Annals of Occupational Hygiene Advance Access originally published online on March 2, 2004
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Ann. occup. Hyg., Vol. 48, No. 4, pp. 327-338, 2004
© 2004 British Occupational Hygiene Society
Published by Oxford University Press
Microbial Dustiness and Particle Release of Different Biofuels
1 National Institute of Occupational Health, Lersø Parkalle 104, DK-2100 Copenhagen, Denmark; 2 School of Engineering, Kristianstad University, S-291 88 Kristianstad; 3 Department of Medical Microbiology, Dermatology and Infection, University of Lund, Sölva Gatan 23, S-22362 Lund, Sweden
Received 18 June 2003; in final form 10 October 2003; published online on 2 March 2004
 |
ABSTRACT |
|---|
 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
|---|
Exposure to organic dust originating from biofuels can cause adverse health effects. In the present study we have assessed the dustiness in terms of microbial components and particles of various biofuels by using a rotating drum as a dust generator. Microbial components from straw, wood chips, wood pellets and wood briquettes were quantified by several methods. Excellent correlations (r
0.85, P < 0.0001) were found: between lipopolysaccharide (LPS) (as determined by 3-hydroxy fatty acid analysis) and endotoxin (as determined by a Limulus test), cultivable bacteria, total number of bacteria and muramic acid; between endotoxin and cultivable bacteria, total number of bacteria and muramic acid; between total number of bacteria and muramic acid; between cultivable fungi and total number of fungi. Straw was dustier than the other biofuels in terms of actinomycetes, bacteria, muramic acid, endotoxin, LPS, particle mass and number of particles. One of the wood chips studied and the straws had comparatively high dustiness in terms of fungi, while both wood pellets and wood briquettes had comparatively low dustiness in terms of all microbial components. An initially high particle generation rate of straw and wood chips decreased over time whereas the particle generation rate of wood briquettes and wood pellets increased during a 5 min rotation period. Particles of non-microbial origin may be the determining factor for the health risk in handling briquettes and pellets. Straw dust contained significantly more microorganisms per particle than did wood chip dust, probably because bacteria were most abundant in straw dust. The concentrations of endotoxin and fungi were high in wood and straw dust; dust from one of the straws contained 3610 EU/mg and dust from one of the chips contained 7.3 x 106 fungal spores/mg. An exposure to 3 mg of straw or wood chips dust/m3 (the Swedish and Danish OEL of unspecific inhalable dust) could cause exposures to endotoxin and fungi higher than levels were health symptoms are seen to develop. The very different levels of dustiness in terms of particles and microbial components of different biofuels shows that dustiness is an important health-relevant factor to consider when choosing among biofuels and when designing worksites for handling of biofuels.
Keywords: bacteria; c.f.u.; dustiness test; endotoxin; fungi; LPS; muramic acid; occupational health; particles; straw; wood chips
|
INTRODUCTION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
|---|
Biofuels represent an important, sustainable energy resource, but workers handling biofuels may be exposed to high levels of microorganisms and endotoxins (e.g. Blomquist et al., 1980; de Davila and Bengtsson, 1993; Madsen, 2002). Occupational health problems associated with microorganisms in dust from wood chips have been reported repeatedly, (Thörnqvist and Lundström, 1982; van Assendelft et al., 1985; Jäppinen et al., 1987) including cases of acute alveolitis and other respiratory symptoms (Kolmodin-Hedman et al., 1987). From studies of farmers and refuse workers it is known that exposure to microorganisms and endotoxins in dust from straw, grain, hay and garbage may cause respiratory diseases and eye irritation (e.g. Malmberg et al., 1985; Sigsgaard et al., 1994; Eduard et al., 2001; Melbostad and Eduard, 2001; Viet et al., 2001). Precautionary action thus should be taken to reduce dust exposure during handling of biofuels.
An important step in a control strategy would be to reduce the dustiness of biofuels by using fuels with low dustiness in terms of microbial components. However, knowledge of the dustiness of different biofuels is very limited. The aim of the present study was to assess the microbial exposure risk from handling biofuels. Therefore, dustiness of different biofuels has been assessed using a rotating drum dustiness tester and the generated dust characterized concerning several microbial components and by particle size. The time dependence of particle release was also measured as it is important in connection with duration of handling processes. Since there are no standard methods of quantifying microorganisms and since different microbial components are of importance (reviewed in Douwes et al., 2003), a range of different methods were used to characterize the microbial components and the results obtained by these methods are compared. The methods included total spore counting, cultivation of microorganisms, quantification of endotoxin (lipopolysaccharide, LPS), by both the Limulus method and by gas chromatography-mass spectrometry (GC-MS), and quantification of ergosterol (from fungi) and muramic acid (from bacterial peptidoglycan) by GC-MS.
|
MATERIALS AND METHODS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
|---|
Description of the fuels
The biofuel samples were collected 1 day before the rotating drum tests. Approximately 5–7 kg of each material was sampled in triplicate and transported to the laboratory. The samples were stored in open black polyethylene bags at 9–15°C until the rotating drum tests were performed.
The different types of biofuels studied are presented in Table 1. Included were straw from conventional farming and organic farming (i.e. farming using natural fertilizers and no use of chemicals), wood chips and pellets and briquettes made from sawdust. The wood chips were chipped 3 days before dust generation and were collected from freshly chipped wood delivered to a heating plant. The wood briquettes and wood pellets were collected at the factory. Straw bales were opened and the straw was collected to obtain as uniform a sample as possible.
|
Three samples of
15 g of each biofuel were weighed before and after drying in an oven (105°C, 12–18 h) for estimating the water content (Table 1).
Generation of aerosols and collection of dust
A rotating drum was used to generate airborne dust and six replicates of the dust were used. The dust generator was a rotating drum with a horizontal axis and a volume of 3.3 m3 as described previously (Breum et al., 1999). The biofuel (3 or 6 kg) was loaded into the bottom of the drum, which was then rotated (7 r.p.m., 5 min). A vacuum pump attached downstream of the drum maintained an airflow of 420 l/min through the drum; excess HEPA-filtered replacement air was supplied at the opposite end of the drum ensuring ambient pressure inside the drum. Dust was sampled on a 140 mm diameter 8 µm cellulose nitrate membrane filter (Sartorius, Göttingen, Germany). An isokinetic probe upstream of the filter delivered a sub-sample (1.9 l/min) of the exhausted air to a particle counter (Grimm model 1200) for collection of data on dust concentrations over time. The particle counter measured number of particles per litre of air in 6 s intervals. The thoracic dust fraction has a 50% cut-off at 10 µm and the respirable dust fraction a 50% cut-off at 3.5 µm and we have presented results for particles 10 and 3.5 µm. Dust for microbiological analysis was sampled on six filter cassettes located 0.2 m upstream from the outlet. Four cassettes contained Teflon filters in closed face filter cassettes (25 mm diameter, 8 µm; Millipore, Bedford, MA) with a 5.6 mm inlet at an airflow of 1.9 l/min (1.25 m/s inlet velocity) and two cassettes contained polycarbonate filters in closed face filter cassettes (25 mm diameter, 0.4 µm; Nuclepore, Cambridge, MA) with a 4.4 mm inlet at an airflow of 1.9 l/min (2.07 m/s inlet velocity).
The masses of dust collected on the Teflon filters and cellulose nitrate filters were determined by weighing the filters before and after sampling. Before weighing the filters were equilibrated at a constant air temperature and humidity for 24 h. Three of the four Teflon filters were frozen at –20°C. One was used to measure ergosterol and one was used to measure LPS and muramic acid; the third filter was used as a spare filter. The dust collected on the fourth Teflon filter was (within 48 h) analysed for endotoxin by the Limulus test. The two polycarbonate filters were pooled and used for counting of microorganisms.
Determination of LPS, peptidoglycan and fungal biomass
Muramic acid was used as a marker of bacterial peptidoglycan/biomass, 3-hydroxy fatty acids (3-OH FAs) with 10–18 carbon chains were used as markers of the LPS (endotoxin) of Gram-negative bacteria and ergosterol was used as a marker of fungal biomass. These marker compounds are covalently linked to various structures in the cell membranes; thus, prior to analysis, a sample must be hydrolysed. Thereafter, the analytes are purified by extraction and finally derivatized. The procedures carried out for the indicated markers are briefly described below.
LPS
The 3-OH FAs are linked to the glucosamine disaccharide moiety of lipid A, which is the toxic part of the typical enteric LPS molecule. Samples were heated in 2 M methanolic HCl, then methyl esters were extracted with n-heptane. The heptane layer was evaporated under a stream of nitrogen, redissolved in heptane:dichloromethane (1:1 v/v) and applied to a disposable silica gel column. The column was washed with diethyl ether and heptane:dichloromethane before use and heptane:dichloromethane was added after applying the methyl ester preparation. The hydroxy fatty acid methyl esters were eluted with diethyl ether and subsequently evaporated. Trimethylsilyl (TMS) derivatives were prepared by adding N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) and pyridine to the sample, followed by heating for 20 min at 80°C. Pentadeuterated 3-hydroxy 14:0 (50 ng added to a sample) was used as an internal standard. The derivatized acids were quantified using gas chromatography–tandem mass spectrometry (GC-MSMS) (Saraf et al., 1999). The amount (moles) of LPS in each sample was calculated by dividing the number of moles of the 3-hydroxy acids by four.
Fungal biomass
Samples were heated in 10% methanolic KOH at 80°C for 90 min, extracted with heptane and evaporated to dryness under a stream of nitrogen. The dried samples were dissolved in dichloromethane:heptane (1:1) and purified. After evaporation of the ether solvent, TMS derivatization was performed by adding BSTFA and pyridine and then heating at 60°C for 30 min. Dehydrocholesterol (100 ng added to the sample) was used as an internal standard. The final preparations were analysed by GC-MSMS (Saraf et al., 1999).
Bacterial biomass/peptidoglycan
Muramic acid is a unique marker of peptidoglycan. Samples were heated in 2 M methanolic HCl at 85°C overnight, after which the internal standard (13C-labelled muramic acid in a methanolysate of 30 µg of 13C-labelled algal cells) was added. The mixture was extracted with heptane and the lower phase was evaporated to dryness under nitrogen and further dried under vacuum. Samples were then acetylated. The reaction mixture was evaporated and dissolved in dichloromethane, washed with a 0.05 M HCl solution and with water, evaporated to dryness, dissolved in chloroform and analysed by GC-MSMS (Saraf et al., 1999).
Determination of endotoxin by the Limulus method
Dust was extracted with 5.0 ml of sterile 0.05% Tween 20 aqueous solution by orbital shaking (300 r.p.m.) at room temperature for 60 min and centrifuged (1000 g) for 15 min. The supernatant was analysed (in duplicate) for endotoxin by the kinetic Limulus amoebocyte lysate test (Kinetic-QCL endotoxin kit; BioWhittaker,Walkersville, MD). A standard curve obtained from an Escherichia coli O55:B5 reference endotoxin was used to determine the concentrations in terms of endotoxin units (EU) (14.0 EU 
1 ng).
Quantification of microorganisms (CAMNEA)
Microorganisms were quantified by a modified CAMNEA method (Palmgren et al., 1986). A sterile 0.05% Tween 80 and 0.85% NaCl aqueous solution was added to a filter cassette (within 2 h after dust generation), which was then shaken (500 r.p.m., 15 min). The numbers of cultivable fungi were enumerated by plating of dilutions on DG 18 agar (Oxoid, Basingstoke, UK) followed by incubation at 25°C. In addition, agar plates were incubated at 45°C to quantify cultivable Aspergillus fumigatus. The number of bacteria (25°C), mesophilic actinomycetes (25°C) and thermophilic actinomyctes (55°C) culturable on Nutrient Agar (Oxoid) with cycloheximide (50 mg/l) were also measured.
The total number of bacteria and fungal spores were determined after staining in 20 p.p.m. acridine orange (Merck) in acetate buffer. Fungi and bacteria were counted by microscopy (Orthoplan; Leitz Wetzlar). The numbers of microorganisms were determined in 40 randomly chosen fields or until a total number of at least 400 spores were counted.
Dustiness and concentrations of microbial components
The dustiness index, denoted Dx, is defined as the amount of generated airborne particle mass or microbial component, x, per mass of tested material, Mbiofuel (Breum et al., 1999). In the present study, particle masses and microbial components, x, were determined in the dust collected on the Teflon or polycarbonate filters and the dustiness is calculated from the equations:
where mass of generated dust collected at the outlet of the drum is Mout. Cdust is the mass of dust per m3 air, Cx is the average amount of microbial component, x, per volume of air and Px is the concentration of microbial component, x, defined as amount of microbial component per mg dust.
The dustiness is used to characterize the biofuel. Determination of the concentrations of microbial components allows comparison of the results with measurements of dust from other sources and environments. Concentrations of airborne dust particles and the generation rate of particles in the size range 0.75–3.5 and 0.75–10 µm versus time after starting the rotating dustiness tester were calculated.
Dust generation rate
The particle generation rate, S, can be calculated from the concentration time series, Ci, by the equation (Hjemsted and Schneider, 1996):
where V is volume of the drum (3.3 m3), 
t is the time between two consecutive measurements (6 s) and 
= V/Q = 472 s is the time constant of the drum (Q = total air flow rate). It is assumed that t << . The concentration time series as measured with the Grimm particle counter at the drum outlet was fitted to the weighted sum of two exponentials:
using a generalized regression method. Using the fitted expression, the intercept, I, at time t = 0 was calculated as I = y(0), and slope, S, at time t = 0 was calculated as:
Statistics
Statistical analysis were performed with SAS (version 8e; SAS Institute, Cary, NC). Because the data for comparing dustiness determined by different methods followed a normal logarithm distribution, they were normal logarithm transformed and Pearson correlations were calculated. The Bonferroni correction has been used (0.05/n) and P-values <0.002 are considered as significant. The dustiness of different biofuels and the concentrations of microbial components in dust from different biofuels were compared using a t-test. Values are expressed as means of data from three sub-samples with the standard error of the mean.
|
RESULTS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
|---|
Correlations between microbial measurements
High correlations were found between four of the bacterial measurements, namely LPS, endotoxin, total bacteria and muramic acid, and between colony-forming units (c.f.u.) and total number of fungi (Table 2). The muramic acid and total number of bacteria correlated better than ergosterol and total number of fungi.
|
The methods showed different sensitivities in detecting low concentrations of microorganisms. Thus, microorganisms in pellet and briquette dust could be quantified by culture and GC-MS, but not by microscopy. Actinomycetes could only be quantified by culture; notably, the concentration of actinomycetes did not correlate significantly with concentrations of other microorganisms.
Dustiness in terms of microorganisms and endotoxin
Of the biofuels tested, straw 4 showed the highest dustiness in terms of mesophilic actinomycetes (1.4 x 107 c.f.u./kg) and straw 1 in terms of thermophilic actinomycetes (2.7 x 104 c.f.u./kg). Wood briquettes and pellets did not release actinomycetes at a detectable level. Dustiness in terms of bacteria, muramic acid, endotoxin and LPS (Fig. 1) was highest for straw. The dustiness in terms of LPS of straw was between 10 and 59 nmol/kg biofuel.
|
The dustiness in terms of cultivable fungi varied between 400 and 2.5 x 108 c.f.u./kg. The dustiness of chips 1 in terms of total number of fungi was more than 10 times higher than of chips 2 (Fig. 2b). The straw differed by up to a factor of 5 in dustiness in terms of total number of fungi (Fig. 2b). Straw 4 had a higher dustiness in terms of ergosterol (Fig. 2a) and cultivable fungi than the three other straws tested. The dustiness of pellets in terms of ergosterol and c.f.u. of fungi (Fig. 2a) was significantly higher than that of wood briquettes.
|
Dustiness in terms of particle mass and particle generation rate
Wood chips 2 was the least dusty fuel (Fig. 3a), caused the lowest number of particles per litre of air (Fig. 3b and Table 4) and exhibited the lowest particle generation rate (Fig. 3c) during the simulated handling. The four straws were the dustiest fuels, but exhibited variations in both dustiness (Fig. 3a) and particle generation rates (Fig. 3c and d).
|
|
While the particle generation rate of straw and chips decreased through at least the first 2 min of simulated handling it increased for wood pellets and wood briquettes (Table 4 and Fig. 3c). Straw 4 released most particles and microorganisms and had the highest negative initial slope, S, on the particle generation curve (particles 0.75–10 µm) of the straws tested (Table 4). Straw and wood chips 2 released more microorganisms than particles (size 0.75–10 µm) and significantly higher numbers of microorganisms per particle were found in straw dust than in chips dust (Table 4). The fraction of particles (0.75–3.5 µm) <1 µm from chips 2 and pellets constituted 47 and 62%, respectively, of the particles, while these small particles from straw constituted only 18–23%.
Concentrations of microorganisms
The concentrations of thermophilic actinomycetes in straw dust varied between 50 and 230 c.f.u./mg and the concentrations of mesophilic actinomycetes in dust from chips 1 and 2 and from straw 2 were not significantly different (average 1.3 x 105 c.f.u./mg). Concentrations of cultivable bacteria ranged between 20 and 60 c.f.u./mg in briquette and pellet dust and between 8 x 104 and 3.1 x 106 c.f.u./mg in straw and wood chip dust. Dust from wood pellets and briquettes contained least muramic acid and the total bacterial concentration was highest in straw dust (Table 3). Bacteria from wood chips were to a larger extent cultivable and contained higher concentrations of muramic acid than bacteria from straw (Table 3).
|
Of all the biofuel dusts, the dust from chips 1 had the highest concentration of total (Table 3) and cultivable fungi (4.15 x 106 c.f.u./mg). Total numbers of fungi in dust from wood briquettes and pellets were below the detection level (Fig. 2b), but cultivable fungi and ergosterol were found in significantly higher concentrations in wood pellet dust (36 c.f.u./mg) than in briquette dust (22 c.f.u./mg, P = 0.03) (Table 3).
Dustiness in terms of A.fumigatus was up to 3.5 x 105 c.f.u./kg fuel for chips 1 and straw 2 and A.fumigatus was present at concentrations up to 1.6 x 103 c.f.u./mg dust. Cladosporium sp. was found in straw dust and was the dominant fungus in conventional grown straw, the concentrations being 7.8 x 104 and 7.0 x 104 c.f.u./mg dust for straws 3 and 4, respectively. Verticillium sp. was found in the organic grown straw, at 756 and 3.6 x 104 c.f.u./mg dust in straws 1 and 2, respectively. Eurotium sp. was found in dust from straw 1 (1.9 x 103 c.f.u./mg) and yeast in dust from wood chips 1 (6.5 x 104 c.f.u./mg dust).
|
DISCUSSION |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
|---|
Straw was dustier than wood chips, wood pellets and briquettes in terms of bacteria (total number, c.f.u. and muramic acid), endotoxin (endotoxin and LPS), number of particles and mass of dust. Two to fifty times more respirable particles were released from straw than from chips, and this may reflect the more than 100 times higher dustiness of straw in terms of total bacteria. In a study where wood chips and straw were exposed to an air flow, chips released a higher number of respirable dust particles than straw (Vandeput et al., 1997). The difference between the two studies may be explained by the likely assumption that release of both fungi and bacteria is high during rotation, while mainly fungi and actinomycetes are released when a material is exposed to an air flow, together with the finding that the ratio of bacteria to fungi was much higher in straw than in wood chips dust. A high dustiness of straw in terms of cultivable fungi and endotoxin has been found previously during mechanical handling of straw (Breum et al., 1999). The straw studied had a higher dustiness in terms of microorganisms and endotoxin than that found for waste in a similar study by Breum et al. (1997). By a modified wind tunnel technique, samples of 20 g wood shavings released cultivable microorganisms (Kotimaa, 1991) at the same levels or lower than we found for wood chips.
The mycotoxin-producing fungus A.fumigatus (Land et al., 1987) detected in dust from both wood chips and straw has often been described as a causal agent of farmers lung (e.g. Lundgren and Rosenhall, 1979; Belin, 1987; Kolmodin-Hedman et al., 1987) and workers handling biomass often produce antibodies towards this fungus (Jäppinen et al., 1987). Verticillium sp. and Cladosporium sp., the dominant fungi in dust from organic (straws 1 and 2) and conventional grown straw (straws 3 and 4), respectively, are also abundant in dust released during harvest (see, for example, Darke et al., 1976), and in an investigation of grain handlers 18% reacted in a skin test to Cladosporium sp. and 35% to Verticillium sp. (Lacey, 1987). Exposure to these fungi has caused respiratory diseases (e.g. Darke et al., 1976; reviewed by Lacey and Crook, 1988). Eurotium sp., found in straw 1 dust, has also been associated with respiratory diseases (e.g. Lacey and Dutkiewicz, 1994).
The water content of some materials is known to affect dust release (reviewed by Hjemsted and Schneider, 1996; Alwis et al., 1999). This study indicates an effect of water content on the particle generation rate and dustiness in terms of particle mass. Thus, chips 2 (high water content) was less dusty and had a lower particle generation rate than chips 1 (lower water content) and straw 4 (lowest water content of straws) released most particles. The instantaneous particle generation rate within the test period differed qualitatively and quantitatively. Chips 1 and briquettes had almost the same dustiness regarding particle mass and number as measured for the entire period of rotation. However, during handling, chips 1 had a high initial dust release followed by a decrease, while the briquettes had a low initial dust release followed by an increase, probably due to attrition. This was reflected in a high intercept I and negative initial slope S for chips 1 and low I and positive initial S for briquettes (Table 4). The initial high dust release of chips 1 and straw is expected to describe a fast release of microorganisms. These observations illustrate the importance of calculating particle generation rates in investigations where dustiness is tested for a given length of time, so as not to obtain misleading exposure-related information for scenarios where handling is very brief or occurs over extended periods of time.
The highest concentrations of endotoxin and LPS were found in straw dust. In comparison with previously published data by Rylander (1997), endotoxin in straw dust was present in the same range of concentrations as for both cotton and poultry house dust, while endotoxin concentrations in pellet and briquette dust were at the low end of the concentrations found in piggery building dust. Endotoxin concentrations of chips dust was in the same range as in dust from poultry houses. Furthermore, the endotoxin concentrations found in wood briquettes, pellets and chip dust were in the range of concentrations Cinkotai et al. (1977) found in airborne dust in cotton mills and by Sonesson et al. (1990) in poultry slaughterhouse dust.
The Swedish and Danish occupational exposure limit (OEL) of unspecific inhalable dust is 3 mg/m3. An exposure to 3 mg/m3 straw dust under conditions of straw release that are well simulated by the method used in this study could theoretically contain between 2860 and 10 840 EU/m3, 0.5 x 106 and 9 x 106 fungi/m3 and 70 x 106 and 140 x 106 bacteria/m3. These levels of endotoxins are much higher than the Dutch OEL of 200 EU/m3 (Ministry of Social Affairs and Work, 2000, available in Dutch at http://home.szw.nl/actueel/dsp_persbericht.cfm, link_id=157&jaar=2000) and fungi at this level are seen to cause such symptoms as eye and nose irritation (Eduard et al., 2001). Similarly, exposure to 3 mg/m3 wood chip dust could cause exposures higher than the Dutch endotoxin OEL, and 10–1000 times higher than the level where eye and nose symptoms seem to develop due to fungi. In contrast, an exposure to 3 mg/m3 pellet or briquette dust would not cause a too high endotoxin and fungal exposure according to the Dutch endotoxin OEL, and studies by Eduard et al. (2001).
The high correlations between LPS and endotoxin and between total number of bacteria and muramic acid indicate that these methods, at least in this study, were good measurements of endotoxin and bacteria. The correlation between dustiness in terms of endotoxin or LPS and dustiness in terms of particle mass was at the same level as or higher than the correlation found by Simpson et al. (1999) between endotoxin and dust from different environments. However, Simpson et al. (1999) also showed, when data from different environments were analysed separately, that the correlation between endotoxin and dust was not significant in all environments and, similarly, Sonesson et al. (1990) showed that correlations between endotoxin and dust as well as LPS and dust concentrations are highly variable. Thus, assessments of endotoxin or dust exposure cannot substitute for each other, even though significant correlations have been found. As Smid et al. (1992) and Nielsen et al. (1997) found, we determined significant correlations between some parameters that were not measurements of the same microorganisms. However, Table 2 shows that correlation coefficients were highest and P values lowest for measurements of the same microbial component.
|
CONCLUSIONS |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
|---|
Straw was the dustiest of the fuels studied in terms of particle mass, number of respirable particles, endotoxin, LPS, cultivable and total number of bacteria, muramic acid and actinomycetes. However, the initial particle generation rate of chips 1 was as high as or higher than that of straw. Wood pellets and briquettes showed the lowest dustiness in terms of all microbial components, and particles of non-microbial origin may be the determining factor for health risk of handling these fuels. The particle generation rate of pellets and briquettes was initially low but increased over time and thus particle exposures will mainly occur after a long time of handling. In contrast, the particle generation rates of straw and chips were initially high but decreased with time.
The concentrations of microorganisms in straw and wood chip dust were high and 3 mg/m3 straw dust (the Swedish and Danish OEL of unspecific inhalable dust) could contain up to 10 840 EU/m3 and up to 9 x 106 fungi/m3 , which is higher than the levels at which health symptoms develop.
High correlations between LPS and endotoxin and between total number of bacteria and muramic acid indicate that the methods used, at least in this study, were good measurements of endotoxin and bacteria.
Acknowledgements—Dorota Pomorska, Mirella Simkus, Dorte Narv, Signe H. Nielsen and Frank Selsmark are acknowledged for technical assistance. The Ångpanneföreningen Research Foundation is gratefully acknowledged for generous financial support.
|
FOOTNOTES |
|---|
* Author to whom correspondence should be addressed. Fax: +45-39-16-52-01; e-mail: amm{at}ami.dk
|
REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSREFERENCES |
|---|
Alwis U, Mandryk J, Hocking AD, Lee J, Mayhew T, Baker W. (1999) Dust exposure in the wood processing industry. Am Ind Hyg Assoc J; 60: 641–6.[Web of Science][Medline]
Belin L. (1987) Sawmill alveolitis in Sweden. Int Arch Allergy Appl Immunol; 82: 440–3.[Web of Science][Medline]
Blomquist G, Ström G, Strömquist LH. (1980) Bestämning av Diasporhalten i Luft vid några Fliseldningsanläggningar, Undersökningsrapport 1980:28 (in Swedish). Arbetarskyddsstyrelsen.
Breum NO, Nielsen BH, Nielsen EM, Midtgård U, Poulsen OM. (1997) Dustiness of compostable waste: a methodological approach to quantify the potential of waste to generate airborne microorganisms and endotoxin. Waste Manage Res; 15: 169–87.
Breum NO, Nielsen BH, Lyngbye M, Midtgård U. (1999) Dustiness of chopped straw as affected by lignosulfonate as a dust suppressant. Ann Agric Environ Med; 6: 133–40.[Medline]
Cinkotai FF, Lockwood MG, Rylander R. (1977) Airborne micro-organisms and prevalence of byssinotic symptoms in cotton mills. Am Ind Hyg Assoc J; 38: 554–9.[Web of Science][Medline]
Darke CS, Knowelden J, Lacey J, Ward M A. (1976) Respiratory disease of workers harvesting grain. Thorax; 31: 294–302.
de Davila EA, Bengtsson L. (1993) Arbetsmiljön vid hantering av trädbränsle och torv för energiproduktion, B 1088, 1–30 (in Swedish). IVL, Sweden.
Douwes J, Thorne P, Pearce N, Heederik D. (2003) Bioaerosols health effects and exposure assessment: progress and prospects. Ann Occup Hyg; 47: 187–200.
Eduard W, Douwes J, Mehl R, Heederik D, Melbostad E. (2001) Short term exposure to airborne microbial agents during farm work: exposure–response relations with eye and respiratory symptoms. Occup Environ Med; 58: 113–8.
Hjemsted K, Schneider T. (1996) Documentation of dustiness drum test. Ann Occup Hyg; 40: 627–43.
Jäppinen P, Haahtela T, Lira J. (1987) Chip pile workers and mould exposure. Allergy; 42: 545–8.[Web of Science][Medline]
Kolmodin-Hedman B, Blomquist G, Löfgren F. (1987) Chipped wood as a source of mould exposure. Eur J Resp Dis; 71 (suppl. 154): 44–51.
Kotimaa MH, Oksanen L, Koskela P. (1991) Feeding and bedding materials as sources of microbial exposure on dairy farms. Scand J Work Environ Health; 17: 117–22.[Web of Science][Medline]
Lacey J. (1987) Exposure of farm workers to fungi and Actinomycetes while harvesting cereal crops and handling stored grain. Eur J Resp Dis; 154: 37–43.
Lacey J, Crook B. (1988) Fungal and actinomycete spores as pollutants of the workplace and occupational allergens. Ann Occup Hyg; 32: 515–33.
Lacey J, Dutkiewicz J. (1994) Bioaerosols and ocupational lung disease. J Aerosol Sci; 25: 1371–404.[CrossRef]
Land CJ, Hult K, Fuchs R, Hagelberg S, Lundström H. (1987) Tremorgenic mycotoxins from Aspergillus fumigatus as a possible occupational health problem in sawmills. Appl Environ Microbiol; 53: 787–90.
Lundgren R, Rosenhall L. (1979) Fliseldarsjuka—en ny variant av allergisk alveolit. Läkartidningen; 76: 4730–1.[Medline]
Madsen AM. (2002) Exposure to airborne microorganisms, endotoxins and dust during work at biofuel plants. In Appropriate environmental and solid waste management and technologies for developing countries, Vol. 5, pp. 2719–2726.
Malmberg P, Rask-Andersen A, Palmgren U, Höglund S, Kolmodin-Hedman B, Stålenheim, G. (1985) Exposure to microorganisms, febrile and airway-obstructive symptoms, immune status and lung function of Swedish farmers. Scand J Work Environ Health; 11: 287–93.[Web of Science][Medline]
Melbostad E, Eduard W. (2001) Organic dust-related respiratory and eye irritation in Norwegian farmers. Am J Ind Med; 39: 209–17.[CrossRef][Web of Science][Medline]
Nielsen BH, Würtz H, Breum NO, Poulsen OM. (1997) Microorganisms and endotoxin in experinmentally generated bioaerosols from composting household waste. Ann Agric Environ Med; 4: 159–68.
Palmgren UG, Ström G, Blomquist G, Malmberg P. (1986) Collection of airborne micro-organisms on Nuclepore filters, estimation and analysis-CAMNEA method. J Appl Bacteriol; 61:401–6.[Medline]
Rylander R. (1997) Evaluation of the risks of endotoxin exposures. Int J Occup Environ Health; 3 (suppl.): 32–6.
Saraf A, Larsson L, Larsson B-M, Larsson K, Palmberg L. (1999) House dust induces IL-6 and IL-8 response in A 549 epithelial cells. Indoor Air; 9: 219–25.[CrossRef][Web of Science][Medline]
Sigsgaard T, Malmros P, Nersting L, Petersen C. (1994) Respiratory disorders and atopy in Danish refuse workers. Am J Resp Crit Care Med; 149: 1407–12.[Abstract]
Simpson JCG, Niven R Mc, Pickering CAC, Oldham LA, Fletcher AM, Francis HC. (1999) Comparative personal exposure to organic dusts and endotoxin. Ann Occup Hyg; 43: 107–15.
Smid T, Heederik D, Mensink G, Houba R, Boleij JSM. (1992) Exposure to dust, endotoxins, and fungi in the animal feed industry. Am Ind Hyg Assoc J; 53: 362–8.
Sonesson A, Larsson L, Schütz A, Hagmar L, Hallberg T. (1990) Comparison of the Limulus Amebocyte Lysate test and gas chromatography-mass spectrometry for measuring lipopolysaccharides (endotoxins) in airborne dust from poultry-processing industries. Appl Environ Microbiol; 56: 1271–8.
Thörnqvist T, Lundström H. (1982) Health hazards caused by fungi in stored wood chips. Forest Products J; 32: 29–32.
van Assendelft AHW, Raitio M, Turkia V. (1985) Fuel chip-induced hypersensitivity pneumonitis caused by Penicillium species. Chest; 87: 394–6.
Vandeput S, Istasse L, Nicks B, Lekeux P. (1997) Airborne dust and aeroallergen concentrations in different sources of feed and bedding for horses. Vet Q; 19: 154–8.[Web of Science][Medline]
Viet SM, Buchan R, Stallones L. (2001) Acute respiratory effects and endotoxin exposure during wheat harvest in notheastern Colorado. Appl Occup Environ Hyg; 16: 685–97.[Medline]
CiteULike 
Connotea 
Del.icio.us What's this?
This article has been cited by other articles:
|
|
 |
|
  U. Svedberg, C. Petrini, and G. Johanson Oxygen Depletion and Formation of Toxic Gases following Sea Transportation of Logs and Wood Chips Ann. Hyg., November 1, 2009; 53(8): 779 - 787. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. M. Madsen, V. Schlunssen, T. Olsen, T. Sigsgaard, and H. Avci Airborne Fungal and Bacterial Components in PM1 Dust from Biofuel Plants Ann. Hyg., October 1, 2009; 53(7): 749 - 757. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. M. Madsen, V. M. Hansen, S. H. Nielsen, and T. T. Olsen Exposure to Dust and Endotoxin of Employees in Cucumber and Tomato Nurseries Ann. Hyg., March 1, 2009; 53(2): 129 - 138. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. M. Madsen and A. K. Sharma Sampling of High Amounts of Bioaerosols Using a High-Volume Electrostatic Field Sampler Ann. Hyg., April 1, 2008; 52(3): 167 - 176. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A.M. MADSEN Exposure to Airborne Microbial Components in Autumn and Spring During Work at Danish Biofuel Plants Ann. Hyg., November 1, 2006; 50(8): 821 - 831. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. LIDEN Dustiness testing of materials handled at workplaces. Ann. Hyg., July 1, 2006; 50(5): 437 - 439. [Full Text] [PDF]
|
|
|
|
|
|
A. M. MADSEN, P. KRUSE, and T. SCHNEIDER Characterization of Microbial Particle Release from Biomass and Building Material Surfaces for Inhalation Exposure Risk Assessment Ann. Hyg., March 1, 2006; 50(2): 175 - 187. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||