Chemistry of Aquatic Humic Surfacants: Characterization and Possible Role in Enhanced Degradation of Herbicides

Abstract

Foam was collected from a sub-alpine stream in Colorado by skimming with a polyethylene container from plunge pools and eddies created by the cascading stream. The foam was fractionated into foam humic substances (FHS) by adsorption onto XAD-8 resin at pH 2.0. A water sample from the stream was filtered and analyzed for total aquatic humic substances (AHS). Characterization included: carboxyl content, C-13 NMR spectospray, foaming ability, surface tension, apparent molecular-weight, and elemental composition. Carboxyl content was largest in the AHS fraction (4.5 meq/g), followed by the FHS fraction (3.4 meq/g). Foaming ability (the height of foam produced in a cylindrical vessel) was inversely proportional to carboxyl content and molecular weight. The total foam fraction had the most foaming ability, followed by the FHS and AHS fractions. Ratios of carbon to carboxyl group, which helped to explain differences in surface activity, were found to be 13:1 for the FHS and 9:1 for the AHS. Microbial degradation experiments were conducted with the total foam, which degraded 32% of its carbon; the FHS fraction, which degraded 18% of its carbon; and the AHS fraction, which degraded 9% of its carbon. Thus, one can conclude that the more surface active the natural surfacant or foam, the more easily it is degraded. The FHS and total foam fractions were used as a carbon source for degradation experiments on several herbicides, including atrazine and alachlor. Neither degrdation of alachlor or atrazine occurred, and we hypothesize that the lack of degradation was a result of the low sediment concentrations in the water samples.

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Shamet, K.A., Thurman, E.M., and Randtke, S.J., 1994, Chemistry of aquatic humic surfacants: characterization and possible role in enhanced degradation of herbicides, in Sensi, N., and Miano, T.M., Humic substances in the global environment and implications on human health, Proceedings of the 6th International Meeting of the International Humic Substances Society, September 20-25, 1992, Monopoli, Italy: Amsterdam, Elsevier, p. 769-774.

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