ELUCIDATING INTERACTIONS AND TRANSFORMATIONS OF POLLUTANTS AND ORGANIC MATTER IN SOIL

Project Information

Principal Investigator	K. goyne
Institution	UNIVERSITY OF MISSOURI
Project URL	View
Relevance to Implications	Some
Class of Nanomaterial	Engineered Nanomaterials
Impact Sector	Environment
Broad Research Categories	Generation, Dispersion, Transformation etc. Characterization
NNI identifier	c4-20

Funding Information

Country	USA
Anticipated Total Funding	n/a
Annual Funding	n/a
Funding Source	USDA
Funding Mechanism
Funding Sector
Start Year	2005
Anticipated End Year	2010

Abstract/Summary

NON-TECHNICAL SUMMARY: Organic agricultural pollutants are detected frequently in streams, lakes, and ground waters of the United States. This research will investigate interactions of these contaminants with organic matter and minerals to identify soil components important for retaining organic agrichemicals on the landscape. Additional proposed research will probe soil organic matter structure, function, and chemical composition in forest and agroecosystems. Data collected from these studies will enhance our understanding of carbon cycling, weathering processes, nutrient release, and pollutant retention and abatement in soil. OBJECTIVES: The aim of this proposal is to elucidate interactions and transformations of pollutant and natural organic compounds in soil. Specifically, research will be conducted to achieve the following four objectives: (1) to assess soil mineral and humic substance influences on sorption and retention of pesticides, pharmaceuticals, plant-made pharmaceuticals (PMPs), and plant-incorporated protectants (PIPs), and determine mechanisms of compound sorption to selected soil components; (2) to investigate nanopore effects on low-molecular weight and polymeric organic compound sorption and retention to mineral surfaces; (3) to determine extents to which organic acids promote dissolution of primary and secondary minerals found in rock and soil; and (4) to characterize organic carbon cycling processes in forested ecosystems and long-term agricultural experiment sites. APPROACH: Interactions between organic agrichemicals and soil minerals, humic acid (HA), and HA-coated minerals will be investigated using macroscopic batch equilibration sorption/desorption studies in conjunction with Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analyses. Similar studies will be performed to assess organic compound sorption into mineral nanopores. Organic acid promoted dissolution experiments will consist of coupling batch dissolution reactions with inductively coupled plasma - mass spectrometry (ICP-MS) analyses to quantify element release. Organic matter cycling experiments include soil sampling at long-term agricultural experiment and paired native prairie sites followed by humic substance extraction using International Humic Substance Society (IHSS) procedures. Extracted humics will be characterized using wet-chemical techniques, elemental analysis (C, N, O, H, P, S), and FTIR and 13C-Nuclear Magnetic Resonance (NMR) spectroscopy to assess long-term agricultural impacts on soil organic matter (SOM). Organic matter (OM) degradation in soil subjected to oscillating redox conditions will be investigated using buried litter bag techniques. Elemental and spectroscopic analyses (FTIR and NMR) will be performed to determine changes in OM chemical composition and structure. PROGRESS: 2005/01 TO 2005/12 (1) Mesoporous (2-50 nm pore diameter) and non-porous SiO2 and Al2O3 adsorbents were reacted with the antibiotic ofloxacin over a range of pH values (2-10) and initial concentrations (0.03-8 mM) to investigate the effects of adsorbent type and intraparticle mesopores on adsorption/desorption. Maximum ofloxacin adsorption to SiO2 surfaces occurs slightly below the pKa2 (pH 8.28) of ofloxacin and sorption diminishes rapidly at pH > pKa2. For Al2O3, maximum sorption is observed at pH values slightly higher than the adsorbent point of zero net charge (p.z.n.c.) and less than midway between the pKa values of the antibiotic. The effects of pH on adsorption and ATR-FTIR spectra suggest that the zwitterionic ofloxacin species adsorbs to SiO2 solids through the protonated N4 in the piperazinyl group and, possibly, a cation bridge; whereas, the antibiotic sorbs to Al2O3 solids through the ketone and carboxylate functional groups via a ligand exchange mechanism. Sorption edge and isotherm experiments demonstrate that ofloxacin exhibits a higher affinity for mesoporous SiO2 and non-porous Al2O3, relative to their counterparts. It is hypothesized that electrostatic repulsion within pore confines decreased ofloxacin sorption to mesoporous Al2O3. In contrast, it appears that the environment within SiO2 mesopores promotes sorption by inducing formation of ofloxacin-Ca complexes, thus increasing electrostatic attraction to SiO2 surfaces. (2) It has been suggested that mobility patterns of P and Y in paleosols could serve as organomarkers to denote the presence of organic ligands secreted by terrestrial organisms on early Earth. In addition, data indicate that Cu depletion may provide a viable oxymarker for determining presence of atmospheric oxygen during soil weathering processes. The potential for utilizing these elements as markers was pursued by investigating dissolution of apatite and chalcopyrite reacted in presence and absence of two aliphatic and aromatic organic acids under oxic and anoxic conditions. In general, results show that organic acids enhance element release from apatite (Ca, P and Y) and chalcopyrite (Cu, Fe, and Y), and increasing organic acid concentrations from 1 to 10 mM results in greater dissolution. The aliphatic organic acid citrate enhances mineral dissolution to the greatest extent and dissolution in the presence of aromatic salicylate or absence of ligand is lowest. Release of Ca, P, and Y from apatite was not impacted by dissolved O2(g) while release of Cu from chalcopyrite was impacted. Aqueous Cu concentrations at the end of batch experiments with chalcopyrite are four orders of magnitude greater under oxic conditions, whereas Fe concentrations are substantially higher under anoxic conditions. These data support the hypothesis that release of P and Y from apatite is enhanced by organic acids and that Cu release is impacted significantly by dissolved O2(g) and, to a lesser extent, organic acids. Thus, it seems plausible that geochemical and mineralogical signatures of P, Y, and Cu may have utility for distinguishing the presence of terrestrial organisms and atmospheric conditions during soil weathering on early earth. MPACT: 2005/01 TO 2005/12 The research investigating uptake of the antibiotic ofloxacin to porous and non-porous minerals has enhanced our knowledge of (1) pharmaceutical interactions with minerals representative of those present in soil and (2) the influence of mineral nanopores on contaminant uptake and retention. Overall, this research improves understanding of potential pollutant interactions with soil, which will impact the fate and transport of these compounds in the environment. Additionally, the nanopore aspect of this study may assist in designing fabricated porous materials that have utility in contaminant remediation efforts. The study investigating use of the elements phosphorus and yttrium as organomarkers and Cu as an oxymarker are relevant to developing tools that geoscientists can use for evaluating conditions present when ancient soils (i.e. paleosols) formed on early Earth. Identifying elements that can be used to establish when life evolved on Earth (i.e., organomarkers) and elements indicative of the presence or absence of atmospheric oxygen (i.e., oxymarkers) can help clarify interpretations of climate and biological activity on early Earth.