Dilute aqueous fulvic acid (FA) solutions were exposed to UV irradiation for various lengths of time at pH 3.5, 7.0, and 11.0. The rate of photo‐oxidation of FA was pH dependent, increasing with increase in pH.In acid solution most of the FA appeared to be oxidized to CO2 + H2O. Organic S was converted to inorganic sulfate. Under neutral and alkaline conditions, organic C was oxidized to inorganic carbonate. About 90% of the initial FA was decomposed by UV irradiation. Only the most stable components, which were benzenecarboxylic and allphatic n‐fatty acids, resisted decomposition. Phenolic acids, the chromophores responsible for the color of FA, were destroyed.Ultraviolet irradiation could be used as a degradative method if one is interested in isolating and identifying the most stable FA components only.

The adsorption of Dyfonate (O-ethyl-S-phenyl ethylphosphonodithioate) was studied on humic acid (HA) saturated with various cations (Fe3+, Al3+, Cu2+, Zn2+, Co2+, Mn2+, Ni2+, Ca2+, Mg2+, and H+). The amount of Dyfonate adsorbed was affected by the cation with which the HA was saturated. The adsorption process could be described empirically by a Freundlich-type isotherm. The K and [Formula: see text] constants of the Freundlich equation decreased and increased, respectively, with increase in temperature. The data suggest a physical type of adsorption.

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Adsorption of S‐2,3,3‐trichloroallyl N,N‐diisopropylthiolcarbamate (triallate) by montmorillonite saturated with various cations was studied by infrared spectroscopy. The coordination of triallate to the exchangeable cations on the clay occurred through the oxygen of the carbonyl group. The triallate‐montmorillonite complexes were stable even on heating to 50C for 15 days, but when shaken with distilled water, the herbicide was completely displaced from the clay.

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