Carcinogens in spacecraft air.

The health effects of long-term exposure to ionizing radiation during spaceflight are a major concern to NASA, especially for missions beyond low-Earth orbit. Experiments involving astronauts will be conducted during the next few years to improve the risk assessment for exposures to ionizing radiation during flights; however, concomitant exposure to certain airborne chemical carcinogens during these experiments could confound the results of radiation experiments. Carcinogens can reach the spacecraft atmosphere from leaking thrusters, from off-gassing materials, from chemical experiments and from human metabolism. The Johnson Space Center Toxicology Group routinely analyzes atmospheric samples collected aboard spacecraft. The exposure limits for radiomimetic compounds such as benzene are reduced because of the potential interaction between radiation and chemical exposures. Analysis of recent spacecraft air samples indicates that the following carcinogens are often present in measurable concentrations: acetaldehyde, dichloromethane, formaldehyde and isoprene. Occasionally, the carcinogens 1,2-dichloroethane, acrolein, benzene and furan are found in atmospheric samples. During normal operating conditions, the low concentrations of and limited periods of exposure to airborne carcinogens are thought to pose minimal health risks to crew members, and should not confound experiments involving sensitive methods to detect biological effects of ionizing radiation.