Stability and mobility of napropamide complexed with dissolved organic matter in soil columns

The herbicide napropamide [N,N-diethyl-2-(1-naphthyloxy)propanamide] has be en shown to complex with various sources of dissolved organic matter (DOM), potentially increasing the risk of ground eater contamination by facilitat ing napropamide transport through soil. Two factors that may reduce the thr eat of facilitated transport of chemicals through soils are soil profile de pth and soil horizon variability, Movement through the soil profile may cau se herbicide complexed with DOM to break apart and readsorb to the soil. Di fferences in soil horizon organic matter content throughout the soil profil e may also alter the potential for facilitated transport of herbicides. Nap ropamide was used in column studies to determine if organic matter differen ces in horizons and soil profile depth would reduce the risk of facilitated transport. A silt loam soil was used with and without sewage sludge amendm ent (SS and NoSS) to represent differences in organic matter content. Resul ts showed that <6% of the applied mass of napropamide moved as DOM complexe s through soil. The majority of complexed napropamide was very stable and r elatively nonadsorbing in solution such that doubling of soil depth only re duced facilitated transport by 20% or less, We present evidence to show tha t napropamide-DOM complexes are relatively nonadsorbing in solution and exh ibit transport characteristics similar to those of a inert compounds in soi l solution.