Presence of endotoxins in different agricultural environments

Gram-negative bacterial endotoxins are contaminants of dusts from agricultural products. They represent a potential health hazard for farmers working in many different processes. However, the occurrence of endotoxins has not been well characterized in the various farming operations. Therefore, two farming activities with potential for generating airborne endotoxins were studied: 1) chopping of baled corn stalks or straw for bedding in New York State, and 2) oat bin unloading in Alabama. Actual airborne endotoxin levels in dusts obtained during bedding chopper operations far exceeded [90 endotoxin units (EU)/m3] the level at which acute pulmonary function decrements occur in cotton dust-exposed individuals. Endotoxin contamination of laboratory-generated dust from an oat sample likewise exceeded these levels. This study documents the presence of potentially hazardous exposures to endotoxins in two common farm processes, which expands the knowledge of airborne endotoxin exposures on the farm.     

Longitudinal changes in inflammatory markers in nasal lavage of cotton workers

Objectives: The aim of this study was to evaluate time-related changes in inflammatory markers in nasal lavage (NAL) in relation to endotoxin exposure and lung function changes. Methods: Endotoxin in cotton dust is well known to elicit proinflammatory mediators involved in acute or chronic respiratory inflammation due to cotton dust. We applied nasal lavage as well as lung function and exposure measurements in a small group (n=11) of cotton workers during 6 weeks of observation (after 2 weeks free of exposure). Several inflammatory markers in NAL, such as interleukin 8 (IL-8), IL-6, and downstream mediators, including soluble tumor necrosis factor receptor 75 (sTNF-R75) and soluble intercellular adhesion molecule 1 (ICAM-1), cell counts, marker of epithelial response (uric acid), and marker of plasma exudation (albumin) were measured. Results: At the exposure levels examined in this study [cotton dust, geometric mean (GM) = 1.10mg/m³; endotoxin, GM = 2,869 EU/m³], several inflammatory markers in NAL such as IL-8, sTNF-R75, and albumin tended to increase through the measurement period with increasing airborne endotoxin concentration (in six workers who had paired measurements in weeks 1 and 6). Although no statistical significance was reached, airborne endotoxin exposure and all inflammatory markers in NAL were relatively higher in cotton workers with a 6-week lung function decrease. Conclusion: The data suggest that inflammatory markers in NAL are associated with repeated airborne endotoxin exposure. Received: 17 January 1997 / Accepted: 10 July 1997     

Human ventilatory response to washed and unwashed cottons from different growing areas.

Thirty volunteer subjects were exposed to controlled amounts of respirable dust generated by the carding of cotton in an experimental cardroom. Eighteen exposures each lasting six hours were performed while carding unwashed and washed cottons from the three major growing regions of the United States. Elutriated dust was analysed gravimetrically and was comparable (0.59 mg/m3 +/- 0.04) for all exposures. Spirometry was recorded before and after each exposure. California cotton resulted in a significantly smaller fall in FEV1 than cotton of the same grade from Texas or Mississippi. All washed cottons resulted in reduced declines when compared with unwashed cottons. For 17 subjects breathing zone personal total dust samples were analysed for airborne endotoxin and compared with the individual's pulmonary function response. A significant correlation between endotoxin exposure and acute decrease in FEV1 was seen. The effect on FEV1 per nanogram of airborne endotoxin was greater for Mississippi cotton than for cotton from the other regions. Airborne endotoxin appears to be an important determinant of acute pulmonary effects of cotton dust. Water washing of cotton results in reduced airborne endotoxin and less bronchoconstriction.     

Human ventilatory response to washed and unwashed cottons from different growing areas

Thirty volunteer subjects were exposed to controlled amounts of respirable dust generated by the carding of cotton in an experimental cardroom. Eighteen exposures each lasting six hours were performed while carding unwashed and washed cottons from the three major growing regions of the United States. Elutriated dust was analysed gravimetrically and was comparable (0.59 mg/m3 +/- 0.04) for all exposures. Spirometry was recorded before and after each exposure. California cotton resulted in a significantly smaller fall in FEV1 than cotton of the same grade from Texas or Mississippi. All washed cottons resulted in reduced declines when compared with unwashed cottons. For 17 subjects breathing zone personal total dust samples were analysed for airborne endotoxin and compared with the individual's pulmonary function response. A significant correlation between endotoxin exposure and acute decrease in FEV1 was seen. The effect on FEV1 per nanogram of airborne endotoxin was greater for Mississippi cotton than for cotton from the other regions. Airborne endotoxin appears to be an important determinant of acute pulmonary effects of cotton dust. Water washing of cotton results in reduced airborne endotoxin and less bronchoconstriction.     

Predictors of airborne endotoxin in the home

We identified home characteristics associated with the level of airborne endotoxin in 111 Boston-area homes enrolled in a cohort study of home exposures and childhood asthma, and we developed a predictive model to estimate airborne endotoxin. We measured endotoxin in family-room air and in dust from the baby's bed, family room, bedroom, and kitchen floor. Level of airborne endotoxin was weakly correlated (r < 0.3) with level of endotoxin in each of the four types of dust samples and was significantly correlated with endotoxin in family-room dust (p < 0.05). Endotoxin in family-room dust accounted for < 6% of the variability of airborne endotoxin. In a multivariate model, certain home characteristics were positively (p < 0.05) associated with airborne endotoxin. These included current presence of dog (difference in level, dog vs. no dog = 72%, partial R(2 )= 12.8%), past presence of dog (partial R(2) = 5.5%), and endotoxin level in family-room dust (partial R(2) = 5.3%). Use of a dehumidifier (partial R(2) = 6.4%) was negatively associated (p = 0.02; difference = -31%) with airborne endotoxin. Other home characteristics were identified as important determinants of increased airborne endotoxin in this model, but individual coefficients were not statistically significant (alpha = 0.05): total amount of fine dust collected in the home (partial R(2 )= 3.8%), concrete floor in family room (3.7%), water damage (3.6%), and use of cool-mist humidifier in past year (2.7%). This multivariate model explained 42% of the variability of airborne endotoxin levels, a substantial improvement over that with dust endotoxin alone. Airborne endotoxin in Boston-area homes appears to be determined by the presence of dogs, moisture sources, and increased amounts of settled dust.     

Airborne endotoxin and its relationship to pulmonary function among workers in an Indian jute mill

Air samples from various processing areas of an Indian jute mill were examined for endotoxin. The authors assessed work-related respiratory symptoms and pulmonary function changes in the dust-exposed workers from the different processing areas using a standard questionnaire and spirometry. Endotoxin was estimated in water extract of jute dust from 3 milling areas, and in outside air, by the Limulus amebocyte lysate gel clot technique. The batching, spinning, and weaving areas of the jute mill showed endotoxin levels of 0.22-4.42 microg/m3, 0.04-1.47 microg/m3, and 0.01-0.07 microg/m3, respectively, values similar to those found in Indian cotton mills. Respiratory morbidities among the workers included typical byssinotic symptoms, along with acute changes in postshift forced expiratory volume in 1 s (FEV1.0) (31.8%). Results of this study demonstrated that increased exposure to bacterial endotoxin in airborne dust is related to byssinotic symptoms among Indian jute mill workers. Findings were similar to those reported previously for workers in the cotton, flax, and hemp industries.     

Modeling, estimation and validation of cotton dust and endotoxin exposures in Chinese textile operations

In support of an epidemiological study of cancer incidence among cotton textile workers in Shanghai, PRC, historical estimates of exposure to cotton dust and endotoxin were developed for subjects drawn from a cohort of 267,400 female textile workers. A large dataset of historical cotton dust measurements were available from 56 of the study factories. Using these data, a series of models were developed to estimate cotton dust exposure by year, factory and process. Model estimates were validated by comparing with independently collected measurements gathered over a 15 year period and indicated a low relative bias (< 2%) and relative accuracy (+/- 61%). Endotoxin exposures were estimated using the endotoxin content of cotton dust by major processes obtained in five separate surveys in these factories. The validated exposures were assigned to the 7,242 jobs held by the 3,812 study subjects. Among the exposed workers, the mean cumulative exposure levels were 113.8 mg m(-3)*years for cotton dust and 6,707.7 EU m(-3)*years for endotoxin, respectively. The overall correlation among cotton dust and endotoxin exposures for these subjects was r = 0.58. Using an unusually rich set of historical cotton dust measurements, along with independently collected exposure measurements for validation and conversion to endotoxin levels, validated estimates of cumulative exposure were constructed for this large case-cohort study in the textile industry.     

Airborne fungi and endotoxin concentrations in different areas within textile plants in Taiwan: a 3-year study

Bioaerosols have been found in many occupational environments, including animal feeding houses, poultry slaughter houses, and cotton textile plants. This study was undertaken to examine a group of bioaerosols, the endotoxins, fungi, and bacteria, inside two textile factories over 3 years in Taiwan, where temperature and humidity are usually high year-round. Airborne dust was collected with filter cassettes attached to personal pumps and analyzed by the Kinetic Limulus Assay with Resistant-parallel-line Estimation. For fungi and bacteria determination, samples were collected using duplicated single-stage impactors, and organisms were counted after incubation. Endotoxin was the major contamination inside textile plants. Indoor levels were substantially higher than outdoor concentrations by 63- to 278-fold. The average values of fungi inside and outside the plants were not significantly different. Airborne bacteria levels were higher inside the plants as compared to outside. The carding sites, using only cotton, had extremely high endotoxin levels, greater than those at sites using synthetic fibers. Cotton, may be a major source of endotoxin contamination. In conclusion, the early stage of textile processing seems to generate high endotoxin and bacteria contamination. Priorities should be given to occupational hygiene programs for workers at various sites in textile plants.     

Exposure assessment to airborne endotoxin, dust, ammonia, hydrogen sulfide and carbon dioxide in open style swine houses

Information is limited for the exposure levels of airborne hazardous substances in swine feed buildings that are not completely enclosed. Open-style breeding, growing and finishing swine houses in six farms in subtropical Taiwan were studied for the airborne concentrations of endotoxin, dust, ammonia, hydrogen sulfide and carbon dioxide. The air in the farrowing and nursery stalls as partially enclosed was also simultaneously evaluated. Three selected gases and airborne dusts were quantified respectively by using Drager diffusion tubes and a filter-weighing method. Endotoxin was analyzed by the Limulus amoebocyte lysate assay. Average concentration of airborne total endotoxin among piggeries was between 36.8 and 298 EU/m(3), while that for respirable endotoxin was 14.1-129 EU/m(3). Mean concentration of total dust was between 0.15 and 0.34 mg/m(3), with average level of respirable dust of 0.14 mg/m(3). The respective concentrations of NH3, CO2 and H2S were less than 5 ppm, 600-895 ppm and less than 0.2 ppm. Airborne concentrations of total dust and endotoxin in the nursery house were higher than in the other types of swine houses. The finishing house presented the highest exposure risk to NH3, CO2 and H2S. Employees working in the finishing stalls were also exposed to the highest airborne levels of respirable endotoxin and dust. On the other hand, the air of the breeding units was the least contaminated in terms of airborne endotoxin, dust, NH3, CO2 and H2S. The airborne concentrations of substances measured in the present study were all lower than most of published studies conducted in mainly enclosed swine buildings. Distinct characteristics, including maintaining swine houses in an open status and frequent spraying water inside the stalls, significantly reduce accumulation of gases and airborne particulates.     

Comparative personal exposures to organic dusts and endotoxin

The aims of the study were to provide valid comparative data for personal exposures to dust and endotoxins for different occupations and to calculate comparative data for the contamination of organic dusts with endotoxin. Nine different occupational settings were studied, drawn from the textile, agricultural and animal handling industries. Samples were collected by personal sampling techniques, using the Institute of Occupational Medicine (IOM) sampling head, glass fibre filters and rechargeable sampling pumps. The dust exposures were calculated by gravimetric analysis and using the calculated volume of air sampled were expressed as mg/m3. Endotoxin exposures were measured using a simple water extraction from the collected dusts, followed by a quantitative turbidimetric assay. Results were expressed as ng/m3, using the calculated volume of air sampled. In addition, the levels of the contamination of dusts with endotoxin for individual industries were expressed as ng/mg of collected dust. Two hundred and fifty-nine samples, collected from 9 different industries and across 36 different sites were analysed. This represented a sampling rate of 25% for the total work force. The average sampling time was 4.62 h. For all the dusts collected, a significant correlation between the collected dust and endotoxin was seen (r = 0.7 and p < 0.001). The highest dust exposures occurred during cleaning activities (grain handling: 72.5 mg/m3). The individuals exposed to the highest median level of dust and endotoxin were the animal handlers (poultry handlers, dust: 11.53 mg/m3, endotoxin: 71,995 ng/m3). Weaving and mushroom cultivation had the lowest exposures for dust and endotoxins. The mostly highly contaminated dusts (median values expressed as ng of endotoxin per mg of collected dust) were found in the animal handling (poultry: 1,030 ng/mg, swine: 152 ng/mg) and cotton spinning (522 ng/mg) industries. Processing of cotton and wool fibres was found to reduce the levels of contamination of dusts with endotoxin. In the study, valid comparative data for personal exposures to organic dusts and endotoxins have been presented. The highest exposures were found amongst animal handlers and during cleaning activities. The results highlight that dust exposures are greater in a number of industries than the set exposure standards. In addition, endotoxin exposures are found to be greater than levels at which harmful effects have been demonstrated.     

History and results of the two inter-laboratory round robin endotoxin assay studies on cotton dust

BACKGROUND: In the US cotton industry, airborne cotton dust levels are regulated, and other countries are moving to specify safety limits for airborne endotoxins. There is concern about potential respiratory health hazards associated with agricultural and other organic dusts. In laboratories, ranking which samples have high and low levels of endotoxin is usually in good agreement between laboratories. When different laboratories assay identical samples, the levels differ. The objective of this research was to evaluate the intra- and inter-laboratory variability for 13 laboratories measuring endotoxin in cotton dust. METHOD: Two inter-laboratory round robin endotoxin assay studies were conducted using cotton dust. In the first round robin, each laboratory used their normal in-house assay method and then used a common extraction protocol. In the second round robin, a common extraction protocol and endotoxin assay kit was used. RESULTS: The intra-laboratory results had small variations but inter-laboratory results had very high variations. The inter-laboratory results using a common extraction protocol showed reduced differences. Using the same extraction protocol and endotoxin assay kit, the intra-laboratory variation was small and inter-laboratory variation was reduced but not enough for inter-laboratory agreement. Most of the laboratories were able to discern between the high and low endotoxin concentration dusts. CONCLUSIONS: Standardization has reduced the differences in results between laboratories and possibly further standardization may bring closer inter-laboratory agreement.     

Worker exposures to airborne dust, endotoxin and beta(1,3)-glucan in two New Zealand sawmills

BACKGROUND: Sawmill workers have an increased risk of developing occupational asthma and other respiratory symptoms. Wood dust and microorganisms have both been suggested to play a role, but few studies have measured microbial exposure levels in sawmills. METHODS: The preliminary study reported in this paper assessed airborne dust, bacterial endotoxin and beta(1,3)-glucan levels in 37 samples from two New Zealand sawmills. RESULTS: Nearly one-third of the measured dust levels exceeded 1 mg/m(3) and only one sample exceeded the legal limit of 5 mg/m(3). Endotoxin levels were clearly elevated with 50% of all measured exposures above 50 EU/m(3) (range: 7-588 EU/m(3)). beta(1,3)-glucan levels were comparable with levels measured in other industries where workers are exposed to organic dust. Workers in the planing department had the highest mean exposures to dust, endotoxin and beta(1,3)-glucan. Dust levels were only weakly correlated with endotoxin and beta(1,3)-glucan levels. CONCLUSIONS: Endotoxin exposures in sawmill workers are at levels sufficient to potentially contribute to the development of respiratory symptoms. Moreover, measurement of dust exposure is a poor proxy for beta(1,3)-glucan and endotoxin exposure in sawmill workers.     

Cotton dust and gram-negative bacterial endotoxin correlations in two cotton textile mills

Exposure to cotton dust is known to cause both acute and chronic respiratory illness. A specific pattern of symptoms called byssinosis is well described to occur among workers in the cotton processing (e.g., yarn preparation) industry. Recent studies have implicated Gram-negative bacterial endotoxin as one of the agents responsible for acute, and possibly chronic, respiratory illness. Laboratory experiments using a model cardroom have found poor correlations between airborne dust and associated endotoxin. This study reports the results of vertical elutriated dust and endotoxin levels in 11 work areas of 2 cotton textile mills in 1986 in Shanghai, China. The overall correlation between dust and endotoxin was strong, r_s + 0.66 and 0.79 (p < 0.0001) for mills 1 and 2, respectively. The dust-endotoxin correlation was relatively poor in early yarn preparation in the workshops and improved in the later preparation areas. Our findings suggest that in these mill settings, dust and endotoxin levels may be well correlated in most work areas. Therefore, dust may be a useful index for monitoring populations employed in the cotton textile industry throughout the world. Additional field studies need to be performed which consider the various determinants of dust and endotoxin levels. © 1993 Wiley-Liss, Inc.     

Branchial challenge of normal subjects with the endotoxin of Enterobacter agglomerans isolated from cotton dust.

Endotoxin produced by a culture of Enterobacter agglomerans isolated from cotton dust was inhaled by 12 normal subjects. No significant airway constriction was obtained in doses equivalent to those experienced in a workshift in a dusty mill. There was a statistically significant difference between this result and the bronchoconstriction that had occurred after flax dust inhalation in the same subjects. It is suggested that Enterobacter agglomerans endotoxin is not the causative agent of the acute bronchoconstriction that follows inhalation of textile dust.     

Branchial challenge of normal subjects with the endotoxin of Enterobacter agglomerans isolated from cotton dust

Endotoxin produced by a culture of Enterobacter agglomerans isolated from cotton dust was inhaled by 12 normal subjects. No significant airway constriction was obtained in doses equivalent to those experienced in a workshift in a dusty mill. There was a statistically significant difference between this result and the bronchoconstriction that had occurred after flax dust inhalation in the same subjects. It is suggested that Enterobacter agglomerans endotoxin is not the causative agent of the acute bronchoconstriction that follows inhalation of textile dust.     

Exposure to dust,endotoxin and micro-organisms in the potato processing industry

Exposure to organic dust components was studied in four potato processing plants because preliminary results showed high exposures accompanied by work-related health complaints. Ambient air concentrations of inhalable dust ranged from below 0.4 up to 44 mg m⁻³ [geometric mean (GM) 0.64 mg m⁻³]. Respirable dust concentrations were considerably lower. Personal concentrations of inhalable dust were somewhat higher, and strongly related to a few working tasks dealing with dried starch or protein. Ambient air concentrations of endotoxin ranged from 0.5 to more than 60 000 endotoxin units (EU) per m³ for the inhalable size fraction (GM = 280 EU m⁻³). For the respirable size fraction, endotoxin concentrations were lower (about the same factor as for dust). Personal endotoxin concentrations were lower than ambient air concentrations, probably because workers did not work the whole period of the shift near endotoxin sources. Endotoxin exposure was evaluated as very high; 23% of the workers had a mean exposure above 1000 EU m⁻³ (100 ng m⁻³). Differences between plants had a large influence on both dust and endotoxin exposure. A fairly good correlation was found between counts of airborne gram-negative bacteria and airborne endotoxin of the respirable size fraction. Ambient air levels of bacteria and endotoxin were strongly related to process water temperature, suggesting that exposure reduction can be achieved by lowering this temperature or by other measures that inhibit bacterial growth. We conclude that recycling of process water probably constitutes an exposure source of bacteria and endotoxin in many facilities.     

Environmental study of poultry confinement buildings

Environmental measurements were made in three poultry confinement buildings in order to characterize gas and particulate contaminants. Levels of total and respirable dust averaged 4.4 and 0.24 mg/m3, respectively. Particle size distribution as measured by cascade impactors was similar in the three confinement houses with a mass median aerodynamic diameter of about 15 microns and a geometric standard deviation of about 2.2. Ammonia levels measured in the active areas of the buildings averaged about 25 ppm. Ammonia concentration was quite high, however, in an unused and unventilated portion of one of the buildings (mean = 170 ppm). CO2 levels ranged from 0.05-0.1%. Levels of CO, H2S, NO2, NOx, CH4, mercaptan, formaldehyde, and hydrocarbons were all below the limit of detection for indicator tubes. Concentrations of airborne bacteria and fungi were on average about 1.5 X 10(5) and 1.0 X 10(4) colony-forming units/m3, respectively. Endotoxin analysis was also performed on the total and respirable dust samples. Endotoxin levels (expressed in air concentration) ranged from 0.77 to 61 ng/m3 for total dust and from 0.71 to 15 ng/m3 for respirable dust. Endotoxin was also measured on the collection media from the individual impactor stages. Endotoxin was detected in all size ranges with the highest concentration of endotoxin per unit of dust found in the smallest (less than approximately 3.5 microns) size fraction. The endotoxin levels tend to be lower than those previously reported in poultry operations.     

Seasonal variation in aerobic bacterial populations and endotoxin concentrations in grain dusts

Settled and respirable grain dust samples were collected at intervals over a 16-month period at two grain terminals on the lower Mississippi River. Total and gram-negative aerobic bacterial (GNB) populations, as well as endotoxin concentrations, were studied. Plate counts indicated that no viable bacteria were found to be present in the respirable samples. Endotoxin concentrations ranged from 0.0 to 6.4 ng (0.0 to 7.9 ng/m3 air) per respirable sample, indicating that bacteria were once viable in dust of respirable size or contamination occurred from larger, non-respirable particles. Numbers of bacteria from settled dusts, both total and GNB, remained relatively stable; however, the genera of the GNB populations varied. Enterobacter agglomerans was the predominant species in warm months, but not in winter. Pseudomonas and Klebsiella species increased in winter and decreased in summer. Other genera found were Citrobacter and Serratia. Endotoxin concentrations in settled dust samples ranged from 1.7 to 5.6 ng/mg dust.     

The role of endotoxin for reactions after exposure to cotton dust

Gram-negative bacteria and their endotoxins are present on all parts of the cotton plant and occur in large numbers after rain or frost. Endotoxins activate pulmonary macrophages that in turn recruit neutrophils into the airways. Platelets accumulate in pulmonary capillaries. The presence of these cells allows for the initiation of acute and chronic inflammation. Dose-response relationships have been demonstrated between endotoxin and fever, chest tightness, and reduction in air flow (bronchoconstriction) in cotton workers. Limited data suggest that after cotton dust exposure, other symptoms, such as airway hyperreactivity and chronic inflammation, are also related to the endotoxin exposure. Tentative thresholds for airborne endotoxins are presented.     

Home endotoxin exposure and wheeze in infants: correction for bias due to exposure measurement error

Exposure to elevated levels of endotoxin in family-room dust was previously observed to be significantly associated with increased wheeze in the first year of life among a cohort of 404 children in the Boston, Massachusetts, metropolitan area. However, it is likely that family-room dust endotoxin was a surrogate for airborne endotoxin exposure. Therefore, a related substudy characterized the relationship between levels of airborne household endotoxin and the level of endotoxin present in house dust, in addition to identifying other significant predictors of airborne endotoxin in the home. We now reexamine the relationship between endotoxin exposure and wheeze under the assumption that the level of airborne endotoxin in the home is the exposure of interest and that the amount of endotoxin in household dust is a surrogate for this exposure. We applied a measurement error correction technique, using all available data to estimate the effect of endotoxin exposure in terms of airborne concentration and accounting for the measurement error induced by using house-dust endotoxin as a surrogate measure in the portion of the data in which airborne endotoxin could not be directly measured. After adjusting for confounding by lower respiratory infection status and race/ethnicity, endotoxin exposure was found to be significantly associated with a nearly 6-fold increase in prevalence of wheeze for a one interquartile range increase in airborne endotoxin (95% confidence interval, 1.2-26) among the 360 children in households with dust endotoxin levels between the 5th and 95th percentiles.