AVS/SEM

Acid Volatile Sulfide/Simultaneous Extracted Metals (AVS/SEM) is a method for sulfide and associated metals in sediment or soil.  Sulfide is a precipitant of heavy metals and is important in controlling the bioavailability of metals in sediment and soil. The relative amounts of SEM and AVS are important in controlling the potential metals bioavailability.

Eurofins analyzes AVS/SEM using U.S. EPA Draft Method, “Determination of Acid Volatile Sulfides and Simultaneously Extractable Metals in Sediment”, EPA-821-R-91-100.  Since the relative amounts of AVS and SEM are important in the prediction of potential metal bioavailability, it is important to use the SEM procedure for sample preparation for metal analysis. AVS are the sulfides removed by the cold acid extraction consisting mainly of hydrogen sulfide and iron sulfide.  The SEM are the selected metals that are solubilized during the acidification step used to determine the AVS. Since this method uses the same conditions for release of both sulfide and metal from the sediment, it provides the most predictive means of assessing the amount of metal associated with the sulfide.

With this method, if the molar concentration of Acid Volatile Sulfide (AVS) exceeds that of the Simultaneously Extracted Metals (SEM) then the metals precipitate and should not be potentially bioavailable. In summary:

Sample collection, preservation and storage are critical for samples collected for AVS/SEM.  The sulfide ion is unstable in the presence of oxygen and therefore sediment samples must be protected from exposure to oxygen during sample collection and storage.  Sediment samples should be collected in wide mouth jars with zero headspace.  The samples should be cooled to 4^oC as soon as possible after sample collection.

To support our clients with the goal of keeping the field samples anoxic,  Eurofins can provide alternative method collection and / or sample handling procedures to minimize exposure of the samples to oxygen from the field collection to the shipment to the laboratory.

Eurofins can offer to support AVS/SEM on sediment cores sent to the laboratory when prearrangements have been made by clients. Eurofins offers this option of processing sediment core samples in a glove-box under nitrogen conditions.  For each project, the client works with the laboratory to define the project specifications.  These specifications would include:

• the number, diameter and length of cores,
• discussion of the vertical shipment sediment cores to the laboratory,
• documentation of the project specific sediment core sub-sampling procedures, and
• cost estimate for sediment core handling.

We also can provide alternate sample collection devices using syringes to collect samples in the field to minimize their exposure to air.