Recent regulatory changes and research findings are contributing to what we need to do and what we need to know to effectively manage selenium in mine waters. From the steady flow of information on selenium, we highlight a few that may be of interest to anyone involved with its management.
Update on Selenium Regulations in North America
In June 2016, the US EPA issued new selenium regulations to achieve the broad protection of aquatic life including fish, amphibians and invertebrates. Because fish are the most sensitive to selenium effects, the new regulations tie water column selenium limits to fish tissue based criteria.
Water column limits:
– 1.5 ppb for lentic
– 3.1 ppb for lotic
Fish tissue criteria:
– 8.5 mg Se per kg of dry weight of whole body
– 11.3 mg Se per kg of dry weight of muscle
– 15.1 mg Se per kg of egg/ovary
Water column limits will take precedence over fish tissue limits until it can be demonstrated that aquatic systems impacted by selenium discharges have reached a steady state.
New Selenium Science
Selenium can exist in many different forms in natural waters and industrial discharge. Selenium species can be inorganic or organic and contain the selenium atom at various oxidation states.
Recent research* completed by Professor Wallschlager’s group at Trent University in Ontario enabled the characterization of selenium species previously unreported by commercial laboratories. More importantly, the research also showed that biological treatment systems transform a portion of selenium undergoing treatment into organoselenium species.
It is well known that organoselenium species accelerate selenium bioaccumulation in fish tissue. It follows that the new research findings by LeBlanc et al., exposed a new risk with biological selenium treatment systems not previously considered by the industry and regulators: residual organoselenium in the treated water could cause more rapid bioaccumulation than the higher levels of selenium found in the raw untreated water.
Implications for Water Treatment
More work needs to be done to understand and quantify these risks. It is necessary to keep in mind that each site and receiving environment is unique. Conclusions about biological treatment and bioaccumulation from one site may not be readily transferable to another.
Similarly, the approach to selenium treatment must be site specific. Many factors go into determining whether a biological or active selenium removal treatment system is most applicable. Being armed with information will help in making that decision.
David Kratochvil, PhD, PEng
*LeBlanc, KL; Wallschlager, D. (2016). Production and Release of Selenomethionine and Related Organic Selenium Species by Microorganisms in Natural and Industrial Waters. Environmental Science and Technology. 50 (12), 6164-6171; DOI 10.1021/acs.est.5b05315