Ionizing Radiation (X-Rays) Emitted from Animals

Prepared by: Michael J. Huerkamp, DVM, Diplomate ACLAM
Date: January 11, 2001

Agent: Ionizing Radiation (X-Rays) Emitted from Animals

The absorbed dose of ionizing radiation is measured by units called: rems, mrems or rads. One rem equals 1 rad or 1,000 mrem. It is the equivalent of absorbing an amount of energy capable of increasing the temperature of one gram of tissue by an insignificant 0.0000025o C. The danger in ionizing radiation is not in its ability to raise the temperature of tissues (we can withstand several degrees increase with a fever), but in its ability to break strong chemical bonds in living tissue setting forth a chain of events leading to cancer or death.

Potential Hazard: Some research animals are given materials that emit radiation. Excessive exposure to radiation may damage tissues and human genetic material and cause genetic mutations, cancer, cataracts, and radiation sickness. Most radiation exposure in animal research facilities is low (< 100 mrem/year). In addition, we are exposed to radiation emitted from the solar system, the earth, the air we breathe, the food we eat, TV sets, smoke detectors, watch batteries and the like each day of our lives. Everything in our world contains small amounts of radioactive atoms. These are either left over from the creation of the world (like Uranium and Radium) or made by interactions with cosmic radiation (like Carbon 14). The earth is constantly bombarded with cosmic radiation from outer space. Each American is unavoidably exposed to an average of 310 mrem per year of “background” radiation from natural sources and consumer products. In the course of work or in receiving medical care, the average American receives an additional 50 mrem/year. At Emory, doctors, nurses, radiation safety workers, animal caretakers, the veterinary staff, and research personnel may encounter radiation levels in excess of background. Welders, airplane and jet crews, dentists, dental hygienists, astronauts, pharmacists, and nuclear power workers may also be exposed to radioactivity in the course of work.

Instantaneous exposure to 400 rem will kill half the people exposed from radiation sickness. The risk of cancer increases about 0.04% for every 1000 mrem/year exposure. Occupational exposure to 300 mrem/year above “background” for a typical career will shorten the life span by 15 days. By comparison, life span is decreased 6 years by smoking 20 cigarettes a day, 2 years by being 15% over weight, and 1 year by average alcohol consumption. To put occupational risk in perspective, the average life span is shortened 320 days by farming, 227 days in construction, 167 days in mining/quarrying, and 40 days in manufacturing.

Recommended Precautions: The methods of care of radioactive animals are dependent upon the radioisotope given including the form, quantity and the route of administration. Standards for care of radioactive animals are given in DAR SOP 400-11 “Guidelines for the Use of Radioactive Materials in Animals.” A DAR veterinarian serves on the Radiation Safety Committee and is a party to the review of all radioisotope use in animals. Areas of radiation use are clearly marked with the universal radiation hazard symbol. As a means of surveillance, at risk DAR staff are badged with radiation dosimeters. These dosimeters are exchanged quarterly and exposures are measured and reported. A DAR veterinarian reviews the reports for any unusual or excessive amounts of exposure. Amounts exceeding the limits given below are informally investigated internally by the DAR and the Radiation Safety Office (RSO). Exposure to three times the ALARA level triggers a formal investigation. Reports of exposures are kept in the DAR office with the Medical Secretary and may be reviewed by employees during normal business hours. The RSO also issues an annual report of cumulative radiation exposure to each employee.

DAR Annual Radiation Exposure Limits, ALARA (10% of State Maximum)
Whole body, blood forming organs, gonads………500 mrem/year (0.5 rem/year)
Lens of Eye……………………………………...1,500 mrem/year (1.5 rem/year)
Extremities of Skin……………………………....5,000 mrem/year (5.0 rem/year)
Fetus…………………………………………………50 mrem/pregnancy (0.05 rem/pregnancy)

References: B.L Cohen and I.S. Lee, Catalogue of risks extended and updates, Health Physics, Vol. 61, September 1991.

J. W. Gofman, Radiation and Human Health, Sierra Club Books, San Francisco, 1981, p.53.