Saturday, September 15, 2007

Surf City Hits the Arctic

(No, this actually isn't a post about global warming.) I've been reading a fair bit about endocrine disruptors lately, and this article in the Guardian caught my eye:

Twice as many girls as boys are being born in some Arctic villages because of high levels of man-made chemicals in the blood of pregnant women, according to scientists from the Arctic Monitoring and Assessment Programme (Amap).

In the communities of Greenland and eastern Russia monitored so far, the ratio was found to be two girls to one boy. In one village in Greenland only girls have been born.

The scientists measured the man-made chemicals in women's blood that mimic human hormones and concluded that they were capable of triggering changes in the sex of unborn children in the first three weeks of gestation. The chemicals are carried in the mother's bloodstream through the placenta to the foetus, switching hormones to create girl children.

It's somewhat hard to know what to make of this since the actual study hasn't been peer reviewed or published yet and the authors make a few crazy statements in the article. But it is certainly quite alarming and even somewhat plausible. A few thoughts:
  • There are probably some subtleties involved with accurately measuring the gender ratio of live births (e.g. confusion with infant mortality), but they would have to have some seriously screwy methodology to find a ratio of 2:1 if something wasn't really going on. No matter what the cause is, a 2:1 sex ratio is a big problem for these communities.

  • The statement that the chemicals are "capable of triggering changes in the sex of unborn children in the first three weeks" just seems crazy to me. I'm no biologist, but I would be shocked if the chemicals could actually change the chromosomes of the fetus. If this effect is real, I'm sure it has more to do with decreasing the viability of male embryos so that fewer survive, or something like that. Enviroblog is similarly skeptical.

  • (Although it is true that endocrine disruptors have been linked to hormonal imbalances leading to ambiguous genitalia in frogs -- see here -- but it doesn't seem like that is the cause of the skewed ratio in this case. Again, hard to tell without reading the paper.)

  • Still, the results seem plausible to me because we know (1) accidental exposure to high-levels of endocrine disruptors in Seveso, Italy in 1976 led to a similar pattern of skewed gender ratios in the decades following exposure, (2) chemicals like PCBs bioaccumulate as you go up the food chain and exposure is likely to be higher in a diet consisting of bear and fish, and (3) Arctic populations have long been shown to have some of the highest blood levels of these chemicals due to weather patterns that concentrate pollution in the polar regions.

  • A recent peer-reviewed study found a much smaller, but detectable shift, toward more girls than boys among live births in the U.S. and Japan since 1970, and they also speculated that chemical pollution might be the cause. The small shift in sex ratio amounts to 250,000 'missing' boys.
This study may come to nothing -- it's always risky to judge based on a popular media report on an un-released study. Still, while I suppose Jan and Dean might enjoy this situation, the rest of us might want to keep an eye on what we're spewing out into the environment.


Andy said...

The fact that the effect is always leaning toward having more girls than boys makes me think, aren't we all physically female at conception? At some point the hardware switches over for us guys, due to release of hormones. Presumably the DNA would still show you to be male, even if you never got the right hormone dose to gain your boy-parts. So would this be some sort of testosterone-blocker/-neutralizer? (Admittedly, that may not be the hormone at work.)

You would think that if boys were made less viable, the effect on the birth-rate would be pretty clear.

Tim said...

Hey Andy - yeah, that's a really good point. I suppose it would be easy to test too - just give everyone in the village a DNA test (well maybe not easy, but do-able). And maybe that's what the paper is about.

Wish I knew anything about biology, seems like its pretty important...