There's a section of the Gulf Coast in the South that has significantly higher rates of cancer than other parts of the country. This section, nicknamed "Cancer Alley," is also home to dozens of chemical factories and petroleum refineries.

Today on Parts Per Billion, we talk with Bloomberg Law's Pat Rizzuto about how the EPA calculates the risk of toxic chemical exposure in areas like Cancer Alley and about how some activists are using the agency's own data to prod it to change.