Sorption of Radioactive Elements in Contaminated Soils and Sediments and Urban Structural and Other Materials

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Objectives for MPD B.8.2

  • Develop a rigorous, standard protocol for sequential extractions of radiologically contaminated soils, sediments, and urban structural and other materials.
  • Apply the standard protocol to produce NIST Standard Reference Materials (SRMs) certified for radionuclide fractionation.

Background: Extensive areas of soils and sediments have been documented as having significant radioactive contamination. It is critical to evaluate the sorption of the radionuclides to soils and sediments to assess the potential of mobilization through the ecosystem, evaluate the health risk to man, and to develop cost-effective strategies for environmental remediation. The “environmental transport and biological availability” of the relevant contaminating radionuclide species is a critical issue. There is a more pressing need to remediate sites where the radionuclides may be in more mobile physico-chemical forms than sites where the contaminants are known to be firmly fixed in the matrix. Recent studies have shown that the speciation of contaminating radio-elements plays a very important role in dictating whether a radionuclide may move into the environment and the food chain. How then does one measure environmental transport and bioavailability of contaminant radionuclides? Unfortunately, there is no widely ac-cepted method available for measurement of this parameter. On the other hand, numerous studies have been performed that involve use of various chemical extraction procedures for separating soil samples into several operationally defined fractions. The interpretation of where an ion appears in such a sequential extraction scheme is often used as a surrogate for the potential mobility of that radioelement in the environment and its bioavailability. In other words, one commonly interprets a species as “mobile” or “labile” if it is present in one of the early, less harsh, treatments in a typical sequential extraction series. A “refractory” label is often assigned should the analyzed material respond to one of the latter, more vigorous, treatments. Although these interpretations are somewhat qualitative in nature, the information is far more useful than simply reporting the total concentration of radioactive elements in samples.

Action Items:

1 – Conduct inter-comparisons using the extraction protocol to evaluate the reproducibility among laboratories.

2 – Initiate the certification of a new line of natural-matrix environmental SRMs for extraction of radionuclides. 3 – In support of the extraction protocol results, develop ab initio molecular orbital computations for radionuclides on mineral surfaces and interior planar positions to evaluate the energetics of the interactions.

4 - Develop surface contaminated urban materials (concrete, metal, glass, paper, marble, and other materials).

5 – Develop an expert consensus draft sequential extraction protocol to assess radionuclide mobility from urban materials.

6 – Optimize the sequential extraction protocol for assessing radionuclide mobility from urban materials.

7 – Develop suite of surface and volumetric radionuclide spiked Standard Reference Materials.

Resource Requirements:

1 – Two NIST full-time employees (FTE) are needed to conduct the Action Items above; ICP-MS support for stable element analysis, computational power for the ab initio computations. Estimated cost $100,000 per year over a 10 year period.

2 – Two full-time employees (FTE) at NIST to coordinate and conduct the certification of the new line of natural-matrix environmental and urban matrix SRMs for extraction of radionuclides. Estimated cost $350,000 per year over a 20 year period.

The study envisioned would consist initially of a relatively small group of professionals (approximately 4 6 scientists in three laboratories) over a period of 3 years. In the second stages of the investigation, several expert personnel and facilities would be brought into the project in an inter-laboratory comparison to evaluate the efficacy and reproducibility of the recommended protocol in different laboratories. The third phase would consist of the certification of benchmark radioactivity reference materials for community use.

Figure B.8.1 – Soil sampling for radioactive contamination

NOTE: In the CIRMS “Second Report on National Needs in Ionizing Radiation Measurements and Standards,” published in October, 1998, this MPD appeared as MPD B.5 and the related MPD B.3. A new MPD number has been assigned, MPD B.8, to avoid confusion with MPD B.5 that had appeared in the first CIRMS “Report on National Needs in Ionizing Radiation Measurements and Standards,” published in January, 1995, that covered a different topic, and MPD B.5 in the second report.