摘要:

Environmental issues related to selenium are complex and not universally understood. This paper provides detailed information regarding selenium and associated aquatic environmental issues, and then introduces and comments on five debate/commentary papers discussing selenium in the context of the title of this paper. Selenium has a complex and not fully understood biogeochemistry in the aquatic environment as well as an unusual mode of toxicity (acute via water column exposure; chronic via food chain exposure). It has the narrowest range between nutritional requirements and toxicity of any essential element, and chronic toxicity is not readily predictable. Selenium contamination of waters or even of tissues does not necessarily indicate a ticking time bomb; there are no generally accepted or universally accepted threshold values for chronic toxicity. Assessing risk must be done site-specifically in a risk assessment framework, focusing on reproductive effects to sensitive exposed fish and waterfowl and on “worst case” hydrologic units. Unless selenium inputs decrease or site-specific biogeochemistry can be shown not to change, continued biological monitoring and testing are required. Provided the necessary investigative and monitoring studies are done, any potential selenium time bombs can be defused.

ISSN:1080-7039    

DOI:10.1080/10807039.1999.10518882

出版商:TAYLOR & FRANCIS    

年代:1999

数据来源: Taylor

摘要:

A selenium time bomb situation is developing in the United States and elsewhere that may result in substantial impacts on fish populations. The selenium time bomb has three components: (1) high food-chain bioaccumulation, (2) steep toxic response curve for fish, and (3) insidious mode of toxicity. If the threshold for selenium toxicity is exceeded, the time bomb explodes and a cascade of events is set into motion that will result in major ecosystem disruption. Several human-related factors are emerging that are capable of igniting the fuse of the time bomb by increasing waterborne concentrations of selenium and providing conditions favorable for bioaccumulation. Some of these factors are (1) mobilization of selenium due to open-pit phosphate mining, (2) use of constructed wetlands to treat selenium-laden wastewater from oil refineries and agricultural irrigation, (3) landfill disposal of seleniferous fly ash from coal-fired power plants, and (4) mobilization of selenium from animal feedlot wastes. Collectively, these threats may be sufficient to cause widespread, unanticipated toxic effects in fish populations. Only environmentally sound risk assessments followed by prudent management actions can defuse the selenium time bomb — once it explodes, it is too late to avoid significant impacts.

ISSN:1080-7039    

DOI:10.1080/10807039.1999.10518883

出版商:TAYLOR & FRANCIS    

年代:1999

数据来源: Taylor

摘要:

Anthropogenic selenium contamination of aquatic ecosystems was first associated with cooling reservoirs of coal-fired power plants in the late 1970s, and later with drainage water from agricultural irrigation activities in the 1980s. In the 1990s, selenium contamination has been raised as a concern in the recovery of currently endangered fish in the Colorado River system. Widespread contamination from seleniferous drain waters from agriculture has been documented in the upper and lower Colorado River basins. Historically, irrigation started in the upper Colorado River basin in the late 1880s. In the 1930s, selenium concentrations in various drains, tributaries, and major rivers in the upper and lower Colorado River basins were in the 100 s and 1000 s of µg/L. Native fish inhabiting large rivers such as the Colorado pikeminnow and razorback sucker were abundant before 1890, but became rare after 1910 to 1920, before the influence of mainstem reservoirs in the upper and lower Colorado River. A hypothesis is presented that selenium contamination of the tributaries and major rivers of the Colorado River basin in the 1890 to 1910 period caused the decline of the endangered fish and continues to inhibit their recovery.

ISSN:1080-7039    

DOI:10.1080/10807039.1999.10518884

出版商:TAYLOR & FRANCIS    

年代:1999

数据来源: Taylor

摘要:

At high dietary levels, selenium causes adverse effects in animals. Aquatic birds are among the more sensitive wildlife species, because their reproduction can be impaired when dietary selenium levels exceed about 4 µg/g (dry weight basis). Fish can also be adversely affected at similar dietary exposures. Conversely, low dietary levels of selenium (below about 0.1 to 0.5 µg/g) cause nutritional deficiencies in domestic animals, fish, and wildlife. Selenium became recognized as a significant environmental contaminant for wildlife in 1983, with the discovery of developmental abnormalities and excessive embryonic mortality in aquatic birds at Kesterson Reservoir, California. There are a number of environmental settings in which selenium warrants concern and must be considered carefully in relation to potential effects to fish and wildlife, and there may still be surprises in which it unexpectedly becomes a significant ecological issue. However, if selenium is included among the chemicals of potential ecological concern when ecological risk assessments are planned and conducted, there is enough information to thoroughly evaluate its environmental significance in much the same way as other contaminants. The main difference is that it is essential to have a good understanding of selenium's occurrence, complex biogeochemistry, and ecotoxicology to avoid serious errors.

ISSN:1080-7039    

DOI:10.1080/10807039.1999.10518885

出版商:TAYLOR & FRANCIS    

年代:1999

数据来源: Taylor

摘要:

Proposed fish toxicity thresholds for interpreting the biological significance of selenium concentrations measured in environmental media include 2 to 5 µg/L in water, 4 mg/kg dw in fish whole body tissue, 10 mg/kg dw in fish ovaries, and 3 mg/kg dw in fish diets. Use of these thresholds would likely identify fish populations as being at risk at numerous sites across the U.S. However, selenium effects on fish populations in the field have only been conclusively demonstrated at a few locations. Based on our critical review, these threshold values are not consistent with USEPA methodology for deriving criteria, in many cases are not supported by the scientific literature, and, as a result, are generally overly conservative. Based on currently available information, we believe the scientific literature is not supportive of generic sediment or water thresholds, but is supportive of alternative separate whole body thresholds of 9 mg/kg dw for warmwater fish and 6 mg/kg dw for larval coldwater anadromous fish, an ovary threshold of 17 mg/kg dw for warmwater fish, and fish dietary thresholds of 10 and 11 mg/kg dw for warmwater fish and larval coldwater anadromous fish, respectively.

ISSN:1080-7039    

DOI:10.1080/10807039.1999.10518886

出版商:TAYLOR & FRANCIS    

年代:1999

数据来源: Taylor

ISSN:1080-7039    

DOI:10.1080/10807039.1999.10518887

出版商:TAYLOR & FRANCIS    

年代:1999

数据来源: Taylor

摘要:

Aquatic birds are exposed to selenium through their diet by ingesting aquatic invertebrates that have accumulated selenium from water and the food chain. However, dietary composition is highly variable among species, over time, and across sites, making it difficult to provide accurate estimations of dietary exposure for particular species at specific locations. Selenium accumulates in the egg, resulting in embryo malformation, embryonic death, and decreased survival of juveniles. If the relationship between egg concentration and these reproductive parameters can be defined with sufficient certainty, then risk assessments can be performed through analysis of egg selenium concentrations. Other researchers have proposed egg toxicity thresholds that lead to conclusions of widespread selenium toxicoses in waterbirds. However, we believe these values are overly conservative and that it is unlikely that selenium is posing a significant risk to wild birds in areas where the current water quality criterion is being met. Through the use of simple statistical models (logit, probit, and Weibull functions) we are able to express mortality and teratogenicity relationships for mallards (Anas platyrhynchos) in such a manner that the risk manager can be presented with information about the probability of reduced duckling survival if mean egg selenium (MES) concentrations are known. Data analysis indicates that the two endpoints (mortality and teratogenesis) cannot be distinguished statistically. Commonly used effects thresholds (the EC10and EC20) correspond to 16 and 21 mg/kg dw MES using the most sensitive endpoint, chick mortality. Both of these values are higher than the 6 mg/kg dw level proposed by Skorupa (1998) who based his estimate on field-observational data potentially confounded by other environmental stress factors. The mortality and teratogenicity endpoints presented here relate selenium exposure to risk to individuals within a population and do not provide information about the probability of selenium causing changes in population growth rates, either at the local or regional levels.

ISSN:1080-7039    

DOI:10.1080/10807039.1999.10518888

出版商:TAYLOR & FRANCIS    

年代:1999

数据来源: Taylor