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Example of field-portable XRF instrumentation
Example of field-portable XRF instrumentation

Rapid Sediment Characterization
(RSC) Tools


> Introduction
> Benefits and Limitations
> Basic Operation
> Demonstrated Uses
> Project Description: Hunters Point Shipyard, CA
> Summary
> References
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Introduction

Because traditional sampling and analysis methods for marine ecosystems do not always provide the information needed for decision making in a timely and cost-effective manner, rapid characterization methods have been developed to speed up site characterization and to reduce its cost. The Environmental Sciences Branch at the Space and Naval Warfare Systems Center, San Diego (SSC San Diego) has developed, tested, and implemented different rapid sediment characterization (RSC) tools and/or methodologies at several Navy marine sediment sites, including Naval Air Station Alameda, CA, Puget Sound Naval Shipyard, WA, and Hunters Point Shipyard, CA. RSC tools are field-transportable and/or laboratory screening tools that measure chemical, biological, or physical parameters on a near real-time basis. The cost-effective collection of data at contaminated marine sites is often hindered by the heterogeneity and complexity of marine ecosystems. Implementing RSC methods at different stages during a site investigation can help focus sampling requirements and facilitate achieving timely and cost-effective results. When used appropriately, these tools can streamline many aspects of the Remedial Investigation/Feasibility Study (RI/FS) process, can be used to support Advanced Chemical Fingerprinting (ACF) studies [1], and can be used to support monitoring programs (see Demonstrated Uses section).

A wide variety of RSC tools can be deployed on site or used in the laboratory to provide rapid, semi-quantitative results. Primary RSC tools and their typically targeted contaminants or parameters include:

  • X-Ray Fluorescence (XRF) spectrometry for metals
  • Immunoassays for polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and pesticides, and
  • Bioluminescent bioassays (e.g., QwikSed bioassay) to estimate toxicity

These rapid sediment characterization (RSC) methods can be used to generate semi-quantitative results on site within minutes or hours, rather than the several days or weeks that other methods require. Also, most of the RSC methods can be used to perform on-site analyses on 10 or more samples per unit per day, which reduces the number of samples needed for analysis at an off-site laboratory. These tools can be used independently or in conjunction with one another, depending upon data requirements and project objectives.

Benefits and Limitations

The major benefits of using RSC methods are that they provide rapid results at a reduced cost compared to standard laboratory analyses, and can improve sampling in general by reducing uncertainty while avoiding the cost of repeated or multiple resamplings; however, because RSC methods are less sensitive than standard laboratory analysis, the data generated using the methods are not equivalent to those generated by standard laboratory analyses. In general, data generated using standard analytical methods (such as U.S. EPA-approved reference methods [i.e., SW-846]) are classified as "definitive data," whereas data generated using rapid, less precise methods of analysis (such as RSC methods) are classified as "screening data." Screening data for organic compounds are semi-quantitative at best, and generally are not contaminant-specific. (Metals analysis by XRF is element-specific, but semi-quantitative nonetheless). Overall, depending on data quality requirements, a well-designed RSC protocol paired with laboratory validation can provide data of sufficient quality (i.e., screening data with definitive confirmation) to support decision-making.

Basic Operation

X-Ray Fluorescence (XRF)

XRF measures the fluorescence spectrum of x-rays emitted when metal atoms are excited by an x-ray source. The energy of the emitted x-rays identifies the metals in a sample, and the intensity of the emitted x-rays indicates their concentration (Figure 1). XRF can identify a wide range of elements from sulfur through uranium, encompassing typical elements found in soils and sediments. Field-portable XRF instruments provide near real-time measurements with minimal sample handling, and thus allow for extensive semi-quantitative analysis on site. Benchtop XRF instruments, although not field-portable, can be used in the laboratory for rapid semi-quantitative analysis of samples as well as for quantitative analyses. In both cases, reasonably low detection limits usually can be achieved. Detection limits are different for each element. For common metals such as lead, zinc, and copper, detection limits using a field-portable XRF unit typically range from 50 to 150 parts per million (ppm). Lower detection limits can be achieved using laboratory, benchtop XRF systems (e.g., Cu and Zn: 20 ppm; Pb: 10 ppm, in wet sediments) [2 and 3]. Analysis time typically requires 2-5 minutes per sample. Commercial XRF instruments are readily available for purchase or lease.

FIGURE 1. Physics of XRF Technology.
FIGURE 1. Physics of XRF Technology.

XRF technologies have been demonstrated and used as a screening tool for over a decade. The EPA carried out a Superfund Innovative Technology Evaluation of XRF Technologies (Evaluation of Field Portable X-Ray Fluorescence Technologies) [4] in 1995 and again in 2005 (XRF Technologies for Monitoring and Measurement for Soil and Sediment) [5]. A Certified EPA Method (Method 6200) specifies the use of XRF as a screening method for analysis of metals by field-portable XRF on dry soil and sediment [6]; however, the use of XRF as a screening tool for wet marine sediments was not fully verified until an Environmental Security Technology Certification Program (ESTCP) project demonstrated good results from XRF analyses of unprepared wet sediment [7].

Immunoassays (IA)

The most common environmental immunoassay is the enzyme-linked immunosorbent assay. This method uses antibodies (i.e., proteins produced by mammalian immune systems) and enzyme conjugates (i.e., enzymes that bind with contaminants of concern [COCs]) to detect and quantify target compounds in field samples. The predominant enzyme used in enzyme conjugation for immunoassays is horseradish peroxidase. In this method, the enzyme portion of an enzyme conjugate serves as a catalyst to change a colorless compound to a measurable colored product that can be detected using a photometer or fluorometer. As COCs leave the enzyme conjugates to bind to the antibody sites, the amount of enzyme conjugate available to catalyze the color reaction gradually decreases. (Figure 2 is a schematic of how the COC part of an enzyme conjugate binds with antibody sites). In effect, the amount of contaminant present in the sample is proportional to and inverse of the color intensity detected by a photometer or fluorometer.

FIGURE 2. Schematic of COC-Enzyme Binding (Source: U.S. EPA, 1996) [8]
FIGURE 2. Schematic of COC-Enzyme Binding (Source: U.S. EPA, 1996) [8]

Detection limits for different compounds (PAHs, PCBs, pesticides) typically range from 0.1 to 1 mg/kg for most commercial applications. Detection limits for PAHs and PCBs, the more commonly measured constituents in marine sediment, are approximately 0.5 mg/kg for PAHs and range from 0.1 mg/kg to 0.2 mg/kg for PCBs depending on the sediment matrix (sand versus silt) and the presence of other contaminants [2 and 9]. Several test kits are commercially available and range in cost from $10 to $40 per sample per kit.

QwikSed Bioluminescent Sediment Toxicity Test

The Navy developed a rapid bioassay system (QwikSed) for conducting contaminated sediment toxicity tests. Toxicity is measured as a reduction in light emitted from a bioluminescent dinoflagellate, such as Gonyaulux polyedra or Ceratocorys horrida, following exposure to a toxicant. Figure 3 shows a schematic of the bioassay procedure.

FIGURE 3. Schematic of the QwikSed bioassay.
FIGURE 3. Schematic of the QwikSed bioassay.

A measurable reduction or inhibition in bioluminescence is an adverse effect and suggests the presence of bioavailable contaminants and other stressors. The toxic response is usually measured within 24 hours from the start of the test and can be conducted for a 4-day acute test or a 7- to 11-day chronic test. The endpoint used to measure light reduction is the inhibition concentration 50 (IC50), a 50 percent reduction in light output when compared to controls.

QwikSed bioassays can evaluate both acute and sublethal chronic effects from exposure to a variety of toxicants. The dinoflagellates in the QwikSed bioassay are at least as sensitive to organic and inorganic toxicants as mysid shrimp, silverside fish, chain diatoms, and sea urchins. The data from the QwikSed bioassay can be correlated with more conventional toxicity tests, such as amphipod and sea urchin development [2 and 10]. This system (also know as QwikLite™) has been commercialized [11] and can be used for several different applications, including landfill leachate assessment, water treatment monitoring, and effluent assessment (see QwikLite™ 200 Testing System).

Demonstrated Uses

Location Year RSC Tools/COC Purpose
Eagle Harbor   2006 IA (PAHs) Collaborative effort with EPA - long term monitoring of remedial capping effort.
NAF El Centro 2006 FPXRF (metals), IA (PAHs) Identify potential IR sites, pre-RI stage in RI/FS process.
NAB San Diego 2005 FPXRF (metals), IA (PAHs, PCBs) Identify potential sediment contamination, pre-RI stage of RI/FS process.
Quantico Marine Base 2005 FPXRF (Pb), IA (DDT) Identify potential sediment contamination, pre-RI stage of RI/FS process.
Skaggs Island Naval Facility 2004 FPXRF (Pb), IA (DDT) Support remedial monitoring during a removal action at a former dumpsite (guide step-outs during each phase of removal and compositing scheme).
Duwamish River 2004 IA (PCBs) Collaborative work with ACoE (Seattle field office) to guide dredge area delineation.
NAVSTA San Diego - Paleta Cr IR Sites 3&4 2004 EDXRF (metals), IA (PAHs, PCBs, DDTs) Identify potential sediment contamination, pre-RI stage of RIFS process.
Allen Harbor 2004 EDXRF (metals), IA (PAHs) Fingerprint PAH sources as part of FS (RSC used as initial screening of samples).
Hunters Pt. Naval Shipyard 2001-2003 EDXRF (metals), IA (PCBs) Delineate sources as part of BERA and FS.
New London Sub Base 2003 EDXRF (metals), IA (PAHs, PCBs) Identify potential sediment contamination, pre-RI stage of RI/FS process.
Elizabeth River 2003 IA (PAHs) Initial screen for fingerprinting projects.
Sinclair and Dyes Inlet (Puget Sound Naval Shipyard) 2003 IA (PCBs) Support Total Maximum Daily Load (TMDL) Study
Sinclair and Dyes Inlet (Puget Sound Naval Shipyard) 2002 EDXRF (metals) Support Total Maximum Daily Load (TMDL Study for Project ENVEST
Pearl Harbor Naval Shipyard 1999 FPXRF (metals), *UVF (PAHs), QwikSed (toxicity) ESTCP Site Demonstration 2
NAS Alameda 1997 FPXRF (metals), *UVF (PAHs), QwikSed (toxicity) ESTCP Site Demonstration 1

IA: Immunoassay; FPXRF: Field-Portable XRF; EDXRF: Energy-Dispersive XRF (Benchtop Unit) *UVF: UV Fluorescence Technique has been replaced with Immunoassay technique

Project Description: Hunters Point Shipyard, CA

Two RSC tools were used for a sediment screening study at Hunters Point Shipyard (HPS) to support a Baseline Ecological Risk Assessment (BERA) sampling design [2 and 12]. Surface sediment samples were collected in a grid pattern from 94 locations in the five offshore areas of concern. Samples were screened for PCBs using immunoassays and for heavy metals using X-ray fluorescence spectrometry at the SSC San Diego laboratory. The results were used to refine the sampling design for a more detailed study of sediment chemistry, toxicity, and bioaccumulation. In particular, screening results were used to ensure that the baseline assessment study sampling stations span the entire range of contaminant concentrations and, therefore, represent the full range of potential exposure. Ten percent of the screening samples were submitted to a standard analytical laboratory to obtain a quantitative analysis of all contaminants of concern, to verify screening results, and to provide additional surface sediment data supporting the assessment study.

In order to evaluate fully the extent of contaminant distribution at the Hunters Point site, SSC researchers examined the screening results for PCBs, copper, lead, zinc, and chromium. Review of the spatial analysis of historical and screening data at HPS revealed that contaminant distributions within the low-volume footprint were structured spatially. High values were found together rather than randomly distributed. This finding confirmed that sediments in near-shore areas were potential source terms and that these areas might be from a different "population" than sediments farther away from shore. For example, the PCB results from one of the areas of concern indicate two potential source areas for elevated PCBs in the offshore sediments—one on the northeast side and another on the west side of the embayment (Figure 4). Implementation of the RSC methods provided a cost-effective means to obtain the necessary spatial coverage to determine the existence of contamination contours, so that a focused sampling design could be developed.

FIGURE 4. Immunoassay screening results from Hunters Point Shipyard compared to a site-specific bioaccumulation benchmark.
FIGURE 4. Immunoassay screening results from Hunters Point Shipyard compared to a site-specific bioaccumulation benchmark.

Summary

RSC tools can streamline many aspects of site investigations, but RSC methods and tools are not necessarily subject to the same quality assurance/quality control protocols, nor are they as sensitive as standard laboratory methods. The method(s) by which users interpret and manage RSC data, therefore, must be addressed by regulators and stakeholders early in the characterization process. Generally, regulators and the user community have accepted RSC results as part of the analytical results in the decision-making process but not as stand-alone data. For these reasons, RSC tool results should be balanced with and supplemented by standard certified laboratory analyses.

References

  1. Space and Naval Warfare Systems Center San Diego (SSC SD). 2003. A Users Guide for Determining the Sources of Contaminants in Sediments. Technical Report 1907. September. http://www.ert2.org/chemicalfingerprinting/guidancedoc.pdf
  2. Battelle. 2001. Guide for Using Rapid Sediment Characterization Methods in Ecological Risk Assessments, Prepared for Naval Facilities Engineering Service Center and Space and Naval Warfare Systems Center San Diego, June 29. http://enviro.nfesc.navy.mil/erb/erb_a/restoration/technologies/invest/fld_chem/
    rsc_guide.pdf
  3. Naval Facilities Engineering Command (NAVFAC). 2000. Rapid Characterization of Metals in Sediments Using X-Ray Fluorescence (XRF) Technology. NFESC TDS-2076-ENV, February. http://costperformance.org/monitoring/pdf/xrf_2.pdf
  4. PRC Environmental Management, Inc. 1995. Superfund Innovative Technology Evaluation Program, Final Demonstration Plan for the Evaluation of Field Portable X-Ray Fluorescence Technologies. Prepared for U.S. Environmental Protection Agency, March 01. http://www.epa.gov/etv/pdfs/testplan/01_tp_covertoc_xray.htm
  5. United States Environmental Protection Agency (USEPA). 2006. ITVR: XRF Technologies for the Monitoring and Measurement for Soil and Sediment. http://www.epa.gov/ORD/SITE/
  6. United States Environmental Protection Agency (USEPA). 1998. Method 6200, Field Portable X-Ray Fluorescence Spectrometry for the Determination of Elemental Concentrations in Soil and Sediment. Rev. 0. January. http://www.epa.gov/epaoswer/hazwaste/test/pdfs/6200.pdf
  7. Space and Naval Warfare Systems Center San Diego (SSC SD). 2000. Integrated Field-Screening for Rapid Sediment Characterization, ESTCP Project #9717. Sept. 30. http://www.estcp.org/Technology/upload/CU-9717-FR-01.pdf
  8. United States Environmental Protection Agency (USEPA). 1996. Region I, EPA-New England: Immunoassay Guidelines for Planning Environmental Projects. October. http://www.epa.gov/NE/measure/ia/ia_guide.pdf
  9. Naval Facilities Engineering Command (NAVFAC). 2001. Rapid Sediment Characterization of PCBs With ELISA. June. NFESC TDS-2086-ENV. http://costperformance.org/monitoring/pdf/elisa_2.pdf
  10. Naval Facilities Engineering Command (NAVFAC). 2000. QwikSed: A Bioluminescent Toxicity Test. February. NFESC TDS-2077-ENV. http://costperformance.org/monitoring/pdf/qwiksed_2.pdf
  11. Assure Controls. 2006. QwikLite™ 200 Testing System. http://www.assurecontrols.com/products-qwiklite.htm
  12. United States Environmental Protection Agency (USEPA). 2001. Rapid Sediment Characterization Tools for Ecological Risk Assessments. March. http://www.clu-in.org/products/newsltrs/ttrend/view.cfm?issue=tt0301.htm
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http://www.clu-in.net/programs/21m2/navytools/rsc/default.cfm
Last modified: December 7, 2006