BPA-Affected Mating? Something's Fishy...

The hot scientific story this week comes courtesy of the University of Minnesota: fish exposed to bisphenol-A (BPA) exhibit diminished sex traits, which leads to aberrant mating behaviors (Check out the original paper by Ward and Blum, or for a more plain-English rundown, try Science Sushi over at SciAm Blogs).

Blacktail shiner, C. venusta
Source: Futurity.org

I've held off on writing about BPA for a long time; it's like a science journalism black hole, dense with conflicting data, politics, and social issues. But I had to weigh in here, because no other outlet seems to have shown proper skepticism, or asked the right questions.

1. Dose - The authors of a 2012 Endocrine Reviews article on low-dose endocrine disruptors point out (p. 18) that the EPA extrapolated reference dose for BPA in humans = 50 ug / kg body weight (Update, 7/12/12 - Check the comments for a more applicable animal toxicity value). That means, according to them, that you could eat a few specks of it with dinner every day for the rest of your life, and suffer no ill effects.

So what does this have to do with the fish paper? Note the dose (p.3): 1280 ug / L. Do the math: 1L of water = 1000 mL, density of water (room temp) = 1 g / mL, thus 1L = 1 kg. How much does a fish weigh, a few grams at most? This study overdoses them by at least a few orders of magnitude. Pardon the pun, but these little guys are literally swimming in BPA. Furthermore, the scientists change out the tank water every 24 hours, so the fish are certainly overexposed relative to their control brethren.

2. Cosolvent Effects - BPA has relatively low water solubility, so the authors dissolve it into their mixture with a cosolvent, triethylene glycol. Well, that's fine, as long as they run the control - water with triethylene glycol and no BPA - which they have. So, what happened? The female fish studied show no appreciable difference (Table 1) between straight H2O and cosolvent-H2O mixtures. Pity the poor blacktail shiner (C. venusta) males, though: they show marked dropoffs in all courtship metrics from cosolvent control water alone! (No BPA added). This data point does not merit discussion in the paper, however.


3. Standard Environment - Coloration and mating behavior definitely both suffer when we lock fish in tanks bombarded with BPA. But what about in the wild? How much BPA do these fish encounter in their native river habitats? Anywhere near these concentrations? Do wild fish caught on-site exhibit these same color losses? Is BPA exposure the sole factor influencing interspecies hybridization?

Readers, I'm no evolutionary biologist, so please set me straight on a few of these points. To clarify, I don't deny that xenobiotics (atrazine, estradiol) can affect marine life, but this particular study seems somewhat subject to interpretation - a scientific 'fish story.'