Transformation Of Organic Pollutants Research Articles

Photochemical activity of organic compounds in ice induced by sunlight irradiation: The Svalbard project

[1] Field experiments in Ny-Ålesund, Spitsbergen Island (Svalbard) demonstrated that water ice can be a suitable reaction medium for photochemical transformations of organic pollutants. Several aromatic carbonyl, chloro, nitro or hydroxy compounds, frozen in the ice-matrix samples, underwent very efficient sunlight-induced chemical changes. The photoproducts, in many cases completely different from those obtained from liquid solution photolysis, might pose a high toxicological risk to biota when they enter the environment. It is concluded that the results could be applicable to natural snow and ice, and that possible photochemical transformations should be considered in the ice-core record studies.

Reductive dechlorination of 1,1,2,2-tetrachloroethane.

Products of the transformation of organic pollutants in the environment are often predicted based on the structure of the parent compounds. In some cases, however, multiple products may result from the same reaction pathway. In this study, the reduction of 1,1,2,2-tetrachloroethane (1,1,2,2-TeCA) is investigated both experimentally and computationally. Experimental results and data available in the literature reveal that the ratio of Z-1,2-dichloroethylene (Z-DCE) to E-1,2-dichloroethylene (E-DCE) produced from the reductive beta-elimination of 1,1,2,2-TeCA is approximately 2:1, and this ratio is independent of the reductant used. The exception is iron metal, which results in a ratio of 4.5:1. Computational results reveal that the 1,2,2-trichloroethyl radicals (1,1,2-TCA*) formed upon the transfer of the first electron are nearly isoenergetic and are in rapid equilibrium. Thus, the conformer population of the 1,1,2,2-TeCA does not dictate the product distribution. Using Marcus theory, it is demonstrated that the Z:E ratio of 2:1 reflects the relative rates of the two possible electron transfer steps to the two radical conformers. Further analysis of the thermochemistry of the reaction reveals that this ratio of rate constants should be essentially independent of the thermodynamic driving force, which is consistent with the experimental results. The different observed product distribution when iron metal is the reductant is hypothesized to result from an organometallic intermediate. The reduction of the 1,1,2,2-TeCA is an overall two-electron process, but the fact that the radicals equilibrate at a rate more rapid than the transfer of the second electron suggests that reductants employed act as decoupled single electron-transfer agents.

Interactions Between Soil Particles and Microorganisms: Impact on the Terrestrial Ecosystem

List of Contributors. Series Preface. Preface. PART I: FUNDAMENTALS OF SOIL PARTICLE-MICROORGANISM INTERACTIONS. Interactions between Microorganisms and Soil Particles: An Overview (C. Chenu and G. Stotzky). A Fractal Approach for Interactions between Soil Particles and Microorganisms (N. Senesi and L. Boddy). Interactions of Organic Materials and Microorganisms with Minerals in the Stabilization of Structure (J. A. Baldock). Impact of Organic Substances on the Formation and Transformation of the Metal Oxides in Soil Environments (A. Violante, G. S. R. Krishnamurti and P. M. Huang). Microbial Mobilization of Metals from Soil Minerals under Aerobic Conditions (E. Kurek). Interactions of Bacteria and Environmental Metals, Fine-grained Mineral Development and Bioremediation Strategies (J. S. McLean, J.-U. Lee and T. J. Beveridge). PART II: IMPACT OF SOIL PARTICLE-MICROORGANISM INTERACTIONS ON THE TERRESTRIAL ENVIRONMENT. (A) ION CYCLING AND ORGANIC POLLUTANT TRANSFORMATION. Effect of Mineral Colloids on Biogeochemical Cycling of C, N, P and S in Soil (G. Guggenberger and K. M. Haider). Impact of Interactions between Microorganisms and Soil Colloids on the Transformation of Organic Pollutants (J. Dec, J.-M. Bollag, P. M. Huang, and N. Senesi). (B) RHIZOSPHERE CHEMISTRY AND BIOLOGY. Chemical and Biological Processes in the Rhizosphere: Metal Pollutants (P. M. Huang and J. J. Germida). Biotic and Abiotic Interactions in the Rhizosphere: Organic Pollutants (T. A. Anderson, D. P. Shupack and H. Awata). (C) ANAEROBIC AND TRANSPORT PROCESSES, AND THE SUBSURFACE TERRESTRIAL ENVIRONMENT. Interactions between Microorganisms and Minerals under Anaerobic Conditions (H. L. Ehrlich). The Role of Mineral Colloids in the Facilitated Transport of Contaminants in Saturated Porous media (M. Elimelech and J. N. Ryan). Index.

Effects of a fluctuating water table: column study on redox dynamics and fate of some organic pollutants

The development of the redox conditions has been studied in an initially aerobic column filled with quartz sand coated with ferrihydrite and subjected to a fluctuating water table. The purpose of this study was to evaluate the effect of water table fluctuations on the redox dynamics and the fate of selected organic pollutants. The column that was percolated continuously with electron acceptors (O 2, NO 3, SO 4) and electron donors (acetate and formate), was first operated under saturated conditions resulting in the classical redox zonation. After 4 months of operation, we started to fluctuate the water level and three drainage–imbibition cycles were run each with a total cycle length of 1 month. The pulse of oxygen introduced by lowering the water table caused a partial and temporal oxidation of previously reduced species. To investigate the effect of the changing redox environment on the transport and transformation of organic pollutants, breakthrough experiments were performed with 4-nitrobenzoate and toluene as model pollutants representative for nitro-substituted and volatile aromatics, respectively. The fate of 4-nitrobenzoate and toluene was studied under saturated conditions in short pulse breakthrough experiments and evaluated using the advection–dispersion model. 4-nitrobenzoate was transformed stoichiometrically into 4-aminobenzoate caused by the reduction of the nitrogroup. The transformation rate varied with depth and with time, dropping from 15.3 nmol g −1 h −1 after the first drainage–imbibition cycle to 1.5 nmol g −1 h −1 after 4 additional months of operation. Toluene was not degraded during the first breakthrough experiment and showed a retardation factor of 2.06 which was ascribed to diffusion into entrapped air, originating from drainage–imbibition cycles, and to sorption to biomass. After the 24-h pre-exposure to toluene, adaptation had occurred and in later experiments toluene was degraded within the first 6 cm. These data show that in an experiment that was well-described in terms of water flow, gas flow, and initial mineral phase composition, the microbial processes induced a chemical and physical heterogeneity. An additional heterogeneity in space and time was introduced by the fluctuating water table. The `history' of the column had consequences for the fate of organic pollutants and resulted in an unpredictable behaviour with respect to their transformation, transport and degradation.

Comparison between Anaerobic-Anoxic-Oxic and Anoxic-Oxic Systems for Coke Plant Wastewater Treatment

Coke plant wastewater produces severe pollution throughout China because coal is the main energy resource. The anoxic-oxic (A2-O) system can be used to treat this type of wastewater for simultaneous removal of NH3-N and COD. A comparative study between an anaerobic-anoxic-oxic (A1-A2-O) system and an A2-O system for coke plant wastewater treatment under the same operational conditions was undertaken to examine removal efficiencies of COD and NH3-N, denitrification performance, and transformation of organic pollutants in each system. The experimental results showed that the A1-A2-O system was comparatively more effective not only in nitrification but also in denitrification performance. The total NH3-N removal efficiency and the anoxic NOx-N removal rate of the A1-A2-O system were about 20% higher and more than twice that of the A2-O system, respectively. Coke plant wastewater subjected to anaerobic treatment resulted in less inhibitory effect on the subsequent nitrification process, and provided a more biodegradable and suitable carbon substrate for denitrifying bacteria. The anaerobic stage played an important role in nitrogen reduction in coke plant wastewater treatment.

Reduction of Substituted Nitrobenzenes by Fe(II) in Aqueous Mineral Suspensions

The kinetics of the reduction of 10 monosubstituted nitrobenzenes (NBs) by Fe(II) has been investigated under various experimental conditions in aqueous suspensions of minerals commonly present in soils and sediments. Aqueous solutions of Fe(II) were unreactive. In suspensions of Fe(III)-containing minerals (magnetite, goethite, and lepidocrocite), Fe(II) readily reduced the NBs to the corresponding anilines in a strongly pH-dependent reaction. Our results suggest that on other mineral surfaces (γ-aluminum oxide, amorphous silica, titanium dioxide, and kaolinite) iron (hydr)oxide coatings are indispensable to promote the reduction of NBs by adsorbed Fe(ll). Apparent pseudo-first-order rate constants, k obs , were used to describe the initial kinetics of the NB reduction, covering several half-lives of the compounds. The distinct effect of substituents on k obs and the observed pronounced competition between different NBs indicate that precursor complex formation as well as the (re)generation of reactive surface sites are rate-determining steps in the overall reduction of the NBs. The results of this study demonstrate that Fe(ll) adsorbed on iron (hydr)oxide surfaces or surface coatings may play an important role in the reductive transformation of organic pollutants in subsurface environments. Our findings may also contribute to a better understanding of the various redox processes involved in groundwater remediation techniques based on Fe(0) as the bulk reductant.

Oxide Surface‐Catalyzed Hydrolysis of Carboxylate Esters and Phosphorothioate Esters

AbstractPathways and rates of organic pollutant transformation may be altered through interaction with the surfaces of oxides and other soil minerals. We examined oxide surface‐catalyzed hydrolysis of representative carboxylate esters and phosphorothioate esters. Ester and hydrolysis product concentrations were monitored in acetate‐buffered suspensions containing 10 g L−1 oxide. Carboxylate esters found susceptible to catalysis in this work possess an auxiliary ligand donor group that, along with the carbonyl O group, form a chelate with surface‐bound metal atoms. Esters possessing an O‐donor auxiliary group (e.g., phenyl salicylate) are susceptible to catalysis by Al2O3, TiO2, and FeOOH surfaces. Esters possessing a N‐donor auxiliary group (e.g., phenyl picolinate) are no longer susceptible to catalysis by Al2O3, reflecting the poor affinity of N‐donor groups for Al complexation. Methyl chlorpyrifos is the most susceptible of the three phosphorothioate esters to oxide‐catalyzed hydrolysis; it possesses an auxiliary ligand donor group analogous to the carboxylate esters examined. Methyl parathion and ronnel, which do not possess a suitable auxiliary ligand donor group, are also susceptible to oxide‐catalyzed hydrolysis, indicating that chelate formation is not required in order for surface catalysis to occur. The presence of methanol and acetonitrile cosolvents diminishes the catalytic effect. The widespread use of these cosolvents in fate studies may have caused rates of oxide and mineral surface‐catalyzed hydrolysis reactions to be underestimated.

New perspectives in aquatic redox chemistry: Abiotic transformations of pollutants in groundwater and sediments

Presented is a review of recent advances in the chemistry of abiotic redox transformations of organic pollutants in anaerobic ecosystems. The goal is to provide an indication of the state of knowledge and the remaining difficulties, rather than an exhaustive review of the existing literature. Particular attention is given to the types of functional groups that undergo reaction and the findings concerning physical and chemical parameters of ecosystems that govern the rates and products of redox transformations. Classes of compounds and structural features within these classes of compounds provide information about the intrinsic nature of the natural reductants. Further information is provided by studies which consider system variables such as sediment concentrations, organic carbon levels, pH, Eh and temperature. While the identity of reducing agents that transform organic pollutants in anaerobic systems remains elusive, the reactivities of these agents are being characterized and compared with surrogate (model) reductants. It is apparent that chemical and biological reduction processes are strongly coupled, and there is increasing evidence for widespread mediation of reductive reactions by bio-organic molecules.

QSAR analyses of oxidation and reduction rates of environmental organic pollutants in model systems

Redox transformations of organic pollutants in the aquatic environment are often the net result of reaction of the substrate with several oxidizing or reducing agents. In order to cope with this multiplicity of reaction pathways, model systems are very useful because they allow one to evaluate the possible contributing reactions in isolation. In a suitable model system, the rate law and rate constant for a particular reaction of environmental interest can be determined. Good correlations (quantitative structure-activity relationships or QSARs) are often found between rate constants for a redox reaction of closely related organic substrates and their one-electron oxidation or reduction potentials. Such QSARs have been observed for reduction of substituted nitrobenzenes by hydroquinones and by iron porphyrins in the presence of reduced sulfur species. Under appropriate conditions, half-wave potentials are proportional to one-electron redox potentials and can be used as an alternative predictor variable in QSAR analysis of redox reactions. This has been done successfully for oxidation of substituted phenols by singlet oxygen. These QSARs can be used to predict reaction rate constants for unstudied compounds. In addition, QSARs developed from model systems are also powerful tools for evaluating the kinetics of redox reactions of organic pollutants and for developing and extending deterministic models of environmental redox reactions of organic pollutants.

Mutagen formation and nitration by exposure of phenylphenols to sunlight in water containing nitrate or nitrite ion

Mutagens have been ascertained to be present in river sediments (Suzuki et al., 1982a; Sato et al., 1983, 1985). Their mutagens in aquatic environments are considered to be attributable not only to the inflow of industrial effluent and domestic sewage containing mutagens but also chemical and biological transformations of organic pollutants to mutagens. In earlier studies, we found that UV irradiation causes mutagen formation in aqueous solution of aromatic compounds in the presence of nitrate or nitrite ion (Suzuki et al., 1982b, 1983, 1985, 1988). The mutagen was proven to be formed through nitration, nitrosation, hydroxylation and oxidation to a quinone of the parent aromatics with radicals of NO, NO 2 and OH derived from photolysis of nitrate or nitrite ion. Aquatic environments are well known to be polluted by various aromatic compounds (Pitt et al., 1975; Basu et al., 1978). Nitrite ion also exists in river, lake and sea waters, though the concentration is very low level (Brinkhoff, 1978; Okada et al., 1979; Zafiriou et al., 1980). The effluents from night-soil treatment plant and sewage treatment plant are known to contain very high concentration of nitrite (Kaiga et al., 1984).

Biological transformation of organic pollutants in groundwater

Recent investigations have discovered surprisingly high numbers of microorganisms in shallow water‐table aquifers. Evidence is accumulating that these microorganisms may, under certain circumstances, transform many of the organic pollutants that enter the subsurface environment. These transformations can lead to total destruction of the pollutant or to the production of new organic pollutants.