Back in 2008, European Food Safety Authority began pressing the chemical industry to provide safety information on a substance called diphenylamine, or DPA. Widely applied to apples after harvest, DPA prevents "storage scald"—brown spots that "becomes a concern when fruit is stored for several months," according to Washington State University, reporting from the heartland of industrial-scale apple production.
DPA isn't believed to be harmful on its own. But it has the potential to break down into a family of carcinogens called nitrosamines—not something you want to find on your daily apple. And that's why European food safety regulators wanted more information on it.