Chaetomium Case Study 2004:

An IDonsite job in December 2003 allowed for an interesting look at a common indoor fungus. An environmental consultant, working in a co-operative housing unit, had encountered significant mould growth in a main floor bathroom. An enclosure was set up and a contractor was hired to remove and/or clean the affected building materials. The contractor conducted the remediation as specified. The occupants of the unit had been re-located while the clean-up was conducted. On a Friday morning, IDonsite came to the site to manage the analysis of clearance air samples at the request of the consultant.

Three air samples were collected on Air-O-Cell cassettes. One sample was collected inside the enclosure, one in the space adjacent to the enclosure, and one outdoors. The samples from the area adjacent to the enclosure and from the outdoor air were characterized by low levels of fungi common to outdoor air. The sample from within the enclosure, however, had modest levels of ascospores from the fungus Chaetomium (approximately 400 elements / m3). Since Chaetomium is rarely isolated from outdoor air in Southern Ontario at any time of the year, the consultant concluded that the spores were most likely being produced within the containment area.

The genus Chaetomium includes over 100 species. It is distinguished from other genera within the Chaetomiaceae by superficial ascomatal growth and a wide apicular ostiole. Some species of Chaetomium are found growing on water-damaged building materials in the indoor environment, especially cellulose-based products. This genus is commonly found growing in the teleomorphic state (sexual reproduction), but may also be found in an anamorphic state (asexual reproduction). Known anamorphs of Chaetomium include species of Acremonium, Botryotrichum, Humicola, Paecilomyces and Scopulariopsis.

The ascospores of Chaetomium species are rather varied in appearance when viewed under the microscope. The ascospores may be limoniform, fusiform, or ovoidal in shape. The spores are typically smooth, darkly pigmented (brown to olivaceous green) when mature, and usually have one or two apicular germ pores. There are, however, many exceptions within the genus in terms of ascospore morphology. Some species may produce spores that are spherical, spores that lack germ pores, or spores that otherwise deviate from the typical range of appearance.

One aspect of Chaetomium spores (not limited to this genus) that can confuse the novice or insufficiently trained/experienced analyst is the collapse of its spores. Some of the factors influencing this occurrence include the species of Chaetomium, the age of the spores, and the mounting solution used. Indeed, one of the better texts commonly used by labs for identifying pollen and mould spores, errantly classifies several images of collapsed ascospores of Chaetomium as Arthrinium spores. This type of error can be reduced if the spores are identified with the aid of a high-powered microscope objective (100x) and by an analyst with a formal post-secondary education that includes fungal identification courses, and who is well experienced at working with a wide variety of indoor fungi from bulk samples and culture.

On this particular job, the consultant re-entered the containment and collected several tape lift samples from suspect areas. Ultimately, a series of tape lift samples revealed that there was Chaetomium growing along the base of the wood framing in an area that had not been examined previously. The contractor returned to the site, remediated the small area that was still affected by fungal growth.

Environmental consultants are typically aware of the advantage of having an experienced analyst on site for clearance (post-remediation). This has been practiced for many years in the remediation of asbestos. One of the unique advantages of having IDonsite working with your firm on a mould remediation project is the ability to track down fungal growth that has caused the site to fail at the time of clearance.

If your firm is relying on a standard fixed-location laboratory at the time of clearance sampling, and the air samples suggest that there is unremediated fungal growth within the contained area, it may take several more sets of samples to pinpoint the remaining area of fungal growth. That approach can lead to unexpected cost increases in terms of time and money, and leave your client displeased with your ability to get them back into the area under containment. With IDonsite, you can troubleshoot your failed remediation area in real time, and with the aid of an expert in mycology who can direct you to the most likely areas of growth, depending on the fungus that has been identified from the air samples.