Urs Jans

Activated Carbon and Carbon Black Catalyzed Transformation of Aqueous Ozone into OH-Radicals

Abstract In an ozone-containing water a suspension of a few milligrams per liter of activated carbon (AQ or carbon black (CB) initiates a radical-type chain reaction that then proceeds in the aqueous phase and accelerates the transformation of O3 into secondary radicals, such as hydroxyl radicals (°OH). This results in an Advanced Oxidation Process (AOP) that is similar to an O3-based AOP involving application of H2O2 or UV-irradiation. We have studied these phenomena by observing the effect of suspensions of AC and CB on the rate of transformation of O3 in lakewater and in well-characterized solutions. In addition, the stoichiometric yield factor of the AC-catalyzed conversion of O3, into °OH has been shown to be comparable to that which is achieved by a slower process in the absence of AC. This comparison has been based on the measured depletion of an O3-resistant organic °OH probe that was added as a trace reference compound and that competed with a kinetic excess of solutes that controlled the lifetim...

Investigation of the reaction of hexabromocyclododecane with polysulfide and bisulfide in methanol/water solutions

Reactions of hexabromocyclododecane (HBCD), a widely used brominated flame retardant, with reduced sulfur species (e.g., polysulfide and bisulfide) were investigated in well-defined solutions under anoxic conditions. It is likely that reactions of HBCD with reduced sulfur species such as polysulfides and bisulfide present in anoxic subregions of coastal water bodies and sediments could have a significant impact on the fate of HBCD. The second-order reaction rate constant of HBCD with polysulfides in 80% methanol/20% water at 40°C is 2.2 (±0.3)×10(-2) M(-1) s(-1). The second-order reaction rate constant of HBCD with bisulfide is 8.9 (±2.8)×10(-4) M(-1) s(-1) under the same conditions. The formation of two products was observed with either of the two reduced sulfur species. The experiments also indicate that the γ-isomer of HBCD is reacting significantly faster with reduced sulfur species than the α-isomer.

Reaction of Tris(2-chloroethyl)phosphate with Reduced Sulfur Species

Tris(2-chloroethyl)phosphates (TCEP) is a widely used flame retardant in the US. It has recently been identified as one of the most frequently detected contaminants in US streams. This contaminant is of toxicological concern in sensitive coastal ecosystems such as estuaries and salt marshes. It is likely that reactions with reduced sulfur species such as polysulfides (S(n)(2-)), bisulfide (HS(-)), and thiophenolate (PhS(-)) present in anoxic subregions of coastal water bodies could have a significant impact on rates of removal of such a contaminant. The kinetics of reaction of reduced sulfur species with tris(2-chloroethyl)phosphate have been determined in well-defined aqueous solutions under anoxic conditions. Reactions were monitored at varying concentrations of reduced sulfur species to obtain the second-order rate constants from the observed pseudo-first-order rate constants. The determined second-order rate constant for the reaction of TCEP with polysulfide at 25°C is 5.0 (±1.4)×10(-4) M(-1) s(-1), with thiophenolate at 50°C is 34 (±2)×10(-4) M(-1) s(-1) and with bisulfide at 50°C is 0.9×10(-4) M(-1) s(-1), respectively. In addition, the degradation products of hydrolysis and the reactions with polysulfides, thiophenolate, and bisulfide with TCEP were studied with GC-FID and LC-MS-MS and were quantified.

Emerging Brominated Flame Retardants in Sediments and Soils: a Review

Brominated flame retardants (BFRs) are an important class of commercial chemicals used in a wide variety of products. Several established BFRs are being phased out and replaced with new compounds that are often also brominated. These compounds are so-called emerging BFRs. Very little is known about these emerging BFRs. The analysis of these emerging compounds in environmental samples can provide valuable insight into their environmental behavior. This review summarizes the studies reporting the analysis of emerging BFRs in sediment and soil samples from 2012 to 2015. A list of the different emerging BFRs detected in sediment and soil samples along with their structure is shown. In addition, the different extraction methods used for sediments and soil samples, the various clean-up methods of the sample extracts, and the instrumental analytical techniques are presented.

Reaction of thiometon and disulfoton with reduced sulfur species in simulated natural environment

The reactions of thiometon and its ethyl analogue, disulfoton, with reduced sulfur species [e.g., bisulfide (HS-), polysulfide (S(n)2-), thiophenolate (PhS-), and thiosulfate (S2O3(2-))] were examined in well-defined aqueous solutions under anoxic conditions. The role of reduced sulfur species was investigated in the abiotic degradation of thiometon and disulfoton. Experiments at 25 degrees C demonstrated that HS-, S(n)2-, PhS-, and S2O3(2-) promoted the degradation of thiometon to a great extent while only S(n)2- and PhS- showed a small accelerating effect in the degradation of disulfoton. Reactions were monitored at varying concentrations of reduced sulfur species to obtain the second-order rate constants. The reactivity of the reduced sulfur species decreased in the following order: S(n)2- > PhS- > HS- approximately S2O3(2-). Transformation products were confirmed by standards or characterized by gas chromatography mass spectrometry. The results illustrate that multiple pathways occur in the reactions with reduced sulfur species, among which the nucleophilic attack at the alpha-carbon of the alkoxy group was the predominant pathway. Activation parameters of the reaction of thiometon and disulfoton with HS- were also determined from the measured second-order rate constants over a temperature range. DeltaH( not equal) values indicated that the reactivity of thiometon toward HS- was much greater than for disulfoton. Nucleophilic attack at the alkoxy group was more important for thiometon than disulfoton. When the measured second-order rate constants at 25 degrees C are multiplied by [HS-] and Sigma[S(n)2-] reported in saltmarsh porewaters, predicted half-lives show that reduced sulfur species present at environmentally relevant concentrations may present an important sink for thiometon in coastal marine environments.

Investigation of the Nucleophilic Attack of Dichlorvos by Reduced Sulfur Species Using 1H NMR

The mechanism of the reaction of dichlorvos through hydrolysis reactions and through the reaction with polysulfide (Sn2-) and thiophenolate (PhS-) was investigated by proton nuclear magnetic resonance (1H NMR). The study confirmed product identities of an organophosphorus insecticide reacting with reduced sulfur species using 1H NMR in oxygen sensitive solutions. The experiments of dichlorvos with polysulfide led to the detection of a previously undetected product. The thiophenolate experiments were further advanced to investigate second-order rate kinetics using an internal standard. The experiments provide new evidence for a nucleophilic attack by the reduced sulfur species at the methoxy carbon of dichlorvos. In addition, the observation of in situ reaction dynamics illustrates the applicability of 1H NMR spectroscopy toward kinetic investigations in environmental science.

Reactions of three halogenated organophosphorus flame retardants with reduced sulfur species

Tris(haloalkyl)phosphates (THAPs) are among the most widely used flame retardants in the U.S. They have been identified as one of the most frequently detected contaminants in U.S. streams. These contaminants are of toxicological concern in sensitive coastal ecosystems such as estuaries and salt marshes. It is likely that reactions with reduced sulfur species such as polysulfides (Sn(2-)) and bisulfide (HS(-)), present in anoxic subregions of coastal water bodies could have a significant impact on rates of removal of such contaminants, especially since no significant degradation reactions in the environment (e.g., hydrolysis, biological degradation) is reported for these compounds. The kinetics of the reaction of reduced sulfur species with three structurally related THAPs have been determined in well-defined aqueous solutions under anoxic conditions. Reactions were monitored at varying concentrations of reduced sulfur species to obtain second-order rate constants from the observed pseudo-first order rate constants. The degradation products were studied with GC-FID and LC-MS. The reactivity of Sn(2-), thiophenolate, and HS(-) were compared and steric, as well as electronic factors are used to explain the relative reactivity of the three THAPs with these three sulfur species.

Oxalate Ion Decomposition under UV Light from Low Pressure Mercury Vapor Lamps

Kinetics of oxalate ion decomposition under UV light from low pressure mercury vapor lamps (LPMVL) was studied in a batch reactor. The effects of UV light intensity (1.38×10−6 to 5.27×10−6 EL−1s−1, where E: Einstein or 1 mole of photons), temperature (15−35°C), initial oxalate concentration ((2.05−21.1) × 10−5 M), initial pH (5.45−8.94) and alkalinity (0–50 mg L−1 as CaCO3) on the photodecomposition kinetics of oxalate in de-ionized water were investigated. Oxalate decay followed split-rate pseudo-first-order kinetics. The decay rate constants decreased with increasing initial oxalate concentration, initial pH, alkalinity and temperature, but increased with UV light intensity. Solution pH increased during oxalate decomposition and reached a plateau as oxalate reached the analytical detection limit in de-ionized water. Addition of carbonate alkalinity virtually eliminated the pH profile. Time-dependent profiles for non-purgeable organic carbon (NPOC) and total carbon (TC) showed that the carbon not accounted for in NPOC is likely to have been converted to CO2. The pH profile of oxalate decay was estimated using closed system carbonate equilibrium analysis. The dissolved oxygen (DO) utilization during oxalate decay ranged between 0.3–0.8 mol O2 / mol oxalate. The effect of DO and the decay of natural dissolved organic carbon (DOC) were also explored. Natural DOC retarded oxalate photodecomposition. The decay rate constants were slightly lower in the absence of DO.