Adsorption and degradation of the weak acid mesotrione in soil and environmental fate implications

• Published in: Journal of environmental quality 2002-03, Vol.31 (2), p.613-618
• Main Authors: DYSON, J. S, BEULKE, S, BROWN, C. D, LANE, M. C. G
• Format: Article
• Language: English
• Subjects: Adsorption; Agronomy. Soil science and plant productions; Applied sciences; Biological and medical sciences; Biological and physicochemical properties of pollutants. Interaction in the soil; Biological Availability; Cyclohexanones - chemistry; Cyclohexanones - metabolism; Degradation; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Half-Life; Herbicides - chemistry; Herbicides - metabolism; Hydrogen-Ion Concentration; Leaching; Organic carbon; Pesticides; Pollution; Pollution, environment geology; Soil and sediments pollution; Soil and water pollution; Soil Microbiology; Soil pH; Soil Pollutants - metabolism; Soil properties; Soil science; Soil texture
• ISSN: 0047-2425; 1537-2537; 1537-2537
• DOI: 10.2134/jeq2002.0613

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 12-[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 (Kd 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 Kd 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 Kd 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.