I was startled by the comment from the shopper just behind me at the checkout counter in the supermarket. 聽鈥淵ou really shouldn鈥檛 be doing that!鈥� Noting the quizzical look on my face, a further clarification was obviously needed. 鈥淚 mean you shouldn鈥檛 be handling the receipt,鈥� she went on. Indeed, I had taken the thermal paper receipt from the cashier and without looking at it tossed it in with the groceries. I now understood my fellow shopper鈥檚 concern. She was worried about my health, concerned that I was exposing myself to bisphenol A (BPA), the notorious endocrine-disrupting chemical that is embedded in the paper.
Thermal paper, also used in airline boarding passes, parcel labels and waiting room tickets, is treated with a chemical that combines with BPA to produce an image. As suggested by the description, 鈥渢hermal,鈥� the reaction requires heat. This is generated by a heated element as the paper passes through the printer. However, there is always some residual BPA that can rub off onto the skin as the paper is being handled. That in some cases can be worrisome.
The public was first alerted to concerns about BPA in the 1990s when it was found to leach out of plastic baby bottles, albeit in trace amounts. The compound had been synthesized a hundred years earlier by Russian chemist Alexander Dianin but no application for it was found until it was used to formulate synthetic shellac in the 1920s. Then in the mid 1930s, Edward Charles Dodds and Wilfrid Lawson at the University of London discovered that injecting BPA into rats produced an effect similar to injecting estrogen, the female sex hormone. Dodds and Lawson were looking for pharmaceuticals to treat gynecological ailments caused by estrogen deficiency. At first BPA looked promising but diethylstilbesterol (DES) also synthesized by Dodds was far more active as an estrogen mimic and BPA was discarded as a drug.
The chemical resurfaced in the 1950s in a totally different context. Chemists discovered that combining BPA with phosgene resulted in the formation of a polymer composed of alternating units of BPA and carbonate. This 鈥減olycarbonate鈥� turned out to be a tough plastic with multiple uses ranging from sports helmets to automobile headlights. When combined with epichlorohydrin, BPA formed an epoxy resin that found application as the coating inside of cans to prevent reaction between the contents and the metal. Although BPA was known to have estrogenic properties there was no concern about polycarbonates or epoxy resins because in these BPA as such no longer existed, it was now part of the insoluble polymer. The trace amounts of 鈥渇ree鈥� BPA left over after the polymerization process were deemed too small to have any significance. However, that assumption turned out to be incorrect.
In 1997, endocrinologists reported that feeding BPA to pregnant mice induces adverse reproductive effects in male offspring at the incredibly low dose of 2 碌g/kg/day. Furthermore, BPA didn鈥檛 behave like a traditional toxin. It did not conform to the 鈥渉igher the dose, the greater the damage鈥� concept. The effect it produced was not directly proportional to the dose! At a very low dose, BPA was found to bind to estrogen receptors on cells and stimulate a response. At a higher dose, the receptor becomes less sensitive and there is less of a response.
It turned out that the response stimulated at a low dose can be biologically very significant, especially during fetal development. BPA can cross the placenta and alter prostate and breast tissue development, possibly creating a higher susceptibility to hormone-dependent cancers later in life. The global trend of girls entering puberty at an early age has also been linked with exposure to estrogen-mimicking chemicals like BPA. In women, such chemicals can reduce egg quality and in men lower sperm counts. Circulating BPA in the bloodstream has also been associated with insulin resistance, cardiovascular disease and even autism.
Since feeding small doses of BPA to humans in an attempt to study its effects is obviously unacceptable, we are left with animal trials, cell culture studies and associations discovered in human epidemiological investigations. Although the evidence is not iron-clad, it is overwhelming in suggesting that exposure to endocrine disruptors such as BPA should be reduced. Manufacturers are moving to replace BPA-based epoxy liners in cans with non-BPA epoxies, acrylics, polyesters, polyethylene, and in some cases natural plant resins. Polycarbonates in food contact materials such as baby bottles have been replaced by glass or other plastics and sport a 鈥淏PA-Free鈥� label. However, in many cases, BPA is replaced with BPS which has similar endocrine-disrupting properties but allows for the 鈥淏PA-free鈥� claim. If the label says 鈥減henol-free鈥� then you can be sure of the absence of BPA.
Now back to the thermal paper. In this case, BPA is not part of a polymer as is the case for polycarbonates and epoxy resins. It is uncombined and is 鈥渇ree鈥� to leach out. This raises two questions. How much of the amount that leaches out can cross the skin and get into the bloodstream and how that compares with a dose that is thought to be dangerous. Not easy to answer. First, there is a very significant difference between ingesting BPA and having it absorbed through the skin. When ingested, it passes from the small intestine into the portal vein that leads directly to the liver where it is very efficiently metabolized and the products are excreted in the urine. When BPA is absorbed through the skin, the liver is bypassed and it circulates in the blood, free to encounter receptors on tissue cells.
Studies have shown that for a 70 kg adult handling a few receipts a day, at most 3.5 micrograms of BPA will be absorbed into the bloodstream although that could increase a hundred-fold if hand cream had been recently applied. Unfortunately, the only safety data available is the 鈥渢olerable daily intake,鈥� which is聽the maximum amount a human can ingest every day for a lifetime without experiencing adverse health effects. Health Canada has determined this to be 1,750 micrograms for a 70 kg adult based on animal studies. How much of the 1,750 micrograms ends up circulating in the blood is not known, but it is likely more than 3.5 micrograms which suggests that the absorption from receipts is not very significant. But that鈥檚 Canada. The European Food Safety Association (EFSA) has imposed a much stricter limit based on finding that miniscule doses in animals have been found to alter immune and reproductive cells. EFSA calculates a maximum daily total of 0.014 micrograms from all sources combined which may be exceeded by handling a couple of receipts and certainly exceeded by a cashier handling thermal paper all day.
Where does this leave us? With a good dose of uncertainty. Because thermal paper has been known to contain up to 2% by weight of BPA, an amount that can give rise to significant absorption, manufacturers are switching to alternative developers like ascorbic acid or sulfonylurea although this is still a small fraction of total production. If I were a woman of a reproductive age, I would avoid handling thermal paper for any significant time. If I were a cashier, I would wear gloves. Since I am not a young woman, nor an infant, and am at a stage in life where I do not worry about my sperm count, I am not concerned about handling thermal paper at the supermarket.
Now back to the good Samaritan who was concerned about my welfare. I politely thanked her and said I was impressed by her being aware of the thermal receipt issue. Seeing that she was quite senior I thought of telling her that she really didn鈥檛 need the latex gloves she was putting on as she was getting ready to take the receipt. But then I thought it wasn鈥檛 the time to get into a discussion of risk analysis which as you can glean from our discussion here is very complicated.
