Gamma Radiation Sterilization of Ponderosa Pine and Birch Sapwood

The sterilizing effects of gamma radiation on microbiologically contaminated ponderosa pine and birch sapwood (beams and cubes) conditioned to moisture contents ranging from 0.5% to 150% were examined.The lethal radiation dosage required depended on the moisture content of the wood and also, perhaps, on the initial concentration of microorganisms within the wood. Fungi were more sensitive to radiation than bacteria, but a radiation dose between 1 and 5 M rads was sufficient to kill all microorganisms in 3/4-inch cubes of both woods. Smaller radiation dosages were required to sterilize wood at either very low or very high moisture contents than at intermediate moisture contents. Both woods had similar lethal dosage requirements for sterilization.Seven fungal species isolated after a radiation dosage of 5 X 105 rads were found to be Fungi Imperfecti. Following gamma irradiation of wood samples, there was no evidence of an aftereffect modifying the growth of microorganisms in the wood