FUNGICIDAL EFFICACY OF SELECTED CHEMICALS IN THYMOL CABINETS
RALPH A. GUSTAFSON, INGRID R. MODARESI, GEORGIA V. HAMPTON, RONALD J. CHEPESIUK, & GLORIA A. KELLEY
MOLD (MILDEW) growth on library and archival holdings can become a significant problem in facilities that are unable to maintain indoor climatic conditions within ranges that will inhibit mold growth. Dormant mold propagules (spores and hyphal fragments) are present in the library environment in significant numbers (Burge et al. 1980; Parker 1987) and, given proper substrate (cellulose) and environment (warm temperatures and high humidity), each will germinate and establish a growing mold colony within a few days. Each of these colonies will produce millions of new propagules, which will repeat the cycle. Controlling this explosive rate of growth is a major concern to the conservator, as many of these molds (mildew molds) are cellulolytic and cause serious biodeterioration of paper. In addition to the physical damage caused by molds, many types of mold spores will cause allergic reactions in sensitive people. Burge et al. (1980), however, investigated the possible role of fungi as allergens in the University of Michigan libraries and concluded that fungal spores were not the source of the observed respiratory complaints associated with library use as measured spore counts were low and there was no distinctive library mycoflora.
The growth of molds on library holdings can be prevented by carefully regulating the indoor environment of the facility. Maintaining the temperature between 60° and 65°F (15°–18°C) and keeping the RH below 60% will inhibit mold growth (Middleton 1977; Strassberg 1978). Further control could be achieved by reducing the number of mold propagules in the library environment (Middleton 1977). Such reduction would also lessen the allergen potential in the facility (Burge et al. 1980). Techniques used to reduce the number of mold propagules range from simple wiping to complete sterilization of the library holdings.
Prior to the 1984 ruling by the Occupational Safety and Health Administration reducing the ethylene oxide permissible exposure level (PEL) to 1 ppm and the action level to 0.5 ppm (Art Hazards News 1984), ethylene oxide sterilizers were the preferred fumigation system for killing molds and mold spores on such materials. Since many facilities with ethylene oxide sterilizers cannot meet these reduced OSHA limits without expensive retrofitting, they have discontinued use of ethylene oxide. This situation has rekindled the interest in using homemade “thymol cabinets” as an alternative to ethylene oxide sterilizers for fumigation of library materials.
In principle, thymol crystals when gently heated in these cabinets generate thymol vapors to fumigate the materials placed in the cabinet (Byers 1983; Haines and Kohler 1986; Middleton 1977; Nagin and McCann 1983). In a reprinted edition of the 1982 Center for Occupational Hazards data sheet by Nagin and McCann (1983, 121) a footnote was added stating that Robert McComb of the Library of Congress suggested substituting ortho-phenylphenol for thymol “in every application” because it is “less toxic and more effective than thymol.” Subsequent to this, several agencies in South Carolina, including the State Archives, built “thymol cabinets” and started using ortho-phenylphenol (personal communication). In addition to thymol and ortho-phenylphenol, other chemicals have been considered for use in controlling mold growth on library materials, and reviews by Strassberg (1978) and Baynes-Cope (1972) are available.
Throughout the literature on mildew control for library materials, there is a paucity of experimental data on the effectiveness of chemicals when used as fumigants in thymol cabinets. Kowalik (1980, 1984) conducted extensive evaluations of several chemicals for fungicidal activity, but his procedures involved direct contact between the chemical and the mold rather than gaseous fumigation systems. Others (Block 1951; Hetherington 1945; Htar 1970; Kaye 1976; Shumard 1953) tested a variety of chemicals, but again, none involved the use of thymol cabinets. The two reports using thymol cabinets give contradictory results. Florian and Byers (cited in Byers 1983) concluded that thymol was fungicidal when used under their conditions. Their research was not published, but Florian provided a copy of the internal report to the authors. Florian and Byers inoculated filter papers with fungal propagules and then exposed the dried filter papers to thymol fumes in a thymol cabinet. Their treatment cycle was 48 hours long and included two 3-hour heating periods using 20-W bulbs as the heat source. Following treatment, they transferred the filter papers to Sabouraud dextrose agar plates to assess viability. Recently, Florian referred to her study (1986), but no data were provided. Haines and Kohler (1986) reported that thymol and ortho-phenylphenol were not completely fungistatic or fungicidal in their thymol cabinets.
The absence of sufficient experimental data in the literature supporting contentions about the effectiveness of various chemicals makes makes it difficult, if not impossible, to select an effective system for book fumigation. The need for an effective fumigation system at Dacus Library, Winthrop College, prompted us to undertake an evaluative study of several chemicals, using appropriate controls and procedures, to determine their potential for use in thymol cabinets.