OSWER 9285.7-84FS
Frequently Asked Questions on the Update to theATSDR Policy Guideline for
Dioxins and Dioxin-Like Compounds in Residential Soil
INTRODUCTION
The Agency for Toxic Substances and Disease Registry (ATSDR) issued an update
(October 15, 2008) to its policy guideline for dioxin and dioxin-like compounds in
residential soil (ATSDR, 2008; 73 Fed. Reg. 61,133). The purpose of this update is to
eliminate confusion regarding the interpretation of ATSDR's "evaluation," "screening"
and "action" levels for dioxin. The update eliminates ATSDR's action level criterion for
dioxins in residential soil that was intended to trigger the consideration of specific public
health actions. However, ATSDR continues to consider health risks associated with
levels of dioxins in soil below 1 ppb to be low under most residential scenarios where the
primary exposure pathway is incidental ingestion through direct exposure to soil. In such
instances, ATSDR public health recommendations may include community health
education or limiting access to contaminated areas. The purpose of these frequently
asked questions are to explain this ATSDR update in relation to EPA's activities at
Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA)
sites and Resource Conservation and Recovery Act (RCRA) corrective action sites.
This update does not change ATSDR's Toxicological Profile (ATSDR, 1998) or
ATSDR's minimal risk level (MRL) for dioxin established in 1998 (Appendix A in
ATSDR, 1998). This update also does not impact the process used for conducting risk
assessments or developing cleanup decisions at CERCLA and Resource Conservation
and Recovery Act (RCRA) sites. The U.S. Environmental Protection Agency's (EPA)
preliminary remediation goal (PRO) for dioxin in residential soil has not changed and
remains at 1 ppb (EPA, 1998).
Background. In 1998, ATSDR developed a policy guideline for dioxin and dioxin-like
compounds in residential soil. The 1998 policy was developed to assist ATSDR health
assessors in evaluating the public health implications of dioxin and dioxin-like
compounds in residential soils near or on hazardous waste sites. The 1998 guideline
established three levels as criteria for comparing dioxin levels in residential soil: a
screening level, an evaluation level and a public health action level. The 1998 guideline
also recommended, for levels between 0.05 ppb and 1 ppb TEQ, evaluation of site-
specific factors, and for levels over 1 ppb TEQ, consideration of specific public health
actions. The 1998 policy guideline is only available, in hard copy, as Appendix B to the
Toxicological Profile for Chlorinated Dibenzo-p-Dioxins. ATSDR has updated the 1998
dioxin soil guideline in order to be consistent with its more recent Public Health
Assessment Guidance Manual (PHAGM) (ATSDR, 2005).
-------
FREQUENTLY ASKED QUESTIONS
Q: What is the role of ATSDR and EPA at contaminated sites?
A: EPA determines cleanup standards at CERCLA and RCRA corrective action sites,
while ATSDR advises EPA and other Federal and state agencies, and the public, on the
health impacts of CERCLA sites.
Q: What is the objective of ATSDR's updated policy?
A: The objective of this update is to provide consistency with the ATSDR Public Health
Assessment Guidance Manual (PHAGM) (ATSDR, 2005) and eliminate the confusion
regarding interpretation of residential dioxin soil levels that exceed the ATSDR
established screening level of 0.05 ppb.
Q: Why is ATSDR updating its 1998 residential dioxin soil policy?
A: The 1998 policy (placed as Appendix B to ATSDR's Toxicological Profile for
ChlorinatedDibenzo-p-dioxins (CDDs) (ATSDR, 1998)) recommended three levels as
criteria for comparing dioxin levels in residential soil: a screening level of 0.05 ppb, an
evaluation level of between 0.05 ppb and 1 ppb, and an action level of 1 ppb. Use of the
1998 policy led to confusion in applying these criteria and subsequently resulted in
inconsistent application of the guideline. ATSDR updated the policy guideline to be
consistent with the more recent ATSDR PHAGM (ATSDR, 2005), which recommends
the use of screening levels for all chemicals, thus ensuring that ATSDR evaluation of
residential soil dioxin is consistent with other contaminants. As ATSDR does not
develop "action levels," the dioxin action level of 1 ppb has been eliminated. With the
deletion of the 1 ppb action level, the evaluation level, or range between screening level
and action level, has been eliminated as well.
Q: When does ATSDR's update go into effect?
A: ATSDR's update is in effect, with issuance in the Federal Register on October 15,
2008 (73 Fed. Reg.61,133), with minor edits announced on Nov. 28, 2008 ( 73, Fed.
Reg.72, 484). The update has been incorporated into Appendix B of the on-line version
of the Toxicological Profile for Chlorinated Dibenzo-p-Dioxins (ATSDR, 1998). The
update document can also be found at the following link:
http://www.atsdr.cdc. gov/substances/dioxin/policv/Dioxin Policy Guidelines.pdf
Q: Does the elimination of ATSDR's public health action level of 1 ppb impact
EPA's residential soil preliminary remediation goal also established at 1 ppb?
A: ATSDR continues to consider health risks associated with levels of dioxins in
residential soil below 1 ppb to be low under most scenarios where the primary exposure
pathway is incidental ingestion through direct exposure to soil. At sites where dioxin
levels are between 0.05 ppb and 1 ppb, ATSDR recommends that appropriate public
health activities may include community health education and/or site access restrictions.
-------
Q: What does ATSDR's updated policy recommend?
A: The updated policy recommends that ATSDR health assessors evaluate, on a site-
specific basis, residential dioxin soil levels that exceed the ATSDR established screening
level of 0.05 ppb, as described in the ATSDR PHAGM (ATSDR, 2005). ATSDR
defines a screening level as follows: a concentration in air, soil, or water (or other
environmental media), which is derived from ATSDR's minimal risk level for dioxin
(MRL) and below which adverse non-cancer health effects are not expected to occur.
Separate levels can be derived to account for acute, intermediate, or chronic exposure
durations.
The level of 0.05 ppb is an ATSDR screening level for dioxin and dioxin-like compounds
(including 2,3,7,8-tetrachlorodibenzo-p-dioxin and other structurally related halogenated
aromatic hydrocarbons) based on non-cancer risks associated with the ingestion of soil in
residential settings. In addition to evaluating dioxin with respect to soil ingestion,
ATSDR health assessors, in applying the 2005 PHAGM, ensure that comprehensive
evaluation of dioxins include the consideration of scenarios and relevant screening levels
where dioxins may enter the food chain pathway.
ATSDR continues to consider health risks associated with levels of dioxins in soil below
1 ppb to be low under most residential scenarios where the primary exposure pathway is
incidental ingestion through direct exposure to soil. In such instances, ATSDR public
health recommendations may include community health education or limiting access to
contaminated areas.
Q: How does the updated policy affect ATSDR's scientific assessment of the toxicity
of dioxin?
A: ATSDR's scientific assessment of dioxin toxicity and ATSDR's MRL for dioxin
have not changed. ATSDR's soil dioxin policy is not based on new scientific data or
reanalysis of existing data.
Q: What is EPA's policy for evaluating dioxin in residential soil at CERCLA sites
and RCRA corrective action sites?
A: EPA generally uses 1 ppb dioxin as a starting point for setting cleanup levels at
RCRA corrective action sites and Comprehensive Environmental Response,
Compensation and Liability Act (CERCLA) removal sites (i.e., non-time critical removal
sites and, time permitting, for emergency and time critical sites) and as a preliminary
remediation goal (PRG) for CERCLA remedial sites for dioxin in surface soil involving a
residential exposure scenario (EPA, 1998). The recommended level of 1 ppb is based on
the direct contact exposure pathway for human health. This level does not apply to other
exposure pathways, such as migration of soil contaminants to ground water or to
agricultural products. The 1 ppb level is recommended unless extenuating site-specific
circumstances warrant different levels or a more stringent state applicable or relevant and
appropriate requirement (ARAR) establishes a cleanup level at CERCLA sites.
-------
The recommended level of 1 ppb is to be used pending the release of EPA's
comprehensive dioxin reassessment report and cross-program assessment of the impacts
of the report.
EPA regional management should continue to consult with the appropriate Office of
Solid Waste and Emergency Response (OSWER) programs on all proposed Fund and
Potentially Responsible Party-lead site decisions under CERCLA, including other Federal
agency-lead and state-lead site decisions, involving the development of dioxin soil
cleanup levels for non-time critical removal sites (time permitting, for emergency and
time critical removal sites) and remedial sites. Consultation should be initiated at the risk
assessment stage. The Office of Site Remediation Enforcement will provide support if
enforcement issues are identified.
In the case of EPA-lead RCRA corrective action sites, Regions should provide the
appropriate Office of Resource Conservation and Recovery programs with proposed dioxin
soil cleanup levels (i.e., prior to notice and comment). For state-lead RCRA corrective
action sites, it is also recommended that states use the 1 ppb dioxin level as a starting point
in setting residential soil cleanup levels. States are encouraged to share their approaches
with EPA Regions in a manner consistent with established procedures for EPA support and
oversight of state RCRA Corrective Action programs.
For consultation procedures, refer to the OSWER Guidance on Non-NPL Removal
Actions Involving Nationally Significant or Precedent-Setting Issues (EPA, 1989), the
OSWER Headquarters Consultation for Dioxin Sites (EPA, 1996), plus the OSWER
Consolidated Guide to Consultation Procedures for Super/and Response Decisions
(EPA, 1997).
Q: How does ATSDR's updated policy impact the CERCLA and RCRA risk
assessment process?
A: The ATSDR update does not impact the process used for conducting risk assessments
or developing cleanup decisions at CERCLA sites and RCRA corrective action sites.
Specifically, the update does not alter the use of EPA's PRO for dioxin in residential
settings; the soil PRO remains 1 ppb.
Q: What is the status of EPA's comprehensive reassessment of dioxin?
A: In 2003, EPA released a comprehensive reassessment of dioxin exposure and human
health effects. A National Academy of Sciences (NAS) expert panel reviewed this
reassessment and identified three key areas for improvement: 1) justification of
approaches to dose-response modeling for cancer and noncancer endpoints; 2)
transparency and clarity in selection of key data sets for analysis; and 3) transparency,
thoroughness, and clarity in quantitative uncertainty analysis. EPA is in the process of
planning its response to the NAS comments.
-------
Q: What are the implications for EPA of the ATSDR update on exposure pathways
other than direct ingestion?
A: One of the purposes of the ATSDR update is to provide for a strengthened emphasis
on exposure pathway analysis beyond direct soil contact. Dietary sources and indirect
exposure pathways may make a significant contribution to dioxin exposure. Assessing
both direct and indirect exposure pathways should result in a more comprehensive
evaluation of exposure conditions at residential sites with dioxin contamination. EPA
believes that the updated ATSDR policy is consistent with the Agency's policy of
recommending 1 ppb as a starting point for developing a dioxin cleanup level in
residential soil. EPA's recommendation is based on direct contact with surface soil.
Other exposure pathways may be of importance at dioxin sites, resulting in the need for
additional site-specific evaluation.
Q: Who should be contacted for information?
A: Content expert contact:
Marlene Berg
OSWER/OSRTI/ARD/SPB
(703)603-8701
berg.marlene@epa.gov
Doug Ammon
OSWER/OSRTI/ARD/SPB
(703) 347-8925
ammon.doug@epa.gov
Communications contact:
Lois Gartner
OSWER/OSRTI/ARD/CIPIB
(703)603-8711
gartner.lois@epa.gov
George Hull
OSWER/IO
(202) 566-2604
hull.george@epa.gov
REFERENCES
U.S. Department of Health and Human Services. 1998. Toxicological Profile for
ChlorinatedDibenzo-p-Dioxins. Agency for Toxic Substances and Disease
Registry, Atlanta, GA. Available at:
http://www.atsdr.cdc.gov/toxprofiles/tpl04.pdf
U.S. Department of Health and Human Services. 2005. Public Health Assessment
Guidance Manual. Agency for Toxic Substances and Disease Registry, Atlanta,
GA. Available at: http://www.atsdr.cdc.gov/HAC/PHAmanual/index.html.
-------
U.S. Department of Health and Human Services. 2008. Update to the ATSDR Policy
Guideline for Dioxins and Dioxin-Like Compounds in Residential Soil. Agency for
Toxic Substances and Disease Registry, Atlanta, GA. Available at:
http://www.atsdr.cdc. gov/substances/dioxin/policy/Dioxin Policy Guidelines.pdf
U.S. Environmental Protection Agency. 1989. Guidance on Non-NPL Removal Actions
Involving Nationally Significant or Precedent-Setting Issues. Office of Solid Waste
and Emergency Response, Washington, D.C. OSWER Directive 9360.0-19.
Available at: http://www.epa.gov/superfund/policy/remedy/pdfs/93-60019-s.pdf
U.S. Environmental Protection Agency. 1996. Headquarters Consultation for Dioxin
Sites. Office of Solid Waste and Emergency Response, Washington, D.C. EPA
540/F-97/014. Available at:
http://www.epa.gov/superfund/policv/remedy/pdfs/92-00419-s.pdf
U.S. Environmental Protection Agency. 1997. Consolidated Guide to Consultation
Procedures for Superfund Response Decisions. Office of Solid Waste and
Emergency Response, Washington, D.C. EPA 540/F-97/009. Available at:
http://www.epa.gov/superfund/policv/remedv/sfremedy/hqconsult.htm.
U.S. Environmental Protection Agency. 1998. Approach for Addressing Dioxin in Soil at
CERCLA andRCRA Sites. Office of Solid Waste and Emergency Response,
Washington, D.C. OSWER Directive 9200.4-26. Available at:
http://www.epa.gov/superfund/policv/remedy/pdfs/92-00426-s.pdf.
------- |