The Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) section 104 (i), as amended by the Superfund Amendments and Reauthorization Act (SARA), requires ATSDR and the EPA to prepare a list, in order of priority, of substances that are most commonly found at facilities on the National Priorities List (NPL) and which are determined to pose the most significant potential threat to human health due to their known or suspected toxicity and potential for human exposure at these NPL sites. CERCLA also requires this list to be revised periodically to reflect additional information on hazardous substances.

This CERCLA priority list is revised and published on a 2-year basis, with a yearly informal review and revision. Each substance on the CERCLA Priority List of Hazardous Substances is a candidate to become the subject of a toxicological profile prepared by ATSDR and subsequently a candidate for the identification of priority data needs. This priority list is based on an algorithm that utilizes the following three components: frequency of occurrence at NPL sites, toxicity, and potential for human exposure to the substances found at NPL sites. This algorithm utilizes data from ATSDR's HazDat database, which contains information from ATSDR's public health assessments and health consultations.

It should be noted that this priority list is not a list of "most toxic" substances, but rather a prioritization of substances based on a combination of their frequency, toxicity, and potential for human exposure at NPL sites.

Thus, it is possible for substances with low toxicity but high NPL frequency of occurrence and exposure to be on this priority list. The objective of this priority list is to rank substances across all NPL hazardous waste sites to provide guidance in selecting which substances will be the subject of toxicological profiles prepared by ATSDR.

There is a Support Document to the CERCLA Priority List of Hazardous Substances that describes in detail how the list is developed. This support document also contains an appendix showing the breakdown of the total scores for each substance on the priority list. To view this support document, click here.

The ATSDR Division of Toxicology has prepared several sets of publications that provide answers to many health concerns that are voiced by community groups and give general information on various properties of each of these substances. Those publications are listed and may be accessed online at the following links:

• ATSDR ToxFAQs™ Sheets
• ATSDR Public Health Statements
• ATSDR Toxicological Profiles

You may also access the previous lists online:

• CERCLA Priority List of Hazardous Substances for 2003
• CERCLA Priority List of Hazardous Substances for 2001
• CERCLA Priority List of Hazardous Substances for 1999
• CERCLA Priority List of Hazardous Substances for 1997

Further information can be obtained by contacting the ATSDR Information Center at:

Agency for Toxic Substances and Disease Registry
Division of Toxicology
1600 Clifton Road NE, Mailstop F-32
Atlanta, GA 30333
Phone: 1-888-42-ATSDR (1-888-422-8737)
FAX:   (770)-488-4178
Email: ATSDRIC@cdc.gov