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That helps explain why industrial chemicals never received the stricter regulatory oversight that drugs and pesticides did. Even if the chemicals used to help make a plastic bottle could infiltrate the human body, the thinking went, surely the dose would be too low to do any harm. But as biomonitoring improved we can now detect human exposure levels as small as one part per trillion, or about one-twentieth of a drop of water in an Olympic-size swimming pool scientists realized that people were carrying far more chemicals than we'd thought. At the same time, scientists learned that some toxins could harm at extremely low levels; the limit considered safe for lead, which can directly reduce IQ, has been lowered from 60 micrograms per deciliter of blood in 1970 to 10 micrograms today. Some chemicals like BPA may have strange effects even at very low doses. Invented in 1891, BPA has been used since the 1940s to harden polycarbonate plastics and make epoxy resin, used in the lining of food and beverage containers, among other products. Polycarbonates can be identified by the recycling number 7 on the bottom of some plastics containing it. Other plastic ingredients including potentially dangerous ones are also indicated by the recycling number, known as the resin identification code.
BPA does its job well, and today some 6 billion lb. (2.7 billion kg) of the chemical are produced globally each year. The problem is, BPA is also a synthetic estrogen, and plastics with BPA can break down, especially when they're washed, heated or stressed, allowing the chemical to leach into food and water and then enter the human body. That happens to nearly all of us; the CDC has found BPA in the urine of 93% of surveyed Americans over the age of 6. If you don't have BPA in your body, you're not living in the modern world.
The levels observed are considered well below the federal safety threshold of 50 micrograms per kg of body weight per day. But that recommendation was made 22 years ago, and in the time since, scientists have learned more about the effects of even a bit of BPA. In 1998, Patricia Hunt, a geneticist at Washington State University, found that female mice dosed with BPA had serious reproductive problems, including defective eggs. More recently, she published a study showing that the offspring of mice exposed to BPA while pregnant can end up with corrupted eggs, a situation that leads to trouble for their offspring. "That's a powerful effect," says Hunt. "You disrupt three generations with one exposure."
As a synthetic estrogen, BPA can mimic hormones, those powerful chemicals, like testosterone and adrenaline, that run the body. Tiny amounts of hormones produce immense biological and behavioral changes, so it stands to reason that a chemical that mirrors a hormone might do the same, especially if a human being were exposed to it during critical periods of development, like the first trimester of gestation. (Children are particularly vulnerable to chemical exposure, not just because their smaller bodies are developing rapidly but also because they eat and drink more relative to their body weight than adults.) That's exactly what dozens of scientists have found in animal studies, linking fetal BPA exposure in rodents to everything from mammary cancer to male genital defects and even neurobehavioral problems.
Nor is BPA the only industrial chemical in common use that may mess with the endocrine system. Phthalates a class of chemicals used to soften polyvinyl chloride plastics, found in products ranging from shower curtains to cosmetics to intravenous-fluid bags have been shown to disrupt hormones in animals and have been linked to reduced sperm counts and other marks of feminization in male rodents. Ditto for a class of long-lived chemical fire retardants known as polybrominated diphenyl ethers (PBDEs), used in electronics, polyurethane foam and other plastics, though they're being phased out. (PBDEs can remain in the body for years. BPA and phthalates are excreted within a day or so, but their ubiquity means we're exposing ourselves anew almost daily.)
While there are fewer studies of endocrine disrupters in humans than in animals, the ones that have been conducted have begun to show worrying associations. Higher levels of phthalates and other endocrine disrupters have been linked to earlier breast development in girls a possible risk factor for breast cancer and endocrine disrupters are a suspect in the rise in hypospadias, a correctable deformity of the urethra in boys. A 2008 study by Shanna Swan, director of the Center for Reproductive Epidemiology at the University of Rochester, found that boys born to women with high phthalate exposure during pregnancy were more likely to have genital abnormalities like undescended testicles and smaller penises than those born to women who had lower exposure. "I worry what will happen to these children as adults, whether they'll have reproductive problems," says Swan. "We're trying to piece that question together."
The science around endocrine disrupters is far from settled. Studies like Swan's show a correlation between phthalate exposure and developmental defects, but that doesn't mean the chemicals are causing the problems. Industry defenders point out that human exposure to BPA and phthalates is still well below safety levels set by the government and that health agencies around the world say the chemicals are safe for humans. And some peer-reviewed studies fail to show a positive connection between endocrine disrupters like BPA and health defects. "I think the research [on BPA] has been overhyped," says Richard Sharpe, an investigator at the Centre for Reproductive Biology at the Queen's Medical Research Institute in Edinburgh. "If you restrict the question to its estrogenic effects, I just don't see them."
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