1. Philadelphia, Pa.
The sprawling Philadelphia-Camden-Wilmington MSA, including parts of four states (Pennsylvania, New Jersey, Delaware and one county in Maryland), is home to more than 50 Superfund sites, which is what pushed it to the number one toxic spot in the country
MSA: Philadelphia-Camden-Wilmington, Pa./N.J./Del./Md.
Number of unhealthy air quality days (2009): 2
Pounds of on-site toxic releases reported (2009): 11.3 million
EWG top water concern: Total trihalomethanes