Environ. Sci. Technol. 2000, 34, 527-529
A Source of PCB Contamination in Modified High-Volume Air Samplers ILORA BASU, JAMES M. O’DELL, KAREN ARNOLD, AND RONALD A. HITES* School of Public and Environmental Affairs and Department of Chemistry, Indiana University, Bloomington, Indiana 47405
Modified Anderson High Volume (Hi-Vol) air samplers are widely used for the collection of semi-volatile organic compounds (such as PCBs) from air. The foam gasket near the main air flow path in these samplers can become contaminated with PCBs if the sampler or the gasket is stored at a location with high indoor air PCB levels. Once the gasket is contaminated, it releases PCBs back into the air stream during sampling, and as a result, incorrectly high air PCB concentrations are measured. This paper presents data demonstrating this contamination problem using measurements from two Integrated Atmospheric Deposition Network sites: one at Sleeping Bear Dunes on Lake Michigan and the other at Point Petre on Lake Ontario. We recommend that these gaskets be replaced by Teflon tape and that the storage history of each sampler be carefully tracked.
Introduction The Integrated Atmospheric Deposition Network (IADN), started in 1990, is a joint project between Canada and the United States. One goal of this project is to measure the spatial and temporal trends of the atmospheric concentrations of polychlorinated biphenyls (PCBs) and to calculate their loadings into the Great Lakes. Air samples, both gas and particle phases, are collected from master stations and satellite stations at shoreline sites around the Great Lakes. There are two quality control sites, each equipped with two side-by-side samplers: The Sleeping Bear Dunes site on Lake Michigan uses one sampler to collect the routine samples and the other to collect field blanks and duplicate samples for a determination of measurement precision (1). The Point Petre site, on the Canadian shore of Lake Ontario, uses two samplers to collect duplicate samples, one of which is analyzed by the Canadian Atmospheric Environment Service and the other by Indiana University. In this way, we can determine the comparability of the results generated by the Canadian and the U.S. laboratories. During the 9 years of this project, there were two instances when the samplers themselves became contaminated with PCBs and when the contamination lasted over extended periods affecting multiple samples. This contamination was easily detected because of discrepancies in the measurement of duplicate samples collected at each site with different samplers. We have traced the source of this contamination to a small gasket that is an integral part of the sampling device, and we recommend a simple way to eliminate this problem. * Corresponding author phone: (812)855-0193; fax: (812)855-1076; e-mail:
[email protected]. 10.1021/es990841+ CCC: $19.00 Published on Web 12/09/1999
2000 American Chemical Society
Methods and Materials Air samples are collected using modified Anderson Hi-Vol air samplers from General Metal Works, model GS 2310; a schematic is shown in Figure 1. The flow controller probe (Figure 2) is inserted through a hole in the side of the cylinder that holds the XAD-2 cartridges. This probe is sealed with a foam gasket, which is held to the outside of the cylinder by a large hose clamp that fits around a wide spot on the probe tube; see Figure 2. Because the diameter of the hole in the cylinder is about 3 mm greater than the diameter of the probe, a portion of the gasket protrudes into the interior of the cylinder and is in the air sampling path. Samples are collected for 24 h, at a rate of 34 m3/h, once every 12 days. XAD-2 (Sigma Chemical Company, St. Louis, MO; mesh size 20-60; surface area, 330 m2/g; pore diameter, 9 nm) is used as the sorbent for the gas phase. Before field deployment, the sorbent is solvent extracted to remove surfactants and other contaminants prior to use. Approximately 40 g of clean XAD-2 is used in a stainless steel cartridge for each sampling event. Whatman Quartz micro-fiber filters (QM-A, 20.3 × 25.4 cm) are used to collect the particle phase (2). Once back in the laboratory, the XAD-2 resin and the filters are Soxhlet extracted with a mixture of 50% acetone in hexane. The extracts are concentrated and chromatographed through 3.5% water deactivated silica gel (Davisil, grade 634, 100-200 mesh, 60 Å) to remove polar interferences and to separate the PCBs from other analytes. The cleaned extracts are then concentrated with a stream of nitrogen to about 1 mL and injected into a Hewlett-Packard 5890 gas chromatograph with a 63Ni electron capture detector (3). A DB-5 fused silica capillary column, 60 m long × 250 µm i.d. with a 0.1 µm film thickness (J & W Scientific, Folsom, CA) is used. The GC temperature program is as follows: held at 100 °C for 1 min, ramped at 1 °C/minute to 240 °C, ramped at 10 °C/min to 280 °C, and held at 280 °C for 20 min. PCB congeners 30 and 204 are used as internal standards (4).
Results and Discussions The Sleeping Bear Dunes site has been a master station in the IADN project since 1991. It is located in an open grassy field on a secondary dune on the northeast coast of Lake Michigan. The site (N 44°45′ 40′′ and W 86°03′ 31′′) is 50 km west of Traverse City. There are practically no industrial influences at this location, and perhaps as a result, the total PCB concentration in the gas phase is very low, averaging (on an annual basis) 130 ( 15 pg/m3 from 1991 to 1997. As mentioned above, this site is equipped with two co-located air samplers (called samplers 1 and 2) for the collection of duplicate samples and field blanks. The total PCB concentrations in the duplicate gas-phase samples from 1992 through May 1997 were in good agreement (the average relative percent difference in the total PCB concentrations between the duplicates was ( 32%). In June 1997, there was a sudden increase in the apparent PCB concentration measured with sampler 1. A close examination of only the 1997 data (see Figure 3) from sampler 1 showed that the problem started immediately after the summer calibration of the samplers, at which time the flow controller probe and the associated gasket in only sampler 1 were changed. These elevated PCB concentrations continued for 5 months, although the PCB concentrations measured with sampler 1 were gradually declining to the levels measured with sampler 2. Contamination from the foam gasket was suspected (see below), and on November 1, 1997, this gasket was replaced with Teflon tape. At this time, the total PCB concentrations VOL. 34, NO. 3, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Schematic diagram of a modified Anderson Hi-Volume sampler (side view).
FIGURE 2. Flow controller probe showing the stainless steel hose clamp, the black foam gasket, and the cable that terminates at the flow controller box (top view).
FIGURE 3. Total PCB gas-phase concentrations (in pg/m3) at Sleeping Bear Dunes in 1997 and 1998 only using sampler 1. as measured with sampler 1 came down considerably, and duplicate measurements from the two samplers were again in general agreement ((43%). By integrating the concentrations measured with sampler 1 from June to November, we estimate that on the order of 10-100 µg of PCB were vaporized from the gasket during that period. 528
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FIGURE 4. Total PCB gas-phase concentrations (in pg/m3) at Point Petre before and after the flow-controller probe gasket change (light bars) compared to PCB concentrations determined with a different sampler (dark bars). The Point Petre site (N 43°50′ 20′′ and W 77°9′ 10′′) in Canada started operation in 1990. The site is only 45 m away from the shore and 40 km southeast of Belleville. The average total PCB concentration from 1990 to 1994 in air from this site was 170 ( 86 pg/m3 (6). In May 1998, an interlaboratory comparison study was begun at this site. Side-by-side samplers were used to obtain duplicate samples that were analyzed by the U.S. laboratory at Indiana University (IU) and by the Canadian laboratory at the Atmospheric Environment Service (AES). It was soon noticed that the total PCB concentrations in air collected by the U.S. sampler were about 3-5 times higher than the historical PCB average and were much higher than the concentrations measured with the Canadian sampler collected on the same dates (see Figure 4). Sampler contamination was again suspected, especially from the foam gasket on the flow controller probe. On August 21, 1998, this gasket was replaced with Teflon tape, and within a couple of weeks, the PCB concentrations came down to the historical average (see Figure 4). The high PCB concentrations in the samples collected on August 28 and September 21 may be the result of residual PCBs adhering to the interior of the sampler. Why was the probe gasket suspected? At Sleeping Bear Dunes, the problem started only after changing the probe. There were no changes in the air flow rate (as determined from the magnehelic readings) or in any other part of the sampler. The PCB concentrations in the sampler blanks (with no air flow) were normal (about 10 pg/m3), and higher concentrations were detected only after active sampling. This suggested that air flow through the sampler was necessary to observe the contamination. Concentrations of PCBs in the particle phase were low, but those in the gas phase were high. Therefore, the samples were likely to have become contaminated by a source between the filter holder and the XAD-2 cartridge. The flow controller probe was the only possible source of contamination at this location; see Figure 1. Although the probe itself is primarily stainless steel, the gasket used to seal the probe in the sampler is made of a black plastic foam, which is capable of absorbing PCBs from other sources during storage. In the case of Sleeping Bear Dunes, the probe and the foam gasket had been stored in the Geology building at Indiana University. This building was built in 1961, and it had a large number of fluorescent light ballasts containing PCBs. Perhaps as a result, the average indoor PCB concentration in this building is about 300 ng/ m3 (7), which is about 3000 times higher than the ambient air at Sleeping Bear Dunes. The gasket most likely sorbed PCBs from the indoor air during its storage in this building.
The sampler used at Point Petre was stored in the attic of a building (no. Q6) at the airport in Champaign, IL for an unknown period of time. Four 55-gallon barrels of PCBcontaining capacitors from old airport radar instruments were also stored in this building from about 1977 to 1997, at which time this waste was removed for disposal. The sampler was first used at Beaver Island, MI for air sampling associated with the Lake Michigan Mass Balance Project from August 1994 through October 1995. Our observations suggest that the inexplicably high PCB values observed on Beaver Island (8) could have been caused by this contaminated sampler. On completion of that sampling campaign, the sampler was again stored in the same no. Q6 building from December 1995 through May 1998, at which time it was installed at Point Petre. It seems clear that the foam gasket in this sampler also accumulated PCBs from indoor air during storage at the Champaign airport and released them back into the air stream during sampling. Since a portion of the foam gasket protrudes into the cylinder, it is likely that the main air stream will directly leach PCBs. Furthermore if there are any minor leaks around the gasket, air will be drawn through the foam, become contaminated with the PCBs, and contaminate the sample. Recommendations. (a) The foam gaskets should be replaced in all such samplers with Teflon tape. (b) All samplers should be thoroughly cleaned before use. (c) A new sampler should be used first in an area where the PCB concentrations have been measured before to check the sampler’s integrity. (d) Duplicate measurements with a validated sampler at the same site are desirable. (e) The sampler history should be maintained and checked before its use.
for their contributions. We thank Tom VanZoeren (at Sleeping Bear Dunes) and Darrel Smith (at Point Petre) for collecting the samples, Jim Osborne (at the Illinois State Water Survey) for tracing the history of the second sampler, and the Great Lakes National Program Office (of the U.S. Environmental Protection Agency) for funding the IADN project (Grant No. GL995656).
Acknowledgments
Received for review July 26, 1999. Revised manuscript received October 19, 1999. Accepted November 2, 1999.
We thank Clyde Sweet of Illinois State Water Survey and Ken Brice of Atmospheric Environment Services, Canada,
Literature Cited (1) Basu, I.; Hites, R. A. Quality Control and Quality Assurance Project Plan, Revision 3; Indiana University, 1995. (2) Sweet, C. W. Standard Operating Procedure for Air Sampling for Semi-volatile Organic Contaminants Using the Organic HighVolume Sampler. in Lake Michigan Mass Balance Study Methods Compendium; EPA 905-R-97-012a; June 1997; Vol. 1, Sample Collection Techniques, pp 1-5-1-29. (3) Basu, I. Analysis of PCBs, Pesticides, and PAHs in Air and Precipitation Samples, IADN Project, Sample Preparation Procedure; 1999. (4) Basu, I. Analysis of PCBs, Pesticides, and PAHs in Air and Precipitation Samples. IADN Project, Gas Chromatography Procedure; 1999. (5) Hillery, B. R.; Basu, I.; Sweet, C. W.; Hites, R. A. Environ. Sci. Technol. 1997, 31, 1811-1816. (6) Hoff, R. M.; Strachan, W. M. J.; Sweet, C. W.; Chan, C. H.; Shackleton, M.; Bidleman, T. F.; Brice, K. A.; Burniston, D. A.; Cussion, S.; Gatz, D. F.; Harlin, K.; Schroeder, W. H. Atmos. Environ. 1996, 30, 3505-3527. (7) Wallace, J. C.; Basu, I.; Hites, R. A. Environ. Sci. Technol. 1996, 30, 2730-2734. (8) Miller, S. M.; DePinto, J. V.; Hornbuckle, K. C. Presented at the Midwest Environmental Chemistry Workshop; Ann Arbor, MI, October 1998.
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