Environ. Sci. Technol. 2006, 40, 6051-6057
Development of a Passive Sampler To Measure Personal Exposure to Gaseous PAHs in Community Settings ZHIHUA FAN,* KYUNG HWA JUNG, AND PAUL J. LIOY Environmental and Occupational Health Sciences Institute, University of Medicine and Dentistry of New Jersey - Robert Wood Johnson Medical School and Rutgers University, 170 Frelinghuysen Road, Piscataway, New Jersey 08854
A sensitive, simple, and cost-effective passive sampling methodology was developed to quantify personal exposure to gaseous polycyclic aromatic hydrocarbons (PAHs). A FanLioy passive PAH sampler (FL-PPS) is constructed from 320 sections of 1-cm long SPB-5 GC columns (0.75-mm i.d. and 7-µm film thickness), similar to a mini-honeycomb denuder. Given the unique feature of the GC column stationary phase, gaseous PAHs are collected on the inner surfaces of the columns by molecular diffusion and thermally desorbed to GC/MS for analysis. The sampling rates of FLPPS were determined in the laboratory using a controlled test atmosphere containing eight PAHs for a range of face velocity, temperature, relative humidity, PAH concentration, and sampling duration. The sampling rate (mean, %RSD, cm3/min) was 26.7 (21%) for acenaphthylene, 37.6 (25%) for acenaphthene, 56.2 (13%) for fluorene, 49.1 (25%) for phenanthrene, 62.7 (22%) for anthracene, 65.4 (24%) for fluoranthene, and 64.4 (18%) for pyrene over a sampling duration of 8-48 h. The sampling rate for naphthalene was ∼14.1 (12%) cm3/min over a sampling period of 8 h but decreased along with an increase of sampling time. The effects of temperature, humidity, face velocity, and PAH concentration on the sampling rate were not significant for all the compounds tested. A reasonable agreement (85% for all the compounds tested. No PAH residues were found in the samplers or in the thermal desorption system after the first desorption. However, large variations were observed for fluoranthene (36%) and pyrene (30%) due to temperature inhomogeneity in the thermal desorption system. VOL. 40, NO. 19, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
6053
TABLE 3. Sampling Rate of the FL-PPS7 Determined at Different PAH Concentrations in the Laboratorya compound
NAP
ACEN
ACE
FLN
PHE
ANT
FLb
PYb
62.7 22% 3-5 8.0 × 10-4 0.056
65.4 24% 8-20 1.21 × 10-3 0.056
64.4 18% 5.0-15 6.0 × 10-4 0.057
sampling rate (cm3/min) average % RSD C (ng/m3) Vp (Pa)c D (cm2/s)d
14.1 12% 10-2000 10.4 0.069
26.7 21% 1.9-2600 8.9 × 10-1 0.064
37.6 25% 7.7-280 2.87 × 10-1 0.064
56.2 13% 65-200 8 × 10-2 0.061
49.1 25% 15-120 1.61 × 10-2 0.059
a The tests were conducted at 0.006 m/s, 23 °C, and 10% RH for 8 h. b Fluoranthene (FL) and pyrene (PY). c Vp: vapor pressure at 25 °C (Sonnefeld et al. 1983, ref 20). d D: diffusion coefficient (cm2/s) was calculated from the method presented in ref 19.
Results and Discussion PAH Concentrations in the Dynamic System. Samples were collected at 23 °C, 10% RH, and 0.006 m/s face velocity on 7 separate days over the testing period to determine PAH concentrations and to test their stability of the dynamic system. The average concentration (SD, ng/m3) was 76 ( 3 for naphthalene, 2600 ( 330 for acenaphthylene, 138 ( 15 for acenaphthene, 79 ( 12 for fluorene, 55 ( 12 for phenanthrene, 4.0 ( 0.9 for anthracene, 17 ( 2 for fluoranthene, and 9.0 ( 2.5 for pyrene in the dynamic system. These results showed that the test atmosphere provided a stable gaseous PAH source for evaluating the FL-PPS performance under different sampling conditions. Unless specified otherwise, duplicate samples were analyzed for each testing condition in subsequent experiments. The percent difference between the duplicates was less than 25%. Selection of GC Column and the Optimal Sampler Geometry for the FL-PPS. The parameters that may affect the FL-PPS sampling rate were examined by comparing the sampling rates obtained from the 7 different passive samplers. As shown in Table 2, the FL-PPS6 constructed from the SPB-5 column had a greater sampling rate than the FL-PPS5 made from the SPB-1 column. These results are consistent with theory presented in the Experimental Section, i.e., the SPB-5 stationary phase has greater affinity to PAH compounds than the SPB-1 stationary phase and therefore results in a greater sampling rate. No significant differences in sampling rate were observed between FL-PPS2 (1-cm long section) and FLPPS3 (2-cm long section tube). These results indicated that the increasing of the tube length from 1 to 2 cm did not increase the sampling rate, i.e., the effective adsorption length of the FL-PPS was equal or less than 1 cm for our testing conditions. FL-PPS6 (0.75-mm i.d., 7-µm film thickness) had the highest sampling rate when compared to FL-PPS2 (0.25mm i.d., 5-µm film thickness) and FL-PPS4 (0.53-mm i.d., 5-µm film thickness). This is because the FL-PPS6 has the largest A/L ratio at any given effective adsorption length greater than 0.01 mm. Also, its film thickness is the greatest among the 3 samplers. FL-PPS1 (made from a MC-5 multicapillary column) had a greater adsorption area than FLPPS6. However, the sampling rate of the FL-PPS1 was lower than FL-PPS6, which was probably due to the thinner film thickness of the MC-5 column, i.e., lower capacity when compared to other columns. Based on the results summarized in Table 2, the SPB-5 column with 0.75-mm i.d. and 7-µm film thickness was selected to construct the operational version of the passive sampler. The sampling rates of the FL-PPS7 (4 adsorption units, 320 tubes) for all of the compounds tested were ∼4 times higher than those obtained from the FL-PPS6 (1 adsorption unit, 80 tubes), indicating the sampling rate increased proportionally to the number of tubes of the sampler, as indicated by eq 3. It is worth noting that 80 is the maximum number of tubes that allows each sampling unit to be placed inside the 1/2 in. i.d. thermal desorption tube for analysis. Based on the analytical detection limit and the PAH 6054
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 40, NO. 19, 2006
concentrations in our testing system, FL-PPS7 provided a high enough sampling rate for measuring PAHs in our tests. The number of the adsorption units could be increased to improve the method sensitivity. Tests were conducted to evaluate the effect of the length of the cover (1.5- and 2-cm long) in the adsorption unit (Figure 1) on sampling rate. No significant difference was observed in the sampling rate between FL-PPS7 (1.5-cm cover) and FL-PPS8 (2-cm cover), indicating no impact of the cover length on the FL-PPS sampling rate. These results were consistent with the diffusion pathway theory described earlier, i.e., the limiting step for sample collection is the diffusion inside the GC tube. Effect of Face Velocity on Sampling Rate. Ambient air face velocity can affect the performance of diffusive samplers because it may influence the effective diffusion path length (8, 9). Under conditions of low external wind speeds, the effective diffusion path length may increase. Under conditions of high external wind speeds, the effective diffusion path length may decrease. This is because a ‘boundary layer’ exists between the stagnant air within the sampler and the turbulent air outside and contributes to the effective diffusion path length. Given the limited flow capacity of the testing system, the effect of face velocity on the FL-PPS7 sampling rates for 5 PAH compounds were tested at 0.006, 0.02, and 0.10 m/s, representing indoor conditions and flows resulting from typical movement of individuals. The temperature was 23 °C, relative humidity (RH) was 10%, and the sampling duration was 8 h. The average (%RSD) sampling rate (cm3/ min) obtained at 3 different face velocities was 19.5 (16%) for naphthalene, 24.1 (3%) for acenaphthylene, 42.7 (8%) for acenaphthene, 62.6 (8%) for fluorene, and 52.4 (19%) for phenanthrene. These results suggest that no significant impact of face velocity in this range on the FL-PPS performance and the FL-PPS is suitable not only for personal sampling conditions but also for most indoor sampling conditions. This result, again, is expected because the FLPPS7 has unique denuder-type configuration. The diffusion processes are not significantly affected by the wind speed outside of the tube. Given the same reason, although the effect of high face velocity on the FL-PPS7 sampling rate has not been tested in the study, it is expected to be low. Effect of Temperature on Sampling Rate. Since the diffusion coefficient is a function of temperature, the effective sampling rate will be affected by the fluctuation of temperature. Based upon theoretical predictions, the diffusion coefficient is proportional to the square root of the absolute temperature (19). Thus, the calculated change in uptake rate with fluctuations of 20 °C would be only ∼3.5%. These small changes are unlikely to be important over the indoor and ambient temperature range likely to be encountered in the field. Tests were conducted at 23, 30, and 40 °C to examine temperature effects on the FL-PPS7 sampling rate. The RH was 10%, the face velocity was 0.006 m/s, and the sampling
duration was 8 h. Tests below 23 °C were not conducted, because it was difficult to generate a test atmosphere for the temperature lower than 23 °C in our laboratory. Nonetheless, decreases in temperature would have similar or less significant effects because (1) the absolute change in the sampling rate resulting from decreases in temperature is the same as that resulting from increases in temperature and (2) increases in temperature increase the volatility of PAHs, i.e., weaken bonding between PAH molecules and the adsorption medium and, therefore, reduce the effective sampling rate. Therefore, change in the sampling rate caused by decreases in temperature (e.g., from 23 °C to 4 °C) can be estimated based on the results obtained from the tests on increases in temperature (e.g., from 23 °C to 40 °C). The average sampling rates obtained at the 3 temperature levels were similar to those presented in the face velocity test, with RSD% of 4-31% for all 5 compounds tested among the 3 temperature levels. These results are consistent with the theory presented above, i.e., changes in temperatures expected under indoor and ambient conditions will not affect the FL-PPS sampling rates significantly. Effect of Relative Humidity (RH) on Sampling Rate. High humidity levels may affect the sorption capacity of adsorbing material; therefore, tests were also conducted at 50% RH, a typical condition found in indoor air, to examine the RH effect on the FL-PPS7 sampling rate. Except for naphthalene (38%), the differences in sampling rates between 50% RH and 10% RH were less than 13% for the other 4 compounds tested, suggesting the RH effect on the FL-PPS7 sampling rates was negligible. Indeed, a slight increase in the sampling rate was observed for most of the compounds at 50% RH. It is suspected that the water vapor may “stabilize” the PAHs on the adsorbent and therefore increase the sampling rate. Effect of PAH Concentrations on Sampling Rates. The effect of PAH concentrations on the FL-PPS7 sampling rate was tested for a range of PAH concentrations generated in the dynamic dilution system (Table 3). The concentration of PAHs in air may affect the sampling rate because a small pressure of the adsorbate (i.e., PAHs) may exist above the sorbent surface after some PAH uptake, increasing progressively as further PAH vapor is adsorbed. A saturation point will be reached after which no more vapor will be adsorbed. The sampling rates obtained at different concentrations were not significantly different among each other. The average sampling rate (%RSD) obtained from all the tests was 14.1 (12%) for naphthalene, 26.7 (21%) for acenaphthylene, 37.6 (25%) for acenaphthene, 56.2 (13%) for fluorene, 49.1 (25%) for phenanthrene, 62.7 (22%) for anthracene, 65.4 (24%) for fluoranthene, and 64.4 (18%) for pyrene over a sampling duration of 8 h. Similar results were obtained when tested for a sampling duration of 24 h. These results indicated that the PAH concentrations tested did not have great impact on the FL-PPS7 sampling rate. In addition, the sampling rates increased with increasing molecular weight (Table 3), indicating that the volatility of the compound is an important factor affecting the FL-PPS sampling rates. Effect of Sampling Duration on Sampling Rate. As discussed above, the FL-PPS7 sampling rate may decrease with increased sampling time, as PAH loading increases. Tests were conducted for a sampling duration of 4, 8, 24, and 48 h to examine the effect of sampling duration on sampling rate. After 8 h, the collected mass (ng) on the sampler increased linearly along with sampling time (R2 ranged from 0.81 to 1.0, Figure 2) except for naphthalene. These results suggest that the sorbent acts as an “infinite” sink for the PAHs in this sampling duration and concentration range, and, therefore, constant sampling rates were obtained for the 7 compounds within a 48-h sampling duration. The collected mass of naphthalene did not increase linearly with the sampling time and stopped increasing after 8 h, suggesting
FIGURE 2. The mass collected on the FL-PPS7 sampler during sampling durations of 4-48 h. NAP, ACEN, and ACE were corresponding to the y-axis on the right.
FIGURE 3. Stability of PAHs on FL-PPS7 stored at 23 °C for 7 days (a) and at 4 °C for 30 days (b). the saturation of naphthalene on the FL-PPS7. This result is explained by the high volatility of naphthalene and weaker bonding between naphthalene and sorbent, so the effective capacity of the sampler was reached after FL-PPS7 was exposed to naphthalene for 8 h. Stability of PAHs on the FL-PPS. The stability of PAHs on the sampler was tested at 4 °C and room temperature (∼23 °C). Samples were prepared under identical conditions. After sample preparation, the passive samplers were sealed and stored at 4 °C or room temperature. Duplicate samples were analyzed on days 0, 1, 2, 3, and 7 for room-temperature condition storage and on days 0, 1, 2, 3, and 7, 14, and 30 at 4 °C storage conditions. The results obtained at each testing period were compared with concentrations obtained on day 0 to examine the stability of the target compounds. The recoveries of all the compounds at day 7 (room temperature) and day 30 (-4 °C) were greater than 85% (Figure 3), indicating that PAHs were stable on the sampler for 7 days at room temperature and for 1 month at 4 °C. The variability VOL. 40, NO. 19, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
6055
in stability for the PAHs at 2-5 days of storage was primarily caused by analytical variation. Field Evaluation. Ten volunteers were asked to wear both FL-PPS7 and an active sampler for 8 h. The active sampling system contained a 37-mm Teflon filter placed upstream of the XAD-2 cartridge, but only the XAD cartridge was analyzed for gaseous PAHs using the method described in the Experimental Section. The sampling rate was 2 L/min. The performance of the FL-PPS7 was evaluated by comparing the results measured by FL-PPS7 with those obtained from the colocated XAD samples. All the tests were conducted between December 2003 and March 2004, but the temperature during each test was not recorded. The percent difference (diff%) of the concentration measured by the two methods was calculated using the following equation
diff% )
C p - Ca × 100 Ca
(5)
where Cp ) the PAH concentration measured by the passive sampling method, and Ca ) the PAH concentration measured by the active sampling method. No comparison was performed for naphthalene, because the sampling rate of naphthalene changed along with the sampling time. Since the FL-PPS7 sampling rates for the 7 gaseous PAHs tested were independent from temperature, relatively humidity, face velocity, PAH concentrations, and exposure duration at the ranges tested in this study, the mean sampling rates presented in Table 3 were used for calculating PAH concentrations during field evaluation. The average percent difference (standard deviation) of the concentrations measured by the active and passive sampling method was -21 ( 23% for acenaphthene, 26 ( 16% for fluorene, 48 ( 44% for phenanthrene, and 35 ( 58% for anthracene. A large difference was observed in one anthracene (132%) and phenanthrene measurement (102%). If excluding the outliners, the agreement between the two methods improved significantly for these two compounds, with an average difference of 30 ( 29% for phenanthrene and 10 ( 22% for anthracene. The acenaphthylene concentration measured by the FL-PPS 7 was almost double (average difference of 114%) that obtained from the active sampling method. The reason was not clear at this point, and more field tests are required to validate the comparison results for this compound. The results for fluoranthene and pyrene were not presented here because of many nondetects during an 8-h sampling period. In addition, a large variation of fluoranthene and pyrene occurred during the field sample analysis due to the poor performance of the thermal desorption system. Except acenaphthene, the concentrations measured by the FL-PPS7 are higher than those measured by the active sampling method. The differences are probably partially caused by the alternation of PAH gas/particle partitioning and collection of PAHs associated with nanoparticles. PAHs exist in both gas and particle phases. When gaseous PAHs are adsorbed on the passive sampler, to maintain PAH gas/ particle equilibrium, PAHs associated with particle phase may be “off-gassing” and collected by FL-PPS7, resulting in positive error. In addition, the diffusion coefficients of nanoparticles (a few nanometers) are in the same order of that for gaseous species. Some PAH associated with nanoparticles may be collected by FL-PPS7, positively biased the measurements. Finally, the active sampling system used in field evaluation may have “sampling artifacts”, which may contribute to the differences observed between the active and passive sampling methods. Further research is required 6056
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 40, NO. 19, 2006
to understand the effects of these processes on the FL-PPS7 performance.
Summary and Limitations The methodology developed in this study provides a costeffective and convenient means for monitoring personal exposures to PAHs in an epidemiological study and subsequently cancer risks. The FL-PPS is small and light weight and can be worn by small children. It can be used in situations where the air flow is very low (e.g., indoor locations) given its denuder-type design. It can be reused after analysis and a simple cleaning process (i.e., baking at 250 °C for 20 min). Combine with thermal desorption analysis, the methodology developed in this study is suitable for trace level PAH measurement in ambient air, but a sampling duration of 24 h or longer is required in order to detect most gaseous PAHs in ambient air. The method detection limits (MDLs) for PAHs are ∼1-3 ng/m3 (estimated as 3 times the standard deviation of the response derived from analysis 7 FL-PPS7 “blanks” over a sampling duration of 24 h). The sampling rate of the FL-PPS can be increased by increasing the number of tubes used for constructing the sampler when used at very low PAH concentrations. There are some limitations of the FL-PPS sampler and the study design presented in the manuscript. The sampler can only measure PAHs distributed in gas phase. Particlephase PAHs have to be estimated. In addition, personal monitoring can introduce additional variables; therefore, field comparison at a fixed location should be conducted in the future to obtain a more accurate comparison between active and FL-PPS passive sampling methods. Field evaluation of the FL-PPS7 at a 24- and 48-h sampling duration under a variety of PAH concentration ranges is needed in order to apply the FL-PPS in future exposure studies. As stated earlier, we experienced large analytical variations and low recovery for higher molecular weight PAHs (such as fluoranthene and pyrene) due to thermal inhomogeneity in the thermal desorption system used in this study. This can be addressed by using a thermal desorption system with a shorter transfer line. An alternative approach is the liquid extraction method. Given the characteristics of the GC column, the sampler can be liquid extracted and reused after extraction. Benzo(a)pyrene was detected in some field samples that were collected by the FL-PPS7 for 24 h and processed with the liquid extraction method. In addition, other SVOCs (such as phthalates) were detected by the FLPPS in our exploratory studies, indicating the potential applications of the FL-PPS for measuring SVOCs besides PAHs. An application of the FL-PPS for a variety of gaseous species is possible if the coating material of the FL-PPS can be modified based on the compounds of interest. The evaluation of those applications is underway, and the results will be reported in the future.
Acknowledgments This study was supported by National Cancer Institute (NCI) through a Research Agreement (1R21CA94550-01).
Supporting Information Available Schematic diagram of the dynamic system to generate a gaseous PAHs test atmosphere. This material is available free of charge via the Internet at http://pubs.acs.org.
Literature Cited (1) Chuang, J. E.; Callahan, P. J.; Lyu, C. W.; Wilson, N. K. Polycyclic aromatic hydrocarbon exposures of children in low-income families. J. Exposure Anal. Environ. Epidemiol. 1999, 9, 85-98.
(2) Dubowsky, S. D.; Wallace, L. A.; Buckley, T. J. The contribution of traffic to indoor concentrations of polycyclic aromatic hydrocarbons (PAH). J. Exposure Anal. Environ. Epidemiol. 1999, 9, 312-321. (3) Naumova, Y. Y.; Eisenreich, S. J.; Turpin, B. J.; Weisel, C. P.; Morandi, M. T.; Colome, S. D.; Totten, L. A.; Stock, T. H.; Winer, A. M.; Alimokhtari, S.; Kwon, J.; Shendell, D.; Jones, J.; Maberti, S.; Wall, S. Polycyclic aromatic hydrocarbons in the indoor and outdoor air of three cities in the U.S. Environ. Sci. Technol. 2002, 36, 2552-2559. (4) Ohura, T.; Amagai, T.; Fusaya, M.; Matsushita, H. Polycyclic aromatic hydrocarbons in indoor and outdoor environments and factor affecting their concentrations. Environ. Sci. Technol. 2004, 38, 77-83. (5) Boffetta, P.; Jourenkova, N.; Gustavasson, P. Cancer risk from occupational and environmental exposure to polycyclic aromatic hydrocarbons. Cancer Causes Control 1997, 8, 444-472. (6) Cooke, M.; Loening, K.; and Merritt, J. Proceedings of 11th International Symposium in Polynuclear Aromatic Hydrocarbons; Battelle Press: Columbus, OH, 1991. (7) National Academy of Sciences. Human Exposure Assessment for Airborne Pollutants; National Academy Press: Washington, DC, 1991. (8) Berlin, A.; Brown, R. H.; Saunders, K. J. Diffusive sampling; Royal Society of Chemistry: London, 1987. (9) Happer, M.; Purnell, C. J. Diffusive Sampling-A Review. Am. Ind. Hyg. Assoc. 1987, 48 (3), 214-218. (10) Cocheo, V.; Boaretto, C.; Sacco, P. High uptake rate radial diffusive sampler suitable for both solvent and thermal desorption. Am. Ind. Hyg. Assoc. 1996, 57, 897-904. (11) Gillett, R. W.; Kreibich, H.; Ayers, G. P. Measurement of indoor formaldehyde concentrations with a passive sampler. Environ. Sci. Technol. 2000, 34 (10), 2051-2056. (12) Palmes, E. D.; Gunnison, A. F. Personal monitoring device for gaseous contaminants. Am. Ind. Hyg. Assoc. 1973, 32, 78-81.
(13) Patil, S. F.; Lonkar, S. T. Determination of benzene, aniline and nitrobenzene in workplace air: a comparison of active and passive sampling. J. Chromatogr., A 1994, 688, 189-199. (14) Zhang, J.; Zhang, L.; Fan, Z.; Ilacqua, V. Development of the personal aldehydes and ketones sampler based upon DNSH derivatization on solid sorbent. Environ. Sci. Technol. 2000, 34, 2601-2607. (15) Battistoni, P.; Fava, G.; Passeri, D.; Ruello, M. L. Sampling rates field estimates of a diffusive sampler for some polycyclic aromatic hydrocarbons. Interm. J. Environ. Stud. 1992, 41, 6370. (16) Jacob, J.; Grimmer, G.; Hildebrandt, A. The use of passive samplers for monitoring polycyclic aromatic hydrocarbons in ambient air. Sci. Total Environ. 1993, 139/140, 307-321. (17) Vo-Dinh, T. Development of a dosimeter for personnel exposure to vapors of polyaromatic pollutants. Environ. Sci. Technol. 1985, 19 (10), 997-1003. (18) Krieger, M. S.; Hites, R. A. Measurement of polychlorinated biphenyls and polycyclic aromatic hydrocarbons in air with a diffusion denuder. Environ. Sci. Technol. 1994, 28 (6), 11291133. (19) Fuller, E. N.; Schettler, P. D.; Giddings, J. C. A new method for prediction of binary gas phase diffusion coefficients. Ind. Eng. Chem. 1966, 58 (5), 18-27. (20) Sonnefeld, W. J.; Zoller, W. H. Dynamic coupled-column liquid chromatographic determination of ambient temperature vapor pressures of polynuclear aromatic hydrocarbons. Anal. Chem. 1983, 55, 275-280. (21) http://www.cdc.gov/niosh/nmam/pdfs/5515.pdf.
Received for review February 28, 2006. Revised manuscript received July 18, 2006. Accepted July 18, 2006. ES060474J
VOL. 40, NO. 19, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
6057
