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5. Fungicides and fumigation

5.1 Fungicides
5.2 Fumigation
5.3 Toxicity of fumigants
Literature cited


Most librarians, archivists and museum personnel share a conviction that mold must be killed. It is perhaps more appropriate and effective to concentrate on prevention, inhibition and removal. As noted earlier, molds are admirably equipped for survival. Even a kill ratio of 99% "is an almost insignificant loss to a fungus which can produce hundreds of thousands of spores in a small colony started from a single spore."1 Fungicides and fumigants broad ranging enough and powerful enough to achieve a 99% mortality for fungi are now known to be toxic to man as well. In considering the use of fungicides and fumigants for the prevention or treatment of mold growth, two basic facts should be kept in mind:

- All biocides are chemically reactive, i.e. they are capable of reacting with and altering materials to which they are applied.

- All biocides have some level of mammalian toxicity.2

The traditional chemical approach to biodeterioration involves two strategies. One strategy, fumigation, interferes with the vital activities of the organism. The other strategy, topical application of fungicides to an object, interferes with their consequences, that is with the chemical reactions of the organism and its substrate. The number of compounds in use today is fairly limited. They include certain metal derivatives, organic chemicals (of which the phenols are the most common), and certain organometal compounds.3 While there is a certain amount of interest in, and testing of more exotic techniques, including irradiation and the use of ozone, "we must not place too much reliance on the hope for brand-new biocidal agents as the solution to the problem."4 Both irradiation and ozone have been found to be damaging to certain materials.

It should be noted that the first strategy, interfering with the vital activities of the organism, can be accomplished without recourse to chemical treatment. Modification of the environmental factors required for the growth of mold is at least as effective as chemical treatments, and certainly far safer for both personnel and materials.

5.1 Fungicides

The term fungicide, as used in this study is limited to those biocides in a liquid medium applied directly to the surface of an affected item. The application may be intended either to prevent the growth of mold, or to kill the mold once growth has begun. Of the fungicides recommended in the literature, most have proved ineffective in terms of long term protection or deleterious to the materials themselves. Those which do seem to have some level of residual toxicity are now known to be hazardous to staff and users who may handle the materials later. Exposure may be by inhalation, ingestion, or adsorption through the skin. Warnings concerning the use of biocides should be rigorously adhered to, both with regard to the actual application and possible residual effects.

Beckwith, Swanson and Iliams conducted a comprehensive series of tests on biocides used a paper protectants and found that 28 commonly recommended fungicides were either ineffective in killing mold or damaging to paper. These included mercuric chloride, chloroform and formaldehyde.5 As recently as 1971, a British Museum pamphlet on biocides for archival and library materials recommended both chloroform and formaldehyde.6

Thymol and orthophenyl phenol crystals disolved in alcohol are often recommended as topical fungicides. Indeed, both have been widely used in the conservation field. Their use has been radically curtailed by recent studies showing that both can damage the eyes and upper respiratory system. Thymol is believed to be the more toxic of the two, affecting the liver, kidneys, central nervous system and the circulatory system as well.7

Of the fungicides recommended in the literature, only alcohol and orthophenyl phenol, at the strength commonly found in household cleaning products such as Lysol, are recommended for topical application and their use should be limited. Until more is known concerning the toxicity of orthophenyl phenol, the use of its crystalline form disolved in alcohol should be avoided. Any recommendations in the literature that are more than a few years old should be viewed with skepticism, since it is only in the last few years that the toxicity of a wide range of biocides has become a matter of concern. Research is still underway to establish precisely what levels of exposure may be acceptable.

It is a longstanding medical principle that one should treat the disease, not the symptom. The application of topical fungicides to items exhibiting mold growth is a classic example of treating the symptom, and fails to address the broader cause of the affliction. Items treated in this manner and returned to the same environment that produced the outbreak are very likely to develop recurring symptoms.

5.2 Fumigation

The term fumigation is used in this study to include any treatment which relies on exposure to the fumes or vapor of a biocidal compound to kill mold. The idea of fumigation is appealing to most librarians and archivists. It does not involve the treatment of individual items and is therefore not costly in terms of staff time. Large numbers of items can be treated at one time, in either fumigation chambers or by sealing areas of the building and fumigating entire collections. The reality of fumigation is far less appealing when considered in terms of its uncertain effectiveness, lack of residual protection, possible alteration or damage of materials, and toxicity to staff and users.

Methods of Fumigation

Fumigation may be carried out in various ways, using a variety of fumigants, some better than others, but all hazardous. If fumigation is necessary, it should be carried out by licenced professionals whenever possible.

Of the fumigation chambers commonly in use, those which incorporate a vacuum are most effective in eliminating mold. The vacuum allows greater penetration of the fumigant, and there is a possibility that it may also have adverse affects on the mold structure, removing oxygen required for growth and possibly rupturing the spores themselves. Vacuum chambers are however extremely expensive to purchase and install. Ethylene oxide is the fumigant most often used in vacuum chambers, and requires an additional chamber for the aeration of materials after fumigation in order to rid organic materials of residual toxins. Sulphuryl flouride is also used in vacuum chambers for the eradication of insects. It is not effective as a fungicide, and very little testing has been done regarding its toxicity and effect on organic materials.

Non-vacuum fumigation chambers are most often used with thymol and orthophenyl phenol vapors as the fumigant. Many institutions maintain small cabinets for fumigation of a limited number of items. Often these fumigation cabinets are improvised from old refrigerators or metal cabinets which were never intended for use as fumigation chambers. These improvised cabinets are particularly dangerous for staff exposed to them on a regular basis. Occassionaly there are recommendations in the literature that fumigation may be carried out in plastic bags. The standard plastic bag available for the disposal of household trash is not a vapor barrier, and cannot contain fumigation vapors effectively.

Fogging of entire areas is most often carried out by professional fumigation companies, and should never be attempted by untrained, unlicenced staff. If fogging is necessary, librarians should know precisely what fumigant was used, and scrupulously observe all restrictions regarding access to the area and exhausting the gas after fogging. Organic materials may retain toxic vapors and information regarding hazards to staff and users should be obtained from the company carrying out the fumigation.

5.3 Toxicity of fumigants

In order that librarians and archivists may more accurately assess the relative hazards of fumigants which may be in use in their institution, the following general information is provided.

Ethylene Oxide

Ethylene oxide was developed in 1859. By the late 1920's it was in common use as a fumigant for grain, and by the 1950's was widely used in museums, libraries and archives. Ballard and Baer provide an excellent study of the history, use, effectiveness, and hazards of ethylene oxide.8

In 1984 the Occupational Safety and Health Administration (OSHA) released a new standard for exposure to ethylene oxide of 1 ppm. Based on animal and human data, OSHA has determined that exposure to EtO "presents a carcinogenic, mutagenic, genotoxic, reproductive, neurologic, and sensitization hazard."9 Safety requirements for use of the gas include methods of exposure control, personnel protective equipment, measurement of employee exposure, training in use of the gas, (often a licence is required),, medical surveillance, signs and labels, regulated areas, emergency proceedures and record keeping requirements. The presence of EtO cannot be detected by humans without the aid of monitoring devices until it reaches a concentration of 300 ppm, far in excess of the OSHA standard.10

Ethylene oxide is known by a variety of other names, including dimethyl oxide, Carboxide, 1,2-Epoxythane, Oxyfume, Pennagas and Oxirane. It is highly flammable, and is usually used in a 10% concentration with a carrier gas.

Methyl Bromide

Methyl bromide is most commonly used in the fumigation of insect infestations, particularly against hard shell insects such as beetles. It is not particularly effective as a fumigant for mold growth, but is occasionally used as one. It is a colorless, transparent, easily liquified gas. It is easily detected, having a strong, chloroform-like smell. It is highly toxic by ingestion, inhalation or absorption through the skin. The tolerance level established by OSHA is 5 ppm. Methyl bromide affects the central nervous system, respiratory system, skin and eyes. Acute effects usually occur 30 minutes to 6 hours after exposure and may include convulsions followed by death due to pulmonary and/or circulatory failure. Chronic effects are usually limited to the central nervous system and include muscular pains, visual, speech and sensory disturbances and mental confusion.

Methyl bromide should not be used for the fumigation of any protein based material, as it seriously damages the protein structure. Leather for example becomes black and brittle when exposed to methyl bromide fumes.

Methyl bromide is also known by the proprietory names Brom-O-Gas, Brozone, MeBr, Meth-O-Gas and Terr-O-Gas.

Sulfuryl Fluoride

Sulfuryl fluoride is most often used in the tropics for the fumigation of termites in building structures. It has very high penetration even without a vacuum. Like methyl bromide it is not known to be effective against mold, but is occasionally used for that purpose. It is an odorless, colorless tasteless gas, and is usually available only to licenced fumigators. The OSHA standard is 5 ppm. It has not been tested extensively, and its carcenogenic and reproductive effects are unknown. It may be ingested by inhalation or absorption through the skin. Acute effects include nausea, vomiting and abdominal pain. Chronic effects include defects in bone and teeth, and in animals lung and kidney damage have been found.

Sulfuryl fluoride is most often available under the trade name Vikane.


Thymol is a white crystal with a distinctive aromatic odor and taste. It is derived from thyme oil and may be mixed with camphor in its crystaline form. It is moderately toxic by ingestion and inhalation. Studies indicate that exposure to thymol vapors can affect the central nervous system and the circulatory system. No precise level for minimum exposure has been established.

Thymol is sometimes used in its gaseous form (produced by heating the crystaline form to release thymol vapor) as a fumigant for small quantities of materials. In order to be safely handled following fumigation, materials must be aerated, preferably in a fume hood. This removes any residual protection against mold growth, but renders the materials safe for staff and patrons. Staff members working with items immediately after fumigation, or in the area of the fumigation chamber should wear respirators approved for organic chemicals. Goggles and heavy weight, vapor barrier gloves should be worn when removing items from a chamber.

Orthophenyl Phenol

Orthophenyl phenol is considered slightly less toxic than thymol. The Merk Index lists it as a "slightly toxic irritant" when inhaled. It is however moderately toxic by ingestion. In its crystaline form it is a white or cream color and is soluble in alcohol. Several sources recommend the substitution of OPP for thymol whenever the latter is recommended. Relatively little testing has been done regarding the toxicity of OPP, and no exposure level is available.

In tests conducted by Haines and Kohler, orthophenyl phenol was found to be a not very effective fumigant. Of the seven fungi tested, fumigation with orthophenyl phenol failed to completely halt mold growth even after 10 days of continuous exposure to the vapors under controlled conditions.11

Literature cited

1. John H. Haines and Stuart A. Kohler. ''An Evaluation of Ortho-phenyl phenol as a fungicidal fumigant for Archives and Libraries." Journal of the American Institute for Conservation. 25:1, Spring, 1986, p.54.

2. A. Baines-Cope. "The Choice of Biocides for Library and Archival Material." Biodeterioration of Materials, Walters and Hueck-Van der Plas, eds. p. 392.

3. G.J.M. Van der Kerk. "The Chemical Approach to Diodeterioration Prevention: Retrospects and Prospects." Biodeterioration of Materials, Walters and Hueck-Van der Plas, eds. pp.3-4.

4. Van der Kerk, p. 10.

5. Carl J. Wessel. "Paper." Deterioration of Materials. Greathouse and Wessel, p. 375.

6. Baines-Cope, p. 383.

7. John P. Barton and Johanna G. Wellheiser, eds. An Ounce of Prevention. Ontario, Toronto Area Archives Group Education Foundation, 1985. p. 63.

8. Mary W. Ballard and Norbert S. Baer. ''Ethylene Oxide Fumigation: Results and Risk Assessment." Restaurator Vol. 7, 1986. pp.143-168.

9. OSHA. Federal Register, Occupational Exposure to Ethylene _ de, Final Standard 29CFR Part 1910 (June 22, 1984). Washington, D.C., U.S. Department of Labor, 1984.

10. Robert F. McGriffin. "A Current Status Report on Fumigation in Museums and Historical Agencies" Technical Report 4. Nashville, Tenn., American Association for State and Local History, 1985.

11. Haines and Kohler, pp. 49-55.

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