Environ. Sci. Technol. 1989,23, 985-988
Formaldehyde Exposures inside Mobile Homes Ken Sexton,*,+ Myrto X. Petreas,$ and Kai-Shen L l d
Office of Health Research, US. Environmental Protection Agency, Washington, DC 20460 and Indoor Air Quality Program, California Department of Health Services, 2 151 Berkeley Way, Berkeley, California 94704 An age-stratified random sample of 470 mobile homes was selected from among the more than 500000 in California. One-week, average indoor formaldehyde concentrations were measured during both the summer (JulyAugust 1984) and the winter (February-March 1985) seasons. Results indicate that (1)formaldehyde concentrations were well-mixed inside the trailers over a 1-week period, (2) relatively little variation was observed in formaldehyde concentrations between summer and winter, (3) average 1-week formaldehyde values were in the range of 0.07-0.09 ppm, and (4) formaldehyde levels appear to be decreasing inside mobile homes manufactured since about 1980, probably as a result of the increased use of low-formaldehyde-emitting building materials. Based on the 470 mobile homes in this study, 31% exceeded the maximum concentration of 0.1 ppm formaldehyde recommended by the American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE),the American Industrial Hygiene Association (AIHA), and the Environmental Protection Agency (EPA).
Introduction Exposure to airborne formaldehyde can cause mucous membrane irritation and may lead to sensitization in some individuals. There is also suggestive evidence that respiratory tract allergy might occur. Moreover, there is increasing concern about the potential of formaldehyde to act as a human carcinogen (1-6). Manufactured housing units (e.g., mobile homes, prefabricated houses) are especially prone to formaldehyderelated problems because they tend to use proportionally more materials that emit formaldehyde than conventional homes, to have relatively smaller interior volumes, and to have lower air-exchange rates (7). In fact, complaints from residents of mobile homes about acute health effects, such as eye and throat irritation, skin rash, dry and sore mouth, coughing and sneezing, runny nose, rapid breathing, and shortness of breath, have prompted formaldehyde measurement programs in Minnesota (8-IO), Texas (11,121, Washington (13, 14), and Wisconsin (15-1 7). Most of these studies were carried out in residences where occupants had reported symptoms. Typically, the measurement protocol called for closure of all doors and windows for several hours and then use of wet-chemical methods (e.g., impingers with an absorbing solution of either sodium bisulfite or water) to collect samples over periods of 30-60 min. There is, therefore, little data available about the distribution of exposures experienced by mobile home residents during normal day-to-day activities. Nor is there adequate information about seasonal variations in indoor formaldehyde concentrations, despite the fact that emission rates from building materials are known to vary according to temperature and relative humidity, as well as with the age for the emitting material (18). Overall, there are insufficient data on the pattern and severity of formaldehyde exposures inside mobile homes with which to make accurate assessments of the US.Environmental Protection Agency.
* California Department of Health Services. 0013-936X/89/0923-0985$01.50/0
attendant public health risks.
S t u d y Design In 1984, a project was undertaken to measure formaldehyde concentrations inside a representative sample of mobile homes within the State of California. Because formaldehyde emissions from building materials decrease over time, newer mobile homes are likely to have the highest indoor concentrations. It was decided, therefore, to select an age-stratified random sample from the approximately 500 000 mobile homes in California. Homes were selected for inclusion in the study so that -60% were manufactured between 1981 and 1984 (i.e., less than 4 years old). Participants in the study were volunteers who were solicited by mail. Data on indoor formaldehyde concentrations, as well as information about housing and occupant characteristics, were obtained in 470 mobile homes for both the summer (July-August 1984) and winter (FebruaryMarch 1985) seasons. A detailed description of the study design and measurement protocol has been published previously (19), as has a summary of nitrogen dioxide measurements in a subset of the mobile homes (20). One-week formaldehyde concentrations were measured in the kitchen and bedroom of each trailer by use of passive monitors. Each monitor consisted of a capped glass tube (approximate dimensions, 2.4 cm X 9 cm) containing a glass-fiber filter treated with NaHS03. Sampling began when the monitor cap was removed and formaldehyde diffused into the tube where it was absorbed on the filter. Monitors were recapped after 7 days and returned to the laboratory for analysis by the chromotropic acid method. Information about relevant housing and occupant characteristics was gathered through the use of self-administered questionnaires. Housing and Occupant Characteristics Data on important housing and occupant characteristics for the study population are given in Table I. The agestratified random sample, which was selected from among all the mobile homes in California, comprised 271 residences (58%) manufactured from 1981 to 1984,86 (18%) manufactured between 1976 and 1980, and 113 (24%) made prior to 1976. Gas, either alone or in combination with other fuels, was used for cooking in approximately 8790 of the mobile homes, and for heating in -94%. Approximately one-third of the study participants were retired persons, 65 years of age or older, and -12% were 19 years or younger. Eighty-three percent of the mobile homes were occupied by one or two people, and less than 3% had five or more occupants. During the week that sampling occurred, no cigarettes were smoked inside 56-5990 of the residences, depending on the season, while two packs or more were smoked inside 12-15% of the participating mobile homes. Results and Discussion A comparison of kitchen and bedroom formaldehyde concentrations for both seasons is provided in Figure 1. These data show that there is a consistent and statistically
0 1989 American Chemical Society
Environ. Sci. Technol., Vol. 23. No. 8, 1989
985
45
Table I. Data on Housing and Occupant Characteristics for 470 Mobile Homes in California"
parameter
1
HCHO CONC. ~BEDR(MIl=0.003*0.960~HCHOCONC. (KITCHEN)
no. of homes, % summer winter (July/Aug (Feb/March 1984)
1985)
year of mobile home manufacture 1981-1984 1976-1980 1971-1975 1966-1970 0.10 ppm >0.40 ppm
>0.05 ppm
329 (70%) 373 (79%) 373 (79%)
147 (31%) 146 (31%) 147 (31%)
3 (1%) 0 0
0 45
l’able 111. Comparison of One-Week Formaldehyde Concentrations Measured Inside Newer (Manufactured 1981-1984) and Older (Manufactured 1957-1980) Mobile Homes
HCHO CONC.(WI~ER)=0.057~0.36. HCHO CMIC.(SU)MER)
0 401
Rz=U.25
*
*
*
no. of mobile year of homes manufacture
season summer
271
winter a
0a
I
E 00
0 05
0 I0
0 25
0 20
0 15
0 30
0 40
0 35
0 45
summer/winter av
FORMALDEHYDE CONCENTRATION (PFU) JULY/AUCUST 1984
Figure 2. Comparison of 1-week formaldehyde concentrations between the summer and winter seasons inside 470 mobile homes.
-
0.35
-
470 271 199 470 271 199 470
temperature and relative humidity, one might expect that highest formaldehyde concentrations would be observed during the summer (9,18,21). For the 470 mobile homes in this study, average formaldehyde levels were slightly higher during the winter. This might result because of more ventilation during the summer, when ambient temperatures and emission rates are highest, and less during the winter, when ambient temperatures and emission rates are lower. Analysis of the amount of time that windows were kept open (from occupants’ diaries) shows that, during the summer, mobile home occupants typically had windows open for -50% of the time, while windows were open -14% of the time in the winter (22). Although ventilation (air exchange rate) was not measured directly, the available evidence suggests that indoor formaldehyde levels during the summer may have been reduced through increased dilution with outdoor air. The release of formaldehyde from pressed wood products and other sources inside mobile homes is known to decrease exponentially with time (18).Previous studies have consistently shown that highest indoor formaldehyde concentrations tend to occur in new mobile homes, with 0.40
1981-1984 1957-1980 1957-1984 1981-1984 1957-1980 1957-1984 1981-1984 1957-1980 1957-1984
199
HCHO ppm
‘Oncn*
x,O
SD,b
0.08 0.06 0.07 0.09 0.06 0.08 0.09 0.07 0.08
1.98 2.02 2.02 1.60 1.80 1.73 1.62 1.79 1.73
geometric mean. *SD., geometric standard deviation.
O R ,
values decreasing gradually over time (8, 11, 15,16). A comparison of mean formaldehyde concentrations in the 271 mobile homes (58%) manufactured between 1981 and 1984 and the 199 (42%) manufactured from 1957 to 1980 is presented in Table 111. As expected, the geometric mean formaldehyde concentration inside newer mobile homes was higher than for older trailers in both seasons. Although differences were relatively small, 0.02-0.03ppm, they were statistically significant in all cases 0, < 0.05). Figure 3 gives a more detailed picture of the relationship between mobile home age and indoor formaldehyde concentrations. Data on annualaverage (mean of summer and winter) formaldehyde levels are plotted according to the year of manufacture for all 470 mobile homes. For those trailers manufactured from 1980 to pre-1966, the data follow the expected pattern, with indoor values gradually decreasing with increasing age. For those mobile homes manufactured after 1980,however, indoor formaldehyde concentrations actually are higher in the older residences (The sample size is too small to permit any inferences
---
MAX = MAXIMUM VALUE
0.30
3
MIN
-
4 0, 0,
0.25
-
U
p:
MAX
I-
2-
8pU
0.20
-
0.15
-
I
0.10
MIN
0.05 MIN
I
I
I
1984
1983
(3)
(1151
I
1982 (1061
I
1981 (47)
I
I
MINIMUM VALUE 75th PERCENTILE 50th PERCENTILE (MEDIAN) 25th PERCENTILE
T
I
I
1
I
I
I
I
1
1
I
1980 (201
1979 (17)
1978 (1s)
1977 (17)
1976 (17)
1075 (9)
1074 (141
1073 (19)
1972 (14)
1971 (15)
I
1970 (7)
I
1960 (7)
I
1968 (10)
1
1967 (4)
I
I
1966 >lo66 (7) (7)
YEAR OF M A N U F A C T U R E (NUMBER OF MOBILE HOMES)
Figure 3. Observed relationship between indoor formaldehyde concentrations and year of manufacture for 470 mobile homes. Environ. Sci. Technoi., Voi. 23, No. 8, 1989 087
about trailers made in 1984). This apparent discrepancy is probably a result of changes in the emissions of formaldehyde from building materials used in mobile homes. In about 1980, the particle board industry began introducing products with lower formaldehyde emission rates in anticipation of federal regulations (23). The makers of manufactured residences, including mobile homes, also began to use increasing amounts of these building materials designed to emit less formaldehyde. It is likely that these changes account for the lower formaldehyde levels observed in mobile homes built after 1980. S u m m a r y and Conclusions Formaldehyde measurements inside 470 mobile homes indicate that occupants are routinely exposed to elevated formaldehyde concentrations, with mean 1-week values in the range of 0.07-0.09 ppm. Formaldehyde concentrations were observed to be well-mixed inside the trailers over periods of 1 week. Although winter values were slightly higher, relatively little variation was found between indoor levels in the summer and those in the winter. Formaldehyde concentrations decreased with mobile home age for those trailers manufactured between 1957 and 1980. The data suggest, however, that for mobile homes manufactured from 1981 to 1983, indoor formaldehyde levels actually increase with age. This is probably a result of the increased use of low-formaldehyde-emittingbuilding materials in the construction of post-1980 mobile homes. The U S . Environmental Protection Agency and the American Industrial Hygiene Association (AIHA) both recommend that outdoor formaldehyde concentrations not exceed 0.1 ppm ( 2 4 , 2 5 ) . Similarly, the American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) recommends that indoor formaldehyde concentrations in nonindustrial settings not exceed 0.1 ppm (26). The Department of Housing and Urban Development (HUD) has promulgated an emissions regulation that is aimed a t keeping formaldehyde concentrations inside mobile homes below 0.4 ppm (18). Based on the 470 mobile homes in this study, 31% exceeded 0.1 ppm during both the summer and winter, while less than 1% exceeded 0.4 ppm in the summer and none in the winter. Because these values represent 1-week, integrated measurements, it is likely that short-term peaks (minutes, hours) were substantially higher. Consequently, the percentage of mobile homes that exceed the stated values will probably be greater when short-term formaldehyde concentrations are taken into account. Exposure to formaldehyde concentrations above recommended levels is a fact of life for many mobile home occupants. Acute health effects among mobile home residents are well documented, and there is increasing concern about possible long-term, chronic health consequences. Better characterization of exposures, especially in new mobile homes, and establishment of the link between exposures and adverse health outcomes are prerequisites for realistic assessment of related public health risks. Acknowledgments
The research presented in this paper was carried out while Dr. Sexton was Director of the California Indoor Air Quality Program. This study would not have been possible without help from the following members of the Air and
988
Environ. Sci. Technol., Vol. 23, No. 8, 1989
Industrial Hygiene Laboratory, California Department of Health Services: B. Chang, S. Hayward, F. Y. Huang, E. Kothny, G. Kulasingam, L. Pierce, L. Webber, and J. Wesolowski. We especially thank the mobile home residents who volunteered to participate in the study. Registry No. HCHO, 50-00-0.
Literature Cited ZARC Monogr. Eval. Carcinog. Risk Chem. Humans 1982, 29(May). Clary, J. J., Gibson, J. E., Waritz, R. S., Eds. Formaldehyde: Toxicology, Epidemiology, Mechanisms; Marcel Dekker, Inc.: New York, 1983. Gibson, J. E., Ed. Formaldehyde Toxicity; Hemisphere Publishing Corp.: New York, 1983. Consensus Workshop on Formaldehyde. EHP, Environ. Health Perspect. 1984,58, 323-381. U.S. Department of Health and Human Services, Fourth Annual Report on Carcinogens, P B 85-134663, 1985. U S . Environmental Protection Agency, Office of Pesticides and Toxic Substances, Assessment of Health Risks to Garment Workers and Certain Home Residents from Exposure to Formaldehyde, April 1987. Spengler, J. D.; Sexton, K. Science (Washington,D.C.)1983, 221,9-17. Garry, V. F.; Oatman, L.; Pleuss, R.; Gray, D. Minn. Med. 1980,63, 107-111. Ritchie, I. M.; Lehnen, R. G. J . Environ. Health 1985,47, 300-305. Ritchie, I. M.; Lehnen, R. G. Am. J . Public Health 1987, 77, 323-328. Norsted, S. W.; Kozinetz, C. A,; Arregers, J. F. Environ. Res. 1985, 37, 93-100. Stock, T. H.; Monsen, R. M.; Sterling, D. A.; Norsted, S. W. 78th Annual Meeting of the Air Pollution Control Association, Detroit, MI, 1985; Paper 85-85.1. Breysse, P. A. Environ. Health Saf. News 1977,25, 1-19. Breysse, P. A. J A M A , J . Am. Med. Assoc. 1981, 245, 267-268. Hanrahan, L. P.; Dally, K. A.; Anderson, H. A.; Kanarek, M. S.; Rankin, J. Am. J. Public Health 1984,74,1026-1027. Dally, K. A.; Hanrahan, L. P.; Kanarek, M. S. Arch. Environ. Health 1981, 36, 277-284. Hanrahan, L. P.; Anderson, H. A.; Dally, K. A.; Eckman, A. D.; Kanarek, M. S. J . Air Pollut. Control Assoc. 1985, 35, 1164-1167. Meyer, B. Urea-Formaldehyde Resins; Addison-Wesley Publishing Co.: Reading, MA, 1979. Sexton, K.; Liu, K.; Petreas, M. X. J . Air Pollut. Control 1986, 36, 698-704. ASSOC. Petreas, M.; Liu, K.; Chang, B.; Hayward, S. B.; Sexton, K.; JAPCA 1988,38,647-651. Konopinski, V. J. Am. Znd. Hyg. Assoc. J. 1985,46,65-68. Liu, K.; Hayward, S. B.; Petreas, M.; Webber, L.; Sexton, K.; Chang, B. 79th Annual Meeting of the Air Pollution Control Association, Minneapolis, MN, 1986; Paper 86-7.7. Department of Housing and Urban Development, Manufactured Home Construction and Safety Standards Fed. Regist. 1984, 49, 31996-32013. American Industrial Hygiene Association Am. Znd. Hyg. Assoc. J. 1968, 29, 505. Sandia National Laboratories, Indoor Air Quality Handbook, SAND 82-1773, Albuquerque, NM, 1982. The American Society of Heating, Refrigerating, and Air Conditioning Engineers, Inc. ASHRAE 62-1981; Ventilation for Acceptable Indoor Air Quality, Atlanta, GA, 1981. Received for review October 27, 1988. Accepted March 15, 1989. This manuscript has not been subjected to EPA's peer and administrative review.
