Mould Growth in Heritage Collections

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CCI Newsletter, No. 32, November 2003

Mould Growth in Heritage Collections

by Sherry Guild, Conservator, Treatment and Development Division - Works on Paper

Conservator using a cleaning screen and low vacuum suction to clean fragile paper.

Conservator using a cleaning screen and low vacuum suction to clean fragile paper.

Conservator working at a class 1 biological safety enclosure.

Conservator working at a class 1 biological safety enclosure. Note that the vacuum cleaner nozzle is secured inside the hood. This helps ensure the nozzle does not accidentally touch the artifact and that the contaminated nozzle remains in the enclosure.

Mould infestation in heritage collections can damage artifacts and may pose a health risk to individuals who work with these collections. Coping with a mould infestation in a heritage collection is a daunting task, one that is likely to raise many questions:

  • Why did the mould grow?
  • How can the problem be corrected?
  • What is the health risk?
  • Should the mould be identified?
  • Can the mould be removed from the artifacts? If so, how?

Over the years, CCI staff have responded to numerous requests for assistance from clients with mould problems. These "calls for help" have been for a few mouldy artifacts or in some cases for an entire collection infested with mould. As a result of this and in response to a need identified by the conservation community, a new Technical Bulletin (Mould Prevention and Collection Recovery: Guidelines for Heritage Collections, Technical Bulletin No. 26) was recently written by Sherry Guild and Maureen MacDonald.

Preventing mould growth in heritage collections is of fundamental importance, and the first half of the publication focuses on this aspect of collection care. Steps to prevent mould infestation should focus mainly on measures that keep the level of moisture in the air and the moisture content of the artifact below the level required for mould growth. Critical factors to control in order to prevent mould growth (i.e. indoor spores, nutrient sources, moisture, air circulation, and temperature) are discussed. Also included are a table describing potential sources of bioaerosol contamination in buildings and a preventive measures checklist. Both can be used as a guide to spot potential problems in a building and collection that might lead to mould growth.

Mould is ubiquitous and normal background concentrations do not usually affect healthy individuals. In contaminated environments, however, the risk of health effects from exposure to mould increases. Every effort should be made to limit human exposure to it. Reactions are varied and depend on the nature of the mould species, the products being produced, the amount and duration of exposure, and the susceptibility of the individual. Mould spores do not have to be viable to retain allergenic or toxigenic properties. Exposure to dormant mould is as much a health risk as exposure to viable mould.

Conscientiously removing visible mould growth and reducing the total number of spores from infested artifacts is necessary. If precautions are taken, small (<0.3 m2 total surface area contaminated by visible mould growth), medium-sized (0.3–3 m2), and large (3–10 m2) outbreaks of mould in a collection can safely be cleaned by following the guidelines and recommendations in the Technical Bulletin. Be sure to use the appropriate personal protective equipment (respiratory protection, goggles, gloves, protective clothing) as indicated for the various levels of contamination. For extensive (>10 m2) mould contamination in the collection, it is advisable to seek professional help.

Close vacuuming is one of the most effective ways to remove mould growth and reduce the total number of mould spores on the artifact. Be systematic and thorough when removing the mould and carefully vacuum the artifact all over, not just where mould growth can be seen. Mould growth invisible to the naked eye may be present on unsuspected areas.

To avoid dispersing mould spores into the environment, a vacuum cleaner fitted with a HEPA (high efficiency particulate air) filter is required. Vacuum cleaners with a variable speed control, used to modify vacuum suction, are recommended.

Other tools and equipment for removing mould, along with various supplies and cleaning and disinfecting solutions, are also described in the Technical Bulletin. Of interest to larger institutions may be a class 1 biological safety enclosure (a ventilated enclosure for personal protection in which the inward airflow is directed away from the operator). This type of enclosure meets health and safety guidelines for working with mould. During operation, the room air is drawn into the front of the enclosure, preventing aerosols from escaping into the room. Before leaving the enclosure, air is forced through an exhaust HEPA filter so that particulate-free air recirculates into the room.

There are no guidelines or regulations for handling artifacts after removing mould, but it may be appropriate to adopt a cautious approach when handling and using these artifacts. We recommend that an artifact be identified in a manner that allows users to take precautions before touching it. This should include wearing disposable gloves when handling the artifact and washing hands with soap and water afterwards.