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This article in JEQ

  1. Vol. 28 No. 5, p. 1429-1435
    Received: Sept 30, 1998

    * Corresponding author(s): williamc@mail.ucr.edu
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Molecular Weight of Dissolved Organic Matter-Napropamide Complex as Affected by Napropamide-Soil Application Methods

  1. C. F. Williams *,
  2. W. J. Farmer,
  3. J. Letey and
  4. S. D. Nelson
  1. Dep. of Environmental Science, Univ. of California, Riverside, CA 92521-0424.



Organic matter amendments to soil are usually thought to improve soil quality. Increased soil organic matter can lead to increased concentrations of dissolved organic matter (DOM). Complexation of DOM with pesticides can lead to increased aqueous phase concentration and therefore enhanced movement through the soil profile. Dissolved organic matter has been shown to form a stable complex with napropamide [2(α-naphthoxy)-N,N-diethyl propionamide] and facilitate its transport through soil columns. Equilibrium dialysis is a common method to determine napropamide DOM complexation. Napropamide was applied to a silt loam soil with (SS) and without (NoSS) sewage sludge application. Solutions from batch equilibrium experiments were analyzed using equilibrium dialysis with various molecular weight cutoffs to determine napropamide DOM complexation. A maximum of 16% of solution phase napropamide was found to be associated with a DOM complex having a molecular weight >500 Daltons. The maximum complex size had a molecular weight <25 000 Daltons. More napropamide was complexed from the SS soil treatments than from the NoSS soil treatments. The presence of a drying event following napropamide application also was found to increase the amount of napropamide complexed in both the SS and NoSS soils. Results show that the amount and molecular weight of napropamide-DOM complexes is affected by organic matter type and application method.

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