Environ. Sci. Technol. 1992, 26, 517-521
Phenoxyalkanoic Acid Herbicides in Municipal Landfill Leachates Peter A. Gintautas, Stephen R. Daniel," and Donald L. Macalady
Department of Chemistry and Geochemistry, Colorado School of Mines, Golden, Colorado 8040 1 Analysis of leachates from six U.S. municipal landfills revealed the presence of chlorinated 2-phenoxypropionic acid herbicides; however, none of the more widely used acetic acid analogues was present at quantifiable levels. All the leachates contained MCPP. 2,4-DP and silvex were detected in four of the six. The herbicide 2,4-DB was also found in four of the leachates. These compounds persisted in the leachates during 2-3 years of storage while significant depletion of total organic carbon (TOC) in general and of low molecular weight carboxylic acids in particular was observed. Since landfills and leachates are microbially active environments (as demonstrated here by the TOC depletion during storage), this unexpected lack of degradation of several phenoxy herbicides poses concerns for possible groundwater contamination. The concentrations of these herbicides present in the leachat,es (0-90 pg/L) are consistent with disposal of small quantities of household hazardous waste or disposal of plant materials which contain the herbicides. Introduction Following World War 11, chlorinated phenoxyacetic acids, principally 2,4-D, MCPA, and 2,4,5-T (Figure l), came into widespread use for broadleaf weed control (1). They remain among the most commonly applied weedkillers, although use of 2,4,5-T on food crops has been restricted since 1969 (2). Other chlorinated phenoxyalkanoic acids (Figure 1)were subsequently introduced as complements to the phenoxyacetic species in either application or action. The phenoxypropionic compounds are more effective in control of several weed varieties while the 4-phenoxybutyric acid compounds are safer in use with some crops (I). Degradation of the phenoxyacetic species in environmental systems has been extensively studied, that of other phenoxyalkanoic acids less so (1). Although these compounds have been shown to undergo photochemical degradation in laboratory studies ( 3 ) ,the significance of this degradation pathway in the environment remains in doubt (4). Much more significant is the decomposition by microorganisms via both direct metabolism and cometabolism. In warm, moist soil, degradation of phenoxyalkanoic acids has been considered sufficiently rapid and complete that "... they are biodegraded in the vegetation or soil; hence, there is no lasting hazard to susceptible crops or persisting contamination of the environment" ( I ) . Furthermore, soils previously treated with phenoxyalkanoic acids exhibit enhanced biodegradation rates for subsequent applications (5). Silvex was introduced in 1953, mecoprop in 1956,2,4-DP in 1961. While these 2-phenoxypropionic acid herbicides were reported by some researchers as more resistant to microbial degradation (6-8) than the phenoxyacetic acids, others have reported extensive degradation of the 2phenoxypropionic compounds (9-13) under a variety of conditions. A survey of groundwater monitoring data (14) revealed detection of silvex in 2.4% of CERCLA sites and 1.4% of RCRA sites, which suggests some environmental persistence. In 1979 (15) the U S . Environmental Protection Agency announced a preliminary ban on use of silvex and 2,4,5-T due to potential oncogenic, fetotoxic, and teratogenic risks 0013-936X/92/0926-0517$03.00/0
associated with their use. In March 1985, all registered uses of silvex and 2,4,5-T were terminated ( I @ , but sale and distribution of existing stocks for limited uses was permitted. Mecoprop and 2,4-DP remain in widespread use. As part of a study in our laboratory of the influence of organic ligands on metal ion mobilization in landfill leachates (17), carboxylic acid components of landfill leachates were identified and quantified. The unanticipated discovery of mecoprop in one of these samples prompted a more specific search for the phenoxyalkanoic acid herbicides in the leachates. The presence of chlorophenoxy acid herbicides in these landfill leachates suggests their degradation in these generally anaerobic, microbially active systems is not complete. Experimental Section Leachates. Leachate samples from six Subtitle D landfills across the United States were provided to our laboratory by Nicholas Loux and Claudia Chafin of the U S . EPA Athens Environmental Research Laboratory. The sites are identified here only in terms of the states in which they are located. The samples were received within 24 h of collection. A replicate sample of each leachate was frozen upon collection and maintained in that condition until extracted for analysis. Refrigerated samples were stored at 277 K in the original collection vessels and were handled only in an inert atmosphere box. Parameters such as pH, Eh, conductivity, alkalinity, and total organic carbon (TOC) were measured on receipt and monitored periodically for approximately 3 years thereafter. Where possible, measurements were performed in the box. Chemicals. Dichloromethane and methanol were pesticide residue grade (J.T. Baker); methyl tert-butyl ether (MTBE) was pesticide residue grade (Burdick and Jackson). These solvents were stored at ambient temperature and used without purification. Methylation was performed using 14% (w/v) boron trifluoride in methanol (Supelco) which was stored at 277 K and used without purification. Anhydrous sodium sulfate was reagent grade (Mallinckrodt); prior to use for drying extracts, it was rinsed repeatedly with the solvent present in the extract and then dried in an oven at. 383 K and atmospheric pressure. Deuterated internal standard solution (1,4-dichlorobenzene-d4, naphthalene-d,, acenaphthene-d,,, phenanthrene-d,,, chrysene-d,,, and perylene-d,,) was purchased from Supelco. The external standards 2-fluoro-4-iodotoluene and 2-fluorobiphenyl were purchased from Aldrich Chemical Co., Milwaukee, WI. Free acid forms of the herbicides (Aldrich) and corresponding methyl ester forms (Chem Service Co.) were used without further purification. All other chemicals were reagent grade materials which were used as received. Instrumentation. Identification and quantification of herbicides were performed using two Extrel ELQ400 mass spectrometers, one interfaced to a Hewlett-Packard 5890 gas chromatograph and the other interfaced to a Varian 3400 gas chromatograph. DB-5 30-m capillary columns (J&W Scientific) were employed in both instruments. Extraction Procedures. Appropriate volumes of unfiltered, refrigerated leachate were extracted on two separate occasions, July-August 1989 (Table I) and June 1990
0 1992 American Chemical Society
Environ. Sci. Technol., Vol. 26, No. 3, 1992 517
H2-CO0 H
~U2-COOH
0
0 CI
9FHZ-CHZ-CHz-COOH c1
I c1
Cl
MCPA 4thloro-o-tolyl-
2,4,5-T
2,4-D
2,4dichlorophenoxyacetic acid
oxyacetic acid
2,4,5-tnchlorophenoxyacetic acid c1
2,4-DB 4-(2,4-dichlorophenoxy)butyricacid CH3-FH-C00H
C H 3-?H-CO0
CH3-FH-C00U
?
0
I
0 I
CI
CI
H
QCH3 CI
MCPP
Silvex
2,4-DP
Mecoprop
Dichloroprop 2-(4chloro-o-tolyl2-(2,4-dichlorophenoxy)propionic acid 0xy)propionicacid Flgure 1. Phenoxyaikanoic acid herbicides. Table I. Extraction Parameters: 1989
leachate vol, mL base-neutral vol, mL acid extract vol, mL
NJ
leachate OR T X
728 0.5 1.5
660 0.3 1.0
0.5 1.5
760 0.3 1.0
UT
WI
642 0.3
0.5
2.0
1.0
783
leachatea FL NJ1 NJ2 NJ3 OR T X UT WI 400 1.0
400 1000 950 930 810 1.0 1.0 1.0 1.0 1.0
1.0
1.0
1.0
1.0 1.0 1.0
"NJ1. NJ2. and NJ3 are analvtical reolicates of the NJ samole. ~~~~~
~
(Table 11). Unfiltered leachate samples that had been maintained frozen since collection were melted and extracted in March 1991 (Table 111). Slightly different procedures were employed in these three cases. In 1989 the leachate pH was adjusted to approximately 10 with NaOH and 10 pL of internal standard solution added. Within 20 min after pH adjustment, the leachate was extracted twice with 100-mL aliquots of dichloromethane using a separatory funnel. The combined extract was dried over Na2S04, concentrated to approximately 5 mL in a Kuderna-Danish apparatus with attached three-ball Snyder column, and blown down to final volume (Table I) using NS. After addition of 10 pL of external standard, the base-neutral extract was analyzed via GC/MS. After adjustment to pH 1, the residual leachate was extracted with three 150-mL aliquots of MTBE using a separatory funnel. The combined extracts were dried over Na2S0,, concentrated to approximately 5 mL in a Kuderna-Danish apparatus with three-ball Snyder column, and blown down to approximately 0.2 mL using N,. Approximately 2 mL of the methylating reagent BF3-CH30H was added to the sample, which was then transferred to 518
leachate" FL NJ OR ORS ORSD T X UT leachate vol, mL 400 500 300 200 base-neutral vol, mL 1.0 1.0 1.0 1.0 acid extract vol, mL 1.0 1.0 1.0 1.0
200 1.0 1,0
400 400 1.0 1.0 1.0 1.0
OR, ORs, and ORSD are the OR sample, OR matrix spike, and OR matrix spike duplicate, respectively.
Table 11. Extraction Parameters: 1990
leachate vol, mL 200 430 base-neutral vol, 1.0 1.0 mL acid extract vol, mL 1.0 1.0
2-(2,4,5-trichlorophen0xy)propionic acid
Table 111. Extraction Parameters: 1991
FL
733
2,4,5-TP
Environ. Sci. Technol., Vol. 26, No. 3, 1992
a small PTFE-lined screw-cap vial. The capped vial was heated at 363 K for 5-10 min. After cooling, approximately 5 mL of NaC1-saturated water was added, the contents were thoroughly mixed, and the derivatized sample was extracted with 1 mL of CH,Cl,. After addition of 10 pL of external standard, the derivatized acid extract was analyzed via GC/MS. Reagent blanks (deionized water containing sodium chloride for ionic strength adjustment) were extracted, derivatized, and analyzed in parallel with leachate samples each day. No phenoxy herbicides were found in any of the blanks. In 1990, base-neutral extraction was performed at pH 8 with CH,C12 using a glass continuous liquid-liquid extraction apparatus (Precision Scientific Glassblowing of Colorado). This modification of the procedure used in 1989 was designed to minimize problems associated with emulsion formation during extraction of some leachates. Emulsion formation was largely eliminated at pH 8 in the continuous extraction apparatus. Acid extraction was performed a t pH 1with CH,Cl, using a glass continuous liquid-liquid extraction apparatus (24-h extraction time). Concentration, derivatization, and analysis procedures were as in 1989. Pertinent volumes are given in Table 11. In 1991, the frozen samples were melted and extracted via the procedure used in 1990. Pertinent volumes are given in Table 111. Quantitative Analyses. Standard solutions of the free acid forms of the herbicides were derivatized by following the procedure described above for the leachate extracts.
inal quantification limit of 1pg/L. Silvex was present in all three replicates with a mean concentration of 7 pg/L and a range of 6-8 pg/L. Since the phenoxyalkanoic acid herbicides are often applied as ester rather than free acid forms (I), the base-neutral extracts were also analyzed for these compounds.
Table IV. Matrix Spike/Matrix Spike Duplicate Resultsa spike compd
sample concn
spike concn
spike added
476 492 532 478 483 483
500 500 500
18 ND ND
MCPP 2,4-DP silvex MCPP 2,4-DP silvex
500 500 500
% rec
RPDb
92 98 106 92 97 97
0 2 10
a Concentrations in micrograms per liter. bRPD, relative percent difference beween matrix spike and matrix spike duplicate concentrations. RPD = [(spike concentration - spike duplicate concentration)/(spike concentration + spike duplicate concentration)/21 X 100.
Both retention time (approximately 5-s windows) and spectral fit criteria were used to identify derivatized herbicides in the extracts. Quantification of each herbicide was obtained from the characteristic single-ion peak areas and relative response factors (RRF) based on the nearest internal standard (IS). RRF =
(target ion area)(IS concentration) (IS ion area)(target concentration)
sample concentration = (target ion area)(IS concentration) (RRF)(IS ion area) The efficiency of the derivatization procedure was evaluated for the derivatized standards using standard solutions of methyl esters of the herbicides (Chem Service). In all cases, the efficiency was greater than 90%. The validity of quantification using characteristic target ion integrations from full scan runs was checked via single-ion monitoring of standards and the 1989 extracts. Resulting concentrations agreed within 1pg/L in all cases; therefore, only full-scan characteristic target ion area quantification was employed for the 1990 and 1991 extracts. Precise quantification limits vary with the volume of sample extracted and the specific compound determined; however, 1pg/L is representative for the analyses reported here. Analytical accuracy and precision were evaluated by performing a matrix spike/matrix spike duplicate (MS/ MSD) procedure on aliquots from the frozen OR leachate sample. The results (Table IV) show recoveries of at least 92% and relative percent differences (RPD) no greater than 10% for the phenoxypropionic acid analytes. In 1990 three aliquots of the NJ leachate were analyzed (Table 11) as another measure of sample and analytical variability. The mean of the three MCPP determinations was 72 pg/L with a range of 57-94 pg/L. The 2,4-DP was present above the quantification limits in one replicate (at 2 pg/L) and was present in the other two extracts just below the nom-
Results and Discussion Analytical results for the three sets of analyses of the six leachates are presented in Table V. The concentrations of herbicides in these six leachates in Table V were calculated from the GC/MS analyses of the acid extracts, assuming 100% efficiency in all extraction and derivatization steps. Consequently, these may be considered as minimal estimates of actual concentrations. The 1989 data for the UT leachate are definitely low due to emulsion formation during extractions; this problem was eliminated in later analyses. No phenoxyalkanoate esters or free acids were found in the base-neutral extracts. The concentrations of phenoxyalkanoic acids found in the frozen samples are generally lower than those found in the refrigerated samples. Since the frozen samples were preserved in polyethylene containers while the refrigerated samples were in glass, sorptive losses to the container may account for some of this difference. The freezing process may also result in precipitation of mineral phases supersaturated in the leachates (e.g., calcite) with attendant sorption of these analytes. The analytical results are reported to provide evidence that no significant loss of phenoxyalkanoic acids occurred during storage of the refrigerated samples prior to analysis. Mecoprop was found in all the samples analyzed while 2,4-D and MCPA were not observed in any of these samples; 2,4,5-T was detected a t concentrations below the quantification limit in two leachates (NJ and OR). Since 2,4-D is the most widely used phenoxy herbicide in the United States (I),these data imply significant differences in degradation rates for these two phenoxy herbicides in leachates. Recoveries of the acetic acid analogues were found to be approximately half those for the propionic compounds from MS/MSD experiments. The absence of acetic acid analogues cannot therefore be attributed entirely to analytical factors. Indeed, Oh and Tuovinen (8) reported that "... MCPP is more persistent than 2,4-D to bacterial degradation". Though analyses for the phenoxy herbicides were not performed on these samples immediately following collection, comparison of the 1989 and 1990 results indicate nondetectable or minimal degradation rates for mecoprop in the leachates. Storage conditions were certainly not identical with those to which the sample matrix would have been exposed in adjacent aquifers. However, the samples were kept at low temperature in the dark under anaerobic conditions not unlike expected landfill conditions. Another sample collected at the WI site 18 months earlier (1986) was found to contain 70 pg/L
Table V. Leachate Chlorophenoxy Acid Herbicide Concentrations (pg/L)" Florida 89 2 14 ND ND ND ND ND ND
FR
MCPP 2,4-DP silvex 2,4-DB
90 6 ND ND ND
New Jersey FR 89 90 79 90 72b 3 5 lb 6 7b 10 6 1 ND
FR 18 4 ND ND
Oregon 89 20
90 21
ND ND ND
2 P ND
FR 4 ND ND ND
Texas 89 3 ND ND ND
90 4 ND ND ND
FR 7 ND ND ND
Utah 89 17' ND le 1'
90 40 P 5
ND
Wisconsin 89 90 66 67 2 3 P ND 1 ND
"FR, samples frozen in the field and preserved frozen until extraction. 89, samples extracted in July and August 1989. 90, samples extracted in June 1990. ND, not detected. P, present but below quantification limit of 1 rg/L. Both detection and quantification limits vary with volume of sample extracted. Average of three analytical replicate determinations. Minimum concentration; extraction of Utah leachate on this date formed an emulsion. Environ. Sci. Technol., Vol. 26, No. 3, 1992
519
WI
7.0‘ 0
’
‘
I
”
500
’
I
”
’
1000
I
DAYS SINCE COLLECTION Figure 2. Variation in W I leachate composition during storage: TOC, total organic carbon in mg of CIL; TIC, total inorganic carbon in mg of CIL.
MCPP but no detectable silvex. The collection and storage conditions for this sample were less stringent than for the later sample, so the two cannot be considered true replicates. Nonetheless, the results are remarkably similar. A similar lack of disappearance can be seen for silvex, at least in the NJ and UT leachates and for 2,4-DP at least in the NJ and WI leachates. These observations concerning absence of degradation cannot be attributed to lack of bioactivity in the leachate samples during the period between the two analyses. Figure 2 illustrates the diminution in TOC concentration observed for the WI leachate during this time period. A 10-fold or greater loss of short-chain carboxylic acids was observed in the WI sample during the storage period. The TOC result for the frozen sample of WI leachate yielded 1150 mg of C/L, essentially identical to that obtained for the refrigerated sample upon receipt. While less dramatic, similar evidence of biological activity was observed for the other leachates. The disappearance of 2,4-DB, which has been reported (9) to degrade more rapidly than the propionic compounds, from the NJ, UT, and WI samples between the two analyses further supports this contention. Leachate production volumes have been estimated (18) for the FL and OR sites as 1.7 X lo7and 1.3 X lo7gal/year (in 1985), respectively. Using the concentrations in Table V, one can estimate the total mass of the various herbicides produced in the leachate. These calculations yield 900 g of mecoprop/year for the FL site and 990 g/year for the OR site. Of course, these are minima, as explained above. The introduction of such quantities of these herbicides into a municipal landfill lies within the realm of reasonable expectation given their widespread domestic use. Such quantities are consistent with disposal of “empty” cans of commercial herbicides or with residual herbicides in disposed plant matter [these herbicides are reported to persist in plants ( I ) ] ,for example. The corresponding calculation for silvex based on the 1990 result for the OR leachate (sampled in 1987) yields 34 g of silvex/year released 2 years after all registered uses of silvex were canceled. The WI landfill opened in 1983,4 years after silvex use was severely restricted; so the presence of detectable levels of silvex in the WI leachate is even more surprising. We conclude that the chlorinated 2-phenoxypropionic herbicides, particularly mecoprop, are ubiquitous in municipal landfill leachates from the United States. These compounds may have been undetected or unidentified in previous studies due to analytical limitations. The very complex matrices of landfill leachates may, for instance, pose difficulties in conventional GC/ECD analyses for these compounds. For example, Reinhard et al. (19) re520
Environ. Sci. Technol., Vol. 26, No. 3, 1992
ported an unidentified chlorinated carboxylic acid with m / z 228 molecular ion (for the methyl ester) in a Canadian landfill leachate plume. Comparisons of analytical procedures with those used in our study (Reinhard, M., private communication) suggest that this compound was mecoprop, or another apparently persistent chlorinated phenoxyalkanoic acid compound, 2-(4-chlorophenoxy)-2methylpropanoic acid. We also found this drug metabolite, which was identified by Garrison et al. (20) in both raw and treated sewage effluent, in four of the landfill leachates. Our studies suggest that the degradation of (chlorophenoxy)propionic acids in landfill leachates is sufficiently slow that transport into groundwater is possible. Systematic studies of degradation pathways would be required to support this implication. Recent studies have shown that both reductive dehalogenation (21) in anaerobic systems and hydrolysis of the phenoxy linkage in anaerobic and aerobic systems (21,22) contribute to degradation of (ch1orophenoxy)acetic acids in model landfill systems. Similar systematic studies of degradation pathways for the (ch1orophenoxy)propionic acids, particularly in anaerobic systems similar to landfills, have not been reported and seem warranted. The presence of propionic but not acetic analogues could, however, arise from differences in the amounts of or processes by which these compounds find their way into landfills (e.g., plant matter residues or household disposal) rather than from degradative differences.
Acknowledgments The assistance of Nick Loux and Claudia Chafin in obtaining samples and that of Analytica Inc. (Golden, CO) in providing facilities for extraction and analysis of some samples is greatly appreciated. The helpful suggestions of Wayne Garrison are also appreciated. Registry No. MCPP, 7085-19-0; 2,4-DP, 120-36-5; 2,4-DB, 94-82-6; silvex, 93-72-1.
Literature Cited (1) Loos, Michael A. In Herbicides: Chemistry, Degradation, and Mode of Action, 1st ed.; Kearney, P. C., Kaufman, D. D., Eds.; Marcel Dekker: New York, 1975; Vol. 1, Chapter 1. (2) Nelson, B. Science 1969, 166, 977. (3) Smith, A. E. Reu. Weed Sci. 1989, 4, 1. (4) Crosby, D. G. In Herbicides: Chemistry, Degradation, and Mode of Action, 1st ed.; Kearney, P. C., Kaufman, D. D., Eds.; Marcel Dekker: New York, 1976; Vol. 2, Chapter 9. (5) Smith, A. E,; LaFond, G. P. In Enhanced Biodegradation of Pesticides in the Enoironment; Racke, K. D., Coats, J. R., Eds.; ACS Symposium Series 426; American Chemical Society: Washington, DC, 1990; pp 14-22. (6) Alexander, M.; Aleem, M. I. H. J. Agric. Food Chem. 1961, 9, 44. (7) Altom, J. D.; Stritzke, J. F. Weed Sci. 1973, 21, 556. (8) Oh, K. H.; Tuovinen, 0. H. Bull. Enuiron. Contam. Toxicol. 1977, 47, 222. (9) Ou, L. T.; Sikka, H. C. J. Agric. Food Chem. 1977,25,1336. (10) Smith. A. E.: Ostwald, T. H. Weed Sci. 1979, 27, 389. (11) Smith,’ A. E. bull. Enuiron. Contam. Toxicol. 1985,34,656. (12) Horvath, M.; Ditzelmuller, G.; Loidl, M.; Streichsbier, F. Appl. Microbiol. Biotechnol. 1990, 33, 213. (13) Bovey, R. W. In T h e Science of 2,4,5-T and Associated Phenoxy Herbicides, 1st ed.; Bovey, R. W., Young, A. L., Eds.; John Wiley and Sons: New York, 1980; Chapter 9. (14) Plumb, R. H. Ground Water Monit. Reu. 1987, 7, 94. (15) Fed. Regist. 1979, Dec 13, 72328. (16) Chem. Mark. Rep. 1985, March 25, 5. (17) Gintautas, P.; Huyck, K.; Daniel, S.; Macalady, D. Metal organic interactions in Subtitle D landfill leachates and
Environ. Sci. Technol. 1992, 26, 521-527
associated ground waters. Workshop on Metal Speciation and Transport in Ground Waters, Jekyll Island, GA, May 24-26, 1989. NUS Corp. Characterization of Municipal Waste Combustion Ashes and Leachates from Municipal Solid Waste Landfills, Monofills, and Codisposal Sites; EPA/530/SW87-028; US.EPA, Office of Solid Waste: Washington, DC, 1988. Reinhard, M.; Goodman, N. L.; Barker, J. Environ. Sci. Technol. 1984,18, 953. Garrison, A. W.; Pope, J. D.; Allen, F. R. In Identification & Analysis of Organic Pollutants in Water, 1st ed.; Keith, L. H., Ed.; Ann Arbor Science Publishers: Ann Arbor, MI, 1976; Vol. 1, Chapter 30. Gibson, S. A.; Sulfita, J. M. Appl. Environ. Microbiol. 1990, 56, 1825.
(22) McAllister, P. J.; Rao Bhamidimarri, S. M.; Chong, R.; Manderson, G. J. Water Sci. Technol. 1991, 23, 413.
Received for review M a y 14, 1991. Revised manuscript received September 29, 1991. Accepted September 30, 1991. Partial support of this work by the Athens Environmental Research Laboratory is gratefully acknowledged. Although the research described i n this paper has been supported i n part by the United States Environmental Protection Agency through cooperative research agreement CR-814290-01 between the Colorado School of Mines and the Athens Environmental Research Laboratory of the E P A , it has not been subjected to Agency review and, therefore, does not necessarily reflect the views of the Agency. No official endorsement should be inferred. Use of trade names does not imply endorsement but they are provided for descriptive purposes.
Source Apportionment of Indoor Aerosols in Suffolk and Onondaga Counties, New York Petros Koutrakis" and Susan L. K. Briggs School of Public Health, Harvard University, 665 Huntington Avenue, Boston, Massachusetts 02 115
Brian P. Leaderer John Pierce Foundation, Yale University, 290 Congress Street, New Haven, Connecticut 065 19
An indoor air quality study was conducted in two New York State counties. Week-long fine particle mass samples were collected indoors in 394 homes and outdoors in a subset of these homes. The aerosol samples were analyzed by X-ray fluorescence for 16 elements. Homes included in this study had one or more of the following sources: cigarette smoking, kerosene heaters, wood-burning stoves, and gas stoves. Homes with none of the above sources were also included. A simple physical model was used to ascertain the contribution of indoor and outdoor sources. Among the four investigated sources, cigarette smoking was found to be the most important source. Kerosene heaters were also important, but to a lesser extent. Gas stoves did not contribute to the observed indoor aerosol concentrations, yet other unknown indoor sources were significant contributors. The results of this study suggest that a simple physical model can be used to predict indoor fine-mass and elemental concentrations.
Introduction Assessment of total human exposures to airborne particles requires the knowledge of indoor pollutant concentrations for two primary reasons: (i) individuals spend a great fraction of their life indoors, especially in cold climates, and (ii) indoor pollutant concentrations can be significantly different from those outdoors. Indoor aerosol concentrations are associated with both indoor and outdoor air pollution sources. The identification of sources and the assessment of their relative contribution can be a complicated process due to the presence of a number of indoor sources, which can vary from building to building. In addition, there are uncertainties associated with estimating the impact of outdoor sources on the indoor environment. In this paper, an attempt is made to investigate the origin of indoor aerosols using results from an extensive indoor/outdoor aerosol monitoring program conducted in Onondaga and Suffolk Counties in New York State. Sampling and Analysis During the-period of January 6 to April 15, 1986, an indoor air quality program was conducted in Onondaga 0013-936X/92/0926-0521$03.00/0
County and Suffolk County, NY. Suffolk County is located on eastern Long Island, east of New York City. Onondaga County is situated in northwestern New York State and includes the city of Syracuse. Week-long fine particle mass samples were collected indoors in 394 homes; outdoor sampling was conducted a t a subset of homes in each county. Homes were selected according to their potential indoor aerosol sources such as cigarette smokers, gas stoves, wood-burning stoves or fireplaces, and kerosene heaters. The fine particle mass measurements were obtained using the Harvard impactor, which collects fine particles with aerodynamic diameters of
