TIME DEPENDENCY OF TRITICONAZOLE FUNGICIDE SORPTION AND CONSEQUENCES FOR DIFFUSION IN SOIL

Diffusion is a key process regarding the redistribution in soils of sy stemic pesticides applied in seed treatments, We investigated the infl uence of nonequilibrium sorption on the diffusivity of triticonazole f ungicide -1-(1H-1,2,4-triazol-1-ylmethyl)-cyclopentan-1-ol] in a loam clay soil from Grignon, France (Typic Eutrochrept). Triticonazole diff usion coefficients were measured in saturated soil columns fbr time pe riods ranging from 1 to 25 d. Nonequilibrium sorption was evaluated fr om measurement of apparent desorption coefficients, and from estimatio n of apparent partition coefficients from a diffusivity model. Tritico nazole availability was also evaluated based on successive aqueous and methanol extractions, and measurement of the nonextractable residues fraction, Triticonazole diffusion in soil was characterized by a stron g time-dependence. Apparent diffusion coefficient decreased from 0.05 cm(2) d(-1) at 2 d to 0.02 cm(2) d(-1) at 25 d, Triticonazole apparent sorption coefficient increased with time of diffusion, from 5 L kg(-1 ) at 1 d to 10.5 L kg(-1) at 25 d, which was greater than the batch eq uilibrium value of 4.35 L kg(-1). The measured and calculated results were very close, showing that nonequilibrium sorption was the key proc ess responsible for the decrease in triticonazole apparent diffusion r ate. The availability of the diffusing residues diminished constantly with time. The water-extractable fraction corresponding to the more av ailable residues decreased from 31% at 1 d to 17% at 25 d, while a res istant fraction was rapidly formed representing 9% after 25 d. Tritico nazole slow desorption behavior was attributed to rate-limiting intras orbent diffusion.