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Degradation of a Nonionic Surfactant in Soils and Peat¹

ABSTRACT

Nonionic surfactants are used to improve water movement into water-repellent soils. The effective longevity of treatment and potential water pollution are affected by surfactant degradation. Degradation of ¹⁴C-labeled Soil Penetrant 3685, a nonionic surfactant, was measured in incubation studies in the laboratory. Three soils and one peat, numerous surfactant concentrations, and two soil-moisture levels were used as experimental variables. Plots of degradation percentage versus time produced "S" type curves. Increasing the concentration increased the lag period prior to most rapid degradation. The most rapid and highest percentage of degradation were generally associated with soil materials having the lowest adsorptive capacity for the surfacant. From about 75 to 85% of the added ¹⁴C was evolved as ¹⁴CO₂ in 1 year for the most favorable conditions for degradation. Degradation rate was decreased by decreasing the soil-moisture content. Degradation of soil organic matter was not greatly affected by surfactant applications—< about 10,000 ppm, but progressively decreased with higher surfactant concentrations.

¹ Contribution of the Dep. of Soil Science and Agric. Engineering, Univ. of California, Riverside CA 92502. The research leading to this report was supported by the Office of Water Resources Research, USDI, under the Matching Funds program of Public Law 88-379 as amended, and by the Univ. of California Water Res. Center. It is a part of Water Resources Research Proj. No. B-141-CAL (Water Resources Center Proj. W-332).

² Staff Res. Associate, Prof. of Soil Physics, Prof. of Soil Science, and Staff Res. Associate, respectively.

Received for publication July 7, 1975. Accepted for publication September 19, 1975.