Personal Inhalable Dust Research Articles

Allergen and endotoxin exposure in a companion animal hospital

BackgroundExposure to allergens, both in general and occupational environments, is known to result in sensitisation and exacerbation of allergic diseases, while endotoxin exposure might protect against allergic diseases. This may...

Exposure to Inhalable Dust, Endotoxins, β(1→3)-Glucans, and Airborne Microorganisms in Horse Stables

Workers in horse stables are likely exposed to high levels of organic dust. Organic dusts play a role in increased risk of inflammatory reactions and are associated with respiratory diseases. The aim of this study was to investigate dust, endotoxin, beta(1-->3)-glucan, and culturable microorganisms exposure levels in horse stables. Ambient (n = 38) and personal (n = 42) inhalable dust samples were collected using PAS-6 sampling heads. As a special measurement, we included sampling near the horses' heads. Samples were analyzed for endotoxin and beta(1-->3)-glucan by Limulus amebocyte lysate assay and an inhibition enzyme immunoassay, respectively. Culturable bacteria and fungi were collected with an Anderson impactor. Geometric means (GMs) of personal exposure to dust, endotoxin, and beta(1-->3)-glucan were 1.4 mg m(-3) (range 0.2-9.5), 608 EU m(-3) (20-9846), and 9.5 microg m(-3) (0.4-631 microg m(-3)), respectively. Exposure levels in the morning shift were higher compared to other shifts. The GMs (ranges) of culturable bacteria and fungi were 3.1 x 10(3) colony-forming unit (CFU) m(-3) (6.7 x 10 to 1.9 x 10(4)) and 1.9 x 10(3) CFU m(-3) (7.4 x 10 to 2.4 x 10(4)), respectively. Variance components for endotoxin and beta(1-->3)-glucan were considerably higher than for dust. Based on dummy variable in a mixed regression analysis, the predominant task explaining exposure levels of dust, endotoxin, and beta(1-->3)-glucan was sweeping the floor. For beta(1-->3)-glucan, feeding the horse was also an important determinant. Dust, endotoxin, and beta(1-->3)-glucan exposure are considerable in horse stables. Bacterial and fungal exposure levels were moderate. Endotoxin exposures were above the Dutch proposed standard limits, suggesting workers in horse stables to be at risk of adverse health effects.

Exposure to Wood Dust and Its Particle Size Distribution in a Rubberwood Sawmill in Thailand

A cross-sectional study on wood dust exposure and respiratory health effects was conducted at one of the largest rubberwood sawmills in Thailand. All workers (N = 340) from all jobs on a day shift were recruited for personal sampling. Overall, the personal inhalable dust (n = 742) and respirable dust (n = 241) of full-shift samples were collected from 27 job titles. These data were used to classify workers into high, moderate, and low exposure groups based on the concentrations found in each job. Static samples were also collected to determine the particle size distribution. Geometric means (GM) are used to present the concentrations of the rubber wood dust. Inhalable dust concentrations were clearly high, ranging between 0.2 to 59.4 mg/m3 and with GM of 4.7 mg/m3. The GM of inhalable dust in each job title enabled classification of the workers into three exposure groups: (1) high exposure; >5 mg/m3, (2) moderate exposure; 2.0–5.0 mg/m3, and (3) low exposure; 0.18–1.9 mg/m3. Among the high exposure group, the highest GM inhalable dust concentrations were found in sawing green lumber (12.8 mg/m3) and cutting dry lumber (7.3 mg/m3). The respirable dust concentrations were generally low, in the range of 0.1 to 6.0 mg/m3 with a GM of 0.5 mg/m3. The largest percentage of dust in major operations belonged to the thoracic fraction; 50% cutoff diameter was smaller than 9 μm. The size distribution of wood dust indicated a high proportion in the large particle sizes.

Inhalable Dust and Protein Exposur in Soybean Processing Plants

Little is known about inhalable dust concentrations in soybean processing plants in southern Africa. This project measured inhalable dust in soybean plants in the region and correlated dust measurements with total protein and soy trypsin inhibitor. Sixty-four personal inhalable dust measurements were taken in three processing plants. Levels of total protein and soy trypsin inhibitor were determined in only two of the three plants. Correlations between inhalable dust, total protein and trypsin inhibitor were determined for 44 of 64 samples. In plants' production areas, inhalable dust levels were 0.24-35.02 mg/m3 (median 2.58 mg/m3). Total protein and soy trypsin inhibitor levels were 29.41-448.82 microg/m3 (median 90.09 microg/m3) and 0.05-2.58 microg/m3 (median 0.07 microg/m3), respectively. No statistically significant correlations between presence of inhalable dust and soy trypsin inhibitor were found. Total protein and soy trypsin inhibitor were better correlated. This study indicates that total protein might be a good proxy for soybean specific protein concentrations in soybean processing plants.

Variability in Endotoxin Exposure Levels and Consequences for Exposure Assessment

Workers in many industries are exposed to endotoxins, which may cause adverse health effects. In exposure assessment, information about exposure variability is essential. However, variability in exposure has rarely been investigated for biological agents and more specifically for endotoxin. Therefore, variance components and determinants of exposure were studied in a large database with >2000 endotoxin measurements. Data from 10 individual studies were combined to create a database with 2010 personal inhalable dust and endotoxin measurements, of which 1650 were repeated measurements. Exposure groups were defined based on job codes. Between- and within-worker variance components were estimated for different grouping strategies, and determinants of exposure were studied using mixed effects models. Inhalable dust and endotoxin exposure levels are summarized for 46 industries and 4 broadly defined sectors. The between-worker variability exceeded the within-worker variability overall and within sectors and subsectors, and variance components were larger for endotoxin than for dust. Between-worker variability also exceeded within-worker variability in nearly half of the exposure groups based upon industries or job code within industries for endotoxin exposure and in 10% of the groups for dust exposure. Among other things, dustiness of the process, contact with animals, bulk production, presence of plant material or a cyclic process appeared as determinants of exposure, which largely explained the between-worker variability. Exposure groups were much less homogeneous for endotoxin exposure than for dust exposure. This is distinctly different than for chemical exposure. Large variability in measured exposure levels is inherent to endotoxin exposure, which is caused in part by determinants that influence growth of microorganisms. These findings have major consequences for the design of future occupational intervention and epidemiological studies. The measurement effort needs to be greater than exposure assessment for chemical agents which demonstrate lower exposure variability, especially when evaluating endotoxin exposure for compliance testing. The established determinants of exposure give direction for potential exposure control, although more information about determinants of day-to-day variability in exposure is still needed to be able to effectively control endotoxin exposure.

Inhalable β(1→3)glucans as a non-allergenic exposure factor in Dutch bakeries

Objectives:To obtain an overview of inhalable β(1→3)glucans levels in Dutch industrial bakeries and explore possible associations with reported respiratory health effects in bakery workers.Methods:β(1→3)glucan levels were analysed in 186 personal...

Exposure to inhalable dust and endotoxins in agricultural industries

Endotoxin is a well-known bacterial toxin that causes several health effects. Animal faeces and plant materials contaminated with bacteria have been identified as important determinants of organic dust related endotoxin exposure. Although high exposure to organic dust and endotoxins has been described regularly in agricultural industries, a detailed overview of levels of airborne exposure to endotoxins in the agricultural industry, as well as a systematic comparison between several specific branches using the same exposure assessment protocols are lacking. In this study, personal endotoxin exposure in a broad spectrum of agricultural industries was investigated and possible determinants of exposure were explored. 601 personal inhalable dust samples were taken in 46 companies of three agricultural industrial sectors: grains, seeds and legumes sector (GSL), horticulture sector (HC) and animal production sector (AP), with 350 participating employees. Dust and endotoxin levels were determined gravimetrically and by using the Limulus Amoebocyte Lysate (LAL) assay, respectively. Basic descriptive analysis and elaborate analysis of variance were performed. Mean exposure levels were high, with large differences between sectors and between companies within the sectors. Highest dust and endotoxin exposures were found in companies of the GSL sector. In all three sectors exposure was higher in the primary production part compared to the (industrial) products processing part of the sector. The Dutch proposed health based occupational exposure limit (50 EU m(-3)) and temporary legal limit (200 EU m(-3)) for endotoxin were often exceeded. Differences in exposure between workers were larger than the day-to-day variability. Identified determinants increasing exposure levels were company, dustiness of the product and contact with animals/faeces. 'Wet' processes resulted in less dusty working environments and thus lowered endotoxin exposure. Overall, exposure to endotoxins over the whole range of agricultural industries is high. A 10-1,000 fold reduction in exposure is needed to reduce endotoxin related health risks.

Exposure to Flour Dust in UK Bakeries: Current Use of Control Measures

In May 2001, a maximum exposure limit (MEL) for flour dust was set in the UK at 10 mg/m(3) [8 h time-weighted average (TWA)] with a short-term exposure limit (STEL) of 30 mg/m(3) (15 min reference period). The purpose of this study was to produce a benchmarking baseline of current control measures and exposure levels, in addition to assessing the provision of training and the knowledge of the UK regulations amongst the bakeries. A total of 208 long-term personal inhalable dust samples (8 h TWA) were collected from workers in 55 bakeries (covering a wide range of industry types and sizes) between October 2002 and December 2003 in England, Wales and Scotland. Standardized occupational hygiene reports were produced for each establishment to provide information about the site (such as the size of the bakery) and the control measures employed (including ventilation, good working practices, knowledge of UK regulations and the extent of training provided). Median inhalable dust exposure (8 h TWA) for the bakery workers was 3.7 mg/m(3) (75th percentile at 7.7 mg/m(3)) and 17% of the dust results exceeded the MEL. Although information about the MEL has been available in the trade press and through recognised trade associations, only 27% of the bakeries were aware of the MEL and STEL. Mixed model regression analysis suggested that determinants of higher exposure included the job category (particularly weighing/sieving or mixing), medium to large bakery size (50 or more employees) and bakeries being located in Scotland. However, having an appointed safety representative was associated with lower exposure. The conclusions derived here are based upon the use of a statistical model, but clearly, if bakeries and individuals employ good working practices, with correct use of local exhaust ventilation, they should be able to comply with the MEL.

The Performance of Personal Inhalable Dust Samplers in Wood-Products Industry Facilities

Click to increase image sizeClick to decrease image sizeKeywords: SamplingParticulate MatterWood DustGravimetric Measurement

Trends in levels of inhalable dust exposure, exceedance and overexposure in the European carbon black manufacturing industry

In an attempt to investigate the relationship between exposure to carbon black and respiratory morbidity, a study of the complete carbon black manufacturing industry in Western Europe was commissioned. As part of this study, a large number of personal inhalable (n=8015) dust exposure measurements was taken during three phases of data collection between 1987 and 1995. Repeated measurements on the same worker were taken in the last two phases, which enabled the estimation of the within- and between-worker components of variance. Simultaneously, the fixed effects of phase and factory were estimated using mixed-effects analysis of variance. The results show that the personal inhalable dust exposure has reduced significantly since the first phase of the study. In addition, the interaction term between phase and factory was significant in most job categories, confirming that the reduction of exposure was not equal across all factories. When all factories were considered together, the probability that the mean exposure of a randomly selected worker (overexposure) or the probability that the exposure on a randomly selected day for a randomly selected worker (exceedance) was higher than 3.5mg m(-3), was 10% or less for all job categories in the last phase. However, when the factories were considered separately, it appeared that the probability of overexposure or exceedance was in excess of 10% for the job categories 'Fitter/Welder', 'Warehouseman' and 'Site crew' for a number of factories. Therefore, even though exposure levels of inhalable dust have dropped considerably across the whole carbon black manufacturing industry in Western Europe, further reductions in exposure levels are required in these areas to make sure that the probability of overexposure and exceedance falls below a level of 10%.

Trends in levels of inhalable dust exposure, exceedance and overexposure in the European carbon black manufacturing industry

In an attempt to investigate the relationship between exposure to carbon black and respiratory morbidity, a study of the complete carbon black manufacturing industry in Western Europe was commissioned. As part of this study, a large number of personal inhalable (n=8015) dust exposure measurements was taken during three phases of data collection between 1987 and 1995. Repeated measurements on the same worker were taken in the last two phases, which enabled the estimation of the within- and between-worker components of variance. Simultaneously, the fixed effects of phase and factory were estimated using mixed-effects analysis of variance.The results show that the personal inhalable dust exposure has reduced significantly since the first phase of the study. In addition, the interaction term between phase and factory was significant in most job categories, confirming that the reduction of exposure was not equal across all factories.When all factories were considered together, the probability that the mean exposure of a randomly selected worker (overexposure) or the probability that the exposure on a randomly selected day for a randomly selected worker (exceedance) was higher than 3.5mg m−3, was 10% or less for all job categories in the last phase. However, when the factories were considered separately, it appeared that the probability of overexposure or exceedance was in excess of 10% for the job categories ‘Fitter/Welder’, ‘Warehouseman’ and ‘Site crew’ for a number of factories. Therefore, even though exposure levels of inhalable dust have dropped considerably across the whole carbon black manufacturing industry in Western Europe, further reductions in exposure levels are required in these areas to make sure that the probability of overexposure and exceedance falls below a level of 10%.

Dust exposures in the wood processing industry.

Workers at four different woodworking processes--two logging sites, four sawmills, one major woodchipping operation, and five joineries situated in the state of New South Wales in Australia--were studied for personal inhalable dust exposures (N = 182). The geometric mean exposure at logging sites was 0.6 mg/m3 (N = 7), sawmills 1.6 mg/m3 (N = 93), woodchipping 1.9 mg/m3 (N = 9), and joineries 3.7 mg/m3 (N = 66). Overall, 62% of the exposures exceeded the current standards. Among joineries, 95% of the hardwood exposures and 35% of the softwood exposures were above the relevant standards. A majority of workers (approximately 90%) did not wear appropriate respirators approved for wood dust, while the ones who did wear them, used them on average less than 50% of the time. The significant determinants of personal wood dust exposures (n = 163) were found to be local exhaust ventilation, job title, use of handheld tools, cleaning method used, use of compressed air, and green or dry wood processed. Type of wood processed (softwood or hardwood) was not found to be statistically significant.

THE SAMPLING EFFICIENCY OF PERSONAL INHALABLE AEROSOL SAMPLERS IN LOW AIR MOVEMENT ENVIRONMENTS

Experimental systems were developed in two laboratories for measuring the sampling efficiency of personal inhalable aerosol samplers in low air movement environments, using sedimenting aerosols. The sampling efficiencies of four types of personal inhalable or total dust sampler were measured; the samplers chosen were the IOM sampler, the GSP conical inhalable sampler, the UK seven-hole sampler and the 37 mm closed face sampling cassette. Isolated samplers or manikin-mounted samplers were slowly rotated in an aerosol chamber, whilst mounted in orientations similar to those in which they are normally used for personal sampling. Measurements were made using nine aluminium oxide test aerosols with aerodynamic diameter values ranging from 6 to 90 μm. Reference concentrations in the aerosol chamber were measured using slowly circling sharp-edged probes with matched forward and aspiration velocities, to simulate isokinetic sampling. Sampling efficiencies for the IOM, GSP and seven-hole samplers measured using this system were generally higher than wind tunnel results previously reported at an external wind speed of 0.5 m s -1. For the 37 mm sampler the results were generally lower than the previous wind tunnel results. Measurements made with the samplers mounted on the torso of the manikin showed positional differences in sampling efficiency, but the average sampling efficiencies were similar whether the samplers were on or off the manikin. The experimental system developed in this work is simpler and gives more reproducible results than the wind tunnel tests of samplers (mounted on a life-size manikin) that are normally used to assess personal sampler performance.

Nasal symptoms and indices of nasal inflammation in flour-dust-exposed bakers

To analyze whether indices of nasal airway inflammation in bakers were related to nasal symptoms and exposure to airborne flour dust. A cross-sectional study was performed in 12 currently flour-exposed bakers. They were examined by nasal lavage (NAL), visual inspection, a test of mucociliary clearance, and nasal peak expiratory flow (nasal PEF). NAL fluid was analyzed according to the inflammatory markers eosinophil cationic protein (ECP), indicating eosinophilic activity; myeloperoxidase (MPO), indicating active neutrophils; hyaluronic acid (HA) from active fibroblasts; tryptase, indicating activation of mast cells; and albumin, indicating plasma exudation. The bakers were also questioned about respiratory symptoms and working history. Their current and cumulative exposure to inhalable flour dust was estimated after exposure measurements and information about earlier work tasks. Office workers (n=16) without occupational exposure to dust or any other known nasal irritant or sensitizer served as controls. Personal inhalable dust measurements among the bakers working as dough makers or bread formers ranged from 1.0 to 3.8 mg/m3. Of the 12 bakers, 10 reported at least 1 nasal symptom (crusts, blockage, or a runny nose), a proportion significantly greater than that of the controls (P=0.009). Bakers with nasal symptoms had higher concentrations of markers of inflammation in their NALs as compared with nonsymptomatic bakers. The difference was significant for MPO (P=0.02) and HA (P=0.04) in relation to a runny nose. Tryptase was detected in only one NAL of the bakers. There was a positive correlation between the cumulative dose of inhalable flour dust and concentrations of MPO and HA in NAL. Two bakers were sensitized to wheat; they had the highest NAL concentrations of inflammatory markers. Our results indicate that flour dust exposure in bakers at levels below the current occupational exposure limit causes nasal mucosal inflammation, which, in turn, is related to nasal symptoms. We propose that the inflammation may be nonallergic, characterized by activation of neutrophils and fibroblasts.

Assessment of particle size distributions of healthrelevant aerosol exposures of primary lead smelter workers

Experiments were conducted at a primary lead smelter to investigate the particle size distributions of lead-containing aerosol to which workers were exposed, using personal inhalable dust spectrometers (PIDS) in specific smelter process areas. A total of 46 PIDS samples were evaluated, taken from the ore storage/mill, sinter plant, blast furnace and dross furnace process areas. Continuous particle size distributions were derived from the raw PIDS data employing a recentlydeveloped optimisation routine, enabling determination of the percentages of inhalable, thoracic and respirable aerosol (in terms of lead content) as fractions of total lead aerosol. In addition, the mass ratios thoracic/inhalable and respirable/inhalable were also determined. Although the parameters of the measured particle size distributions ranged widely, some clear trends emerged. Firstly, the aerosols were coarser than had been expected based on measurements of previously reported workplace particle size distributions. This is thought to be due to the fact that the PIDS collects larger particles more efficiently than other instruments which have been used for such measurements. Secondly, there were significant differences in particle size distribution between process areas, in particular that the aerosol in the blast furnace area was generally finer than in the sinter plant. Such results may be used to support the results of workplace studies (reported elsewhere) into the differences between exposures to inhalable and ‘total’ aerosol as measured using different sampling instruments, especially when they are used together with knowledge of the physical processes governing the performances of such instruments.

Humoral Immune Responses to Pig Urinary Proteins and Respiratory Health of Pig Farmers

ABSTRACT Pig stable dust may contain large amounts of potentially allergenic pig urinary proteins (PUP). In this study, inhibition enzyme immunoassays were used to measure airborne PUP expo-sure, and high levels (up to 200 μgeq/m3) could indeed be demon-strated in personal inhalable dust samples of pig farmers. IgE and IgG4 anti-PUP were assessed in the sera of 191 pig farmers, for whom also questionnaire and bronchoprovocation data were avail-able. IgE anti-PUP was found in only 5-7%, and was at best weakly associated with respiratory symptoms. In contrast, IgG4 anti-PUP was found in many subjects, and titres were negatively associated with respiratory health problems, and also with bronchial hyperreac-tivity to histamine. Anti-PUP IgG4 antibodies thus seem to protect pig farmers from developing respiratory symptoms and BHR.

Evaluation of Two Inversion Techniques for Retrieving Health-Related Aerosol Fractions from Personal Cascade Impactor Measurements

Personal cascade impactors are widely used in occupational aerosol exposure assessment. Appropriate algorithms must be used to determine the total particle size distribution from masses collected on the stages of the cascade impactor. Such algorithms should be regarded as integral components of the measurement system. When evaluating algorithms for reconstruction of size distributions from cascade impactor data, the eventual use of the size distribution must be considered. So, from an industrial hygiene perspective, an appropriate basis for comparison of given measurement systems is the accurate retrieval of the inhalable, thoracic, and respirable aerosol fractions as described by the new, internationally accepted, particle size-selective sampling conventions (which are expected to form the basis of future aerosol standards). This article compares two inversion routines in terms of their abilities to retrieve these aerosol mass fractions relative to the masses that would have been obtained using an ideal sampler that perfectly followed the sampling convention. The routines were used to invert measurements made with the Institute of Occupational Medicine personal inhalable dust spectrometer, a miniature cascade impactor that aspirates the inhalable aerosol fraction, and the results are presented graphically as contours of equal mass bias. The simplest algorithm, based on the a priori assumption of lognormality, appears to provide the best results.

Inversion techniques for personal cascade impactor data

We examined two inversion procedures for solving the Fredholm integral equation of the first kind to obtain aerosol particle size distributions from a set of measured masses collected on the various stages of a personal cascade impactor. The problem is essentially ill-conditioned, in that many solutions satisfy exactly an integral equation slightly perturbed from the original due to measurement error. The two methods, although derived from different families of inversion techniques, fit into the general framework of Tikhonov regularization. Both try to optimize the a posteriori degree of matching of the solution to the measured data and the a priori judgments about the likelihood of a solution in terms of its smoothness. The first method uses a weighted least squares optimization and zeroth-order regularization to fit a priori bi-modal log-normal distribution functions, using an intermediate step to define an appropriate starting point for the optimization routine. The second involved “blind” inversion of the impactor data to express the second derivative of the particle size distribution function as a linear combination of orthogonal basis functions, chosen so that the resulting solution is smooth and positive. The orthogonal functions are constructed from the eigenvectors and eigenvalues of a kernel covariance matrix. The personal inhalable dust spectrometer (PIDS), used to illustrate the application of these methods, is an eight-stage cascade impactor which selects the inhalable fraction of the aerosol by means of a specially designed inlet. Both inversion methods explicitly include consideration of the aerosol that is collected in the sampler entry between the inlet and the first impactor stage, something that applies to all cascade impactors but which has not usually been taken into account in the past. An important parameter in inversions, the expected value of measurement error for each stage, was estimated from a series of wind-tunnel experiments. Both methods work well for simulated PIDS data as well as for experimental wind-tunnel data for a wide range of sets of aerosol size distribution parameters.

Assessment of particle size distributions in workers' aerosol exposures.

A full description of the regional dosimetry of inhaled workplace aerosols requires information about the particle aerodynamic size distributions of inhaled aerosols for appropriate health-related species. Therefore, since the late 1970s, interest has risen in how to assess workers' aerosol exposures in terms of particle fractions which may be inhaled and penetrate down to different parts of the human respiratory tract. The personal inhalable dust spectrometer (PIDS) was proposed as a versatile sampling instrument for assessing workers' exposures along these lines. Raw data from this cascade impactor-based instrument are obtained initially in terms of discrete particulate masses collected on the individual impactor stages. Recovery of the desired particle size distribution is difficult because the mathematical inversion problem is 'ill-posed' (i.e., there are many possible solutions that would be consistent with the observed masses). However, a routine has been developed that involves considerations of the detailed deposition characteristics of the impactor stages, measurement errors and a priori assumptions about the shape of the expected particle size distribution (e.g., log-normal). These differ from other such routines in that account is taken not only of aerosol deposited at the impactor stages but also that collected inside the entry system. Hence the final result covers the whole inhalable range, for particles up to and exceeding 100 microns in aerodynamic diameter. The PIDS has recently been used in studies in several industries to examine inhalable particle size distributions for individual exposed workers. This paper considers the results of such studies, and discusses how they may be used to provide information not only about the inhalable, thoracic and respirable fractions identified in the latest particle size-selective sampling criteria (upon which it is expected that future aerosol standards will be based), but also other health-related fractions that may be defined numerically (including, for example, alveolar deposition fractions for workers with different breathing patterns relevant to the type of work undertaken).

WOOD DUST EXPOSURE DURING FURNITURE MANUFACTURE—RESULTS FROM AN AUSTRALIAN SURVEY AND CONSIDERATIONS FOR THRESHOLD LIMIT VALUE DEVELOPMENT

A survey of time-weighted average (TWA) personal inhalable dust exposures for woodworkers in 15 Australian furniture factories was undertaken. There was significant variation in the individual dust measurements with mean exposures of 3.2, 5.2, and 3.5 mg/m3 for wood machinists, cabinetmakers, and chair framemakers, respectively. Hardwoods, softwoods, and reconstituted woods are used in the industry, but only minor differences in mean exposures or particle size distributions were found for the broad categories. In addition, a modified British Medical Research Council respiratory questionnaire was used to obtain information about work-related symptoms and job activities. Compared with a control group, the woodworkers reported more eye, ear, and nasal problems, with the differences being statistically significant. However, among the woodworkers themselves, with the exception of several nasal symptoms, the prevalences of reported symptoms were poorly correlated with gravimetric measurements of personal dust exposure. The problem of selection bias in cross-sectional studies is discussed. For a mean TWA personal exposure of about 3 mg/m3, hardwood users were more likely to report nasal symptoms than users of reconstituted wood. The question of appropriate exposure standards for woods in general is addressed by reference to those important health effects, besides sino-nasal cancer, that have been investigated. Further exposure guidelines should be formulated for groups of woods that are known to cause a common health effect, such as nasal/respiratory sensitization.