Nigel J. Bunce

Treatment methods for the remediation of nitroaromatic explosives.

The production and use of nitroaromatic explosives for military operations have resulted in their dissemination into the environment, where their presence in waterways and soil poses an ecological and health hazard. This paper reviews technologies that are available or under investigation to remediate areas contaminated with these compounds.

Competitive inhibition by inducer as a confounding factor in the use of the ethoxyresorufin-O-deethylase (EROD) assay to estimate exposure to dioxin-like compounds

The ethoxyresorufin-O-deethylase (EROD) assay has been extensively used in whole animals and in cell culture as a biomarker of exposure to environmental contaminants such as dioxin-like compounds (DLCs). This paper addresses two controversial phenomena that arise when DLCs are examined by the EROD assay. Firstly, the maximum level of induced EROD activity varies with the identity of the inducing compound; secondly, the induced EROD activity reaches a concentration-dependent maximum level that is followed by an apparent reduction in activity when the concentration of inducer is further increased. These phenomena are completely explained by competitive inhibition of the EROD enzyme-substrate reaction by the dioxin-like compound. A kinetic model explains the biphasic appearance of EROD induction curves as a function of a compounds binding affinity with the Ah receptor (Kd) and its binding affinity to CYP 1A1 (Ki) which results in inhibition of the EROD enzyme-substrate reaction. These results limit the reliability of the information obtained from calibration curves of EROD activity versus concentration of a standard DLC such as 2,3,7,8-tetrachlorodibenzo-p-dioxin.

STRUCTURE AND CHEMISTRY OF NAFION-H: A FLUORINATED SULFONIC ACID POLYMER

Abstract This paper deals with the structure and chemistry of Nafion-H, the acidic form of Nafion, which is the trade name for a perfluorinated polymer manufactured by E. I. du Pont de Nemours & Co., Inc. Nafion-H and its salts are available from Dupont in both membrane and powder forms. Nafion composites with Teflon mesh (polytetrafluoroethylene) added to give increased mechanical strength are also available. In addition, sulfonated fluorocarbons modified with other chemically active polymers have been made by Dupont and by competing companies such as Ashai Chemical Industry Co., Ashai Glass Co., Tokuyama Soda Co., and Toya Soda Co.

Electrochemical remediation of acid mine drainage

Acid mine drainage (AMD), which has long been a significant environmental problem, results from the microbial oxidation of iron pyrite in the presence of water and air, affording an acidic solution that contains toxic metal ions. Electrochemical treatment of AMD offers possible advantages in terms of operating costs and the opportunity to recover metals, along with cathodic reduction of protons to elemental hydrogen. This work describes the electrolysis of synthetic AMD solutions containing iron, copper and nickel and mixtures of these metals using a flow-through cell divided with an ion exchange membrane. Iron was successfully removed from a synthetic AMD solution composed of FeSO4/H2SO4 via Fe(OH)3 precipitation outside the electrochemical cell by sparging the electrolysed catholyte with air. The work was extended to acidic solutions of Fe2+, Cu2+, and Ni2+, both singly and in combination, and to an authentic AMD sample containing principally iron and nickel.

Photorearrangement of azoxybenzene to 2-hydroxyazobenzene: a convenient chemical actinometer

Abstract— In ethanolic solution, the intramolecular photorearrangement of azoxybenzene occurs with quantum yield close to 0.02 over the range 250–350 nm. The reaction, which is independent of temperature and of concentration of reactant, is conveniently monitored by measuring the absorbance of the product, 2‐hydroxyazobenzene, as its anion in alkaline solution.

Prospects for the use of electrochemical methods for the destruction of aromatic organochlorine wastes

This paper reviews the underlying science and the prospects for developing electrochemical technology to destroy chlorinated aromatic compounds. Direct and mediated electrolysis are considered, in both homogeneous and surfactant media, and a series of future research needs is identified.

Competition between electrochemical advanced oxidation and electrochemical hypochlorination of acetaminophen at boron-doped diamond and ruthenium dioxide based anodes

This work was undertaken to distinguish four pathways for the electrochemical oxidation of acetaminophen as a model organic substrate: (i) direct electron transfer from the substrate to the anode, (ii) reaction of the substrate with HO• at boron-doped diamond anodes, (iii) non-radical (two-electron) oxidation of the substrate at Ti/RuO2 anodes, and (iv) electrochemical hypochlorination if Cl– is present. Pathway (i) was isolated as a slow reaction when boron-doped diamond (BDD) was used as the anode in the range of water stability, whereas in the corresponding reaction with Ti/RuO2 only pathway (iii) could be detected. Pathway (ii) predominated for BDD in the potential range of water oxidation, and was the only mechanism leading to mineralization of the substrate. Comparison between chemical hypochlorination and electrochemical oxidation at Ti/RuO2 in the presence of chloride ion indicated that the latter process principally involves mediated hypochlorination. Oxidation at boron-doped diamond anodes in th...

Kinetic models for association of 2,3,7,8-tetrachlorodibenzo-p-dioxin with the Ah receptor

Saturation binding studies of the interaction between 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and the Ah receptor obtained from the hepatic cytosol of Wistar rats have been carried out. The conventional Scatchard analysis for determination of the equilibrium constant for ligand-receptor binding has been shown to be inappropriate due to thermal inactivation of the unoccupied receptor. Simulation models of the receptor-ligand binding kinetics which take into account receptor degradation have been developed and the results are consistent with two alternative kinetic models. In Model 1, reversible 2,3,7,8-TCDD-receptor binding occurs in parallel with inactivation of the unbound receptor; analysis of the observed data using this model suggests that the previously determined equilibrium constants (Kass) for association of the ligand with the receptor are orders of magnitude too low and the total initial receptor concentrations are somewhat underestimated. In Model 2, the unbound receptor is converted unimolecularly to an activated state which then undergoes competitive degradation or entrapment by ligand. Experiments have been carried out over the temperature range 4-37 degrees C, enabling activation parameters to be obtained. According to Scheme 1, the activation enthalpies for association of receptor with ligand and for thermal inactivation of the unoccupied receptor are high, and numerically almost identical (delta H++ ca 125 kJ mol-1). These reactions are strongly entropically driven and this is consistent with association being accompanied by a conformational change in the receptor protein, and the previously postulated binding of the ligand to a hydrophobic pocket. According to Scheme 2, there is only one enthalpy of activation because both inactivation and entrapment by 2,3,7,8-TCDD are fast processes which follow the same slow activation step. On the basis of this latter model, a 10(-9) M concentration of 2,3,7,8-TCDD is sufficient to trap roughly two-thirds of the activated receptors.

Photodechlorination of PCB's: Current status

Polychlorinated biphenyls (PCBs) are commonly used as an insulating medium for electric power transformers, in addition to a number of other industrial uses. This brief review summarizes current knowledge on the subject of PCB photochemistry. (JMT)

Screening assay for dioxin-like compounds based on competitive binding to the murine hepatic Ah receptor. 1. Assay development.

PCDDs, PCDFs, and related analytes were assayed by binding the analytes competitively with fixed aliquots of radiolabeled 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and C57BL/6 mouse hepatic Ah receptor. Additive binding to the receptor was observed for a wide range of structural types of chlorinated aromatic compounds. The results of the assays were expressed as TCDD equivalents, i.e., the concentration of unlabeled TCDD that would give the same assay as the mixture of analytes. The detection limit was approximately 100 pg of TCDD equivalent when the reference radioligand was [ 3 H] TCDD. The assay does not require prior knowledge of the identities of the components of the mixture and is intended for use as a prescreening tool ratherthan as a replacement for the conventional analysis by GC/MS.