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Update to ATSDR Policy Guideline for Dioxins and Dioxin-Like Compounds in Residential Soil

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AGENCY:

Agency for Toxic Substances and Disease Registry (ATSDR), U.S. Department of Health and Human Services (HHS).

ACTION:

Request for public comments on the revised Policy Guideline document used by health assessors to evaluate health hazards associated with exposure to dioxins and dioxin-like compounds in residential soil.

SUMMARY:

ATSDR is seeking public comment on the draft revision of its 1998 Policy Guideline for Dioxins and Dioxin-Like Compounds in Residential Soil. The policy is intended to assist health assessors who must evaluate the public health implications of dioxin and dioxin-like compounds (e.g., 2,3,7,8-tetrachlorodibenzo-p-dioxin [TCDD], chlorinated dibenzodioxins [CDDs], chlorinated dibenzofurans [CDFs], and other structurally related groups of chemicals from the family of halogenated aromatic hydrocarbons) in residential soils near or on hazardous waste sites. The 1998 policy established a screening level of 0.05 ppb TEQ (50 ppt), an evaluation level (>0.05 ppb TEQ, <1 ppb), and an action level of 1 ppb TEQ (1,000 ppt) for dioxins in residential soil.

ATSDR revised the 1998 policy because it has been used inconsistently over the past eight years. The ATSDR “action” level has been misinterpreted by health assessors and others as ... (1) A soil concentration that defines a public health hazard, (2) an ATSDR clean-up level which implies the need for site remediation, and (3) an initial screening level that defines a safe level of exposure, below which there is no public health concern. In addition, the “action” level triggered a set of “potential public health actions”, including surveillance, research, health studies, community education, and exposure investigations. However, ATSDR believes that these actions could be considered in some circumstances when the 1 ppb level in soil is not exceeded. In response to these concerns ATSDR has updated its Policy Guideline for Dioxins and Dioxin-Like Compounds in Residential Soil. The key elements in the updated ATSDR Policy Guideline for Dioxins and Dioxin-Like Compounds in Residential Soil are as follows:

  • Deletion of the 1 ppb action level as the criteria for taking specific public health actions.

The 1-ppb dioxin soil concentration should not be used as a comparison value for defining public health hazards in public health assessments and consultations. The 1-ppb action level can be cited by health assessors as the Superfund Dioxin Cleanup policy criteria (EPA 1989, 1998).

Retention of the 0.05 ppb Screening Level

The minimal risk level (MRL)-based environmental media evaluation guide (EMEG) of 0.05 ppb for dioxin TEQ in soil is retained as the basis for screening soil concentrations. Levels exceeding this screening level should be evaluated as described in the ATSDR Public Health Assessment Guidance Manual (PHAGM) (ATSDR 2005). This clarification will ensure that evaluation of dioxins and dioxin-like compounds in soil will be done in the same manner as all other soil contaminants.

Recommendation To Conduct Exposure Pathways Analyses for Dioxins and Dioxin-Like Compounds

The focus of the guideline is the assessment of direct exposure to soil contamination, particularly soil ingestion. However, health assessors should be aware of the potential impact of indirect exposure pathways on exposed populations in site-specific health assessments. This document does not provide specific guidance on how these indirect pathways should be assessed. However, the PHAGM document does provide assistance in evaluating indirect exposure pathways such as food chain contamination (ATSDR 2005).

Updated TEFs

The 2006 World Health Organization Toxicity Equivalency Factors (TEFs) for dioxins and dioxin-like compounds have been included in the updated document.

Background Information

In 1998, the Agency for Toxic Substances and Disease Registry (ATSDR) adopted a Final Policy Guideline for Dioxin and Dioxin-Like Compounds (De Rosa et al. 1999a). The 1998 policy guideline was accompanied by a Technical Support Document for ATSDR Policy Guideline (De Rosa et al. 1999b). The initiative to develop this policy guideline was based on a request from the U.S. Environmental Protection Agency (EPA) to evaluate the protectiveness of the EPA Superfund Policy for Dioxins in Residential Soils, which established 1 part per billion (ppb) (1,000 parts per trillion [ppt]) total dioxin toxicity equivalents (TEQ) as the starting point for making clean-up decisions. In addition, the 1998 policy guideline was to provide guidance to health assessors in evaluating the public health implications of dioxin and dioxin-like compounds (e.g., 2,3,7,8-tetrachlorodibenzo-p-dioxin [TCDD], chlorinated dibenzodioxins [CDDs], chlorinated dibenzofurans [CDFs], and other structurally related groups of chemicals from the family of halogenated aromatic hydrocarbons) in residential soils near or on hazardous waste sites. As stated in the 1998 document, “these guidelines and procedures apply to human exposure for direct ingestion of soils contaminated with dioxin and dioxin-like compounds in residential areas and may not be appropriate for other exposure scenarios.” The 1998 Policy Guideline established a screening level of 0.05 ppb TEQ (50 ppt), an evaluation level (>0.05 ppb TEQ, <1 ppb), and an action level of 1 ppb TEQ (1,000 ppt) for dioxins in residential soil and made recommendations for specific considerations or public health actions.

ATSDR has established environmental screening values for chemicals to be used by health assessors to assess exposures. No other chemical has an action level as was established for dioxins in soil in the 1998 policy guideline. This inconsistency alone has led to confusion regarding the appropriate screening value for soil dioxin levels.

The primary objectives of the updated Policy Guidelines are to provide greater consistency in ATSDR Health Assessments and to bring dioxin assessments in line with how all other chemicals are evaluated by the agency.

Summary of Peer Review for Document

The public comment draft of the revised policy has undergone internal review and clearance within ATSDR. In addition, the revised draft was reviewed by the National Center for Environmental Health/Agency for Toxic Substances and Disease Registry (NCEH/ATSDR) Board of Scientific Counselors (BSC). Public testimony was received during the meeting of the NCEH/ATSDR BSC. ATSDR also received peer review comments from health assessors in several state health departments.

Information about the “Update to ATSDR Policy Guideline for Dioxins and Dioxin-Like Compounds in Residential Soil”, including the draft document, fact sheet, peer review Start Printed Page 78442comments and ATSDR responses, is available on the ATSDR Web site at: http://www.atsdr.cdc.gov/​substances/​dioxin/​policy/​index.html.

DATES:

Comments concerning this document must be received by February 27, 2007.

ADDRESSES:

Public comments should be forwarded to Ms. Athena Gemella, ATSDR, Office of Science, 1600 Clifton Road, N.E., Mail stop E-28. Atlanta, GA. 30333, or e-mail at AGemella@cdc.gov.

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FOR FURTHER INFORMATION CONTACT:

Ms. Athena Gemella, Office of Science, telephone (404) 498-0621.

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Dated: December 22, 2006.

Kenneth Rose,

Acting Director, Office of Policy, Planning and Evaluation, National Center for Environmental Health/Agency for Toxic Substances and Disease Registry.

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[FR Doc. E6-22388 Filed 12-28-06; 8:45 am]

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