Bioaccumulation and Effects of Selenium in Wildlife

Abstract

Selenium is a naturally occurring trace element that is essential for animal nutrition, but the range between dietary requirements and toxic levels is relatively narrow. The greatest abundance of Se is in igneous rocks (although bioavailability may be low), but high concentrations are found in some sedimentary rocks and fossil fuels. Human activities affecting biological availability of Se from these various sources can increase the potential for adverse effects on wildlife. Two examples include disposal of Se-containing drainage water from agricultural fields and fly ash from coal-fired power plants. This chapter provides a general review of characteristics and environmental occurrence of Se, procedures for collection and analysis of biological samples, and the occurrence and significance of Se (e.g., toxic effects) in plants and animals. The primary focus is on potential adverse effects of elevated Se in wildlife, particularly those animals that may be affected by disposal of subsurface agricultural drainage waters, and on their food chains. This problem was first documented in the U.S. Fish and Wildlife Service's studies at Kesterson Reservoir in the San Joaquin Valley of California, where Se from agricultural drainage water bioaccumulated to high enough levels in plants and animals to cause mortality and impair reproduction of aquatic birds. Research results from Kesterson Reservoir are summarized as a case history. Briefly, aquatic plants, invertebrates, fish, frogs, snakes, birds, and mammals at Kesterson Reservoir contained much higher Se concentrations than those at the reference sites, often averaging 100 times greater. The most pronounced effects in wildlife species were found in birds that fed regularly in Kesterson Reservoir. These effects included high incidences of embryonic mortality and deformity as well as mortality of adult birds attributed to Se toxicity. Similar effects of Se toxicosis may occur as a result of agricultural drainage in other areas, such as the southern San Joaquin Valley where embryonic deformities similar to those at Kesterson have been found in recent studies.