Science News and other outlets reporting on BPA-free receipts identify for the first time a substitute chemical being used by one of the largest manufacturers of thermal paper. It has been referred to incorrectly in blogs as “bisphenol sulfonate” or “diphenyl sulfone,” but it is actually a chemical known as bisphenol S (Update, 11/15/10: 4,4′-sulfonylbisphenol). As the name indicates, it is structurally very similar to bisphenol A (BPA). And although it has not been studied as much as BPA, preliminary studies show that it shares hormone-mimicking properties as well.
In 2005, a group of Japanese scientists compared BPA and 19 other related compounds for their ability to mimic the female hormone estrogen. They tested the effects on human cells and found that bisphenol S was slightly less potent than BPA, but not by much: bisphenol S was active at 1.1 micromolar concentration, BPA at 0.63 micromolar. One micromolar is roughly equivalent to a packet of sugar in 3,000 gallons of water.
Other researchers have found that bisphenol S is much less biodegradable than BPA. In their study of eight bisphenol compounds, bisphenol S was the most persistent.
While much more is known about the effects of BPA – particularly at ultra-low doses – the existing data on bisphenol S suggests the substitution should be made with caution. Hormone-mimicking behavior and environmental persistence are intrinsic hazards that should be avoided. As the Science News story mentions, an assessment by the U.S. Environmental Protection Agency’s Design for the Environment program may shine more light on the matter.