The Inhalable Mycobiome of Sawmill Workers: Exposure Characterization and Diversity

A cross-sectional study on occupational exposure to microorganisms, endotoxin, hydrogen sulfide, and dust during work at drilling waste treatment plants

This cross-sectional study aims to obtain knowledge about workers' exposure to airborne dust, bacterial and fungal species, endotoxin, biofilm formation, and hydrogen sulfide (H2S) in drilling waste treatment plants. In total, 408 full-shift personal samples, 66 work areas, 40 drilling waste, and reference (outdoor air and seawater) samples were analyzed. Some workers were exposed to high levels of endotoxin (207 EU/m3), bacteria (3.8 × 104 colony forming units (CFU)/m3 and 9.8 × 104 DNA copies/m3), or fungi (1.4 × 107 CFU/m3 and 3,600 copies/m3). The exposure levels to endotoxin, bacteria, and peaks of H2S were dependent on the treatment technique. All types of drilling waste contained large concentrations of bacteria compared to the seawater references. Elevated concentrations of airborne bacteria were found close to drilling waste basins. In total, 116, 146, and 112 different bacterial species were found in workers' exposure, work areas, and the drilling waste, respectively. An overlap in bacterial species found in the drilling waste and air (personal and work area) samples was found. Of the bacterial species found, 49 are classified as human pathogens such as Escherichia coli, Enterobacter cloacae, and Klebsiella oxytoca. In total, 44 fungal species were found in the working environment, and 6 of these are classified as human pathogens such as Aspergillus fumigatus. In conclusion, across the drilling waste treatment plants, human pathogens were present in the drilling waste, and workers' exposure was affected by the drilling waste treated at the plants with elevated exposure to endotoxin and bacteria. Elevated exposure was related to working as apprentices or chemical engineers, and working with cleaning, or slop water, and working in the daytime.

Occupational exposure to inhalable pathogenic microorganisms in waste sorting

This study assessed microorganisms in personal inhalable work air samples aiming to identify potential human pathogens, and correlate exposure to adverse health outcomes in waste workers. Full-shift personal exposure was measured in six different waste sorting plants. Microbial concentrations in inhalable air samples were analysed using MALDI-TOF MS for cultivable, and next generation sequencing (NGS) for non-cultivable microorganisms. Concentrations of bacterial and fungal CFUs varied substantially within and between waste sorting plants, ranging from no identifiable organisms to a maximum concentration in the order of 105 CFU/m3. Bacillus and Staphylococcus were among the most abundant bacterial genera, whilst fungal genera were dominated by Aspergillus and Penicillium. Approximately 15% of all identified species were human pathogens classified in risk group 2, whereas 7% belonged to risk group 1. Furthermore, significant correlations between concentrations of fungi in risk group 1 and self-reported adverse symptoms, such as wheezing were identified in exposed workers. The combination of culture-based methods and NGS facilitated the investigation of infectious microbial species with potential pathophysiological properties as well as non-infectious biological agents in inhalable work air samples and thereby contributed to the risk assessment of occupational exposure in waste sorting.

Exposure Characterization of Wood Dust Particulate, Endotoxins, and (1-3)-β-d-Glucans, and Their Determinants in Mozambiquan Wood Processing Workers

OBJECTIVES

Dust generated from wood processing comprises a heterogeneous mixture of inorganic and organic particles, including wood fragments, microorganisms, endotoxins, (1-3)-β-d-glucans, and allergens. This study characterized exposure to wood dust and its determinants in the Mozambiquan wood processing industry.

METHODS

A total of 124 personal inhalable samples, collected from a stratified random sample of 30 workers, were analysed for dust particulate, endotoxins, and (1-3)-β-d-glucans. Mixed-effects models were developed to investigate significant exposure determinants.

RESULTS

The geometric mean (GM) inhalable dust particulate concentrations were 3.29 mg m-3, 98 endotoxin units (EU) m-3, and 123 ng m-3 for (1-3)-β-d-glucans. Significant predictors for higher particulate levels included machinery (GMR = 1.93), sawing (GMR = 2.80), carpentry (GMR = 2.77), or painting (GMR = 3.03) tasks. Lebombo-ironwood species was associated with higher dust particulate levels (GMR = 1.97). Determinants of endotoxin concentrations included working with dry wood and damp cleaning methods, which were associated with lower levels. Working in closed buildings (GMR = 3.10) and dry sweeping methods were associated with higher (1-3)-β-d-glucan concentrations (GMR = 1.99).

CONCLUSIONS

Work tasks in certain exposure groups (machinery, sawing, carpentry, painting), processing certain wood species (Lebombo-ironwood) and working in closed buildings were associated with higher exposures, whilst using dry wood and damp cleaning practices reduced exposure levels.

Wood dust and asthma

PURPOSE OF THE REVIEW

Review recent developments on asthma associated with wood dust, given the increasing scale of wood handling and processing activities globally.

RECENT FINDINGS

Work in wood industries is associated with a significantly increased risk of respiratory symptoms, rhinitis and asthma. This can be attributed to traditional processing techniques and newer technologies producing complex bioaerosol exposures, which may include chemicals. Meta-analysis studies indicate strong evidence for wood dusts as occupational sensitizers for asthma, but the underlying mechanisms remain poorly understood. The global prevalence of asthma in wood workers ranges between 6-18% and for rhinitis 16-33%. Exposure estimates show wide variation. Risk factors include atopy and exposure to certain wood species, elevated current and cumulative particulate exposures.

SUMMARY

Future studies should focus on better characterization of wood dust allergens and other bioaerosol components, specific immunoglobulin E responses to different wood species, pathophysiological mechanisms underlying asthma, and modelling dose-response relationships using refined exposure metrics for dust particulate and other bioaerosol components. There is a need for improved health-based international exposure standards and effective workplace control measures to reduce exposures to wood dust particulate (hard and soft woods), endotoxin and β-glucan, to reduce the risks of asthma in wood workers.

Divergent TLR2 and TLR4 Activation by Fungal Spores and Species Diversity in Dust from Waste Sorting Plants

This manuscript presents the results of an exploratory study on the relationships between NF-κB response through Toll-like receptor (TLR) activation by dust characterized by fungal spore concentrations and species diversity. Personal total dust samples were collected from Norwegian waste sorting plants and then characterized for fungal spores and fungal species diversity, as well as for other bioaerosol components, including endotoxins and actinobacteria. The ability of the dust to induce an NF-κB response by activating TLR2 and TLR4 in vitro was evaluated, as well as the relationship between such responses and quantifiable bioaerosol components. The average concentrations of bioaerosols were 7.23 mg total dust m^-3, 4.49 × 10⁵ fungal spores m^-3, 814 endotoxin units m^-3, and 0.6 × 10⁵ actinobacteria m^-3. The mean diversity measurements were 326, 0.59, and 3.39 for fungal richness, evenness, and Shannon index, respectively. Overall, fungal operational taxonomic units (OTUs) belonging to the Ascomycota phylum were most abundant (55%), followed by Basidiomycota (33%) and Mucoromycota (3%). All samples induced significant NF-κB responses through TLR2 and TLR4 activation. While fungal spore levels were positively associated with TLR2 and TLR4 activation, there was a trend that fungal species richness was negatively associated with the activation of these receptors. This observation supports the existence of divergent immunological response relationships between TLR activation and fungal spore levels on one hand and between TLR activation and fungal species diversity on the other. Such relationships seem to be described for the first time for dust from waste facilities. IMPORTANCE This manuscript presents results on multifactorial characterization of bioaerosol exposure in Norwegian waste sorting plants and the potential of such airborne dust to induce NF-κB reactions through TLR2 and TLR4 activations in an in vitro reporter cell model system. Our data revealed that increasing fungal spore levels in the dust is associated with increased activation of TLR2 and TLR4, whereas increasing fungal OTU richness is associated with decreasing activation of these receptors. The NF-κB-induced responses by the collected dust represent, therefore, effective measures of potential key immunological effects induced by a complex mixture of hazardous components, including characterized factors such as endotoxins, fungal spores, bacteria, and many other uncharacterized components. The key immunological events reported here are suggested as holistic alternatives to today's bioaerosol exposure characterization approaches for epidemiological studies in the future.

An assessment of occupational exposure to bioaerosols in automated versus manual waste sorting plants

Occupational exposure during waste sorting is associated with several health outcomes. This study obtained knowledge about the impact of work in fully automated waste sorting plants (AWSP; n = 3) vs manual waste sorting plants (MWSP; n = 3) on personal exposure (n = 71) to bioaerosols and exposure-related health effects. Personal full-shift air samples were collected using various filter-based active sampling devices that were placed in the workers' breathing zone. Personal exposure to inhalable and thoracic dust, endotoxin and microorganisms varied considerably between and within types of waste sorting plants (WSP). Workers at AWSP were on average exposed to 0.34 mg/m³ inhalable dust, 0.15 mg/m³ thoracic dust, and 51 EU/m³ endotoxins (geometric mean (GM) levels), whereas GM exposure levels at MWSP were 0.66 mg/m³ for inhalable dust, 0.44 mg/m³ for thoracic dust, and 32 EU/m³ for endotoxins. Exposure to submicronic fungal fragments did not differ between types of plants and ranged from levels below the detection limit (limit of detection, LOD) to levels in the order of 10⁶ fragments/m³. Higher levels of fungal fragments and fungal spores were found at AWSP compared to MWSP with a GM of 2.1 × 10⁵ spores/m³and with a GM of 1.2 × 10⁵ spores/m³, respectively. Actinobacterial spores were found in samples from AWSP only, with exposure levels ranging from 1.9 × 10⁴ to 1.1 × 10⁷ spores/m³. Exposure to microbial DNA varied within and between WSP and was on average in the order of 10⁴ copies/m³ for fungi and 10⁵ copies/m³ for bacteria. Health symptoms, such as sneezing, congested nose and runny nose were significantly more common among exposed workers compared to the unexposed control group.

Trends in Occupational Infectious Diseases in South Korea and Classification of Industries According to the Risk of Biological Hazards Using K-Means Clustering

Against the backdrop of the COVID-19 pandemic, it is necessary to identify these risks and determine whether the current level of management is appropriate to respond to the risk of biological hazards depending on the occupation. In this study, the incidence and fatality rates of occupational diseases were calculated using industrial accident statistics of South Korea, and trends by year using joinpoint regression and relative risk by industry using k-means clustering were evaluated for infectious diseases. We found that infectious diseases had the third highest incidence and fourth highest fatalities among all occupational diseases. In the incidence rate, joinpoints appeared in 2009 and 2018, and the annual percent change changed to 7.79, -16.63, and 82.11. The fatality rate showed a consistent increase with an annual percent change of 4.37, but it was not significant. Industries were classified into five groups according to risk, and the legal control measures of certain industries were not sufficient. Follow-up studies are needed to rectify the structural limitations of industrial accident statistics.

Algorithm to assess the presence of Aspergillus fumigatus resistant strains: The case of Norwegian sawmills

Association between selection pressure caused by the use of azole fungicides in sawmills and the development of fungal resistance has been described. The aim of this study was to implement an algorithm to assess the presence of Aspergillus section Fumigati resistant strains in sawmills.Eighty-six full-shift inhalable dust samples were collected from eleven industrial sawmills in Norway. Different culture media were used and molecular identification to species level in Aspergillus section Fumigati was done by calmodulin sequencing and TR₃₄/L98H and TR₄₆/Y121F/T289A mutations were screened by real-time PCR assay and confirmed by cyp51A sequencing. Six Fumigati isolates were identified as A. fumigatus sensu stricto and two of these grew on azole-supplemented media and were further analyzed by real-time PCR. One was confirmed to be a TR₃₄/L98H mutant.The obtained results reinforce the need to assess the presence of A. fumigatus sensu stricto resistant isolates at other workplaces with fungicide pressure.

Microbial Occupational Exposure Assessments in Sawmills—A Review

The composition of airborne microflora in sawmills may vary to a great degree depending on the kind of timber being processed and the technology of production being used. Cases of allergy alveolitis and asthma have been reported in woodworkers who were exposed to wood dust largely infected with microorganisms. The aim of this review article is to identify studies where the microbial occupational exposure assessment was performed in sawmills and the characteristics of the contamination found, as well as to identify which sampling methods and assays were applied. This study reports the search of available data published regarding microbial occupational exposure assessment in environmental samples from sawmills, following the Preferred Reporting Items for Systematic Reviews (PRISMA) methodology. The most used sampling method was air sampling, impaction being the most common method. Regarding analytical procedures for microbial characterization, morphological identification of fungi and bacteria was the most frequent approach. Screening for fungal susceptibility to azoles was performed in two studies and four studies applied molecular tools. Regarding microbial contamination, high fungal levels were frequent, as well as high bacteria levels. Fungal identification evidenced Penicillium as the most frequent genera followed by Aspergillus sp. Mycotoxins were not assessed in any of the analyzed studies. Microbial occupational exposure assessment in sawmills is crucial to allow this risk characterization and management.

Bioaerosol Exposure and in vitro Activation of Toll-like Receptors in a Norwegian Waste Sorting Plant

Background

The global shift toward greener societies demands new technologies and work operations in the waste-management sector. However, progressive industrial methods do not necessarily consider workers’ health. This study characterized workers' exposure to bioaerosols and investigated the bioaerosols’ potential to engage the immune system in vitro.

Methods

Full shift personal aerosol sampling was conducted over three consecutive days. Dust load was analyzed by gravimetry, fungal and actinobacterial spores were analyzed by scanning electron microscopy, and endotoxin by limulus amebocyte lysate (LAL) assay. In vitro exposure of HEK cells to airborne dust samples was used to investigate the potential of inducing an inflammatory reaction.

Results

The total dust exposure level exceeded the recommended occupational exposure limit (OEL) of 5.0 mg/m³ in 3 out of 15 samples. The inhalable endotoxin level exceeded the recommended exposure level by a 7-fold, whereas the fungal spore level exceeded the recommended exposure level by an 11-fold. Actinobacterial spores were identified in 8 out of 14 samples. In vitro experiments revealed significant TLR2 activation in 9 out of 14 samples vs. significant TLR4 activation in all samples.

Conclusion

The present study showed that the dust samples contained potentially health-impairing endotoxin, fungi, and actinobacterial levels. Furthermore, the sampled dust contained microbial components capable of inducing TLR activation and thus have the potential to evoke an inflammatory response in exposed individuals.

The airborne mycobiome and associations with mycotoxins and inflammatory markers in the Norwegian grain industry

Grain dust exposure is associated with respiratory symptoms among grain industry workers. However, the fungal assemblage that contribute to airborne grain dust has been poorly studied. We characterized the airborne fungal diversity at industrial grain- and animal feed mills, and identified differences in diversity, taxonomic compositions and community structural patterns between seasons and climatic zones. The fungal communities displayed strong variation between seasons and climatic zones, with 46% and 21% of OTUs shared between different seasons and climatic zones, respectively. The highest species richness was observed in the humid continental climate of the southeastern Norway, followed by the continental subarctic climate of the eastern inland with dryer, short summers and snowy winters, and the central coastal Norway with short growth season and lower temperature. The richness did not vary between seasons. The fungal diversity correlated with some specific mycotoxins in settled dust and with fibrinogen in the blood of exposed workers, but not with the personal exposure measurements of dust, glucans or spore counts. The study contributes to a better understanding of fungal exposures in the grain and animal feed industry. The differences in diversity suggest that the potential health effects of fungal inhalation may also be different.