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Anabaena is a Cyanobacteria, a prokaryotic blue-green algae
Rhaphoneis is a plankton
Grass Shrimp
Blue Crab
Silk Snapper
Black-Necked Stilt
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Linking Selenium Sources to Ecosystems
Food web from particulates through prey to predators


Introduction

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Refining

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GUIDELINES

Selenium Biochemistry

Selenium is an essential micronutrient in bacteria and animals. Beneficial effects in humans stem mainly from Se’s role as an antioxidant. However, Se is the most toxic of all biologically essential elements in mammals. Toxic effects occur via biochemical pathways unable to distinguish Se from sulfur, thus substituting Se-containing amino acids in structural and functional proteins during critical stages of development and growth. Hence, dramatic effects such as congenital anomalies (monstrosities) occur in embryos of aquatic birds.

Nutritional guidelines and national guidelines for risk have been developed. The guidelines for food webs show the narrow difference between concentrations considered safe and those considered harmful. Nutritional guidelines may not be directly comparable across classes or within species because selenium toxicity is dependent on the sensitivity of the animal, the chemical form of the Se, and the dose and duration of exposure. For example, the threshold for chronic toxicity in humans (dry weight, whole diet) is based on a longer exposure time than that for horses and sheep. Despite these complexities, five western states at 11 sites have human health advisories for fish consumption because of Se. Children (< age 15) and pregnant women are advised not to consume any fish or game from a posted area, whereas adult males and non-pregnant women should consume no more than one meal each two-week period of approximately 120 grams of fish or game flesh (i.e., muscle).

Ecological risk threshold ranges are indicative of the endpoints used to measure adverse biological effects. Thresholds for marginal and substantive risk are well established for water, sediment, diet, fish tissue, and bird eggs. Because the difference between essential and toxic levels for Se is narrow, concern or marginal risk levels, which are between levels considered safe (no effect) and those considered harmful (substantive risk or the toxicity threshold), are intended to provide protection for the environment. The equality of the criterion for the protection of aquatic life and the ecological threshold at which substantive risk occurs (i.e., 5 µg/L) demonstrates a need to establish a set of criteria that fully encompasses both aquatic and semi-aquatic food web components.

Selenium Guidelines
Compilations of Se health and risk criteria are available for: (a) nutrition, adequate/chronic toxicity (Puls (1988); U.S. Department of Health and Human Services (1989, 1996); (b) protection of aquatic life (U.S. Environmental Protection Agency, 1987; U.S. Department of Health and Human Services (1996); (c) protection of animal life (Puls, 1988); (d) human health advisory, consumption of fish (Fan et al., 1988); and (e) human health advisory, drinking water (U.S. Department of Health and Human Services, 1996).

Guidelines for risk to aquatic life (i.e., ecological thresholds) take into account food webs in that they were derived for water, sediment, diet, fish tissue, and bird eggs (Stanley et al., 1996; U.S. Department of Interior, 1998; http://www.usbr.gov/niwqp/guidelines/index.htm). The criterion for a hazardous Se waste is designed to protect ground water from the leaching of toxic substances based on an extraction procedure of solid wastes (U.S. Department of Health and Human Services, 1996). All values for solids are given in dry weight.



Guidelines for Se are listed for ecological risk thresholds, hazardous wastes, and for protection from toxicity.

 


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