LETTUCE SEEDLING RESPONSE TO DETERGENTS RECOMMENDED FOR SPACE TRAVEL

Abstract

Water contributes approximately 90% of the life support consumables in a closed space environment, therefore, regeneration of pure water from waste streams is important for long term space travel. Controlled Ecological Life Support Systems (CELSS) will rely on plants to produce food, oxygen, consume CO2 and purify water. Igepon TC42, Amide coco N-methyl N-2-sulphoethyl sodium salt, is the main ingredient of the soap recommended for showering and hand washing aboard Space Station Freedom. To determine the soap concentration which causes plant toxicity, lettuce seeds were germinated in 0.1 strength modified Hoagland's nutrient solution and a series of increasing concentrations of Igepon. After 5 days, the seedlings were examined and primary root length measured. The dose response curve indicates an Igepon acute toxicity threshold of 0.2 g l-1 Below the threshold concentration the curve is similar to that of the control, but drops linearly upon reaching the toxic threshold. Seedlings exposed to concentrations of soap greater than the toxic threshold exhibited root damage characterized by the browning of cells in bands above the root cap resulting in reduced growth rates. The damaged cells enlarged becoming round in appearance prior to departing from adjacent cells. The underlying cells appeared clear and uniform making up a thinner, more fragile root mass when compared to undamaged root regions.