Eric J. Weber

Chemical- and Sediment-Mediated Reduction of the Azo Dye Disperse Blue 79

Disperse Blue 79, a large volume disperse azo dye, and 2-bromo-4,6-dinitroaniline (BDNA), an important intermediate in the preparation of Disperse Blue 79, were readily reduced chemically and in three anoxic sediment-water systems studied; half-lives were on the order of minutes to hours. No reduction of Disperse Blue 79 or BDNA was observed however in a sediment-water system containing sediment with low organic carbon. The reaction kinetics of Disperse Blue 79 in the reducing sediments are biphasic, that is, the initial rapid loss of dye is followed by a much slower rate of transformation. The reaction pathways for the chemical and sediment-mediated reduction of Disperse Blue 79 were quite similar, suggesting that the chemical reduction of such complex chemicals can provide valuable insight into their reaction pathways in environmental systems. For Disperse Blue 79, a number of reaction products resulting from the reduction of both the azo linkage and aromatic nitro groups were formed. The sediment-mediated reduction of BDNA was regioselective resulting in the formation of a 3-bromo-5-nitro-1,2-diaminobenzene, which was further reduced at a much slower rate to 6-bromo-1,2,4-triaminobenzene. These results suggest that Disperse Blue 79 and BDNA may undergo reduction in some natural anoxic sediments, resulting in the subsequent release of potentially hazardous aromatic amines to the water column

Transformation of dyes and related compounds in anoxic sediment: kinetics and products.

The reactions of several to, anthraquinone, and quinoline dyes were studied in settled sediments. Several 1-substituted anthraquinones were lost from sediment with half-lives less than 10 days. For monosubstituted 1-amino and 1-methylamino (Disperse Red 9) compounds, the most stable product is the intramolecularly hydrogen-bonded anthrone. The 1,4-diaminoanthraquinone (Disperse Violet 1) and 1,4-diamino-2-metoxyanthaquinone (Disperse Red 11) were lost without formation of detectable products except for a demethylation product of the latter. Both the anthrone from Disperse Red 9 and the demethylation product of Disperse Red 11 reacted with halflives of a few months, but other major products were not detected

Hydrolysis kinetics of Reactive Blue 19-Vinyl Sulfone

Abstract The hydrolysis kinetics of Reactive Blue 19-Vinyl Sulfone (RB 19-VS) were studied in phosphate buffer over a pH range of 4–11 and a temperature range of 25–85°C. The hydrolysis of RB 19-VS is base-mediated and leads to quantitative formation of the 2-hydroxyethylsulfone (RB 19-OH). The half-life for RB 19-VS at pH = 7.0 at 25°C was calculated to be 46 years.

Computational electrochemistry: aqueous one-electron oxidation potentials for substituted anilines

Semiempirical molecular orbital theory and density functional theory are used to compute one-electron oxidation potentials for aniline and a set of 21 mono- and di-substituted anilines in aqueous solution. Linear relationships between theoretical predictions and experiment are constructed and provide mean unsigned errors as low as 0.02 V over a training set of 13 anilines; the error rises to 0.09 V over a test set of eight additional anilines. A good correlation is also found between oxidation potential and a simple computed property, namely the energy of the highest occupied molecular orbital for neutral anilines in aqueous solution. For the particular case of the substituted anilines, a strong correlation between oxidation potential and pKa is found, and a still stronger correlation between oxidation potential and physical organic descriptors for aromatic substituents is also found, albeit over a reduced data set.

Quantitative structure‐activity relationships for chemical reductions of organic contaminants

Sufficient kinetic data on abiotic reduction reactions involving organic contaminants are now available that quantitative structure-activity relationships (QSARs) for these reactions can be developed. Over 50 QSARs have been reported, most in just the past few years, and they are summarized as a group here. The majority of these QSARs concern dechlorination reactions, and most of the rest concern nitro reduction reactions. Most QSARs for reduction reactions have been developed mainly as diagnostic tools for determining reduction mechanisms and pathways. So far, only a few of these QSARs are sufficiently precise in formulation, yet general in scope, that they might be useful for predicting contaminant fate. Achieving the goal of developing predictive models for the kinetics of contaminant reduction in the environment will require a delicate balance between process-level rigor and practical levels of approximation.

Toward Identifying the Next Generation of Superfund and Hazardous Waste Site Contaminants

Background This commentary evolved from a workshop sponsored by the National Institute of Environmental Health Sciences titled “Superfund Contaminants: The Next Generation” held in Tucson, Arizona, in August 2009. All the authors were workshop participants. Objectives Our aim was to initiate a dynamic, adaptable process for identifying contaminants of emerging concern (CECs) that are likely to be found in future hazardous waste sites, and to identify the gaps in primary research that cause uncertainty in determining future hazardous waste site contaminants. Discussion Superfund-relevant CECs can be characterized by specific attributes: They are persistent, bioaccumulative, toxic, occur in large quantities, and have localized accumulation with a likelihood of exposure. Although still under development and incompletely applied, methods to quantify these attributes can assist in winnowing down the list of candidates from the universe of potential CECs. Unfortunately, significant research gaps exist in detection and quantification, environmental fate and transport, health and risk assessment, and site exploration and remediation for CECs. Addressing these gaps is prerequisite to a preventive approach to generating and managing hazardous waste sites. Conclusions A need exists for a carefully considered and orchestrated expansion of programmatic and research efforts to identify, evaluate, and manage CECs of hazardous waste site relevance, including developing an evolving list of priority CECs, intensifying the identification and monitoring of likely sites of present or future accumulation of CECs, and implementing efforts that focus on a holistic approach to prevention.

Identifying Indicators of Reactivity for Chemical Reductants in Sediments

To conduct site-specific exposure assessments for contaminants containing reducible functional groups, it is imperative to know the identity and reactivity of chemical reductants in natural sediments and to associate their reactivity with easily measurable sediment properties. For this purpose the reactivity, as defined by pseudofirst order reduction rate constants for p-cyanonitrobenzene (pCNB), was measured in twenty-one natural sediments of different origins that were incubated to attain both anoxic (less reducing) and anaerobic (microbially reducing) conditions. The reactivity of the anoxic sediments increased with pH and an increasing amount of Fe(II) added. A good electron balance between pCNB reduction and Fe(II) consumption was observed for anaerobic sediments of high solids loading (50 g/L), but not when solids loading was 5 g/L. Based on cluster and regression analysis, pCNB reactivity in the anaerobic sediments correlates strongly with aqueous Fe(II) concentrations for sediments with low organic carbon (OC) content (<4.2%), but with dissolved OC concentrations (DOC) for the sediments with high OC content (>6.4%). These observations indicate surface-associated Fe(II) and reduced DOC are the predominant reductants in the anaerobic sediments, and that aqueous Fe(II) and DOC will serve as readily measurable indicators of pCNB reactivity in these systems.

Estimation of water solubility and octanol/water partition coefficient of hydrophobie dyes: Part I: Relationship between solubility and partition coefficient

Abstract Three regression approaches are examined for use in estimating water solubilities and octanol/water partition coefficients, two fundamental equilibrium constants that are widely used in predicting the fate of organic chemicals in aquatic systems. Approaches examined are regression of solubility against partition coefficient, determination of the product of solubility and partition coefficient, and application of an equation from Yalkowsky and Valvani (3. Pharm. Sci., 69 (1980) 912). The regressions are based on data for water solubility, octanol/water partition coefficient, entropy affusion, and melting point of 20 disperse and solvent dyes. In the study all three methods produced more reliable data on dyes than other equations available in the literature. Root-mean-square deviations are on the order of a factor of four to six for all three methods. Factors such as purity, polymorphism, tautomerization, polarization and hydrogen bonding are suggested as factors precluding the development of highly reliable prediction relationships between solubility and partition coefficient of dyes. Sources of error in both the data and methodologies are discussed. The study also provided information on entropies affusion, which ranged from 50.7 to 136 and averaged 78.8 J mol K. Anthraquinone dyes exhibited much lower entropies affusion than did many azo dyes. Thus use of an average entropy in estimation is inappropriate for dyes and leads to more error than neglecting the change in heat capacity.

Identification of Unsaturated and 2H Polyfluorocarboxylate Homologous Series and Their Detection in Environmental Samples and as Polymer Degradation Products

A pair of homologous series of polyfluorinated degradation products have been identified, both having structures similar to perfluorocarboxylic acids but (i) having a H substitution for F on the α carbon for 2H polyfluorocarboxylic acids (2HPFCAs) and (ii) bearing a double bond between the α-β carbons for the unsaturated PFCAs (2uPFCAs). Obtaining an authentic sample containing 2uPFOA and 2HPFOA, we optimized a mass-spectrometric multiple-reaction-monitoring (MS/MS) technique and then identified uPFCA and HPFCA homologous series in sludge-applied agricultural soils and fodder grasses for cattle grazing. Analysis of samples from a degradation experiment of commercial fluorotelomer-based polymers (FTPs), the dominant product of the fluorotelomer industry, confirmed that commercial FTPs are a potential source of uPFCAs and HPFCAs to the environment. We further confirmed the identity of the uPFCAs by imposing high-energy ionization to decarboxylate the uPFCAs then focused on the fluorinated chains in the first MS quadrupole. We also employed this high-energy ionization to decarboxylate and analyze PFCAs by MS/MS (for the first time, to our knowledge). In exploratory efforts, we report the possible detection of unsaturated perfluorooctanesulfonate in environmental samples, having a conceptual double-bond structure analogous to uPFOA. Using microcosms spiked with fluorotelomer compounds, we found 2uPFOA and 2HPFOA to be generated from unsaturated 8:2 fluorotelomer acid (8:2 FTUCA) and propose β- and α-oxidation mechanisms for generation of these compounds from 8:2 FTUCA. In light of these experimental results, we also reexamined the proposed biodegradation pathways of 8:2 fluorotelomer alcohol.

Reduction of perchlorate in river sediment

The transformation of perchlorate was investigated in river sediment during laboratory batch and column studies to determine if reduction of perchlorate is a viable pathway in natural sediment without previous exposure to perchlorate. Perchlorate at an initial concentration of 10 microM was reduced quantitatively to chloride in 3 d after a lag phase of 2 d in sediment slurries amended with lactate. Raising the initial concentration of perchlorate to 1,000 microM increased the lag phase to 20 d before reduction occurred. At perchlorate concentrations greater than 1,000 microM, the reduction of perchlorate was not observed within 40 d. We speculate that the high concentration of perchlorate specifically was problematic to the microbes mediating the reduction of perchlorate. High levels of nitrate inhibited the reduction of perchlorate as well. In sediment slurries amended with 870 microM sodium nitrate, the reduction of perchlorate at an initial concentration of 100 microM did not occur before day 15 of the experiment, but complete removal of nitrate had occurred by day four. Sediment column studies further demonstrated the dependence of perchlorate reduction on endogenous nitrate levels.