Consumers became wary of plastic products containing the chemical Bisphenol A (BPA) and began to avoid them after it was determined to be an endocrine disrupter. More than 130 studies linked BPA to a long list of health problems, including heart disease, breast and prostate cancer, diabetes, infertility, and the feminization of males.

Companies responded to consumer concern by removing BPA from many products, including babies' sippy cups, water bottles, and other soft plastics that come into contact with food.

Some companies began advertising their products as "BPA-free" and replaced BPA with Bisphenol S (BPS). But scientists at UCLA have found that BPS may be no safer. They discovered that BPS influences key brain cells and genes that control the growth and function of organs involved in reproduction.

"Our study shows that making plastic products with BPA alternatives does not necessarily leave them safer," said senior author Nancy Wayne, a reproductive endocrinologist and a professor of physiology at UCLA's David Geffen School of Medicine.

Using zebrafish as a model, Wayne found that exposure to low levels of BPA and BPS —
equivalent to the traces found in polluted river waters — altered the embryos' function in as few as 25 hours.

"Egg hatching time accelerated, leading to the fish equivalent of premature birth," said Wayne. "The embryos developed much faster than normal in the presence of BPA or BPS."

Wayne and her colleagues also found that the number of endocrine neurons increased up to 40 percent, suggesting that BPA overstimulates the reproductive system.

"Exposure to low levels of BPA had a significant impact on the embryos' development of brain cells that control reproduction, and the genes that control reproduction later in life," she said.

"We saw many of these same effects with BPS found in BPA-free products. BPS is not harmless."

Wayne theorizes that overstimulation of the neurons that regulate reproduction could lead to premature puberty and disruption of the reproductive system.

She believes that the same problems connected with BPA are also a concern with BPS and that the chemicals are likely to harm human health.

"Our findings are frightening and important," Wayne said. "Consider it the aquatic version of the canary in the coal mine."