Volume 10, Number 1
Feb 1986

Gamma Radiation Approval Seen

The food industry may soon be given permission to preserve a greater variety of foods, using larger doses of ionizing radiation, if the Office of Management and Budget approves new regulations of the Food and Drug Administration. Levels of 1 kGy (1 kiloGray or 100,000 reds) would be permitted for

fresh produce, and 30 kGy (three times the old limit) for herbs and spices. Other foods that had been radiated all along (potatoes, pork) will now have to be labeled. Congress is favorable to the new levels, but some consumer groups are opposed. Perhaps for this reason, a new word has been invented for the labeling: "picowaved."

Ionizing radiation kills insects, bacteria and other microorganisms, including mold. In the food industry, the usual source is cobalt-60, which emits principally gamma rays. Treated materials are not left radioactive, although above a certain level the radiation has an aging effect, a source of concern to conservators using gamma radiation against mold and insect infestations. This topic was discussed in two articles last year in this Newsletter. Both of them recommended combining radiation with heat, because of the synergistic effect, which permits levels of radiation many times lower than otherwise. Joseph Hanus (p. 34, April) reviewed research on radiation with and without heat for killing the molds common in libraries and archives, and concludes that only 0.5 kGy at 500 or 60°C (122°-140°F) would cause total destruction of all molds without harmful effects on paper, parchment or books. A Restaurator article briefly described on page 102 (Nov.) found that 200 krad (2 kGy) at 144°F (62°C) killed all fungus.

Conservators would, of course, be working with dry materials for which the new government regulations permits 30 kGy. The regulations do not cover artifacts and archival material, but this shows that dry foods will probably be irradiated at levels that will affect their chemical makeup. Whether this will have any health effect on humans remains to be seen. There has been some research but it is not conclusive. No ill effects have been proven yet.

The significance of this development for conservation is the likelihood that food-irradiation facilities will become common enough and large enough to offer services to libraries and archives, especially archives. (Johns Hopkins Medical institutions' experience with large-volume disinfestation with gamma radiation is reported on p. 25 of Volume 8 of this Newsletter, and general information is given on p. 28. Johns Hopkins' material received 0.45 megarads (4.5 kGy) without added heat).

It remains to be seen whether the irradiation companies will want the business of libraries and archives. If public resistance to irradiated food leads the companies to look for business anywhere they can find it, they may be hospitable. It also remains to be seen whether libraries and archives will want the kind of heatless radiation they can offer.

In his October lecture, "Attacking Fungal Growth in Paper" (Paper Conservation News, December 1985), Dennis Allsopp said that gamma radiation was far more effective than thymol, and the only sure way to obtain total penetration of the object. He also said that humidity control was the most effective way to control mold growth.