Part III—Is It So Bad?
“Well, I’m still skeptical,” Steve said after looking at the data. “I mean, I think it’s pretty convincing that this stuff is in the water, but so what? There could be lots of things in water. That doesn’t mean it’s bad, you know.”
“OK, but look at this experiment,” Susan responded, showing him Figure 1 from the Howdeshell, et al., 2003 paper.
“Susan, I hope you explain your findings more clearly in your research paper. You know if you just show a bunch of tables you’re going to get a bad grade.”
“I know, I will. But don’t you see what’s going on in this figure?”
“Well, not immediately,” Steve responded. “There are a lot of bars, and why are they measuring DNA?”
“They’re measuring the amount of cell proliferation,” Susan explained. “Obviously, the more cells there are, the more DNA there is.”
“OK, I got that,” Steve answered a bit annoyed at her tone.
“What are all of these different labels on the x axis, though?” he asked.
“Well, they wanted to test if the BPA is estrogenic or acting like estrogen,” Susan explained. “Estrogen causes breast cancer cells to divide. They added estrogen, or water from the cages, to human breast cancer cells. See these first four bars?”
Steve nodded. “Those show that adding estrogen increases cell number because it increases DNA amount in the well holding the cells.”
“OK,” Steve nodded, “and this next group of bars shows the controls, right?”
“Right—they took the water from the glass containers and from the used polypropylene, which didn’t produce any BPA. But see here,” she moved her finger to the next set of bars, “the water from the used polycarbonate cages acted just like estrogen did.”
“What’s the ‘LY’ mean?” Steve asked.
“LY is an antiestrogen,” Susan answered. “See what it does?”
Steve continued to look at the graph. “Yes, I do, that is interesting.”
Susan turned the page to show Steve Figure 2. “OK, here they used HPLC to separate out the different chemicals that could be in the water from the cages. Table A is water from a used polycarbonate cage, and Table B is water from a used polypropylene cage.”
“Yes, look,” Steve pointed out, “here is where the BPA is in the used polycarbonate cage, and there’s that increase in cell number again. It really does cause those cells to divide. Do you think that means BPA can cause breast cancer?”
“I don’t know,” Susan answered thoughtfully, “they don’t really address that. These were breast cancer cells in the first place.”
“What does this next table show?” Steve asked, referring to Table 2.
“Well, this was an in vivo study, so they could actually look at the whole animal and see if the BPA was having any negative effect.”
“What would you test, though?” Steve asked.
“They tested how much the uterus grew in female mice that had not yet gone through puberty,” Susan answered.
“It doesn’t look like there’s much of a difference.”
“No, it doesn’t, and they say in the paper that they don’t think uterine weight like this is a good measure of estrogenic activity.”
“Do you think they’re just saying that because they’re biased?” Steve asked. “Do they say what else they should test?”
“Yes, they say that the transcriptional activity of estrogen receptor is very sensitive, and so is the fetal male prostate.”
“Really? That’s interesting,” Steve commented.
Questions
- What were the positive and negative controls used for each of the figures discussed in this section? Why were these included, specifically?
- Why do you think they included the data in Table 2?
- Susan and Steve seem pretty convinced by these data. Are you? Defend what it is that either makes you agree or disagree.
Go to Part IV—Human Implications
Image credits: Figure 1, Figure 2 and Table 2 from Kembral L. Howdeshell et al., “Bisphenol A Is Released from Used Polycarbonate Animal Cages into Water at Room Temperature,” Environmental Health Perspectives, 111:9, 2003. Reproduced with permission from Environmental Health Perspectives.
Originally published at http://www.sciencecases.org/water_bottle/case3.asp
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