Thermochemical properties and phase behavior of halogenated polycyclic aromatic hydrocarbons

Formation Enthalpies of C3 and C4 Brominated Hydrocarbons: Bringing Together Classical Thermodynamics, Modern Mass Spectrometry, and High-Level Ab Initio Calculations

The enthalpies of formation of brominated C3-C4 hydrocarbons were critically evaluated using experimental data sources ranging from classical thermodynamics methods to modern high-precision mass spectrometry and reported in a time span of a century. The experimental data were used in conjunction with the results of modern high-level ab initio calculations. To facilitate quantitative analysis, a recently developed local coupled cluster-based computational protocol was extended to organic compounds containing univalent Br. Several erroneous data sources were identified in a course of the study. Possible reasons for the inconsistency between the ΔfHm° values recommended by the Committee on Data of the International Science Council (CODATA) and Active Thermochemical Tables for HBr in the gas and aqueous solution were discussed. The most up-to-date recommendations based on the comprehensive analysis of collected information are provided for 23 brominated hydrocarbons. For several compounds under consideration, the recommended values were previously lacking, while improved values and uncertainties were obtained for those with existing recommendations.

Diabetes: a potential mediator of associations between polycyclic aromatic hydrocarbon exposure and stroke

Epidemiological evidence suggests associations between exposure to polycyclic aromatic hydrocarbons (PAHs) and cardiovascular diseases (CVD), while diabetes is a common risk factor for CVD. The present study aims to clarify the effect of high PAH exposure on diabetes and stroke in general population. A total of 7849 individuals aged 20 years or older from the National Health and Nutrition Examination Survey 2007-2016 were included in the study. The logistic regression analysis modeled the association between PAH exposure and diabetes as well as stroke. The analysis yielded odds ratios (ORs) and 95% confidence intervals (CIs). The study also evaluated the potential mediating role of diabetes in the relation between PAH exposure and stroke via mediating effect analyses. Of the 7849 eligible participants, 1424 cases of diabetes and 243 cases of stroke were recorded. After adjusting for covariates including age, gender, smoking status, drinking status, education level, marital status, physical activity, hypertension, low-density lipoprotein cholesterol, and BMI, the ORs for stroke in the highest quartile (Q4) of total urinary PAHs were 1.97 (95% CI 1.11-3.52, P = 0.022) as compared to the lowest quartile (Q1) of total urinary PAHs. The ORs for diabetes in the Q4 of total urinary PAHs were 1.56 (95% CI 1.15-2.12, P = 0.005), while the ORs between Q4 and Q1 for stroke and diabetes concerning exposure to 2-hydroxynaphthalene were 2.23 (95% CI 1.17-4.25, P = 0.016) and 1.40 (95% CI 1.07-1.82, P = 0.015), respectively. The mediation analysis found that diabetes accounted for 5.00% of the associations between urinary PAHs and the prevalence of stroke. Urinary metabolites of PAH have been linked to stroke and diabetes. Increasing the risk of diabetes may play a significant role in mediating the association between exposure to PAHs and increased risk of stroke. Monitoring and improving glucose metabolism in individuals with high exposure to PAHs may aid in reducing the prevalence of stroke.

Application of gas chromatographic retention times to determine physicochemical properties of nitrated, oxygenated, and parent polycyclic aromatic hydrocarbons

Nitrated and oxygenated polycyclic aromatic hydrocarbons (NPAHs and OPAHs) are receiving attention because of their high toxicity compared with parent PAHs. However, the experimental data of their physicochemical properties has been limited. This study proposed the gas chromatographic retention time (GC-RT) technique as an effective alternative one to determine octanol-air partition coefficients (K_OA) and sub-cooled liquid vapor pressures (P_L) for 11 NPAHs, 10 OPAHs, and 19 parent PAHs. The slopes and intercepts of the linear regressions between temperature versus K_OA and P_L were provided and can be used to estimate K_OA and P_L for the 40 targeted compounds at any temperature. The internal energies of phase transfer (ΔU_OA) and enthalpies of vaporization (ΔH_L) for all targeted compounds were also calculated using the GC-RT technique. High-molecular-weight compounds may release or absorb higher heat energy to transform between different phases. NPAHs and OPAHs had a non-ideal solution behavior with activity in octanol (γ_oct) in the range of 19-53 and 18-1,078, respectively, which is larger than the unity threshold. A comparison among four groups of PAH derivatives showed that a functional group (nitro-, oxygen-, chloro-, and bromo-) in PAH derivatives increased γ_oct for corresponding parent PAHs by tens (mono-group) to hundreds of times (di-group). This study suggests that the GC-RT method is applicable for indirectly measuring the physicochemical properties of various groups of organic compounds.

Atmospheric deposition of chlorinated and brominated polycyclic aromatic hydrocarbons in central Europe analyzed by GC-MS/MS

Chlorinated and brominated polycyclic aromatic hydrocarbons (ClPAHs and BrPAHs) are persistent organic pollutants that are ubiquitous in the atmospheric environment. The sources, fate, and sinks in the atmosphere of these substances are largely unknown. One of the reasons is the lack of widely accessible analytical instrumentation. In this study, a new analytical method for ClPAHs and BrPAHs using gas-chromatography coupled with triple quadrupole mass spectrometry is presented. The method was applied to determine ClPAHs and BrPAHs in total deposition samples collected at two sites in central Europe. Deposition fluxes of ClPAHs and BrPAHs ranged 580 (272-962) and 494 (161-936) pg m-2 day-1, respectively, at a regional background site, Košetice, and 547 (351-724) and 449 (202-758) pg m-2 day-1, respectively, at a semi-urban site, Praha-Libuš. These fluxes are similar to those of PCBs and more than 2 orders of magnitude lower than those of the parent PAHs in the region. Seasonal variations of the deposition fluxes of these halogenated PAHs were found with maxima in summer and autumn, and minima in winter at Košetice, but vice versa at Praha-Libuš. The distribution of ClPAHs and BrPAHs between the particulate and dissolved phases in deposition samples suggests higher degradability of particulate BrFlt/Pyr and BrBaA than of the corresponding ClPAHs. A number of congeners were detected for the first time in the atmospheric environment.

Intensity dependence of multiply charged atomic ions from argon clusters in moderate nanosecond laser fields

We report the laser intensity dependence of multiply charged atomic ions (MCAIs) Arⁿ⁺ with 2 ≤ n ≤ 8 from argon clusters in focused nanosecond laser fields at 532 nm. The laser field, in the range of 10¹¹-10¹² W/cm², is insufficient for optical field ionization but is adequate for multiphoton ionization. The MCAI sections of the mass spectra for clusters containing 3700 and 26 000 atoms are dominated by Arⁿ⁺ with 7 ≤ n ≤ 9, extending to Ar¹⁴⁺. While the distributions of the MCAIs remain largely constant throughout the intensity range of the laser, the abundance of Ar⁺ relative to the abundances of the MCAIs increases dramatically with increasing laser intensity. Consequently, exponential fittings of the yields result in a larger exponent for Ar⁺ than for MCAIs, and the exponents of MCAIs with 2 ≤ n ≤ 8 are similar, with only slight variations for different charge states. The width of the arrival time and, hence, the corresponding kinetic energy of Ar⁺ also increases with increasing laser intensities, while the width of the arrival time of MCAIs remains constant throughout the range of measurements. These results call for more detailed theoretical investigations in this regime of laser-matter interactions.

Method Development and Determination of Chlorinated Polycyclic Aromatic Hydrocarbons in Different Matrices

The aim of this study was to develop an analytical method, which separates selected chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) from fat, and fat-free or vegetable matrices. The method contains extraction-, cleanup-, and quantification steps. Integration of automated analysis actions, as in extraction and cleanup, should enhance the reproducibility, precision, and efficiency of the method. This was confirmed by validation of the overall analytical process. In the end, as a performance check, the developed method was applied on different matrices, e.g., tea, rice, grilled pork, and eel and predator eggs, as a non-food example. An inter-laboratory check was initiated as replacement for the lack of proficiency tests. Due to the high level of automation, both personnel and time effort are very low. In addition, the method is very robust with regard to the variability of the solvent selection and the loss of analytes by evaporation to dryness. It could be demonstrated that the developed method is applicable to different matrices with reproducible and precise results. This applies also to low-fat food and feed.

New classes of organic pollutants in the remote continental environment - Chlorinated and brominated polycyclic aromatic hydrocarbons on the Tibetan Plateau

Halogenated polycyclic aromatic hydrocarbons are carcinogenic and ubiquitous environmental organic pollutants. The abundance and sources of these compounds have not been studied in remote environments. We collected and analyzed air, soil, lichen, and moss samples from the Tibetan Plateau. Concentrations of chlorinated polycyclic aromatic hydrocarbons were 0.78-4.16 pg/m³ in air, 3.11-297 pg/g in soil, 260-741 pg/g in lichens, and 338-934 pg/g in mosses. Concentrations of brominated polycyclic aromatic hydrocarbons were 0.15-0.59 pg/m³ in air, 0.61-72.3 pg/g in soil, 33.5-64.9 pg/g in lichens, and 20.5-72.5 pg/g in mosses. The dominant congeners were 9- and 2-chlorophenanthrene, 1-chloropyrene, 3-chlorofluoranthene, and 1-bromopyrene. We found correlations between congener concentrations in lichens and in air, and lichens effectively predicted near-ground atmospheric concentrations of the pollutants. The enrichment of photochemically stable compounds in high-altitude environments is influenced by their physicochemical properties. Principal component analysis with multivariate linear regression of chlorinated polycyclic aromatic hydrocarbons measured in lichens provided an assessment of the relative source contributions, and suggested that in Medog County of Tibetan Plateau, 48% was likely from long-range combustion sources, 26% was from local burning sources, and 26% was from photochemical formation.

Chlorinated polycyclic aromatic hydrocarbons in surface sediment from Maowei Sea, Guangxi, China: occurrence, distribution, and source apportionment

Chlorinated polycyclic aromatic hydrocarbons (ClPAHs) with three to five aromatic rings have been documented to ubiquitously occur in environmental matrices. In this study, residual concentrations and profiles of 20 individual ClPAHs were determined in 35 surface sediment samples from Maowei Sea, a semi-enclosed shallow inland bay located in the northwestern part of South China Sea. The concentrations of ΣClPAHs in sediment ranged from 313 to 9650 pg/g dw with a detection rate of 43-100%. Of the individual ClPAH congeners, 9-ClPhe was the most abundant in Maowei Sea with the concentrations that ranged from 99.9 to 3610 pg/g dw (mean 1120 pg/g dw). High-molecular-weight ClPAH congeners (four to five rings) were predominant in sediments from sampling locations near a petrochemical industrial complex, whereas low-molecular-weight ClPAH congeners (three rings) were predominant in sediments from estuarine and mangrove locations. A positive matrix factorization (PMF) model in combination with dioxin-like toxic equivalency quotient (TEQ) results was used to apportion sources of ClPAHs. Vehicular emission, combustion/chemical industrial processes, and two other unknown sources accounted for 40.1, 25.5, 20.8, and 13.6%, respectively, of ClPAH sources in sediment; their contribution to TEQs in sediments were 24.2, 40.5, 19.3, and 16.0%, respectively. Further investigations are needed to elucidate potential sources and ecological risks of ClPAHs in sediments.

Study on the volatility of halogenated fluorenes

This work reports the experimental determination of relevant thermophysical properties of five halogenated fluorenes. The vapor pressures of the compounds studied were measured at different temperatures using two different experimental techniques. The static method was used for studying 2-fluorofluorene (liquid and crystal vapor pressures between 321.04 K and 411.88 K), 2-iodofluorene (liquid and crystal vapor pressures between 362.63 K and 413.86 K), and 2,7-dichlorofluorene (crystal vapor pressures between 364.64 K and 394.22 K). The Knudsen effusion method was employed to determine the vapor pressures of 2,7-difluorofluorene (crystal vapor pressures between 299.17 K and 321.19 K), 2,7-diiodofluorene (crystal vapor pressures between 393.19 K and 415.14 K), and (again) 2-iodofluorene (crystal vapor pressures between 341.16 K and 361.12 K). The temperatures and the molar enthalpies of fusion of the five compounds were determined using differential scanning calorimetry. The application to halogenated fluorenes of recently developed methods for predicting vapor pressures and enthalpies of sublimation and vaporization of substituted benzenes is also discussed.

Quantum Chemical and Kinetic Study on Polychlorinated Naphthalene Formation from 3-Chlorophenol Precursor

Polychlorinated naphthalenes (PCNs) are the smallest chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) and are often called dioxin-like compounds. Chlorophenols (CPs) are important precursors of PCN formation. In this paper, mechanistic and kinetic studies on the homogeneous gas-phase formation mechanism of PCNs from 3-CP precursor were investigated theoretically by using the density functional theory (DFT) method and canonical variational transition-state theory (CVT) with small curvature tunneling contribution (SCT). The reaction priority of different PCN formation pathways were disscussed. The rate constants of crucial elementary steps were deduced over a wide temperature range of 600−1200 K. The mechanisms were compared with the experimental observation and our previous works on the PCN formation from 2-CP and 4-CP. This study shows that pathways ended with Cl elimination are favored over those ended with H elimination from the 3-CP precursor. The formation potential of MCN is larger than that of DCN. The chlorine substitution pattern of monochlorophenols has a significant effect on isomer patterns and formation potential of PCN products. The results can be input into the environmental PCN controlling and prediction models as detailed parameters, which can be used to confirm the formation routes of PCNs, reduce PCN emission and establish PCN controlling strategies.

Atmospheric chlorinated polycyclic aromatic hydrocarbons in East Asia

This study estimates atmospheric concentrations of chlorinated polycyclic aromatic hydrocarbons (ClPAHs) and polycyclic aromatic hydrocarbons (PAHs) in East Asia using a Gas Chromatograph with High Resolution Mass Spectrometer (GC-HRMS). ClPAHs are ubiquitously generated from PAHs through substitution, and some ClPAHs show higher aryl hydrocarbon receptor (AhR)-mediated activities than their parent PAHs. Atmospheric particles were collected using a high-volume air sampler equipped with a quartz-fiber filter. We determined the ClPAH concentrations of atmospheric particles collected in Japan (Sapporo, Sagamihara, Kanazawa, and Kitakyushu), Korea (Busan), and China (Beijing). The concentrations of ClPAHs were highest in the winter Beijing sample, where the total mean concentration was approximately 15-70 times higher than in the winter samples from Japan and Korea. The concentrations of Σ19ClPAHs and Σ9PAHs were significantly correlated in the Kanazawa and the Busan samples. This indicates that within those cities ClPAHs and PAHs share the same origin, implying direct chlorination of parent PAHs. Toxic equivalent concentrations (TEQs) of the total ClPAHs and PAHs were lowest in Kanazawa in the summer, reaching 1.18 and 2610fg-TEQm(-3) respectively, and highest in Beijing in the winter, reaching 627 and 4240000fg-TEQm(-3) respectively.

Occurrence and source of chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) in tidal flats of the Ariake Bay, Japan

In this study, we hypothesize that natural photochemical reactions of polycyclic aromatic hydrocarbons (PAHs) in tidal flats are responsible for the occurrence of chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs). This study aims to survey the impact of photochemical reactions using a combination of field surveys and lab-scale experiments. Concentrations and profiles of PAHs and Cl-PAHs in road dust and sediments collected from seven tunnels and two watersheds, respectively, were determined. In the lab-scale experiments, anthracene was irradiated with ultraviolet (UV) light under various salinity conditions. No detectable Cl-PAHs were found in the road dust. However, Cl-PAHs were detected in the sediments from 700 to 6.1 × 10(3) pg g(-1) and specifically from downstream sites. 2-Monochloroanthracene (2-Cl-ANT) and 9,10-dichloroanthracene (9,10-di-Cl-ANT) were dominant in the sediments. In the Domen River watershed, the ∑Cl-PAHs and the salinity showed a significant positive correlation (p < 0.01) in the sediments, while such a correlation was not found for PAHs. 2-Cl-ANT, 9-monochloroanthracene, and 9,10-di-Cl-ANT were identified as transformation products in the UV irradiation experiments. Production of these Cl-PAHs was dependent on the solution salinity. These results support our hypothesis, and we conclude that photochemical reactions significantly contribute to the occurrence of Cl-PAHs in the studied tidal flats.

Thermochemical and Vapor Pressure Behavior of Anthracene and Brominated Anthracene Mixtures

The present work concerns the thermochemical and vapor pressure behavior of the anthracene (1) + 2-bromoanthracene (2) and anthracene (1) + 9-bromoanthracene (3) systems. Solid-liquid equilibrium temperature and differential scanning calorimetry studies indicate the existence of a minimum melting solid state near an equilibrium temperature of 477.65 K at x₁ = 0.74 for the (1) + (2) system. Additionally, solid-vapor equilibrium studies for the (1) + (2) system show that the vapor pressure of the mixtures depends on composition, but does not follow ideal Raoult's law behaviour. The (1) + (3) system behaves differently from the (1) + (2) system. The (1) + (3) system has a solid solution like phase diagram. The system consists of two phases, an anthracene like phase and a 9-bromoanthracene like phase, while (1) + (2) mixtures only form a single phase. Moreover, experimental studies of the two systems suggest that the (1) + (2) system is in a thermodynamically lower energy state than the (1) + (3) system.