THE TETHYAN CONNECTION: SELENIUM POISONING OF FISH AND WILDLIFE IN NATURE

Organic-carbon enriched geologic features such as the abundance of phosphate deposits and petroleum-generating basins located in the Tethyan oceanic realm are typically enriched in selenium as are bituminous coals and Cretaceous sedimentary rocks of the Pierre and Niobarra Formations, just to mention a few prominent examples. Anthropogenic disturbance of geologic selenium sinks has repeatedly led to episodes of fish and wildlife poisoning when elevated levels of selenium are mobilized into aquatic ecosystems. Well documented examples have been associated with core human economic activities such as irrigation agriculture, coal-fired electricity generation, and petroleum refining. Other examples have been associated with coal mining, phosphate mining, copper mining, and uranium mining/milling.

Research on the ecotoxicology of selenium has revealed that the margin between nutritional requirements and toxicity can be very narrow for sensitive species of fish and wildlife. The thresholds for selenium-induced reproductive toxicity among oviparous vertebrates, such as fish and waterbirds, can be less than one order of magnitude above nutritionally optimal exposures. A general review will be presented of common toxicological effects of selenium on fish and wildlife, threshold exposure-response relationships, and what has been learned with regard to the limits of environmental tolerance vis-à-vis redistribution of selenium from geologic sinks. Selenium deficiency has been a long-standing concern for animal husbandry and some human populations, but for animals in nature selenium toxicity is increasingly becoming recognized as an environmental dilemma.