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Specialty Metals Analysis | Eurofins TestAmerica

Specialty Metals Analysis

How Can Eurofins TestAmerica Help You?

In addition to the many specialty tests described throughout our website site, Eurofins TestAmerica offers numerous non-routine test methodologies for metals analysis.  These tests include Acid Volatile Sulfide / Simultaneous Extracted Metals (AVS/SEM),  Sequential Extraction Procedure (SEP), and Physiological Based Extraction Test (PBET) for Bioassessible Arsenic (As) and Lead (Pb)For some projects, the ecological or human health risk can not be accurately measured by the total concentration of the metals alone. For other projects, the in an increased awareness of specific metals species requires specialized analysis.  Eurofins TestAmerica has been at the forefront of commercializing these specialize tests supporting our clients with these tests for many years. 

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Acid Volatile Sulfides/Simultaneously Extracted Metals (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 TestAmerica Pittsburgh 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:

Ratio of SEM>AVS (greater than 1)

Metals concentration exceeds that of sulfide, the metals are potentially bioavailable.

Ratio of SEM<AVS (less than 1)

Sulfide concentration exceeds that of the metals, the metals should not be bioavailable.

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 4oC as soon as possible after sample collection.

To support our clients with the goal of keeping the field samples anoxic,  Eurofins TestAmerica Pittsburgh 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 TestAmerica Pittsburgh can offer to support AVS/SEM on sediment cores sent to the laboratory when prearrangements have been made by clients. Eurofins TestAmerica Pittsburgh 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. 

Sequential Extraction Procedure Metals (SEP)

The use of natural attenuation as a remediation technique requires an understanding of the natural processes occurring at a site. For metals, natural attenuation typically involves a decrease in metal toxicity and/or mobility through dispersion, dilution, sorption and/or redox processes. A way to determine the geochemical fractionation of these metals in a laboratory scale operations is with the Sequential Extraction Procedure (SEP). Eurofins TestAmerica Knoxville has analyzed for as many as 23 different elements using this method. The data produced from this procedure are used for characterizing metal fate and transport, evaluating potential remedial alternatives for metal impacted soil, and estimating metal bioavailability for metals in soils or sediments. While this procedure cannot be used to identify the actual form of a given metal in a soil, it is useful in grouping metals into immobilization phases or fractions. 

Eurofins TestAmerica Knoxville is at the forefront of developing SEP for metals. A wide variety of SEP methods have been developed to target metals bound to specific functional fractions of soil and sediment.   Eurofins TestAmerica's SEP approach is a form of the consensus method for extraction developed by the National Institute of Standards and Technology (NIST) (Schultz, et. al., 1996).

Although the steps vary based on the data needs of each project there are seven potential steps in the SEP.  

The Seven Potential Steps for SEP Metals:

  • Step 1 – Exchangeable Fraction
  • Step 2 – Organic-Bound Fraction
  • Step 3 – Carbonate Fraction
  • Step 4 – Non-Crystalline Materials Fraction
  • Step 5 – Metal Hydroxide Fraction
  • Step 6 – Acid/Sulfide Fraction
  • Step 7 – Residual Fraction

The results obtained from the SEP are compared with the total metal levels. The cumulative concentration of metals extracted sequentially by the seven SEP steps generally agrees very well with the total metals results.

Quality control associated with Eurofins TestAmerica Knoxville’s SEP Analysis

Eurofins TestAmerica Knoxville developed a SEP method that incorporates the blank and check samples typically associated with a rigorous promulgated method. Eurofins TestAmerica’s Quality Assurance (QA) program is incorporated into the method to include the following quality control samples in each batch of samples prepared using the SEP: method blanks, laboratory control sample/laboratory control sample duplicates and a laboratory duplicate.

The SEP data allow our clients to evaluate the geochemical relationships that are used to understand the conditions under which contaminants may be released to the surrounding environment. SEP methods define each fraction based on the way in which metals are bound to the substrate and the types of metallic compounds that are formed. The advantage of the SEP for metals is that it provides a more holistic picture of metals chemistry in environmental media. SEP is most useful for sediments and sources in transitional states where understanding chemical form will aid in predicting fate, transport, and bioavailability.

Physiological Based Extraction Test (PBET) for Bioassessible Arsenic (As) and Lead (Pb)

The extent of arsenic and lead human health risk cannot be accurately assessed by total concentrations of the metals alone.  Bioassessability is an in vitro (performed outside a living organism) measurement of the physiological solubility of Arsenic and/or Lead that may be available to enter the body.  The physical and chemical properties of the metals, arsenic and lead, as well as the surrounding matrix will often decrease the human body's ability to absorb these metals.   

Bioaccessibility testing allows our clients to better consider the potential human health concerns of these metals. The bioaccessible concentration is defined as the maximal amount of contaminant that is released into a synthetic gastrointestinal fluid. This represents the physiological solubility of the metal that may be available for absorption into the body.

Eurofins TestAmerica Seattle performs the Physiological Based Extraction Test (PBET) test which follows our SOP based on the information from the Solubility/Bioavailability Research Consortium, EPA SW-846 Method 1340, and EPA 9200.2-86.

Summary of the PBET Method:

Soils are first dried and sieved.  Two different digestions are performed on the fines.  Total concentration is measured using conventional methods.  The in vitro procedure consists of an extraction fluid being introduced to soils thereby leaching lead and arsenic. The containers in which the fluid and soil are mixed are then placed in an apparatus that simulates gastric conditions. The extract produced is referred to as the bioaccessable fraction. Once completed, the solution is analyzed for lead and/or arsenic. The concentrations of lead and/or arsenic found in the extract are then compared to the concentration of the total metal int the fines, thereby producing a bioavailable ratio value.

Eurofins TestAmerica Seattle reports a percentage of Bioaccessible Arsenic as a ratio of the Bioaccessible Arsenic reported to the Total Arsenic on the fines.  Eurofins TestAmerica Seattle does not calculate the Relative Oral Bioavailability (RBA).

PBET References:

EPA Superfund website (https://www.epa.gov/superfund/soil-bioavailability-superfund-sites-guidance) for   “SOP for an InVitro Bioaccessibility Assay (IVBA) for Lead in Soil (EPA 9200.2-86 - April, 2012). 

EPA Superfund website (same as above) for Guidance for Sample Collection for IVBA for Lead in Soil ( EPA 9200.3-100 - March, 2015).  Note: 5 day drying time to a constant mass (constant mass is acceptable)

July 2016  EPA Memorandum which discusses fine sieving  (150 microns sieving: http://semspub.epa.gov/src/document/HQ/100000133) – this is less than the 250 micron sieving cited in the SOP IVBA and SW-846 EPA Method 1340, but is available if needed.  

EPA SW-846 Method 1340 (https://www.epa.gov/hw-sw846/sw-846-test-method-1340-vitro-bioaccessibility-assay-lead-soil) - Feb 2017

 

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