On the east side of Houston, the white plumes of the Texas oil and chemical refineries are a constant backdrop for residents of the Manchester neighborhood.

Some residents say the air has a chemical-based smell that they find hard to describe but disappears once they drive a few miles away from the homes that stretch along the Houston Ship Channel, a waterway connecting the plants to the ocean. They claim that the pollution is taking a toll on their health, although the scientific evidence does not prove that.