Fall and Rise of the Wetlands of California's Great Central Valley by Garone Philip

Author:Garone, Philip [Garone, Philip]
Language: eng
Format: epub
ISBN: 978-0-520-94849-5
Publisher: University of California Press
Published: 2011-09-22T04:00:00+00:00

THE SCIENCE OF SELENIUM

The chemistry of selenium reveals why it is highly toxic above certain thresholds. First discovered by Jon Jakob Berzelius in 1817, selenium has an atomic structure and chemical properties that are similar to sulfur. Several biochemical reactions do not discriminate between selenium and sulfur, and in the presence of excess selenium organisms bind it, rather than sulfur, into amino acids, the building blocks of proteins. In embryos, incorporated selenium interferes with the ability to utilize oxygen, resulting in deformities. In adults, selenium damages internal organs and the respiratory system.48 From water and sediments, the latter of which act as a sink or collecting medium, selenium enters the aquatic food chain as it is accumulated by phytoplankton, algae, rooted vegetation, and invertebrates. Eventually the selenium moves to organisms in the higher trophic levels, or categories of consumers, including birds and terrestrial predators, where it accumulates in their organs or tissues. It is the bioavailability of selenium, determined by its metabolic pathways, rather than its concentration per se, that determines the expected level of toxic effects, including teratogenesis, or embryonic malformation.49

The effects of selenium on plant and animal communities in aquatic environments were essentially unknown before the Fish and Wildlife Service conducted studies at Kesterson from 1983 through 1985. The main focus was on aquatic bird species, chosen for their differing food habits and abundance during the nesting season, but the service also studied mosquitofish, bullfrogs, gopher snakes, and mice and voles to assess selenium’s impact on fish, amphibian, reptile, and mammal populations. At least 39 percent of the 579 waterbird nests monitored to hatching from 1983 through 1985 contained at least one dead or deformed embryo or chick. Whereas the 1983 discoveries were of embryos and newly hatched chicks only, beginning in 1984 the Fish and Wildlife Service found adult birds dead from selenium poisoning as well. These discoveries at Kesterson are particularly revealing when compared to observations from the nearby Volta Wildlife Area. During the three years of the study, the service found only 4 dead embryos, and none with deformities, in 339 eggs (1 percent) at Volta. By contrast, the service identified 604 dead or deformed embryos in 2,689 eggs (22 percent) at Kesterson. Furthermore, there were no signs of survival at Kesterson among the nearly 440 black-necked stilt and American avocet chicks that hatched in 1984 and 1985.50

Expanding the selenium research beyond Kesterson, the U.S. Fish and Wildlife Service, the California Department of Fish and Game, and the U.S. Geological Survey conducted additional studies in the Grasslands area west of the San Joaquin River during 1984. The Grassland Water District was then supplementing its 50,000 acre-feet of guaranteed fresh water from the Bureau of Reclamation with approximately 80,000 acre-feet of irrigation return flows, including both surface and subsurface drainage. In June the USGS found selenium concentrations as high as 4,200 μg/L in drainage water flowing into the Grassland Water District.51 Elevated levels of selenium were found in aquatic plants, fish, and birds throughout the area.

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