Organic dust consists of particles with a biological origin. Airborne levels of bacteria, fungi, endotoxins, and glucans have been investigated in epidemiological studies of mucous membrane irritation, inflammation, and airway obstruction. Organic dust can be measured by gravimetry of filter samples. Microorganisms can be quantified by culture, microscopic, and DNA-based methods. Culture methods underestimate microbial exposure and have poor precision. However, high sensitivity and identification of species that indicate fungal contamination have advantages in indoor air studies. Microscopic and DNA-based methods quantify microorganisms independent of cultivability. Specific organisms can even be quantified with molecular techniques. Quantification of specific organic dust components is preferred to dust levels. However, no occupational exposure limits exist for specific agents, although criteria for endotoxin and fungal spores have been proposed. In exposure assessments of microbial agents, larger numbers of samples may be needed compared to chemical agents because of higher exposure variability.

Key terms discussion paper; endotoxin; endotoxin exposure; exposure; exposure assessment; fungal spore; fungus; measurement method; measurement strategy; microorganism; organic dust; quantitative assessment; quantitative exposure assessment; work ­environment