As stated above, the committee determined that oxidizing agents in soil and airborne dust do not pose a health hazard to astronauts if proper filtration and humidification levels are maintained. However, if NASA decides not to implement the necessary engineering controls or for other science-related reasons chooses to measure the oxidation properties of Martian airborne dust and soil, then the measurement should be performed on the surface of Mars rather than via a sample return. The committee is concerned that the oxidants might dissipate during a sample return transfer unless the sample is maintained in near-Martian conditions during transit. If NASA chooses to measure the oxidizing characteristics of the Martian environment, the committee recommends exposing a variety of materials, such as space suit material, to the Martian atmosphere and observing the effects of oxidants on the materials by optical or other measurement techniques.

Organic carbon “includes all compounds of carbon, including straight chain, closed ring and combinations, except such binary compounds as the carbon oxides, carbides, carbon disulfide, etc.” (Lewis, 1997). Organic compounds are the proverbial building blocks of life. However, their presence does not necessarily indicate that life is or ever was present. Certain organic compounds can be highly toxic to humans, even if those compounds are not associated with a life-form. This threat should be evaluated in planning the first human mission to Mars.

Organic compounds on Mars, if present, could have come from several sources, including meteorite impact, photochemical synthesis, and Martian biologic activity. At the two Viking landing sites, it was determined that within the limits of the gas chromatography-mass spectrometer experiment, the Martian soil contained no organic compounds to a detection limit of 1 ppb (Biemann et al., 1977). Experimental conditions restricted detection to organic compounds that could be volatilized and/or pyrolyzed (i.e., released from the soil) at up to 500 degrees Celsius. While this constraint precluded the direct detection of living organisms and very high molecular weight materials such as some polymers, the temperature was high enough to volatilize all known organic compounds within the mass detection range of the mass spectrometer (12 to 215 atomic mass units). The temperature was also sufficient to pyrolyze many larger organic compounds into smaller products detectable by the mass spectrometer. Overall, the gas chromatography-mass spectrometer results strongly indicate the absence of appreciable quantities of organic carbon on the Martian surface.

This lack of detectable quantities of organic carbon is most likely a result of the abundance of a strong oxidizing agent on the surface that is produced by ultraviolet radiation from the Sun. Any hazard would most likely come from handling subsurface samples that might contain organic compounds. SNC meteorite samples indicate that there may be very small amounts (in the parts per billion range) of organic compounds in the subsurface, which would not represent a hazard. The committee also believes that there will not be any threat from organic compounds in the airborne dust, because oxidants in the atmosphere would have broken down those compounds.

The committee concludes that if organic carbon is not detected in Martian soil, there is no hazard from organic compounds. If organic carbon is present, it may present a hazard to the astronauts through one of two mechanisms: toxicity or infection from a life-form. The former is discussed in this chapter, while the latter is deferred to the discussion of biohazards in Chapter 5.

From a review of the EPA IRIS database, the committee found that organic chemicals pose a risk similar to that posed by toxic metals at the same concentration. Therefore, the committee concludes that if organic carbon is present at a concentration of more than 150 ppm in soil to which astronauts might be exposed, a possible threat exists. Filtration systems that reduce astronaut exposure to organic carbon to concentrations less than 150 ppm would mitigate this threat.

If experiments determine that organic carbon is present in concentrations greater than 150 ppm, the subsurface soil should be considered a toxic hazard until proven otherwise. NASA must then determine which compounds constitute the organic carbon by returning a sample from that specific location to Earth. The reader will learn in Chapter 5 that the need to assess the potential threat posed by a hazardous life-form consisting of organic carbon requires a more stringent measurement of organic carbon concentration. For this reason, the committee's recommendation on the measurement of organic carbon on Mars is deferred to Chapter 5.

Front Matter (R1-R12)

Executive Summary (1-6)

1. Introduction (7-8)

2. The Mars Program in Context (9-14)

3. Physical Environmental Hazards (15-27)

4. Chemical Environmental Hazards (28-36)

5. Potential Hazards of the Biological Environment (37-44)

Appendix A: Statement of Task (45-47)

Appendix B: Biographical Sketches of Committee Members (48-50)

Appendix C: Acronyms and Abbreviations (51-52)