Airborne germ collection
The airborne germ collection is a method for determining the cultivable airborne mold spores in the room air. In addition to other methods such as particle collection , which is used to determine the total spore concentration , and MVOC measurement (MVOC = microbial volatile organic compounds), with which volatile metabolic products can be detected, airborne germ collection is one of several ways of examining room air for mold contamination . It is used to point to hidden indoor mold sources by collecting a defined volume of air on nutrient media or filters . It is seldom used to check the success of renovations, as the airborne germ collection is only suitable for this to a very limited extent (see below).
The collection of airborne germs is a very widespread method of examining room air. A distinction must be made between the collection of mold spores from the air by filtration or by impaction . In both processes, a defined amount of air is sucked in with the aid of a pump and the mold spores contained in the air are deposited on a filter (filtration) or directly on the nutrient medium (impaction). The impaction procedure is more common and well known. The statements about airborne germ collections refer to this as a rule. Such a collection of airborne germs is not to be confused with a "do-it-yourself measurement", in which Petri dishes with a nutrient agar solution are set up for a certain period of time and the spores that have settled on them are then grown and examined. Since they are usually not reproducible, the results of such DIY kits are not reliable.
preparation
Before the interior measurement, the area to be examined must not be ventilated for at least eight hours so that the current spectrum of germs in the interior is not too strongly influenced by the outside air. Particular attention should also be paid to the choice of date if an outside air sample is to serve as a reference, since the natural spore load is strongly influenced by the local weather conditions.
execution
In order to offer a suitable substrate for the broadest possible range of species, several different nutrient media are used for each measuring point. Malt extract agar and DG18 agar for molds are usually used . If bacteria are also to be examined, CASO agar is an option. The nutrient media are placed in Petri dishes in the sampling system, which sucks in the air in a controlled manner and distributes it evenly over the entire nutrient medium surface. As a rule, parallel to the airborne germ measurement in the room to be examined, a sample of the outside air is also used as a reference value for the assessment, in order to be able to differentiate between natural mold exposure and possible mold infestation. In some cases, however, it makes sense to choose another room without mold infestation as a reference instead of the outside air sample, for example if outside air is not expected to be affected. The germ spectrum is also strongly dependent on the season and temperature.
If an atypical change can be seen after culturing the agar plates , this indicates an indoor source. This would be the case, for example, if the samples from the examined room show a significantly higher level of pollution than the reference sample, or if there are spores that could not be detected in the outside air at the time of measurement.
Expressiveness
The great advantage of airborne germ collection compared to the two other methods mentioned above is that the molds discovered in this way can be determined much more precisely, often down to the species level. On the one hand, this enables a more detailed assessment of the hazard potential (for example by classifying it into risk groups). On the other hand, the species distribution may provide clues that help to localize and assess the damage.
Basically, it should be noted that such a room air examination is a snapshot. The spore load, both in nature and in the case of mold infestation in the interior, is often subject to considerable fluctuations, both in terms of occurrence and spore distribution. It is strongly dependent on the size and shape of the respective spores (flight characteristics!) As well as air circulation, movement in the room, moisture, dust load. The disadvantage of the method is that many types of mold can hardly or not at all be detected with it. This is due, on the one hand, to the fact that the spores are put under stress by the sampling, which reduces their germination capacity. Some spores cannot generally be grown on the usual culture media. Others grow more slowly and are stunted or overgrown by other colonies. Still others have such poor flight characteristics that the probability that they can be picked up from the air by the sampling device is extremely low. The last group includes typical indicator fungi for moisture damage such as Stachybotrys , Chaetomium and Acremonium , which also form mycotoxins . In the case of hidden damage in particular, it can therefore happen that, despite extensive infestation, only inconspicuous mold concentrations can be detected in the room air. On the other hand, if the spore load is high, the mold colonies may grow into one another on the culture media. This makes a quantitative evaluation impossible.
For the reasons mentioned above, the informative value of the airborne germ collection on its own is very limited, but it can be helpful in combination with other methods. A particle collection carried out in parallel for the purpose of determining the total spore concentration can put the results of the airborne germ collection into a representative overall picture. Processes such as particle measurement, which do not require cultivation of the samples, were developed, precisely because usually only some of the mold spores actually present can be cultivated, and on the other hand allergic or toxic effects can also arise from non-cultivable microorganisms and their components.
Without additional measuring methods, the airborne germ collection is unsuitable as a remediation control. The procedure proposed by the WTA is currently establishing itself as a generally recognized rule of technology, in particular since the German Environment Agency's mold guideline also referred to the relevant information sheet. The method of choice here is to determine the total spore load. In addition, a mobilization takes place in which sedimented particles are specifically whirled up.
Individual evidence
- ^ A b c Judith Meider: Mold analysis: basics, methods, examples . 1st edition. Rudolph Müller, Cologne 2016, ISBN 978-3-481-03374-3 , p. 80.88 .
- ↑ a b c d Indoor Air Hygiene Commission of the Federal Environment Agency (ed.): Guide to the prevention, recording and remediation of mold infestation in buildings . 2017, ISSN 2363-8311 , p. 21.95,101-102 .
- ↑ Manfred Hinker, Martina Seibert (ed.): Mushrooms in interiors and at work . Springer Verlag Wien, Vienna 2013, ISBN 978-3-7091-1234-2 , pp. 209 .
- ↑ Scientific-Technical Working Group for Building Preservation and Monument Preservation eV (Ed.): Aims and control of mold damage restoration in interiors . Fraunhofer IRB, November 2016.