Adsorption and Desorption of Metolachlor and Metolachlor Metabolites in Vegetated Filter Strip and Cultivated Soil

Abstract

Previous studies have indicated that dissolved-phase metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(methoxy-1-methylethyl) acetamide] transported in surface runoff is retained by vegetative filter strips to a greater degree than either metolachlor oxanilic acid 12-[(2-ethyl-6-methylphenyl) (2-methoxy-1-methylethyl)amino]-2-oxo-acetic acid] (OA) or metolachlor ethanesulfonic acid [2-[(2-ethyl-6-methylphenyl) (2-methoxy-1-methylethyl-1)amino]-2-oxoethanesul-fonic acid] (ESA), two primary metabolites of metolachlor. Adsorption-desorption of ESA and OA in vegetated filter strip soil (VFSS) has not been evaluated, yet these data are required to assess the mobility of these compounds in VFSS. The objective of this experiment was to compare metolachlor, ESA, and OA adsorption and desorption parameters between VFSS and cultivated soil (CS). Adsorption and desorption isotherms were determined using the batch equilibrium procedure. With the exception of a 1.7-fold increase in organic carbon content in the VFSS, the evaluated chemical and physical properties of the soils were similar. Sorption coefficients for metolachlor were 88% higher in VFSS than in CS. In contrast, sorption coefficients for ESA and OA were not different between soils. Relative to metolachlor, sorption coefficients for ESA and OA were at least 79% lower in both soils. Metolachlor desorption coefficients were 59% higher in the VFSS than in the CS. Desorption coefficients for ESA and OA were not different between soils. Relative to metolachlor, desorption coefficients for ESA and OA were at least 66% lower in both soils. These data indicate that the mobility of ESA and OA will be greater than metolachlor in both soils. However, higher organic carbon content in VFSS relative to CS may limit the subsequent transport of metolachlor from the vegetated filter strip.

Aspect of the degradation and adsorption kinetics of atrazine and metolachlor in andisol soil

“…For metolachlor, K f ranging from 3.72 to 6.61 and n ranging from 0.97 to 1.17 were reported by Krutz et al (2004). The K d values determined for metolachlor in this paper are also within the range of the K d reported in the literature (Krutz et al, 2004).…”

“…The K f values reported for atrazine include 0.2-4.2 L kg -1 (Brouwer et al, 1990), 3.8-6.5 L kg -1 (Sharon and Koskinen, 1990), 0.4-3.1 L kg -1 (Moreau and Mouvet, 1997), and 1.5-2.0 L kg -1 (Seybold and Mersie, 1996). For metolachlor, K f ranging from 3.72 to 6.61 and n ranging from 0.97 to 1.17 were reported by Krutz et al (2004). The K d values determined for metolachlor in this paper are also within the range of the K d reported in the literature (Krutz et al, 2004).…”

What happens when pharmaceuticals meet colloids

“…Humic substances can sorb pharmaceuticals through cation exchange and cation bridging, and the desorption may be characteristic of hysteresis (Essington 2004;Krutz et al 2004). As humic substances commonly exist in surface coating and pore blocking with other soil matrix, they may inhibit interlayer diffusion of organic pollutants or occupy sorption sites to reduce the sorption and promote desorption of PCs (Pils and Laird 2007).…”

“…The higher Freundlich coefficients and lower constants for desorption isotherms suggest that there was hysteresis (Essington, 2004;Krutz et al 2004). The sorption of TCs by humic substances may result from the interactions between polar or charged functional groups of TCs and humic substances via cation exchange/bridging and hydrogen bonding (Fig.…”

Composition and design of vegetative filter strips instrumental in improving water quality by mass reduction of suspended sediment, nutrients and Escherichia coli in overland flows in eastern escarpment of Mau Forest, Njoro River Watershed, Kenya

“…In recent years, vegetated filter strip (VFS) has emerged as a low-cost, locally implementable, best management practice option to minimize these health risk, particularly for small-scale operations or to reduce risk from open pasture-derived overland flow (Stout et al 2005; Liu et al 2008; McLaughlin et al 2013; Yu et al 2013). However, recent literature has emphasized the importance of determining local hydrological parameters (including soil, water quality and temperature) in the design and implementation of these VFSs (Krutz et al 2004; Trask et al 2004; Stout et al 2005; Guber et al 2009; Sabbagh et al 2009; Islam et al 2013) and focusing on locally implementable and sustainable solutions. As global climate change will result in increased periods of both flooding and drought in vulnerable areas, site-specific mitigation strategies to reduce public health risk of contamination of surface waters by overland flow must be explored, along with delineation of parameters influencing the efficacy of these mitigation strategies (Boxall et al 2009; Chiang et al 2012).…”