Gamma radiation has not been widely used for mass disinfection in archives and libraries anywhere in the world, as yet. Several papers on this problem have pointed out the possibility of using gamma radiation for disinfection but most of them are experimental works only. Three main factors enter into the decision to use gamma rays for disinfection of paper and parchment documents and books.
The first is establishment of a dosage level which is effective for all possible types of mold and bacteria but will not damage paper and parchment. It seems possible to achieve this result by making use of the synergistic effect of radiation and heat.
The least scrutinized factor seems to be the initiation of degradation reactions which can occur later on during storage of the documents; they can be initiated by gamma rays in the disinfection process.
The third factor is connected with the equipment of gamma radiation, which is rather complicated and requires some special precautions.
The problem of using gamma radiation for mass disinfection of archival documents in Czechoslovakian archives was studied by H. Horáková. 1 in her work, she studied two basic problems: establishment of the minimum effective gamma radiation dose for killing molds, and determination of the total gamma radiation effect on certain physical and chemical properties of paper. The source of gamma rays was cobalt 60.
The following types of molds for establishment of minimum effective lethal dose were used: Aspergillus flavus, Aspergillus niger, Trichoderma viride, and Ulocladium botrytis. A lethal dose for the first three types of mold of 6 kGy (600 krad) has been established. However, cultured Ulocladium botrytis was not affected by radiation of 6 kGy. It has been found that 8 kGy is the minimum effective radiation dose.
The same results have been obtained in Roumania. 2 L.A. Beljajeva, 3 on testing sterilization of 30 types of molds typical for libraries, found a minimum effective dose of 7 kGy. The most resistant were cultures of Stemphylium and Stachybotritis atra.
For estimating the effect of radiation on physical and chemical properties of paper, the following papers were tested: Whatman 1, all-rag paper from the first half of the 19th century, and glazed groundwood-free paper from the second half of the 19th century. The papers were irradiated by dosages of 3 kGy, 5 kGy, 8 kGy, 12 kGy, 18 kGy and 26 kGy.
The folding endurance of all papers decreased with higher doses of radiation. At the dose of 8 kGy the decrease in folding endurance was insignificant, but it was very rapid after accelerated aging at 105°C for 72 hours. The copper number of all tested papers increased, showing a significant increase in the number of reducing groups in the cellulose, as well as a decrease in degree of polymerization.
The estimated dose of 8 kGy is effective for sterilization of molds, but it also causes degradation of treated papers. This means that this type of radiation is not suitable for disinfection of archival documents and books.
In further research on gamma radiation as a means of disinfecting books and documents, 4 a flux of S kGy/hr and a total dose of 18 kGy were required to kill all the fungi tested, although lesser dosages were lethal for many species. Radiation adversely affected the paper, especially its ability to withstand artificial aging.
In this field, however, use of the synergistic effect of radiation and heat seems to be indicated. 5, 6 It was found that higher temperatures significantly decreased the minimum effective radiation dose. J. Urban7 tested four types of molds--Aspergillus flavus, Penicillium spinulosum, Chartonium globosum, and Aspergillus niger--and found that the dose of 6 kGy eliminated all cultures tested. By raising the temperature to 60°C it was possible to decrease the minimum effective radiation dose to 0.5 kGy. From the practical point of view it seems very convenient to raise the temperature to 50°C before radiation. This effect would allow a twenty-fold decrease in minimum effective dosage. It means that a dose of about 500 Gy could cause total destruction of molds without harmful effect to paper, parchment and books.
The Preservation Radiation Centre of Stredoceské Muzeum in Roztoky at Prague, in collaboration with microbiological laboratories, has started an experimental program on evaluation of the synergistic effect of radiation with temperatures up to 48°C, with the goal of decreasing the minimum effective radiation dose to below 800 Gy.
For further information in this field, readers may contact RNDr. Ing. Juraj Urban, CSc., research worker at the Preservation Radiation Centre, Stredoceské múzeum, Roztoky pri Prahe, Czechoslovakia.
A recent report in the Abbey Newsletter, 8and the experience of the Medical Archives of the Johns Hopkins Medical Institutions, show that the use of gamma rays could be promising in mass disinfection treatment of books and archival documents.
1. Horáková, H., "Vyuziti gamma zareni pro dezinfekci archivnich dokumentü." Zpravodaj CVTS, Statni ustredni archiv v Praha, 17, Praha 1981, p. 17-19.
2. Paun, J., Oprea, F., Goldhaar, J., "Folofirea radiacliilor gamma pentru dezinfectia documentelor de archiva." Revista archivelor (Bucuresti) I, p. 79-82, 1978.
3. Beljajevova, L. A., "Gamma-izlucenije kak sredstvo dezinfekcii knig ot spor plesnjevych gribov." Mikrobiologia 5 (29), p. 762, 1960.
4. Pavon, F., "Gamma radiation as fungicide and its effects on paper." Amer. Inst. Conserv. Bull. 16 (1), p. 15-44, Winter 1975-76.
5. Barkai, J., Golan, R., Kahan, R. S., and Padova, R., "Synergistic effects of gamma radiation and heat on the development of Penicillium digitatum." Phytopatology 59, p. 922, 1969.
6. Ben Arie, R., Barkai, J., Golan, R., "Combined heat-irradiation treatments to control storage rots of Spadona pears." Int. J. Appl. Radiat. Isotop. 20, p. 637, 1969.
7. Urban, J., "Moznosti radiacni techniky pri asanaci napademych knihovnickych fondü." Zpravodaj CVTS, Statni ustredni archiv v Praze, Straznice 1983, p. 101-105.
8. "Gamma Radiation." The Abbey Newsletter 8 (2), p. 25, 1984.