What: The federal Toxics Release Inventory (TRI) tracks the releases of more than 650 chemicals from more than 21,000 facilities nationwide. The Environmental Protection Agency then issues an annual report showing the major toxics, the companies responsible for the releases and the amount.

Why: The Emergency Planning Community Right to Know Act and Pollution Prevention Act require the EPA to track these specific chemicals because of their threat to human health and the environment.

How it works: The facilities collect their own data and submit it to the EPA, which then reviews the information for quality control.

What did the 2012 TRI show? Nationwide 3.63 billion pounds of toxic chemicals were either released into the environment or disposed of, a reduction of 12 percent from the previous year, according to the EPA. The decrease is attributed to a dip in disposals from metal mines.

North Carolina ranks 21st among U.S. states and territories in amount of releases. In the Triangle, Chatham County reported the greatest amount, followed by Wake County.

727 Number of TRI facilities in N.C.

74,927,833 Pounds of chemicals released/transferred to other sites for waste management in N.C.

17 Number of TRI facilities in Wake County, 363,373 pounds released/transferred

9 In Durham County, 89,650 pounds

4 in Orange County, 16,694 pounds

8 in Chatham County, 1,381,388 pounds

Chromium, ammonia, lead top toxics released in the Triangle

How do I learn more? You can search the TRI database by ZIP code, county and state. Go to www.epa.gov/tri/nationalanalysis.