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 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

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