DOI: 10.5061/dryad.70rxwdbwd
title: Data from: Sorption and desorption of bicyclopyrone on soils

description: Bicyclopyrone is a herbicide that is targeted for the control of
 herbicide-resistant weeds. However, there is a lack of extensive data on
 its sorption and factors that control its sorption in the soil
 system. In this study, we evaluated a series of 25 different
 soils, with a variety of soil properties to assess if an empirical
 relationship could be developed to predict the sorption coefficient for
 bicyclopyrone. Overall, there were no statistically significant
 relationships observed with organic carbon, cation exchange capacity, or
 clay content. There solely was a moderate negative correlation
 with soil pH (R=-0.65).  Additionally, Freundlich isotherm
 analysis suggests that the KD could be adequate to characterize the
 sorption behavior for the range of soils evaluated here.
description: Bicyclopyrone sorption was determined on each soil in triplicate
 using the batch equilibration method with radiolabeled compounds. The
 <sup>14</sup>C spiking solution for BCP was prepared by
 diluting <sup>14</sup>C-bicyclopyrone
 [pyridinyl-3-<sup>14</sup>C; specific activity = 95.3 µCi
 mg<sup>-1</sup>; 8,880 Bq mmol<sup>-1</sup>; 99.5%
 purity] with unlabeled BCP (Syngenta Crop Protection, LLC) to result in a
 stock solution of 10 mg L<sup>−1</sup> with an overall
 activity of 1,090 Bq mL<sup>-1</sup> (65,450 DPM
 mL<sup>-1</sup>). A 0.5 mL aliquot of this spiking solution
 was added to 9.5 mL of 0.01 M CaCl<sub>2</sub> to achieve a 10
 mL solution volume. This solution (0.5 mg L<sup>−1</sup> BCP)
 was added to 1 g of soil in a 20 mL glass scintillation vial for a series
 of 25 different USDA soil series. Samples were then placed horizontally on
 a reciprocal shaker and allowed to equilibrate for 24 h (180 rev
 min<sup>-1</sup>) in the dark. Following centrifugation (20
 min, 1500 × g), 2 mL of supernatant was removed and ﬁltered (0.45
 μm). Then a 1 mL aliquot of the ﬁltered solution was mixed with 5 mL of
 scintillation cocktail [EcoLite(+)™; MP Biomedicals, LLC, Solon, OH] and
 analyzed for <sup>14</sup>C by liquid scintillation counting
 (LSC) (HITACHI AccuFLEX LSC-8000, GMI Ramsey, MN, 10-minute counting
 window).  No statistically significant sorption of the BCP to
 scintillation vials, syringes or syringe ﬁlters was observed (98-100%
 recovery, data not shown). The sorbed concentration of BCP on the soil was
 estimated by the following: <i>C</i><sub><i>s</i></sub><i>=</i><i>C</i><sub><i>i</i></sub><i>-</i><i>C</i><sub><i>e</i></sub><i>m</i><i>V</i> , where C<sub>i</sub> is the initial concentration (mg L<sup>-1</sup>), C<sub>e</sub> is the equilibrium concentration (mg L<sup>-1</sup>), V is the total volume of the liquid phase (L), and m is the mass of the soil (g). The equilibrium concentration was determined by the LSC of the liquid phase using the following equation: <i>C</i><sub><i>e</i></sub><i>=</i><i>LS</i><i>C</i><sub><i>e</i></sub><i>-Blank</i><i> *</i><i> C</i><sub><i>i</i></sub><i>LS</i><i>C</i><sub><i>i</i></sub> , where <i>LSC<sub>e</sub></i> is the disintegrations per minute of the sample following equilibration with the soil, <i>Blank</i> is the disintegrations per minute of the scintillation cocktail and vial alone, <i>C<sub>i</sub></i> is the liquid phase concentration of the initial standard (mg L<sup>-1</sup>), and <i>LSC<sub>i</sub> </i>are the disintegration of the corresponding BCP standards (without soil added). The partitioning coefficient (K<sub>D</sub>) is estimated by the following: <i>K</i><sub><i>D</i></sub><i>=</i><i> C</i><sub><i>S</i></sub><i>C</i><sub><i>e</i></sub> .   <b>Sorption Isotherms – Multiple Concentrations</b> Sorption isotherms were generated for 7 selected soils which were selected based on the initial screening above for a range of observed K<sub>D</sub> values. The isotherm was determined utilizing initial BCP solution concentrations of 0.1, 0.5, 1, 2.5, 5, 10, and 20 mg L<sup>−1</sup>. Individual samples were run in duplicate using methods analogous to the single concentration batch K<sub>D</sub> determination described earlier.  Equilibrium liquid (C<sub>e</sub>) and solid (C<sub>s</sub>) concentrations were then analyzed by fitting to different linear forms of four sorption models: Langmuir, Freundlich, Temkin, and the Dubinin-Radushkevich models (Horsfall, Spiff, & Abia, 2004; Hunt & He, 2015). 
description: Excel file with separate worksheets for the batch-isotherm
 (K<sub>D</sub>) and the multi-point isotherm
 datasets.