort to resolve these scientific issues, EPA has agreed with other federal agencies that a scientific review of these scientific questions should be undertaken by the National Academy of Sciences. EPA will not disseminate a new draft risk assessment until this review is completed and the work of the panel has been fully evaluated.

What does the interim assessment guidance say about site remediation?

The EPA assessment guidance does not establish cleanup standards. The 1999 Interim assessment guidance specifically recommends that "risk assessors and risk managers continue to use the standing provisional RfD range of 0.0001 to 0.0005 mg/kg-day for perchlorate related assessment activities." In absence of site specific risk assessment factors, this provisional RfD range can be converted to a preliminary remediation goal of 4-18 ppb, and is a screening tool and/or point of departure in performing site-specific risk assessment activities. For example, at cleanups conducted pursuant to CERCLA, the NCP (40 CFR 300.430(e) (2) (i)) states, "Preliminary remediation goals should be modified, as necessary, as more information becomes available through the RI/FS." Under CERCLA, risk managers consider other factors in determining remediation requirements, such as cost, effectiveness, community acceptance, protectiveness, and implementability of remedial alternatives. Thus, for completed pathways of exposure, results of the site-specific risk assessment are used to establish acceptable exposure levels for a site, and are evaluated along with other factors in the NCP in selecting remedial alternatives. The preliminary nature of the RfD and the process for considering perchlorate for regulation under the Safe Drinking Water Act leave uncertainty for current response actions. Under these circumstances, it would be appropriate for remediation managers to carefully consider focusing their efforts on cost-effective measures to disrupt human exposure pathways to mitigate human health risk while development of regulatory standards proceeds.

What does the interim assessment guidance say about drinking water standards?

EPA assessment guidance also is not a presumptive drinking water standard. As the Memorandum states, the derivation of a reference dose is the first step toward developing a primary drinking water standard under the authority of the Safe Drinking Water Act. EPA's Office of Water (OW) has a number of tasks that it must complete before deciding whether a drinking water standard is warranted. In addition, OW must apply risk management factors in developing, proposing and promulgating such a standard.

Interpreting any assessment guidance as a presumptive or default drinking water standard ignores important risk management features, improperly short-circuiting procedures and statutory requirements. Therefore, EPA counsels States and others not to use the Agency's interim assessment in order to establish drinking water standards.

What is the legal effect of this guidance and the 1999 Interim Guidance?

This guidance and the 1999 Interim Guidance do not impose legally-binding requirements, standards or procedures on EPA, states, tribes, or any other entity, and may not apply to a particular situation based upon the circumstances. They are intended to inform, but not to prescribe, decisions that may be made, and they should be considered one of many sources of information that may influence site-specific decisions. EPA and state or tribal decision makers retain the discretion to adopt approaches on a case-by-case basis that differ from this guidance and the 1999 Interim Guidance.

This guidance document provides direction to EPA Regions, states and tribes involved in environmental cleanups. It also provides guidance to the public and the regulated community on how EPA intends to assess possible perchlorate contamination. This document does not, however, substitute for CERCLA, RCRA or other EPA regulations, nor is it a regulation itself.

Interested parties remain free to raise questions and objections about the appropriateness of the application of this and the 1999 interim policy to a particular situation, and EPA will consider whether or not the recommendations or interpretations in the guidances are appropriate in that situation. The guidances do not address contaminants other than perchlorate.

It has been reported in the media that EPA has proposed to set a perchlorate standard equivalent to 1 ppb in drinking water. Is that true?

No. In January 2002, EPA published an external review draft document entitled, "Perchlorate Environmental Contamination: Toxicological Review and Risk Characterization" (the "2002 Draft Assessment"). This document did not propose a drinking water standard, nor did it establish any cleanup policy or any regulatory standard. At the bottom of each page, EPA advises all readers: "Draft--Do Not Quote or Cite." The document was published because EPA's peer review policy requires that external peer reviews be conducted in public with opportunity for public participation and comment.

ORD is evaluating all of the scientific information available, including two peer reviews, but has not completed this review. In order to complete this review, EPA has agreed with other federal agencies to submit certain scientific questions to the National Academy of Sciences for review prior to the RfD being finalized. When this review is completed in accordance with all applicable procedures, ORD will issue a final risk assessment. Only the final risk assessment represents ORD's views of the science.

What is meaning of the "4-18 ppb range" cited in the 1999 Interim Guidance and in the Memorandum?

The purpose of the assessment guidance is to provide toxicological factors to be used in the risk characterization portion of a site specific risk assessment. Its purpose is not to suggest or prescribe what levels of perchlorate ought to be considered safe. Actual risks will vary across sites, due to site specific risk assessment factors, which, when applied, estimate different risk levels even where concentrations of an environmental contaminant are identical.

As stated in the 1999 Interim Guidance, the provisional reference dose ("RfD") range for perchlorate derived by EPA's Office of Research and Development (ORD) is 0.0001 to 0.0005 mg/kg-day. The 4-18 ppb range for drinking water is derived by using a simple risk characterization calculation using the provisional RfD, and standard defaults for body weight of 70 kg (154 lbs.) and tap water consumption (two liters per day) over a lifetime, which takes into account effects on sensitive sub-populations. This value is used as a departure point for risk characterization, in absence of site specific risk assessments or applicable promulgated state standards. Such a range should not be considered an "action level" that could be adopted by states and could trigger the initiation of a response as part of a cleanup process.

What is the meaning of the advice in the Memorandum to "carefully consider the lower end of the provisional range"?

The "4-18 ppb range" is intended as a screening tool to see if site specific risk assessment is needed, as the 1999 Interim Guidance recommends. Risk managers may use this range as a point of departure in screening sites for further action. These values also may be used, along with other factors in the NCP, such as technical feasibility, cost, community acceptance, and implementability, for development of a remedial action goal in a feasibility study.

Moreover, the 4-18 ppb range addresses the need to protect sensitive subpopulations. As stated in the January 22, 2003 guidance, "the 4 to 18 ppb range is considered to be protective based on recent ongoing analyses and taking into account the most sensitive receptors." No additional adjustment for sensitive subpopulations is needed. Accordingly, all values from the high end to the low end of the 4-18 ppb range is protective of sensitive subpopulations. If there are additional aggravating high-risk factors at the site (e.g., coexposure with another contaminant at the site that has been demonstrated to act synergistically with perchlorate in producing adverse effects), then the lower end of the provisional range should be carefully considered. Where water in question is not currently used as a source of drinking water or does not result in other human exposure, then it would be appropriate to consider values at or above the high end of the 4-18 ppb range.