From:  http://www.atsdr.cdc.gov/cxcx3.html

Top 20 Hazardous Substances

from the 

CERCLA Priority List of Hazardous Substances for 2001

What is the Top 20 List?

Further information about the evaluation process and the complete set of 275 substances on the current list can be accessed online at:
       CERCLA Priority List of Hazardous Substances for 2001. 

Each of the Top 20 substances listed below is identified with their 2001  Rank Number and includes a link to an ATSDR publication, the ToxFAQs^TM  Sheet, which has further health and chemical information about that substance. 

The ATSDR Division of Toxicology has prepared several sets of publications that provide answers to many health concerns that are voiced by community groups and give general information on various properties of each of these substances. Those publications are listed and may be accessed online at: 

• ATSDR ToxFAQs^TM  Sheets 
• ATSDR Public Health Statements 
• ATSDR Toxicological Profiles 

Top 20 Substances

1. Arsenic
2. Lead
3. Mercury
4. Vinyl Chloride
5. Polychlorinated Biphenyls (PCBs)
6. Benzene 
7. Cadmium
8. Benzo[a]pyrene
9. Polycyclic Aromatic Hydrocarbons
10. Benzo(b)fluoranthene
11. Chloroform
12. DDT, p'p'-
13. Aroclor 1254
14. Aroclor 1260
15. Trichloroethylene
16. Dibenz[a,h]anthracene
17. Dieldrin
18. Chromium, Hexavalent
19. Chlordane 
20. Hexachlorobutadiene

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

Agency for Toxic Substances and Disease Registry 

Division of Toxicology 

1600 Clifton Road NE, Mailstop E-29 

Atlanta, GA 30333 

Phone: 1-888-422-8737 

Fax: 1-404-498-0057 

E-mail: ATSDRIC@cdc.gov.