Joe Schwarcz: Does danger lurk in plastic bottles?

plastic bottlesResearchers were surprised to see that snails reared in some plastic water bottles produced almost twice as many offspring as their brethren raised in glass bottles. This wasn’t some experiment by restaurateurs looking to add more snails to the menu. There wouldn’t be much point, since these were New Zealand mud snails, less than half a centimetre in size, with not much meat on them. But the snails are pretty meaty when it comes to research about endocrine-disrupting chemicals.

These little creatures are fascinating in that they can reproduce asexually. The females are born with embryos in their reproductive system ready to develop into baby snails when stimulated by natural hormonal activity. But the development can also be prompted by exposing the snails to an external source of estrogen or estrogen-like compounds. And that means the snails can be used to detect the presence of chemicals with hormonal activity — or, as they are popularly called, endocrine disruptors.

This area of research was set ablaze in the 1990s with some scientists claiming to have found a link between such compounds and a variety of health effects, ranging from reproductive and behavioural problems to obesity and cancer. The most widely investigated hormone mimic since then has been bisphenol A, or BPA, used to make polycarbonate plastics and epoxy resin linings in food cans. But even with 20 to 30 research papers cranking out new data every month, there is much controversy about what effect, if any, exposure to BPA, or indeed to any other hormone-like compound, has on human health. Virtually every paper ends by calling for more research.

Back in 2009, Prof. Jorg Oehlmann at Goethe University in Germany answered the call by assigning graduate student Martin Wagner a project on endocrine disruptors. One day, Wagner had a refreshing idea as he contemplated the task while sipping from a bottle of water. The possibility of bisphenol A leaching from refillable bottles made of polycarbonate had already caused a great deal of commotion, but Wagner wondered whether plastics that were not made with BPA might also release endocrine disruptors. Hence the experiments with snails.

Oehlmann and Wagner found that snails immersed in a culture medium in bottles made of polyethylene terephthalate (PET), the common plastic used in single-serve water bottles, experienced an estrogen effect, while those raised in glass bottles did not. This observation spurred further research using actual samples of bottled water and a more sensitive test based on the reaction of a specific type of yeast with estrogens. By and large, the results mirrored the snail findings, verifying the presence of estrogenic compounds. Of course, the presence of such compounds cannot be equated with the presence of harm. Let’s remember that we are awash in estrogen mimics, both natural and synthetic. Beans, lentils, sesame seeds, tea, peanuts, milk and various medications contain estrogenic compounds.

The interesting conundrum here is why bottled water should have any hormone-like activity at all. The snail experiment implies that chemicals are being leached from the plastic, but that’s a puzzler, since neither ethylene glycol nor terephthalic acid, the two compounds used to make PET, exhibit hormone-like activity. The answer may lie in the greater complexity of plastics than is implied by the popular definition that these are materials composed of giant molecules (polymers) made by joining small molecules together in a chain. In actual fact, there are dozens of additives, ranging from antioxidants and polymerization catalysts to colour modifiers and ultraviolet-light absorbers, some of which may well have estrogen-like properties. Exactly what additives are used is hard to determine, since plastic formulations are proprietary. The German researchers believe they may have identified di(ethylhexyl)fumarate as one of the compounds in bottled water that blocks estrogen receptors on cells, but its origin is a matter of mystery.

The complexity of the endocrine-disruptor controversy is further illustrated by a lawsuit that was brought against two Texas companies by Eastman Chemical, manufacturer of Tritan, a hard clear plastic that is marketed as “BPA-free” and “estrogen activity-free.” Scientists from CertiChem and PlastiPure had published a paper in which they reported that many plastics advertised as being free of any estrogen activity actually leached endocrine disruptors, especially when the plastics were exposed to heat or ultraviolet light.

CertiChem’s testing method was questionable, Eastman argued in the lawsuit, also pointing out that the company was associated with PlastiPure, which sold plastics guaranteed to be free of such activity and was set to benefit from claims that competitors’ products were contaminated with endocrine disruptors. At the trial, both sides trotted out an array of experts who flung accusations at each other. The “independent” tests presented by Eastman that showed no estrogen activity were tainted, PlastiPure’s witnesses claimed, because the company had paid for the testing. Eastman acknowledged that it had paid for the study, but emphasized that it had no further involvement. More importantly, the study was done on animals, which Eastman pointed out was more meaningful than CertiChem’s study using cultured cell lines.

After all was said and done, the jury found for Eastman. But while this case was settled in the courtroom, endocrine disruptors remain on trial in the public arena, with alarmist charges of great threat to our health being countered with comforting words and supporting data from regulatory agencies. At current exposure levels, Health Canada and the U.S. Food and Drug Administration maintain, endocrine disruptors are of no great concern. Unfortunately, as with many such controversies, the consumer is left to struggle with the conflicting views.

At this point, the only conclusion I’m prepared to draw — and that with no great conviction — is that routine heating of foods in plastic is not advisable. As far as bottled water goes, concerns about the environment trump worries about estrogenic activity when it comes to avoidance. But if you want to raise New Zealand mud snails, it seems plastic water bottles are the way to go. Make sure you keep the creatures captive, though, because in the wild they become an invasive species, squeezing out native snail populations that serve as food for fish.

Joe Schwarcz

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