Gamers say they chug their fuel for the sugar and caffeine, but drinkers of Mountain Dew and some other citrus-flavored drinks are also getting a dose of a synthetic chemical called brominated vegetable oil, or BVO. 

Patented by chemical companies as a flame retardant, and banned in food throughout Europe and Japan, BVO has been added to sodas for decades in North America. Now some scientists have a renewed interest in this little-known ingredient, found in 10 percent of sodas in the United States.