title: The degradation rate of thiamethoxam in European field studies.
abstract: BACKGROUND
  Thiamethoxam is a systemic and contact pesticidal active substance in the neonicotinoid class of insecticides used worldwide to control a range of insects. Recently, concerns have been expressed regarding possible effects of neonicotinoids on bees and other wildlife. The DT50 of thiamethoxam in soil may be crucial to assessing the potential long-term exposure of non-target organisms to thiamethoxam. There are currently no detailed publicly available data for the field soil degradation of thiamethoxam under European conditions. We give field soil DT50 values of thiamethoxam from studies conducted in several European locations, under a range of realistic agronomic conditions.
  
  
  RESULTS
  Field soil DT50 values normalised to 20 °C ranged between 7.1 and 92.3 days (geomean = 31.2 days; n = 18).
  
  
  CONCLUSIONS
  The degradation rate of thiamethoxam was not significantly affected by application type, cropped fields versus bare soil, soil pH, organic matter content or repeated annual applications. Soil photolysis and leaching were negligible; therefore, calculated DT50 values were taken to represent microbial degradation. The field degradation rates of thiamethoxam were faster than those previously reported from laboratory degradation studies. They demonstrate that thiamethoxam will degrade to concentrations that are <10% of the maximum within a year of application, and will not accumulate in soil after repeated applications.
authors.affiliation: Exponent International Ltd, Harrogate, North Yorkshire, UK.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Hilton
authors.affiliation: Exponent International Ltd, Harrogate, North Yorkshire, UK.
authors.forename: Tim D
authors.initials: TD
authors.lastname: Jarvis
authors.affiliation: Syngenta Ltd, Jealott's Hill Research Centre, Bracknell, Berkshire, UK.
authors.forename: Dean C
authors.initials: DC
authors.lastname: Ricketts
mesh_terms: D000818:Animals; D001516:Bees / Q000187:drug effects*; D006863:Hydrogen-Ion Concentration; D007306:Insecticides / Q000737:chemistry / Q000378:metabolism; D000073943:Neonicotinoids; D009574:Nitro Compounds / Q000737:chemistry* / Q000378:metabolism; D010078:Oxazines / Q000737:chemistry* / Q000378:metabolism; D010575:Pesticides / Q000737:chemistry* / Q000378:metabolism; D012987:Soil / Q000737:chemistry*; D012989:Soil Pollutants / Q000737:chemistry* / Q000378:metabolism; D000077922:Thiamethoxam; D013844:Thiazoles / Q000737:chemistry* / Q000378:metabolism
chemical_list: D007306:Insecticides; D000073943:Neonicotinoids; D009574:Nitro Compounds; D010078:Oxazines; D010575:Pesticides; D012987:Soil; D012989:Soil Pollutants; D013844:Thiazoles; D000077922:Thiamethoxam
keywords: DT50; degradation; insecticide; neonicotinoid; soil; thiamethoxam