JAIC 1990, Volume 29, Number 2, Article 4 (pp. 153 to 168)
JAIC online
Journal of the American Institute for Conservation
JAIC 1990, Volume 29, Number 2, Article 4 (pp. 153 to 168)




NONE OF the eight chemicals evaluated in this study show much promise as a chemical fumigant for use in a thymol cabinet. Seven of the eight showed little or no fungicidal activity, and the only fungicidal one (paraformaldehyde) is too hazardous to consider as an alternative to ethylene oxide. Paraformaldehyde is a polymer of formaldehyde and, when heated produces formaldehyde gas. Formaldehyde has been identified as a mutagen and a carcinogen, and the current exposure level standard is 3 ppm (NIOSH 1987). Although thymol exhibited some fungicidal activity against the cultures, it was completely ineffective in killing molds on books. Ortho-phenylphenol showed no fungicidal activity when 25-W or 40-W bulbs were used with a 4-hour heating cycle. Preliminary results using thymol, ortho-phenylphenol, paradichlorobenzene, and naphthalene with an 8-hour heating cycle and 40-W bulbs increased the fungistasis and fungicidal activity but did not produce a 100% kill of all molds (data not shown). It is apparent from this work, the work of Haines and Kohler (1986), and Florian's comments (1986) that ortho-phenylphenol is of no value as a fumigant in thymol cabinets. Dow Chemical, the owner of the trademark on Dowicide (ortho-phenylphenol) does not support the use of this chemical as a fumigant in thymol cabinets (written personal communication).

The controversy over the use of ortho-phenylphenol in thymol cabinets (Haines and Kohler 1986; Nagin and McCann 1983; Florian 1986) stems from a footnote that was added to the authorized reprinting in Ritzenthaler (Nagin and McCann 1983) of the 1982 Center for Occupational Hazards data sheet. Although Nagin and McCann do not suggest using ortho-phenylphenol in thymol cabinets, the added footnote states that ortho-phenylphenol “should be substituted for thymol in every application” (Nagin and McCann 1983, 121).

Our work and the work of Haines and Kohler (1986) raise questions about the effectiveness of thymol as a fumigant. Neither the results included in this report nor our preliminary culture results with an 8-hour treating period (data not included) demonstrate that thymol is completely fungicidal against the four organisms included in this study. Haines and Kohler (1986) also report that thymol is not completely fungistatic or fungicidal. Furthermore, our results using books showed no thymol fungicidal activity at all against the indigenous molds on the books.

Nagin and McCann (1983) and Byers (1983) recommend using 15–20-W bulbs as heating elements, and Byers (1983) suggests that bulbs with a higher wattage should not be used. Our temperature recordings for 15-W bulbs do not exceed 34C in e watch glass, well below the melting point of thymol (51.5C). In our cabinets, only bulbs of 25-W or 40-W produced temperatures in the watch glass high enough to melt thymol, and only 40-W bulbs generated temperatures high enough to melt ortho-phenylphenol (see fig. 2). Our results show that 40-W bulbs produce greater fungistatic or fungicidal activity than 25-W bulbs. In view of this it seems unlikely that 15–20-W bulbs would generate sufficient chemical vapors of thymol or ortho-phenylphenol to kill mildew molds. Although the maximum temperature reached in the watch glasses was 57C (135F), the temperature in the chamber where materials would be located did not exceed 32C (90F). This result suggests that cabinet fumigation with 40-W bulbs would not cause heat damage to the materials and might be useful if a suitable chemical could be identified.

All eight chemicals included in this study pose serious health hazards. Naphthalene, paradichlorobenzene, formaldehyde (paraformaldehyde), and ortho-phenylphenol are listed as potential carcinogens (National Institute for Occupational Safety Hazards 1987; Sax 1981; Sax and Lewis 1986). Although the other four chemicals are not specifically identified as potential carcinogens, they are toxic, and excessive exposure could produce skin, eye, and possibly respiratory irritation (National Institute for Occupational Safety Hazards 1987; Sax and Lewis 1986; Windholz 1983). It is mentioned in the literature that ortho-phenylphenol is “less toxic” than thymol, and this is correct when comparing LD50 data for oral administration to rats. However, a thorough review of the NIOSH-RTECS data sheets (National Institute for Occupational Safety Hazards 1987) suggests that ortho-phenylphenol may be more hazardous due to its potential carcinogenicity. This demonstrates that a careful review of all aspects of chemical toxicity using the most up-to-date information is necessary before reaching conclusions of chemical safety.

Our work has not identified a chemical that would be effective and safe for use as a fumigant in thymol cabinets. Molds are notoriously difficult to kill, particularly in the dormant, dessicated state that they would be in on books and paper. Proper maintenance of indoor temperature and humidity seems to be the most effective way of controlling mildew growth. However, environmental control is not fungicidal, and any lapse in control could easily result in rapid growth and spread of mildew molds.

It is interesting to speculate about the actual need to fumigate books and papers as a means of mold (mildew) control. A simple scenario illustrates such speculation. Givens: Mold propagules are everywhere; provided the proper substrate and environment, they will germinate and produce mold colonies that develop millions of new propagules; these new propagules disseminate, and the growth cycle is repeated many times; and fumigation does not leave any inhibiting residue on the materials. Result: Mold growth everywhere!

Due to the tremendous reproductive potential of molds, it may not be of value to take preventive measures other than ensuring appropriate indoor climate control (Parker 1987). However, it can be argued that a minimal physical removal of mold growth (brushing, wiping, vacuuming) will reduce the number of mold spores that could cause allergic reactions in the users of the facility. This result alone seems important enough to warrant physical removal, outdoors, of mold propagules from holdings prior to placing these items in circulation.


This work was supported by a grant (CLR 804) from the Council on Library Resources, Washington, D.C. Appreciation is also extended to all the faculty members of Winthrop College who lost their personal libraries to water damage following a campus building fire. Their loss was our gain, as we had several hundred mildewed books to include in our study. Appreciation is extended to the Chemistry and Physics Department for use of computer hardware and software for preparation of figures 2–7 and to Mary Lou Florian for sharing her data with us.

Copyright 1990 American Institute for Conservation of Historic and Artistic Works