Environ. Sci. Technol. 1989, 23, 1112-1 116
Rodgers, M. 0. Ph.D. Dissertation, Georgia Institute of Technology; Atlanta, GA, 1986. King, G. W.;Mode, D. Can. J. Chem. 1962,40,2057-2065.
Metcalf, R. L., Eds.; Wiley: New York, 1974;Vol. 4. Finlayson,B. J.;Pitts, J. N., Jr. Science (Washington, D.C.) 1976,192,111-119.
Cox, R. A. J. Photochem. 1974,3,291-304. Cox, R. A. J. Photochem. 1974,3,175-188. Davis, D. D.; Bradshaw, J. D.; Sandholm, S. T. Annual Report to the Coordinating Research Council; Georgia Institute of Technology: Atlanta, GA, August, 1985. Bradshaw, J. D.; Rodgers, M. 0.; Davis, D. D. Appl. Opt. 1984,23,2134-2145. Vasudev, R.;Zare, R. N.; Dixon, R. N. Chem. Phys. Lett. 1983,96,399-402. Grosjean, D. Environ. Sci. Technol. 1985,19,1059-1065. Bradshaw, J. D.; Rodgers, M. 0.;Davis, D. D. Appl. Opt. 1982,21,2493-2500. Davis, D. D.; Heaps, W. S.; Philen, D.; Rodgers, M.; McGee, T.; Nelson, A.; Moriarty, A. J. Rev. Sci. Instrum. 1979,50, 1505-1516. Rodgers, M. 0.; Davis, D. D., submitted for publication in Environ. Sci. Technol. Davis, D. D.; Rodgers, M. 0.;Fischer, S. D. Geophys. Res. Lett. 1981,8,73-76.
Stockwell,W. R.; Calvert, J. G. J. Geophys.Res., C: Oceans Atmos. 1983,88,6673-6682.
Platt, U.;Perner, D.; Harris, G. W.; Winer, A. M.; Pitts, J. N., Jr. Nature (London) 1980,285,312-314. Harrison, G. W.; Carter, W. P. L.; Winer, A. M.; Pitts, J. N., Jr.; Platt, U.; Perner, D. Environ. Sci. Technol. 1982, 16,414-419. Nash, T. Tellus 1974,26,176-180. Ferm, M.; Sjodin, A. Atmos. Environ. 1985,19,979-985. Penkett, S.A.; Sandalls, F. J.; Jones, B. M. R. VDI-Ber. 1977,NO.270,47-54. Sjodin, A.; Ferm, M. Atmos. Environ. 1985,19,985-992. Perner, D.; Platt, U. Geophys. Res. Lett. 1979,6,917-920. Platt, U.;Perner, D. J . Geophys. Res., C: Oceans Atmos. 1980,85,7453-7458. Harris, G. W.; Winer, A. M.; Pitts, J. N.; Platt, U.; Perner, D. Springer Ser. Opt. Sci. 1983,39,106-113. Rodgers, M. 0.;Asai, K.; Davis, D. D. Appl. Opt. 1980,19, 3597. Rodgers, M.0.;Davis, D. D. XVII Informal Conference on Photochemistry; Boulder, CO, June 1986. Rodgers, M. 0.; Bradshaw, J.; Sandhold, S. T.; KeSheng, S.; Davis, D. D. J. Geophys. Res., C: Oceans Atmos. 1985, go, 12819-12834.
Received for review September 14,1987.Accepted June 13,1988. We acknowledge the support of this research by the Coordinating Research Council, Inc., under contract CAPA-19-80(3-83).
A Quiet Sampler for the Coilection of Semivolatile Organic Pollutants in Indoor Air Nancy K. Wllson"
Atmospheric Research and Exposure Assessment Laboratory, US. Environmental Protection Agency, Research Triangle Park, North Carolina 2771 1 Mlchael R. Kuhlman, Jane C. Chuang, and Gregory A. Mack
Battelle Columbus Division, Columbus, Ohio 43201 James E. Howes, Jr.
Combustion Engineering-Environmental, Incorporated, Chapel Hill, North Carolina 275 14
A prototype air sampler that is quiet and transportable was designed and constructed for the collection of semivolatile organic compounds in indoor air. The sampler combines a filter and adsorbent in series and can be operated at a flow rate sufficient to collect enough organic matter for chemical analysis and microbioassay. The acoustic insulation of the sampler allows it to meet a noise criterion of NC-35, roughly the sound level in a quiet conference room. Operation of the sampler with its exhaust both vented and not vented showed that the sampler itself does not significantlyaffect the levels of polynuclear aromatic hydrocarbons in indoor air. Therefore it is unnecessary to vent the sampler outdoors during indoor air sampling for these compounds, thus minimizing the effect of the sampler on the house air exchange rate. Introduction
Several studies (1-9) have shown that many polynuclear aromatic hydrocarbons (PAHs) and nitrated PAHs found in air are carcinogens, mutagens, or both. The analytical methodology to determine these compounds is established. However, methodology for sampling semivolatile organic compounds [those with vapor pressures roughly 10-2-10-8 kPa (lO-'-lO-' Torr)] in indoor air is not equally estab1112 Environ. Sci. Technol., Vol. 23, No. 9, 1989
lished. Devices currently used in air sampling to collect adequate material for chemical analysis and bioassay (IO, 11) are not suitable for air sampling in homes because of their size, noise, and lack of portability. In a previous indoor air study (2,8,9),we put the sampler pump outside the house in an insulated enclosure to minimize the noise level. We made different modifications, which depended on the structure of each house sampled, to allow connection of the sampling module to the pump by passing the connecting tube through a window port. These modifications of the sampling system increased the difficulty in sampling and the inconvenience experienced by the residents. We have therefore developed an indoor air sampler that is quiet, transportable, and reasonably unobtrusive and that can be located entirely inside the house during sampling. Besides the physical requirements mentioned above, a principal requirement for the indoor sampler described here is that it collect quantities of particles and vapors sufficient for both chemical analysis and microbioassay. Another requirement is that it collect the sample in a time short enough that an individual's time profile of exposure to the compounds of interest can be defied. We examined available data on the typical concentrations of PAHs and other compounds of interest in indoor air and estimated the mass required to analyze the target compounds accu-
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rately. We then could specify the air sample volumes required to obtain useful data (12,13). A t a sampling rate of 224 L/min (8 ft3/min), quantifiable amounts of most PAHs should be colleded in 1-3 h. One hour or less should be required for pesticides such as chlordane or dichlorvos. To obtain sufficient mass for microhioassay, however, about 100 m3 of air must be sampled. Thus, a sampling rate of 224 L/min should provide adequate samples for both chemical analysis and microhioaasay in 8 h. This flow rate is readily achievable with commercially available blowers of moderate size. At 224 L/min, approximately 10% of the total air volume of a typical 140 m2 (1500 ft2) house with an air-exchange rate of 0.4 h-l (average of 26 homes with a range of 0.2-2.0 h-9 would be sampled. Larger flow rates are undesirable because they cause unacceptable perturbations of the indoor environment. To maintain a representative air-exchange rate and to simplify the indoor air sampling process, it is desirable to vent the exhaust from the sampler into the house rather than outdoors. Because we used an oilless blower, we did not expect to find significant amounts of PAHs in the motor's exhaust emissions. However, we needed to determine whether significant changes in the measured indoor air pollutant concentrations resulted from operation of the sampler itself. Therefore, we operated three prototype samplers under both vented and unvented conditions in the Same room and analyzed the collected samples for PAHs. We examined the PAH data using standard analysis-of-variance techniques to determine whether the sampler exhaust should be vented outdoors during sampling.
Methods and Materials Sampler Design. Our primary objective for the indoor sampler was to simplify sampling in occupied homes. The main sampler characteristics that can be controlled to improve its acceptability by the residents are its size and noise level. Because the noise level of any sampler can he reduced by use of a larger acoustically insulated enclosure, these two aspects are in competition. The compromise between sound and size reduction resulted in a sampler cabinet 91 cm high X 58 cm long X 47 cm wide (36 in. X 21 in. X 18 in.). We selected the construction materials to minimize weight, yet provide a rugged, well-sealed cabinet with good acoustic damping. The cabinet is of 5/sin. plywood with grooved joints sealed with latex caulk. Semirigid glass fiberboard, cut to tit the various enclosures and baffles within the cabinet, is the principal sound-ahsorbing medium. One side of the acoustic housing can he removed for inspection of the unit's interior, although this is seldom necessary. The blower motor, an Amtex bypass vacuum motor (Model 116100-00, Ametek, Kent, OH), is coupled to the air inlet plenum with vibration-isolation mounts and a closed-cell foam gasket. This provides an airtight seal between the mounting flange and the inlet chamber. The electrical connections, the flow controller (Model GMW260B, General Metal Works, Cleves, OH), recorder (Rustrak Model 288-FIA, Rustrak, East Greenwich, RI), and switches are in an aluminum circuit box affixed to the acoustic housing. The sample inlet is a commercially available PS-1 inlet (General Metal Works), the top of which is 145 cm (57 in.) from the floor. This inlet consists of a 104-mm filter holder for collection of particles, followed in series hy a glass cartridge that holds an adsorbent such as polyurethane foam or XAD-2 resin for collection of vapor-phase compounds (15). A PM-10 size-selective inlet (10 pm cutoff) was also designed and tested for this unit. An initial
Flgure 1. Air flows in the indoor sampler.
evaluation showed that the inlet for aerosol particles achieves a cut point of 10 pm and is insensitive to slight variations in the sampling flow rate (13). However, further development is necessary for the adaptation of the PM-10 inlet to this sampler before field applications. A diagram of the sampler and its air flows is shown in Figure 1. Note that the flow path of the motor cooling air is internally separated from the flow path of the sampled air. The sampler exhaust is directed away from the sampler housing and is diluted by room air before it can come in contact with the sampling media. The sound pressure level produced by the blower motor used in these samplers is 92-104 dB, comparable to that produced by a subway train passing 6 m away. We designed the acoustic cabinet for the sampler to meet a noise criterion value of NC-35 (14), which is typical of the maximum acceptable background noise level in a sleeping room. We measured the sound levels produced by two sampler prototypes at a height of 1.5 m (4.9 ft), at a distance 1.5 m from the sampler inlets. The results of these measurements appear in Figure 2, which shows that these samplers operate at a sound level less than NC-33. The use of the acoustic enclosure thus results in a reduction in sound energy to 1/800000th of the unquieted sound energy. Although an operator must start the sampling, the sampler records the sampling flow rate and ends the sampling period by the action of a timer. Thus, once started, the sampler can operate unattended. The flow controller installed in these units provided a very stable flow rate throughout all the sampling periods tested (8,16, and 24 h), with a variation less than 3%. Evaluation of Sampler Contribution t o t h e Indoor PAH Levels. We tested three newly built samplers in an unoccupied office in our laboratories. The room was closed, and no one entered the room during the sampling periods. Table I summarizes the sampling plan. For the vented tests, we led the sampler exhaust through a 4in.-diameter duct into a well-ventilated hallway. For the Environ. Scl. Technol.. Vol. 23,No. 9. 1989 1113
was sampled at the above flow rate and the measured air-exchange rates (approximately half the room volume was sampled in each hourly period, and there were approximately two air exchanges per hour). The quartz-fiber filter and the XAD-2 cartridge from each test were Soxhlet-extracted together for 16 h with dichloromethane. Half of each extract was concentrated to 1 mL with Kuderna-Danish (K-D) evaporation. An aliquot was analyzed for selected PAHs with a Finnigan 4500 quadrupole mass spectrometer equipped with a gas chromatograph and an INCOS 2300 data system as described previously (15). To evaluate the influence of sampler venting on the levels of PAHs found in indoor air, we developed a statistical model to obtain estimates of the differences in PAH concentrations measured under vented and unvented conditions. The model for the data analysis is
Yijk = b
-
OCTAVE BAND CENTER FREWENCIES IN HERTZ
Flgure 2. Ndse crlterion curves for two of the samplers designed and built for this study.
Table I. Summary of the Sampling Plan for Evaluation of the Prototype Sampler with and without Venting test no."
sampler
1
A A A A A A A A A A B
2 3 4 5 6 7
8 9 10 11 12 13 14 15 16 17 18 19 20
B B B C C C C B B
venting conditnb
total vol sampled, m3
NV V V NV V V NV V NV NV NV V NV V NV V V NV NV V
355 299 346 346 346 346 346 346 346 346 314 314 318 314 312 307 314 312 319 317
"The order 0- Jampler testing could not - e randomizeL -ecause of the limited availability of samplers. NV denotes not vented, V denotes vented oubide. The air-exchange rate was 2.16 h-' without venting and 2.30 h-' with venting.
unvented tests, we simply vented the exhaust into the room being sampled. To collect particles and vapors, we used a quartz-fiber filter (104 mm QAST, Pallflex) and an XAD-2 (Supelco) cartridge in series. The preparation of the XAD-2 cartridges is described elsewhere (15). We operated the samplers at a flow rate of approximately 224 L/min for 22 h at room temperature. To monitor the air-exchangerates during both vented and unvented tests, we injected sulfur hexafluoride into the room and then analyzed 1.0 cm3 of the room air every 10 min for 90 min, using gas chromatography with electron capture detection. Approximately 24% of the total air volume of the room 1114
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+ vi + sj + vsij + Eijk
where Yijk is the concentration of the PAH for the kth replicate using the j t h sampler and the ith venting condition, p is the overall average PAH concentration, Vi is the effect due to the ith venting condition, Si is the effect due to the j t h sampler, VSij is the effect due to the interaction of the jth sampler and the ith venting condition, and E,, is the random error associated with the kth replicate using the jth sampler and the ith venting condition. The total error term Eijkaccounts for the unknown variability in the measurements, which includes both the measurement error and day-to-day variability. Because of the day-to-day variability in PAH concentrations, statistical analysis of the entire data set is required to determine whether or not the sampler contributes a detectable artifact to the measured values. This daily variability, coupled with the limited number of samples, could cause artifact values as high as a 30% variation in values measured in a typical home to go undetected in the data. Our main concern is the difference in measured PAH concentrations among samples collected under vented and unvented conditions. From the model, this can be represented by the value V, - VIwhere V Iis the effect on the PAH concentration when the exhaust from the sampler is vented outside and V , is the effect on the PAH concentration when the sampler exhaust is not vented. The difference in these two values estimates the average effect of sampler venting on PAH levels in indoor air.
Results and Discussion Selected PAHs were measured in room air by using the prototype samplers under vented and unvented conditions. The PAH concentrations found are given in Table 11. No cigarette smoking or other activity took place in the room during the sampling periods. Therefore the levels of PAHs found in these tests may represent typical clean office air. We found very high levels of naphthalene, ranging from 506 to 1630 ng/m3. The naphthalene levels in the field blank (a filter/adsorbent cartridge subjected to the same procedures as those for the real samples, but with no air drawn through it) corresponded to 2 ng/m3, less than 0.5% of the levels determined from the real samples. Some carcinogenic PAHs, for example, benzo[a]pyrene, cyclopenta[c,d]pyrene, and dibenz[a,h]anthracene, were also present in the room air, but at low levels (less than 1.0 ng/m3). Generally, the levels of target PAHs in the room air were within the range of typical residential indoor air concentrations (2). Only two- to four-ring PAHs (for example, naphthalene and pyrene) were present in the blank sample, and the levels of these compounds in the blank
Table 11. Measured PAH Concentrations compound naphthalene acenaphthylene acenaphthylene,dihydro phenanthrene anthracene fluoranthene Pyrene cyclopenta[c,d]pyrene benz [a]anthracene chrysene benzo[e]pyrene benzo[a]pyrene benzo[g,h,i]perylene dibenz[a,h]anthracene coronene
mean concn (fu), ng/m3 not venteda vented 860 f 240 15 f 7 120 f 50 210 f 60 9.6 f 4.2 22 f 10 11 f 5 0.24 f 0.14 0.22 f 0.10 0.48 f 0.22 0.20 f 0.11 0.16 f 0.12 0.31 f 0.24 0.12 f 0.09 0.19 & 0.18
1160 f 360 17 f 3 120 f 20 240 f 90 9.6 f 2.6 20 f 2 9.1 f 1.2 0.37 f 0.24 0.24 f 0.12 0.45 f 0.18 0.27 f 0.12 0.25 f 0.17 0.49 f 0.26 0.17 f 0.11 0.39 f 0.21
a Ten measurements were made under each venting condition: five with sampler A, three with sampler B, and two with sampler m
Table 111. Summary of Statistical Analyses of PAH Data compound naphthalene acenaphthylene acenaphthylene, dihydro phenanthrene anthracene fluoranthene Pyrene cyclopenta[c,d]pyrene benz[a]anthracene chrysene benzo[e]pyrene benzo[a]pyrene benzo[g,h,i]perylene dibenz[a,h]anthracene coronene
v, - VI:
ng/m3
Fvalue
dfb
-230 -1.4 -0.92 -30 -0.25 2.6 1.6 -0.14 -0.024 -0.034 -0,068 -0.091 -0.19 -0.053 -0.20
2.38 0.44 0.004 3.78 0.22 0.89 1.53 1.64 0.48 2.42 5.28 2.14 6.65 13.55' 23.63'
(1, 2.29) (1, 2.20) (1, 2.42) (1, 4.67) (1, 6.12) (1, 2.49) (1, 2.51) (1, 2.08) (1, 2.24) (1, 10.22) (1, 2.67) (1, 2.15) (1, 2.63) (1,7.41) (1, 3.52)
Estimate of the average difference between PAH levels under vented and nonvented conditions. Approximate degrees of freedom for F test. 'Significant at u = 0.05, which implies that there is onlv a 5 out of 100 Drobabilitv that there is no effect of venting.
were generally less than 2 % of those found in real samples. We have shown in previous studies (2,15)that less than 10% variability is obtained in the overall analytical method including Soxhlet extraction, K-D concentration, and GC/MS analysis. We applied analysis-of-variancetechniques to the PAH data to analyze for significant differences in PAH levels due to venting conditions. A summary of the statistical analyses is given in Table 111. Included in this table are the estimates for the differences in PAH concentrations with and without venting and the F values and degrees of freedom for the difference test for significance between venting conditions. The equations used to calculate these values are detailed elsewhere (16). Table I11 shows that the difference in concentration under the two venting conditions is significantfor only two compounds: coronene and dibenz[a,h]anthracene. However, the differences are negative, meaning that the observed PAH levels were higher with the exhaust vented. In both cases, the difference is small and may not have practical significance. The differences observed between vented and unvented conditions are within the range of day-to-day variations in the background PAH concentrations and measurement error and do not indicate any sampler effect.
In the preliminary sampler performance tests, we encountered no functional difficulties in the use of these samplers. They can be relied upon to provide samples for a specified duration at a very stable flow rate, with no need for adjustment of the flow rate when sampling sites are changed. One precaution that should be taken results from the use of the room air for motor cooling. This room air is not "cleaned" by the sampling media and could contain components that can be adsorbed by the acoustical insulation inside the sampler. These components might desorb in the next sampling location and contaminate the sampled air. Allowing the samplers to run overnight in a wellventilated clean location should usually prevent this contamination. We have not seen evidence of this problem in real sampling situations after a preliminary sampler break-in period of operation. Another aspect that maffect sample validity is the seal achieved with the PS-1sampling head. The design of these commercially available heads is adequate for use with our samplers. However, some aspects of the sampler head design could be improved. It was difficult, especially for an inexperienced operator, to obtain reliable airtight seals around the top of the sorbent trap. We recently completed a small field study using these samplers (17) for sampling PAHs and other selected semivolatile compounds in indoor air. The samplers operated reliably and effectively and were entirely acceptable to the residents of the sampled homes. A statistical comparison (18)of the results to those obtained in an earlier study (2, 8,9), which was done without the use of these new samplers, supports our finding of no significant effect of sampler venting on measured indoor PAH levels.
Conclusions The prototype samplers are quiet, easy to operate, and able to collect enough material for chemical analysis and microbioassay. Their operation does not appear to affect significantly the PAH levels in indoor air. Therefore, there is no need to vent the sampler exhaust outdoors during indoor air sampling for these compounds. The advantages gained by not venting the exhaust outdoors are as follows: maintenance of a representative air-exchange rate during the sampling period, reduction of the inconvenience to residents, and reduction of the sampling costs. A PM-10 inlet can be attached to the sampler to allow collection of only those particles smaller than 10 pm. Acknowledgments We thank Steve Hannan for technical assistance and Steve Naber for statistical analyses. Registry No. Naphthalene,91-20-3; acenaphthylene,208-96-8; dihydroacenaphthylene, 83-32-9; phenanthrene, 85-01-8; anthracene, 120-12-7; fluoranthene, 206-44-0; pyrene, 129-00-0; cyclopenta[c,d]pyrene, 27208-37-3; benz[a]anthracene, 56-55-3; chrysene, 218-01-9; benzo[e]pyrene, 192-97-2; benzo[a]pyrene, 50-32-8; benzo[g,h,i]perylene, 191-24-2; dibenz[a,h]anthracene, 53-70-3; coronene, 191-07-1.
Literature Cited (1) Arey, J.; Zielinska, B.; Atkinson, R.; Winer, A. M. Atmos. Environ. 1987, 21, 1437-1444. (2) Chuang, J. C.; Mack, G. A.; Koetz, J. R.; Petersen, B. A. EPA/600/4-86/036; Environmental Monitoring Systems Laboratory, U.S. EPA, Research Triangle Park, NC, 1987. (3) Garner, R. C.; Stanton, C. A.; Martin, C. N.; Chow, F. L.; Thomas, W.; Hubner, D.; Herrmann, R. Enuiron. Mutagen. 1986,8, 109-117. (4) Pyysalo, H.; Tuominen, J.; Wickstrom, K.; Skytta, E.; Tikkanen. L.: Nurmela. T.: Mattila.. T.:. Pohiola. V. Atmos. Environ. 1987,21, 1167-1180. I
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Siak, J.; Chan, T. L.; Gibson, T. L.; Wolff, G. T. Atmos. Environ. 1985, 19, 369-376. Tokiwa, H.; Kitamori, S.; Nakagawa, R.; Horikawa, K.; Matamala, L. Mutat. Res. 1983, 121, 107-116. Miller, M.; Alfheim, I.; Larssen, S.; Mikalsen, A. Environ. Sci. Technol. 1982, 16, 221-225. Lewtas, J.; Goto, S.; Williams, K.; Chuang, J. C.; Petersen, B. A.; Wilson, N. K. Atmos. Environ. 1987,21, 443-449. Chuang, J. C.; Mack, G. A.; Petersen, B. A.; Wilson, N. K. Polynuclear Aromatic Hydrocarbons: Chemistry, Characterization, and Carcinogenesis; Cooke, M., Dennis, A. J., Eds.; Battelle Press: Columbus, OH, 1986; pp 155-171. Lewis, R. G.; Jackson, M. D. Anal. Chem. 1982,54,592-594. Mumford, J. L.; Harris, D. B.; Williams, K.; Chuang, J. C.; Cooke, M. Environ. Sci. Technol. 1987,21, 308-311. Chuang, J. C.; Mack, G. A.; Mondron, P. J.; Petersen, B. A. EPA/600/4-85/065; Environmental Systems Monitoring Laboratory, U.S. EPA, Research Triangle Park, NC, 1987. Ortiz, C. A.; McFarland, A. R. J . Air Pollut. Control Assoc. 1985,35, 1057-1060. Harris, C. M. Handbook of Noise Control, 2nd ed.; McGraw-Hill: New York, 1979, pp 28-8, 28-9. Chuang, J. C.; Hannan, S. W.; Wilson, N. K. Enuiron. Sci. Technol. 1987,21, 798-804.
(16) Chuang, J. C.; Naber, S. J.; Kuhlman, M. R.; Hannan, S.
W.; Mack, G. A. EPA/600/X-87/372; Environmental Systems Monitoring Laboratory, U S . EPA, Research
Triangle Park, NC, 1987. (17) Wilson, N. K.; Chuang, J. C. Polynuclear Aromatic Hydrocarbons, Proceedings, 1Ith International Symposium, Cooke, M. J., May, W. E., Eds.; Lewis Publishers: Chelsea, MI, in press. (18) Mack, G. A.; Stockrahm, J. W.; Chuang, J. C. EPA/6OO/
4-88/000, Atmospheric Research and Exposure Assessment Laboratory, U.S. EPA, Research Triangle Park, NC, in press.
Received for review May 6, 1988. Revised manuscript received April 6, 1989. Accepted May 3, 1989. Although the research described in this article was funded wholly or in part by the United States Environmental Protection Agency through Contract 68-02-4127 to Battelle Columbus Division, it has not been subjected to Agency review. Therefore, it does not necessarily reflect the views of the Agency, and no official endorsement should be inferred. Mention of trade names or commercial products does not constitute endorsement or recommendation for use.
Accumulation and Diagenesis of Chlorinated Hydrocarbons in Lacustrine Sediments Steven J. Elsenrelch,**tPaul D. Capel,$ John A. Robbin$,§and Rlchard BourbonniereII
Environmental Engineering Sciences, Department of Civil and Mineral Engineering, University of Minnesota, Minneapolis, Minnesota 55455, Water Resources Division, U S . Geological Survey, St. Paul, Minnesota 55101, Great Lakes Environmental Research Laboratory, National Oceanic and Atmospheric Administration, 2205 Commonwealth Blvd., Ann Arbor, Michigan 48 104, and National Water Research Institute, Canada Centre for Inland Waters, Burlington, Ontario L7R 4A6, Canada Two sediment cores were taken from the Rochester Basin of eastern Lake Ontario and analyzed for the radionuclides 210Pband 137Csand several high molecular weight chlorinated hydrocarbons (CHs). The two sites are geographically proximate but differ in sedimentation rate, permitting sedimentation-dependent processes to be factored out. The 210Pbchronology showed a mixed depth of 3-5 cm and an intrinsic time resolution of 11-14 years. Vertically integrated numbers of deposit-feeding oligochaete worms and burrowing organisms are insufficient to homogenize the sediment on the time scale of CH inputs, which are non steady state. US. production and sales of polychlorinated biphenyls (PCBs), DDT, Mirex, and hexachlorobenzene (HCB), as determinants of the shape of the input function, adequately predict the overall shape and, in many cases, details in the sedimentary profile. Sediment focusing factors (FF) inferred from 13"Cs and 21"Pbinventories averaged 1.17 and 1.74 for cores E-30and G-32, respectively. This permitted CH accumulation rates to be corrected for focusing. Apparent molecular diffusion coefficients modeled for many of the CHs were about (1-3) x cmz/s.
Introduction Hydrophobic organic compounds (HOCs) of anthropogenic origin are delivered to lacustrine and marine systems t University
of Minnesota.
* U.S. Geological Survey. 0 NOAA. 'I Canada
1118
Centre for Inland Waters.
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by atmospheric transport and deposition, direct and indirect discharges, and riverine inputs. Examples of these organic compounds are polychlorinated biphenyls (PCBs) and other chlorinated hydrocarbons (CHs) used as pesticides (e.g., DDT; Lindane) or generated as byproducts of industrial production [e.g., hexachlorobenzene (HCB)], PCBs, for example, are characterized by their low aqueous solubilities ( 10-9-10-6 mol/L), low vapor pressures (10-8-104 Torr), and resistance to extensive chemical and biological transformation (1,2). Low aqueous solubilities and general hydrophobic nature of these CHs result in high partition coefficients applied to abiotic and biotic particles of 104-106 L/ kg. The primary removal process for these organic compounds in large lakes is adsorption to or partitioning into particles and subsequent sedimentation. The sorptive properties of HOCs are largely controlled by the organic carbon (OC) content of particles, which is itself concentrated in the clay- or fine-size particles (3-5). Thus HOCs will follow the path of the average clay-size particles and be focused into the more quiescent, depositionalbasins of the lake, estuary, or bight. In the Laurentian Great Lakes, organic contaminant residence times are about 2-3 times the fine-particle residence times of 1year determined from mass balance and radioactive tracer studies (6-1 1). Once delivered to the bottom sediments, contaminant and particle burial is slowed by the effects of resuspension (9,12,13)and mixing of surface sediments by aquatic organisms (7, 14-17). The net effect of these processes is to increase the residence time of the contaminant in the ecosystem, inhibit burial in deep sediments, and alter the depositional history of the contaminant in-
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