On November 3, 2011, the Agency for Toxic Substances and Disease Registry ("ATSDR") published its 2011 Priority List of Hazardous Substances. Pursuant to Section 104(i)(2)(A) of the Comprehensive Environmental Response, Compensation, and Liability Act ("CERCLA"), ATSDR, in collaboration with EPA, is charged with developing a list of hazardous substances, in priority order, that are most commonly found at sites on the National Priorities List ("NPL") and pose the most significant potential threat to human health. The Substances Priority List consists of the hazardous substances receiving the top 275 highest scores according to ATSDR's priority calculation. ATSDR calculates a priority score for each hazardous substance that is determined to be a "candidate" for the list, based on its presence in at least one environmental media at three or more NPL sites. For 2011, the candidate list was 847 substances long.
In calculating each substance's score, ATSDR uses three criteria: (1) frequency of occurrence at NPL sites; (2) toxicity; and (3) potential for human exposure. Each of these criteria is given equal weight of a possible 600 points each and the total score received by the hazardous substances, based on adding the scores for all three criteria, is used to develop the priority list. Frequency is scored based on a comparison of the substance's frequency to the frequency of the most prevalent substance, lead. Toxicity is assessed through Reportable Quantities, where assigned, or by using the methodology employed to determine reportable quantities. Finally, potential for human exposure is scored by evaluating both the concentration of the substances in different media at sites and the exposure status of populations at sites.
Ordinarily, this list is revised every two years. However, the latest list is the first revision since 2007 as a result of an agency database change. As in the past, the highest ranked substance is arsenic. Compared to the 2007 list, the 2011 list adds seven new substances and drops seven previously listed substances. The added substances are:
- 2,3-Dimethylnaphthalene (#209)
- Dimethylaniline (#254)
- Metolachlor (#267)
- 2-Chloroaniline (#268)
- 1,2,3-Trichloropropane (#269)
- Thallium (#274)
-
1,2,3,7,8,9-Hexachlorodibenzofuran (#275)
The following substances were removed from the list:
- Iodine-129
- Americium
- Actinium-227
- Calcium Arsenate
- Hydrogen Fluoride
- Methyl parathion
-
1-methylnapththalene
The 2011 Priority List of Hazardous Substances can be found here.