Selenium: When a good nutrient goes bad

Authors


Selenium (Se) is an essential element necessary for proper metabolic functions. Selenium deficiency can result in chronic or fatal consequences to humans (Keshan disease [heart muscle dystrophy, which affects about 1 billion people globally] and Kashin-Beck disease [a permanent and disabling osteoarticular disease affecting growth, bones, and joint cartilage]) and to animals (white muscle disease—mineralization of the heart muscle) (ATSDR 2003; Lenz and Lens 2009). Sufficient Se not only prevents these diseases, but can help prevent certain types of cancer or diabetes and can reduce susceptibility to influenza. I take a Se pill every day as recommended by my doctor; I suspect that many of you do the same either directly or as part of a multivitamin tablet. But, like everything, too much of a good thing can in fact be bad for you—or for the environment. Selenium was named after the moon (Selene) and, like the moon, it has two contrasting faces (light and dark): it is a necessary element for metabolic functions but it can become toxic at higher concentrations.

The April 29, 2009, issue of the Canadian newspaper The Edmonton Journal carried a story about Se killing horses. Specifically, the article reported that the 21 polo horses of the Lechuza Polo team from Caracas, Venezuela, that fell ill and then died on April 21, 2009, shortly before they were scheduled to begin the featured match of the US Open Polo tournament, did so as the result of an accidental Se overdose.

Sometimes death is not accidental. Spiller and Pfiefer (2007) report on two cases of “murder by Se,” a new phenomenon. In one case, a wife was murdered by her husband; in the other case, a husband was killed by either his wife or his pregnant girlfriend (or both). The cases present a clear message here, not to leave your Se pills out if you are having marital troubles. In case you cannot find your pills, initial symptoms of Se poisoning in humans include defective nails and skin, hair loss, and paralysis; more acute symptoms include nausea, vomiting, diarrhea, and cardiovascular irregularities.

Human activities, including oil refining, fossil fuel combustion, mining, and agriculture, are increasing Se concentrations in the environment such that, as discussed in a Learned Discourse in the previous issue of this journal, Se is of increasing concern globally (Chapman 2009). Accidental poisoning from a coal-fired power plant resulted in population-level impacts to fish in two lentic aquatic ecosystems in the United States: Belews Lake and Hyco Reservoir, both in North Carolina. Similarly, agricultural sources of Se resulted in population-level effects to waterbirds in Kesterton Reservoir, California, also in the United States. Concern currently exists that similar effects could occur or be occurring elsewhere due to increasing Se concentrations in the environment. Government and industry are sufficiently concerned regarding potential effects of Se in the aquatic environment (reproductive effects to egg-laying vertebrates) that they jointly sponsored a recent (February 22–28, 2009) SETAC Pellston Workshop on the “Ecological Assessment of Selenium in the Aquatic Environment” (a summary of the key findings is available at http://www.setac.org/node/265).

The current issue of this journal contains two articles on Se—one dealing with a conceptual management model, the other with appropriate quality assurance/quality control for the determination of environmentally relevant Se tissue-residue thresholds. The SETAC North America meeting in New Orleans will feature a session on “Ecological Assessment of Selenium in Aquatic and Terrestrial Environments.”

Interestingly, as concern grows over increasing Se concentrations in the environment, concern is also growing over insufficient Se intake by much of the human population (Rayman 2002), particularly in a form or species that is adequately bioavailable (Finley 2006). That is one face of this element; the other is too much bioavailable Se causing toxicity.

Concern also exists that “the world's rare selenium resources need to be managed carefully” and that Se needs to be recovered from mining and other industrial releases, possibly as part of chemical or biological treatment activities (Haug et al. 2007). Presently, Se is extracted as a by-product of copper mining and, aside from nutrition, is used in the glass industry for coloring, in electronics due to its photoelectric and semiconducting properties, in photography to transfer images to xerography, in the pharmaceutical industry as a catalyst, and as a constituent of fungicides, antidandruff shampoos, and mammographic instruments. It may well have other uses (for a future hypothetical use and a lot of laughs, rent the movie “Evolution” starring David Duchovny and Orlando Jones and remember, “there is always time for lubricant!” [http://www.youtube.com/watch?v=vq1FNIGap-0]). Selenium may become increasingly scarce over time and thus less available for nutritional and other beneficial uses.

Bottom line, Se provides an amazing case study for integrated environmental assessment and management (IEAM) for several reasons: 1) it is beneficial in proper dosages; but 2) damaging in excess or in lower than metabolically required dosages; 3) concentrations are increasing in the environment; but 4) need to be recovered both to prevent environmental damage and to enable future beneficial uses. We encourage authors to submit articles to this journal dealing with the IEAM of Se and, of course, of other stressors (chemical, biological, physical).

In the meantime, keep taking your Se supplements—in moderation (remember that the dose make the poison!)—and keep them in a secure place. Selenium is an interesting and challenging two-faced element that deserves both our respect and our attention.

Ancillary