Organic carbon-mineral interactions with implications on water reuse and carbon cycling
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Authors
Shahriar, Abrar
Issue Date
2023
Type
Dissertation
Language
Keywords
Alternative Title
Abstract
Soil organic carbon (OC)-mineral associations play an important role in regulating the fate and transport of pollutants in soils, biogeochemical cycles of carbon, as well as response to climate change. With the reuse of reclaimed water for agriculture as a promising strategy for the sustainable management of water resources, residual trace organic pollutants in reclaimed water can exert potential risks to human health. Predictive modeling about how the organic pollutants (including ionizable organic compounds) behave at the soil OC-mineral-water interface can help determine the environmental risks of water reuse for agriculture. Molecular-level understanding of OC-mineral associations, i.e., identification of the chemical structures of organic ligands occurring in soil environment, can shed light on not only predicting the plant uptake of organic pollutants for water reuse but also carbon stability in soil environment under dynamic climate. This study aims to: 1) develop a screening model for estimating the environmental risks of organic pollutants in reclaimed water for agricultural irrigation accounting for the sorption of pollutants by soil OC-mineral complexes; 2) identify the chemical nature of unknown organic ligands in soils derived from degradation of plant macromolecules (lignin). The fate of five different pharmaceuticals and personal care products (PPCPs) was predicted in agricultural grazing farms irrigated with reclaimed wastewater by our developed model. The degradation rate constant of the PPCPs was found to be a critical factor regulating the concentration of compounds in soil and plants. Without considering the sorption of organic pollutants by organic matter and minerals in the soil environment, the environmental risks of widely occurring pollutants can be overestimated. The model was developed to simulate the pH-dependent speciation and fate of ionizable PPCPs (iPPCPs) in soils and their plant uptake during the application of reclaimed wastewater to agricultural soils. Assuming sorption only for neutral compounds on soil organic carbon led to a miscalculation of iPPCP concentrations in plant tissues by up to one and a half orders of magnitude. Overall, the results demonstrated the importance of considering pH and speciation of iPPCPs when simulating their fate in the soil-plant system and plant uptake. To identify the organic ligands, a method that combined high-performance liquid chromatography (HPLC) with high-resolution Orbitrap mass spectrometry (HRMS), screening for Fe isotopologues, and metabolomic analysis was utilized. Lignin-derived model compounds (such as caffeic acid, coumaric acid, vanillin, and cinnamic acid)) were used to validate and optimize the protocol before applying the protocol to identify the chemical structure of unknown organic ligands generated from microbial degradation of lignin by Pseudomonas putida. Fe complexes and corresponding apo-ligands were determined by isotopic pattern matching, accurately predicting the molecular formula, identifying the apo-ligands with MS/MS data, and predicting the structure of organic ligands utilizing the MS/MS peaks. Library search based on the MS results also uncovered additional organic ligands as well as molecular networking analysis grouped apo-ligands and complexes with similar chemical natures in the same clusters which helped to identify further interesting compounds. The approach has the potential to be employed in a wider array of complex environmental samples to discover compounds that possess significant potential for binding with Fe-containing as well as other soil minerals.