A plastic bottle can contain from two to two hundred different chemicals, additives like softeners, hardeners and dyes. But certain chemicals found in plastics—and present in other substances such as flame retardants, pesticides, and cosmetics— have come under scrutiny for their ability to act like hormones in the human body and affect human health. A growing body of research links exposure to these chemicals to a host of health problems including obesity, diabetes, learning disorders, infertility, birth defects, and cardiovascular disease. A series of recent studies estimated that exposures to these chemicals likely cost Europe more than $200 billion annually in health care expenses and lost wages.
There's near-consensus among scientists who study hormones that even small amounts of these chemicals can disrupt the endocrine system—indeed, the Endocrine Society published this view in an official position statement in 2009. Yet, they remain lightly regulated in the U.S.
Don't miss Part 2 of this series: 7 Things Hormone Researchers Want You To Know About Plastic Safety
“The evidence is so strong within the scientific literature that very low doses of these chemicals affect a wide variety of disease and developmental processes, and there isn’t much evidence otherwise," says Deborah Kurrasch, a developmental biologist and endocrinologist at the University of Calgary. "We’re able to reproduce each others’ studies and collectively the burden of proof has been met for us. With 95 percent confidence we believe this is real.”
Two endocrine disrupting chemicals have attracted particular attention: Bisphenol-A, or BPA, a chemical used in hard and clear plastics, and a class of chemicals known as phthalates, which can help make plastics softer. Most of the concern has been focused on plastics that come in contact with food or drinks and on plastic children's toys that might wind up in babies’ mouths. This is because endocrine disruptors from plastics typically enter our bodies through the mouth.
Regulation of BPA has spread internationally. In 2008, Canada banned BPA from baby bottles and in 2010 declared it toxic. The European Union, as well as China and Malaysia limit its use. And in 2012, France banned BPA from all items that come into contact with food. The U.S. Food and Drug Administration has been slower to act. In 2013, it banned BPA and some phthalates from certain baby products, but regulation has stopped there. After scientific review, the FDA maintains that “current approved uses of BPA in food containers and packaging are safe” and says that BPA is safe at current exposure levels.
While drugs must be tested and determined to be safe before they go to market, U.S. law assumes most consumer products like baby toys are safe until proven otherwise. Food contact items like plastic bottles are an exception –the FDA has to be reasonably sure that the chemicals in them won’t cause harm. But the regulatory and industry approach to determine chemical safety has been to determine whether chemicals act like poisons – and generally not whether they act like hormones. And some scientists are concerned that this could lead to false conclusions of safety.
Endocrine Disruptors: Like Hormones, But Different
The human endocrine system secretes hormones to regulate and control communication among organs, affecting our brain development, immune system, cell growth, genital development, and much more. Our endocrine system helps us maintain our body weight and temperature. In a newly forming fetus, hormones have a particularly important role because they help tell cells which organs or body parts to become.
Some man-made chemicals can disrupt this process. Scientists term a chemical an endocrine disruptor if they see evidence that it interferes with natural hormone activity. In the body, hormones are produced by glands, then travel through the bloodstream and bind with specific receptors inside of cells, triggering a series of changes. Endocrine disrupting chemicals can affect the body by binding to these receptors, mimicking the effects of naturally-occurring hormones. They can also block the receptors, so that the body’s hormones cannot act upon their targets. Chemicals that mimic or block the activity of estrogens are the best known and most studied, but researchers have found endocrine disruptors that can also interfere with the functioning of progesterone, testosterone, thyroid hormones, or multiple hormones at once.
Human bodies are sensitive to hormonal changes throughout our lives-- but especially at key times like when we're in the womb, going through puberty, or when pregnant—and that is part of why there’s growing attention to compounds that can mimic or disrupt how hormones work in our body.
Unsafe At Any Dose?
One reason there’s still debate about risk posed by chemicals like BPA is that their impacts are difficult to measure. "Endocrine disruptors are kind of insidious because they affect things like neurodevelopment, and behavior and reproduction in more subtle ways, explains Sarah Evans, a neuroscientist at Mount Sinai Hospital’s Children's Environmental Health Center in New York City. “So it’s very difficult to screen chemicals as endocrine disrupting chemicals in a rapid way that will cover all of the possible outcomes."
Traditional toxicology tests use higher doses of a potential poison to predict what a safe lower dose would be. But according to the Endocrine Society, an international organization of endocrinologists that publishes the journal Endocrinology, this method is inappropriate for testing endocrine disruptors for various reasons. One issue is that very small doses of certain endocrine disrupting chemicals may negatively impact one area of health, while a higher dose of the same chemical could result a completely different outcome. In other words, it’s possible to be looking in the wrong place and not notice health impact from a high dose but still have observable health impacts at a lower dose.
In the late 1990s, leading developmental endocrinologist Frederick vom Saal was among the first to test impacts from hormone-disrupting chemicals at the same low levels at which hormones themselves can impact the human body. In one study, vom Saal and his team fed BPA to pregnant mice at a dose proportional to the amount a human would ingest during the first hour after application of a plastic dental sealant. When researchers examined the male offspring, they found smaller epididymides (testicular sperm ducts) and 20 percent lower sperm count than male mice whose mothers had not been exposed to BPA in pregnancy.
Now, many endocrinologists and more toxicologists are starting to use a similar approach. In a study published last year, Kurrasch exposed zebrafish embryos- which develop similarly to human embryos, to very low doses of BPA and a structurally similar chemical cousin called BPS. (BPS has become popular as a BPA-substitute since BPA started to get a bad name.) When exposed to these chemicals at very low doses as embryos, the fish were hyperactive later in life. “What we show is that the zebrafish exposed to BPA or BPS were getting twice as many neurons born too soon and about half as many neurons born later, so that will lead to problems in how the neurons connect and form circuits,” Kurrasch said in a University of Calgary press release.
Vom Saal says regulatory agencies need to start testing plastics at extremely low levels. "A trillionth of a gram of a hormone in a milliliter of blood ...is enough to alter the course of development of tissue in the fetus and lead to disease later on in life," he says. Until plastics are tested at such minute levels, he says, we are in the dark about what levels of exposure are safe -- especially for babies developing in the womb.
Establishing safe levels of endocrine disruptors is hard for one particularly troubling reason: The chemicals are already prevalent in our environment and our bodies.
When testing a new medicine or treatment, researchers compare the outcomes of a group of people taking the drug with a group who are not taking it -- a control group. That’s how they ensure accurate results. But there’s no control group of people who have never been exposed to endocrine disruptors. Most of us have already have them in our bodies, according to Tom Zoeller, a biologist at the University of Massachusetts who serves on a United Nations advisory group on endocrine-disrupting chemicals. “Every baby born in this country probably has somewhere around 100 manufactured chemicals in their cord blood,” including endocrine disrupting chemicals, he says.
In 2011, with funding from the National Institutes of Health, two plastics testing companies, Certichem and Plastipure, tested more than 450 plastic food or drink containers from stores such as Target, Walmart, Trader Joe’s and Whole Foods. In the largest and most comprehensive study of its kind, the companies found that more than 70 percent of them leached chemicals with estrogenic activity. The number rose to 90 percent when they tested across a variety of food types, since some chemicals leach more into fatty foods than others.
The study suggested that a great majority of commercially available plastics—including new replacements for BPA--can “leach detectable amounts of chemicals with estrogenic activity. (Certichem and Plastipure base their business on testing plastics and other products for estrogenic activity and helping manufacturers develop alternatives. As Mother Jones reported in March, plastic manufacturers dispute their findings.)
Other studies have found that heat – whether from sunlight, a microwave or a dishwasher - increases the leaching of chemicals from plastics– including endocrine disrupting ones. This is the case even for several BPA-free products.
In a 2004 CDC study, urine samples from 2,517 people aged six and older were tested for BPA. The chemical was found in 93 percent of the test subjects. This was at concentrations that had induced effects in some animal studies. CDC studies have found many other chemicals with known endocrine disrupting activity in similar concentrations, in the overwhelming majority of people tested.
Experts say there’s no one particular compound or exposure at fault. Humans are exposed to numerous endocrine disrupting chemicals throughout our lives-- from flame retardants on our clothes and furniture to chemicals in our personal care products like lotions and shampoos. Kurrasch says she thinks society will come to take the threat of endocrine disruptors more seriously. “I think it’s just a matter of time before we talk about endocrine disruptors causing harm, just like how we talk about smoking causing harm," she says.
Note: The U.S. Food and Drug Administration, which regulates food-contact items, declined to be interviewed for this story. A spokesperson stated via email that "direct and indirect food additives are reviewed by FDA experts in toxicology, chemistry and other scientific disciplines." For a recent report on BPA, the spokesperson wrote that "FDA scientists specializing in toxicology, analytical chemistry, endocrinology, epidemiology and other fields reviewed more than 300 scientific studies on BPA published by researchers between November 2009 and July 2013."
How do Hormones work? (PBS Frontline)
Rethinking the Evidence on BPA (Newsweek)
Shia Levitt is a frequent contributor to Sound Medicine. She has reported for numerous other public radio programs, including a related story on greening hospitals for Marketplace.