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Hydrolysis of Propazine by the Surface Acidity of Organic Matter¹

ABSTRACT

Propazine [2-chloro-4, 6-bis (isopropylamino)-s-triazine] hydrolysis in acidic aqueous soil-free systems was pH dependent, increasing with lower pH values. At a given pH, degradation followed first-order kinetics. At 23.5C, the relationship was log t (days) = 0.59 pH –0.21. Adsorption of propazine by organic matter prepared from Michigan peat was also pH dependent, but both molecular and cationic adsorption occurred. An increased rate of degradation in the presence of organic matter was postulated as due to hydrolysis by ionized surface hydrogen. Increasing the calcium saturation resulted in decreased hydrolysis. Increasing the CaCl₂ concentration of the propazine-organic matter-aqueous system had no effect on acid hydrolysis. In the salt-amended systems, an increased hydrolysis, to be expected from the lower pH in the ambient solution, was apparently offset by a decreased hydrolysis due to the lowered amounts of ionized surface hydrogen.

¹ Contribution from the US Soils Laboratory, SWC, ARS, USDA, Beltsville, Md. 20705.

² Soil Scientist.

Received for publication February 2, 1972. Accepted for publication April 4, 1972.