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Bacterial DNA in house and farm barn dust.

BACKGROUND: Early in life, natural exposure to microbial components (eg, endotoxin) may mitigate allergy and asthma development in childhood. Bacterial DNA is a potent stimulus for the innate immune system; its immune stimulatory potential in dust is unknown. OBJECTIVES: We sought to quantify bacterial DNA and endotoxin content in dust from urban homes, rural homes, farm homes, and farm barns and to determine if dust DNA is immune-stimulatory. METHODS: Total DNA, bacterial DNA, and endotoxin were measured in 32 dust samples. To measure bacterial DNA content, a quantitative polymerase chain reaction assay specific for bacterial ribosomal DNA was developed. Peripheral blood mononuclear cells from 5 adults were stimulated with endotoxin-free dust DNA with/without lipopolysaccharide (LPS) from selected dust samples. IL-12p40, IL-10, and tumor necrosis factor-alpha were measured in cell supernatants by enzyme-linked immunosorbent assay. RESULTS: Bacterial DNA in dust correlated with endotoxin (r = 0.56, P <.001) and total DNA content (r = 0.51, P =.003). The highest bacterial DNA levels were measured in farm barns (mean, 22.1 microg/g dust; range, 1.3 to 56.2), followed by rural homes (6.3 microg/g; 0.2 to 20), farm homes (2.2 microg/g; 0.1 to 9.1), and urban homes (0.6 microg/g; 0.1 to 1.2). Farm barn DNA significantly potentiated (P < or =.05) LPS-induced IL-10 and IL-12 p40 but not tumor necrosis factor-alpha release (13-fold, 3-fold, and 1.5-fold increases, respectively). DNA from 6 urban homes did not demonstrate this LPS-potentiating effect. CONCLUSIONS: Endotoxin is a marker for bacterial DNA, which is also higher in locales of lower asthma and allergy prevalence. DNA from farm barn dust augments the immune modulatory effects of endotoxin and may combine with exposure to other such naturally occurring microbial components to mitigate allergy and asthma development.

Adult↗

House dust mite (Dermatophagoides farinae and Dermatophagoides pteronyssinus) prevalence in the rooms and hallways of a tertiary care hospital.

BACKGROUND: House dust mites, Dermatophagoides farinae and Dermatophagoides pteronyssinus, are important components in the development of asthma. OBJECTIVE: We measured the prevalence of house dust mites in a tertiary care hospital located in a temperate geographic region where dust mites were prevalent in homes. METHODS: The density of Dermatophagoides spp. was measured in hospital hallways, carpeted patients' rooms, and noncarpeted patients' rooms by vacuuming the floor in the summer and winter seasons. Bedrooms in the homes of employees were sampled as a summer control group. A total of 141 dust samples was obtained. RESULTS: No D. farinae or D. pteronyssinus was found in 60 hospital dust samples that were obtained during the winter season. Although mites were found in some locations in the hospital during the summer dust collection, mite density in these locations and the average mite density for all samples were insignificant. During the summer dust samples from the bedroom carpets of all employees' homes sampled were positive for mites, with many homes having moderate or high populations (range, 22 to 8340 mites per gram of dust). CONCLUSIONS: The dust mite prevalence in a hospital could be kept very low even though mite levels in employees' homes were moderate to high. The factors responsible for the low mite density in the hospital were maintenance of low relative humidity, use of low-pile carpets, and good housekeeping and laundering practices.

Animals↗

Trimellitic anhydride (TMA) dust induces airway obstruction and eosinophilia in non-sensitized guinea pigs.

Trimellitic anhydride (TMA) causes asthma after a latency period of sensitization. In non-sensitized humans and animals, limited studies indicate that TMA exposure may also cause symptoms of asthma without a latency period. Our previous studies (J. Pharmacol. Exp. Ther. 296 (2001) 284) in a guinea pig model of TMA-induced asthma demonstrated that sensitization and the complement system were required for eosinophilia. TMA conjugated to guinea pig serum albumin (TMA-GPSA) was used to elicit the response. Since occupational exposure to TMA occurs by inhalation of dust, the present studies determined if exposure to TMA dust in a non-sensitized guinea pig elicited airway obstruction and inflammation, and whether a significantly greater response occurred after a latency period of sensitization. Guinea pigs were intradermally injected with either corn oil (non-sensitized animals) or 30% TMA (sensitized animals). Three weeks later they were challenged by intratracheal insufflation with 1 mg TMA dust or lactose dust (control) using a dry powder delivery device. Pulmonary resistance, dynamic lung compliance, mean arterial blood pressure and heart rate were monitored for 10 min. In non-sensitized guinea pigs, significant increases in pulmonary resistance and decreases in dynamic lung compliance and blood pressure occurred after TMA challenge. In sensitized animals, the same dose of TMA caused significantly greater effects compared to non-sensitized animals. In a separate experiment, cellular infiltration into the lung was determined 24 h after challenge with TMA dust or lactose dust. In both non-sensitized and sensitized animals, eosinophils in the lung tissue were increased after TMA dust challenge compared to controls. Thus, these studies suggest that the response in non-sensitized animals differs depending on whether TMA dust or TMA-GPSA is used to elicit the response. TMA dust elicits significant airway obstruction and eosinophilia in a non-sensitized animal, with even greater airway obstruction occurring in a sensitized animal.

Administration, Inhalation↗

The relationship of housing and household characteristics to the indoor concentrations of Der f 1, Der p 1, and Fel d 1 measured in dust and air samples.

BACKGROUND: Indoor dust mite and cat allergens have been related to the risk of atopic conditions. If allergen levels are influenced by modifiable residential characteristics, potential interventions to prevent disease could be deployed. OBJECTIVE: To evaluate relationships between allergen concentrations in air and dust samples and selected house and household characteristics using a large prospective study with multiple sequential allergen measurements from each residence. METHODS: Fel d 1, Der f 1, and Der p 1 were measured in paired air and dust samples collected at intervals throughout 4 years in suburban homes. House and household characteristics were examined for relationships to allergen concentrations in both univariate and multiple variate analyses. RESULTS: The relationships between house and household characteristics and allergen concentrations in both air and dust were complex. When the housing variables were considered in multiple variate analysis, concentrations of Der f 1 in dust increased with increasing number of residents and relative humidity and declined when forced air heating was used. Dust concentrations of Der p 1 were lower in new homes and during forced air heating use but higher with higher relative humidity and in the presence of dogs. The presence of cats was the dominant determinant of Fel d 1 in both air and dust, but when homes without cats were analyzed separately, dust levels of Fel d 1 were inversely related with relative humidity. CONCLUSIONS: Air and dust concentrations of Der p 1 and Der f 1 were positively related to relative humidity and the size of the family. Fel d 1 was positively related to the presence of cats. The relationship of other house or household characteristics was inconsistent but different for Der f 1 and Der p 1.

Air Conditioning↗

Predictors of group 5 grass-pollen allergens in settled house dust: comparison between pollination and nonpollination seasons.

BACKGROUND: Some sensitive pollen-allergic patients may experience perennial symptoms, and for these patients it is vitally important to know the concentration of grass-pollen allergens in their homes. The main objective of this study was to detect predictors associated with high grass allergen concentration in settled house dust during and outside the grass pollination season. METHODS: We detected group 5 grass-pollen allergens in dust samples from randomly selected homes of three counties in the region of Sachsen-Anhalt: Hettstedt (n=183), Zerbst (n=152), and Bitterfeld (n=119). Dust samples were collected from the floors of living rooms (LR) and children's rooms (CR) from April 1996 to March 1998. RESULTS: Phl p 5 was detected in settled house dust in 91% of the homes. The range was between undetectable (<30 ng/m2) and 4300 ng Phl p 5/m2 sampling area during grass pollination, and 1300 ng Phl p 5/m2 outside the pollination season, respectively. We observed a partially higher concentration of indoor allergenic activity several weeks after the grass-pollen peak. A positive association was found between Phl p 5 levels and total dust amounts throughout the year. Thus, we assume that grass allergens accumulate in settled house dust. During pollination, the Phl p 5 levels are 1.8 times higher in homes where vacuuming of carpets takes place only once a week or less than in those vacuumed daily. Furthermore, higher concentrations of Phl p 5 in settled floor dust can be expected in homes located within suburban areas (mean ratio [MR] 1.74) and prefabricated slab buildings (MR=1.54). CONCLUSIONS: Quite high levels of Phl p 5 accumulate in settled house dust even during periods when no grass pollen is present in the atmosphere. The removal of dust by frequent cleaning reduces the indoor exposure to grass allergens. Such information is essential to train patients in allergen avoidance.

Air Pollutants↗

Occupational allergic contact dermatitis caused by wood dusts.

Exposure to wood dusts may cause various skin and mucosal symptoms. Allergic dermatoses, caused by wood dusts, diagnosed at the Finnish Institute of Occupational Health during 1976-1999 are reported here. 16 had allergic contact dermatitis and, 2 had contact urticaria. 9 men (3 cabinet makers, 3 joiners, 1 carpenter, 1 knifemaker and 1 machinist) were mainly exposed to tropical hardwoods. 1 man had dermatitis caused by western red cedar. 5 patients, 3 men and 2 women, were exposed to Finnish pine or spruce dusts, and 1 man to aspen. 7 also had rhinitis, 4 asthma or dyspnoea and 3 conjunctivitis. On patch testing, 10 men reacted to 9 different wood dusts, including teak (5), palisander (3), jacaranda (2), mahogany (2), walnut (2) and obeche (1). Reactions to wood allergens, including lapachol (2), deoxylapachol (1), (R)-3,4-dimethoxydahlbergione (2), 2,6-dimethoxy-1,4-benzoquinone (1), mansonone A (2) and salicyl alcohol (1), were noted in 4 cases. All but 1 of 5 patients exposed to pine or spruce dusts reacted to the sawdusts, all 5 to colophonium, 3 to abietic acid, 2 to tall oil resin, 3 to wood tar mix and 4 to other wood gum resins. Of the 2 CU patients, 1 was prick and RAST positive to obeche, 1 reacted with urticarial dermatitis to punah wood dust on chamber exposure. Occupational allergic dermatoses are mainly caused by the dusts of hardwoods, mostly due to Type IV allergy, but may also be caused by softwood dusts. Patch tests can be done with wood dusts, but should be confirmed by patch testing with wood allergens if possible.

Adult↗

Dust-borne bacteria in animal sheds, schools and children's day care centres.

A total of 316 bacterial strains, including psychrophiles, mesophiles and thermophiles, were isolated and identified from indoor dusts in schools, children's day care centres and animal sheds. Several species which had not previously been reported from indoor environments were found: Sphingomonas, Brevibacterium, Nocardiopsis, Deinococcus and Rhodococcus/Gordona. A new psychrophilic actinomycete genus was also found in animal sheds, representing a new undescribed peptidoglycan type and an unusual whole-cell fatty acid composition. The indoor dusts of animal sheds contained mainly the Gram-negative genera Pseudomonas, Pantoea, Flavobacterium and Xanthomonas early in the indoor feeding season, but changed to a composition dominated by Bacillus, Micrococcus and mesophilic and thermophilic actinomycetes towards the end of the season. The dust contained, and air-borne bacterial flora in schools and day care centres were dominated by, Gram-positive bacilli and actinomycetes, notably Bacillus cereus, Brevibacillus brevis, B. licheniformis, B. subtilis and species of Arthrobacter, Corynebacterium, Rhodococcus/Gordona, Nocardiopsis sp., Deinococcus, Staphylococcus and Micrococcus. Indoor air and dust contained Klebsiella oxytoca, Acinetobacter calcoaceticus, Ac. lwoffi, Bacillus cereus and Nocardiopsis dassonvillei with the status of hazard group II. Indoor dusts of animal sheds contained eight different 3-hydroxy fatty acids, the 2-hydroxy fatty acid 14:0 and two 10-methyl fatty acids, whereas in dusts from schools and day care centres, these were below the detection level (< 3.5 ng mg-1). The 3-and 2-hydroxy fatty acids could be assigned to one or more of the dust-contained cultivable strains, but 10-methyl C16:0 was not present in any of the strains isolated. The dusts from schools and children's day care centres contained 0.2-0.3 ng of endotoxin mg-1 and 0.5-1.4 ng of beta-D-glucan mg-1, whereas the dusts from animal sheds contained more 0.3-41 ng mg-1 and 8-35 ng mg-1, respectively.

Air Microbiology↗

Inhaled endotoxin and decreased spirometric values. An exposure-response relation for cotton dust.

The early stages of byssinosis, the chronic lung disorder caused by the inhalation of cotton dust, are characterized by repeated episodes of mild and reversible obstruction of airways on exposure to cotton dust. To define the relation between exposure to endotoxin and the airway response to inhaled cotton dust, we pooled and analyzed data from several previous studies of experimental exposure. The pooled data set involved a total of 108 separate sessions of exposure to dust and 32 different cottons. Each dust-exposure session had involved exposing a group of 24 to 35 prescreened healthy subjects to dust from one of the cottons for six hours. The following data were obtained for each session: average concentrations of airborne dust (range, 0.12 to 0.55 mg per cubic meter) and endotoxin (range, 6 to 779 ng per cubic meter) as determined in air samples collected by vertical elutriators, and group mean percentage change in forced expiratory volume in one second (range, +0.5 to -9.1 percent), as determined by preexposure and postexposure spirometry. When data from the 108 exposure sessions were pooled, the dust concentration was not correlated with the group mean percentage change in forced expiratory volume in one second (r = -0.08; P = 0.43). In contrast, a clear exposure-response relation was observed between endotoxin concentration and group mean percentage change in forced expiratory volume in one second (r = -0.74; P less than 0.0001). Logarithmic transformation of endotoxin values clarified this relation at low-exposure concentrations and improved the correlation (r = -0.85; P less than 0.0001). Our observations strongly support the hypothesis that endotoxin has a causative role in the acute pulmonary response to inhaled cotton dust.

Adult↗

Aeolian dust in Colorado Plateau soils: nutrient inputs and recent change in source.

Aeolian dust (windblown silt and clay) is an important component in arid-land ecosystems because it may contribute to soil formation and furnish essential nutrients. Few geologic surfaces, however, have been characterized with respect to dust-accumulation history and resultant nutrient enrichment. We have developed a combination of methods to identify the presence of aeolian dust in arid regions and to evaluate the roles of this dust in ecosystem processes. Unconsolidated sandy sediment on isolated surfaces in the Canyonlands region of the Colorado Plateau differs greatly in mineralogical and chemical composition from associated bedrock, mainly aeolian sandstone. Detrital magnetite in the surficial deposits produces moderately high values of magnetic susceptibility, but magnetite is absent in nearby bedrock. A component of the surficial deposits must be aeolian to account for the abundance of magnetite, which formed originally in far-distant igneous rocks. Particle-size analysis suggests that the aeolian dust component is typically as much as 20-30%. Dust inputs have enriched the sediments in many elements, including P, Mg, Na, K, and Mo, as well as Ca, at sites where bedrock lacks calcite cement. Soil-surface biologic crusts are effective dust traps that apparently record a change in dust sources over the past several decades. Some of the recently fallen dust may result from human disturbance of land surfaces that are far from the Canyonlands, such as the Mojave Desert. Some land-use practices in the study area have the potential to deplete soil fertility by means of wind-erosion removal of aeolian silt.

Colorado↗

Differential pressure response of 25-mm-diameter glass fiber filters challenged with coal and limestone dust mixtures.

This article summarizes results of research conducted by the National Institute for Occupational Safety and Health (NIOSH) at its Pittsburgh Research Laboratory. The objective of this work was to determine the correlation between the mass (M) of respirable coal and limestone dusts collected on 25-mm-diameter glass fiber filters mounted in cassettes and the increase in differential pressure (deltaP) that develops across the filters when drawing at constant air flow. Test aerosols were generated inside a laboratory dust chamber using various coal dusts, limestone dust, and mixes of the two. Dusts with different particle size distributions were deposited on the filters by sampling from the chamber through cyclone preclassifiers at different flow rates. Results show that the relationship between differential pressure increase (cm water) and dust mass (mg) is linear and can be approximated by the equation deltaP = KM. The K values (slopes) range from 1.14 to 1.64, depending on the parent coal of the samples. The influence of particle size distribution was also found. The overall K value for all the data summarized in this article is 1.35, with R2 = 0.84 for the summary equation. When calibrated for individual work sites, or other circumstances where great variability in dust characteristics is avoided, the relationship between collected dust mass and increase in differential pressure may provide an exploitable principle for measurement of respirable dust concentrations.

Calcium Carbonate↗

Comparative occupational exposures to formaldehyde released from inhaled wood product dusts versus that in vapor form.

Particle boards and other wood boards are usually made with formaldehyde-based resins. Woodworkers are thus exposed to formaldehyde in vapor form as well as from airborne dust once it enters their respiratory tract. These workers remain exposed to formaldehyde released from the dust still present in their upper respiratory tract, even after their work shift. In assessing the risk associated with formaldehyde exposure, one needs to consider the relative importance of these two sources of exposure. This study proposes two kinetic models to estimate and compare the exposures. For various exposure scenarios, one model predicts the amount of formaldehyde absorbed from the ambient vapor form and the other predicts the amount absorbed by the respiratory tract upon its release from wood product dust. Model parameters are determined using data from published studies. Based on a daily work shift of 8 hr, with a dust concentration in air of 5 mg/m(3) and a formaldehyde concentration bound to dust of 9 microg/mg, model simulations predict that the amount of absorbed formaldehyde released from wood dust is approximately 1/100 of the amount absorbed from the ambient vapor form at a concentration level of 0.38 mg/m(3) (0.3 ppm). Since the formaldehyde concentration in wood dust used above is much higher than usually observed while the dust and vapor form formaldehyde concentrations are of the order of acceptable upper values, these results indicate that the formaldehyde exposure from wood dust is comparatively negligible.

Absorption↗

Windblown dust contributes to high PM2.5 concentrations.

The revised National Ambient Air Quality Standards for PM include fine particulate standards based upon mass measurements of PM2.5. It is possible in arid and semi-arid regions to observe significant coarse mode intrusion in the PM2.5 measurement. In this work, continuous PM10, PM2.5, and PM1.0 were measured during several windblown dust events in Spokane, WA. PM2.5 constituted approximately 30% of the PM10 during the dust event days, compared with approximately 48% on the non-dusty days preceding the dust events. Both PM10 and PM2.5 were enhanced during the dust events. However, PM1.0 was not enhanced during dust storms that originated within the state of Washington. During a dust storm that originated in Asia and impacted Spokane, PM1.0 was also enhanced, although the Asian dust reached Washington during a period of stagnation and poor dispersion, so that local sources were also contributing to high particulate levels. The "intermodal" region of PM, defined as particles ranging in aerodynamic size from 1.0 to 2.5 microns, was found to represent a significant fraction of PM2.5 (approximately 51%) during windblown dust events, compared with 28% during the non-dusty days before the dust events.

Air Pollution↗

Aflatoxin in respirable airborne peanut dust.

Laboratory shelling and pilot handling operations were conducted to determine if peanut dust generated by such operations contained significant amounts of aflatoxin. Air samples were collected from points of highest dust concentration. No aflatoxin B1 was detected in dust from uncontaminated lots. Aflatoxin B1 levels of 700 ppb and 7.6 ng/m3 were detected from highly contaminated lots. The contamination of the dust was directly proportional to the contamination of the lots handled or shelled. In the shelling tests, the level of contamination of the dust samples was about one-ninth of the level of contamination of the peanuts. In the handling tests, the level of contamination of the dust samples was about half the contamination level of the peanuts. These results indicate that most of the contaminated dust was probably removed by handling operations prior to shelling. Although workers are not routinely exposed to such levels of contaminated dust, these findings suggest the need for a more thorough study of peanut dust during handling or processing of contaminated peanuts.

Aflatoxin B1↗

Grain dusts and grain plant components vary in their ability to recruit neutrophils.

Occupational exposure to grain dusts can cause bronchitis, particularly to grain sorghum dust. Bronchitis is associated with the presence of increased numbers of neutrophils. To determine how grain dusts could cause neutrophil recruitment to the airways, extract of whole-grain sorghum, corn, and soybean dusts and of pulverized components of these plants were made with Hanks balanced salt solution (HBSS) and used in direct neutrophil chemotaxis experiments. The glume of the grain sorghum plant, the structure holding the seeds in place, caused the migration of the greatest number of neutrophils compared to HBSS [132 +/- 7 vs. 60 cells/high-power field (hpf) +/- 2 SEM, p < .001], followed by whole-grain sorghum dust (121 +/- 5 cells/hpf). Next, bovine bronchial epithelial cells (BBECs) were obtained from fresh lungs and grown to near confluence before challenge with a 10% solution of grain dust and grain plant extracts. The grain sorghum glume and whole-grain sorghum dusts caused release of the greatest amount of neutrophil chemotactic activity (NCA) from BBECs compared to the medium M199 negative control (141 +/- 6 and 153 +/- 7, respectively, vs. 64 cells/hpf +/- 3 SEM, p < .001). The ability to cause neutrophils to migrate by direct and indirect means did not correlate with levels in the grain dusts of endotoxin, which is known to cause release of NCA from bronchial epithelial cells. Therefore, this article describes additional mechanisms by which grain dusts can cause pulmonary inflammation and that are independent of endotoxin levels.

Animals↗

Pulmonary function status of workers exposed to hardwood or pine dust.

Wood dusts may have substantial health impacts beyond those of nuisance dust. This project reports results linking pulmonary function changes with exposure to maple and pine dust. A cross-sectional survey of 1157 woodworkers was conducted in 1978 in accordance with NHLBI standards for respiratory epidemiologic surveys. Area dust levels were determined, permitting definition of groups exposed to estimated high, medium or low cumulative levels of dry hardwood or softwood dust. Prevalence of reduced (lower fifth percentile of normal) pulmonary function was ascertained, using prediction equations, for Forced Vital Capacity (FVC), Forced Expiratory Volume in 1 second (FEV1), FEV1/FVC and Maximal Mid-expiratory Flow Rate (MMEFR). Relationships between pulmonary impairment and dust exposure were examined, adjusting for smoking status by means of the log odds ratio method. The results support an association between dry hardwood or softwood dust exposure and reduced pulmonary flow rates. The odds ratios for reduced pulmonary function, comparing low and high hardwood (maple) dust exposure, were 3.12 for FEV1/FVC and 2.14 for MMEFR. Comparing low and medium hardwood exposure, the odds ratios were 2.61 for FEV1/FVC and MMEFR. Comparison of low and high softwood (pine) dust exposure yielded odds ratios of 4.03 for FEV1/FVC and 2.45 for MMEFR. The ratios noted are significant at p less than .05.

Adult↗

Health effects of wood dust--relevance for an occupational standard.

Wood dust is coming under increasing scrutiny as an industrial exposure posing greater risk than that of a nuisance dust. In light of this increased interest, this paper will review key reports of wood dust-related health effects, and will summarize the available information which relates exposure levels to effects. Numerous case reports exist of skin reactions and obstructive-pattern respiratory changes of either a hypersensitivity or irritant nature for various woods. Reports have also been published of apparently non-allergic obstructive respiratory effects including lung function test reductions and reduction of mucociliary clearance. Wood dust exposure also appears to be linked to the occurrence of adenocarcinoma of the nasal sinuses. Occasional reports link wood dust to other types of cancer, but these relationships are much less consistent than the association with nasal cancer. Various standards have been proposed for wood dust. Most are lower than the nuisance dust standard currently applicable in the U.S. This review of several key papers on wood dust permits some association of exposure data and effects, particularly with suppressed mucociliary clearance, from which it may be suggested from the available evidence that a standard of 2 mg/m3 total suspended wood dust, not differentiated by type of wood, would protect against observed effects except for extreme allergic hypersensitivity.

Air Pollutants, Occupational↗

A chemical and engineering analysis of dust in textile mills.

Proximate chemical analysis was conducted on the carding, spinning and weave rooms of textile mills. The dust was found to be composed of inorganic, cellulosic and noncellulosic organics in carding and spinning. The percentage of noncellulosic organic (the component of cotton dust considered to be responsible for byssinosis in cotton textile workers) in ring spinning was found to be one-half the percentage composition of the card room dust. The cellulosic percentage of spinning room dust is elevated above that found in card rooms. In weave rooms the composition of dust is a function of the fabric being produced, environmental control systems, and machinery. In all weave rooms where dust levels were sufficiently above background, all components of the dust were accounted for by the proximate chemical analysis without the presence of a noncellulosic organic component. The card room, spinning room and weave room produce dusts that are very different in composition, to the extent that the proximate chemical analysis could identify the area of origin of dust samples from a textile mill.

Cellulose, Oxidized↗

Estimation of long term dust exposures in the Vermont granite sheds.

Analysis of variance models were used to analyze 1153 personal samples of respirable granite dust collected in the Vermont granite sheds in 1970 and 1976. The best fitting model described dust concentrations in terms of job, shed, season, survey year, and included interaction terms between shed, season, and survey. This model explained 46% of the total variability in dust levels, and was used to estimate median annual dust concentrations for every job and shed in the industry. The analysis of variance suggested that dust levels varied more between sheds than between jobs within a shed, and that winter dust levels were significantly higher than summer levels. Dust levels in the 1970s were estimated by the average of the seasonally adjusted levels in the two surveys. Dust estimates in each job and shed were combined with personal work histories, and three procedures for estimating each worker's lifetime exposure were evaluated. The cumulative exposure index with uniform weights for each dust year of exposure was selected as the most physiologically plausible measure of total dose.

Air Pollutants, Occupational↗