Improving Infrared Spectroscopy Characterization of Soil Organic Matter with Spectral Subtractions

Soil organic matter (SOM) underlies numerous soil processes and functions. Fourier transform infrared (FTIR) spectroscopy detects infrared-active organic ...

University of California Davis

Attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy and quantum chemical calculations were used to elucidate the influence of solution chemistry (pH, amino acid concentration) on the binding mechanisms of glutamic and aspartic acid to rutile (α-TiO(2)). The amino acids, glutamate and aspartate, contain carboxyl and amine groups whose dissociation over a pH range results in changes of molecular charge and reactivity, including reactions with mineral surfaces. At pH 3, a decrease of IR bands corresponding to protonated carboxyl groups is observed upon reaction with TiO(2) and indicates involvement of distal carboxyl groups during sorption. In addition, decreased IR bands arising from carboxyl bonds at 1400 cm(-1), concomitant to shifts to higher wavenumbers for ν(as)(γ-COO(-)) and ν(as)(α-COO(-)) (particularly at low glutamate concentrations), are indicative of inner-sphere coordination of both carboxyl groups and therefore suggest a "lying down" surface species. IR spectra of aspartate reacted with rutile are similar to those of solution-phase samples, without peak shifts indicative of covalent bonding, and outer-sphere coordination is predicted. Quantum chemical calculations were carried out to assist in elucidating molecular mechanisms for glutamate binding to rutile and are in reasonable agreement with experimental data. The combined use of ATR-FTIR data and quantum calculations suggests three potential surface configurations, which include (1) bridging-bidentate where glutamate is "lying down" and binding occurs through inner-sphere coordination of both α- and γ-carboxyl groups; (2) chelating-monodentate in which glutamate binds through inner-sphere coordination with the γ-carboxyl group in a "standing up" configuration (with or without protonation of the α-carboxyl); and (3) another bridging-bidentate configuration where glutamate is binding to rutile via inner-sphere coordination of the α-carboxyl group and outer-sphere coordination with the γ-carboxyl ("lying down").

Evaluating glutamate and aspartate binding mechanisms to rutile (α-TiO2) via ATR-FTIR spectroscopy and quantum chemical calculations.

Attenuated total reflectance (ATR) Fourier transform infrared (FTIR) spectroscopy has been used to probe the binding of bacteria to hematite (α-Fe2O3) and goethite (α-FeOOH). In situ ATR-FTIR experiments with bacteria (Pseudomonas putida, Pseudomonas aeruginosa, Escherichia coli), mixed amino acids, polypeptide extracts, deoxyribonucleic acid (DNA), and a suite of model compounds were conducted. These compounds represent carboxyl, catecholate, amide, and phosphate groups present in siderophores, amino acids, polysaccharides, phospholipids, and DNA. Due in part to the ubiquitous presence of carboxyl groups in biomolecules, numerous IR peaks corresponding to outer-sphere or unbound (1400 cm(-1)) and inner-sphere (1310-1320 cm(-1)) coordinated carboxyl groups are noted following reaction of bacteria and biomolecules with α-Fe2O3 and α-FeOOH. However, the data also reveal that the presence of low-level amounts (i.e., 0.45-0.79%) of biomolecular phosphorous groups result in strong IR bands at ∼1043 cm(-1), corresponding to inner-sphere Fe-O-P bonds, underscoring the importance of bacteria associated P-containing groups in biomolecule and cell adhesion. Spectral comparisons also reveal slightly greater P-O-Fe contributions for bacteria (Pseudomonad, E. coli) deposited on α-FeOOH, as compared to α-Fe2O3. This data demonstrates that slight differences in bacterial adhesion to Fe oxides can be attributed to bacterial species and Fe-oxide minerals. However, more importantly, the strong binding affinity of phosphate in all bacteria samples to both Fe-oxides results in the formation of inner-sphere Fe-O-P bonds, signifying the critical role of biomolecular P in the initiation of bacterial adhesion.

ATR-FTIR spectroscopic evidence for biomolecular phosphorus and carboxyl groups facilitating bacterial adhesion to iron oxides.

Environmental release of veterinary pharmaceuticals has been of regulatory concern for more than a decade. Monensin is a feed additive antibiotic that is prevalent throughout the dairy industry and is excreted in dairy waste. This study investigates the potential of dairy waste management practices to alter the amount of monensin available for release into the environment. Analysis of wastewater and groundwater from two dairy farms in California consistently concluded that monensin is most present in lagoon water and groundwater downgradient of lagoons. Since the lagoons represent a direct source of monensin to groundwater, the effect of waste management, by mechanical screen separation and lagoon aeration, on aqueous monensin concentration was investigated through construction of lagoon microcosms. The results indicate that monensin attenuation is not improved by increased solid-liquid separation prior to storage in lagoons, as monensin is rapidly desorbed after dilution with water. Monensin is also shown to be easily degraded in lagoon microcosms receiving aeration, but is relatively stable and available for leaching under typical anaerobic lagoon conditions.

Effects of solid-liquid separation and storage on monensin attenuation in dairy waste management systems.

Biosolids are a potentially valuable source of carbon and nutrients for agricultural soils; however, potential unintended impacts on human health and the environment must be considered. Virtually all biosolids contain trace amounts endocrine-disrupting chemicals derived from human use of pharmaceuticals and personal care products (PPCPs). One potential way to reduce the bioavailability of PPCPs is to co-apply biosolids with biochar to soil, because biochar's chemical (e.g., aromaticity) and physical properties (e.g., surface area) give it a high affinity to bind many organic chemicals in the environment. We developed a soil-specific extraction method and utilized a luciferase-based bioassay (CALUX) to detect endocrine active chemicals in a biosolids-biochar co-amendment soil greenhouse study. Both biochar (walnut shell, 900 °C) and biosolids had positive impacts on carrot and lettuce biomass accumulation over our study period. However, the walnut shell biochar stimulated aryl hydrocarbon receptor activity, suggesting the presence of potential endocrine active chemicals in the biochar. Since the biochar rate tested (100 t ha) is above the average agronomic rate (10-20 t ha), endocrine effects would not be expected in most environmental applications. The effect of high temperature biochars on endocrine system pathways must be explored further, using both quantitative analytical tools to identify potential endocrine active chemicals and highly sensitive bioanalytical assays such as CALUX to measure the resulting biological activity of such compounds.

Use of nuclear receptor luciferase-based bioassays to detect endocrine active chemicals in a biosolids-biochar amended soil.

With increasing demand for recycled wastewater for irrigation purposes, there is a need to evaluate the potential for manufactured nanomaterials in waste water to impact crop production and agroecosystems. Copper oxide nanoparticles (CuO NPs) have previously been shown to negatively impact the growth of duckweed (Landoltia punctata) a model aquatic plant consumed by water fowl and widely found in agricultural runoff ditches in temperate climates. However, prior studies involving CuO NP toxicity to duckweed have focused on systems without the presence of dissolved organic matter (DOM). In the current study, duckweed growth inhibition was shown to be a function of aqueous Cu concentration. Growth inhibition was greatest from aqueous CuCl and, for particles, increased with decreasing CuO particle size. The dissolution of CuO NPs in ½ Hoagland's solution was measured to increase with decreasing particle size and in the presence of Suwannee river humic and fulvic acids (HA; FA). However, the current results suggest that HA, and to a lesser extent, FA, decrease the toxicity of both CuO NPs and free ionized Cu to duckweed, likely by inhibiting Cu availability through Cu-DOM complex formation. Such results are consistent with changes to Cu speciation as predicted by speciation modeling software and suggest that DOM changes Cu speciation and therefore toxicity in natural systems.

Dissolved organic matter reduces CuO nanoparticle toxicity to duckweed in simulated natural systems.

Although biochars may provide agricultural benefits, the potential risks related to agricultural dust emissions have not been adequately investigated. This study examines the impact of biochar type (WS 900: walnut shell, 900°C; PW 500, PW 700 and PW 900: pine wood, 500, 700, 900°C), biochar application rate (0, 1, 2, 5% wt.) and soil water content (low, medium and high) on dust emissions in two different textured-soils (silt loam, sandy loam). Dust was produced via a dust generator simulating soil disturbance (e.g, tillage) and dust fractions with an aerodynamic diameter under 100μm and 10μm (PM and PM) were collected. The data indicate that the higher application rate of WS 900 led to higher PM and PM emissions while PW biochar treatments emitted equivalent amounts of dust as controls (non-amended soils). Dust emissions were exponentially reduced as soil water content increased, irrespective of biochar's presence. Specific markers for biochar, benzene polycarboxylic acids (BPCAs), were used to estimate the biochar content within dust. Results indicate that the increased dust emissions from WS 900 treatments mainly derive from soil particles due to the greater dispersion potential of WS 900 biochar. The collected data also reveal that PM dust contains less biochar particles than PM, attributed to biochars originally containing negligible amounts of particles <10μm.

Estimating potential dust emissions from biochar amended soils under simulated tillage.

The accumulation of arsenic (As) in rice grain is a public health concern since As is toxic to humans; in particular, inorganic As can cause many chronic diseases including cancer. Rice crops are prone to accumulating As, in part, due to the anaerobic soil conditions triggered by the traditional continuously flooded irrigation practice. The objective of this study was to determine how the severity and the timing (i.e. crop stage) of a single soil drying period impact total As concentration and As speciation within the rice (both white and brown) grain, compared to a continuously flooded (CF) control. Drying the soil until the perched water table reached 15 cm below the soil surface (same severity as in the "Safe Alternate Wetting and Drying"), which in this study corresponded to a soil (0-15 cm) water potential of ~0, did not decrease grain As concentrations, regardless of timing. Drying the soil to Medium Severity [MS: soil (0-15 cm) water potential of -71 kPa] or High Severity [HS: soil (0-15 cm) water potential of -154 kPa] decreased total As by 41-61%. However, inorganic As did not always decrease because the severity and the timing of soil drying affected As speciation within the grain. Overall, the soil had to be dried to HS and/or late in the growing season (i.e., at booting or heading instead of at panicle initiation) to decrease inorganic As concentration in the rice grain. This study indicates that the imposition of a single soil drying period within the growing season can mitigate As accumulation in rice grain, but it depends on the severity and timing of the drying period. Further, irrigation management affects As speciation within the rice grain and this must be considered if regulations on inorganic As are based on a percentage of total As measured.

Sanjai J. Parikh

Department of Land,
Air and Water Resources,
Department of Land, Air and Water Resources

University of California Davis

Improving Infrared Spectroscopy Characterization of Soil Organic Matter with Spectral Subtractions

Sanjai J. Parikh

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Land,Air and Water Resources,Department of Land, Air and Water Resources

University of California Davis

Improving Infrared Spectroscopy Characterization of Soil Organic Matter with Spectral Subtractions

Department of Land,
Air and Water Resources,
Department of Land, Air and Water Resources