Manufacturers who market their products as “BPA-free” aren’t just sending consumers a message about chemical composition. The underlying message is about safety — as in, this product is safe or least more safe than products that do contain BPA. However earlier this month, another study found that a common BPA alternative — BPS — may not be safer at all.

“BPS works very similarly to BPA,” said Nancy Wayne, a reproductive endocrinologist and professor of physiology at the University of California-Los Angeles David Geffen School of Medicine. “We’re not the first to show this, but what’s captured people’s attention is that we did the work side by side — observing the effects of BPS alongside BPA. For people who are concerned about (endocrine-disrupting chemicals)…this is a big deal.”

Wayne co-authored a study published this month in the journal Endocrinology that found BPS (Bisphenol S), a common replacement for BPA (Bisphenol A), speeds up embryonic development in animal models and adversely impacts the reproductive system. The study is the first to examine the impacts of BPA and BPS on brain cells and genes involved in reproductive functions.

A known endocrine disrupter, the chemical BPA is used to make plastics and epoxy resins and is found in food and beverage containers, paints, adhesives, dental sealants, paper products and water supply pipes. According to the National Institute of Environmental Health Sciences, most of us are exposed to BPA through food and drink, and BPA is so ubiquitous that federal public health officials estimate that nearly all of us have detectable levels in our bodies. The U.S. Food and Drug Administration says that BPA is safe at current levels in the food supply, though the agency did ban BPA in baby bottles, children’s cups and infant formula packaging.

To conduct the study, Wayne and her research colleagues observed the effects of BPA and BPS on zebrafish embryos. Wayne told me that zebrafish have become very popular animal models for understanding the genetic regulation of organ and cellular development for two main reasons. First, their embryos are transparent, so scientists can actually watch their development. (“It’s amazing biology,” Wayne noted.) Second, the zebrafish was one of the first animals after humans to have its genome cloned — that means all of its genes are known, which is critical to understanding the genetics of organ, tissue and cellular development. (And in case it’s not completely obvious, scientists can’t do these types of studies on humans.)

“Humans are not rats, humans are not chimpanzees,” Wayne said. “However, we all have similar cellular organizations and share many of the same genes that are affected in similar ways by chemicals. We should be concerned when a growing body of literature is showing that BPA is altering cellular functions. I think it’s a wake-up call.”

Here’s what Wayne and her colleagues found: When exposing the zebrafish embryos to low levels of BPA and BPS — levels equivalent to what’s found in polluted river waters or what the researchers called “ecologically relevant levels” — the embryos grew much faster, speeding up the hatching time and leading to what we’d call premature birth. BPA and BPS exposures also affected the development of brain cells that control reproduction as well as the genes that control reproduction into adulthood. BPA impacted the brain cells that control puberty and fertility, increasing the number of endocrine neurons by up to 40 percent, which the researchers said suggested that BPA overstimulates the reproductive system. Similar effects were found with BPS.

Wayne and fellow researchers also found that BPA and BPS manifest their effects through both estrogen and thyroid pathways. This is important because BPA is typically thought of as an estrogen mimic, which is how it impacts the endocrine system; however, the study found evidence that it could also be stimulating thyroid hormones, which are critical to fetal brain development. BPS, which is considered a safer alternative to BPA because of its lower estrogenic activity, showed similar effects, leading researchers to write: “Therefore, BPA-free plastic products are not necessarily safer than products containing BPA.”

Wayne and study co-authors Wenhui Qiu, Yali Zhao, Ming Yang, Matthew Farajzadeh and Chenyuan Pan write:

The present study provides foundational information using a unique model system for investigating mechanisms by which endocrine disrupting chemicals interfere with early-life development. Moreover, this is the first study to describe the impact of low-level BPA and BPS exposure on the Kiss/Kissr system (part of the zebrafish reproductive system) during embryonic development in any species. It also provides important supporting evidence that BPS is not necessarily a safer alternative to BPA, as suggested by earlier studies focusing solely on its estrogenic activities.

So, why is this important to human health? While BPA, and now BPS, has been shown to impact animal reproductive systems, the risk for humans is not yet definitive. Still, many scientists who study these chemicals hypothesize that they may be contributing to a number of worrisome human health trends, including increasing rates of premature birth, earlier onset of puberty, more genital malformations in babies, and a rise in reproductive and prostate cancers.

“We don’t have a smoking gun in humans,” Wayne told me. “But it’s consistent with what we see in animal models. We have a strong suspicion that endocrine-disrupting chemicals in the environment could be contributing to this.”

As for how consumers can act on the new findings, Wayne is realistic: “We’re not going to get rid of plastics — that’s not going to happen. But we can try to control what we can control,” she said. She told me that after she first began studying BPA in 2007, she went home and threw out all of her plastic food containers, along with the food inside them, and switched to glass containers. Her advice to consumers is to do the same — purchase foods and drinks packaged in glass whenever possible and consider switching out plastic storage containers with glass or stainless steel.

In the next phase of research, Wayne plans to study the long-term effects of BPA and BPS exposures — from embryo to adult — to learn more about their impacts on the reproductive system and gain clearer insights into the effects of continuous environmental exposure. She noted that she doesn’t have federal grant support for her research, but she hopes other scientists interested in endocrine-disrupting chemicals “will become inspired” and build on the work she’s published. As she put it: “That’s how science advances.”

Wayne’s study noted that 5.5 billion kilograms of BPA were projected to be produced in the U.S. and Europe by 2015. And a total of about 2.5 million kilograms of BPA were released into the environment in 2007, with more than 13,000 kilograms released directly into water.

“BPS is not necessarily safer — we just swapped one endocrine-disrupting chemical for another,” Wayne said. “I hope we can continue as a scientific community to push this research forward.”

To request a full copy of the BPA/BPS study, visit Endocrinology or the UCLA Newsroom.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for nearly 15 years.