Emission of bioaerosols from livestock facilities - Methods and results from available bioaerosol investigations in and around agricultural livestock farming

The present report reviews literature from throughout the world on methods and results of bioaerosol investigations in and around agricultural livestock farming and summarises the most important points. The global trend towards intensification and industrialisation of animal production, with regional concentration of livestock facilities and increasing numbers of animals and greater stock densities, has led to an increase in bioaerosol emissions to the environment in certain areas and to increasing concern about health impairment of the population in the vicinity. The main sources of the bioaerosols are the animals and their faeces, the litter and feed. If the particles become airborne, they can be emitted from the stables into the environment. Hundreds of different viruses, bacteria and moulds have been detected in agricultural livestock farming worldwide. The bacterial group of the Staphylococcaceae appears to be most suitable for animal husbandry as a specific indicator or guiding parameter. Bioaerosols can be measured online with particle spectrometers and offline using classical methods, i.e. sampling on site with subsequent evaluation by means of culture-based or molecular biological methods in the laboratory. The classical detection methods are best suited to the complexity of bioaerosols in agricultural livestock farming. The sampling of bioaerosols should be carried out as far as possible using standardised systems that have high physical and biological collection efficiency, in order to ensure comparability of the data. The selection of a suitable collection system should primarily depend on the issue in question. After the bioaerosols have been collected in a sample, evaluation is usually carried out via cultivation and / or various biochemical and molecular biological methods. Especially the latter, in combination with the classical culture-based methods, enable a detailed insight into the composition of bioaerosols. However, further standardisation of the methods for bioaerosols is necessary here. Endotoxins, on the other hand, are predominantly detected using the LAL test, although this test remains relatively susceptible to disturbances. Most data on bioaerosol measurements in agricultural livestock farming available for this review are from the USA and Germany. Here, the concentrations of bacteria, moulds and endotoxins were measured in the stalls of pigs, cattle and chickens. The highest concentrations of airborne bacteria were found in stalls for chickens, followed by turkeys, ducks, sheep, goats, pigs, cattle, horses and rabbits, with the different husbandry and production stages having a significant influence. Emission factors published for airborne microorganisms also differ in part considerably depending on the animal species and the type of keeping, also as a result of different sampling conditions, collection methods and different methods for determination of the concentrations. The concentrations of the airborne bacteria in livestock during the day and night can deviate by a factor of ten. The deviation may further increase by a factor of 1000 if emission factors are calculated on the basis of the specific volumetric flow rates. This must be taken into account in the calculation of annual average values of emission factors. During transportation, i.e. the transport of bioaerosols via the air, the microorganisms are largely exposed to wind and weather. The extent to which they are carried is primarily dependent on two parameters: the tenacity, i.e. the ability to survive the airborne condition, and the size and composition of the bioaerosol particles, i.e. how quickly they sediment. How long microorganisms are viable in the air is dependent on very many factors and, due to the relatively unsuitable test systems used in the past, this aspect has not been studied sufficiently. Regarding particle size, most of the airborne microorganisms found in livestock farming have a significantly larger particle size or mass fraction than would be expected from the size of the individual cells of the organisms. 30% to 70% of the bacteria can be found in mass fractions larger than PM10, whereby the distribution of the different bioaerosol components can vary considerably and is not uniformly correlated with the distribution of the dust fractions. The immission concentrations of bioaerosols exponentially decrease with the distance from the emission source, mainly depending on the particle size and meteorological conditions. Instead of carrying out complex measurements, the spread of bioaerosols can also be simulated with computer models. Up to now, however, these models have often overestimated the emissions, since night reduction, particle size distributions and death rates of the microorganisms are still not taken into account. From hundreds of publications, it has long been known that bioaerosols, probably interacting synergistically with other air pollutants, have a negative impact on the health of people who work in animal stalls and also on that of the animals. No dose / effect relationship has been established so far. To date there has been no clear statement as to the possible danger to residents living in the vicinity of livestock farms. Therefore, no general limit values have been formulated for bioaerosols, above which a detrimental effect on health is to be expected, except to a certain extent for endotoxins. Instead, an environmental assessment of individual cases usually takes place as a precautionary principle. A number of precautionary measures are available to reduce bioaerosol emissions. Thanks to good stall management and a hygiene concept supported by technical solutions, e.g. exhaust air cleaning, a significant reduction of bioaerosols originating from livestock husbandry of well over 90% can be achieved. It remains to be seen whether a dose/response relationship for bioaerosols or at least a valid environmental medical assessment of the emissions will be possible in the future. Until then, in the medium term, the indicator organisms and guiding parameters for bioaerosols from livestock husbandry should be (re)considered and viruses should be included. This comprises the validation and further development of high-volume collectors for bioaerosols. In the case of dispersion modelling, the particle size distributions of the microorganisms and the different levels of emissions between day and night must be considered for the short term. This also applies to tenacity, where new measurement systems are needed in order to obtain meaningful data. It should also be a medium-term goal to reduce bioaerosol concentrations already in the stalls. Concepts for adapted exhaust air cleaning systems are available for this purpose, which, together with further measures, can lead to a reduction of 90% to 99%. There is still a lot to do.