Modifications of Soil Microbial Activity and Triticonazole Biodegradation by Pesticide Formulation Additives

Abstract

Pesticide seed coating represents an example where formulating agents can modify pesticide fate because they are jointly applied in the coating. The influence of additives used to formniate commercial pesticides on degradation in soil of triticonazole [5‐((4‐chlorophenyl) methylene)‐2,2‐dimethyl‐1‐(1H‐1,2,4‐1riazole‐1‐ylmethyl)cyclopentanol] was considered. The studied additives were three different surfactants, one antifoam, one polymer adhesive, and one solvent. Two doses of some formulating additives commonly included in the commercial formulations were used. The individual effects on overall microbial activity and on triticonazole degradation were monitored during laboratory incubations. Total microbial activity was monitored by respirometric measurements and total soil microbial biomass was determined by fumigation‐extraction. The 14C‐triticonazole behavior was characterized by extraction and monitoring of mineralization kinetics. Only the solvent (propylene glycol) and the nonionic micellar surfactant significantly increased the quantities of organic C mineralized. Triticonazole degradation was modified only after the incorporation of formulation additives at high doses (equivalent to 1 g C additive kg−1 soil). The triticonazole degradation increased with the level of available organic C in the case of the solvent, arguing for degradation by a cometabolic pathway. Degradation decreased with the incorporation of the antifoam and the nonionic and anionic (sodiumalkylnaphthalensulfate) surfactants. High concentrations of formulation additives can modify triticonazole behavior in soils, but at the low levels (equivalent to 0.5 g C additive kg−1 soil), degradation data of triticonazole as an active ingredient alone can be used to describe formulated triticonazole behavior.

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%).…”

“…There have been examined in previous studies with triticonazole and its commercial formulation directly applied to the soil. 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.…”

Laboratory Degradation Studies of Bentazone, Dichlorprop, MCPA, and Propiconazole in Norwegian Soils

“…By using representative commercial formulations we probably provide results more relevant to agricultural practice, compared with other studies using technical standards. Charnay et al (2000) reported that additives used to formulate commercial pesticides influenced soil degradation of triticonazole.…”

Comparison of Triticonazole Dissipation after Seed or Soil Treatment

“…It was found that the mineralization of TTZ is very slow and that its bioavailability for degradation is small due to strong and time‐dependent sorption. It was also concluded in that study and in another study (Charnay et al, 2000a) that formulation additives at normal application rates had no significant effect on TTZ bioavailability.…”