Bisphenol A (BPA) - a substance that may have harmful health effects - occurs in 94 percent of thermal cash register receipts, scientists are reporting. The recycling of those receipts, they add, is a source of BPA contamination of paper napkins, toilet paper, food packaging and other paper products.

The report, which could have special implications for cashiers and other people who routinely handle thermal paper receipts, appears in ACS' journal Environmental Science and Technology.

Kurunthachalam Kannan and Chunyang Liao explain that manufacturers produce more than 8 billion pounds of BPA worldwide every year. Research links BPA with a variety of harmful health effects. BPA has been used in plastic water bottles, the lining of food cans and a variety of other products.

But how much do non-food sources contribute to humans' daily BPA exposure? BPA coats the surfaces of thermal receipts, where it acts as a developer for the printing dye.

To see whether this source of BPA was a concern, the researchers analyzed hundreds of samples of thermal cash register receipts and 14 other types of paper products from the U.S., Japan, Korea and Vietnam.

They found BPA on 94 percent of the receipts. The only receipts with that were BPA-free were those from Japan, which phased out this use of BPA in 2001. BPA was in most of the other types of paper products, with tickets, newspapers and flyers having the highest concentrations.

But these levels still paled in comparison to BPA on receipts, which the study said are responsible for more than 98 percent of consumer exposure to BPA from paper. The researchers estimate that receipts contribute about 33.5 tons of BPA to the environment every year in the U.S. and Canada.

They note that handling of paper products can contribute up to 2 percent of the total daily BPA exposures in the general population, and that fraction can be much higher in occupationally exposed individuals.