The Latest ATSDR Substance Priority List of Chemicals and Elements Posing the Most Significant Risk at NPL sites

The rankings are out and three metals top the chart: arsenic, lead, and mercury. The Agency for Toxic Substances and Disease Registry (ATSDR) has released its 2017 list of substances at EPA-managed contamination sites posing the most significant risk to human health.  

CERCLA/SARA (Superfund)  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) that 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.

ATSDR typically publishes the substance priority list every two years, in addition to performing an annual informal review and revision. The total points ranking is determined using an algorithm that prioritizes substances based on frequency of occurrence at NPL sites, toxicity, and potential for human exposure to the substances found at NPL sites. ATSDR notes that this priority list is not a list of “most toxic” substances, but instead is a prioritization of substances based on the ranking algorithm.

A total of 275 substances are listed on the entire ATSDR 2017 Substance Priority list.  Here are the Top 50 substances listed. 

Rank, Substance Name, Total Points, CAS #

1. Arsenic   1674 points   7440-38-2

2. Lead    1531 points     7439-92-1

3. Mercury   1458 points    7439-97-6

4. Vinyl Chloride   1358 points   75-01-4

5. Polychlorinated Biphenyls   1345 points    1336-36-3

6. Benzene   1329 points     71-43-2

7. Cadmium   1320 points    7440-43-9

8. Benzo(a)pyrene   1306 points    50-32-8

9. PAHs (PNAs)   1279 points    130498-29-2

10. Benzo(b)fluoranthene   1251 points    205-99-2

11. Chloroform    1203 points    67-66-3

12. Arolcor 1260   1191 points     11096-82-5

13. DDT, P,P’   1183 points      50-29-3

14. Arolcor 1254   1172 points     11097-69-1

15. Dibenzo(a,h)anthracene   1156 points     53-70-3

16. Trichloroethylene    1155 points     79-01-6

17. Hexavalent Chromium    1148 points      18540-29-9

18. Dieldrin   1144 points     60-57-1

19. Phosphorus, White    1141 points      7723-14-0

20. Hexachlorobutadiene   1130 points      87-68-3

21. DDE, P,P’     1127 points      72-55-9

22. Chlordane     1126 points      57-74-9

23. Arolcor 1242     1126 points      53469-21-9

24. Coal Tar Creosote     1124 points      8001-58-9

25. Aldrin     1116  points     309-00-2

26. DDD, P,P’     1114 points     72-54-8

27. Arolcor 1248     1105 points    12672-29-6

28. Heptachlor     1102 points      76-44-8

29. Arolcor     1101 points     12767-79-2

30. Benzidine    1093 points     92-87-5

31. Acrolein    1090 points     107-02-8

32. Toxaphene    1089 points     8001-35-2

33. Tetrachloroethylene    1078 points     127-18-4

34. Hexachlorocyclohexane, Gamma     1076 points      58-89-9

35. Cyanide     1071 points     57-12-5

36. Hexachlorocyclohexane, Beta    1054 points     319-85-7

37. Disulfoton    1049 points      298-04-4

38. Benzo(a)anthracene     1047 points      56-55-3

39. 1,2-Dibromoethane     1043 points      106-93-4

40. Endrin    1039 points      72-20-8

41. Diazinon    1038 points      333-41-5

42. Hexachlorocyclohexane, Delta    1036 points      319-86-8

43. Beryllium    1031 points      7440-41-7

44. Endosulfan     1029 points      115-29-7

45. Arolcor 1221     1028 points      11104-28-2

46. 1,2-Dibromo-3-Chloropropane     1027 points     96-12-8

47. Heptachlor Epoxide    1022 points      1024-57-3

48. Endosulfan Alpha     1019 points      959-98-8

49. Cis-Chlordane   1017 points     5103-71-9

50. Carbon Tetrachloride   1014 points     56-23-5

According to ATSDR, the ranking of hazardous substances on the substance priority list is based on three criteria, which are combined to result in the total score. The three criteria are:

• Frequency of Occurrence at NPL sites: A substance has to be identified at three or more NPL hazardous waste sites or facilities to be considered a candidate for this list.

• Toxicity: Final Reportable Quantities (RQs) are used to assess the toxicity of candidate substances during the listing activity. If a final RQ is not available, the RQ methodology is applied to candidate substances to establish a Toxicity/Environmental Score (TES). This process is only used in scoring the substances with respect to their toxicity, and does not represent regulatory values.

• Potential for Human Exposure The exposure component is based on two parts: (1) the concentration of the substances in environmental media at sites, and (2) the exposure status of populations at sites. ATSDR’s science database is the source of this data with concentration and exposure data obtained from ATSDR public health assessments and health consultations.

Using these three criteria, the hazard potential of each candidate substance is ranked according to the following algorithm:

Total Score (1,800 point max.) = NPL Frequency (600 point max.) + Toxicity (600 point max.) + Potential for Human Exposure (300 concentration + 300 exposure points max.)

The algorithm generates a candidate list of substances based on their total score. The top 275 scoring substances becomes the Priority List of Hazardous Substances. There are currently 857 candidate substances for the priority list. 

Merit Laboratories is one of the leading environmental laboratories for supporting projects with environmental contamination.  Please contact Merit to discuss your project testing needs and find out how we can help you achieve your site-specific data quality objectives.