When you are spending money at a store, the cost may be more than the amount shown on the cash register receipt. According to some researchers, there is a cost to health. That’s because handling the receipt transfers a chemical known to have hormone-disruptive properties to the skin from where it can migrate into the bloodstream. That chemical is bisphenol A, commonly abbreviated as BPA. This is a multi-functional substance that is a component of polycarbonate plastic as well as the epoxy resin that lines food cans. In the case of receipts, it is coated onto the paper to the extent of about 20 mg/g and acts to develop the image when heat is applied. There is some fascinating chemistry involved here. “Leuco” dyes are chemicals that can exist in a colourless or coloured form depending on temperature and acidity. In this case, the paper is treated with the colourless form. When heat is applied, as directed by a printer head, the colorless form combines with BPA, here acting as an acid, to form the coloured image.
A number of studies have shown that BPA can be transferred to the skin from thermal paper. This is done by having subjects handle the paper and then extracting their skin with a solvent such as ethanol and then testing the ethanol for bisphenol A content. Such studies have clearly shown that some of the chemical is transferred and that the transfer is significantly enhanced if previously a sanitizer or moisturizing cream had been applied to the hands. Following the handling of receipts, the concentration of bisphenol A in the blood and urine can also be measured. Indeed, some researchers believe that for most people, cash register receipts represent the most significant exposure to BPA.
The amount of BPA that shows up in the blood after handling receipts has been found to be more than if a comparable amount were consumed. That’s because orally ingested BPA travels through the liver where it is metabolized with the remnants being excreted in the urine. By contrast, transdermal passage does not lead to quick detoxication by the liver. There is also the issue that when BPA is transferred to the fingers, it can further contaminate other substances that are handled, such as food. In one study, eating French fries after handling cash receipt paper resulted in higher blood levels of BPA than after eating the fries with hands that had not touched such paper.
Of course, one cannot equate the mere finding of a chemical in the blood or the urine with the presence of risk. Indeed, high urinary levels may mean that the chemical is being efficiently excreted. However, some researchers maintain that the levels found after handling thermal paper, around 20 nanograms per mL, are comparable to those that in epidemiological studies have been associated with health effects such as obesity, miscarriage, reduced libido, impaired sperm quality and altered immune, liver, thyroid and kidney function. These studies, though, are just associations and cannot prove a cause and effect relationship. For example, diet can influence both the amount of BPA ingested, since it is found in many canned foods, as well as the rate at which it is excreted in the urine. So a higher urinary level of BPA in the urine may just be a marker for a different diet or a different level of hygiene, both of which rather than BPA may account for the health effects.
Nevertheless, it seems advisable to avoid unnecessary exposure to BPA and the wearing of gloves by cashiers is a good idea although nobody has studied what chemicals may be transferred to foods when handled by gloved cashiers. But there is enough concern about BPA on thermal paper to stimulate researchers to find alternatives and some are already apparently available since in studies not all such paper is found to contain BPA. One other problem is that when thermal paper is discarded and ends up in the waste stream, it can transfer BPA to other papers and plastics and end up in recycled materials from where it can again enter the body upon handling. Of course, we have to keep in mind that BPA is just one of the thousands of chemicals that find their way into our bloodstream through ingestion, inhalation or skin exposure. Many of these, including a host of naturally occurring compounds found in soy, flax, cabbage, liquorice as well as synthetics like PCBs, perfluoroalkyl substances, phthalates and pesticides have hormone-like effects. BPA is just one of many suspects when it comes to examining the effects of chemicals on health. But it is a suspect to keep an eye on.