Many consumers avoid products that contain bisphenol-A (BPA) because the estrogen-imitating chemical has been linked to an array of health effects in people and animals. But new research published Thursday suggests that an ingredient that has replaced BPA in many items may have a similar effect on the heart.

BPA-free labels have been popping up on many plastic bottles, cash register receipts, food packaging, and other products.

Although the label implies a sense of safety, "our research suggests that BPS and potentially other BPA substitutes aren't necessarily free of health problems," said Hong-Sheng Wang, a professor of pharmacology at the University of Cincinnati College of Medicine.

Exposure to BPS, or bisphenol-S, caused irregular heartbeats in female lab rats, according to the study by Wang and colleagues published in the journal Environmental Health Perspectives. The findings were "remarkably similar—if not identical to—what we find in BPA," Wang said.

The scientists discovered that BPS changes how the rats' cells respond to estrogen, a result that has been suggested in previous studies. Specifically, BPS interferes with the way calcium is stored in heart muscle cells, causing leakage as well as extra absorption. That, in turn, alters heartbeats.

This is the same way that BPA affects rats' hearts, "raising the concern of potential cardiac toxicity of BPS," Wang said.

Little Known about Exposures

The scientists removed the rats' hearts and kept them alive and beating for some time by running a solution through them that contains oxygen, glucose, and other nutrients. Then they added BPS and monitored the effect on cells. This technique is commonly used to measure the impact of various chemicals on the heart.

Wang said the rats were exposed to doses that may be similar to the amounts that people encounter from water bottles, receipts, and other items. However, very little is known about human exposures; much more is known about BPA, which is found in the blood of virtually every person tested.

Because BPS is so similar to BPA, it's not surprising that it may have similar health effects, said Frederick vom Saal, a University of Missouri-Columbia biology professor who studies the chemicals but was not involved in the new study.

Previous research, he said, found that BPS stimulates human breast cancer cells at a slightly higher dose than BPA does. Also, in a recent study with zebrafish, BPS disrupted prenatal brain development.

"So the idea that BPS is safe as an alternative to BPA is clearly not true," vom Saal said.

Rats are commonly used to investigate the potential impact of chemicals on the human heart because people and rodents share similar cardiovascular physiology.

The changes were only found in female rats; male rats showed no increase in irregular heartbeats after exposure to BPS.

Any potential human health impacts from using products containing BPS are unknown. No human studies have been conducted.

The American Chemistry Council, which represents chemical manufacturers, declined to comment on BPS because it represents companies that make BPA, not BPS.

Can BPS Be Avoided?

Some hard plastic water bottles and other products labeled BPA free are also labeled BPS free, including popular Nalgene bottles. But in many cases it is difficult for consumers to determine if a product contains BPS.

Roughly half of the BPA-free thermal paper used for cash register receipts may contain BPS, according to a preliminary analysis. Some receipts contain both chemicals.

"I think it would be prudent to test BPS and other chemicals with a similar structure, instead of just assuming that they are safe," Wang said.