Ohio, Pennsylvania and Florida are the states with the most toxic air pollution from coal and oil power plants, according to a new report by an environmental advocacy group.

The Natural Resources Defense Council (NRDC) used Environmental Protection Agency data to rank the top 20 worst states for air pollution from power plants.

According to the report, half of all air pollution from industrial sources in the United States comes from coal- and oil-fired power plants. [LiveScience ]

20 most toxic states, from worst to best:

1. Ohio
2. Pennsylvania
3.  Florida
4. Kentucky
5. Maryland
6. Indiana
7. Michigan
8. West Virginia
9. Georgia
10. North Carolina
11. South Carolina
12. Alabama
13. Texas
14. Virginia
15. Tennessee
16. Missouri
17. Illinois
18. Wisconsin
19. New Hampshire
20. Iowa

Overall, U.S. power plants emitted 771 million pounds of toxic chemicals in 2009, with the electric sector responsible for 49 percent of all industrial toxic air pollution that year, or 382 million pounds. [Top 10 Alternative Energy Bets]

Accounting for 12 percent of U.S. industrial air pollution, Ohio's power plants emitted 44.5 million pounds of harmful chemicals in 2009. For comparison, the 20th ranked state, Iowa, was responsible for just 1 percent of U.S. industrial air pollution, or 2.5 million pounds of harmful chemicals.

The researchers also looked specifically at mercury air pollution, finding Ohio and Pennsylvania also took the top two spots in this measure.

The EPA is attempting to revise its public health protections to make its Mercury and Air Toxics standard stricter, but lawmakers including House Energy and Commerce Committee chair Fred Upton (R-MI) have vowed to block the new measures. According to the EPA, the proposed standards would prevent up to 120,000 cases of childhood asthma each year and save 17,000 lives per year by 2015.