How Low Can it Go? The Story of BPA

By Susan Goldhaber MPH — Jun 22, 2022
Do you remember doing the limbo as a kid? The idea was to see how low you could bend your body to get under a stick that got increasingly close to the floor. Today’s regulatory process is the modern version of the limbo. The problem is that science can’t even measure how low they want the limbo stick to go.
Image courtesy of Gary G on Pixabay

Earlier in June, the FDA agreed to reevaluate the safety of bisphenol A (BPA) in plastics, coating, and other materials that contact food. This was based on a petition from environmental groups that cited the lowering of the safe limit of BPA by experts from the European Food Safety Authority (EFSA).

The lowering of the safe limit by EFSA is part of an overall trend of regulatory agencies lowering their safe limits for trace amounts of chemicals. In this article, I will examine what is happening with BPA and how it fits into a more significant trend of using science to justify the desired outcome.      

What is BPA?

BPA is a chemical that has been used to make certain plastics and resins since the 1950s. BPA is found in polycarbonate plastics, often used in containers that store food and beverages, such as water bottles and other consumer goods. BPA is also found in epoxy resins that coat the inside of metal products, such as food cans, bottle tops, and water supply lines, and in some dental sealants and composites.

Tiny amounts of BPA can migrate from the food contact material into foods and beverages. The Center for Disease Control (CDC) estimates that the typical person has exposure to 2.4 micrograms (µg) of BPA daily. (A microgram is one-millionth of a gram). BPA does not accumulate in the body; within 24 hours, it is eliminated through urine.   

The FDA approved its use in food packaging material, concluding in 2008 that an adequate margin of safety exists for BPA at the estimated levels of exposure from food contact uses, and reaffirmed its safety in 2014. The current FDA limit on BPA in food packaging is 50 µg per kilogram of body weight.

Health Concerns

There have been endless efforts to scare the public about BPA. This campaign has been so successful that many water bottles now contain the label “BPA-free,” indicating to consumers that being free of BPA will promote a long and healthy life.    

BPA has been linked to just about every adverse health effect imaginable. A recent press release announcing that the FDA agreed to reevaluate safe levels of BPA said that “even very low levels of BPA exposure can be harmful and lead to issues with reproductive health, breast cancer risk, behavior, and metabolism.”

Exposure to BPA has also been linked with greater odds of asthma among school-age girls, lower lung function in children, and an increased risk of childhood obesity, all cause mortality and post-partum depression.

While an endless amount of fear is disseminated, there is little scientific fact.

What Does the Science Show?

BPA demonstrates toxicology's fundamental principle: “The dose makes the poison.”  The levels of BPA that people are exposed to are so low that no health effects have been noted; animal studies have only reported adverse health effects at very high levels.

In 2010, the US government began planning a significant collaborative effort between the National Institute of Environmental Health Sciences and the National Center for Toxicological Research to fund research on the health effects of BPA. The program consisted of a 2-year study in rats that examined a broad range of doses and health endpoints and several studies that evaluated the impact on the offspring of pregnant rats exposed to various doses of BPA. 

The results were published in 2018, concluding that doses of 2,500 µg/kg and below did not cause any adverse effects in rats, while a dose of 25,000 µg/kg caused some impact, including effects on the female reproductive tract and male pituitary gland. Over 100 studies have investigated the potential health risk from exposure to BPA in humans. The vast majority have shown no health effects. Here is an example.

The meta-analysis consisted of 3,007 pregnant women with urine samples collected and measured for BPA from 1999 to 2010. For most women, a single urine sample was collected, while approximately 700 women had two urine samples collected over their pregnancy. BPA is totally eliminated from the body within 24 hours; these BPA samples only indicate BPA levels in the women within 24 hours of testing. Nevertheless, the authors used these measurements to determine BPA exposure to their children.   

When the children of these women were 7 to 10 years of age, they were assessed for the presence of asthma and wheezing, and their lung function was measured. The study authors concluded that “In utero exposure to BPA was associated with higher odds of current asthma (odds ratio = 1.13, 95% confidence interval = 1.01, 1.27) and wheeze (odds ratio = 1.14, 95% confidence interval 1.10, 1.30) … among girls, but not with wheeze nor lung function either in overall nor among boys.”

There is so much wrong with this study that it is hard to know where to begin. The level of BPA in the urine measured once or twice during pregnancy has nothing to do with the actual cumulative exposure to the child. In addition, asthma is a multicausal disease, and this study did not examine any other possible causes other than BPA. [1]. Finally, while an odds ratio of 1.13 or 1.14 shows an association between BPA and asthma, is this 13 or 14% difference clinically significant, especially given other risk factors not considered.

How do Scientists Determine Safe Levels of Chemicals?

For over 40 years, scientists have used risk assessment to determine safe levels of chemicals. The basic principle consists of looking at scientific studies in humans and animals and then determining the lowest level at which adverse health effects were noted. Since there are many uncertainties surrounding this number, the scientists reduce the number by an “uncertainty factor,” lowering the threshold to ensure it is protective for all people.

A major problem in today’s risk assessment is that scientists can measure more effects at lower and lower levels. Some scientists have determined safe levels based on studies that measure effects in cells and biochemical effects that have no actual application to human health. The EFSA expert panel is a perfect example.            

What did the EFSA Expert Panel Do?

The EFSA expert panel determined their safe level for BPA, termed the tolerable daily intake (TDI), based on a study in mice that examined BPA’s effect on a type of T cell involved in our immune response. This study found an increase in these cells in the spleen of offspring mice whose mothers were exposed to BPA in their drinking water while pregnant. This study resulted in a new TDI calculation - 0.04 nanogram (ng)/kg, 100,000 times lower than the current TDI of 4 ug/kg; a level 10,000 times less than the level of BPA that can be accurately measured in laboratories. [2]

Why didn’t the EFSA expert panel base their TDI on the large U.S. government study intended to resolve these issues?  After all, this study represents eight years of planning and research between major U.S. government agencies and academic institutions and is the largest and most comprehensive study to date. Was this because the study didn’t lead to the desired policy outcome and number?

The purpose of risk assessment is to use science to determine the relative toxicity of chemicals. In my opinion, the reason the EFSA expert panel didn’t base their TDI on the extensive U.S. study is that this would result in a TDI of approximately 25 ug/kg, a level that would be detectable by current analytical methods, but was above the level that activists would find acceptable.   

The current trend of setting acceptable levels as low as possible for every chemical, regardless of their toxicity, goes against the principles of risk assessment and common sense. There is also a fundamental problem when levels are set that can’t be detected, creating uncertainty for businesses and industries trying to comply and confusion and anxiety in the general public.

The current trend of setting safe levels as low as possible is a kind of scientific limbo stick that leads to fear in the general public and a lack of confidence in science.  

[1] 15% of the pregnant women were smoking and presumably continued creating an environment filled with second-hand smoke.

 [2] A nanogram (ng) is a billionth of a gram; if you slice a single grain of rice into 25,000,000 parts, one of these parts weighs one nanogram. It is also the weight of a single cell in the body.

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