You might want to put down that shiny red apple and reach for another snack. Europe has banned the importation of grown-in-the-U.S.A. apples that have been sprayed with a pesticide.
In 2008, the European Food Safety Authority (EFSA) began looking into the potential side effects of a chemical called diphenylamine (DPA). DPA, which is applied to apples after harvest to prevent brown spots from forming, isn't known to be harmful on its own, but it does have the potential to break down into a family of carcinogens. According to Mother Jones, a study found three unknown chemicals on DPA-treated apples, but the Environmental Working Group (EWG), who did the study, couldn't determine whether any of them were carcinogenic.
Still, the EFSA banned the use of DPA on apples in 2012 and then slashed the tolerable level of DPA on imported apples to 0.1 parts per million—while the U.S. Environmental Protection Agency (EPA) approves the use of up to 10 ppm of DPA on apples (that's 100 times more than the new European limit).
Mother Jones reports that the EPA has no plans to reevaluate the safety of DPA in light of the EFSA's new rules.
This information sounds crazy-scary, but neither American food safety experts nor European ones actually know whether DPA is actually harmful to ingest (don't you feel better already?). Europe has simply decided to act preemptively until more research can shed more light one way or the other on the subject. If you're an American (or a European in the U.S.), and you're hoping to avoid DPA, your best bet is to purchase organic apples.