Exposure to hazardous substances is of significant concern to ATSDR. For the past number of years, ATSDR has been tabulating the substances to which people have been exposed at hazardous waste sites, and recently much interest has been focused on this tabulation. Therefore, ATSDR's Division of Toxicology will henceforth publish the following Completed Exposure Pathway report along with the CERCLA Priority List of Hazardous Substances. A completed exposure pathway (CEP) is an exposure pathway that links a contaminant source to a receptor population. The CEP ranking presented here is based on a site frequency count, and thus lists the number of sites at which a substance has been found in a CEP. ATSDR's HazDat database contains this information which is derived from ATSDR's Health Assessments and Consultations. Since this CEP report focuses on documented exposure, it provides an important prioritization based on substances to which people are exposed.

This CEP ranking is very similar to a sub-component in the CERCLA priority list algorithm called "Exposure to Contaminant". This sub-component is part of the potential-for-human- exposure component of the listing algorithm, and is an incident count of substances in a completed exposure pathway. An incident count, rather than a site count, is more appropriate for the priority list because it adds more discrimination to the less frequent substances on the list. Another difference between the two exposure counts is that since the priority list is mandated by CERCLA, it only uses data from CERCLA sites on the National Priorities List (NPL), whereas this CEP ranking utilizes data from all sites in HazDat. 

The substances on the CEP list are similar to the substances on the CERCLA Priority List of Hazardous Substances. However, there are some substances that are frequently found in CEPs, but have a very low toxicity (e.g., sodium). These low toxicity substances are not on the CERCLA priority list because it incorporates three different components - toxicity, frequency of occurrence, and potential for human exposure - to determine its priority substances. Thus, due to their low toxicity, these substances are not on the CERCLA priority list and consequently are not the subject of toxicological profiles. 

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 

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

All Sites = all sites with ATSDR activities;
NPL Sites = current and former sites on the National Priorities List;
CAS = Chemical Abstracts Service;
CEP = Completed Exposure Pathway.