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Determination of Regulatory Organic Compounds in Radioactive Waste Samples. Semivolatile Organics in Aqueous Liquids Bruce A. Tomkins,* John E. Caton, Jr., G. Scott Fleming, Manuel E. Garcia,’ Sara H. Harmon, Robert L. Schenley, Cheryl A. Treese? and Wayne H. Griest Organic Chemistry Section, Analytical Chemistry Division. Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 -6120
The regulatory semivoiatlie organic compounds present In radioactive aqueous waste samples are extracted and concentrated in a small-scale version of a standard EPA procedure normally used for groundwaters. Decontamination is sufficient to permit analysis of the extract In a conventional gas chromatography/mass spectrometry laboratory. The performance of the modified procedure, based on surrogate standards, matrix spikes and matrix spike duplicates, and blanks, is comparable to that of the standard method. The modlfied procedure was applled to a variety of aqueous radioactive waste tank samples. Only 12 of the EPA Appendix V I I I compounds were present, and none In concentrations exceedlng the reportlng limit (500 or 2500 pg/L). The most common semivolatile present was trlbutyl phosphate, an organic extractant commonly used in radlochemical processing, at 2000-30000 pg/L.
T h e U S . Environmental Protection Agency (EPA) mandated closure and decommissioning of Department of Energy nuclear waste storage tanks requires the chemical characterization of highly radioactive aqueous liquids to determine their regulatory status and to select appropriate treatments and disposal. In a previous paper (I), the characterization of volatile organic compounds, which can be removed from aqueous samples using an inert sparge gas, was described. The characterization must also include semivolatile organic compounds, which cannot be sparged from aqueous samples, but can be readily extracted and concentrated by using liquidliquid extraction procedures. The EPA identifies the regulatory semivolatile organic compounds in its Appendix VI11 and describes their quantitation in nonradioactive wastes in its Solid Waste Manual 846 (SW-846) ( 2 ) . Specifically, EPA Method 3510, “Separatory Funnel Liquid-Liquid Extraction” (2),of SW-846 describes the extraction and concentration of the compounds of interest, while Method 8270, “Gas Chromatography/Mass Spectroscopy (GC/MS) for Semivolatile Organics: Capillary Column Technique” (2), covers the identification and quantitation of these compounds. Unfortunately, the direct application of these procedures to the characterization of the aforementioned waste would result in the contamination of the GC/MS instrument and would expose laboratory staff to unsafe levels of radiation. This paper describes modifications to EPA Method 3510 that not only permit the operator to use much smaller volumes of radioactive waste as the sample, thereby reducing his radiation exposure, but also produce a final extract that is essentially uncontaminated by radioactivity. The performance of the modified procedure, based upon the usual surrogate *To whom correspondence should be addressed. Present address, Environmental Compliance Division, Oak Ridge National Laboratory, Oak Rid e, TN 37831-6222. Present address, Hewlett-backard Co., P.O. Box 22940, One Energy Center, Suite 200, Pellissippi Parkway, Knoxville, TN 37932.
standards, matrix spikes, and blanks, is comparable to that achieved for nonradioactive groundwater using conventional EPA methods.
EXPERIMENTAL SECTION Sample Collection. The aqueous radioactive waste samples were collected as described in detail elsewhere (3). Briefly, a small vacuum pump was used to draw the sample from a particular depth in the waste tank into a precleaned 250-mL widemouth jar (I-Chem, Hayward, CA). Approximately 15-25 mL of headspace was left in the jar. All samples were screened and tagged in the field for a and P l y radiation before transferring to a lead pig and shipping to the analytical laboratory. Surrogates, Spikes, and Internal Standards. An ampule of Acid Surrogate Standard MixCLP (Supelco, Inc., Bellefonte, PA, part no. 4-8875) was diluted to exactly 10 mL with Purge & Trap methanol (Baxter Healthcare Corp., Burdick & Jackson Division, Muskegon, MI), then transferred to a 20-mL screwcap vial supplied with a solid cap and Teflon liner. The concentration of each acid surrogate, viz. 2-fluorophenol, phenol-d5;and 2,4,6tribromophenol, was 200 pg/mL. An ampule of Base-Neutrals Surrogate Standard Mix-CLP Supelco, part no. 4-8925) was treated similarly. The concentration of each base-neutral surrogate, viz. nitrobenzene-d6,2-fluorobiphenyl, and 4-terphenyl-d,,, was 100 pg/mL. These surrogate mixtures were replaced at least every other week. Two separate matrix spike stock solutions were prepared, one for acid and the other for base-neutral species. The acid stock solution contained ca. 10 mg/mL of the following species: phenol, 2-chlorophenol, 4-chlor0-3-methylpheno1, 4-nitrophenol, and pentachlorophenol. The base-neutral stock solution contained ca. 5 mg/mL of the following species: l,4-dichlorobenzene; Nnitrosodipropylamine; 1,2,4-trichlorobenzene; acenaphthene; 2,4-dinitrotoluene; and pyrene. The neat matrix spikes were purchased from Supelco. A 200-pL aliquot of each stock was placed in the same volumetric flask and diluted to exactly 10 mL with Purge & Trap grade methanol (Baxter). The diluted matrix spike solution contained 100 fig/mL of each base-neutral matrix spike and 200 pg/mL of each acid matrix spike. This working solution was replaced at least monthly. Supelpreme-HC Internal Standards Mix (Supelco, part no. 4-8902) was added to the finished extract. This mix contains 4 mg/mL each of the following components in methylene chloride: acenaphthene-dlo; chrysene-d12;1,4-dichlorobenzene-d4;perylene-d12;and phenanthrene-d,,. This mixture was not diluted and was usually replaced at least every 3 to 4 weeks. Extraction Procedure. The liquid-liquid extractions for semivolatile organic compounds were performed after gross a and P l y activity measurements were completed. This information was needed to determine how much sample could be taken safely for extraction in a radiochemical hood. A 20-mL aliquot of aqueous sample was transferred to a 40-mL volatile organics analysis (VOA) vial (Shamrock Glass, Co., Seaford,DE, part no. 6-06K). These vials are precleaned according to EPA 40 CFR 136 and EPA 40 CFR 141 and are used as received. The natural pH of the sample was determined with wide-range pH paper. Three distinct cases were observed: (a) pH > 10; (b) pH < 2; (c) pH 6-9. The sample pH determined the order in which the acid and base-neutral fractions were extracted: Sample pH > 10. One-milliliter aliquots of the acid and base-neutral surrogates (all samples) and matrix spike (matrix
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spike and matrix duplicate samples only) were added to the sample. The sample was then extracted 3 times with 5 mL of methylene chloride (High Purity, B & J Brand, Baxter) by mixing sample and solvent gently, end over end, at least 30 times. In a smaller number of cases, the two layers formed an emulsion which did not break within approximately 5-10 min. In these cases, the mixture was centrifuged briefly (normally about 1-2 min was sufficient) in a benchtop clinical laboratory centrifuge to break the layers. The methylene chloride layer contaminated with aqueous sample was retrieved from the VOA vial with a Pasteur pipet and transferred to a disposable 10-mL polypropylene syringe barrel equipped with an Acrodisc CR, 0.45-pm porosity, Teflon membrane filter in a disposable assembly (Gelman Sciences, Inc., Ann Arbor, MI, part no. 4404). The methylene chloride layer dripped from the filter free of water into a second 40-mL VOA vial. All methylene chloride extract layers were pooled. The pH of the sample was adjusted to 10 with 1 M sodium hydroxide solution. The subsequent extraction and concentration steps were identical with those described above. Sample pH 6-9. The sample was rendered basic (pH > 10) with 1 M sodium hydroxide solution, then extracted as other samples with pH > 10. Two 100-pL aliquots of the final methylene chloride extract were drawn for gross a and @ radiochemical screening. The samples were checked further for radioactive contamination by using standard probe and smear techniques and then transferred to a conventional laboratory for quantitation of semivolatile organics by GC/MS (described below). Method Performance Evaluation. Method performance was evaluated through the use of matrix spikes, matrix spike duplicates, and water blanks. A matrix spike and spike duplicate pair and blank accompanied each lot of samples (usually three to six aqueous radioactive liquids) prepared daily. Gas Chromatographic Screening. All of the extracts were screened by gas chromatography to identify those that either required dilution or contained little organic matter and would not require GC/MS analysis (see below). A Hewlett-Packard Model 5840 gas chromatograph was equipped with a Model 7671A automatic sampler (Hewlett-Packard)and a Megabore DB-5 fused silica column (0.53 mm i.d. X 30 m, 1.5-pm film thickness, J & W Scientific, Folsom, CA). The column oven was programmed from 35 "C (hold for 4 min) to 270 "C (hold for 30 min) at 10 OC/min. The inlet and flame ionization detector temperatures were 270 and 290 "C, respectively. The autosampler injected a single 1.6-pL aliquot from each extract. The instrument was not calibrated quantitatively, but multicomponent standards of 20 and 4 pg/mL concentrations were run with each set to verify sensitivity. The standards included the acid and base-neutral target compound list (TCL) constituents specifically named by the EPA Contract Laboratory Program (CLP),as well as additional compounds selected from Appendix VIII. GC/MS Identification and Quantitation. The final identification and quantitation of the semivolatile organic analytes were performed by using SW-846 Method 8270, "Gas Chromatograph-Mass Spectrometric Analysis for Semivolatile Organics: Capillary Column Technique", as described in ref 2. Supplementary Semivolatile Appendix VI11 Standards and Organic Extractant Standards. Standards containing additional semivolatile organic compounds listed in Appendix VIE, such as pesticides, chlorinated aromatics, nitrogen heterocyclics, and aromatic amines, were prepared using neat materials purchased from either the Aldrich Chemical Co. (Milwaukee, WI) or Chem Service, Inc. (West Chester, PA), in 95% or greater
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purity. In addition, Mr. James Botts, the Group Leader of the Transuranium Analysis Laboratory, Oak Ridge National Laboratory, Oak Ridge, TN, provided small samples of organic extractants commonly used in radiochemical processing. All materials were used as received, and diluted in B & J Brand methylene chloride (Baxter) to 20 mg/L.
RESULTS AND DISCUSSION The aqueous radioactive waste samples described in this paper have been stored in underground waste storage tanks with headspace for up to 40 years. The major radionuclides present are the usual products of uranium fission, vis. 13'Cs and, rS% ' exhibiting activity up to 6 X lo5and 1 X lo4 Bq/mL, respectively. Other radionuclides, such as 6oCo, 233U, and tritium, were commonly observed, but a t hundred-fold less activities. A number of inorganic anions and cations were also observed in the aqueous waste samples. The sample pH ranged between 0.5 and 13, with the great majority exceeding 8. Nitrate and sulfate were the dominant anions with concentrations up to 31 000 and 83 000 mg/L, respectively. The concentrations of sodium and potassium have not yet been measured but are expected to range from micrograms per liter to grams per liter. The major cation measured was uranium (up to 4000 mg/L). Lower concentrations of ten RCRA target metals were occasionally observed, particularly chromium and mercury. The very high radiation fields limited access to the tank contents, and the high specific activity of the tanks precluded the collection of samples by using the standard EPA protocols. Compromise procedures had to be utilized, as described in detail elsewhere (3). Each sample was subjected to a variety of organic, inorganic, and radiochemical characterizations, each with its own requirement for holding time and minimum sample volume. In all cases, the extraction of the semivolatile organics followed the determination of the regulatory target volatile organics and was performed in most cases within 14 days of receipt of sample. This arrangement satisfied the EPA SW-846 holding time for aqueous samples analyzed for semivolatiles. The collection and conventional liquid-liquid extraction of 1-L samples (volume specified by EPA SW-846 Method 3510) bearing the stated activity was judged extremely hazardous to both the team sampling the radioactive waste storage tank and the analyst performing the sample preparation (4). For that reason, the sample volumes taken for semivolatile organic extraction were scaled back by a factor of 50. A 20-mL sample volume contained the maximum level of radiation, based on the activity of 137Cs,which could be handled individually using a "Contamination Zone" radiochemical hood. The risk of radiation exposure and contamination was therefore reduced to more manageable and safer levels, but a t the expense of analytical sensitivity. Given the hostile nature of the samples, the exchange between operator safety and method sensitivity was acceptable. The reporting limits were 50-fold those of the conventional SW-846 method, viz. 500-2500 pg/L. The liquid-liquid extraction of even small volumes of aqueous radioactive waste proved challenging. Vigorous mixing of sample and methylene chloride extraction solvent invariably resulted in a stable emulsion. Gentle mixing, in which the sample vial was turned end-over-end, provided good mixing and easy separation of the layers. Sometimes even the end-over-end mixing produced emulsions which ultimately had to be broken by centrifugation. The methylene chloride layer was drawn from the bottom of the VOA vial using a disposable Pasteur pipette. Other examples of complicating sample behavior included buffering, NO, formation, and precipitation. While most basic samples were acidified to pH
