BPA is used to coat thermal paper, which reacts with dye to form black print on receipts handled by millions of Americans every day.

"Hawking famously showed that black holes radiate energy according to a thermal spectrum," said Paul Nation, an author on the paper and a graduate student at Dartmouth.

Braun notes that for people who handle only a couple of receipts a day, thermal paper is unlikely to be a major source of exposure.