The topic of selenium has garnered attention in various industries for decades now, but the challenge associated with removing selenium from wastewaters has not diminished. In order to understand the most effective form of treatment for this unusual element that is both an essential micronutrient but also toxic at relatively low concentrations, the molecular form, or speciation, of selenium must be understood.
The two most common inorganic forms present in industrial wastewaters and agricultural runoff are selenite and selenate. Numerous treatment options are available for selenite, but conventional options like iron co-precipitation are ineffective for selenate. Several reviews have identified biological treatment as one of the best options for selenate removal, in part because it is cost-effective and has been proven in full-scale installations. Therefore, it is prudent for industries needing to implement selenium treatment and collaborative service providers to characterize waste streams via speciation analysis before and during bench- or pilot-scale studies.
Systems for biological treatment of selenium-laden waters take many forms, but anaerobic bioreactors are one of the most common iterations. In most of these systems, reduction of selenite and selenate to elemental selenium (Se0) is the desired outcome. This elemental selenium is mostly insoluble and can be removed from the effluent via filtration or temporarily retained in the reactor until backflushing of the system can be performed. Well-maintained and optimized bioreactors have been shown to treat industrial wastewaters containing mg/L concentrations of selenium down to single-digit µg/L levels.
Depending on the bacterial strains involved, the chemical environment, proper operation and maintenance, and the availability of nutrients, other less-desirable selenium species may be formed by bioreactor systems. Figure 1 shows a chromatogram of an effluent from a bioreactor used to treat a wastewater initially containing only selenite and selenate. Of particular note are the appreciable concentrations of the reduced selenium species, selenosulfate and selenocyanate (SeCN), as well as the organic selenium species that are present. While the toxicity of all these species have not been fully characterized and their bioaccumulation can be influenced by other constituents in the water, it has been shown that the bioavailability of certain species like selenomethionine can be several orders of magnitude higher than those of inorganic selenium.
The SETAC North America 39th Annual Meeting will be held in Sacramento November 4-8 this year. Come learn more about the unexpected ways alligators can potentially cause you harm you when Elizabeth Madonick, BAL Technical Services Specialist, presents a poster on the concentrations of total mercury and methylmercury in alligator meat on Tuesday, November 6th! Contact us any time after November 8th if you would like to receive a PDF copy of this interesting research.
The same week, Russ Gerads and Jamie Fox will be attending the International Water Conference in Scottsdale, Arizona. Jamie will be presenting on “Compliance with Selenium Aquatic Life Criterion and the Importance of Speciation for Treatment Selection and Monitoring” during the session on Trace Contaminants: Detection, Removal, and Recovery on November 5th. If you are interested in receiving a copy of this presentation, please feel free to contact us after November 12th.
Inductively coupled plasma mass spectrometry (ICP-MS) is a powerful and efficient tool for the determination of low-level metals; however, the high salt content of seawater can lead to elevated method detection limits and inaccurate results. Several methods have been developed that utilize reaction-based chemistry (e.g., hydride generation and coprecipitation) to remove selenium from the saline matrix prior to analysis. Trace-level detection limits have been achieved with these methods; however, reaction-based chemistry has inherent limitations and is susceptible to interferences from elevated concentrations of common constituents found in seawater and procedural inefficiencies.
The need to improve method robustness, reduce operational costs, and increase data quality motivated BAL scientists to generate this new method to meet both our client’s needs and the needs of regulatory agencies around the world. As part of our commitment to quality, BAL’s new method has undergone extensive validation confirming both inorganic and organic molecular forms of selenium are represented in our results, making it a truly species-independent quantitative approach.
Monitoring elements at environmentally-relevant concentrations in seawater is critical for developing accurate environmental assessments and evaluating the effectiveness of various pollution controls. BAL’s improved methodology allows for an unprecedented level of data quality at concentrations as low as just a few parts-per-trillion.
If you would like to learn more about trace-level selenium quantitation in saline samples, contact us!
Efficient selenium treatment and understanding ecological risks associated with the contaminant requires detailed molecular information to make educated decisions. As with any element, the molecular form of selenium, or chemical species, dictates how the element will interact with the environment and respective organisms. To support the increasing demands of the marketplace, Brooks Applied Labs continues to expand the suite of selenium species our proprietary methods can quantitate. Two organic selenium species, dimethylselenoxide and methaneselenonic acid, have been added to our capabilities to allow our clients to better understand the bioaccumulation of selenium and risk to the relevant aquatic habitats.
More than a dozen selenium species have been identified in both natural and anthropogenically-impacted waters, including volatile forms like dimethylselenide and reduced forms like selenocyanate. As analytical technology advances, more information regarding the complexity of selenium chemistry is available. This is especially important in situations where biological activity can produce complex organic selenium species, as found in natural environments as well as bioreactor treatment systems. Government agencies in North America and other parts of the world are increasing their understanding regarding the implications of the different molecular forms of selenium and have already implemented regulations accordingly.
BAL currently supports the identification and quantitation of the following selenium species:
- Methylseleninic acid
- Methaneselenonic acid
- Selenomethionine oxide
- Elemental selenium
- Other more esoteric selenium species
When you work with Brooks Applied Labs, you not only benefit from our state-of-the-art instrumentation and robust methods, but also from our experienced staff who can provide guidance regarding how your data objectives align with today’s technology. Including speciation analyses alongside more traditional total elemental analyses can provide you with greater confidence in your data, particularly when the results of these two separate analyses agree. And in cases where the two analyses may differ, our staff will work with you to interpret the results and recommend alternative approaches to identify the source of the discrepancy. To learn more about how partnering with Brooks Applied Labs can help ensure the success of your project, please contact us today!