Sorption of prochloraz on primary soil organomineral size separates

The adsorption and desorption of the fungicide prochloraz (N-propyl-N-[2-(2 ,4,6-trichlorophenoxy) -ethyl]-1-H-imidazol-1-carboxamid) to two whole soil s and their sand, silt, and clay-size separates were investigated in batch experiments. The size separates were isolated using ultrasonic dispersion i n water and repeated gravity sedimentation. For both soils, clay (<2 mu m) and silt (2-20 mu m) sorbed more prochloraz per kg of soil than did sand (2 0-2000 mu m) and whole sea. Based on unit mass of organic matter, however, whole seas anal size separates were equally effective adsorbers, On a unit surface area (BET N-2) basis, the silt- and sand-size separates were the mo st efficient sorbents, Adsorption and desorption isotherms, obtained after 1 and 24 h equilibration, were best described by the Freundlich model Sorpt ion-desorption nonsingularity was observed for all size separates, and in g eneral the degree of nonsingularity increased with contact time. Several so rption parameters were well correlated to soil organic C content and to par ticle porosity, fire latter likely representing the pore volume available f or diffusion of pesticide toward sorption sites. Adsorption kinetics and ad sorption-desorption nonsingularity could be well described by a two stage-t wo rate model, Adsorption kinetics were characterized by a rapid initial ad sorption with most of the pesticide being bound within 10 min followed by a slow adsorption period, When using pesticide transport models that account s For particle-mediated transport, it is important to consider that the pot entially mobile clay- and silt-size separates typically have higher adsorpt ion capacity than the average capacity of the whole soil.