PHYTOTOXIC EFFECTS OF GRAY WATER DUE TO SURFACTANTS

Recycling wastewater containing soaps and detergents for plant growth is highly desirable when fresh water is limited, This is especially tr ue during times of drought and is imperative in some specialized situa tions such as a regenerative space habitat. To regenerate food, water, and air, the National Aeronautics and Space Administration's Controll ed Ecological Life Support System (CELSS) must recycle wastewater comm only known as gray water, The anionic surfactant Igepon is the princip al ingredient of many detergent formulations and soaps and is a prime candidate for use in a space habitat, To determine if gray water would have phytotoxic effects on crops grown in a CELSS, 'Waldmann's Green' lettuce (Lactuca sativa L.) was grown in nutrient solutions containin g varying concentrations of Igepon TC-42, Igepon concentrations of 250 mg.L-1 or higher in nutrient solutions resulted in phytotoxic effects in lettuce, Thus, the toxic threshold of Igepon is <250 mg.L-1. Toxic ity symptoms include browning of the roots within 4 hours of exposure to Igepon followed by suppression of root dry mass within 24 hours, Pl ant death never resulted from exposure to Igepon used in these experim ents, although roots were killed, The phytotoxic effect of Igepon was not persistent; plants initially displaying acute toxicity show clear signs of recovery within 3 days of initial exposure, Further, when fre sh plants were exposed to these same nutrient solutions 3 days or more following initial Igepon addition, no phytotoxic effect was observed, The elimination of the phytotoxicity was associated with a decrease i n fatty acid components in the nutrient solution associated with Igepo n, The degradation of phytotoxicity appears to be associated with micr obes present on the surface of the roots and not directly due to any p lant process or instability of the surfactant.