Abstract
ABSTRACT: Pesticide soil sorption is a primary factor that influences the fate of pesticides in the environment, affecting regulation of microbiological and chemical degradation, volatilization and leaching. The main goal of this research was to study the effect of the organic phase of volcanic soils on sorption of agricultural pesticides. Sorption and desorption of eight agricultural pesticides were studied on eight volcanic soils that varied in the fulvic and humic constituents of their organic matter. For all pesticides, sorption was well described by a Freundlich isotherm where 1/nads values indicated that the sorption mechanism could be mainly explained by physical reactions in all soils. Kf values for carbaryl and flumioxazin were the highest with average values of 7.78 and 7.16 mL g-1, respectively. By contrast, hexazinone and metsulfuron-methyl had the lowest average Kf: 0.86 and 0.81 mL g-1, respectively, indicating that they were the least attracted to the soils. The organic fraction of the soil was the main soil factor related to the sorption of all study pesticides. Particularly, humic acid content regulated the sorption between pesticide and soil, especially through the carboxylic groups.
Highlights
Fate of pesticides in soil is affected by multiple variables that include physic-chemical soil properties, pesticide physicochemical properties, climatic conditions and agronomic soil management (Bollag et al, 1992; Sarmah et al, 2009; Fenoll et al, 2011)
A primary factor governing environmental fate of chemicals is soil-pesticide interactions because they regulate the availability of a pesticide in soil solution, affecting rates of microbiological and chemical degradation, volatilization, and leaching (Sánchez-Camazano et al, 1996; Habernahuer et al, 2001; Yu et al, 2006; Fenoll et al, 2011)
Soil organic phase characterization showed that soil varied mainly in their humic fractions, while fulvic fractions were more homogenous between them
Summary
Fate of pesticides in soil is affected by multiple variables that include physic-chemical soil properties, pesticide physicochemical properties, climatic conditions and agronomic soil management (Bollag et al, 1992; Sarmah et al, 2009; Fenoll et al, 2011). Other chemicals, usually those with LogKow values less than 3, which indicates similar leaching potential, exhibit important differences in sorption dynamics according to organic matter content (Sánchez-Camazano et al, 1996; Kogan et al, 2007; Fenoll et al, 2011). A cause for these differences could be the weathering of soil organic matter in soils, which results in variable concentration of humic and fulvic acids. The amount and ratios of humic and fluivic acids could subsequently affect the specific pesticide reactivity with the organic-clay fraction (Senesi, 1995; Borisover and Graber, 1997; Haberhauer et al, 2002; Iglesias et al, 2009; Alister et al, 2011)
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