Newsletter >> Winter 2018 >> As-Se speciation

A practical approach to arsenic and selenium speciation

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Robert Brunette

ROBERT BRUNETTE
Business Development Director, Eurofins Frontier Global Sciences


Arsenic and Selenium speciation is more important than ever as these measurements are being applied every day in a diverse number of applications from environmental and human health risk assessments, to inclusion in discharge permits in order to demonstrate compliance with new regulations. Further when exceeding regulatory effluent limits for Total As and Se, knowing the form or species of the Arsenic and Selenium can offer critical information to wastewater engineers in developing the most cost effective and efficient way to remove these metals from industrial sources.

A practical approach to As and Se Speciation: With the increasing number of projects requiring As and Se speciation measurements, the following are some important considerations when approaching this type of project:

1.   Measuring “Regulatory Recognized” Arsenic and Selenium Species: Keeping focus on the more regulatory recognized toxic species of Arsenic and Selenium can be very important to overall strategy and use of this data. The following species of Arsenic and Selenium have in general been widely recognized (through environmental and human health toxicological testing) and determined to be the more toxic, bio-available, bio-accumulative forms.

2.   Known As and Se Species vs. Unknown Species: Known species are those that have been documented using National Institute of Standards and Technology (NIST) traceable standards. “Unknown” As and Se species can be seen on the chromatogram as a peak but there are no standards and therefore no sure way to identify and quantify those forms with utmost accuracy. Measuring unknown forms can be both expensive, time consuming and generating data like this can later be requested by regulatory agencies and in some cases has created uncertainties that have held up permit renewal. Overall, it is always critical to consider measuring only the As and Se species that are required or requested by the regulatory agency.

The three peaks indicate, from left to right: Se(IV), Se(VI), and Selenocyanate.

3.   A Practical Approach To Estimating Unknown As and Se Species: In those cases where it does warrant the measurement of unknown As and Se species, if possible, consider first a more practical approach to first measure the more regulatory recognized forms of As and Se and then “estimate” the “other” known or unknown species by subtracting from the Total As and Se measured in the sample:
Total As – Estimated Total Inorganic As [ As(III) + As(V) ] = Estimated Organic As (or Other)
Total Se – Estimated Total Inorganic As [ Se(IV) + Se(VI) + SeCN] = Estimated Organic Se (or Other)
This approach can offer significant time and cost savings and help determine how important the “other” forms of As and Se are for your samples. For example, if the Total As – Total Inorganic = very small number, how important is it for your project to actually measure the known and unknown species that fall into this category?

4.   Using Known/Validated Arsenic and Selenium Speciation Methods: Non-validated methods for As and Se speciation can lead to both scientific defensibility and legal challenges later if the analysis methods are not promulgated/EPA methods. For regulatory required measurements of As speciation, Eurofins Frontier offers EPA 1632. For Se Speciation, we are not aware of any EPA methods; therefore it is critical that the laboratory offering this analysis have both years of experience and hold certification for the method that they offer. Eurofins Frontier offers our HPLC-ICP-MS Se Speciation method that we are IS0-17025 certified and another recognized technique that employs HPLC-UV-HG-AFS (pending ISO-17025 certification).

Eurofins Frontier Global Sciences serves as the worldwide Center of Excellence for trace metals and metals speciation. If you are interested to learn more about these methods, please contact Robert Brunette (RobertBrunette@EurofinsUS.com).