Completed Exposure Pathway (CEP) Site Count Report

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Completed Exposure Pathway (CEP) Site Count Report

What is the CEP Site Count Report?

Exposure to hazardous substances is of significant concern to ATSDR. Therefore, ATSDR’s Division of Toxicology and Human Health Sciences publishes the following Completed Exposure Pathway Site Count Report along with the Priority List of Hazardous Substances (also called the Substance Priority List). A completed exposure pathway (CEP) links a contaminant source to a receptor population, and people are likely to have been exposed to the substance. 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. This information is derived from ATSDR public health assessments and health consultations. The CEP report therefore focuses on documented exposure, and lists hazardous substances according to exposure frequency.

How does the CEP report differ from the Substance Priority List?

This CEP ranking is similar to a subcomponent in the substance priority list algorithm called “Exposure to Contaminant”. This subcomponent is part of the potential-for-human-exposure component of the listing algorithm, and is a count of the number of completed exposure pathways that substances appeared in, not the number of sites where it was in a CEP. (A substance can appear in more than one pathway at a given site.) A pathway count, rather than a site count, is more appropriate for the substance 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 substance priority list is mandated by CERCLA, it only uses data from CERCLA sites on the National Priorities List (NPL), whereas this CEP report uses data from all ATSDR-activity sites at which a CEP has been detected.

The substances in the CEP report are similar to the substances on the substance priority list. However, some substances in the CEP report have a very low toxicity (e.g., sodium) and as a result are not included in the substance priority list. Since the substance priority list uses toxicity, frequency of occurrence, and potential for human exposure to determine its priority substances, other low-toxicity substances will not appear on the list and, consequently, will not become subjects of toxicological profiles. Also, the CEP report includes substance groups, process wastes, and other environmental hazards at hazardous waste sites that do not have a Chemical Abstracts Service Registry Number (CAS number). Substances without CAS numbers have been excluded from the substance priority list in order to focus the development of toxicological profiles on well identified substances. Substances without CAS numbers appear on this report with a “pseudo-CAS” assigned by ATSDR that begins with HZ.

What is the utility of the CEP report?

The CEP Report presents a straightforward measure of the extent to which the public is being exposed to particular substances. Public health officials can use the CEP Report for a quick overview of the substances most frequently involved in exposures at ATSDR sites and events.

For a spreadsheet of the current and past CEP Reports, including substances past the top 100 and pathway counts, see the Full SPL Spreadsheet on our SPL Resources page. The CEP Report is produced at the same time from the same data as the SPL. The Summary Statistics and general statements about the data in the SPL’s Cover Notes also apply.

ATSDR 2022 Completed Exposure Pathway Site Count Report

ATSDR 2022 Completed Exposure Pathway Site Count Report
2022 Rank Substance Name All Sites/Events NPL Sites CAS RN
1 LEAD 583 312 7439-92-1
2 ARSENIC 524 278 7440-38-2
3 TRICHLOROETHYLENE 462 328 79-01-6
4 TETRACHLOROETHYLENE 373 246 127-18-4
5 BENZENE 296 156 71-43-2
6 CADMIUM 292 176 7440-43-9
7 CHROMIUM 248 150 7440-47-3
8 MERCURY 244 115 7439-97-6
9 MANGANESE 224 123 7439-96-5
10 COPPER 216 119 7440-50-8
11 POLYCHLORINATED BIPHENYLS 215 131 1336-36-3
12 ZINC 196 113 7440-66-6
13 ANTIMONY 158 93 7440-36-0
14 CHLOROFORM 156 102 67-66-3
15 VOLATILE ORGANIC COMPOUNDS N.O.S. 155 93 HZ1900-01-T
16 NICKEL 153 87 7440-02-0
17 BENZO(A)PYRENE 149 74 50-32-8
18 VINYL CHLORIDE 144 101 75-01-4
19 METHYLENE CHLORIDE 139 77 75-09-2
20 TOLUENE 137 71 108-88-3
21 1,1,1-TRICHLOROETHANE 136 104 71-55-6
22 BARIUM 136 72 7440-39-3
23 1,1-DICHLOROETHENE 132 102 75-35-4
24 IRON 127 70 7439-89-6
25 1,2-DICHLOROETHANE 124 88 107-06-2
26 VANADIUM 123 64 7440-62-2
27 CARBON TETRACHLORIDE 119 73 56-23-5
28 POLYCYCLIC AROMATIC HYDROCARBONS 117 75 130498-29-2
29 BERYLLIUM 114 54 7440-41-7
30 BENZO(A)ANTHRACENE 110 55 56-55-3
31 BENZO(B)FLUORANTHENE 104 46 205-99-2
32 NAPHTHALENE 102 50 91-20-3
33 ALUMINUM 101 59 7429-90-5
34 DI(2-ETHYLHEXYL)PHTHALATE 100 66 117-81-7
35 CHRYSENE 100 50 218-01-9
36 1,1-DICHLOROETHANE 97 76 75-34-3
37 PHENANTHRENE 96 43 85-01-8
38 THALLIUM 94 48 7440-28-0
39 XYLENES, TOTAL 92 43 1330-20-7
40 INDENO(1,2,3-CD)PYRENE 90 41 193-39-5
41 BENZO(K)FLUORANTHENE 89 42 207-08-9
42 ETHYLBENZENE 88 42 100-41-4
43 COBALT 85 39 7440-48-4
43 DIBENZO(A,H)ANTHRACENE 85 39 53-70-3
45 DIELDRIN 84 44 60-57-1
46 SELENIUM 84 38 7782-49-2
47 METALS N.O.S. 83 53 HZ0900-01-T
48 1,2-DICHLOROETHENE, CIS- 82 54 156-59-2
49 SODIUM 76 38 7440-23-5
50 BENZO(GHI)PERYLENE 72 29 191-24-2
51 DDT, P,P’- 71 44 50-29-3
52 PENTACHLOROPHENOL 69 46 87-86-5
53 1,2-DICHLOROETHENE, TRANS- 62 52 156-60-5
54 SILVER 62 30 7440-22-4
55 DDE, P,P’- 59 35 72-55-9
56 FLUORANTHENE 58 24 206-44-0
57 PYRENE 56 24 129-00-0
58 2-METHYLNAPHTHALENE 54 26 91-57-6
59 HEPTACHLOR EPOXIDE 54 25 1024-57-3
60 AROCLOR 1260 53 34 11096-82-5
61 DDD, P,P’- 52 30 72-54-8
62 MAGNESIUM 52 26 7439-95-4
63 DIBENZOFURAN 51 26 132-64-9
64 CYANIDE 50 25 57-12-5
65 1,2,4-TRIMETHYLBENZENE 49 11 95-63-6
66 BROMODICHLOROMETHANE 48 30 75-27-4
67 CHLOROBENZENE 47 34 108-90-7
68 ACETONE 47 21 67-64-1
69 1,2-DICHLOROETHYLENE 46 38 540-59-0
70 BENZO(A)PYRENE EQUIVALENTS 46 25 HZ1500-50-T
71 CHLORDANE 45 30 57-74-9
72 ASBESTOS 45 13 1332-21-4
73 CALCIUM 43 26 7440-70-2
74 2-BUTANONE 43 24 78-93-3
75 CHROMIUM, HEXAVALENT 42 23 18540-29-9
76 ALDRIN 42 18 309-00-2
77 FLUORENE 42 16 86-73-7
78 CARBAZOLE 41 17 86-74-8
79 AROCLOR 1254 40 29 11097-69-1
80 ANTHRACENE 39 13 120-12-7
80 1,4-DICHLOROBENZENE 39 13 106-46-7
82 HEPTACHLOR 38 16 76-44-8
83 DIBROMOCHLOROMETHANE 37 22 124-48-1
84 POTASSIUM 37 20 7440-09-7
85 TCDD EQUIVALENTS 37 19 HZ0400-03-T
86 ACENAPHTHYLENE 37 14 208-96-8
87 NITRATE 36 22 14797-55-8
88 CHLOROMETHANE 36 14 74-87-3
89 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN 35 26 1746-01-6
90 PESTICIDES N.O.S. 35 19 HZ1200-01-T
91 ACENAPHTHENE 35 12 83-32-9
92 1,3,5-TRIMETHYLBENZENE 35 8 108-67-8
93 DIOXINS N.O.S. 34 23 HZ0400-05-T
94 STYRENE 33 11 100-42-5
95 HEXACHLOROCYCLOHEXANE, GAMMA- 32 17 58-89-9
96 HYDROGEN SULFIDE 31 4 7783-06-4
97 1,1,2-TRICHLOROETHANE 30 22 79-00-5
98 1,1,2,2-TETRACHLOROETHANE 30 21 79-34-5
99 METHYL-T-BUTYL ETHER 30 10 1634-04-4
100 DI-N-BUTYL PHTHALATE 29 11 84-74-2

All Sites/Events = all sites and events with ATSDR activity; NPL Sites = current and former sites on the National Priorities List (EPA NPL status of Final, Proposed, Removed, and Deleted); CAS RN = Chemical Abstracts Service Registry Number; CEP = Completed Exposure Pathway; N.O.S. = Not Otherwise Specified.

Contact Information

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

Agency for Toxic Substances and Disease Registry
Division of Toxicology and Human Health Sciences
1600 Clifton Road NE, Mailstop S106-5
Atlanta, GA 30329
Phone: 1-800-CDC-INFO 888-232-6348 (TTY)
Email: cdcinfo@cdc.gov

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