5.2 Evaluation of the results
5.2.3 Assessment of air samples
Assessing the concentration and composition of mould fungi spores in indoor air serves primarily as an indication of invisible (hidden) mould.
Judging the probability of the presence of a mould source in the indoor space using air samples requires a high level of expertise. An isolat-ed studying of only the results of indoor air measurements may lead to an erroneous assessment of the case. The specific individual situa-tion must be assessed in each case taking into account both from all information obtained during the site inspection and in further inves-tigations. It must be born in mind that the results of airborne bacteria counts may not contain evidence of indoor sources, despite the pres-ence of extensive mould damage.
The seasonal and possibly local influence of outdoor air on species com-position, on the concentration of cultivable mould fungi or on the total spore count must be particularly taken into account when assessing air samples. Annex 7 and Annex 8 contain tables with empirical values for concentrations of cultivable mould fungi and for the total spore count in indoor and outdoor air in summer and winter in Germany.
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When assessing the results, it must be remembered that these are short-term measurements. Mould fungi concentrations in indoor air can have high temporal and spatial fluctuations since fungi spores are not even-ly distributed in the room and their concentration can change from day to day.
Assessment of the concentration and composition of mould fungi spores in indoor air serves predominantly as an indication of in-visible (hidden) mould infestation.
A quantitative exposure and risk assessment is not possible and the derivation of health-related guidelines or limiting values is also not expected in the near future.
For specific health issues in individual cases, it may be useful to use additional methods for the detection of certain types of mould fungi (e.g. by cultivation at 36 °C for pathogenic and facultatively pathogenic species).
Determining the genus or species composition of an air sample is neces-sary in order to detect differences in the spectrum vis-à-vis outdoor air and the occurrence of fungal genera or species indicating moisture or structural damage (moisture indicators, see Chapter 1). Certain problems in individual cases may also require the detection of mould fungi that have a special health significance (e.g. Aspergillus fumigatus, Stachybot-rys chartarum) (see Section 5.2).
Furthermore, it must be taken into account that spores from different species of mould fungi can have very different airborne dissemination capabilities. Therefore, in order to assess the sources of mould in an in-door space, it is important to distinguish the individual species of mould fungi according to their nature of spore dissemination.
Experience shows that mould fungi species with dry spores with a good airborne dissemination capability can lead to increased spore concentra-tions in the air, even in the case of minor material damage. The spores of these species are usually relatively small and are formed in large num-bers. They are not embedded in a slime matrix which means that indi-vidual spores or small spore aggregates can be easily spread by slight air movements. The leading species for this type of dissemination are spe-cies of genera Penicillium and Aspergillus. However, significantly lower air pollution can be detected when materials are colonised by mould fun-gi whose spores are relatively large or are collected in slime substances after their formation and therefore have a poor airborne dissemination capability. The leading species for this type of dissemination are many species of the genera Acremonium or Fusarium and Stachybotrys.
The following assessment aids have the aim of determining the probabil-ity of the presence of a hidden or invisible mould infestation. The meas-ured values do not provide for a quantitative exposure and risk assess-ment with regard to health effects.
The three ranges given below can be used as assessment and orientation aids for determining mould fungi in indoor air (see Tables 9 and 10):
▸ the background load range for important mould fungi genera or species,
▸ a transition range within which there are elevated concentrations of certain mould fungi genera or species that may indicate indoor sources,
▸ a range of concentrations that exceed this transition range and are highly likely to indicate an indoor source.
It is important to note that not all situations can be evaluated with the proposed scheme. A schematic approach based exclusively on Tables 9 and 10 is problematic. This means that assessing an air sample in late autumn, for example, may be difficult if the spore content of outdoor air is greatly reduced over a short period (October–November with cold and humid weather). During this period, sedimented spores originating from the outdoor air can strongly influence the result of an air sample taken in the indoor space (if they are disturbed before or during a sampling) and feign an increased load in the indoor air in relation to the outdoor air.
Conversely, unusually contaminated outdoor air samples can also make it difficult to interpret the results. The application of the tables therefore requires a high level of expertise.
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Table 9
Assessment aid for air samples – culturable mould fungi (CFU/m3)
Parameter Background load
indoor source unlikely
Indoor source possible Indoor source likely
Cladosporium and other fungi genera that can reach elevated concentrations in outdoor air (e.g. sterile mycelia, yeasts, Alternaria, Botrytis)
If there are no more spores of a genus in indoor air than in outdoor air.
Iotype ≤ Ootype
If the concentration of a genus in indoor air is more than 1 times and up to 2 times that of outdoor air.
Ootype < Iotype ≤ Ootype x 2
If the concentration of one genus in indoor air is more than 2 times that of outdoor air.
Iotype > Ootype x 2
CFU sum of all atypical outdoor air types
If the difference in concentration between indoor and outdoor air does not exceed 150 CFU/m3. IΣaotype ≤ OΣaotype + 150
If the difference in concentration between indoor and outdoor air is between 150 CFU/m3 and 500 CFU/m3.
OΣaotype + 150 < IΣaotype
≤ OΣaotype + 500
If the difference in con-centration between indoor and outdoor air exceeds 500 CFU/m3.
IΣaotype > OΣaotype + 500
One genus
(CFU sum of all related species) of atypical out-door air types.
If the difference in concentration between indoor and outdoor air does not exceed 100 CFU/m3.
IOgatype ≤ OOgatype + 100
If the difference in concen-tration between indoor and outdoor air is between 100 CFU/m3 and 300 CFU/m3. OOgatype + 100 < IOgatype
≤ OOgatype + 300
If the difference in con-centration between indoor and outdoor air exceeds 300 CFU/m3.
IOgatype > OOgatype + 300 One species of atypical
outdoor air types with good airborne dissemination e.g. Aspergillus spp.
If the difference in con-centration between indoor and outdoor air does not exceed 50 CFU/m3*.
IOaotype ≤ OOaotype + 50
If the difference in concen-tration between indoor and outdoor air is between 50 CFU/m3 and 100 CFU/m3* OOaotype + 50 < IOaotype
≤ OOaotype + 100
If the difference in con-centration between indoor and outdoor air exceeds 100 CFU/m3.
IOaotype > OOaotype + 100 One species of atypical
outdoor air types with poor airborne dissemination e.g. Phialophora spp., Stachybotrys chartarum
If the difference in con-centration between indoor and outdoor air does not exceed 30 CFU/m3*.
IOaoptype ≤ OOaoptype + 30
If the difference in concen-tration between indoor and outdoor air is between 30 CFU/m3 and 50 CFU/m3*.
OOaoptype + 30 < IOaoptype ≤ OOaoptype + 50
If the difference in con-centration between indoor and outdoor air exceeds 50 CFU/m3.
IOaoptype > OOaoptype + 50
The five lines of the table are not meant to be independent criteria but should be considered together in a comprehensive assessment.
The data refers to air samples that were taken under normal use or similar conditions in normal living rooms without raising dust in accordance with DIN ISO 16000-16 and DIN ISO 16000-18 (see also Annex 7).
* Concentrations of less than 100 CFU/m3 or less than 50 CFU/m3 cannot be detected with satisfactory accuracy in a sample volume of 100 l or 200 l since quantitative evalua-tion with sufficient statistical certainty is only feasible above 10 colonies per slide. Nevertheless, the detecevalua-tion of individual colonies of these mould fungi may give an initial indication of a potential indoor source.
CFU Colony forming units
I Indoor air concentration in CFU/m3 O Outdoor air concentration in CFU/m3
otype typical outdoor air species or genera (extramural fungi such as Cladosporium, sterile mycelia, possibly yeasts, possibly Alternaria, possibly Botrytis)
aotype atypical outdoor air species or genera (intramural fungi such as fungi with high indication of moisture damage e.g. Acremonium spp., Aspergillus versicolor, A. penicillioides, A. restrictus, Chaetomium spp., Phialophora spp., Scopulariopsis brevicaulis, S. fusca, Stachybotrys chartarum, Tritirachium (Engyodontium) album, Trichoderma spp.) Σaotype Sum of atypical outdoor air species (other than otype)
Oaotype One species that is atypical in outdoor air with good airborne dissemination Oaoptype One species that is atypical in outdoor air with poor airborne dissemination Ogatype One genus that is atypical in outdoor air
Table 10
Assessment aid for air samples – total spore collection (spores or mycelial fragments/m3)
Spore type Background exposure
indoor source unlikely
Indoor source possible Indoor source likely
spore types that can reach elevated concentrations in outdoor air
e.g. Ascospores type Alternaria/Ulocladium type, Basidiospores type Cladosporium type
Counting basidio- and ascospores from typical outdoor air species is not relevant for detecting mould sources. However, an outdoor air influence can generally be detected from the concentration of these spores and a plausibility test can be carried out on the specified sample origin (outdoor air, indoors, storage, cellar).
When assessing spores of the Cladosporium and Alternaria/Ulocladium genera in the case of indoor infestation, it is not possible to define general concentrations that indicate mould growth because outdoor air concentrations fluctuate widely, the depot effect of settled dust and poor spore release. When mould infestation with Cladosporium spp. is suspected, whether the same types of Cladosporium occur outdoors and indoors should in particular be checked.
Penicillium/Aspergillus type
If the concentration difference between indoor air and outdoor air does not exceed 300 spores/m3 IΣP+A ≤ OΣP+A + 300
If the concentration difference between indoor air and outdoor air is between 300 spores/m3 and 800 spores/m3 OΣP+A + 300 < IΣP+A ≤ OΣP+A + 800
If the concentration differ-ence between indoor air and outdoor air exceeds 800 spores/m3
IΣP+A > OΣP+A + 800 Other typical spores
from moisture damage Scopulariopsis type Acremonium.murorum type Paecilomyces type Microascus type Ascotricha type (Alternaria type, Ulocladium type)
If the concentration difference between indoor air and outdoor air does not exceed 100 spores/m3 IΣmtype ≤ OΣmtype + 100
If the concentration difference between indoor air and outdoor air is between 100 spores/m3 and 300 spores/m3 OΣmtype + 100 < IΣmtype ≤ OΣmtype
+ 300
If the concentration difference between indoor air and outdoor air exceeds 300 spores/m3
IΣmtype > OΣmtype + 300
Typical spores from moisture damage with poor airborne spread
Chaetomium type Stachybotrys type Chromelosporium type Pyronema type
If there are less spores in the indoor air than in the outdoor air
Imptype ≤ Omptype
If the concentration difference between indoor air and outdoor air does not exceed 20 spores/m3* Omptype < Imptype ≤ Omptype + 20
If the concentration difference between indoor air and outdoor air exceeds 20 spores/m3* Imptype > Omptype + 20
Mycelial fragments If the concentration difference between indoor air and outdoor air does not exceed 150 mycelial fragments/m3
Imycel ≤ Omycel + 150
If the concentration difference between indoor air and outdoor air is between 150 mycelial fragments/m3 and 300 mycelial fragments/m3 Omycel + 150 < Imycel ≤ Omycel
+ 300
If the concentration difference between indoor air and outdoor air exceeds 300 mycelial fragments/m3
Imycel > Omycel + 300
The five lines of the table are not meant to be independent criteria but should be considered together in a comprehensive assessment.
The data refers to air samples that were taken under normal use or similar conditions in normal living rooms without raising dust in accordance with DIN ISO 16000-20 (see also Annex 8).
* Concentrations of less than 10 spores/m3 or less than 5 spores/m3 cannot be detected with satisfactory statistical accuracy in a sample volume of 100 l or 200 l even when evaluating the total track, since quantitative evaluation is only feasible above 10 spores per slide. Nevertheless, the detection of individual spores of these moulds may give an indication of a potential indoor source.
O Outdoor air concentration in spore count/m3, I Indoor air concentration in spore count/m3 ΣP+A Total spore count of Penicillium and Aspergillus types
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