Selenium
(endorsed 2025)
Guideline
Based on health considerations, the concentration of selenium in drinking water should not exceed 0.004 mg/L.
General description
Selenium (Se) and selenium salts are widespread in the environment. Selenium is released from natural and human-made sources (such as the burning of coal). Selenium is also a by-product of the processing of sulfide ores, chiefly in the copper refining industry.
The major use of selenium is in the manufacture of electronic components. It is used in several other industries, and selenium compounds are used in some insecticides, in hair shampoos as an antidandruff agent, and as a nutritional feed additive for poultry and livestock.
Selenium copper alloys have also been identified as a potential replacement for lead copper alloys in plumbing products. Further information on lead replacements in plumbing products (such as selenium copper alloys) is available in Information Sheet 4.1 – Metal and metalloid chemicals leaching from plumbing products.
Selenium concentrations in drinking water source waters are generally very low and depend on local geochemistry, climatic conditions (e.g. drought), pH and the presence of iron salts. Selenium in water is mainly present as inorganic compounds, predominantly selenate.
Weathering of rocks and soil may result in low levels of selenium in water, which may be taken up by plants (SLR 2022). Food is the major source of intake for Australians. Cereal and grain products contribute most to intake, while fish and liver contain the highest selenium concentrations.
Typical values in Australian drinking water
In major Australian reticulated drinking water supplies, mean selenium concentrations are less than 0.0025 mg/L (SLR 2022). Some remote areas of Australia have recorded higher concentrations. For example, in 2004 mean values of selenium concentrations for various water supply systems in the Northern Territory ranged from 0.0005 – 0.015 mg/L, with the high values reported in Kings Canyon and Daly Waters (PWNT 2004).
Treatment of drinking water
Selenium concentrations in drinking water source waters can be reduced by a range of treatment options included but not limited to coagulation with ferric chloride and lime softening. Coagulation with alum is much less effective. Reverse osmosis and ion exchange resins are also treatment options. Activated alumina adsorption is an effective means of treatment, but only at a pH below 5. Removal of selenium in water can also be achieved through chemical clarification with ferric sulfate at a pH below 5 (WHO 2011). However, exposure to selenium in drinking water is most likely to occur past the point of water supply (i.e. the water meter) as any leaching of selenium from some lead-free plumbing products would most likely occur within premises (see Section 9.6; Information Sheet 4.1).
Measurement
Selenium can be measured in drinking water through inductively coupled plasma mass spectrometry (US EPA Method 200.8, 1994), inductively coupled plasma atomic emission spectroscopy (SLR 2022) or hydride generation followed by atomic absorption spectroscopy (APHA Method 3500-Se, 2023). The limit of reporting ranges from 0.0001 mg/L to 0.001 mg/L.
Health considerations
Selenium is an essential element for many species, including humans. Signs of selenium deficiency in humans are not well established but may include effects on the cardiovascular system, immune system, endocrine system and male reproductive system.
Selenium compounds are readily absorbed in humans. Selenium is metabolised in the liver then distributed to other organs and tissues such as the pancreas, nervous system, skin and hair, bone, muscle, lungs and kidneys. The toxicity of selenium may vary among the different selenium compounds and additional research may be required to clarify the importance of the chemical form on overall toxicity (SLR 2023).
There have been a number of reports of ill effects attributed to short- and long-term exposure to high levels of selenium. Most ill effects have resulted from occupational exposure (e.g. inhalation of dust) or accidental poisoning. Acute or chronic nutritional toxicity from selenium is comparatively rare. Nutritional toxicity results when an excessive amount of a specific nutrient is consumed which leads to adverse health effects.
Selenosis is known to occur in humans from supplemental intakes of selenium of 0.2 - 40.8 mg/day (Aldosary et al. 2012; Lippman et al. 2009; MacFarquhar et al. 2010). A large long-term human clinical trial (HCT) study (over 34,000 men) investigated the effects of selenium supplementation (0.2 mg selenium per day) and/or Vitamin E supplementation over a 4 to 7-year period on the development of certain cancers (Lippman et al. 2009). The study identified a marginally statistically significant increase in the rate of mild dermatitis and alopecia (an early indication of selenosis) in patients taking selenium. This study was also used by the European Food Safety Authority (EFSA) to establish a tolerable upper intake level for selenium of 0.255 mg/day for adults from total dietary sources (EFSA 2023). This level was defined by EFSA as the maximum level of total chronic daily intake of a nutrient (from all sources) which is not expected to pose a risk of adverse health effects to humans.
Studies in humans suggest that there is no association between exposure to selenium and mortality from cardiovascular disease, coronary heart disease or stroke. There is limited evidence around an association between selenium and an increase in prostate cancer at supplemental doses of 0.2 - 0.4 mg/day, and a possible association with Type 2 diabetes at supplemental selenium doses from 0.055 - 0.2 mg/day. A review found that there is insufficient evidence to indicate an association between selenium and several other health outcomes, such as mortality from Parkinson’s disease, increased cholesterol, amyotrophic lateral sclerosis, melanoma, urinary tract tumours, or multiple myeloma (SLR 2023).
A review found that selenium compounds may be genotoxic within in vivo and in vitro systems, at doses that cause other adverse health effects (SLR 2022). Except for selenium sulfide, experiments with laboratory animals indicate that selenium compounds are not carcinogenic, with some selenium compounds potentially displaying an anticarcinogenic effect. Results for selenium sulfide indicate that it causes liver and lung tumours in mice. The International Agency for Research on Cancer has concluded that selenium is not classifiable as to its carcinogenicity in humans (Group 3, inadequate evidence in humans and in animals) (IARC 1987).
Derivation of guideline
The health-based guideline value of 0.004 mg/L (rounded) for selenium in drinking water was derived as follows:
where:
0.255 mg/day is the adjusted minimal lowest observed adverse effect level (LOAEL) for mild selenosis (alopecia and dermatitis) in adult males receiving supplementary selenium in the diet (Lippman et al. 2009). The minimal LOAEL for mild selenosis of 0.2 mg/day as added selenium was adjusted by adding this to the dietary selenium intake likely to have been ingested by the adult male participants in the study (i.e. 0.055 mg/day, which is the normal recommended amount of selenium in the North American diet to prevent selenium deficiency as reported in NIH (2021)) (SLR 2023).
0.1 is the proportion of daily intake attributable to the consumption of water.
2 L/day is the average amount of water consumed by an adult.
3 is the safety factor applied as the effect was mild and the LOAEL is a minimal LOAEL. Consideration was given to balancing the essentiality of selenium with the potential for adverse effects. An uncertainty factor for human variability was not included as the study included a large population of 8,752 adult males and there is no indication that females or children are more susceptible to the effects of selenium.
The calculated value of 0.00425 mg/L is rounded to a final health-based guideline value of 0.004 mg/L as per the rounding conventions described in Chapter 6.
Review history
The fact sheet was initially endorsed in 1996. This update of the fact sheet was based on reviews of the available evidence completed in 2022 and 2023 (SLR 2022, 2023; see Administrative Report for more information).
References
Aldosary BM, Sutter ME, Schwartz M, Morgan BW (2012). Case series of selenium toxicity from a nutritional supplement. Clinical Toxicology, 50(1):57–64.
EFSA (European Food Safety Authority) (2023). Scientific opinion on the tolerable upper intake level for selenium. EFSA Journal, 21(1): e07704. https://doi.org/10.2903/j.efsa.2023.7704
IARC (International Agency for Research on Cancer) (1987). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: Overall Evaluations of Carcinogenicity. An updating of IARC monographs volumes 1 to 42. World Health Organization, IARC, Supplement 7.
Lippman SM, Klein EA, Goodman PJ, Lucia MS, Thompson IM, Ford LG, Parnes HL, Minasian LM, Gaziano JM, Hartline JA, Parsons JK, Bearden JD III, Crawford ED, Goodman GE, Claudio J, Winquist E, Cook ED, Karp DD, Walther P, Lieber MM, Kristal AR, Darke AK, Arnold KB, Ganz PA, Santella RM, Albanes D, Taylor PR, Probstfield JL, Jagpal TJ, Crowley JJ, Meyskens FL Jr, Baker LH, Coltman CA Jr (2009). Effect of selenium and vitamin E on risk of prostate cancer and other cancers: the Selenium and Vitamin E Cancer Prevention Trial (SELECT). Journal of the American Medical Association, 301(1):39–51.
MacFarquhar JK, Broussard DL, Melstrom P, Hutchinson R, Wolkin A, Martin C, Burk RF, Dunn JR, Green AL, Hammond R, Schaffner W, Jones TF (2010). Acute selenium toxicity associated with a dietary supplement. Archives of Internal Medicine, 170(3):256–261.
NIH (2021). Selenium Fact Sheet for Consumers. National Institutes of Health, US Department of Health and Human Services. Updated March 22, 2021.
SLR (2022). Evidence Evaluations for Australian Drinking Water Guideline Chemical Fact Sheets –Selenium Technical Report. SLR Consulting Australia Pty Ltd. Report prepared for the National Health and Medical Research Council, May 2022.
SLR (2023). Evidence Evaluations for Australian Drinking Water Guidelines Chemical Fact Sheets – Lead Replacements in Plumbing – Selenium Evaluation Report. SLR Consulting Australia Pty Ltd. Report prepared for the National Health and Medical Research Council, November 2023.
Standard Methods Committee of the American Public Health Association (APHA), American Water Works Association, and Water Environment Federation (2023). 3500-Se Selenium In: Standard Methods For the Examination of Water and Wastewater. Lipps WC, Baxter TE, Braun-Howland E, editors. Washington DC: APHA Press.
US EPA (1994). Method 200.8: Determination of Trace Elements in Waters and Wastes by Inductively Coupled Plasma-Mass Spectrometry, Revision 5.4. Cincinnati, OH.
WHO (2011). Selenium in Drinking Water. Background document for development of WHO Guidelines for Drinking-water Quality. World Health Organization.
NOTE: Important general information is contained in PART II, Chapter 6.
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