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Bioaerosols in Midwest greenhouses and respiratory symptoms among the workers.
Adhikari-A; Reponen-T; Grinshpun-S; Wilkins-JR III
Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, R03-OH-009241, 2010 Oct; :1-36
Estimated economic impacts of the US Green Industry are 1,964,339 jobs and $147.8 billion in output, of which 27% is represented by the greenhouse and nursery sectors. These two sectors are rapidly growing components of American agriculture that present a variety of challenges for occupational safety and health. A large number of workers, many foreign born, encounter a variety of potential respiratory hazards in greenhouse work environments. Exposure to bioaerosols, including microorganisms of pathogenic, toxic and allergenic species and pollen in an enclosed environment could magnify concerns about respiratory hazards encountered elsewhere in traditional agriculture. Rates of bioaerosol exposures and respiratory disorders in greenhouse workers have been strikingly high in some countries. This problem has not been fully studied in the US. There is a lack of quantitative information on workers' exposure to bioaerosols and relevant respiratory symptoms, particularly in the Midwestern region of the United States. The objectives of this CDC-NIOSH R03 pilot project were: (1) to investigate exposure levels to airborne culturable and total fungi, bacteria (total culturable bacteria and actinomycetes), endotoxin, and (1-->3)-ß-D-glucans in three Midwest greenhouses during summer and winter using multiple exposure assessment methods; (2) characterize the load of microorganisms on greenhouse floors and determine potential microbial source strengths of the floors for aerosolizing microbial biocontaminants, and (3) to estimate the prevalence of rhinitis, wheezing, asthma, and other respiratory symptoms/conditions among greenhouse workers. Stationary inhalable aerosol samples were collected from each greenhouse using Button Inhalable Aerosol Samplers. Control samples were collected from offices and nearby outdoor locations. A microbial source strength tester was used to examine the aerosolization potential of microbial contaminants from greenhouse floors. Additionally, surface samples were collected by sterile cotton swabs. Temperature, relative humidity, and wind velocity were recorded. Airborne culturable fungi, bacteria, and actinomycetes were analyzed in the extracts from field samples by cultivation in nutrient agar media. Endotoxin and (1-->3)-ß-D-glucan in the extracts from field samples were analyzed by specific kinetic chromogenic LAL assays. The prevalence of respiratory symptoms among greenhouse workers (n = 35) and control subjects (office workers; n = 14) was estimated with a standardized questionnaire. The collected data indicate that workers employed in Midwest greenhouses may be exposed to elevated levels of inhalable culturable microorganisms [fungi and bacteria collectively on the order of 10(2) - 10(5) CFU/m3], endotoxin [10(1) to 10(3) EU/m3], and (1-->3)-ß-D-glucan [10(1) to 10(2) ng/m3]; exposure levels are comparable to those previously measured in animal confinements and greenhouses of European countries. Seasonal variations were observed for some bioaerosol components. Fungi dominated in summer whereas bacteria and endotoxin dominated in winter. Levels of (1-->3)-ß-D-glucan in two seasons were not significantly different. The prevalence of respiratory symptoms was generally higher among greenhouse workers compared to controls. Although the crude/unadjusted Prevalence Ratios ranged from 1.2 - 4.4, the differences were not statistically significant based on Fisher's Exact Tests. To conclude, greenhouses in the Midwestern United States are a significant source of workers' exposures to airborne microbial contaminants. Elevated levels of airborne microbial contaminants were observed in three greenhouses with significant seasonal variations. The contaminants were likely to have originated from the greenhouse work areas as indicated by the indoor to outdoor ratios. Lack of correlations between exposure variables assessed by various methods indicates that employing several exposure assessment methods and investigating multiple bioaerosol exposure matrices would be more informative. The prevalence of self-reported respiratory symptoms was generally higher among greenhouse workers compared to controls; on the other hand the differences were not statistically significant, possibly due to the small sample size and relatively low statistical power of the study. Overall, we believe our pilot data on exposure levels and prevalence of respiratory symptoms among the greenhouse workers warrants further study in a larger group of subjects. Bioaerosol exposure levels coupled with assessment of workers' respiratory symptoms described in this project report will be relevant in improving specific methods and tools to assess worker exposures to inhalable biohazards and in advancing the understanding of the pathophysiology of respiratory disorders among greenhouse workers. The approach developed in this pilot project for bioaerosol exposure matrix can be applied in the future for assessing exposure in future large scale studies in greenhouses as well as in other agricultural occupational environments. The pilot data collected in this small research project can be utilized later for future sample size calculations for larger studies on respiratory symptoms among greenhouse workers in the United States.
Respiratory-system-disorders; Biohazards; Aerosols; Microorganisms; Soil-bacteria; Sociological-factors; Plants; Agriculture; Agricultural-workers; Allergens; Allergic-reactions; Allergies; Bacteria; Racial-factors; Exposure-assessment; Exposure-levels; Airborne-particles; Fungi; Endotoxins; Bronchial-asthma; Seasonal-factors; Analytical-processes; Air-contamination; Sampling
Atin Adhikari, PhD, Assistant Professor, Department of Environmental Health, University of Cincinnati, P.O. Box 670056, 3223 Eden Avenue, Cincinnati, OH 45267-0056
Final Grant Report
NTIS Accession No.
National Institute for Occupational Safety and Health
University of Cincinnati
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division