Total Halogen Research Articles

Evaluation of hexabromocyclododecane (HBCD), polybrominated dibenzo-p-dioxins/furans (PBDD/Fs) and polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) outflows during the destruction of HBCD wastes in a hazardous waste incinerator

This paper presents an evaluation of hexabromocyclododecane (HBCD), polybrominated dibenzo-p-dioxins/furans (PBDD/Fs) and polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) outflows during the destruction of HBCD waste stockpiles in IZAYDAS Hazardous Waste Incinerator (HWI) in Kocaeli, Türkiye. HBCD wastes containing 100 % pure HBCD were in 25 kg packages with 63 % Br content were co-incinerated in a 3-day test burn with average feed rate of 26 kg/h. HBCD, PBDD/Fs and PCDD/Fs were measured in the outlet streams to quantify the amount of unintended POPs releases associated with the processing of HBCD waste and to observe the POP removal performance of air pollution control equipment (APCE) of the incinerator. Total mass outflow rate of HBCDs is calculated as 2.6 g/day, corresponding to destruction efficiency of 99.9996 %. Total toxicity of the brominated dioxins was measured as 0.00044 ng TEQ/Nm3 on average, while highly brominated congeners are dominant. PCDD/F concentrations in the outflow streams during HBCD test burns are produced similar congener distributions with those given in the previous studies, with the dominance of 7,8-chlorinated congeners. Mass flows in the outlet streams indicated that the efficiency of ESP and wet scrubbers for the removal of PCDD/Fs and HBCDs. Flue gas concentrations of PCDD/Fs, HBCDs and PBDD/Fs obtained in HBCD burn test indicated that burning HBCD wastes cause no significant emissions as operational parameters and total halogen content in the menu are kept within the incinerator limits.

Simultaneous removal of brominated and chlorinated species during the production of oils by e-waste plastics catalytic hydropyrolysis

The production of added-value chemicals via pyrolysis of plastic wastes, such as those from electrical and electronic equipment (WEEE), needs addressing their usual contamination with halogens (mainly Br and Cl). This work compares the conversion via pyrolysis and hydropyrolysis of a real WEEE plastic, having a complex composition, in two different reactor configurations: down-flow (DF) and up-flow (UF). Likewise, the effects of incorporating a Pd/Al2O3 catalyst and using two different pressures (1 and 6 bar) have been assessed. With the DF mode, pyrolysis at 1 bar leads to an oil yield above 80 wt% and a total halogen content of about 600 ppm (vs 1600 ppm in the water-washed WEEE plastic). Under DF catalytic hydropyrolysis at 6 bar, this high oil yield is maintained while its dehalogenation degree is improved (142 ppm). Operating with the up-flow configuration, under 6 bar and H2 presence, leads to some reduction in the oil yield (about 70 wt%) but significantly decreases the oil halogen content (55 ppm Cl and total elimination of Br). These results have been related to the slower pyrolysis and longer residence time in the thermal zone of the UF configuration, which favours the halogen-trapping effect of the char fraction, and the pressure-enhanced hydrodehalogenation activity of the catalyst. This study highlights the environmental benefits of the proposed process, emphasizing the lower halogen content in the resulting oils and promoting a more sustainable approach to plastic waste valorisation.

Observational Evidence of Unknown NOx Source and Its Perturbation of Oxidative Capacity in Bermuda's Marine Boundary Layer

AbstractNitrogen oxides (NOx) are key intermediates in the atmospheric cycling of reactive nitrogen, the spatiotemporal distribution of which modulates ozone (O3) production. Field campaigns were conducted at the Tudor Hill Marine Atmospheric Observatory, Bermuda, in the spring and summer of 2019 to explore atmospheric cycling of NOx and its modulation of photochemical O3 production in the marine boundary layer. In aged, clean marine air, an atypical NO2 diel profile with a solar noon peak of 69 ± 5 pptv was recorded, challenging the classic U‐shaped diel profile with a solar noon valley characterized by fast photolysis and oxidation consumption in the daytime. This result indicated an unknown daytime NOx source excluded from the current near‐explicit chemical model, which underestimated the solar noon NOx level by 20–56 pptv and source rate by 9.7–33.5 pptv hr−1, considering the upper and lower limits of total OH reactivity and halogen photochemistry in the marine boundary layer. The observed HONO level accounted for ∼56% of the unknown NOx source, implying an unknown NOx regeneration pathway with HONO as an intermediate. The photochemical nature of the unknown NOx source maximized perturbation of photochemical OH and O3 production. The O3 abundance and production rate were underestimated by 2–4 ppbv and 28%–80%, respectively, and the OH abundance and source rate were 7%–55% and 21%–57% lower than the estimated levels with the constraint of NOx, respectively. The unknown NOx source requires urgent revision of the current understanding of reactive nitrogen cycling and the oxidative capacity of the clean marine atmosphere.

Potential of Microbial Communities to Perform Dehalogenation Processes in Natural and Anthropogenically Modified Environments-A Metagenomic Study.

Halogenated organic compounds (HOCs) pose a serious problem for the environment. Many are highly toxic and accumulate both in soil and in organisms. Their biological transformation takes place by dehalogenation, in which the halogen substituents are detached from the carbon in the organic compound by enzymes produced by microorganisms. This increases the compounds' water solubility and bioavailability, reduces toxicity, and allows the resulting compound to become more susceptible to biodegradation. The microbial halogen cycle in soil is an important part of global dehalogenation processes. The aim of the study was to examine the potential of microbial communities inhabiting natural and anthropogenically modified environments to carry out the dehalogenation process. The potential of microorganisms was assessed by analyzing the metagenomes from a natural environment (forest soils) and from environments subjected to anthropopression (agricultural soil and sludge from wastewater treatment plants). Thirteen genes encoding enzymes with dehalogenase activity were identified in the metagenomes of both environments, among which, 2-haloacid dehalogenase and catechol 2,3-dioxygenase were the most abundant genes. Comparative analysis, based on comparing taxonomy, identified genes, total halogens content and content of DDT derivatives, demonstrated the ability of microorganisms to transform HOCs in both environments, indicating the presence of these compounds in the environment for a long period of time and the adaptive need to develop mechanisms for their detoxification. Metagenome analyses and comparative analyses indicate the genetic potential of microorganisms of both environments to carry out dehalogenation processes, including dehalogenation of anthropogenic HOCs.

Characterizing the Organohalogen Iceberg: Extractable, Multihalogen Mass Balance Determination in Municipal Wastewater Treatment Plant Sludge.

The large number and diversity of organohalogen compounds (OHCs) occurring in the environment poses a grand challenge to analytical chemists. Since no single targeted method can identify and quantify all OHCs, the size of the OHC "iceberg" may be underestimated. We sought to address this problem in municipal wastewater treatment plant (WWTP) sludge by quantifying the unidentified fraction of the OHC iceberg using targeted analyses of major OHCs together with measurements of total and extractable (organo)halogen (TX and EOX, respectively; where X = F, Cl, or Br). In addition to extensive method validation via spike/recovery and combustion efficiency experiments, TX and/or EOX were determined in reference materials (BCR-461 and NIST SRMs 2585 and 2781) for the first time. Application of the method to WWTP sludge revealed that chlorinated paraffins (CPs) accounted for most (∼92%) of the EOCl, while brominated flame retardants and per- and polyfluoroalkyl substances (PFAS) accounted for only 54% of the EOBr and 2% of the EOF, respectively. Moreover, unidentified EOF in nonpolar CP extracts points to the existence of organofluorine(s) with physical-chemical properties unlike those of target PFAS. This study represents the first multihalogen mass balance in WWTP sludge and offers a novel approach to prioritization of sample extracts for follow-up investigation.

Determination of trace organic chlorides in hydrogen for fuel cell vehicles by gas chromatography coupled with ion mobility spectrometry.

A method for the determination of organic chlorides in hydrogen for fuel cell vehicles by gas chromatography coupled with ion mobility spectrometry was established. Organic chlorides were separated by a non-polar gas chromatography column and detected in the negative ion mode of the ion mobility spectrometer. The effect of operating parameters of ion mobility spectrometer including drift gas flow rate and drift tube temperature on sensitivity and resolution were evaluated. Under the optimized conditions, the detection limits of seven organic chlorides were from 0.65 to 6.73nmol/mol, which met the requirement of detection for the specification limit of 50nmol/mol of total halogen impurities in hydrogen for fuel cell vehicles. Compared with gas chromatography-mass spectrometry, and gas chromatography coupled with electron capture detector under the same gas chromatography conditions, gas chromatography coupled with ion mobility spectrometry method demonstrated higher sensitivity for detection of organic chlorides under study. Based on the portability of the device and its detection capabilities, gas chromatography coupled with ion mobility spectrometry has the potential to perform online detection of impurities in hydrogen for fuel cell vehicles.

Impact of abiotic and biogeochemical processes on halogen concentrations (Cl, Br, F, I) in mineral soil along a climatic gradient.

In contrast to earlier ideas that halogens behave inertly in soil, extensive biogeochemical cycling of fluorine (F), chlorine (Cl), bromine (Br) and iodine (I) has been shown for temperate forests. To further advance our understanding of halogen behaviour in soil beyond humid temperate forests, we sampled soil profiles in protected areas along the Chilean Coastal Cordillera, representing a pronounced climatic gradient spanning from arid to humid. Halogen concentrations in soil were analysed by combustion ion chromatography. Highest average total halogen concentrations occurred at the arid site (Cl, F: 4270 and 897 mg kg-1) as well as the humid end of the climatic gradient (Br, I: 42.6 and 9.8 mg kg-1). Vertical distribution patterns of halogens were most pronounced at the humid end of the gradient and became less distinct under drier climate. The climatic gradient demonstrates the important role of biotic processes (e.g. the halogenation of organic matter) on the retention of halogens in the soil. However, this climate-specific role may be overridden by mainly abiotic processes within a given climate zone (e.g. weathering, leaching, sorption to secondary soil minerals, evaporative enrichment), resulting in vertical relocation of halogens in the soil. Since some of these processes oppose each other, complex interactions and depth distributions of F, Cl, Br and I occur in the soil. In summary, our findings provide new insights into the fate of halogens in mineral soil of different climatic zones, which is important, for example, when radiohalogens are deposited on a large scale after nuclear accidents.

Halogen (F, Cl, Br, I) contents in silt and clay fractions of a Cambisol from a temperate forest

AbstractIn spite of considerable efforts to understand the role of halogens (F, Cl, Br, I) in soil, concentration data for different soil size fractions is still sparse and information on the sorption behavior of halogens in natural soils is limited. We determined total halogen concentrations in different soil horizons and particle size fractions (i.e., coarse silt with 20–63 µm, medium and fine silt with 2–20 µm, coarse clay with 0.2 to <2 µm and medium clay with 0.02–0.2 µm) of a Cambisol from a temperate forest ecosystem in SW Germany. Furthermore, we estimated the minimum proportions of sorbed halogens onto clay minerals and pedogenic oxides for different soil horizons and different particle size fractions.Vertical depth profiles of halogens in the individual soil particle size fractions matched with the bulk soil vertical patterns. The lack of vertical differences of total halogens concentrations (Ftot, Brtot, and Itot) in the mineral soil during soil development may be due to steady state or equilibrium conditions between weathering, sorption processes, and surface input. In contrast, the vertical depth pattern of Cltot tended to decrease, suggesting the process of Cl accumulation in the topsoil and nutrient uplift. While F was likely mainly incorporated into the crystal lattice of clay minerals and gibbsite occupying OH-sites, significant amounts of the halogens with larger ionic radii (Cl, Br, and I) were sorbed. The largest amounts (around 90% Cl and 70% Br and I, respectively) were sorbed on the smallest particle size fraction investigated (medium clay fraction; 0.02–0.2 µm), although this fraction only contributed about 1 wt% to the bulk soil. This is probably related to the highest sorption capacity of small particles due to their large surface area.Our study provides new data on sorption behavior of the various halogens in soils of forest ecosystems, which is different between F and the heavier halogens (Cl, Br, I) and further depends on soil particle sizes. The understanding of the chemical behavior of halogens in soils has implications for the retention processes of pollutants in landfills or radioactive waste disposal.

Halogen activation in the plume of Masaya volcano: field observations and box model investigations

Abstract. Volcanic emissions are a source of halogens in the atmosphere. Rapid reactions convert the initially emitted hydrogen halides (HCl, HBr, and HI) into reactive species such as BrO, Br2, BrCl, ClO, OClO, and IO. The activation reaction mechanisms in the plume consume ozone (O3), which is entrained by ambient air that is mixed into the plume. In this study, we present observations of the oxidation of bromine, chlorine, and iodine during the first 11 min following emission, examining the plume from Santiago crater of the Masaya volcano in Nicaragua. Two field campaigns were conducted: one in July 2016 and one in September 2016. The sum of the reactive species of each halogen was determined by gas diffusion denuder sampling followed by gas chromatography–mass spectrometry (GC-MS) analysis, whereas the total halogens and sulfur concentrations were obtained by alkaline trap sampling with subsequent ion chromatography (IC) and inductively coupled plasma mass spectrometry (ICP-MS) measurements. Both ground and airborne sampling with an unoccupied aerial vehicle (carrying a denuder sampler in combination with an electrochemical SO2 sensor) were conducted at varying distances from the crater rim. The in situ measurements were accompanied by remote sensing observations (differential optical absorption spectroscopy; DOAS). The reactive fraction of bromine increased from 0.20 ± 0.13 at the crater rim to 0.76 ± 0.26 at 2.8 km downwind, whereas chlorine showed an increase in the reactive fraction from (2.7 ± 0.7) × 10−4 to (11 ± 3) × 10−4 in the first 750 m. Additionally, a reactive iodine fraction of 0.3 at the crater rim and 0.9 at 2.8 km downwind was measured. No significant change in BrO / SO2 molar ratios was observed with the estimated age of the observed plume ranging from 1.4 to 11.1 min. This study presents a large complementary data set of different halogen compounds at Masaya volcano that allowed for the quantification of reactive bromine in the plume of Masaya volcano at different plume ages. With the observed field data, a chemistry box model (Chemistry As A Boxmodel Application Module Efficiently Calculating the Chemistry of the Atmosphere; CAABA/MECCA) allowed us to reproduce the observed trend in the ratio of the reactive bromine to total bromine ratio. An observed contribution of BrO to the reactive bromine fraction of about 10 % was reproduced in the first few minutes of the model run.

Automated ICP-MS method to measure bromine, chlorine, and iodine species and total metals content in drinking water

The disinfection of drinking water is an important aspect to human health. However, this process leads to potentially harmful disinfection by-products that should be monitored prior to drinking water reaching homes and businesses. Agencies such as the World Health Organization and United States Environmental Protection Agency set recommended levels for disinfection by-products and trace elements to keep the consumer healthy. In this work a single platform, automated total metals (adapted EPA 6020B method) and halogen speciation method is presented for water analysis that can help laboratories become more efficient while providing new capabilities. Samples from around the Atlanta, GA, USA region were collected and analyzed to investigate the effects of the local counties’ water before and after the water treatment processes. The detection limits for this method were found to be 29 ng L−1 bromide, 31 ng L−1 bromate, 5.5 ng L−1 iodide, 1.8 ng L−1 iodate, 0.7 µg L−1 chloride, 2.6 µg L−1 chlorite, 6.8 µg L−1 chlorate, and 9.5 µg L−1 perchlorate. This halogen speciation method is completed in under 3 min per sample and can be automated into a single analytical run with trace elemental analysis when combined with an ICP-MS.

Halogens in amphibole and mica from mantle xenoliths: Implications for the halogen distribution and halogen budget of the metasomatized continental lithosphere

Abstract This study reports halogen contents (F and Cl) of amphibole and phlogopite derived from mantle xenoliths and one peridotite massif, for amphibole and phlogopite megacrysts and ultramafic magmatic cumulates (hornblendites) found in alkaline volcanic rocks from 12 localities in Europe and Africa. Amphibole and phlogopite contain more F than Cl with F/Cl ratios reaching about 160 in phlogopites and 50 in amphiboles. Phlogopites are higher in F (median of 3400 μg/g) than amphibole (median of 1000 μg/g), while median Cl contents are higher in amphibole (290 μg/g) compared to phlogopite (180 μg/g). The Cl contents and the F/Cl ratios in amphibole and phlogopite from mantle xenoliths exhibit large differences between samples of the same region, recording very large variations of halogen contents in the continental lithosphere. We suggest that the halogen content in such samples largely depends on the initial composition of percolating melts and fluids in the continental lithosphere. During reaction of these agents with peridotitic wall-rocks, Cl is preferentially retained in the fluid as it is much more incompatible compared to water and F. This desiccation effect continuously increases salinity (Cl content) and decreases the F/Cl ratio in the agent with time, causing variable Cl contents and F/Cl ratios in amphibole and phlogopite at a specific locality. Subsequent partial melting processes may then sequester and re-distribute, especially Cl among amphibole, phlogopite and melts/fluids as a result of its strong incompatibility, whereas F is much less affected as it behaves slightly compatible. The impact of even small amounts of amphibole and mica on the total halogen budget in the continental lithosphere is significant and both minerals can effectively contribute to the high halogen contents typical of alkaline melts.

Vegetation canopy effects on total and dissolved Cl, Br, F and I concentrations in soil and their fate along the hydrological flow path

Although halogens are omnipresent in the environment, detailed understanding of processes involving chlorine (Cl), bromine (Br), fluorine (F) and iodine (I) in the terrestrial halogen cycle is still sparse. Our objectives were to (i) assess vertical depth profiles of total and water-extractable inorganic halogen concentrations (Cltot, Brtot, Ftot, Itot) in solid soil, (ii) test the effect of a tree canopy, and (iii) follow the fate of dissolved inorganic halogens along the hydrological flow path. More than 200 soil samples and ecosystem solutions (rainwater, soil solution, adit and creek water) collected in the Schwarzwald, SW Germany, were analyzed by combustion ion chromatography and ion chromatography for total and inorganic halogen concentrations.We found decreasing Cltot concentrations with increasing soil depth which were indicative of biological chlorination of organic matter and nutrient uplift, both associated with Cl accumulation in upper soil horizons. Vertical patterns of total Br, F and I were contrary to Cltot concentrations and were related significantly (positively) to pedogenic oxides, revealing their dependence on abiotic processes. The presence of a canopy at our study site resulted in significantly higher halogen concentrations in throughfall compared to rainfall and higher Brtot concentrations in the organic layer. We attribute this difference to leaching from leaves and needles and wash-off of dry deposition. There were hardly any differences in halogen concentrations along the hydrological flow path except for significantly higher inorganic I concentrations in soil solution compared to rainfall due to equilibrium reactions between the soil solution and the solid soil phase. Highest inorganic F concentrations of up to 0.2 mg L−1 were detected in creek water samples and may originate from the weathering of fluorite-bearing veins. Our study indicates halogen-specific processes underlying Cl, Br, I and F cycling in ecosystems.

ON MECHANISMS OF OXYGEN INFLUENCE ON GAS-PHASE PARAMETERS AND SILICON REACTIVE-ION ETCHING KINETICS IN HBr + Cl2 + O2 PLASMA

The effects of both HBr/O2 and Cl2/O2 mixing ratios in HBr+Cl2+O2 gas mixture on plasma parameters, steady-state densities of active species and Si etching kinetics were studied under the typical conditions of reactive ion etching process: total gas pressure (p = 10 mTorr), input power (W = 500 W), bias power (Wdc = 200 W). The data on internal plasma parameters and plasma chemistry were obtained using a combination of Langmuir probe diagnostics and 0-dimensional (global) plasma modeling. It was found that the variation in HBr/O2 mixing ratio at constant Cl2 fraction in a feed gas is characterized by the stronger impact on the steady-state plasma composition through both electron-impact and atom-molecular reaction kinetics as well as allows one to obtain the wider change in the total halogen atom density. It was shown that changes in both HBr/O2 and Cl2/O2 mixing ratios toward O2-rich plasmas lowers the Si etching rate that exhibits no evident correlations with total halogen atom flux and ion energy flux. The model-based analysis of Si etching kinetics allowed one to conclude that the effective reaction probability for Si + Cl/Br heterogeneous reaction depends on the flux of oxidative species – oxygen atoms and OH radicals. The reasons may be 1) the oxidation of silicon resulting in higher reaction threshold energy; and 2) the decreasing fraction of free adsorption sites for Cl/Br atoms due to the oxidation of reaction products into the lower volatile SiBrxOy and SiClxOy compounds.

Radiant characteristics of high power excilamps with binary exciplexes of XeCl and XeBr

The characteristics of the coaxial binary excilamps containing two exciplexes of XeCl* and XeBr* were studied based on the dielectric barrier discharge with various annular gap, driven by sinusoidal electronic control gear. The effect of the gas pressure, halogen fraction, and discharge gap were investigated. The optimum total pressure is 150–200 mbar and 200–250 mbar for 308 nm and 282 nm, respectively, leading to about 200 mbar for the total radiant efficiency. The optimized total halogen percentage is in range of 0.2%–0.3%, which is slightly increased, with a higher bromine ratio. Additionally, the radiant efficiency shows weak dependence on the discharge gap.

Plasma parameters, gas-phase chemistry and Si/SiO2 etching mechanisms in HBr+Cl2+O2 gas mixture: Effect of HBr/O2 mixing ratio

Features of plasma chemistry as well as peculiarities of etching mechanisms for Si and SiO2 in the HBr + Cl2 + O2 gas mixture with variable HBr/O2 mixing ratio were investigated using a combination of experimental and theoretical approaches. Plasma diagnostics by Langmuir probe and 0-dimensional (global) plasma modeling provided the information on gas-phase plasma parameters, formation/decay kinetics of plasma active species and the steady-state plasma composition. It was found that the substitution of HBr for O2 at constant Cl2 fraction in a feed gas 1) leads to a weak increase in electron density, ion density and the ion energy flux; 2) influences the kinetics of neutral species through reactions involving O atoms and their reaction products; and 3) results in increasing total halogen atom density. It was shown also that the change in HBr/O2 mixing ratio causes the opposite behaviors of Si and SiO2 etching rates and lifts the SiO2/Si etching selectivity up to ∼10 in highly oxygenated plasmas. The analysis of Si and SiO2 etching kinetics with model-predicted fluxes of plasma active species indicated the different etching mechanisms for these materials.

Highly fluorescent carbon dots synthesized with binary dopants for “turn off” and “turn off-on” sensing and cell imaging

In the present study, highly fluorescent carbon dots were prepared by using citric acid as the carbon source with the binary dopants, i.e. melamine and formaldehyde, named as MF-CDs. The co-dopants played a crucial role to enhance the fluorescence quantum yield of the MF-CDs, reaching 48%, in which melamine was the major nitrogen source, while formaldehyde was the co-dopant to regulate the state of nitrogen in the MF-CDs. The fluorescence of the MF-CDs was found to be quenched by Hg2+, and then recovered equally by individual halogen ions (eg. Cl−, Br− and I−). Correspondingly, the “turn off” and “turn off-on” sensing systems were separately established to detect Hg2+ and total halogen ions with good accuracy and reliability. In addition, the fluorescence of the MF-CDs was quenched by ClO−, and recovered by Fe2+; the “turn off” sensor was established to detect ClO− in tap water with low limit of detection of 0.18 μM, and the “turn off-on” sensor was to determine the ferrous succinate in ferrous succinate tablets. Furthermore, owing to the low cytotoxicity, the MF-CDs were successful for cellular labeling on HepG2 cells. The developed binary dopants were effective to enhance the fluorescence quantum yield and endow the MF-CDs with some special properties, which would help to widen the applicability of the carbon dots.

Waste oil management: Analyses of waste oils from vehicle crankcases and gearboxes

In accordance with waste strategy for Turkey, the study was carried out to analyses waste engine crankcase oils and waste gearbox oils generated from vehicle maintenance services in order to determine their suitability for recycling, recovery or final disposal based on regulation published by Turkish Ministry of Environment and Forestry on 21 January 2004. The regulation requires all waste oil neither abandoned nor released into the environment and all batches must be analyzed for arsenic, cadmium, chromium, lead, chlorine, total halogens, polychlorinated biphenyls, and flash points. The content analysis showed that the heavy metal concentrations in waste engine crankcase oils were varied considerably, between the metals analyzed, lead the highest is followed by chromium, arsenic and cadmium. In addition, higher amount of chlorine and total halogens, were detected in some samples, while polychlorinated biphenyls concentrations remained below regulatory limits for all samples. The analyses revealed that waste engine crankcase oils from fifteen to thirty five years old vehicles contained chromium, lead, chlorine and total halogens levels above legal limits set by Ministry of Environment and Forestry for recycling. Conversely, in comparison to the findings from the analyzed series of old vehicles, the waste engine crankcase oils samples from new vehicles and all waste gearbox oils are eligible for recycling.

Transformer Oils Potential for PCBs Contamination

Polychlorinated biphenyls (PCBs) are a class of synthetic organic chemicals consisting of from one to ten chlorine atoms bonded totwo phenyl rings that create up 209 possible variations referred to as congeners. PCBs were commercially produced world-wide on a large scale between the 1930s and 1980sthat had been used widely in variety of commercial equipment like transformers, capacitors and other electrical equipment because of their useful quality as being a fire retardant. But due to their persistence and ubiquitous distribution in the environment, PCBs were banned from the U.S in the 1970s and internationally through the Stockholm Convention on Persistent Organic Pollutants. Although banned by law and punished heavily, large numbers of PCB-contaminated transformers are still in service. Thus, there remains a huge reservoir of PCBs with the potential to serve as sources of contamination to the environment. In this study, using EN 12766 test method: “Petroleum products and used oils-Determination of PCBs and related products”, PCBs were analyzed in the random samples collected from different regions of Turkey. The samples also used for screening for the presence of total halogens and chlorine. Test results of the study showed that PCBs were present in certain transformers but concentrations in the most of samples did not exceed the limit value of 50 ppm.However, there was a significant relationship between the PCB concentrationsand the halogens.Finally, the contaminated transformer oils were evaluated according to Regulation on Control ofWaste Oils.

Experimental Design Optimization of the Determination of Total Halogens in Coal by Combustion–Ion Chromatography

Determination of total halogens in coal was investigated with oxygen bomb combustion followed by ion chromatography. Experimental parameters were optimized by fractional factorial design and response surface methodology. Fractional factorial design was employed in screening experiments to evaluate the influence of the oxygen pressure, catalyst, absorption solution, reduction reagent, bomb cooling time, and a combustion aid on the combustion of coal in an oxygen bomb. Response surface methodology was conducted to further refine the results obtained by fractional factorial design and to define parameters for the procedure. The accuracy and precision of combustion with ion chromatography were evaluated by the use of two certified reference materials and by fortified in-house coal standards. The limits of detection and quantification for total halogens were 0.84 and 2.80 milligrams per kilogram, respectively, for 500 milligram samples. Ion chromatography provided relative standard deviations less than 4 percent, recoveries exceeding 95 percent, and was convenient. This method is recommended for routine determination of total halogens in coal because of its reliability.

Revealing halogen bonding interactions with anomeric systems: An ab initio quantum chemical studies

A computational study has been performed using MP2 and CCSD(T) methods on a series of O⋯X (X=Br, Cl and I) halogen bonds to evaluate the strength and characteristic of such highly directional noncovalent interactions. The study has been carried out on a series of dimeric complexes formed between interhalogen compounds (such as BrF, BrCl and BrI) and oxygen containing electron donor molecule. The existence and consequences of the anomeric effect of the electron donor molecule has also been investigated through an exploration of halogen bonding interactions in this halogen bonded complexes. The ab initio quantum chemical calculations have been employed to study both the nature and directionality of the halogen molecules toward the sp3 oxygen atom in anomeric systems. The presence of anomeric nO→σ*CN interaction involves a dominant role for the availability of the axial and equatorial lone pairs of donor O atom to participate with interhalogen compounds in the halogen-bonded complexes. The energy difference between the axial and equatorial conformers with interhalogen compounds reaches up to 4.60kJ/mol, which however depends upon the interacting halogen atoms and its attaching atoms. The energy decomposition analysis further suggests that the total halogen bond interaction energies are mainly contributed by the attractive electrostatic and dispersion components. The role of substituents attached with the halogen atoms has also been evaluated in this study. With the increase of halogen atom size and the positive nature of σ-hole, the halogen atom interacted more with the electron donor atom and the electrostatic contribution to the total interaction energy enhances appreciably. Further, noncovalent interaction (NCI) studies have been carried out to locate the noncovalent halogen bonding interactions in real space.