Two Words: Plastics and Toxicology

water_bottleThe story of bisphenol A (BPA), the organic compound used to make the stiff plastic of water bottles, CDs and other consumer products, has been well told by the media. Once thought to be harmless to humans in the amounts used for plastic production, BPA has since been deemed an “endocrine disruptor” by researchers finding disturbing results in rats and humans. While debate continues to rage over how dangerous the compound really is, the battle is increasingly split into the familiar teams of physicians/scientists/consumer groups vs. industrial lobbyists. But how did BPA become the latest toxic substance to make the leap from journal articles to newspapers?

BPA’s narrative arc and current recommendations for avoiding it were the topics last week at the Department of Pediatrics weekly Grand Rounds. Susan Buchanan and Mark Mycyk of the Great Lakes Region Pediatric Environmental Health Specialty Unit visited to give a tag-team presentation on how the alarm was sounded on BPA and how the regulation controversy has unfolded around the world.

As Mycyk framed it, the discovery of BPA’s harmful effects resulted from nothing less than a revolution in toxicology, the study of what is or isn’t a poison. The answer isn’t always clear, Mycyk said, quoting 16th century scientist Paracelsus: “All things are poison and nothing is without poison, only the dose permits something not to be poisonous.” How scientists calculate what that dose is for each compound has changed over the years, but still relies on testing high doses in animals (usually rats) and deploying math to extrapolate to low doses and humans.

fig4That’s easy to do when the dose-response curve is a straight line – trace backwards from the point where the compound is toxic to where it is presumably safe, and voila. This method was traditionally used for chemicals encountered daily in the form of pharmaceuticals, pesticides, and plastics, Mycyk said.

“Big doses cause big problems, but they are incorporated into everyday life at lower doses which were initially considered safe doses,” Mycyk said.

But as scientific methods and instrumentation improved, the ability to test lower doses revealed some disturbing trends. For some chemicals, the dose-response curve was a not a straight, upward line, but an upside-down U-shape – a “non-monotonic dose-response curve.” For such compounds, the toxicity can actually be higher at low or intermediate doses, or the effect can change from stimulation to inhibition, throwing off all scientific estimates.

BPA made for a striking and disturbing example of this toxicological revision. The compound was known since the 19th century as a “weak estrogen,” chemically similar to the hormone but thought to be biologically inert in anything but massive doses. But in the last 10 years, new studies have revised the acceptable daily intake for human beings downward by as much as 100 times. Animal studies have found that very low BPA levels produce higher rates of mammary tumors, decreased sperm, and early puberty. A human study that looked at BPA concentrations in urine found that high levels of the chemical correlated with increased rates of cardiovascular and liver disease.

“This is very, early preliminary literature,” Mycyk said. “But this is a really important study that generated a lot of media attention and a lot of attention from science and industry. It’s very scary; it’s actually changed our understanding of how these endocrine disrupters work.”

For her half of the talk, Buchanan summarized the growing pressure to ban or limit BPA in consumer products, and the industry and government pushback to those efforts. Although the evidence mounts for harmful effects of BPA at low doses, industrial companies produce more than 6 billion pounds of the compound each year, a market they will not let disappear without a fight. So while several states and at least one city (Chicago) have banned the compound, and retail giants Wal-Mart, Target, and Toys-R-Us are phasing out products containing BPA, industry groups continue to insist that it is “well tested, and approved by agencies as safe for use.” The FDA, under the auspices of the Toxic Substances Control Act, has been slow to act, issuing an update in January that essentially called for no more than further study. The EPA, meanwhile, still uses an estimated safe dose based on a rat study from 1982, Buchanan said, though they have also recently announced a “BPA action plan.”

“So the EPA has admitted that there’s something going on here and we probably need to look at this,” Buchanan said. “This was a big step.”

But regulatory agencies move extremely slowly, so Buchanan offered a selection of tips that pediatricians can pass along to parents worried about their young child’s exposure to BPA. 

  • Encourage breastfeeding (to avoid potential exposure through plastic baby bottles)
  • If bottles are used, avoid boiling water in them (to prevent leeching of BPA)
  • Avoid canned foods (can lining can contain BPA)
  • Discard worn bottles or sippy cups
  • Use safe alternatives, such as glass or BPA-free plastics

Buchanan admitted that some of these measures were more reasonable than others – the BPA-containing lining for canned foods, in particular, has not been conclusively proven to be a problem. But the burden and stress of having to pick and choose safe products should not be put on the consumer, she said.

“To me, avoidance is not the answer,” Buchanan said. “We need to get toxins out of our consumer products.”

About Rob Mitchum (525 Articles)
Rob Mitchum is communications manager at the Computation Institute, a joint initiative between The University of Chicago and Argonne National Laboratory.
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