Molecular weight of dissolved organic matter-napropamide complex as affected by napropamide-soil application methods

Organic matter amendments to soil are usually thought to improve soil quali ty. increased soil organic matter can lead to increased concentrations of d issolved organic matter (DOM). Complexation of DOM with pesticides ran lead to increased aqueous phase concentration and therefore enhanced movement t hrough the soil profile, Dissolved organic matter has been shown to form a stable complex with napropamide [2(alpha-naphthoxy)-N,N-diethyl propionamid e] and facilitate its transport through soil columns. Equilibrium dialysis is a common method to determine napropamide DOM complexation. Napropamide w as applied to a silt loam soil with (SS) and without (NoSS) sewage sludge a pplication. Solutions from batch equilibrium experiments were analyzed usin g equilibrium dialysis with various molecular weight cutoffs to determine n apropamide DOM complexation. A maximum of 16% of solution phase napropamide was found to be associated with a DOM complex having a molecular weight >5 00 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 w eight of napropamide-DOM complexes is affected by organic matter type and a pplication method.