Time Dependency of Triticonazole Fungicide Sorption and Consequences for Diffusion in Soil

Abstract

Diffusion is a key process regarding the redistribution in soils of systemic pesticides applied in seed treatments. We investigated the influence of nonequilibrium sorption on the diffusivity of triticonazole fungicide [(1RS)‐(E)‐5‐(4‐chlorophenyl‐methylen)‐2,2‐dimethyl‐1‐(1H‐1,2,4‐triazol‐1‐ylmethyl)‐cyclopentan‐1‐ol] in loam clay soil from Grignon, France (Typic Eutrochrept). Triticonazole diffusion coefficients were measured in saturated soil columns for time periods ranging from 1 to 25 d. Nonequilibrium sorption was evaluated from measurement of apparent desorption coefficients, and from estimation of apparent partition coefficients from a diffusivity model. Triticonazole 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 strong time‐dependence. Apparent diffusion coefficient decreased from 0.05 cm2 d−1 at 2 d to 0.02 cm2 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 equilibrium value of 4.35 L kg−1. The measured and calculated results were very close, showing that nonequilibrium sorption was the key process responsible for the decrease in triticonazole apparent diffusion rate. The availability of the diffusing residues diminished constantly with time. The water‐extractable fraction corresponding to the more available residues decreased from 31% at 1 d to 17% at 25 d, while a resistant fraction was rapidly formed representing 9% after 25 d. Triticonazole slow desorption behavior was attributed to rate‐limiting intrasorbent diffusion.

Influence of soil type and water content on release of triticonazole from coated maize seed

“…Instead, under optimal conditions of soil microbial activity (28 °C; 90% field capacity), triticonazole mineralization in soil is small (<1%), indicating high stability of the molecule and little cleavage of the benzyl radiolabelled ring. This accords with previous studies showing triazole fungicides to be very stable in soil,20 and indicating slow and linear triticonazole mineralization 9, 12. HPLC analysis (data not shown) revealed that the extractable radioactivity of all the samples mainly consisted of the parent content (>80%).…”

“…After seven days of incubation, non‐extractable residues in soils were between 3 and 8% of initial radioactivity (Table 4). Previous experiments have also shown similar amounts of bound residues immediately after treatment 12. Bound residues may arise from physical trapping in the internal voids of soil organic matter 18, 19.…”

“…The degradation of triticonazole was found to be slow and due mainly to microbial co‐metabolic transformations that could be characterized by first‐order mineralization rate constants 8, 9. Batch equilibrium studies showed that triticonazole equilibrium sorption was related to soil organic matter content and could be approximated by a linear isotherm 10–12. However, the fate of triticonazole in soil when incorporated in the seed coating has not been quantified.…”

Sorption Kinetics of Atrazine and Diuron in Soils from Southern Brazil

“…[27,30] Diffusion is one of the main mechanisms involved in the formation of bound residues of pesticides in soil. [27,30] Diffusion is one of the main mechanisms involved in the formation of bound residues of pesticides in soil.…”

Investigating Potential Water Quality Impacts of Fungicides Used to Combat Soybean Rust in Indiana

“…Beigel et al (1997) demonstrated that the diffusion and sorption coefficients of the fungicide triticonazole in soil was time dependent, which enabled them to predict the temporal variation of triticonazole concentration in soils. Jamet and Eudeline (1992) compared the mobility of 17 triazole fungicides in a silt loam soil and concluded that their mobility was inversely related to their octanol/water partition coefficient.…”