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Abstract

The global trend towards intensification and industrialization of animal production with regional concentration of livestock plants and increasing numbers of animals and stockpiles leads to a raise in bioaerosol emissions to the environment in certain areas and to an increasing concern about health impairment of the population in the vicinity. The essential sources of the bioaerosols are the animals and their faeces, the litter and the feed. The particles from there get into the airborne state and emit from the stables also into the environment. Hundreds of different viruses, bacteria and mold fungi have been detected worldwide in agricultural livestock farming. The bacterium 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 standardized systems which have high physical and biological collection efficiency in order to ensure comparability of the data. The selection of the collection system should always depend on the question primarily. After the bioaerosols have been collected in a sample, the evaluation is usually carried out via cultivation and / or various biochemical and molecular biological methods. Especially the latter allow, in combination with the classical culture-based methods, for a detailed insight into the composition of bioaerosols. But here a further standardization of the methods for bioaerosols is necessary. Endotoxins, on the other hand, are predominantly detected by the LAL test, which, however, is still very 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, molds and endotoxins were measured in the stables of pigs, cattle and chickens. The highest concentrations of airborne bacteria were found in stables for chickens, followed by turkeys, ducks, sheep, goats, pigs, cattle, horses and rabbits, with the different husbandry and production stages having a significant influence. In the emission of the stables, the published emission factors for airborne microorganisms differ considerably for the animal species and part of the keeping system, also by the different sampling conditions, collection methods and different methods for the 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 to 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 micro-organisms 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 depending on very many factors and, due to the previously used test systems, only insufficiently studied. Regarding the particle size, most of the air-borne microorganisms are found in the agricultural livestock farming in significantly larger particle size or mass fractions than the size of the individual cells of the organisms can be assumed. 30% to 70% of the bacteria can be found in mass fractions larger than PM10 though, where the distribution of the different bioaerosol components can be very different and not uniformly correlated with the distribution of the dust fractions. The immission concentrations of bioaerosols exponentially decrease with the distance to 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, the models have often surpassed the emissions, since night reduction, particle size distributions and abortions are still not taken into account. From hundreds of publications, it has been known for a long time that bioaerosols probably interact synergistically with other air pollutants on livestock breeders' health, of the staff working there and also 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 the inhabitants of animal husbandry. Therefore, no general limit values are formulated for bioaerosols, except for a certain extent for endotoxins, which can be expected to have a detrimental effect on health. Instead, an environmental assessment of individual cases usually takes place from the precautionary principle. A number of measures are available to reduce the bio-aerosol emissions as a precaution. Thanks to a good stable management and hygienic concept supported by technical solutions, for example, the exhaust air purification, a significant reduction of livestock husbandry originating bioaerosols of well over 90% can be achieved. Whether in the future the derivation of a dose / response relationship for bioaerosols or at least a valid environmental medical assessment of the emissions is possible remains to be seen. 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 the tenacity, where new measurement systems are needed in order to obtain meaningful data. It should also be a medium-term goal to reduce the bio-aerosol concentrations already in the stable. Concepts for adapted exhaust air purification plants are available for this purpose, which together with further measures can lead to a reduction of 90% to 99%. There still is a lot to do.

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