What’s in My Water Bottle? by Janna R. McLean

Part IV—Human Implications

“Well, I’m more convinced than before,” Steve admitted after reviewing the data. “It certainly seems to be a problem for rats.”

“Not just rats, Steve, those breast cancer cells were human, remember. Besides, they also explain that this could be a problem for animals that we keep in water in these cages, like fish and frogs. Here’s what they say.” Susan read aloud from the paper:

In guppies (Poecilia reticulata), BPA exposure (274 µg/L for 21 days) in adulthood significantly decreased the number of mature sperm stored in deferent testes canals before ejaculation by 50%, relative to control males (Haubruge et al. 2000). A significant decrease in spermatozoa has also been reported for fathead minnows (Pimephales promelas) after exposure to 16 µg/L BPA in water for 164 days in adulthood (Sohoni et al. 2001).

“Still, what about people? We’re not really affected by this, are we? I mean, tests of cells alone, does that really say something about what we’re drinking and eating?”

“Here, check out the last paragraph in this paper,” Susan said as she handed it to him.

BPA migration into human serum has been reported with the use of polycarbonate and polysulfone plastic hemodialysis equipment (Yamasaki et al. 2001). Another potential route of BPA exposure in the laboratory is polyvinyl chloride (PVC) pipes used in the supply of tap water; BPA is added as a stabilizer in the production of PVC products.

“So maybe we get some BPA from tap water—where’s the evidence that it’s bad for humans?” Steve asked.

“Actually, there have been some interesting findings that show that it is,” Susan replied. “Let me see,” she said as she rifled through her papers. “Ah, here are some of those findings. So, you know how girls seem to be going through puberty sooner than they used do?”

“Uh, well, I don’t think I had noticed that.”

“Well, I have. I thought maybe it was hormones in milk. And maybe it is. But this group of researchers (Howdeshell et al., 1999) suggests it has to do with BPA. They gave pregnant mice BPA fed in oil (or just oil as a control). They used a dose that is equivalent to what would be found in the environment. They took the babies and put them with foster mothers once they were born. Here’s what they found. What do you think of that?”

“Well, this is kind of confusing,” Steve commented as he stared at Figure 1. “I guess they were looking at reproductive maturity issues, but they talk about whether the mice were next to a male or not—that gets confusing to me!”

“You can ignore that, though it is interesting,” Susan answered. “If you just look at panels a, b, and c, you can see that the weight of mice at weaning was larger for the mice whose mothers had been fed BPA. And they also are ready to mate earlier, by about two days.”

“Is two days a lot?” Steve asked.

“Well, mice do mature a lot faster than we do, so I would think two days is meaningful. They do show that there is a significant difference.”

“Now, look at the results of this study (Figure 2) by Masuno and colleagues,” Susan continued. “They looked at the effects of BPA on obesity.”

“Obesity?” Steve asked. “Why obesity? Though I do have to admit I’ve read in the newspapers that more and more people are becoming obese—some people are even calling it an epidemic.”

“Well, what they explain is that estrogen has an effect on lipid metabolism, at least in rats. I wonder if that’s why women gain weight easier than men,” she added with a frown. “Anyway, these folks were studying whether BPA could change 3T3 fibroblasts into adipocytes. These are fibroblasts that do change into adipocytes in the presence of insulin, for example. As they change, they express more lipoprotein lipase (LPL) and less triacylglycerol (TG), and that’s what they measured in this graph.”

“So,” Steve said thoughtfully, “exposure to BPA could actually make people fatter? So maybe it’s not video games or too much sugar that’s responsible for people gaining so much weight?”

“That’s right!” Susan replied. “Who would think that you could get fat from drinking out of plastic containers?”

Questions

1. In the quotes that Susan shows, the authors state that levels of BPA can affect sperm production in fish. Would fish raised in used polycarbonate cages be subjected to these levels? Explain.
2. In the experiment where pregnant mice were fed BPA, the baby mice were raised with foster mothers. Why did they do that?
3. What is the evidence that BPA causes obesity? Explain what is or is not convincing about it.

Final Assignment

Write an essay that is at least one page long, double-spaced and typed, that addresses the following paragraph:

BPA has been found in the linings of metal cans as well as dental sealants in addition to water from polycarbonate containers. Overall, comment on how valid you think the data are that were presented in this case study and explain the reasoning behind your evaluation. Discuss how serious you think this problem is. Then consider your place in society as a scientifically educated person. What should you do to help solve the problem or perhaps eliminate unnecessary concern?

References

Howdeshell, K.L., A.K. Hotchkiss, K.A. Thayer, J.G. Vandenbergh, and F.S. vom Saal. 1999. Environmental toxins: Exposure to bisphenol A advances puberty. Nature 401:763–764.

Howdeshell, K.L., P.H. Peterman, B.M. Judy, J.A. Taylor, C.E. Orazio, R.L. Ruhlen, F.S. vom Saal, and W.V. Welsons. 2003. Bisphenol A is released from used polycarbonate animal cages into water at room temperature. Environmental Health Perspectives 111:1180–1187.

Masuno, H., T. Kidani, K. Sekiya, K. Sakayama, T. Shiosaka, H. Yamamoto, and K. Honda. 2002. Bisphenol A in combination with insulin can accelerate the conversion of 3T3-L1 fibroblasts to adipocytes. Journal of Lipid Research 43:676–684.

http://www.jlr.org/cgi/content/full/43/5/676

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