Paraquat sorption- and organic matter-induced modifications of soil spectral induced polarization (SIP) signals

Abstract

Summary Quantifying the capacity of soils to immobilize sorbing contaminants of concern relies on batch sorption experiments, typically performed at skewed solid-to-liquid ratios. The geophysical method spectral induced polarization (SIP) provides a powerful non-invasive monitoring alternative that can capture changes in soil electrical properties driven by contaminant sorption, yielding an approach whereby immobilization can be monitored in situ. Here, we present SIP signals obtained from a series of columns packed with a water saturated natural sandy-loam soil, with and without solid organic matter (SOM) amendment, contaminated with increasing concentrations of the herbicide paraquat. Our results highlight that soil polarization drops proportional to increasing amounts of sorbed paraquat in the SOM-free soil, exhibiting a Langmuir-type leveling-off behavior. The addition of 8%-SOM yielded an increase in both the real (σ') and imaginary (σ'') conductivity of the uncontaminated treatment, driven by the contribution of charged sites in the SOM. Further, SOM modified the dependence between σ'' and sorbed paraquat, likely driven by continued polarization within the polydisperse SOM with continued paraquat addition. However, the time constant ($\tau $), derived using the Cole-Cole model, shed light on a saturation-type dependence governed by a drop in ion mobility with increasing sorption. Thus, aiding the interpretation of sorption-driven SIP signals.

Capturing In Situ Glyphosate (De)sorption Kinetics in Floodplain Aquifer Sediment Columns: Geophysical Measurements and Reactive Transport Modeling

“…The spectral induced polarization (SIP) method, in particular, has shown promise as a contaminantretention monitoring tool. 3 Herein, we focus on an experimental case study of SIP-based sorption monitoring of a model IOC, the herbicide glyphosate (N-(phosphonomethyl)glycine).…”

“…Mellage et al 3 expanded the application of SIP to monitor the sorption of organic cations by quantifying the σ″ of a natural soil amended with increasing amounts of paraquat. Their static incubation results yielded a clear inverse linear relationship between σ″ and adsorbed paraquat in pure mineral soil, whereas the Cole−Cole time constant served as a better predictor of sorption behavior in the organic matter containing soil.…”

“…The findings reported to date suggested that SIP can serve as a sorption-monitoring proxy and help to better capture contaminant sorption kinetics even under seemingly complete sorption, that is, when none or little of the contaminant can be detected in the aqueous phase. While sorption-related studies remain limited at present to well-characterized single or double ion geochemical systems and static (equilibrium) experiments for organic cations, 3 an increasing body of literature has highlighted the potential of time-lapse SIP measurements to capture reactive transport phenomena in porous media. 34,36−40−42 In this study, we monitored the transport of glyphosate in flow-through columns, packed with a mixture of quartz sand and natural calcareous sediment from a shallow tufaceous aquifer in an agricultural floodplain via combined pore water concentration time series monitoring, SIP, and a solid-phase characterization.…”

“…Noninvasive geophysical measurements have been successfully applied to monitor the sorption of ionic species in sediments without reliance on traditional batch incubations. The spectral induced polarization (SIP) method, in particular, has shown promise as a contaminant-retention monitoring tool . Herein, we focus on an experimental case study of SIP-based sorption monitoring of a model IOC, the herbicide glyphosate ( N -(phosphonomethyl)­glycine).…”

“…The findings reported to date suggested that SIP can serve as a sorption-monitoring proxy and help to better capture contaminant sorption kinetics even under seemingly complete sorption, that is, when none or little of the contaminant can be detected in the aqueous phase. While sorption-related studies remain limited at present to well-characterized single or double ion geochemical systems and static (equilibrium) experiments for organic cations, an increasing body of literature has highlighted the potential of time-lapse SIP measurements to capture reactive transport phenomena in porous media. ,− − …”