“Parents who warm up baby bottles could be putting their child at risk of ‘gender bending’ chemicals,” the Daily Mail reported. The Guardian said, “Scientists found that polycarbonate plastic bottles release a known environmental pollutant 55 times more quickly when filled with boiling water.”
The newspaper stories are based on a study that looked at the amount of bisphenol-A (a constituent of polycarbonate) released from new and used water bottles under conditions that simulated normal usage during backpacking, mountaineering, and other outdoor activities. It found that using boiling water to fill the bottles resulted in a greater leaching of the bisphenol-A from the bottles into the water.
The risk associated with the use of bisphenol-A food packaging is a contentious area and there are conflicting results and opinions. The Food Standards Agency suggests that “bisphenol-A has the potential to interact with our hormone systems”, but states that there is currently “no conclusive evidence of a link between harmful effects on human reproductive health and exposure to these chemicals”.
Babies’ bottles were not the subject of this particular study. The findings from this study may prompt the research that is needed to clarify whether hot contents increase the leaching of bisphenol-A from babies’ bottles and whether there are any harmful effects of bisphenol-A for humans.
Where did the story come from?
Dr Hoa Le and colleagues from the Department of Pharmacology and Cell Biophysics at the University of Cincinnati College of Medicine, USA carried out this research. The study was funded by a grant from the National Institutes of Health. It was published in the (peer-reviewed) medical journal: Toxicology Letters .
What kind of scientific study was this?
The study was a laboratory study which investigated whether bisphenol-A would be released from plastic bottles under normal use and conditions. The researchers used new or used polycarbonate (PC) drinking bottles, or new drinking bottles made of high-density polyethylene (HDPE). They bought the new bottles and the old bottles were donated by people at a climbing gym and had been used under normal conditions for between one and nine years.
The researchers filled the bottles with water and then rotated them for seven days to mimic the motion of water. They drew samples of water for analysis from these bottles on days one, three, five and seven. The experiments were repeated using both types of new bottle and the used PC ones. In addition, they filled two new PC bottles and one used PC bottle with boiling water (100°C) and rotated them at room temperature for 24 hours, removing samples for testing when the water had cooled. To see whether heating the plastic had a long term effect on the release of biphenol-A, they then emptied and cleaned the bottles that had held the heated water and added more room temperature water and re-sampled it for analysis after a further 24 hours. A technique called Elisa (Enzyme-Linked ImmunoSorbent Assay) was used to measure the amount of bisphenol-A released from the bottles.
In a final part to the experiment, researchers explored what effect the bisphenol-A that had been released into the water samples would have on cells. Rat nerve cells were washed with water from the bottles and the researchers looked at the concentration of lactate dehydrogenase – a chemical which may be linked to levels of oestrogen.
What were the results of the study?
The researchers found that very low amounts of bisphenol-A were released from the HDPE bottles. In contrast, higher concentrations were released from both the new and used PC bottles. Over the seven days at room temperature, the levels of bisphenol-A released increased over time for the PC bottles (both new and used). There was slightly less bisphenol-A released from the used PC bottles but the difference between new and used was not statistically significant.
The study also found that double the seven-day amount of bisphenol-A was released into the bottles in just 24 hours when the water was poured in at 100°C.
In rat nerve cells, increased levels of lactate dehydrogenase were released when the cells were exposed to water from the PC bottles, but not when they were exposed to the water from HDPE bottles.
What interpretations did the researchers draw from these results?
The researchers say that their studies have confirmed the findings of previous research that bisphenol-A (BPA) can migrate from polycarbonate plastics and that this has an effect on cells (it is “bioactive”). They conclude that exposure of polycarbonate to heated water results in 15 to 55 times greater rate of “BPA migration” – the leaching of this chemical out of the plastic container into the contents of the bottle – compared with water poured in at room temperature.
What does the NHS Knowledge Service make of this study?
This study adds evidence to a contentious and debated area surrounding the safety of polycarbonate drinking bottles. Although this study did not use babies’ bottles, it raises issues about the safety of polycarbonates in general. There are a few points to keep in mind:
- As the researchers say, few studies have assessed the relationship between exposure to bisphenol A and human health. Until more studies are conducted in humans, it is not possible to speculate on the effects that levels of bisphenol-A may have on humans. Any sign of hormonal release in rat nerve cells exposed to bisphenol-A does not mean that the same effect would be seen in humans. It is not possible to state that these effects, if they were similar in humans, would be “gender bending” as the Daily Mail stated.
- This study did not specifically consider what happens in babies’ bottles so the findings might not be able to be generalised to them. For parents who are concerned, there are PC-free alternatives available. This study will undoubtedly prompt the research that is required to answer the question about the safety of PC bottles finally; however, this will take some time.
Sir Muir Gray adds...
Even though I think the risk of “gender bending” is not proven, the message is simple – breast is better.