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Journal of Environmental Quality Abstract - Organic Compounds in the Environment

Adsorption and Degradation of the Weak Acid Mesotrione in Soil and Environmental Fate Implications

 

This article in JEQ

  1. Vol. 31 No. 2, p. 613-618
     
    Received: Jan 22, 2001


    * Corresponding author(s): jeremy.dyson@syngenta.com
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doi:10.2134/jeq2002.6130
  1. J.S. Dyson *a,
  2. S. Beulkeb,
  3. C. D. Brownb and
  4. M. C. G. Lanea
  1. a Syngenta, Jealott's Hill International Research Station, Bracknell, Berkshire RG42 6ET, UK
    b Soil Survey and Land Research Centre, Cranfield University, Silsoe, Bedford MK45 4DT, UK

Abstract

The ability of soils to adsorb and degrade pesticides strongly influences their environmental fate. This paper examines the adsorption and degradation of a weak acid, a new herbicide mesotrione [2-[4-(methylsulfonyl)-2-nitrobenzoyl]-1,3-cyclohexanedione], in 15 different soils from Europe and the USA. Experiments were conducted to understand the influence of soil properties, covering a wide range of soil textures, soil pH values (4.4 to 7.5), and organic carbon contents (0.6 to 3.35%). Mesotrione adsorption (K d values ranged from 0.13 to 5.0 L/kg) was primarily related to soil pH, and to a lesser extent by percent organic carbon (%OC). As soil pH rose, mesotrione K d values got smaller as mesotrione dissociated from the molecular to anionic form. Mesotrione degradation (half-lives ranged from 4.5 to 32 d) was also related to soil pH, getting shorter as soil pH rose. Simple regression of mesotrione adsorption against soil pH and %OC and against degradation provided a close fit to the data. The correlation between mesotrione adsorption and degradation means that K d and half-life values are only relevant for use in environmental fate assessment if these values are “paired” for the same soil pH and %OC. The implications were as illustrated for leaching, raising important issues about combining pesticide adsorption and degradation behavior in environmental fate assessments.

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Copyright © 2002. American Society of Agronomy, Crop Science Society of America, Soil Science SocietyPublished in J. Environ. Qual.31:613–618.