fluence of indoor sources and characteristics of the structure appear to be important in determination of indoor levels of respirable particles. In the Waltham and Newton homes, respirable particles seemed to be well mixed throughout the house. Concentrations were similar in the rooms monitored, and no statistically significant differences were found. In the Brighton residence, which is a single-floor, four-room apartment, some high values were found in the bedroom. This is surprising because of the relatively small size of the living unit. However, it has been noticed that cooking odors tend to concentrate and linger in this room, probably because of lower ventilation rates. A study of ventilation rates using sulfur hexafluoride as a tracer gas detected consistently higher SF6 levels in the bedroom of this apartment vs. in the kitchen or the living room. These observations persisted for several hours after uniformly mixing the SF6 tracer. I t suggests lower air exchange rates in this room than for the apartment in general. The large, 3-story, 12-room Victorian home in Watertown also had significantly different room concentrations. SF6 tracer studies indicated uniform decay rates for the first and second floor but not for the third floor. The third floor sampler measured significantly lower RSP concentrations. The decay rate of initially uniformly mixed SF6 was lower than the rest of the house. This study indicates that, while there is generally good mixing of respirable particles inside homes, interroom difference can occur. Smoking, ventilation differences, and localized sources within a certain room can contribute to interhome differences in daily and longer-term RSP concentrations. Upon comparison of the interhome and daily variations in RSP concentrations, the between-room differences are less important. One caveat must be mentioned. If we are interested in personal exposures, short-term interroom differences in pollution concentrations may be important, If individuals are responsible for generating indoor particles in cooking, smoking, vacuuming, or other activities, they may be maximizing their personal exposures.
for 30 days. Margaret Reed, William Turner, Douglas Dockery, and James Ware deserve special thanks for contributing their specific expertise. L i t e r a t u r e Cited (1) Dockery, D. W. Doctoral Thesis, Harvard School of Public Health, Boston, MA, May 1979, p 90. (2) Szalai, A., Ed. “The Use of Time: Daily Activities of Urban and Suburban Populations in Twelve Countries”; Mouton: Paris, 1972; p 114. (3) Ferris, B. G., Jr.; Speizer, F. E.; Spengler, J. D.; Dockery, D.; Bishotx Y. M. M.: Wolfson., M.:, Humble. C. Am. Rev. ResDir. Dis. 1979, iio,767-79. (4) SDenaler. J. D.: Dockerv. D. W.: Turner. W. A,: Wolfson. M. J.: Fe&s,B. G., Jr. Atmos Environ 1981,15, 23-30. ( 5 ) Myers, R. Master’s Degree Research Project, Harvard School of Public Health, Boston, MA, May 1978. (6) Lebowitz, M. University of Arizona, Tuscon, AZ, personal communication. (7) Turner, W. A.; Spengler, J. D.; Dockery, D. W.; Colome, S. D. J Air Pollut. Control Assoc. 1979,29, 747-9. (8) Lippmann, M.; Harris, W. B. Health Phys. 1962,8,155. (9) Spengler, J. D.; Evans, J. D.; Dockery, D. W.; Wolfson, M. J. “Indoor-Outdoor Quality Assurance and Procedures Manual”; Harvard School of Public Health Boston, MA, 1977. (10) Ju, Carol. Master’s Thesis, Harvard School of Public Health, Boston, MA, June 1980, Appendix A. (11) Cochran. W. G.: Cos. G. M. “ExDerimental Designs”. 2nd ed.: Wiley: New York; pp 110-2. (12) Sokal, R. R.; Rohlf, F. J. “Biometry”: W. H. Freeman: San Francisco, CA, 1969; p 237. I
Received for review October 8,1980. Accepted January 28,1981. The Haruard Sin City Study is supported by the National Institute of Environmental Health Sciences Grant No. ES-01108 and by the Electric Power Research Institute Contract No. RP1001-1. Carole Ju’s work was partially supported by the Health Research Administration of the Public Health Service, Grant No. 2-AO3-AH00608. Supplementary Material Available: Tables A-1-A-4 lzsting all observations for all four homes ( 4 pages), along with the indoor/ outdoor daily ratios, will appear following these pages in the microfilm edition of this volume of the journal. Photocopies of the supplementary material from this paper or microfiche (105 X 148 m m , 24X reduction, negatives) may be obtained from Business Operations, Books and Journals Division, American Chemical Society, 1155 16th St., N w . , Washington,DC 20036. Full bibliographic citation (journal, title of article, author) and prepayment, check or money order for $4.00 for photocopy ($5.50foreign) or $4.00 for microfiche ($5.00 foreign), are required.
Acknowledgment We appreciate the cooperation of the residents in the homes where samples were collected, living with humming pumps
NOTES
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Anaerobic Degradation of Halogenated 1 and 2-Carbon Organic Compounds Edward J. Bouwer,’ Bruce E. Rittmann,? and Perry L. McCarty Environmental Engineering and Science, Department of Civil Engineering, Stanford University, Stanford, California 94305
Introduction Concern has been raised Over the presence of trihalomethanes and other low-molecular-weight, halogenated organics in drinking waters and wastewaters. ~h~ trihalomethanes are produced from chlorination of waters containing humic materials ( l - 4 ) , and many of the halogenated organics are known or suspected carcinogens or mutagens ( 3 ) ,Evidence t Present address: Department of civil ~ Illinois, Urbana, IL 61801.
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suggests that they are quite persistent in the environment, are transported easily through soil by groundwater movement ( 5 ) , and break through rapidly in granular activated carbon beds (6).Field evidence for long-term degradation of some of the halogenated organics has recently been obtained at the Palo Alto groundwater recharge project (7), and laboratory studies were instigated in an attempt to confirm these observations. This Dauer - - reDorts on the dearadability of some of the same halogenated compounds and aerobic condi~ ~ ~ i ~under~anaerobic , tions when present at low concentrations (10-200 pg/L).
0013-936X/81/0915-0596$01.25/0
@ 1981 American Chemical Society
rn Trihalomethanes, trichloroethylene, and tetrachloroethylene a t concentrations commonly found in surface water and groundwater were incubated aerobically in the presence of primary sewage bacterial cultures and anaerobically in the presence of mixed methanogenic bacterial cultures. No aerobic conditions were found under which these compounds could be degraded. Anaerobic degradation was observed for the trihalomethanes, but the 2-carbon chlorine-substituted aliphatic compounds remained unchanged or were degraded only slightly. The brominated trihalomethanes were degraded
rapidly in both anaerobic sterile controls and seeded cultures, indicating a chemical mechanism. However, the rate of decomposition increased in the presence of microbial activity. Chloroform degradation was much slower, occurred only in anaerobically seeded cultures, and appears to be biologically mediated. However, a combination of chemical and biological mechanisms cannot be rejected. These batch culture results are consistent with field evidence of long-term degradation of trihalomethanes during groundwater recharge of advanced-treated sewage effluent.
Procedures and Materials The organic compounds used in this study were reagentgrade chloroform (Mallinckrodt Chemical Co., St. Louis, MO), trichloroethylene and tetrachloroethylene (Matheson Chemical, Norwood, OH), dibrornochloromethane (Columbia Organic, Columbia, SC), and bromodichloromethane (Aldrich Chemical Co., Milwaukee, WI). Anaerobic experiments were carried out with the anaerobic medium described by Owen e t al. (8).Sterile 160-mL serum bottles were purged with N2 gas and filled with deoxygenated, anaerobic medium by using an anaerobic pipet (8). Each bottle, except for the sterile controls, was seeded with 1mL of a methanogenic mixed culture grown in a laboratory-scale digester fed waste-activated sludge and operated a t 35 OC. An aqueous solution containing the organic compounds was added to each bottle, and the bottles were immediately sealed without head space by using a Teflon disk and an aluminum cap. The aqueous solution contained 32 pg/mL of each organic compound and was prepared by diluting a stock solution of the halogenated compounds in methanol (55 mg/mL of methanol) with deionized water passed through a 4-cartridge MILLI. Q water purification system (Millipore Corporation, Bedford, MA, 01730). The bottles were incubated in the dark a t 35 "C in an inverted position to minimize gas leakage. Aerobic experiments were carried out with the following sterile, mineral medium (all concentrations in mg/L): 20.0 NaHC03; 8.5 KH2P04; 28.5 K2HP04; 33.4 Na2HP04; 0.25 FeCly6HzO; 1.7 NH4C1;22.5 MgS04; 27.5 CaClz; pH 7.1. The 160-mL sterile serum bottles were filled with mineral medium, and a bacterial inoculum (primary sewage effluent from the Palo Alto, CA, Water Pollution Control Facility) was added to all bottles (2 mL/L) except the controls. The addition of organic compounds to each bottle and the final sealing with Teflon disk and aluminum cap were identical with the anaerobic procedure. The initial dissolved-oxygen concentration was 8-9 mg/L, and the amount of organic carbon added was sufficient to deplete only -2 mg/L of this so that aerobic conditions were maintained throughout the incubation period. All bottles were incubated without agitation in the dark a t 20 OC. Three series of bottles were prepared for the anaerobic and aerobic conditions with low, medium, and high concentrations of each halogenated compound (ca. 10,30, and 100 pg/L, respectively). Every 2-4 weeks throughout the duration of the study, a subset of the bottles was removed and assayed for the halogenated compounds by using the pentane-extraction, gas-chromatographic procedure described by Henderson, Peyton, and Glaze (9).
a 2-week lag period. Degradation a t the high concentration of 157 pg/L was less conclusive, but there appears to have been a gradual reduction in chloroform concentration relative to the sterile controls. No appreciable anaerobic degradation of trichloroethylene (Table 11) and tetrachloroethylene (Table 111)was observed for all concentrations. The small decrease in the values relative to the controls after 1 2 weeks may indicate slow decomposition, but the results are not conclusive. Anaerobic results for bromodichloromethane (Table IV) and dibromochloromethane (Table V) indicate a decline in concentrations in the control as well as in the seeded samples. However, much more rapid degradation to below the detection limit (0.1 pg/L) occurred in the seeded cultures. The results for the aerobic studies are summarized in Table VI. The mean control concentration is given in pg/L, and a coefficient of variation (standard deviatiodmean concentration) is given as a percent of the mean Concentration. The concentrations of the compounds remaining in the seeded bottles are also given as a percent of the mean control con-
Results Table 1shows the change in concentration of chloroform over a 16-week period in the presence of methanogenic bacteria. At an initial concentration of 16 pg/L, anaerobic degradation took place within 2 weeks, and the concentration was eventually reduced to less than 1pg/L. Degradation also occurred with an initial concentration of 34 pg/I, but followed
Table 1. Anaerobic Degradation of Chloroform in the Presence of Methanogenic Bacteria time
high concn, pg/L
week 0 week 6 week 12 week 16
157 97 115 104
week 2 week 4 week 8 week 12 week 16
117 90 78 65 34
medium concn, pg/L
low concn, pg/L
Controls 34 38 40 38
16 12 14 13
Seeded Cultures 29 1
10 5 0.2
3.0 1.9 1.8 1.8 0.2
Table II. Anaerobic Degradation of Trichloroethylene in the Presence of Methanogenic Bacteria time
high concn, pg/L
week 0 week 6 week 12 week 16
187 113 103 92
week 2 week 4 week 8 week 12 week 16
127 105 127 86 69
medium concn, pg/L
low concn, pg/L
Controls 42 43
33 34
18 13 11 11
Seeded Cultures 34 40 42
30 30
12 12 14 8 9
Volume 15, Number 5, May 1981 597
Table 111. Anaerobic Degradation of Tetrachloroethylene in the Presence of Methanogenic Bacteria time
high concn, pg/L
medium concn, pgfL
low concn, pgfL
Controls week 0 week 6 week 12 week 16
176 110 99 88
week 2 week 4 week 8 week 12 week 16
130 93 133 68 56
36 44 32 33
17 12 10 10
Seeded Cultures 32 35 54 24 20
10 11 16 5 7
Table IV. Anaerobic Degradation of Bromodichloromethane in the Presence of Methanogenic Bacteria lime
high concn, pgfL
medium concn, pgfL
low concn, pgfL
Controls week 0 week 6 week 12 week 16
161 69 57 46
week 2 week 4 week 8 week 12 week 16
