Bisphenol A (BPA) – The Case for Polycarbonate Water Bottles

By Dr. Joe Schwarz

What was it that Alexander Pope said?  “A little learning is a dangerous thing; Drink deep, or taste not the Pierian spring; There shallow thoughts intoxicate the brain; And drinking largely sobers us again.”  But the poet never had to think about drinking that spring water out of a polycarbonate bottle, did he?  Today, such thoughts cannot be avoided.  Bisphenol A (BPA), a chemical that can leach out of polycarbonate bottles, is clearly the “toxin du jour.”  Environmental organizations label it as a clear threat to our health and some politicians have even begun to clamor to ban any substance that can release BPA.  The issue merits investigation.

Numbers, numbers, numbers!  They’re the cornerstones of toxicology.  Ignore them and you risk either endangering your health or stressing yourself with needless worries.  And such stress can also have health consequences!  So it’s important to know what is worth worrying about and what is not.  Toxins by definition are poisonous substances, so certainly are worth worrying about.  But of course as toxicologists point out, “only the dose makes the poison.” 

We know that two aspirin tablets are safe but swallowing a whole bottle of pills can be lethal.  A blood sugar reading of 4 mmol/L causes no concern, but 10 mmol/L raises a red flag.  However, in the complex world of toxicology, the interpretation of numbers is rarely that simple.  Especially when it comes to exposure to substances that have no immediate consequences, but which even in vanishingly small doses may trigger subtle effects over the long term.  Chemicals with hormone-like behaviour fall into this category.  And according to some researchers, such substances may even challenge the notion that risk is proportional to increasing dose.  Tiny amounts, they claim, may have more serious consequences than larger doses.  Welcome to the world of “environmental endocrine disruptors.”  Welcome to the world of bisphenol A (BPA).

BPA is the chemical that has people reaching for the panic button.  And hoping that the button isn’t made of polycarbonate (PC), a plastic that can release trace amounts of bisphenol A into the environment.  Polycarbonate plastics are ubiquitous.  Compact discs, DVDs, hockey helmets, eyeglasses, water pipes, automobile headlights, bullet-proof shields, dental sealants, cell phone and lap-top casings all benefit from the virtually unbreakable properties of polycarbonates.  Bisphenol A is one of the components used to make polycarbonates and can indeed be released in trace amounts from the plastic over time.  This is of particular concern when polycarbonates or epoxy resins, which are also made with bisphenol A, are used in food or beverage applications.  Refillable water bottles, baby bottles, water filter jugs, food-processor bowls and protective linings inside food cans can all leach BPA into their contents. 

So why does this raise eyebrows?  Because some rodent studies, as well as laboratory experiments that have exposed cells to trace amounts of BPA have suggested that the compound’s estrogen-like behaviour can cause problems ranging from birth defects and impaired blood sugar control to breast and prostate irregularities.  All of this would be only of academic interest had researchers not found that almost every one of us is contaminated with the chemical.  BPA has been found in our blood and in our urine.  Unfortunately our ability to detect trace amounts of chemicals has surpassed our ability to interpret what the numbers mean.  Hence the debate about the risks of BPA exposure.

And there is certainly debate!  Producers of BPA maintain that the amounts to which we are exposed are inconsequential, while some researchers claim that BPA even at levels of parts per trillion, as found in our bodies, is potentially harmful.  Accusations, sometimes with venomous overtones, fly back and forth.  Supporters of the “bisphenol A is a health hazard” side accuse industry of distorting the numbers, while industry spokesmen are quick to drill holes in the research that damns BPA.  It is quickly broken down in the body, they point out, and it is not BPA, but one its breakdown products that is actually measured in the urine.  This compound, they maintain, does not have estrogenic properties and is not an indication of the body load of BPA. 

Furthermore, they argue, the human is not a giant rat.  Indeed, studies have shown that rodents employ a different detoxication mechanism than humans, and do have more circulating BPA after exposure than we would have.  Then there is the issue of type of exposure.  Many of the rodent studies have used injected or implanted BPA, which is a different type of exposure than ingestion.  But the PBA critics fight back.  Injecting BPA into pregnant rodents is an appropriate way to study effects on the fetus, they retort.  And as far as humans go, while indeed detoxification reactions do swing into action, these are much less efficient in children and babies, who are therefore at greater risk.  And so it goes.

What then do we make of the battle of these scientists?  Scrutiny of the findings by an independent panel of experts would seem to be a logical step.  And that step has been taken.  Both in Europe, where regulations about toxic exposure are far more stringent, as well as in the U.S.  The European Food Safety Authority (EFSA) is made up of experts who provide independent advice on risk management.  Based on the maximum dose that produces no observable toxic effects in animals, and building in a safety factor of 100, EFSA in 2006 concluded that the Tolerable Daily Intake (TDI) for humans is 50 micrograms of BPA per kg of body weight per day.  The panel then went on to calculate exposure for all age groups based on data from leaching experiments and found that in all cases exposure was less than 30% of the TDI, which of course already has a huge safety factor built in.  Not everyone is swayed by the expert opinion; one American researcher maintains that she has found abnormal egg development in female mice at a dose of 20 micrograms per kg per day, which she says is uncomfortably close to the exposure that some pregnant women experience.

In the U.S., the National Toxicology Program’s Expert Panel analyzed the literature in 2007 and expressed “some concern that exposure to Bisphenol A in utero, as well as in infants and children, causes neural and behavioral effects” but passed off all other concerns as negligible.  This did not sit well with the Environmental Working Group, a high profile watchdog organization in the U.S. that has accused the panel of “having been unduly influenced by industry and having issued a report that failed to meet the most basic scientific standards.”  With all this mudslinging, and with both sides spouting numbers that seem to back their position, what is the poor consumer to do?  Should we be terrified of our water bottles and canned foods? 

The current media focus on BPA was stimulated by a couple of studies that measured the amount of this chemical that leached into water stored in polycarbonate bottles.  Such studies are motivated by one of the well-established chemical characteristics of BPA, namely that it has hormone-like effects.  And since hormones can be physiologically active at very small doses, the potential effects of BPA certainly merit investigation, especially given that some hormone-driven cancers appear to be increasing.  Of course, before we attempt to evaluate the meaning of the amount of BPA leaching out of bottles, we have to have some idea of the dose at which the chemical presents a hazard.  Although there is no universal agreement on what constitutes a safe intake, there is a consensus among regulatory agencies that rodents treated with 5 milligrams of BPA per kg of body weight do not experience any adverse effects.  This is referred to as the “no observed adverse effect level,” or NOAEL.  Building in a safety factor of 100, these agencies have proposed a Tolerable Daily Intake (TDI) for humans of 0.05 milligrams per kg.

Now let’s get back to the bottles.  And let’s consider “worst case scenarios.”  So we’ll focus on baby bottles, because if BPA presents a risk, it is expected to be most significant during the developmental stage.  In the most recent study, the maximum amount of BPA that leached into water from a polycarbonate bottle was 8 nanograms per milliliter.  Let’s assume a baby were to drink a liter of this water.  One milligram is a million nanograms, so the total intake would be 0.008 milligrams.  If the baby weighs 5 kg (11 lbs), we have an intake of 0.0016 mg per kg of body weight.  This is about one-thirtieth the TDI and one three-thousandth the “no observable adverse effect level,” in test animals!

That’s theory.  What about measuring how much BPA we are actually exposed to?  That’s been done.  The Centers for Disease Control in the U.S. sampled urine from over 2000 people aged 6-85 and found an average of about 2.7 nanograms per mL.  Since bisphenol A does not accumulate in the body, the urinary output can be used to estimate the amount taken in through food and water.  This calculates to 50 nanograms per kg body weight.  And how does that compare to the TDI?  It is 1000 times less!  And one hundred thousand times less than the dose that causes no effect in test animals!  Some researchers argue that the calculation of oral intake based on urinary output is flawed, and that if one goes by studies in animals the value should be at least 100 times greater.  Even if we were to accept this highly contentious argument, we are still looking at an intake that is a thousand times less than the dose that causes no effect in test animals.  So there seems to be a pretty significant safety factor here, even if one wants to argue about the exact value of the NOAEL.

Since the human is not a giant rat, (although there are some exceptions), the possibility exists that we are more sensitive to hormone disrupting chemicals than rodents.  But if that is the case, we have a lot more to worry about than just BPA.  Remember the joke about the drunk who was walking back and forth below a street lamp?  What did you lose, he was asked?  My keys, came the reply.  Did you drop them here?  No, he answered, but this is the only place where there is light!  Right now, the light is being cast on bisphenol A, while numerous hormone-like substances lurk in the darkness. 

Take lavender scented soaps and lotions, for example.  These have been linked with breast growth in young boys.  As it turns out, lavender oil activates estrogen regulating genes in human breast cells.  Alfalfa sprout extracts display increased breast cancer cell proliferation above levels seen with estradiol, an estrogen.  Soybeans contain natural estrogenic compounds, and so does milk.  Milk represents a far greater estrogenic exposure than we experience from BPA.  Our average daily intake of estrogens through milk is about 370 nanograms which is roughly what would be found in 50 mL of water from a polycarbonate bottle.  Nobody is suggesting the banning of milk even though it contains a good dose of estrogenic compounds.  And neither should they.

And that’s not all.  Nonylphenol, an ingredient in numerous detergents, is estrogenic.  It ends up in sewage, along with the natural estrogens and birth control pill remnants excreted by women.  Sewage treatment plants do not remove these substances and they can end up in surface water as well as in ground water when sewage sludge is spread on fields as fertilizer.  In other words we are awash in a sea of both natural and synthetic hormone disrupting substances and it is unrealistic to accuse a specific one of being the devil incarnate. 

This does not mean that we should be cavalier about hormone-like substances in the environment.  Even though there is no evidence that at the levels encountered BPA presents a risk to humans, we can’t rule out the possibility that babies may not excrete BPA as efficiently as adults, or that the chemical may have a synergistic effect when combined with other endocrine disrupting substances.  Baby bottles made of glass or other plastics are available, and it seems a good idea to search for viable alternatives to the epoxy lining in canned foods.  But panic over drinking from polycarbonate bottles is unwarranted, and talk of banning polycarbonate plastics is naive. 

Finally, how about a little perspective?  We talk about banning a substance that in theory may have some adverse effect, while we allow the sale of cigarettes, which are known to kill millions annually.  And drunk drivers do their share as well.  It seems we do need a sobering drink from that Pierian spring.