For a parent of a young child, each plastic plate, saucer, or bottle thrown from the high chair is a gift of technology when it doesn’t shatter into thousands of pieces. For the rest of us, plastic is the material of choice for items too numerous to tally. At the same time, many of us have simmerings of concern that plastic may be exposing us to harmful chemicals when it is heated, boiled, microwaved, frozen, left in the baking sun, dishwashed, scrubbed, chewed on, or dropped for the umpteenth time. And what about teething toys parents sterilize in a pot of boiling water, or toddlers’ cups and straws used warm from the dishwasher, or plastic bowls used to mix instant cereal?
Bisphenol A (BPA) and xenoestrogens
In the 1950s a manmade chemical, BPA, was found to be a good starting material for the synthesis of polycarbonate, a unique, sturdy plastic. But, earlier, during the 1930s, a study in the scientific journal Nature reported that BPA had estrogen-like properties when fed to rats. (BPA apparently was being investigated as a potential synthetic estrogen.) Since then, hundreds of studies have confirmed that BPA is a xenoestrogen. Xenoestrogens are compounds that affect living organisms in ways similar to the naturally occuring hormone estrogen. BPA attaches to estrogen receptors, which are proteins within the nucleus of cells that mediate estrogen’s actions in humans and many animals, of both sexes. BPA also interacts with thryoid hormone receptors, androgen receptors, and may interfere with an key enzyme that converts androgens into estrogens.
In 1996 the Environmental Protection Agency categorized xenoestrogens, including BPA, as endocrine disruptors, which are chemicals that can have significant influence on the endocrine (hormonal) and reproductive systems. BPA is a weak estrogen, meaning it is not as poweful as our natural hormone. Still, routine exposure to weak estrogens may influence the production of natural estrogen, alter the response of cells, or interact with estrogen-sensitive medications. There may be additive effects of exposure to this and other xenoestrogens in everyday chemicals (such as in pesticides and herbicides). In addition, a new type of estrogen receptor was recently discovered on the surfaces of cells to which BPA attaches and triggers certain cellular responses as strongly as estrogen does, and at very low doses.
The question of BPA’s safety has its ardent defenders and equally ardent skeptics. One point of contention is whether significant amounts of BPA get into foods and beverages from containers, and then into us. In 1998, researcher Frederick vom Saal published proof that BPA was leaching from plastic tableware, bottle tops, and the plastic linings of some metal canned foods during the heated canning process. Scientists went a step further to discover that foods processed in cans lined in plastic had detectable levels of BPA. In 1999, studies confirmed reports by the Food and Drug Administration that 95 percent of baby bottles sold in the United States were leaching BPA when heated and scratched. In 2005, the Centers for Disease Control and Prevention (CDC) reported that 95 percent of Americans excrete at least 100 parts per trillion of BPA in their urine, demonstrating that we all are getting at least some exposure from plastics. A 2008 CDC research study confirmed this, and found the amounts of BPA to often exceed the current safety threshold of exposure set by the EPA.
Debates continue, however, about how much BPA leaches from polycarbonate, and under what conditions. For instance, researchers at the Department of Pharmacology and Cell Biophysics at the University of Cincinnati College of Medicine reported in January that BPA leached from high-quality polycarbonate water bottles at rates ranging from 0.20 to 0.79 nanograms per hour. After holding boiling water, the bottles leached 55 times that amount. The researchers concluded that “the amounts of BPA found to migrate from polycarbonate drinking bottles should be considered as a contributing source to the total ‘EDC-burden’ [endocrine-disrupting compound-burden].”
The Bisphenol A Global Industry Group dismisses the findings in its online information by calling this yet another “scare story,” while ceding that “increased migration into boiling water is not news at all since it is well known as a general phenomenon that migration levels increase with increasing temperature.” The group discounts several other scientific studies as scare stories that promote myths among consumers.
What’s the harm in BPA?
Studies funded by the plastics industry support the stance that BPA exposure produces no ill effects and is well below governmental safety limits. Industry literature continues to assert that low doses of BPA are safe, as are plastics made with it. The American Plastics Council funded an expert panel’s input, which concluded in 2004, after reviewing 19 published animal studies for “potential male reproductive impacts” in particular, that evidence for low-dose effects of BPA was weak.
But a year later, scientists from the University of Missouri and East Carolina University, concerned that the review was too limited, conducted their own extensive literature review. They concluded “the opposite is true,” finding instead that “as of December 2004, there were 115 published in vivo [live animal] studies concerning low-dose effects of BPA, and 94 of these report significant effects. In 31 publications with vertebrate and invertebrate animals, significant effects occurred below the predicted ‘safe’ or reference dose of 50 micrograms per kilogram per day BPA.”
Further, the independent reviewers stated that “chemical manufacturers continue to discount these published findings because no industry-funded studies have reported significant effects of low doses of BPA, although 90 percent of government-funded studies have reported significant effects.” They further add that studies that showed no adverse health effects of BPA often had “used a strain of rat that is inappropriate for the study of estrogenic responses.”
The kinds of effects reported in the animal studies are many and varied, but often involve reproduction (in both males and females), fetal development, and cancer. Examples are miscarriages, low sperm count and testosterone levels, prostate cancer, polycystic ovarian disease, and abnormal fat cell growth. Exposure during fetal development leads to abnormalities in sexual organs and sex differentiation, genetic damage to oocytes (immature eggs), precancerous lesions, and altered hormone levels later in life. (BPA rapidly crosses the placenta from pregnant animals into the fetus.) In June of 2006, the Environmental Science and Technology Journal published a study showing that low doses of BPA alters the brains of female mice to behave more like their male counterparts. Another study found that BPA at doses similar to amounts already found in people altered DNA in animals. There are new reports that BPA causes insulin resistance, the condition of prediabetes, in mice. In addition, BPA alters how DNA is used in several different cellular activities, some of which are linked with human diseases and health problems.
How much is too much?
While independent studies in animals support BPA as a chemical with biological effects, the amounts that cause harm in animals vary. Some toxicologists argue that BPA and other xenoestrogens do not pose a health hazard due to their weakness in comparison to estrogen. But researchers at Tufts University published a study indicating that even the tiniest dose of BPA can have an estrogenic effect. Ana Soto, BPA researcher and professor of cellular biology at Tufts, asserted in the Environmental Science and Technology Journal online that “There is plenty of evidence now that low-dose levels lead to problems.” Soto was coauthor of a study that found that female fetal mice exposed during embryonic development to tiny amounts of BPA—2,000 to 20,000 times lower than what is considered safe in people—had fewer cells in an area of the brain related to gender-specific behavior, and behaved like males when they matured.
A key question is whether the amount of BPA leached from plastics can affect the human body as it does in animals. Studies involving people or human tissue are still scarce. BPA has been shown to have an estrogenic effect on cultures of human breast cancer cells, and to cause mutations in human cells in laboratory experiments. In April of this year, the National Toxicology Program (within the National Institutes of Health) released the most comprehensive examination of BPA studies to date. It found that human studies based on measurements of BPA in urine and blood show a correlation of higher levels of BPA with altered reproductive hormone levels in men and women, polycystic ovary syndrome, recurrent miscarriage, and chromosomal defects in fetuses.
But the report also states, “Drawing firm conclusions about potential reproductive or developmental effects of bisphenol A in humans from these studies is difficult because of factors such as small sample size, cross-sectional design, lack of large variations in exposure, or lack of adjustment for potential confounders. However, the NTP Expert Panel on Bisphenol A concluded that several studies collectively suggest hormonal effects of bisphenol A exposure.” The report further states that thorough studies are warranted.
Over the last several decades, a number of health trends have been identified but not sufficiently explained. Among them are low sperm count, infertility, early puberty, genetic abnormalities, birth defects of the sexual organs, diabetes, and obesity. While there are probably many significant factors contributing to each of these health conditions, xenoestrogens could be among them.
What to do?
Amidst the controversy surrounding BPA, it’s understandable to become alarmed and unsure of what to believe. What’s more, plastic is incredibly practical. How can we protect ourselves and our families from possible harmful effects while maintaining our fast-paced lifestyles?
Change is already underway. Several companies are now marketing products specifically as BPA-free alternatives, such as baby bottles made of other kinds of plastic or glass. Nalgene, maker of popular reusable drinking containers, has announced it will avoid plastic containing bisphenol A. Wal-Mart will no longer sell baby bottles with bisphenol A. Legislation may play an increasing role, too: San Fransisco has banned BPA in products intended for children under the age of three, and Canada has banned polycarbonate baby bottles. New York Senator Charles Schumer has introduced legislation in Congress that would prohibit the use of bisphenol A in all products for children aged seven and younger; the bill would also allow states to pass laws restricting BPA plastics without federal interference.
As consumers, there are relatively simple changes we can make to reduce exposure to BPA. Avoid exposing plastic containers to high heat, harsh detergents, and heavy wear and tear. Switch to hand washing plastic water bottles, baby items, and food containers with a biodegradable, earth-friendly dish soap like Ecover or Seventh Generation Dish Liquid. Don’t leave beverage bottles or food containers in the car, where temperatures can soar. When microwaving foods, use a glass or ceramic container and cover with wax paper (not plastic wrap, which contains phthalates, other xenoestrogens of concern).
When buying plastic containers, those with numbers other than 7 shouldn’t have BPA. Plastics have a numbering system defined by the Society of the Plastics Industry in which each number corresponds to composition, as follows: #1, polyethylene terephthalate (PETE); #2, high-density polyethylene (HDPE); #3, polyvinyl chloride (PVC or vinyl); #4, low-density polyethylene (LDPE); #5, polypropylene (PP); #6, polystyrene (PS), and #7, all other plastics and combinations of them. BPA is found in some #7 plastics.
Better yet, switch to glass, ceramic, or stainless steel containers when you can. If you must rely on plastic while on the go, use glass storage containers at home. Since school lunchrooms, gyms, and pool areas generally don’t permit glass, buy non-BPA plastic containers. Freezing plastics has not been shown to cause leaching of BPA (a current debate), so putting water or other beverage bottles in the freezer seems harmless. But don’t use any polycarbonate container that becomes worn and cloudy.
David Feldman, a doctor and emeritus professor of endocrinology at the Stanford University School of Medicine, supports a “better safe than sorry” approach. Feldman and coworkers first identified BPA’s potential to interact with our endocrine systems in the early 1990s. In an April 2008 press release from the university, Feldman counseled, “The prudent thing for current or expectant parents or those planning a pregnancy to do would be to limit their child’s exposure to bisphenol A by avoiding bottles and cups that are made of polycarbonate, and to microwave food in glass containers whenever possible. Not only do [children] weigh much less than adults, making their relative exposure greater, but they are also still developing estrogen-sensitive breast and prostate tissue. For adults, however, canned foods and beverages may be the most important source of bisphenol A. I don’t microwave food in plastic containers, or wash the containers in the dishwasher because heat and some detergents cause leaching. I try to limit the amount of canned food I eat, or rinse the food before consuming the contents.”
The tempo and routine of our lives change continuously. Being aware of the obstacles and making small adjustments is a good practice. Maybe you can switch to using glass storage containers at home and plastic when you are on the go. Perhaps you will commit to washing plastic containers by hand, or gradually replacing them with high-density polyethylene (HDPE) or other non-BPA products. These are some of the easy solutions you can take to replace nagging doubts about plastics with a confidence that you are moving toward a healthier lifestyle.
Ilyse Simon is a registered dietitian and freelance writer from Kingston.
This article appears in July 2008.
