Skip directly to search Skip directly to A to Z list Skip directly to navigation Skip directly to page options Skip directly to site content

Substances Most Frequently Found in Completed Exposure Pathways at Hazardous Waste Sites

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 2017 Completed Exposure Pathway Site Count Report

2017 Rank Substance Name All Sites/Events NPL Sites CAS RN
1 LEAD 544 292 7439-92-1
2 ARSENIC 495 262 7440-38-2
3 TRICHLOROETHYLENE 442 312 79-01-6
4 TETRACHLOROETHYLENE 345 226 127-18-4
5 BENZENE 278 143 71-43-2
6 CADMIUM 267 164 7440-43-9
7 CHROMIUM 226 140 7440-47-3
8 MERCURY 223 103 7439-97-6
9 POLYCHLORINATED BIPHENYLS 208 128 1336-36-3
10 MANGANESE 201 110 7439-96-5
11 COPPER 191 107 7440-50-8
12 ZINC 167 97 7440-66-6
13 VOLATILE ORGANIC COMPOUNDS N.O.S. 155 93 HZ1900-01-T
14 BENZO(A)PYRENE 143 69 50-32-8
15 CHLOROFORM 142 94 67-66-3
16 VINYL CHLORIDE 137 99 75-01-4
17 ANTIMONY 136 79 7440-36-0
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 119 67 75-09-2
22 POLYCYCLIC AROMATIC HYDROCARBONS 115 74 130498-29-2
23 1,2-DICHLOROETHANE 112 80 107-06-2
24 TOLUENE 112 65 108-88-3
25 BARIUM 112 60 7440-39-3
26 IRON 108 62 7439-89-6
27 VANADIUM 107 59 7440-62-2
28 CARBON TETRACHLORIDE 105 65 56-23-5
29 BENZO(A)ANTHRACENE 101 48 56-55-3
30 DI(2-ETHYLHEXYL)PHTHALATE 96 63 117-81-7
31 BENZO(B)FLUORANTHENE 93 37 205-99-2
32 CHRYSENE 92 44 218-01-9
33 1,1-DICHLOROETHANE 89 73 75-34-3
34 BERYLLIUM 88 42 7440-41-7
35 PHENANTHRENE 87 36 85-01-8
36 NAPHTHALENE 86 41 91-20-3
37 METALS N.O.S. 83 53 HZ0900-01-T
38 ALUMINUM 83 50 7429-90-5
39 DIELDRIN 83 44 60-57-1
40 INDENO(1,2,3-CD)PYRENE 82 35 193-39-5
41 BENZO(K)FLUORANTHENE 81 35 207-08-9
42 THALLIUM 77 40 7440-28-0
43 XYLENES, TOTAL 77 38 1330-20-7
44 ETHYLBENZENE 74 39 100-41-4
45 DIBENZO(A,H)ANTHRACENE 71 28 53-70-3
46 DDT, P,P’- 68 42 50-29-3
47 COBALT 68 32 7440-48-4
48 PENTACHLOROPHENOL 67 44 87-86-5
49 BENZO(GHI)PERYLENE 65 24 191-24-2
50 SODIUM 64 32 7440-23-5
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 1,2-DICHLOROETHENE, TRANS- 51 46 156-60-5
55 DDD, P,P’- 51 30 72-54-8
56 HEPTACHLOR EPOXIDE 51 24 1024-57-3
57 FLUORANTHENE 49 18 206-44-0
58 AROCLOR 1260 48 31 11096-82-5
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 DIBENZOFURAN 44 20 132-64-9
67 BROMODICHLOROMETHANE 43 28 75-27-4
68 SILVER 41 18 7440-22-4
69 MAGNESIUM 40 21 7439-95-4
70 ALDRIN 40 17 309-00-2
71 1,2,4-TRIMETHYLBENZENE 38 6 95-63-6
72 AROCLOR 1254 36 26 11097-69-1
73 BENZO(A)PYRENE EQUIVALENTS 36 19 HZ1500-50-T
74 FLUORENE 36 13 86-73-7
75 PESTICIDES N.O.S. 35 19 HZ1200-01-T
75 TCDD EQUIVALENTS 35 19 HZ0400-03-T
77 ACETONE 35 18 67-64-1
78 HEPTACHLOR 35 15 76-44-8
79 CARBAZOLE 35 12 86-74-8
80 2,3,7,8-TETRACHLORODIBENZO-P-DIOXIN 33 24 1746-01-6
81 ACENAPHTHYLENE 33 12 208-96-8
82 2-BUTANONE 32 21 78-93-3
82 DIOXINS N.O.S. 32 21 HZ0400-05-T
82 NITRATE 32 21 14797-55-8
85 CHROMIUM, HEXAVALENT 32 16 18540-29-9
86 1,4-DICHLOROBENZENE 32 10 106-46-7
87 ANTHRACENE 32 9 120-12-7
88 CALCIUM 31 21 7440-70-2
89 DIBROMOCHLOROMETHANE 31 19 124-48-1
90 HEXACHLOROCYCLOHEXANE, GAMMA- 31 17 58-89-9
91 ACENAPHTHENE 29 9 83-32-9
92 HYDROGEN SULFIDE 29 4 7783-06-4
93 1,1,2-TRICHLOROETHANE 27 21 79-00-5
94 1,1,2,2-TETRACHLOROETHANE 27 19 79-34-5
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 F-57
Atlanta, GA 30329
Phone: 1-800-CDC-INFO 888-232-6348 (TTY)
Email: Contact CDC-INFO

 Top of Page

TOP