The route and rate of thiamethoxam soil degradation in laboratory and outdoor incubated tests, and field studies following seed treatments or spray application

Abstract

Soil DT values decreased with increasingly realistic tests (laboratory OECD307 to soil cores to soil cores with a light/dark cycle to field trials). The majority of the differences were associated with the soil treatment in OECD307 studies which destroys soil structure and retards the degradation rate; and from the impact on soil pore water movement in light/dark conditions. Degradation rates in the field were comparable between spray application and seed treatments. Maximum clothianidin concentrations were four-fold lower for seed treatments than for spray application in field studies. © 2018 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Is there a risk to honeybees from use of thiamethoxam as a sugar beet seed treatment?

“…Approximately 6% mol/mol of applied thiamethoxam was represented by clothianidin (based Thiamethoxam (µg/kg) <LOQ <LOQ 2.08 ± 0.57 3.18 ± 0.57 1.21 ± 0.12 0.56 ± 0.06 1.58 ± 0.21 <LOQ Clothianidin (µg/kg) 2.80 ± 0.23 1.53 ± 0.11 2.95 ± 0.45 1.00 ± 0.08 0.91 ± 0.07 1.37 ± 0.12 3.58 ± 0.17 0.92 ± 0.12 Mean TMX + CTD soil residue a (µg/kg) 3.26 ± 0.26 2.03 ± 0.11 5.03 ± 0.94 4.18 ± 0.60 2.12 ± 0.17 1.93 ± 0.14 5.15 ± 0.24 1.41 ± 0.12 Abbreviation: LOQ, limit of quantification. on limited sampling), which supports the low formation of clothianidin from thiamethoxam when used as a seed treatment (Hilton et al, 2019). The greater persistence of clothianidin in European field studies (PPDB, 2020), when compared with thiamethoxam (geomean DT 50 31 days; Hilton et al, 2019), is reflected in the data from this study.…”

“…Approximately 6% mol/mol of applied thiamethoxam was represented by clothianidin (based 3 Mean residues of thiamethoxam (TMX) and clothianidin (CTD; µg/kg) detected in soils sampled from control plots and treated plots once before drilling with thiamethoxam-treated sugar beet seed (57.1-64.1 g a.i./ha) in spring 2017, from control plots once before drilling of succeeding crops (spring 2018) and mean ± SE residues of thiamethoxam and clothianidin (µg/kg) detected in soils from treated plots during cultivation of the succeeding crop on the same plots (spring/summer 2018) Thiamethoxam (µg/kg) <LOQ <LOQ 2.08 ± 0.57 3.18 ± 0.57 1.21 ± 0.12 0.56 ± 0.06 1.58 ± 0.21 <LOQ Clothianidin (µg/kg) 2.80 ± 0.23 1.53 ± 0.11 2.95 ± 0.45 1.00 ± 0.08 0.91 ± 0.07 1.37 ± 0.12 3.58 ± 0.17 0.92 ± 0.12 Mean TMX + CTD soil residue a (µg/kg) 3.26 ± 0.26 2.03 ± 0.11 5.03 ± 0.94 4.18 ± 0.60 2.12 ± 0.17 1.93 ± 0.14 5.15 ± 0.24 1.41 ± 0.12 Abbreviation: LOQ, limit of quantification. on limited sampling), which supports the low formation of clothianidin from thiamethoxam when used as a seed treatment (Hilton et al, 2019). The greater persistence of clothianidin in European field studies (PPDB, 2020), when compared with thiamethoxam (geomean DT 50 31 days; Hilton et al, 2019), is reflected in the data from this study.…”

“…on limited sampling), which supports the low formation of clothianidin from thiamethoxam when used as a seed treatment (Hilton et al, 2019). The greater persistence of clothianidin in European field studies (PPDB, 2020), when compared with thiamethoxam (geomean DT 50 31 days; Hilton et al, 2019), is reflected in the data from this study. Persistence of clothianidin residues does not, however, translate to continual accumulation (Xu et al, 2016).…”

“…In a summary of 18 field dissipation studies performed with thiamethoxam, including multiyear studies, thiamethoxam residues were revealed to be concentrated within 20 cm depth, and cultivation did not result in consistent transport to lower soil layers (Hilton et al, 2016(Hilton et al, , 2019. In addition, seed-treatment-specific studies where soil cores were taken to 1 m depth demonstrated no detectable thiamethoxam residues below 50 cm (Hilton et al, 2019). These field dissipation studies, together with laboratory data demonstrating the importance of microbial viability of soil for the degradation of thiamethoxam, support the hypothesis that the primary degradation mechanism is microbial with leaching through the soil profile only occurring under extreme conditions (Hilton et al, 2016).…”

The Impact of Disturbed Soil Structure on the Degradation of 2 Fungicides Under Constant and Variable Moisture

“…A number of studies have investigated pesticide degradation in unsieved soil under laboratory conditions, using a variety of methodologies (Lechón et al 1997;Topp et al 1994;McDonald et al 2006;Hilton et al 2019). Typically, degradation in sieved soil has been compared to cores containing either undisturbed soil or sieved soil which has been repacked into cores to a similar bulk density.…”