BioTox: A Biologically-Based Soil Toxicity Instrument

Recently, NASA requested proposals for the Mars Surveyor 2001 Orbiter, Lander, and Rover. The University of Colorado's BioServe Space Technologies Center and several industrial affiliates proposed a Mars soil toxicity instrument, BioTox, for the Lander's "soil box." The purpose of the BioTox experiment is to assess the overall toxicity of Mars soil to living organisms. Environmental toxicity is of major concern for future human missions to Mars. Prior Mars missions suggest that oxides predominate in surface soils, posing potential problems for the operation of machinery and, ultimately, problems for use in construction and habitability of a human base. An industry standard assaying method using a species of bioluminescent bacteria (Vibrio fischeri) is suggested for evaluating samples of Mars soil. Soil will be mixed into an aqueous solution, and toxicity evaluated by measuring the soil's effect on cellular respiration. It is proposed that these bacteria can be transported to Mars in a freeze-dried state, reconstituted in seconds, and the test performed in minutes. An easily performed direct photometric measurement of the light output of the organisms greatly simplifies the instrumentation. Secondary parameters also measured by this experiment are the soil pH, salinity, turbidity, scattering spectroradiometric properties of the aqueous solution, soil color, and inferences of organic versus heavy metal toxins. Although Planetary Protection guidelines encourage nonbiologically based experiments, it is believed that sterilization, a triple-walled container, and back-up fixative procedures will permit safe, effective, biological challenge experiments aboard lander missions. Sending a biological experiment to Mars provides a direct opportunity for testing biological viability in the harsh Martian world and will answer questions of relevance to human landings.