Spore trap data should be reliable if results are to be used in assessing indoor spore types and concentrations and ultimately to evaluate the validity of exposure potential or remedial success. Spore trap results are primarily used in indoor mold investigations to:
- assess the airborne spore concentrations and the potential for human mold exposure
- justify remedial recommendations and implementation
- evaluate quality control and post-remedial assessments of mold remediation projects.
In an earlier article, Understanding Spore Trap Results, we discussed the factors that influence the reliability of spore trap results. These factors include:
- The amount of air sampled
- The non-uniform distribution of spores in the air
- Related to the non-uniform distribution of spores in the air, is the distance from the source to the air sampling point. For actively growing mold, the spore concentration is higher closer to the moldy structures/materials
- Changes in fungal spore types and concentrations within the day. The release of spores from moldy materials is not continuous and is dependent on ambient conditions such as temperature, air movement and relative humidity (rh). Ambient conditions also influence the types of spores released. For example, at very high humidity fewer spores of Aspergillus/Penicillium are released than at low rh
- The experience of the analyst.
How to improve spore trap results
Bearing in mind the factors that influence the reliability of spore trap results, how can we then improve the spore trap results? Below are some suggestions on how we could minimize the effect of the above factors. Professional judgement is required as some of the some of the suggestions may not be applicable in every situation. Since most of the suggestions involve increasing the number of samples collected, it is important to evaluate whether the added cost and sampling time are worth it.
Amount of air sampled
By increasing the amount of air sampled we can improve the spore trap results. As was discussed in article, Understanding Spore Trap Results, by collecting 75L of air we’re sampling only 7.5% of 1000L, the ideal amount of air that should be sampled. Unfortunately increasing the amount of air especially in a dusty environment, would lender the spore traps difficult if not impossible to analyze. We therefore recommend collecting at least 150L or more whenever the environmental conditions allow. If sampling a dust free environment, collecting more than 150L would be recommended. If using the 15L per minute pumps, it would take slightly more than an hour to collect a sample which, to some extent, takes care of the changes of spore concentration with time.
Non-uniform distribution of spores in the air
Since the spores are not uniformly distributed in the air, the only way to minimize the effect of this factor is to take more than 1 sample at different locations within the same room. For example if collecting air samples in a room, you could take a sample from each corner of the room and one in the middle, that means a total of 5 samples. If dealing with huge open spaces, the number of samples to collect would be more. Also, if dealing with very tiny rooms, you could collect only 2 samples.
The spatial and temporal variability of spore concentration in the air
The spatial (relating to space) and temporal (relating to time) variability of spore concentration in the air can be minimized by taking samples at different locations and at different times within the day. For examples we can decide to take some samples at same locations early in the morning, at noon and in the evening.
The important thing is first to define the purpose for spore trap air sampling. Then design a sampling strategy that is practical and that would give you data good enough for your defined purpose.
Michael Oberle, Markus Reichmuth, Reto Laffer, Cornelia Ottiger, Hans Fankhauser and Thomas Bregenzer (2015). Non-Seasonal Variation of Airborne Aspergillus Spore Concentration in a Hospital Building. Int. J. Environ. Res. Public Health 2015, 12, 13730-13738.
Robertson, L.D and Robert Brandys (2010). A multi-laboratory comparative study of spore trap analyses. Mycologia January/February 2011 vol. 103 no. 1 226-231.
Hyvärinen A; Vahteristo M; Meklin T; Jantunen M; Nevalainen A; Moschandreas D (2001). Temporal and spatial variation of fungal concentrations in indoor air. Aerosol Science and Technology 35, 688 – 695.