Ambient Water Quality Guidelines for Selenium
Prepared pursuant to Section 2(e) of the
Original signed by Margaret Eckenfelder
Cataloguing in Publication Data
Prepared by N. K. Nagpal. Cf. p.
1. Water quality - Standards - British Columbia.
TD227.B7N34 2001 363.739'462'09711 C2001-960248-0
This document is one in a series that establishes ambient water quality guidelines (Table 1). This document is mainly based on a report originally prepared by the British Columbia Ministry of Environment, Lands and Parks in 1997 and then updated in year 2001. It sets guidelines for selenium (Se) to protect drinking water, freshwater and marine aquatic life, wildlife and agricultural water uses.
Guidelines were not set for recreational and industrial water uses, since relevant Se toxicity data for these uses were not available in the literature.
Selenium can be both beneficial as well as toxic to biota. In aquatic environments, organisms accumulate Se from both water and food. The bioaccumulation of Se through the diet, however, is usually greater than the direct uptake from water. Therefore, toxic effects of selenium in food may be more significant than the waterborne Se.
The guidelines are summarized in Table 1.
Table 1: Summary of Water Quality Guidelines for Selenium
THE MINISTRY OF WATER, LAND AND AIR PROTECTION develops province-wide ambient water quality guidelines for variables that are important in the surface waters of British Columbia. This work has the following goals:
Ambient water quality objectives for specific waterbodies will be based on the guidelines and also consider present and future uses, waste discharges, hydrology/limnology/oceanography, and existing background water quality. The process for establishing water quality objectives is more fully outlined in Principles for Preparing Water Quality Objectives in British Columbia, copies of which are available from Water Quality Section of the Water Management Branch.
Neither guidelines nor objectives which are derived from them, have any legal standing. The objectives, however, can be used to calculate allowable limits or levels for contaminants in waste discharges. These limits are set out in waste management permits and thus have legal standing. The objectives are not usually incorporated as conditions of the permit.
The definition adopted for a guideline is:
The guidelines are province-wide in application, are use-specific, and are developed for some or all of the following specific water uses:
The guidelines are set after considering the scientific literature, guidelines from other jurisdictions, and general conditions in British Columbia. The scientific literature gives information on the effects of toxicants on various life forms. This information is not always conclusive because it is usually based on laboratory work which, at best, only approximates actual field conditions. To compensate for this uncertainty, guidelines have built-in safety factors which are conservative but reflect natural background conditions in the province.
The site-specific water quality objectives are, in most cases, the same as guidelines. However, in some cases, such as when natural background levels exceed the guidelines, the objectives could be less stringent than the guidelines. In relatively rare instances, for example if the resource is unusually valuable or of special provincial significance, the safety factor could be increased by using objectives which are more stringent than the guidelines. Another approach in such special cases is to develop site-specific guidelines by carrying out toxicity experiments in the field. This approach is costly and time-consuming and therefore seldom used.
Guidelines are subject to review and revision as new information becomes available, or as other circumstances dictate.
Selenium is an essential trace element for animal nutrition. It can also be toxic to plants, animals and humans at higher concentrations. The severity of selenium effects in food and water depends on the amount ingested and the length of exposure. A number of systemic effects including respiratory, cardiovascular, gastrointestinal, haematological, musculoskeletal, renal, dermal, endocrine, and changes in body weight have been reported in humans and animals exposed to selenium. However, little is known about the specific mechanisms by which Se and its compounds exert their toxicity. Selenium can replace sulphur in biomolecules, especially when the selenium concentration is high and the sulphur concentration is low in the organism. Skin, hair, and nail damage are among the significant indicators of chronic selenium exposure.
Selenium poisoning in animals has been reported in areas of high Se concentration in soils (e.g., seleniferous soils). Clinical signs of acute selenium poisoning in animals and humans include excessive salivation, garlic odour of the breath, shallow breathing, and diarrhea. Other signs of acute Se poisoning in animals include vomiting, dysponea, tetanic spasms, and death from respiratory failure.
Plants and animals raised in areas where selenium concentration is low in soils and plants may develop diseases as a result of selenium deficiency. Deficiency of Se and vitamin E has been shown to cause muscular dystrophy in sheep and cattle, exudative diathesis in chickens, and liver necrosis in swine and rats. Signs specific for Se deficiency in the absence of vitamin E deficiency include pancreatic degeneration in chicks, and poor growth, reproductive failure, vascular changes, and cataracts in rats.
Selenium is considered a rare element because there are no large deposits anywhere in the world. It is mainly obtained as a by-product of the electrolytic refining of copper. Canada is among the leading producers of selenium in the world. According to Statistics Canada, Canada produced 286,000 kg Se in 1992. Selenium and its compounds are used in many products:
The concentration of Se in natural waters is generally low, but varies widely. In seleniferous areas, Se levels are high and may exceed acceptable limits. In British Columbia, total Se concentration in rivers and streams is generally low at less than 0.001 mg/L; however, levels up to about 0.2 mg Se/L have been measured in areas contaminated by effluents from coal mines.
1. DRINKING WATER
It is recommended
that the total concentration of selenium in drinking water
should not exceed
To protect freshwater aquatic life from adverse effects, the mean concentration of total selenium should not exceed 2 µg/L in the water column, 2 µg/g dry weight in the sediment and 1 µg/g wet weight/body weight in the tissue. The mean concentration is calculated based on at least five weekly samples taken over a 30-day period in the water column or five tissue or sediment samples taken during a single sampling event.
The tissue and sediment guidelines are designed to protect from Se bioaccumulated through the food chain. They are based on three factors: (a) safe levels of the substance in tissues and sediments, (b) potential for Se to bioaccumulate in the aquatic environment, and (c) sediment Se-water column Se relationships. Therefore, they are consistent with the recommended water column guidelines. However, they are interim in nature at this time because there were insufficient data in the literature for a full guideline according to the CCME protocols for the sediment and tissue residue guidelines.
The recommended water quality guideline replaces the 1987 CCME guideline of 1 µg Se/L in the water column, which was based on the International Joint Commission (1981) recommended numerical limit for the Great Lakes. CCME did not recommend sediment or a tissue residue guidelines to protect freshwater life.
marine aquatic life, the mean concentration of total selenium
should not exceed
The sediment and tissue guidelines for marine environments are the same as recommended for the freshwater life. There were not sufficient data in the literature to derive independent sediment and tissue guidelines for marine environments. However, the available data in the literature presented some evidence that will support the application of the freshwater guidelines to marine environments.
CCME (1987) did not recommend selenium guidelines to protect marine life.
To protect wildlife from adverse effects, the mean concentration of total selenium should not exceed 4 µg/L.
An average alert level of 7 µg Se/g dry weight in eggs (or 1.4 mg Se/g wet weight, assuming 80% moisture content) is recommended to assess the site-specific effects of selenium to avian life in the environment. This alert level was based on reported selenium concentrations in avian eggs from contaminated (EC10 concentration) and uncontaminated environments
CCME did not recommend a water quality or a tissue (eggs) guideline to protect wildlife against the adverse effects of selenium.
The mean concentration of total selenium in irrigation water supplies should not exceed 10 µg/L.
The recommended guideline replaces the CCME (1987) guidelines of 20 µg Se/L for continuous use and 50 µg Se/L for the intermittent use on all soils.
To protect livestock water use, the mean concentration of total selenium in livestock water should not exceed 30 µg/L.
The recommended guideline replaces the CCME (1987) guideline of 50 µg Se/L.
Selenium is ubiquitous in the environment. Its impact on the environment depends upon several factors related to Se sources and environmental variability. Therefore, care must be exercised when the water quality guidelines are applied to assess environmental impacts of selenium.
Selenium is present in the environment in both organic and inorganic forms. In aquatic environments, dissolved selenium binds or combines with organic particulate matter and subsequently settles in the sediment. This is especially true in slow-moving water or a lake. Such environments can build up large deposits of organic-rich selenium that are conducive to further storage and remobilization of Se through the benthic-detrital food web and rooted plants. The water quality guidelines recommended in this document recognize this issue and, therefore, should be protective of aquatic life in lentic environments.
In fast-flowing waters (e.g., streams and rivers), however, accumulation of selenium through the food chain is often inefficient because of the lack of rooted plants and organic-rich sediment. Bioaccumulation of selenium from water alone is not considered to be as significant as from the food chain. Site-specific assessment of the environment (e.g., sediment selenium levels, etc.) may be desirable in such situations, since the recommended guideline may be over-protective.
The water quality guidelines recommended in this document are primarily based on data collected under controlled conditions, using species adapted to different climate conditions. Selenium has been shown to interact with other elements, which may result in reduced or enhanced Se toxicity. Also, the characteristics of organisms indigenous to British Columbia may differ from those of the species tested in the literature, with regard to selenium bioaccumulation potential and toxicity. Additional assessment techniques may be required to address such issues, including measurement of Se concentrations in fish and/or sediment and long-term bioassays with resident species using local waters. Long-term bioassays are complex and costly; they are likely to be undertaken for waterbodies with high resource values, which are threatened by controllable point sources of selenium pollution.
As noted above, selenium toxicity in aquatic environments depends upon many factors. Also, the potential for selenium bioaccumulation through the food web may vary in lentic and lotic environments. Furthermore, it has been noted that in certain natural environments fish can tolerate selenium concentrations that may exceed those found to be toxic in other environments or in the laboratory. Obviously, in such environments, there will be a need to develop site-specific water quality objectives to account for local environmental conditions. However, in a given watershed, both lotic (fast-flowing water) and lentic (still or slow-moving water) conditions can be found simultaneously. A site-specific water quality objective protective of the most sensitive environment should be preferred option in such situations.
When concentrations of selenium in undeveloped waterbodies are less than the recommended guidelines, then more stringent values, if justified, could apply. In some cases, socioeconomic or other factors (e.g., higher background levels) may justify objectives that are less stringent than the guidelines. Site-specific impact studies would be required in such cases.
The recommended sediment guideline assumed that sediment-Se and water column-Se content was related and was consistent at 5% total organic content (TOC). Obviously, this sediment-Se guideline may change as TOC changes. For lotic (rivers and streams) environments, an appropriate guideline may be calculated using the following relationship:
ln Sse = 0.657 [ln(Wse * TOC)] - 0.877
where ln is natural logarithm, Sse is selenium in sediment (µg/g dw), Wse is selenium in the water column (µg/L), and TOC is percent total organic carbon in sediment. The validity of this relationship in lentic (lake) environments has not been tested in the literature. As noted above, the use of this relationship is paramount on the sensitivity of the entire system, including the lakes and reservoirs.