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- Author or Editor: Theodore Wydeven x
Recycling wastewater containing soaps and detergents for plant growth is highly desirable when fresh water is limited. This is especially true during times of drought and is imperative in some specialized situations such as a regenerative space habitat. To regenerate food, water, and air, the National Aeronautics and Space Administration's Controlled Ecological Life Support System (CELSS) must recycle wastewater commonly known as gray water. The anionic surfactant Igepon is the principal 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 containing 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. Toxicity symptoms include browning of the roots within 4 hours of exposure to Igepon followed by suppression of root dry mass within 24 hours. Plant death never resulted from exposure to Igepon used in these experiments, 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 fresh 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 in fatty acid components in the nutrient solution associated with Igepon. The degradation of phytotoxicity appears to be associated with microbes present on the surface of the roots and not directly due to any plant process or instability of the surfactant.
Anionic surfactants are the major class of surfactants used in detergent, laundry and related industries. Hence, they are a major contaminate of both domestic and industrial waste streams. Lettuce (Lactuca sativa cv Waldemann's Green) was grown in nutrient solutions with the addition of the anionic surfactant, Igepon TC-42. The toxic response of lettuce to Igepon was that the roots turned brown and became necrotic within 24 h following exposure. Growth was supressed for approximately 4 days following exposure to concentration greater than 0.35 mM; new roots formed rapidly and growth resumed. When fresh plants were transferred to the solutions containing Igepon 48 h following introduction of the surfactant no signs of toxicity were observed. This would indicate that either the first series of plants absorbed the toxic material or the Igepon was decayed or degraded in the nutrient solution. The rapid recovery of plants from this stress suggests the potential of a wide range of strategies that could be developed for utilizing waste streams containing anionic surfactants.