Environ. Sci. Technol. 1989,23, 1408-1412
Techniques of Water Resources Investigations; Skougstad, M. W., Fishman, M. J., Friedman, L. C., Erdmann, D. E., Duncan, S. S., Eds.; US.Geological Survey: Reston, VA, 1979;Book 5,Chapter Al. Small,H.; Stevens, T. S.; Bauman,W. C . Anal. Chem. 1975, 47,1801-1809. Bremner, J.M.; Keeney, D. R. Soil Sei. SOC.Am. R o c . 1966, 30, 577-582. Zapico, M.M.; Vales, S.; Cherry, J. A. Groundwater Monit. Rev. 1987,7442. Garabedian, S. P. Ph.D. Dissertation, Massachusetb Institute of Technology, Boston, MA,1987.
(38) Levy, B.S.;Chambers, R. M. Hydrol. Processes 1987,1 , 385-389. (39) Trudell, M. R.; Gillham, R. W.; Cherry, J. A. J. Hydrol. 1986,83,251-268. (40) Ceazan, M. L. Masters Thesis, Colorado School of Mines, Golden, CO, 1987. (41) Mariiky, J. A.;Baldwin, R.; Reddy, M. M. J. Phys. Chem. 1985,89,5303-5307.
Received for review November 21, 1988. Revised manuscript received May 19,1989. Accepted July 26, 1989.
Personal Exposures to Acidic Aerosols and Gases Mlchael Brauer, Petros Koutrakis, and John D. Spengler'
Department of Environmental Science and Physiology, Harvard University, School of Public Health, 665 Huntington Avenue, Boston Massachusetts 021 15 Exposures to aerosol strong H+, SO:-, NH4+,NO3-, NO;, and the gaseous pollutants SOz, HN03,HN02,and NH3were monitored in the metropolitan Boston area with a personal annular denuder/filter pack sampling system. The personal exposure measurements were compared to measurements collected at a centrally located ambient monitoring site. Concentrations of acidic aerosols and gases measured by personal monitoring were found to differ significantly from those measured at the fixed outdoor location. Personal exposures to aerosol strong H+ were slightly lower than concentrations measured at the stationary site due to the neutralization of acidic particles and their incomplete penetration into indoor environmenta. Concentrations of SO:- and NH4+measured by personal monitoring were similar to those measured by the fixed location ambient monitor. Personal measurements of SOz and HN03 were much lower than those measured outdoors, reflecting deposition of these gases on indoor surfaces. The formation of HN02via reactions of nitrogen oxides on indoor surfaces resulted in personal exposures to HN02 that were substantially higher than outdoor concentrations. Personal exposures to the basic gas, NH3, were also higher than ambient measurements. To our knowledge, this pilot study represents the first use of annular denuders for personal exposure monitoring and promises to open up a new area of personal exposure sampling techniques. The results of this study support the use of personal monitoring to determine human exposures. By applying the personal monitoring techniques used in this study to representative samples, it will be possible to determine population exposures to acidic aerosols and gases.
Introduction Recently, concern over adverse ecological and health effects from acid rain and its precursors has led to numerous studies of particulate and gaseous atmospheric acidity (1). This research has focused on the environmental fate of airborne acidity and its effects on the ecosystem (2). Additionally, several epidemiological investigations have suggested human health effects from exposure to particulate and gaseous acidity (3-7). While these studies attempted to relate respiratory health and concentrations of atmospheric acidity, all relied on stationary site monitors to provide surrogate measurements for personal exposure. Such studies neglect spatial variability within the study area and indoor/outdoor concen1408 Envlron. Sci. Technol., Vol. 23, No. 11, 1989
tration differences (8,9). Since exposure to constituents of airborne acidity arises from outdoor and indoor sources, as well as from penetration of outdoor pollutants indoors, we felt it necessary to characterize personal exposures to these compounds and to determine the contributions of indoor and outdoor environments to personal exposures (10,11). In this study we measured personal exposures to acidic aerosols and gases with personal annular denuder sampling instruments and compared these to ambient measurements collected with a similar annular denuder system.
Methods A personal impactor/annular denuder/filter pack system, shown schematicallyin Figure 1, was designed by our group and modified for this study to simultaneouslycollect acidic gases (SOz, HNO and HNOJ and NH3in addition to aerosol species ( S O F , NO3-, NO2-, NH4+,and strong H+). The components of the personal sampler have been described in detail elsewhere (12).The personal sampler is based upon the Harvard-EPA annular denuder system (HEADS), which was used as the stationary site monitor in this study (13-15). The personal annular denuder samplers were connected to personal sampling pumps and operated at a flow rate of 4 L min-'. The HEADS were operated at a flow rate of 10 L min-'. Sampling was conducted in the metropolitan area of Boston, MA, for 24 days during July and August of 1988. Analytical procedures have been described elsewhere (12-16). Detection limits were based on the working sensitivity of the ion chromatographic analysis and correspond to approximately 1.0, 1.1, 1.7, and 3.6 ppb.m3 for SO2, HN03, HN02, and NH3, respectively. Detection limits for the aerosol species were 12.7,31.5,42.4,84.7,and 49.0 nmol for S042-, NO3-, NO2-, NH4+,and strong H ' , respectively. Mean sampling volumes for the entire study were 14.1,5.4,4.0,and 1.3 m3for central site, personal total, personal indoor, and personal outdoor samples, respectively. To determine the detection limit for a given sample, the ppb.m3 or nmol values were divided by the mean sampling volume for the sample type of interest. Data are presented in box plots and as results of regression analysis. For the box plots, all data (including samples below the detection limit) are included. The regression analysis excluded values below the detection limit, as well as clear outliers in cases where sampling problems justified their exclusion.
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Figure 1. Schematlc of personal impactor/annular denuder/fltter pack sampling system. Total sampler length is 36.5 cm.
For every 24-h sample, two volunteers each wore both a total exposure (24-h) personal sampler and an identical system that was operated either indoors or outdoors. Specifically, one person turned a sampler on only when they were indoors, while the other individual activated a sampler only while outside. During working hours and early evenings the volunteers remained together. The total and indoor personal samplers continued to operate in the volunteers' bedrooms at night. Three homes in a suburban area approximately 5 miles from the central monitoring site were used for nighttime indoor measurements. No systematic differences were observed between samples collected at the different homes, although an air conditioner was used occasionally in one home. When the air conditioner was operated, the aerosol concentrations were substantially lower than those obtained at the other home on the same sampling day. For these days the samples from the air-conditioned home were excluded from the regression analysis. With this sampling scheme we were able to estimate the contributions of indoor and outdoor exposures to a person's total (24-h) exposure. These personal exposure concentrations were then compared with 24-h measurements made at a fixed-location outdoor monitoring site. The stationary central monitoring site, located in downtown Boston, was elevated (250 m) above street level to decrease the influence of local pollution sources on measured concentrations and to increase the likelihood that these central site samples collected regional long-range transported pollution. To increase the ability to determine the relationship between ambient measurements and personal exposures to particulate H+, a sampling bias was deliberately introduced into the study to preferentially select for high personal outdoor exposures. The volunteers intentionally spent more time outside on days when meteorological conditions (intensity of solar radiation, absence of rain, visibility degradation) suggested that Sod2-and H+levels would be higher.
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Figure 2. Concentration distributions (In ppb) for central ske and personal samples of (A) SO,, (B) HNO,, (C) HNO,, and (D) NH,.
Results and Discussion
The mean concentration of SO2 at the central site was approximately 5 times higher than in the personal total and indoor samples (Figure 2A). Since people spend a majority of their time indoors, personal exposure is usually dominated by indoor exposure (9). Personal indoor and total measurements of SOz were dominated by nighttime indoor exposures, which were likely to have low SO2concentrations due to the deposition of SO2on indoor surfaces Environ. Sci. Technol., Vol. 23, No. 11, 1989
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Table I. Regression of Central Site and Personal Samples for (A) Gases and (B) Aerosolsa
personal intercept f N sample type slope f SE SE (A) gasb
so,
HN03
R2
44 31 31 25 2 25
total indoor outdoor total indoor outdoor
0.13 f 0.02 NS 0.43 NS NS 0.15 f 0.03 0.13 f 0.08 0.49 NS 0.94 f 0.11 NS 0.74
42 31 27 43 30 29 13 13 13
total indoor outdoor total indoor outdoor total indoor outdoor
0.60 f 0.07 0.71 f 0.12 1.38 f 0.20 0.80 f 0.09 0.97 f 0.20 1.45 f 0.27 0.23 f 0.04 0.27 f 0.06 NS
(B)aerosol'
so*2NH,+ H+
31.0 f 7.76 0.63 NS 0.53 NS 0.62 NS 0.65 NS 0.44 NS 0.49 8.3 f 1.55 0.76 NS 0.59
OThe personal sample is the dependent variable for regression. SE, standard error. NS, not significantly different from zero at p < 0.001. Correlations for HN02, NH NO3-, and NO, were not significant for any sample type. $Intercept f SE in ppb. 'Interce~tf SE in nmol
and the absence of indoor SOz sources. The mean value of the central site concentration was also higher than the outdoor personal sample. This can be explained by the difference between the two measurements, both of which were outdoor samples. The central site sample was a 24-h sample while the outdoor sample was collected over a shorter duration, restricted to daylight hours. During these hours, convective processes and the oxidation rate of SO2 to S042- is greatest. Consequently, the outdoor sample contained a lower concentration of SO2 and a higher concentration of SO4* than the central site sample. Since both the central site and the total samples were 24-h average concentrations, they were correlated (Table IA). In contrast, the outdoor personal SO2 and central site SO2were not correlated. As with SOz, the total and indoor personal concentrations of HNO, were substantially lower than the central site and outdoor personal measurements (Figure 2B). The concentration differences reflect deposition of HNO, onto indoor surfaces. While the central site concentrations are greater than those of the personal outdoor samples, the absence of any HN03 indoors indicates that personal exposure to HNO, is dominated by outdoor exposure. Although the diurnal pattern of HN03 concentrations suggests that peak concentrations would be present during the daytime, the personal outdoor samples were collected at ground level where deposition of HN03 may result in lower concentrations than a t the central site (17). The decrease in HNO, production a t night, in addition to its high deposition velocity, explains why personal indoor, and consequently total, HN03 concentrations were lower than at the central site. Similar to our findings for SOz, our results suggested that personal exposure to HNO, was dominated by outdoor exposure. In contrast to the other acid gases (SO2and HN03), our HN02 measurements revealed a distinctly different pattern. Personal indoor and total concentrations of HN02 were uncorrelated with, and higher than, outdoor and central site concentrations, indicating that personal exposure to HN02was dominated by indoor exposure (Table IA,Figure 2C). Indoor concentrations of HN02 result from the reaction of nitrogen oxides (NO,) on indoor surfaces (18-21). The chemical mechanism of this process was 1410
Envlron. Sci. Technol., Vol. 23,No. 11, 1989
recently suggested to involve a heterogeneous reaction between an adsorbed H20-N02 complex and gaseous NO2 (22).The overall reaction may be summarized as 2NOdg) + H2O(g) HNO2(g) + HNOdads) (1) The HN03 produced is highly reactive with surfaces and therefore remains adsorbed. In contrast, HN02 is less reactive and persists in the indoor air for an extended period of time. High levels of indoor HN03 (>30 ppb) have been observed in several recent studies, although the kinetics of the NO2 to HN02 conversion process have yet to be clearly defined (18-20). Since the indoor locations where our samples were collected had no unvented NO, sources, we reason that outdoor NO, penetrate indoors and subsequently react on surfaces to produce HN02. Outdoor NO2 concentrations in the suburban Boston area during the study were 5-30 ppb. It was clear that the total exposure to HN02 was dominated by the indoor concentration, as the central site HN02 concentration was nearly one-third of the total exposure even though both samples were collected over the same 24-h period. While HN02 is formed in low concentrations outdoors, it is photolyzed during the day, leading to similar central site and personal outdoor concentrations. NH3 is important for its ability to neutralize acid aerosols and gases, forming ammonium salts (reactions 2-4). NH&) + H,SO,(s) NH,HSO~(S),(NH4)3H(S04)2(~), (NH4)2S04(~)(2)
-
-
NH3(g) + HNOdg) e NHi"&s) (3) NH3(g) + HNO2(g) e NH&JO~(S) (4) All personal NH, measurements were higher than the central site measurement (Figure 2D). However, the absence of a correlation between personal and central site concentrations of NH3 suggested that personal exposure to NH, may be dominated by NH3 emitted from people in exhaled breath or from skin and hair. Concentrations of NH3 as high as 750 ppb have been measured in exhaled breath, but special tests showed that we could not attribute the high personal NH3 concentrations to contamination by the volunteers breathing directly into the denuders (23). Transient exposure to high concentrations from outdoor sources, such as sewer systems, is also a possible contributor to the high personal NH3 measurements. Personal indoor NH3 concentrations were lower than personal outdoor samples since most of the indoor sample was collected during the night, when the sampler was at bedside, some distance away from individuals. Particulate S042-concentrations were correlated and similar for the central site and the total and indoor personal samples, suggesting high penetration of SO4* indoors (Table IB, Figure 3A). Comparison of indoor and ambient concentrations gives a minimum estimated aerosol penetration of 70%. The estimated penetration is a minimum value since it compares indoor measurementa, dominated by nighttime concentrations, with central site measurements that are dominated by high daytime concentrations. However, our penetration estimate agrees with that of an extensive home sampling study (IO). The personal outdoor concentrations were higher and more variable than the other samples, reflecting short-duration exposures during the period of the day when S042-production was highest. Each of the personal measurements were correlated with central site SO4* concentrations, due to the outdoor origin of S042- and its ability to penetrate indoors. NH4+concentrations followed a pattern similar to that of S042- (Figure 3B), largely due to the coexistence of the two ions (reaction 2). Central site, personal total, and
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personal indoor NH4+concentrations were all similar and somewhat lower than personal outdoor levels. Since NH4+ ions mainly result from the neutralization of acidic sulfates, NH4+concentrations were correlated with SO4* (mean R2 = 0.87) and H+ (mean Rz = 0.61) concentrations for all samples. The ratio of indoor personal to central site concentrations was higher for NH4+than for S04z-since neutralization of indoor HNOz was an additional indoor NH4+source (reaction 4), resulting in concentrations of NH4+that were slightly higher than those predicted strictly from outdoor concentrations. Similarly, the indoor to central site ratio of NOz- was greater than the corresponding SO4* ratio, suggesting indoor formation of NOzby reaction 4 (Figure 3). Indoor NO3- results from the penetration of NH4N03 aerosols of outdoor origin (formed by reaction 3) or from the oxidation of NH4NOzaerosols indoors (Figure 3D). Aerosol strong acidity is mainly associated with S04z-. Concentrations of H+ were lower than SO4* concentrations since HzS04particles were partially neutralized by NH3 (Figure 3C). The extent of neutralization can be estimated from the regression of central site SO4* on H+ (R2= 0.83, slope = 0.28, intercept NS). For total personal exposure (R2= 0.48, slope = 0.09, intercept NS) and indoor personal (R2= 0.78, slope = 0.09, intercept NS) samples, aerosol sulfate concentrations were less acidic, due to neutralization by high indoor NH, levels. For the outdoor personal samples, SO?- and H+ were also correlated (R2= 0.55, slope = 0.12, intercept NS), indicating that the personal outdoor H+exposure resulted from high concentrations of acidic sulfates, of which only a small fraction was not neutralized by the time the sample was collected. H+ concentrations were high in personal outdoor samples due to the high rate of SOz oxidation to HzS04 during the sampling period, resulting in acid levels that were sufficiently high to overcome neutralization by the large amount of NH3 collected during this sample duration. It is also possible that high H+levels did not coexist tem-
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porally or spatially with high levels of NHS.
Conclusion Through personal monitoring it may be demonstrated that exposures to constituents of atmospheric acidity differ from those inferred from fured-site ambient measurements. Although personal exposure to summer particulate acidity is driven by outdoor sources, spatial and temporal mobility of humans results in concentrations that differ from those obtained at a central site. Studies of population exposure to acidic species will help to quantify the relationships between personal exposure and ambient and indoor concentrations. The sampling equipment used in this study can be reduced in size and weight for application to comprehensive population exposure studies. These personal annular denuders permit high flow rate collection of both particle- and vapor-phase acidity. Given the substantial contribution of indoor HNOz to total acid exposure, it will be important to separately characterize both particle- and vapor-phase acidity in future studies. Our results are preliminary and suggest that among the important questions to be addressed are the penetration of H+ indoors, the indoor concentrations of NH3, and the indoor source generation rate of HNOP The understanding of these factors will be necessary to accurately charackrize personal exposures and to properly attribute health outcomes to sources of exposure. Acknowledgments We thank Larry Stone of University Research Glassware for fabricating the personal samplers. Additionally, we thank Dr. J. M. Wolfson, Dr. J. L. Slater, and Dr. G. J. Keeler for their assistance in planning the study and in development work. Finally, the study could not have been undertaken without the support of the volunteers and laboratory staff Aaron Martinez, Zev Hardman, Sarah Spengler, Steve Ferguson, and Christine Donoghue. Envlron. Sci. Technol., Vol. 23, No. 11, 1989
1411
Environ. Sci. Technol. 1989, 23, 1412- 1419
Registry No. SO2, 7446-09-5; HN03, 7697-37-2; HN02, 7782-77-6; NHS, 7664-41-7; NH4+, 14798-03-9; H+, 12586-59-3. L i t e r a t u r e Cited Schwartz, S. E. Science 1989, 243, 753-163. Schindler, D. W. Science 1988, 239, 149-157. Lippmann, M. EHP, Environ. Health Perspect. 1985,63, 63-70. Lippmann, M. EHP Environ. Health Perspect. 1989, 79, 3-6. Bates, D. V.; Sizto, R. In Aerosols: Research, Risk Assessment and Control Strategies; Lee, Z., Schneider, Z., Grant, Z., Eds.; Lewis Publishers: Chelsea, MI, 1987; pp 761-771. Bates, D. V.; Sizto, R. EHP, Environ. Health Perspect. 1989, 79, 69-72. Speizer, F. E. EHP, Environ. Health Perspect. 1989, 79, 61-68. Spengler, J. D.; Sexton, K. Science 1983, 221, 9-16. Spengler, J. D.; Soczek, M. Enuiron. Sci. Technol. 1984, 18, 268A-280A. Dockery, D. W.; Spengler, J. D. Atmos. Environ. 1981,15, 335-343. Sinclair, J. D.; Psota-Kelty, L. A,; Weschler, C. J. Atmos. Environ. 1988, 22, 461-469. Koutrakis, P. et al., Atmos. Enuiron. (in preparation).
Koutrakis, P. et al. Environ. Sci. Technol. 1988, 22, 1463-1468. Slater, J. L., Brauer, M., Koutrakis, P., and Keeler, G. J. In Proc. of the 1988 EPAIAPCA Symposium on Measurement of Toxic and Related Air Pollutants. pp. 176-181. Brauer, M.; Koutrakis, P.; Wolfson, J. M.; Spengler, J. D. Atmos. Enuiron. 1989,23, 1981-1986. Koutrakis, P.; Wolfson, J. M.; Spengler, J. D. Atmos. Environ. 1988, 22, 157-162. Allegrini, I. et al. Sci. Total Environ. 1987, 67, 1-16. Pitts, J. N.; Wallington, T. J.; Biermann, H. W.; Winer, A. M. Atmos. Environ. 1985, 19, 763-767. Biermann, H. W.; Pitts, J. N., Jr.; Winer, A. M. In Advances in Air Sampling; ACGIH, Lewis Publishers: Chelsea, MI, 1988; pp 265-289. Brauer, M., unpublished observations. Nishimura, H.; Hayamizu, T.; Yanagisawa, Y. Environ. Sci. Technol. 1986,20, 413-416. Jenkin, M. E.; Cox, R. A.; Williams, D. J. Atmos. Environ. 1988,22, 487-498. Larson, T. V.; Covert, D. S.; Frank, R.; Charlson, R. J. Science 1977, 197, 161-163.
Received for review March 20, 1989. Accepted July 17, 1989. Supported by EPA Cooperative Agreement CR-812667-02-2 and NIEHS Training Grant ES07155.
Destruction of Chlorination Byproducts with Sulfite Jean-Phlllppe Crouet and David A. Reckhow Environmental Engineering Program, Department of Civil Engineering, University of Massachusetts, Amherst, Massachusetts 0 1003
The observation that sulfite can destroy mutagenic activity in chlorinated waters has important implications with respect to the use of S(IV) in water treatment and sample preservation. The purpose of this study was to evaluate the reaction of sodium sulfite with specific organohalides formed during the chlorination of drinking water. In the first phase, chlorinated fulvic acid solutions were analyzed by closed-loop stripping and GC/MS. Compounds susceptible to decomposition were identified by treating some solutions with sulfite and some without. Phase two included a series of kinetic experiments using pure solutions of chloropicrin, trichloroacetonitrile, dichloroacetonitrile, dibromoacetonitrile, l,l,l-trichloropropanone, chloral, 1,l-dichloropropanone, 2,3,6-trichloroanisole, and 3-chloro-4-(dichloromethyl)-5hydroxy-2(5H)-furanone (MX). The reactions were found to be first order in the compound and first order in sulfite (specifically, [Sot-]). Each of the reactive compounds gave reduced products (loss of halogen) at rates that suggest the use of sulfite is a feasible means of controlling selected chlorination byproducts in drinking water treatment. Introduction
It is well-known that the chlorination of humic substances leads to the formation of volatile and nonvolatile halogenated compounds. In general, these compounds are the same as those observed after chlorination of natural surface water or drinking water. These compounds are also believed to be responsible for much of the mutagenic act Present address: University of Poitiers, France; at the time of this work, Dr. Croue was an employee of the Compagnie General des Eaux.
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tivity found in finished drinking waters. Recent work suggests that many chlorination byproducts are destroyed by reaction with sodium sulfite, a reducing agent added to remove residual chlorine before analysis (1-3). Knowledge of the reactions of commonly used reducing agents with disinfection byproducts is critical for the proper development of analytical procedures. Because the U S . Environmental Protection Agency (EPA) is considering the adoption of more restrictive chlorination byproduct standards, there is an urgent need for new or improved control technologies. Most approaches to chlorination byproduct control fall under one of three categories: (A) removal of organic precursors, (B) minimization of chlorine contact, and (C)removal of byproducts. The first two have been responsible for most of the progress to date in reducing byproduct levels. The direct removal of chlorination byproducts has been less widely practiced, because of poor performance using current technologies (e.g., coagulation of low molecular weight byproducts) or high costs associated with newer technologies (e.g., activated carbon adsorption). The research presented here has implications with respect to a new and inexpensive process for byproduct removal, chemical reduction with S(IV) species. Since sulfur dioxide and its aqueous forms are used for dechlorination in drinking water systems, the application of these compounds represents a currently available and acceptable technology. Background
Hazardous Chlorination Byproducts. Most of the chlorination byproducts that are being considered for regulation by the U.S.EPA and state agencies are among the group of haloorganic mutagens or suspected carcinogens [e.g., halonitriles, haloketones ( 4 , 5 ) ] . Researchers at the US.EPA Health Effects Laboratory in Cincinnati
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