Completed Exposure Pathway (CEP) Site Count Report

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 past CEP Reports and a spreadsheet with substances past the top 100, including pathway counts, see the CEP Report Archive.

ATSDR 2019 Completed Exposure Pathway Site Count Report

ATSDR 2019 Completed Exposure Pathway Site Count Report
2019 Rank Substance Name All Sites/Events NPL Sites CAS RN
1 LEAD 554 298 7439-92-1
2 ARSENIC 507 269 7440-38-2
3 TRICHLOROETHYLENE 450 320 79-01-6
4 TETRACHLOROETHYLENE 350 232 127-18-4
5 BENZENE 283 146 71-43-2
6 CADMIUM 274 168 7440-43-9
7 CHROMIUM 231 143 7440-47-3
8 MERCURY 225 105 7439-97-6
9 POLYCHLORINATED BIPHENYLS 212 131 1336-36-3
10 MANGANESE 206 113 7439-96-5
11 COPPER 194 110 7440-50-8
12 ZINC 169 99 7440-66-6
13 VOLATILE ORGANIC COMPOUNDS N.O.S. 155 93 HZ1900-01-T
14 CHLOROFORM 146 96 67-66-3
15 BENZO(A)PYRENE 146 72 50-32-8
16 ANTIMONY 141 83 7440-36-0
17 VINYL CHLORIDE 138 100 75-01-4
18 NICKEL 131 77 7440-02-0
19 1,1,1-TRICHLOROETHANE 123 98 71-55-6
20 1,1-DICHLOROETHENE 121 96 75-35-4
21 METHYLENE CHLORIDE 121 68 75-09-2
22 1,2-DICHLOROETHANE 115 82 107-06-2
23 POLYCYCLIC AROMATIC HYDROCARBONS 115 74 130498-29-2
24 TOLUENE 113 65 108-88-3
25 BARIUM 112 60 7440-39-3
26 IRON 111 64 7439-89-6
27 CARBON TETRACHLORIDE 109 67 56-23-5
28 VANADIUM 107 59 7440-62-2
29 BENZO(A)ANTHRACENE 103 50 56-55-3
30 DI(2-ETHYLHEXYL)PHTHALATE 98 65 117-81-7
31 BENZO(B)FLUORANTHENE 96 40 205-99-2
32 CHRYSENE 94 46 218-01-9
33 NAPHTHALENE 92 46 91-20-3
34 1,1-DICHLOROETHANE 89 73 75-34-3
35 BERYLLIUM 89 43 7440-41-7
36 PHENANTHRENE 88 37 85-01-8
37 INDENO(1,2,3-CD)PYRENE 84 37 193-39-5
38 METALS N.O.S. 83 53 HZ0900-01-T
39 ALUMINUM 83 50 7429-90-5
40 DIELDRIN 83 44 60-57-1
41 BENZO(K)FLUORANTHENE 83 37 207-08-9
42 THALLIUM 80 43 7440-28-0
43 XYLENES, TOTAL 78 38 1330-20-7
44 DIBENZO(A,H)ANTHRACENE 77 33 53-70-3
45 ETHYLBENZENE 74 39 100-41-4
46 DDT, P,P’- 68 42 50-29-3
47 COBALT 68 32 7440-48-4
48 PENTACHLOROPHENOL 67 44 87-86-5
49 SODIUM 65 33 7440-23-5
50 BENZO(GHI)PERYLENE 65 24 191-24-2
51 1,2-DICHLOROETHENE, CIS- 60 43 156-59-2
52 SELENIUM 59 25 7782-49-2
53 DDE, P,P’- 57 35 72-55-9
54 AROCLOR 1260 52 33 11096-82-5
55 1,2-DICHLOROETHENE, TRANS- 51 46 156-60-5
56 DDD, P,P’- 51 30 72-54-8
57 HEPTACHLOR EPOXIDE 51 24 1024-57-3
58 FLUORANTHENE 49 18 206-44-0
59 CYANIDE 48 24 57-12-5
60 2-METHYLNAPHTHALENE 48 22 91-57-6
61 PYRENE 48 19 129-00-0
62 1,2-DICHLOROETHYLENE 45 38 540-59-0
63 CHLOROBENZENE 45 33 108-90-7
64 CHLORDANE 45 30 57-74-9
65 ASBESTOS 45 13 1332-21-4
66 BROMODICHLOROMETHANE 44 28 75-27-4
67 DIBENZOFURAN 44 20 132-64-9
68 BENZO(A)PYRENE EQUIVALENTS 42 22 HZ1500-50-T
69 SILVER 41 18 7440-22-4
70 MAGNESIUM 40 21 7439-95-4
71 ALDRIN 40 17 309-00-2
72 AROCLOR 1254 38 27 11097-69-1
73 1,2,4-TRIMETHYLBENZENE 38 6 95-63-6
74 FLUORENE 36 13 86-73-7
75 CHROMIUM, HEXAVALENT 35 19 18540-29-9
75 PESTICIDES N.O.S. 35 19 HZ1200-01-T
75 TCDD EQUIVALENTS 35 19 HZ0400-03-T
78 ACETONE 35 18 67-64-1
79 HEPTACHLOR 35 15 76-44-8
80 CARBAZOLE 35 12 86-74-8
81 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN 33 24 1746-01-6
82 DIOXINS N.O.S. 33 22 HZ0400-05-T
83 ACENAPHTHYLENE 33 12 208-96-8
84 2-BUTANONE 32 21 78-93-3
84 NITRATE 32 21 14797-55-8
86 DIBROMOCHLOROMETHANE 32 19 124-48-1
87 1,4-DICHLOROBENZENE 32 10 106-46-7
88 ANTHRACENE 32 9 120-12-7
89 CALCIUM 31 21 7440-70-2
90 HEXACHLOROCYCLOHEXANE, GAMMA- 31 17 58-89-9
91 HYDROGEN SULFIDE 30 4 7783-06-4
92 ACENAPHTHENE 29 9 83-32-9
93 1,1,2,2-TETRACHLOROETHANE 28 20 79-34-5
94 1,1,2-TRICHLOROETHANE 27 21 79-00-5
95 HEXACHLOROCYCLOHEXANE, ALPHA- 27 15 319-84-6
96 BORON 27 14 7440-42-8
97 DI-N-BUTYL PHTHALATE 27 10 84-74-2
98 BUTYL BENZYL PHTHALATE 27 7 85-68-7
99 1,2-DICHLOROPROPANE 26 18 78-87-5
100 PHENOL 26 14 108-95-2

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.

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 S102-1
Atlanta, GA 30329
Phone: 1-800-CDC-INFO 888-232-6348 (TTY)
Email: cdcinfo@cdc.gov

Page last reviewed: January 17, 2020