Selenium occurs naturally in metal sulfide ores and it’s a common byproduct of commercial operations that refine these ores. It is used for glassmaking and engineering pigments. While trace amounts of the element are critical for cellular function and can be found in many multivitamins, even infant formula, selenium becomes toxic if ingested in large amounts.
Selenium can be released into water resources naturally, through weathering, and by industrial activities like surface mining, coal-fired power plants, and irrigation. A new understanding of its potential to enter waterways and potentially harm wildlife has prompted the U.S. EPA to update the selenium criterion for its water quality standards.
“The 2016 criterion reflects the latest scientific information, which indicates that toxicity to aquatic life is driven by organisms consuming selenium-contaminated food rather than by being exposed only to selenium dissolved in water,” the EPA told Water Online. “States can adopt EPA’s recommended criteria, or alternative scientifically-sound approaches, as part of water quality standards to protect the designated uses of the water bodies.”
While the criterion is merely a recommendation, if municipalities do choose to adopt it there would be effects on local wastewater permitting requirements. Furthermore, selenium is currently under review by the EPA as it updates its ambient water quality criteria for the protection of human health and additional regulation may come. The EPA has also recently proposed federal selenium aquatic life criteria for the San Francisco Bay and the element fell under regulation for its 2015 effluent guidelines for the steam electric power generating industry.
The EPA released draft technical support documents in conjunction with its Clean Water Act update to help utilities adapt to its selenium recommendations. Among choices they will face will be how to determine selenium contamination.
“States and authorized tribes have some flexibility available to them when they adopt EPA’s 2016 selenium criteria,” the EPA said. “Options include deriving site-specific fish tissue criterion elements, adopting a performance-based approach for site-specific water column translations, adopting water quality standard variances, revising designated uses, providing for dilution allowances, and granting compliance schedules. The draft document related to adoption and implementation describes how each option can fit within a state’s or authorized tribe’s water quality standard adoption and implementation process.”
The EPA would like to see utilities adopt a four-part criterion, which now takes into account selenium’s presence in the food web, not just the water column as previous recommendations did. The criterion consists of two “fish tissue elements,” such as egg-ovary and whole-body, and two “water column elements,” such as average exposure over a month and intermittent exposure.
“The relationship between the concentration of selenium in the tissues of fish and the concentration of selenium in the water column can vary substantially among aquatic systems,” the EPA said. “Because of the site-specific nature of this relationship, EPA provided two methodologies for deriving site-specific water column translations as an appendix to the criterion document.”
Some municipalities should pay closer attention to selenium than others. According to the EPA, mining activities that lead to selenium release are most common in phosphate-rich areas of southeast Idaho, Wyoming, Montana, and Utah, and in coal mining areas of West Virginia, Kentucky, Virginia, and Tennessee. Soil that has high potential to leach selenium is found in the western U.S. and Great Plains regions and some groundwaters in California, Colorado, Kansas, Oklahoma, South Dakota, and Wyoming contain elevated concentrations of selenium.