Posted by: Green Knight | December 11, 2010

Selenium Poisoning

When I was still in California in the early ’80s, a big environmental story was waterfowl at the Kesterson Wildlife Refuge in the San Joaquin Valley suffering low breeding rates, infertility, and deformities in chicks, which turned out to be the result of naturally-occurring selenium in valley soil deposits, which accumulated in irrigation runoff water that was being disposed of in the refuge. Selenium is one of the twelve trace or micronutrients, along with some other metals, but unlike the rest, where the gap between how much you need to be healthy and how much makes you sick (i.e. produces toxic effects) is very wide, the gap for selenium is quite narrow. This is one reason people should be careful about taking selenium supplements, or feeding it to their livestock, without having some tests done first.

What’s really interesting is that certain kinds of plants NEED the stuff, and metabolize it into more toxic forms that can then be uptaken by other plants, animals that feed on them, and bodies of water where it kills birds, amphibians, even insects. During the Kesterson research to find other locations where this might occur, an entire forgotten literature was rediscovered, going back to the 1930s, detailing livestock and human ailments anywhere there was marine shale bedrock, which is seleniferous in most of the Western and Plains states. Maladies like “alkali disease” and the “blind staggers” turned out to have been caused by too much selenium.

Of historical interest, I read recently on a US Geological survey page that “Selenium poisoning may have been a critical factor in the delay of the cavalry scheduled to relieve General Custer at the Battle of the Little Big Horn in Montana. A “peculiar sickness” developed in the horses traveling through what are now known to be high selenium regions.” The USGS page also discusses how sulfur interferes with the absorption of selenium by plants or animals.

For a fascinating recounting of the science, the economic impacts, the cover-ups and the attempts at remediation, read “Death in the Marsh” by Tom Harris, the Sacramento Bee reporter who did an exhaustive investigation over 7 years (Island Press, 1991).

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