Lab Science News

The toxicity and environmental impact of organochlorine pesticides and polychlorinated biphenyls (PCBs) is well documented. Routine environmental analysis of these compounds has remained largely unchanged since the advent of EPA method 8081 and EPA method 8082. However, recent instrumental advances and implementation of ultra-trace extraction techniques have allowed for significant improvements in detection limits.

The CAS Kelso laboratory has developed procedures that produce detection limits low enough to meet the requirements of the majority of studies. The extraction and analysis procedures include modifications to increase sensitivity, but still meet the requirements of the traditional EPA SW846 methods. Samples are prepared according to EPA Method 3520C with modifications, including a 2L continuous liquid-liquid extractor. Special glassware handling techniques are incorporated to minimize potential background contamination.

Development work is in progress to migrate the procedure to solid phase extraction (SPE) resulting in enhanced method performance. The instrumental portion of the analysis meets EPA Method 8081/8082 requirements. Combining Agilent Gas Chromatograph (GC) equipped with a micro-electron capture detector (micro-ECD) and a programmable temperature vaporizing (PTV) inlet with increased sample volume, ground water detection limits can be reduced ten to forty-fold over the limits listed in the methods.

Table 1 shows the current Method Detection Limits (MDL), Method Reporting Limits (MRL), and the mean recoveries. A relatively high level of accuracy can be achieved at or near the lowest point in the calibration curve (i.e., considering the levels spiked, the recoveries are excellent).

Unlike conventional split/splitless inlets, several hundred microliters can be injected into a PTV inlet. The PTV injector is cryogenically cooled and the excess solvent is vented. When most of the solvent is eliminated, the vent is closed and the target analytes are swept onto the column. Programming the PTV inlet properly is critical. Optimization of vent time and temperature are important in eliminating enough solvent while retaining the analytes of interest. Liner selection is also critical in retaining target compounds while the solvent is swept away. A Gerstel multi-baffled liner coated with 2μm of VB5 (5% diphenyl/95% dimethyl polysiloxane), supplied by Valco Instruments Company, Inc. (VICI), retained the lower molecular weight pesticides and Aroclors and consistently met the EPA criteria for 4,4’-DDT and Endrin analyte degradation.

As mentioned, sample preparation is critical to being able to utilize the potential of the instrumentation. Emphasis must be placed on careful handling of samples and extracts to avoid background contamination and/or loss of analyte during the procedure. If the proper techniques are employed, excellent sensitivity can be achieved.

Mercury is responsible for over three-quarters of all contaminant-related advisories for threats to human health. During the 1990’s, the number of mercury related fish consumption advisories more than doubled, despite significant decreases in the total mercury emissions over the last 20 years. The increase in advisories is probably the result of more testing rather than more contamination.

While the contamination is showing up in lakes and fish, most mercury does not come from effluent, rather is derived from atmospheric deposition. Atmospheric transport and subsequent bioaccumulation of mercury can affect aquatic ecosystems far from mercury sources. According to EPA estimates, emissions from coal-fired utilities account for 13 to 26 percent of the total (natural plus anthropogenic) airborne emissions of mercury in the United States. Thus, the EPA has begun to regulate emissions from power plant boilers and process heaters.

The impending MACT (Maximum Achievable Control Technologies) regulation (due out in 2004) is prompting affected manufacturers to assess the chloride, mercury and selected metals content of their fuels. The best way to meet the regulations is to burn fuels that are low in chloride, mercury and other metals. Early testing shows that mercury is more of a problem than chloride, particulate matter or selected metals.

Method Summary
Low level mercury measurements are conducted by EPA Method 1631. The analytical technique is very sensitive. In this method, an aqueous sample is oxidized with bromine monochloride and sparged with nitrogen onto a gold trap. The mercury is thermally desorbed from the gold trap into a cold vapor atomic fluorescence spectrometer. CAS can achieve a method detection limit (MDL) of 0.06 ng/L (ppt), which is three orders of magnitude less than the conventional cold vapor mercury method.

While the original method was designed for aqueous samples, CAS has implemented the “Appendix to Method 1631: Total Mercury in Tissue, Sludge, Sediment and Soil by Acid Digestion and BrCl Oxidation.” CAS has achieved an MDL of 0.3 ug/Kg in solid samples.

Sampling
The clean sampling techniques described in EPA Method 1669 should be used for sampling. Since most mercury contamination comes from the atmosphere, it is very easy to contaminate water samples. Other sources of contamination are metal containers, talc powdered gloves, improperly cleaned and stored equipment, and dust and dirt. By following these clean sampling procedures, it has been shown that much of the historical data for mercury in seawater was erroneously high because of contamination from sampling.

When it is necessary to measure dissolved mercury, field filtering with an in-line filter can be performed as long as care is taken to insure that the filter is clean and free of contamination. It may be more efficient to send an unpreserved sample to the laboratory for filtering under clean conditions. This is particularly true if an in-line filtering device is not available.

Quality Assurance
Quality assurance is performed at CAS in accordance with the EPA method, ensuring scientifically valid and legally defensible results. Matrix spikes should be at the compliance level of 1 to 5 times the background level, so it is helpful to know the compliance level or the approximate amount of mercury expected in the samples. Besides matrix spikes, the method calls for measuring standards at 5 ng/L from two sources and analyzing many different blanks to assess potential contamination originating either in the field or in the laboratory. The blanks include: equipment, field, bottle, bubbler and reagent blanks, in addition to the usual method blank.

Why choose CAS?
The CAS Kelso laboratory has been performing this method for over six years in our clean laboratory. In addition to a variety of water matrices, CAS has experience analyzing hundreds of samples on several types of solid matrices: fish, coal, oil, sawdust and bark. We have a documented history of freedom from contamination and excellent recovery of ongoing precision and recovery standards and MS/MSDs within the QC acceptance criteria of Method 1631.

References:
Federal Register, Vol. 68, No. 8, January 13, 2003, pg 1666.
Krabbenhoft & Schuster, USGS Fact Sheet FS-051-02, June 2002.

The Department of Antiquities Conservation of the J. Paul Getty Museum recently requested assistance from CAS’ Simi Valley Air Quality Laboratory to sample and analyze the atmosphere surrounding a second century Egyptian mummy. About six years ago, the mummy was sealed in a case containing ambient air. The museum wished to determine the volatile and semivolatile organic compounds off-gassing from the mummy. One purpose of the study was to determine the impact of off-gassing on other artifacts that were to be displayed with it.

Compounds of interest included low molecular weight organic acids, volatile organic chemicals, and the semivolatile compound, guaiacol. Guaiacol is a component of cedar oil and one of the embalming fluids used by the Egyptians.The other chemicals were associated with previous restoration activities with the mummy.

In order to collect the samples, two holes were drilled in the case housing the mummy. Sampling ports consisting of Teflon tubing (1/4” OD) and a ferrule and female Swagelok fitting were installed in the holes. The ports were sealed off at the time of installation and only opened during sampling periods.

Two sampling and analytical methods were used to address the compounds of interest. Volatile organic compounds were sampled in evacuated passivated stainless steel canisters (SUMMA-like) and then analyzed for tentatively identified compounds (TICs) by gas chromatography/ mass spectrometry (GC/MS) following US EPA Method TO-15. This technique involves identifying the most predominant compounds by Jeanette Campbell - Simi Valley, CA in the sample by comparing their mass spectra with those from the NIST library, which contains mass spectra from more than 120,000 compounds. Heavier compounds were sampled on Tenax TA tubes and then thermally desorbed and analyzed by GC/MS following EPA Method TO-17. These samples were analyzed for guaiacol and other TICs, including acetic acid.

Compounds of both biogenic (e.g., isobutyric acid) and synthetic origin were identified in the samples (see Figure 1 on page 3). Acetaldehyde, 3-methylbutanal, pentanal, furfural and methyl methacrylate were present above their odor threshholds. Several of these compounds had an “odor character,” that might have contributed to the “characteristic mummy odor” described by one of Getty’s researchers.

An important outcome of this project was the side-by-side comparison of the efficacy of two sampling methodologies that are frequently used to evaluate organic compounds in indoor air investigations. Neither media type collected the full range of compounds of interest. Lighter compounds were only detected in the SUMMA-like canister sample. In contrast, heavier, higher boiling point compounds were only identified in the samples collected on the Tenax sorbent tube. Midrange compounds (e.g., boiling points of 70oC to 240oC) were detected using both sampling media and showed similar quantitative and qualitative results.

Although boiling point appeared to be the primary determinant of the compounds that were collected by the two types of media, other properties (vapor pressure, polarity, lability) may also have had an impact. For example, the labile compound, isobutyric acid, was only detected in the solid sorbent samples even though its boiling point (155o C) is in the more volatile range, which may be collected by SUMMA canisters.

The Mummy project presented the laboratory with a unique opportunity to evaluate an environment containing a wide range of compounds. The results of this project suggest that for indoor air investigations, the use of multiple sampling media may generate more meaningful data than reliance on a single type.

CAS would like to thank Cecily Grzywacz, Scientist in the Science Department of the Getty Conservation Institute and Marie Svoboda, Associate Conservator of Antiquities at the J. Paul Getty Museum for allowing us to present the results of their project.