Modelling approaches to compare sorption and degradation of metsulfuron‐methyl in laboratory micro‐lysimeter and batch experiments

Abstract

Results of laboratory batch studies often differ from those of outdoor lysimeter or field plot experiments--with respect to degradation as well as sorption. Laboratory micro-lysimeters are a useful device for closing the gap between laboratory and field by both including relevant transport processes in undisturbed soil columns and allowing controlled boundary conditions. In this study, sorption and degradation of the herbicide metsulfuron-methyl in a loamy silt soil were investigated by applying inverse modelling techniques to data sets from different experimental approaches under laboratory conditions at a temperature of 10 degrees C: first, batch-degradation studies and, second, column experiments with undisturbed soil cores (28 cm length x 21 cm diameter). The column experiments included leachate and soil profile analysis at two different run times. A sequential extraction method was applied in both study parts in order to determine different binding states of the test item within the soil. Data were modelled using ModelMaker and Hydrus-1D/2D. Metsulfuron-methyl half-life in the batch-experiments (t1/2 = 66 days) was shown to be about four times higher than in the micro-lysimeter studies (t1/2 about 17 days). Kinetic sorption was found to be a significant process both in batch and column experiments. Applying the one-rate-two-site kinetic sorption model to the sequential extraction data, it was possible to associate the stronger bonded fraction of metsulfuron-methyl with its kinetically sorbed fraction in the model. Although the columns exhibited strong significance of multi-domain flow (soil heterogeneity), the comparison between bromide and metsulfuron-methyl leaching and profile data showed clear evidence for kinetic sorption effects. The use of soil profile data had significant impact on parameter estimates concerning sorption and degradation. The simulated leaching of metsulfuron-methyl as it resulted from parameter estimation was shown to decrease when soil profile data were considered in the parameter estimation procedure. Moreover, it was shown that the significance of kinetic sorption can only be demonstrated by the additional use of soil profile data in parameter estimation. Thus, the exclusive use of efflux data from leaching experiments at any scale can lead to fundamental misunderstandings of the underlying processes.

Long‐Term Sorption and Sequestration Dynamics of the Antibiotic Sulfadiazine: A Batch Study

“…This was different for the nonsterile treatments (see below), where both the RES and NER fractions showed pronounced initial sorption. This behavior is also reported in the literature for SDZ (e.g., Schmidt et al, 2008; Junge et al, 2011) and for other organic contaminants (Heistermann et al, 2003).…”

A Field Study of the Fates of Arsenal and Escort Applied on the Cumberland Plateau in Tennessee

“…Rapid movement of metsulfuron-methyl in soil, as we found to occur at the Cumberland Plateau study site, has been reported for several soils and in glacial till subsoil (Heistermann et al, 2003;Jorgensen et al, 2002;Ismail and Tet-Vun, 2003). The organic carbon and other components of the soil at our study site exhibited very low affinity in retaining the herbicides.…”

“…The organic carbon and other components of the soil at our study site exhibited very low affinity in retaining the herbicides. The rapid transport through the soil may also be attributed to "multi-domain" flow, or movement of water through "macro-pores" in the soil produced by earthworms, decaying roots and other sources (Heistermann et al, 2003;Jorgensen et al, 2002). As noted in the introduction, imazapyr and metsulfuron-methyl are similar in terms of soil retention and water solubility, hence the similar rate of transport observed for the two compounds is expected.…”

Do Lab-Derived Distribution Coefficient Values of Pesticides Match Distribution Coefficient Values Determined from Column and Field-Scale Experiments? A Critical Analysis of Relevant Literature

“…The measured BTCs were evaluated using equilibrium (seven cases) or kinetic models (nine cases). The studies include chlorsulfuron (Veeh et al, 1994, four studies), isoproturon (Lennartz, 1999, one study; Besien et al, 2000; one study; Pot et al, 2005, two experiments), ETD (Dressel, 2003, four experiments), picloram (Gaber et al, 1992, one experiment), metsulfuron‐methyl (Heistermann et al, 2003, one experiment), simazine (Poletika et al, 1995, one experiment), and TBA (Lennartz, 1999, one experiment).…”

“…In case of equilibrium sorption, a linear model (Henry isotherm) written as or a nonlinear model in the form of the Freundlich equation has been used in literature: where S is the sorbed mass (M M −1 ), C the solute concentration (M L −3 ), K d the distribution coefficient (L 3 M −1 ), K f the Freundlich sorption constant (M 1−n L 3n M −1 ), and n the Freundlich exponent. An overview of the type of isotherm used to fit the sorption constants from batch experiments is shown in Table 1 Some sorption constants were derived from sorption kinetic studies using a two‐site nonequilibrium sorption model (e.g., Gaston and Locke, 2000) or a two‐site nonequilibrium model that includes the formation of bound residues (Gaston and Locke, 1994; Heistermann et al, 2003). In these cases, the K d coefficients represented the equilibrium sorption to all kinetic sorption sites.…”