Return to Standards Table

SELENIUM
CASRN: 7782492

Update: March 1996

Current Massachusetts Regulatory Limit
MMCL: 0.05 mg/L. ORS has adopted the MCL published by the U.S. EPA (56 FR 3256 (1/30/91).

Federal Regulatory Limit
The MCL of 0.05 mg/L is equal to the MCLG of 0.05 mg/L.

Basis for Criteria
The MCLG is based on the RfD presented below and assumes that a 70 kg adult ingests 2 L/day of drinking water. A relative source contribution factor of about 40% (estimated from human intake data as described below) is incorporated into the final value.

RfD: 3 x 10-3 mg/kg/day *
UF: 15 MF: 1

Since selenium is an essential element, U.S. EPA feels that applying an uncertainty factor of 100 or greater to the LOAEL cannot be justified as it would result in a value below that considered safe and adequate by the National Academy of Science (NAS) (i.e., 0.05 mg/day) and thus may not protect against adverse effects resulting from selenium deficiency. The factor of 15 is judged to provide a balance between the potential deficiency and toxicity effects of selenium (54 FR 22062).

Based on the above RfD, a total acceptable selenium intake per day for a 70 kg adult may be calculated as 0.003 mg/kg/day x 70 kg, or approximately 0.210 mg/day. As discussed below, dietary selenium intake is 0.125 mg/day. Since it is assumed that exposure to selenium via inhalation is zero, by subtraction, 0.210 mg/day - 0.125 mg/day leaves about 0.085 mg/day. The ratio 0.85 mg/day/0.210 mg/day is approximately equal to 40%.


* This RfD was derived from the information used to derived the Adjusted Acceptable Daily Intake (AADI) value of 0.106 mg/L. In the first step of this derivation, a LOAEL of 3.2 mg/kg/day was divided by an uncertainty factor of 15 to get an allowable dose in mg/day. To express this dose in mg/kg/day (thus analogous to the definition of an RfD), this value was divided by a default body weight of 70 kg.


Critical Effects
Selenium is toxic at high doses and is an essential element in the low dose range. In animals, a level of 0.1 mg selenium per kg food has been considered to be the general level of dietary requirement (56 FR 3526). The NAS (1989) has determined a recommended daily allowance for selenium of 55 and 70 mg/day for North American females and males, respectively. Dietary intake of selenium in the United States is approximately 0.125 mg/person/day.

Signs of selenium toxicity (selenosis) include liver dysfunction, hair and nail loss.

A human study examined selenium toxicity and deficiency effects in an area of China with unusually high environmental concentrations of selenium. The minimum daily intake in an area of chronic selenosis was 3.2 mg. This level was identified as the LOAEL of this study (Yang et al., 1983). In a subsequent study also conducted in China, the same investigators also propose that 0.400 mg selenium per person per day is a maximal daily intake of selenium (Yang et al., 1989).

Cancer Assessment: D
Data are currently inadequate in both animals and humans for the classification of selenium as a carcinogen.

Class
Inorganic, heavy metal

Analytical Information
PQL
: 0.01 mg/L

Analytical Methods
U.S. EPA 270.2; Atomic absorption spectrophotometry

PQLs and analytical methods may have been updated since this guidance value was last revised. Updated analytical methods for drinking water and their associated PQLs may be found at http://www.epa.gov/safewater/methods/methods.html.

Other Regulatory Data
Any Health Advisories, Reference Doses (RfDs), cancer assessments or Cancer Potency Factors (CPFs) referenced in this document pertain to the derivation of the current guidance value. Updated information may be obtained from the following sources:

Health Advisories - The U.S. EPA provides guidance for shorter-term exposures for chemicals based on their non-cancer effects. Current health advisories may be more current than those used to derive MCLs and may be found at http://www.epa.gov/waterscience/drinking/standards/dwstandards.pdf.

RfDs, cancer assessments and CPFs - For specific information pertaining to derivation of drinking water criteria, consult the Federal Register notice that announces the availability of the most current guidance for that chemical. In addition, information on other current RfDs and CPFs as well as cancer assessments for specific chemicals may be found in the U.S. EPA Integrated Risk Information System (IRIS) at http://www.epa.gov/iris/. Please note that the information in IRIS may differ from that used in the derivation process as published in the Federal Register notice.

References
Federal Register. November 13, 1985. Part IV. Environmental Protection Agency. 40 CFR Part 141. National Primary Drinking Water Regulations; Synthetic Organic Chemicals, Inorganic Chemicals and Microorganisms; Proposed Rule. (50 FR 46936).

Federal Register. May 22, 1989. Part II. Environmental Protection Agency. 40 CFR Parts 141, 142, and 143. National Primary and Secondary Drinking Water Regulations; Proposed Rule. (54 FR 22062).

Federal Register. January 30, 1991. Part II. Environmental Protection Agency. 40 CFR Parts 141, 142, and 143. National Primary Drinking Water Regulations; Final Rule. (56 FR 3526).

NAS (National Academy of Sciences). 1989. Recommended Dietary Allowances, 10th ed. National Academy Press, Washington, DC. p. 217-224.

Yang, G., et al., 1983. Endemic Selenium Intoxication of Humans in China. American Journal of Clinical Nutrition. 37:872-881.

Yang, G., S. Yin, R. Zhou, et. al. 1989. Studies of safe maximal daily dietary Se-intake in a seleniferous area in China II. Relation between Se-intake and the manifestation of clinical signs and certain biochemical alterations in blood and urine. J. Trace Elem. Electrolytes Health Disc. 3(2):123-130.