The translucent exterior of a plastic soda bottle hides a secret in plain sight: hundreds of synthetic chemicals embedded in its seemingly innocuous material. These chemicals give the plastic its structure, flexibility and durability, among other qualities—the same traits that also make plastic last for centuries, causing it to accumulate and endure in nature.
Before this plastic enters the natural ecosystem, the chemicals inside can leach out of water bottles and other food containers, entering the body and potentially endangering human health, according to a mounting body of research. In particular, plastic contains endocrine-disrupting chemicals (EDCs) that could wreak havoc on certain messaging systems in the human body.
As their name suggests, these chemicals act on the endocrine (hormone) system in possibly dangerous ways. Most direct research into their health effects comes from studies on animals and lab-grown cells (testing these chemicals directly on the human body would be unethical), as well broader epidemiological studies in humans that have linked EDC exposure with adverse health outcomes. But research has a hard time keeping pace with the rapid and constant creation of new chemicals. There are more than 16,000 chemicals used in plastics manufacturing, and over 1,000 industrial chemicals used today are suspected EDCs. But aside from a small percentage of substances that are regulated, plastic producers aren’t required to disclose the chemical ingredients they use.
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The specific cocktail of chemicals that lurks in the products we buy is therefore something of a mystery.“You know what’s in a packet of biscuits when you buy it, but you don’t know what [chemicals are] in the wrapping,” says Sarah Dunlop, a neuroplasticity researcher at the University of Western Australia and director of Plastics & Human Health at the Minderoo Foundation, a charitable organization.
What we do know is that EDCs are packed into plastics and that they canleach out. And despite the slow pace of research, the evidence has been steadily accumulating for decades. It now paints an increasingly concerning picture that should motivate us to regulate plastic production, several researchers say.
EDCs are Ubiquitous in Plastics
EDCs cover a vast family of substances that include many synthetic industrial chemicals such as bisphenols, flame retardants, per- and polyfluoroalkyl substances (PFAS), or “forever” chemicals, and phthalates, among others. They’re found in everything from electronics to carpets and paints to cosmetics—and in plastics. In this material, their applications are broad: phthalates are known as plasticizers and give many plastics their flexibility and durability, whereas PFAS have nonstick qualities that come in handy in the production of molds for plastic products—and leave behind a telltale chemical residue that can migrate into whatever substance the plastic goes on to contain. EDCs also turn up in other places we might least expect. Following a safety assessment, the FDA last month announced grease-proofing substances containing PFAS had been completely phased out for food packaging paper and paperboard by manufacturers in the U.S.
Bisphenol A (BPA), one member of the large bisphenol chemical family, is used to make epoxy resins that line the insides of food tins and drink cans, and it is even woven into the polyester fibers in some clothing.
“These chemicals are used everywhere, and plastics are extremely pervasive throughout our entire built environment,” says Bethanie Carney Almroth, an ecotoxicologist at the University of Gothenburg in Sweden who investigates chemicals in plastics. “We’re exposed to them in every way every day.” Some recycled plastics contain concentrated levels of these chemicals that could be compounding our exposure. Research also shows that this exposure is direct. Most EDCs are lipophilic, meaning they can combine with dissolved fats, so people are exposed to them via the oil in sweat, through skin and into our body, and most concerningly, through the fats in our food. EDCs can leach from plastic food packaging and storage containers directly into the fatty ingredients they contain, Carney Almroth says.
Synthetic EDCs have a similar structure and size to dozens of hormones including estrogen, testosterone and thyroid hormones. So once they’re inside the body, their masquerade threatens to throw the meticulously choreographed endocrine system into disarray.
Developmental Disruption
Usually the body’s endocrine system works like a well-oiled machine: a mechanism sets off a series of steps where endocrine glands release certain hormones in precise quantities at precise times to reach receptors spread throughout the body. That precision is key in triggering the required response. But synthetic EDCs mimic, block and otherwise disrupt this normal functioning.
“If you introduce a chemical that is not supposed to be there, it can activate a receptor that can lead to a cascade of signaling that is not supposed to happen in that moment,” says Marina Fernandez, a neuroendocrinologist at the Experimental Medicine and Biology Institute, a research center affiliated with the University of Buenos Aires.
The effect of this faulty signaling could be serious and wide-ranging because the endocrine system helps to moderate everything from fertility and reproduction to growth, metabolism, immunity and brain development. “What’s important is not only the amount that you’re exposed to but when you’re exposed to it,” Carney Almroth says.Pregnancy and fetal and infant development are all considered periods of heightened vulnerability to the effects of EDCs. For example, several studies have drawn a link between exposure to EDCs during pregnancy anddisrupted reproductive development in male offspring in wildlife and humans.
That’s implicated in fertility problems.In research where scientists exposed pregnant rodents to different types of phthalates (chemicals found in some plastics), their male offspring showed a shorter distance between the anus and genitals, or anogenital distance (AGD), a developmental marker that indicates the animal was exposed to lower levels of male sex hormones in utero. Years later a notable study showed that pregnant people with higher phthalate levels in their urine similarly gave birth to sons with a shorter AGD. Later research showed that men with a decreased AGD also had a lower sperm count.
“In utero, in neonatal development, things happen very quickly and in a very orchestrated manner. Disruptions in the pathways during that period can lead to changes that are permanent, that you will see later in life,” Fernandez says.
Fernandez’s work has focused on BPA, and she has shown that newborn rats injected with this chemical have reduced fertility and develop ovarian cysts in adulthood. BPA has been shown in some studies to trigger a proliferation of cells in human breast tissue, which could be a precursor to tumors. One idea is that because BPA mimics estrogen, an ingredient that’s crucial to female sexual and reproductive development, it can disrupt the normal development of the ovaries.
“Normally a hormone would lock onto a receptor with exquisite timing, triggering the signaling that needs to go on [in] the cell to make it grow, divide and produce other growth hormones,” Dunlop says. “Along comes [BPA] and it sticks on all the receptors and wreaks havoc because it causes signaling to go astray.”
These are just some examples of the myriad ways that EDCs may interact with rodents’ and humans’ hormones and health. Large observational studies have linked phthalate exposure to a higher likelihood of having a preterm birth, as well as to disruptions in insulin function that implicate these chemicals in diabetes. And a review study showed an association between developmental exposure to flame retardants (which contain phthalates) and reduced IQ in children.
Although relatively few studies have directly investigated the impact of EDCs specifically from plastic on human health outcomes, there are some examples. One investigation showed that female plastic industry workers had an increased risk of fertility problems. Another found that both male and female workers had higher levels of phthalate metabolites, or byproducts, in their bodies.
Safe Exposure?
This growing evidence base has motivated some countries to start regulating plastic chemicals. For instance, the European Union has banned some types of phthalates in children’s toys and the use of BPA in plastic baby bottles. Many researchers think there is no “safe” consumption level for EDCs because these chemicals don’t act in a predictable, linear way on cells that can be managed by simply capping the amount we put into the body. But even so, organizations including the European Food Safety Authority (EFSA), an agency that provides independent scientific advice to the E.U., has established a (strikingly low) safe limit of 0.2 nanograms of BPA per kilogram of body weight per day. The U.S. Food and Drug Administration is currently reconsidering its own proposed safe limits (set at 50,000 nanograms/kg/day) of the chemical.
These interventions are overshadowed by the scale of the problem, however. “With the new [E.U.] BPA concentration [limits], you can exceed your daily tolerable exposure level by eating one [145-gram (5-ounce)] can of tuna. That’s from the chemicals in the [epoxy resin] packaging material,” Carney Almroth says. Even chemical-specific bans don’t work very well because industries often replace regulated chemicals with chemically similar ones that affect the body in the same way. Human biomonitoring studies—which analyze chemical levels in samples of blood, tissue and urine—in Europe show that while quantities of regulated phthalates have declined in the urine of sampled adults, the amount of unregulated new phthalate substitutes has been increasing. Similarly, some plastics producers have replaced BPA with a chemically similar alternative called bisphenol S, which is now believed to have similar or even worse effects.
To understand how pervasive the problem has become, take the widespread bans on BPA in baby bottles: despite that regulation, research tells us that this chemical still gets into infants throughbreast milk. “When [lactating people] are exposed to food packaging and BPA in their diet, they have chemicals that they’re passing on to the infant,” says Ninja Reineke, a chemist with an expertise in EDCs at CHEM Trust, a U.K.–German charity that campaigns for chemical regulation.
And though plastic chemicals affect people everywhere, those in some areas bear the brunt of the issue, Carney Almroth says. In low-income regions that receive much of the world’s plastic waste exports or where people’s jobs—such as waste picking or factory work—put them at greater exposure to plastic chemicals, the health burden is likely higher. Even so, in a global survey of the research on plastic and health, scientists found that “only three papers in total out of the 3,500 we looked at came from a low-income country,” says Bhedita Seewoo, a research associate in plastics at the Minderoo Foundation, who worked with Dunlop to develop the global Plastic Health Map. “That’s a really big gap in information because those countries are probably the most exposed [to plastics] as well.”
Regulating Plastics
Carney Almroth believes we can take action while the necessary research continues to fill such gaps. “We have enough data now for there to be consensus saying that, ‘yes, these exposures are occurring and resulting in adverse health outcomes in humans.’”
For her part, Reineke believes it will be crucial to move past regulation on a chemical-by-chemical basis. Typically chemical bans happen once research has established a specific harm—which might explain why just 1 percent of the 13,000 chemicals in plastics have been regulated in international agreements so far. “There are so many of these chemicals, and the system to deal with them doesn’t keep up,” Reineke says. “We’re still playing catch-up.” Instead countries need to start doing batch bans of structurally similar chemicals to protect human health, she says.
Going a step further, “we really need chemicals in plastic to be rigorously tested for safety before being introduced in consumer products,” Seewoo says. She’s hopeful that a global plastic treaty that’s currently being negotiated by the world’s nations could shine a spotlight on plastic chemicals and bring some necessary regulation into this space.
What’s really needed is the kind of systemic change that this international regulation could bring. The problem is too large and invisible for people to navigate in their daily life, Carney Almroth says. Still, there may be small steps we can take individually to minimize our exposure. For instance, she advises against heating up food in plastic because this increases chemical leaching. Dunlop’s tip is to avoid buying food packaged in plastic where possible and not to be fooled by appearances—many tinned and canned products may contain plastic, too.
Fernandez says that in the end, we shouldn’t underestimate our power as consumers: “We have the voice to make industries accountable for what they are selling to us,” she says. “It is our right as consumers to have products that we can safely use.”