¹H and¹⁹F nuclear magnetic resonance microimaging of water and chemical distribution in soil columns

Abstract

Nuclear magnetic resonance (NMR) microimaging is a noninvasive and nondestructive technique that has great potential for the study of soil processes. Hydrogen-1 NMR microimaging techniques were used to examine the distribution of water in four different soil cores. Fluorine-19 NMR microimaging is also used to study the transport of three model contaminants (hexafluorobenzene, sodium fluoride, and trifluralin) in soil columns. The 1H water distribution studies demonstrate that NMR microimaging can provide unique detail regarding the nature and location of water in soils. Image distortion (magnetic susceptibility) was observed for soil samples low in water (20-28% by weight) and that contained an iron content of 0.73 to 0.99%. Highly resolved images were obtained for the organic-rich soil (Croatan sample) and also facilitated the analysis of bound and unbound soil water through varying spin echo times. The contaminant studies with 19F NMR demonstrated that preferential flow processes can be observed in soil cores in as little as 16 h. Studies with hexafluorobenzene produced the highest quality images whereas the definition decreased over time with both trifluralin and sodium fluoride as the compounds penetrated the soil. Nonetheless, both 1H and 19F NMR microimaging techniques demonstrate great promise for studying soil processes.

Characterizing the pore size distribution of a chloride silt soil during freeze–thaw processes via nuclear magnetic resonance relaxometry

“…& Kinger, 2007) and pore size variation during dehydration (Shi, Zhang, Zhang, Zhang, & Yao, 2016). Nuclear magnetic resonance relaxometry has been widely applied to measure the unfrozen water content of frozen soils (Black & Tice, 1989;Tian, Wei, Wei, & Zhou, 2014;Watanabe & Mizoguchi, 2002;Watanabe & Wake, 2009;Xiao, Lai, You, & Zhang, 2017).…”

A review of non-invasive imaging methods and applications in contaminant hydrogeology research

“…At the pore scale, the exact location and morphology of individual NAPL ganglia were resolved, typically in three dimensions, and in a variety of low-iron bearing porous media including glass beads (Johns and Gladden, 1999) (Figure 7a), rock fractures (Becker et al, 2003) (Figure 7b), silica gel (Zhang et al, 2002) (Figure 7c), organic-rich soil cores (Simpson et al, 2007) and estuarine sediments (Reeves and Chudek, 2001). In several cases, measured NAPL surface area and/or NAPL-water interfacial area were determined at selected time points during column flushing with water, and the corresponding effects on NAPL dissolution were evaluated (Johns and Gladden, 1999; Zhang et al, 2002).…”

Nuclear Magnetic Resonance Analysis of Natural Organic Matter

“…NMR micro -imaging of complex porous systems such as soils and sediments is highly benefi cial for water and contaminant distribution and fl ow studies (Simpson et al, 2007b ) but can also be applied to study tissues, bioreactors, biofi lms, plants, wood, and food products (Van As and Van Dusschoten, 1997 ;Humbert, 2001 ). NMR micro -imaging, also referred to as magnetic resonance imaging (MRI), has great potential as a tool to study environmental processes in situ , in real time and also results in a spatially resolved image of the nuclei of interest.…”

“…Recently, Simpson et al (2007b) explored the use of 19 F NMR micro -imaging techniques for use in contaminant -soil studies. The fate of hexafl uorobenzene (F 6 C 6 ) added to a miniature soil core was monitored over a 24 -h period.…”