Microtox utilizes a bioluminescent bacteria (Allivibrio fischeri) to determine the toxicity of a particular substance and/or substrate.[1][2] During cellular metabolism, these bacteria naturally emit light as a part of cellular respiration, which can be measured as luminescence.[3] When exposed to toxic substances, a decrease in luminescence can be observed and percent change in luminescence can be directly correlated to toxicity.[3] Allivibrio fischeri were specifically chosen, as these bacteria could be preserved by freeze-drying to increase shelf life and use.[3] Both solid phase (soils and sediment) and aqueous acute toxicity testing (described below) can be conducted using this technology.[4]