Sorption of aged dicamba residues in soil

Abstract

The effect of aging (residence time in soil) on dicamba (3,6-dichloro-2-methoxybenzoic acid) and a major metabolite, 3,6-dichlorosalicylic acid (3,6-DCSA) sorption was determined in an unamended and a carbon-amended sandy loam and in a silt loam soil. During the incubation, sequential solvent extraction with 0.01 M calcium chloride solution and aqueous acetonitrile + hydrochloric acid was used to determine the solution and sorbed concentrations of dicamba and 3,6-DSCA, and sorption coefficients were calculated. Dicamba was weakly sorbed to soil (Kd < 0.7). In contrast to some other classes of pesticides, sorption of dicamba did not significantly increase with aging, at least not until < 15% of the applied dicamba remained. 3,6-DSCA was strongly sorbed to soil (Kd > 8) and the Kd-a value increased by a factor of 2-6 during a 28-day aging period. Addition of a carbon source to the soil had minimal effect on the strength of sorption of aged dicamba. However, it did appear to decrease 3,6-DSCA availability to soil micro-organisms; once formed 3,6-DSCA was not further mineralized. While it appears that sorption can be well characterized for weakly sorbed pesticides using the batch equilibration method with freshly treated soils, this procedure may not be adequate for more strongly sorbed pesticides and their degradates.

A simple method to determine mineralization of 14C‐labeled compounds in soil

“…The extent of mineralization of [ 14 C]glyphosate in the present study was somewhat lower than that reported by Zablotowicz et al , whereas mineralization of [ 14 C]2,4‐D and [ 14 C]dicamba was similar to previous findings . The capability of soda lime pellets in trapping a quantifiable amount of several hundred disintegrations per minute, as shown in the examples of [ 14 C]dicamba and [ 14 C]aminopyralid at 5 d after application, suggests a practical application of this system to evaluate a potential mineralization of compounds that are not degraded readily in soil.…”

“…The capability of soda lime pellets in trapping a quantifiable amount of several hundred disintegrations per minute, as shown in the examples of [ 14 C]dicamba and [ 14 C]aminopyralid at 5 d after application, suggests a practical application of this system to evaluate a potential mineralization of compounds that are not degraded readily in soil. It must be noted, however, that the rate of mineralization of the compounds in soil can be influenced by many factors, including the physicochemical properties of soil types, microbial populations, and other environmental conditions such as moisture content and temperature . Note, too, that the rate of mineralization of the compounds used in the present study can vary depending on experimental conditions.…”

“…When the mineralization of organic compounds in soil is evaluated, use of labeled compounds is essential to distinguish CO 2 produced by the degradation of exogenous organic compounds from CO 2 emitted via natural respiration of soil microorganisms. A conventional closed system has been used widely to study the mineralization of 14 C-organic compounds in soil, in which the [ 14 C]CO 2 produced is trapped in sodium hydroxide (NaOH) solution. The radioactivity in the solution is then quantitatively counted [1][2].…”

Physicochemical Study of the Sorption of Pesticides by Wood Components

“…The desorption isotherms (not shown) were fitted to the Freundlich equation ( r 2 ≥ 0.68; p < 0.05). The values of desorption constants and hysteresis coefficients (Table 4) indicated high sorption irreversibility for both compounds, as reported for desorption of paraquat (Pateiro‐Moure et al, 2007), and dicamba (Menasseri et al, 2004) from soils.…”

Changes in sorption of indaziflam and three transformation products in soil with aging

“…On the other hand, FDAT sorption did not show any correlation with soil physicochemical characteristics (Alonso, 2012). Several studies previously conducted with similar methods reported the increase in K d,app values with the increase in incubation time for different soil types, pesticides, and metabolites (Bresnahan et al, 2004;Koskinen et al, 2003;Menasseri et al, 2004;Regitano et al, 2006). The mechanism responsible for sorption increasing with time is not known.…”