Sunday, August 1, 2010

Chernobyl, 24 years on

An article on the BBC this morning discusses (in the usual BBC "style") the recent findings of a study by researchers conducting a wildlife census in the Chernobyl "exclusion zone," published in Ecological Indicators. The researchers concluded that the radiation contamination had a "significant impact" on the local ecology.
The actual article (available for a fee from Elsevier here... don't get me started on Elsevier, those murderers of the spirit of science) concludes that, within statistically significant correlation, mammals and birds in the exclusion zone had increased instances of "effects," and that "standard breeding bird censuses can be used as an informative bio-indicator for the effects of radiation on abundance of animals."

First things first - before we go all vigilante and decide that nuclear power is too dangerous, let's put things in perspective. The Chernobyl disaster (which cannot be duplicated in the US, France, UK or elsewhere because the fundamental reactor design in Russia at the time was flawed) released somewhere around 10^19 becquerels (nearly 300 MegaCuries) of radiation into the environment - that's the equivalent of the radiation dose you'd get from naturally occurring radioactive potassium by eating about one hundred thousand million million pounds of bananas. We're talking big doses here. Big, unreproducible doses.

Second, we need to be certain we know what, precisely, "effects" are. Here, they simply mean variations in abundance. They went out and physically counted the number of spiderwebs, the number of starlings, the number of foxes, and so on, for nine different "taxa" (ie, biologically similar groups, like "birds" or "mammals"). We're not talking about increased instances of cancer, or birth defects, or anything like that. Purely the number of creatures counted.

Now, for the results - there was a correlation between background radiation (from the disaster) and taxa abundance. This correlation remained when possible confounding effects were taken into account; things like time of day, cloud cover, temperature, or presence of water sources. The correlation was strongest, by a significant fraction, in birds. And, as one might expect, the effect (variation in abundance) was greater in taxa of higher population densities, and was also higher for taxa with higher "natal dispersal ability" (ie, the ability to travel, which comes at a significant biological cost: "dispersal is costly in terms of production of free radicals from physical activity due to actual dispersal and/or from immune response to novel antigens encountered in the new environments during dispersal"). And so we find that birds are the most susceptible to the undesired radiation in the environment.

But this is nothing new. Scientists have long known that birds are good indicators of ill effects in the environment - in fact, even before science began looking for indicators, miners were taking canaries with them into the mines as warnings against deadly carbon monoxide gas. That bird populations are affected by a sudden, increased level of radiation in the environment shouldn't surprise us. But what we don't know - and what the study doesn't tell us - is why those bird populations are dwindling, what the mechanisms are, whether or not the radiation is killing them slowly or is affecting their ability to produce offspring.

This, I suppose, remains to be seen.

Møller, A., & Mousseau, T. (2010). Efficiency of bio-indicators for low-level radiation under field conditions Ecological Indicators DOI: 10.1016/j.ecolind.2010.06.013

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