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The presence of hazardous air pollutants (HAPs) entrained in end-use natural gas (NG) is an understudied source of human health risks. We performed trace gas analyses on 185 unburned NG samples collected from 159 unique residential NG stoves across seven geographic regions in California. Our analyses commonly detected 12 HAPs with significant variability across region and gas utility. Mean regional benzene, toluene, ethylbenzene, and total xylenes (BTEX) concentrations in end-use NG ranged from 1.6-25 ppmv─benzene alone was detected in 99% of samples, and mean concentrations ranged from 0.7-12 ppmv (max: 66 ppmv). By applying previously reported NG and methane emission rates throughout California's transmission, storage, and distribution systems, we estimated statewide benzene emissions of 4,200 (95% CI: 1,800-9,700) kg yr-1 that are currently not included in any statewide inventories─equal to the annual benzene emissions from nearly 60,000 light-duty gasoline vehicles. Additionally, we found that NG leakage from stoves and ovens while not in use can result in indoor benzene concentrations that can exceed the California Office of Environmental Health Hazard Assessment 8-h Reference Exposure Level of 0.94 ppbv─benzene concentrations comparable to environmental tobacco smoke. This study supports the need to further improve our understanding of leaked downstream NG as a source of health risk.

An ever-growing burden of scientific evidence links air pollution to different aspects of human health even at very low concentrations; the impact increases for those living in urban environments, especially the youngest and the elderly. This study investigated the exposure to air pollution of urban school children of Milan, Italy, by personal and biological monitoring, in the frame of the MAPS-MI project. A total of 128 primary school children (7-11 years) were involved in a two-season monitoring campaign during spring 2018 and winter 2019. Personal exposure to airborne VOCs and eBC, and biological monitoring of urinary benzene (BEN-U) and methyl-tert-butyl ether (MTBE-U) were performed. Time-activity patterns, environmental tobacco smoke (ETS), spatial, and meteorological information were evaluated as determinants in mixed effects regression analysis. Children personal exposure was mostly quantifiable with median (5th-95th percentile) levels 1.9 (0.8-7.5) μg/m

Enhanced bioremediation combined with in-situ chemical oxidation has the potential to remediate groundwater contaminated with organics. To explore the remediating effects of these two approaches and to evaluate their combined feasibility, traditional gasoline (no ethanol) and ethanol-gasoline (10% ethanol, v/v) were released into experimental sand tanks (TG-tank and EG-tank, respectively) under the same water-flow conditions. Nitrate and sulfate were added to enhance bioremediation and then persulfate was injected to encourage chemical oxidation. Two push–pull tests, using persulfate and bromide respectively, were conducted to compare their behavior. The results showed that nitrate reduction, rather than sulfate reduction, enhanced BTEX (benzene, toluene, ethylbenzene, and xylene) biodegradation, but the presence of ethanol inhibited these processes. The detected concentration of BTEX in the TG-tank was lower than that in the EG-tank, and the first-order decay rate constants of BTEX in the TG-tank and EG-tank under nitrate-adjusted conditions were 0.0058 and 0.0016 d−1, respectively. The first persulfate injection (10 g L−1) resulted in 86 and 94% concentration decreases of BTEX in the TG-tank and EG-tank, respectively, at first-order decay rates of 0.0180 and 0.0181 d−1, respectively. However, the subsequent persulfate injections at 20 and 50 g L−1 had no significant removal effect on BTEX. Persulfate oxidation made pH decrease (but it quickly recovered) and did not significantly inhibit nitrate reduction. This study suggests that enhanced nitrate reduction can be combined with persulfate oxidation for the in-situ remediation of groundwater contaminated by petroleum hydrocarbons.

A monitoring campaign, the first of this kind for a heavy traffic urban area of Vietnam, was conducted which generated nearly 200 daily filter samples of PM2.5, PM10, and black carbon (BC), 1300 online hourly PMx (PM10, PM2.5, and PM1), 900 hourly/bi-hourly BTEX data, 700 h of traffic counts, and online meteorology records. PMx and BTEX levels show large horizontal gradients across this small urban area of 300 m width suggesting that the pollution data should be generated with sufficient spatial resolutions for assessment of the exposure and health effects. This paper focuses on analyzing PMx with reference to the previously published BTEX to provide a more complete picture of the traffic-related pollution in the area. Spatio-temporal variations of pollutants are analyzed in relation to traffic flows and fleet compositions, weekday-weekend effects, local and regional meteorology. PM10 and BTEX levels had larger variations between the sites indicating their stronger associations with the traffic activities than the finer particles. Twenty-four-hour (24 h) PM2.5 levels ranged between 19 and 191 µg/m3 with high PM1/PM2.5 ratios of above 0.8 at ambient site (AA) and above 0.7 at roadsides. Multivariate relationship analysis (PCA) for the bi-hourly datasets of meteorology, traffic flows, and pollutant levels indicated overwhelming influence of on-road traffic fleet compositions on the roadside pollutants levels. At AA, PCA results showed a complex interaction between local emissions, meteorological conditions, and regional/long-range transport. Higher pollution levels were associated with the airmass types having the continental origin and pathways.

Gasoline evaporation and spills may cause high air pollution at gas stations. This study aimed to assess exposure to volatile organic compounds (VOCs) at gas stations among customers. Ambient air samples were collected in the fuel dispensing area of 51 gas stations in the Greater Memphis Area, USA, in summer 2017. For the comparison purpose, samples were collected in the ambient air at 20 community sites and in the indoor air of 30 homes, 11 offices, and 15 running vehicles in the same region. Air sampling used Tenax TA thermal desorption (TD) tubes and samples were analyzed by TD-gas chromatography/mass spectrometry (GC/MS) for 70 target compounds. Gasoline-related VOCs were identified using factor analysis, and exposure at gas stations was evaluated using Monte Carlo analysis. Benzene, toluene, ethylbenzene, and xylenes (BTEX) showed the highest concentrations ranging from 2 to 15 μg/m3, ten times higher than those in the community air. Factor analysis confirmed gasoline as the common source of aromatic compounds. VOC concentrations had no association with the number of cars present or environmental parameters. Exposure to aromatic compounds at gas stations represented 2% of the total exposure (i.e., the sum of indoor and outdoor exposures) but 38% of the outdoor exposure among customers. The exposure levels were below the acute health thresholds and presented 0.3 × 10−6 lifetime excess cancer risk. In conclusion, customers’ exposure to VOCs at gas stations has negligible non-cancer and cancer risks. It is also suggested that customers stand away from the nozzle to avoid high personal exposures during refueling.

l-cysteine-modified Fe3 O4 nanoparticles (l-cys@nFe3 O4 ) were synthesized successfully and used as catalyst to activate persulfate (PS) for benzene, toluene, ethylbenzene, and xylenes (BTEX) degradation. The composite was fully characterized, and the l-cys@nFe3 O4 had more protrusions and l-cys was combined on the surface of nFe3 O4 . The removals of BTEX were 78.2%, 85.1%, 85.3%, 81.2%, respectively, in PS/l-cys@nFe3 O4 system, while only 52.7% 57.8%, 60.8%, and 56.3% of BTEX removals reached under the same condition for nFe3 O4 chelated with l-cys in 48 h. Four successive cycles of BTEX degradation were completed in PS/l-cys@nFe3 O4 system. The synergistic mechanisms of BTEX degradation in PS/l-cys@nFe3 O4 system were investigated by electron paramagnetic resonance (EPR), benzoic acid (BA) probe and X-ray photoelectron spectroscopy (XPS) tests. SFe bond in l-cys-Fe complexes promoted the electron transfer between nFe3 O4 core and the solution, iron and iron at the interface, thereby promoting the Fe3+ /Fe2+ cycle and the catalytic capacity of nFe3 O4 . The optimal pH of PS/l-cys@nFe3 O4 system was 3, while HCO3- and Cl- exhibited negative influences on BTEX degradation. Only 14.2%, 15.5%, 15.9%, and 15.6% BTEX had been removed in the presence of 0.12-M PS and 8.0 g/L l-cys@nFe3 O4 under the actual groundwater condition. However, expanding the dosage of PS and l-cys@nFe3 O4 was an effective strategy to overcome the adverse effect. PRACTITIONER POINTS: L-cys@nFe3 O4 were synthesized successfully and used as catalyst to activate PS for BTEX degradation. Four successive cycles of BTEX degradation were completed in PS/L-cys@nFe3 O4 system. lS-Fe bond in L-cys@nFe3 O4 promoted the electron transfer between PS and nFe3 O4 core.

The effective approaches to eliminate impacts of ethanol on the biodegradation of benzene, toluene, ethylbenzene, and xylene (BTEX) are concerned in the bioremediation of groundwater contaminated with ethanol-blended gasoline. In situ chemical oxidation (ISCO) is a common technique widely used for the remediation of contaminated groundwater. However, the selectivity of ISCO for BTEX and ethanol removal is poorly understood. Therefore, a batch experiment was performed with different aquifer materials, including calcareous soil, basalt soil, granite soil, dolomite, and sand. Gasoline was used to provide dissolved BTEX and ethanol reagent was used as additive to improve the quality of gasoline and to reduce the possibility of air pollution caused by gasoline. Persulfate (PS) was used as a chemical oxidant to oxidize organic contaminants. The target concentrations of BTEX and ethanol were 20 mg/L and 1000 mg/L, respectively. The results showed that ethanol could be preferentially degraded in the absence of PS and inhibit BTEX biodegradation. However, BTEX could be preferentially removed prior to ethanol in all aquifer materials used at ambient temperature, when PS was added at a PS/BTEX molar ratio of 150. Over 94% BTEX in sand, dolomite, and granite soil was preferentially removed with the first-order decay rate constants of 0.890–2.703 day−1 within the first ~ 10 days, followed by calcareous and basalt soil at the constants of 0.123–0.371 day−1. Ethanol could compete with BTEX for sulfate radical at the first-order decay rate constants of 0.005–0.060 day−1 for the first 25 days, which was slower than that of BTEX. The pH quickly decreased to 6.2 in calcareous soil. Rich organic matter in calcareous and basalt soil had an inhibition effect on BTEX oxidation by PS. The pH buffer in calcareous soil may imply the potential of PS oxidation combined with bioremediation in carbonate rock regions.

Toxic gaseous organic air pollutants such as benzene, toluene, ethylbenzene, and xylene isomers (m, p, and o-x) (BTEX) are considered hazardous due to its adverse impacts on human health and on climate change. This review identifies the major research questions addressed so far and the research gap in research articles, published between 2001 and 2022, focusing on the ambient BTEX concentrations in different locations in India along with its sources, ozone formation potential (OFP), and associated health risks. The ambient levels of BTEX were also compared with those of other Asian countries. A comparison of ambient BTEX levels with different microenvironments in India is also presented. BTEX concentrations were found in the range of 30.95 to 317.18 µg m−3 and multi-fold higher in urban environments than those measured in the rural air. In most reported studies, the order of occurrence of BTEX compounds was toluene > benzene > xylene isomers > ethylbenzene and winter had higher concentrations than in other seasons, including summer. As far as BTEX levels in classified areas of urban environments are concerned, traffic locations have shown the highest BTEX concentrations, followed by residential, commercial, and industrial locations. OFP indicated that xylene isomers and toluene contributed to ozone formation. The major gaps in reported studies on BTEX measurement are (1) source apportionment; (2) impact on lower tropospheric chemistry, human health, and climate change; and (3) removal techniques from air. published

Refinery effluents represent an emission source of hydrocarbons (HCs) and other constituents to the environment. Thus, characterisation of effluent quality in terms of concentrations of key parameters relative to permitted standards is important and for total petroleum hydrocarbons (TPH), the specific composition of the HC mixture can affect its toxicity to aquatic organisms. Therefore, this study was designed to analyse TPH, benzene, toluene, ethyl benzene, xylenes (BTEX), polycyclic aromatic hydrocarbons (PAHs), (bio) chemical oxygen demand, total nitrogen, total suspended solids and selected metals before, and after, treatment steps to demonstrate removal efficiencies across 13 refineries with variable wastewater treatment systems. Final discharge concentrations of the measured parameters were by 97% within the so called Best Available Technique Associated Emission Levels (BAT-AELs). Further, TPH composition was characterised using high-resolution two-dimensional gas chromatography (GCxGC) analysis to understand the mass distribution by carbon number and specific chemical class. Measurements were compared to SimpleTreat model predictions for validation. SimpleTreat successfully predicted the shape of the effluent composition since it is essentially a removal constant applied to the influent composition. The predictions were of similar magnitude as, or were greater than, the effluent concentrations since SimpleTreat is based on typical performance and is intended to be conservative. This was especially true for aromatic constituents. Reduction in potential HC exposures also coincided with a decrease in predicted toxicity using a mechanistic oil toxicity model, PETROTOX. Overall, the results indicate that EU petroleum refineries are likely to achieve a high performance level regarding effluent treatment.

Background The fire at the Intercontinental Terminals Company (ITC, Deer Park, La Porte, TX, USA) from March 17 to 20, 2019 resulted in substantial releases of chemical contaminants to the environment, including the surface waters of the Houston Ship Channel. Objective To characterize spatial and temporal trends, as well as potential human health risks, from these releases. Methods Out of 433 substances with available data, seven were selected for analysis: benzene, toluene, ethylbenzene, xylenes, oil and grease, suspended solids, and total petroleum hydrocarbons. Spatial and temporal concentration trends were characterized, and hazard quotients and cancer risks were calculated to estimate the potential for human health impacts from these contaminants. Results Temporal analysis showed presence of these chemical contaminants in water immediately after the event; their concentrations dissipated substantially within 4 weeks. The spatial distribution of contaminants indicated the highest concentrations in the waterways within about 1 km of the ITC. The greatest potential human health risks stemmed from presence of benzene. Significance A short-term but substantial spike in the concentrations of a number of hazardous contaminants occurred near the incident, with concentrations returning to apparent baseline levels within 1 month likely due to a combination of volatization, dilution and degradation.

This study evaluated the occurrence and human exposure risk of mono-aromatic hydrocarbons (MAHs) such as benzene, toluene, ethylbenzene, and o,p-xylene (BTEX) in soils from petroleum product jetty from the Niger Delta, Nigeria. Samples were collected from the top (0-15 cm), sub (15-30 cm), and bottom (30-45 cm) soil depths. The MAHs components were determined using Headspace gas chromatography-mass spectrometer (HS-GCMS). The individual and ƩMAHs concentrations ranged from not detected (ND) to 1528 µg kg-1 and ND to 2512 µg kg-1 respectively. The total cancer risks were within the low category. The source identification indicated that the origin MAHs species are attributed to solvent, paints, and gasoline-diesel spill and particulate emission from gasoline/diesel combustion exhaust in the vicinity of the petroleum product jetty. This depicts the presence of low molecular weight petroleum fractions such as gasoline and kerosene that could exhibit toxicological and carcinogenic effects to organisms in soils within the jetty. Clean-up actions should be carried out to prevent the accumulation of MAHs in soil-plant uptake and the potential ecological and human exposure risks of MAHs in the surrounding soil and aquatic ecosystem

The International Agency for Research on Cancer (IARC) classifies benzene in group 1 (carcinogenic to humans). Particulate matter (PM) has recently also been classified in this category. This was an advance toward prioritizing the monitoring of particles in urban areas. The aim of the present study was to assess levels of PM2.5 and BTEX (benzene, toluene, ethylbenzene, and xylene), the influence of meteorological variables, the planetary boundary layer (PBL), and urban variables as well as risks to human health in the city of Fortaleza, Brazil, in the wet and dry periods. BTEX compounds were sampled using the 1501 method of NIOSH and determined by GC-HS-PID/FID. PM2.5 was monitored using an air sampling pump with a filter holder and determined by the gravimetric method. Average concentrations of BTEX ranged from 1.6 to 45.5 μg m−3, with higher values in the wet period, which may be explained by the fact that annual distribution is influenced by meteorological variables and the PBL. PM2.5 levels ranged from 4.12 to 33.0 μg m−3 and 4.18 to 86.58 μg m−3 in the dry and wet periods, respectively. No seasonal pattern was found for PM2.5, probably due to the influence of meteorological variables, the PBL, and urban variables. Cancer risk ranged from 2.46E−04 to 4.71E−03 and 1.72E−04 to 2.01E−03 for benzene and from 3.07E−06 to 7.04E−05 and 3.08E−06 to 2.85E−05 for PM2.5 in the wet and dry periods, respectively. Cancer risk values for benzene were above the acceptable limit established by the international regulatory agency in both the dry and wet periods. The results obtained of the noncarcinogenic risks for the compounds toluene, ethylbenzene, and xylene were within the limits of acceptability. The findings also showed that the risk related to PM is always greater among smokers than nonsmokers.

The use of motorized transportation in Indonesia is now proliferating. The higher the use of motorized vehicle-based transportation in an area, the higher the potential for air pollution. One of the air pollutants is a mixture of benzene, toluene, ethylbenzene, and xylene (BTEX). This study examines the effect of coconut shell-derived activated carbon adsorbent mass which is adjusted with different thicknesses on its adsorption ability for BTEX. The adsorbent is used to adsorb the emissions of the 1990 GL-Pro motorcycle with premium fuel. The results of gas chromatography-mass spectroscopy (GC-MS) show that motor vehicle emissions contain BTEX and other hydrocarbons. ANOVA variant analysis showed that the difference in mass of activated carbon in the range of this study did not provide a significant difference in BTEX adsorption.Keywords: adsorbent; motor vehicle emissions; BTEX pollutants; coconut shell

The release of volatile organic compounds (VOCs) from stationary and mobile sources increases the concentration of these pollutants in the environment. These compounds have the potential to cause adverse effects on human health and the environment. The adoption of management and engineering procedures to control the emission of these pollutants to the air has become essential. The aim of this study was to use an advanced oxidation process namely the catalytic ozonation to reduce the concentration of these pollutants in industrial output. In this experimental study, the catalytic ozonation process in the presence of ZnO nanoparticles coated on zeolite media was used in a laboratory scale to treat the air contaminated with BTEX compounds as indicators of VOCs. For this purpose, First the nanocomposites were synthesized based on chemical co-precipitation method. SEM, XRD, BET and FT-IR analyses were performed to investigate the characteristics of nanocomposites. The variables including initial concentrations of BTEX (50–200 ppm), polluted air flow rate (5–20 l/h), humidity (0–75%) and ozone dose (0.25–1 g/h) were investigated. The concentration of BTEX compounds was measured by the Gas Chromatography (GC) technique according to the NIOSH 1501 manual. The results of SEM, XRD, BET and FT-IR analyses showed the proper synthesis of nanocomposites. According to the laboratory results, the optimal conditions of the process were found to be as follows: the initial concentration of pollutants equal to 50 ppm, inlet air flow rate of 5 l/h, relative air humidity of 25–35%, and inlet ozone concentration equal to 1 g/h. Under these conditions, the removal efficiency of the compounds: benzene, toluene, ethylbenzene and xylene were obtained 98, 96, 92 and 91%, respectively. Simple ozonation and adsorption processes were less efficient than catalytic ozonation. This process had the ability to reduce the concentration of BTEX compounds to standard level.

The purpose of this study was to study the spatial and temporal variation of BTEX in the ambient air of Leon, Guanajuato, Mexico, to assess the inhalation health risk to the local population from exposure to these compounds. BTEX were monitored using passive samplers during two sampling seasons (rainy 2019 and cold dry 2020), and samples were analyzed by gas chromatography with flame ionization detection. BTEX ratios and meteorological analysis suggested that the concentrations were mainly influenced by vehicular and local sources located to the SE of the study area. The sum of average concentrations of BTEX in rainy and cold dry seasons were of 3.52 ± 0.36 µg m−3 and 4.11 ± 0.38 µg m−3, respectively. Mean concentrations were of 0.74, 1.59, 0.48, and 0.69 µg m−3, for benzene, toluene, ethylbenzene, and p-xylene, respectively. The highest levels of BTEX were found in sites with an urban land-use type of medium-intensity industrial zones with high population density. The lower BTEX concentrations found during the rainy season were probably due to higher solar radiation and temperatures that favored their photochemical degradation. Bi-variate and multivariate analysis showed that the BTEX species were strongly correlated with each other and with temperature and solar radiation, indicating that they originated from common sources. Benzene and toluene correlated strongly with CO and SO2, indicating that they could originate from vehicular exhaust emissions and high-sulfur fuel combustion sources. The health risk assessment showed that the Leon city adult population is at possible risk of developing cancer in their lifetime due to exposure to the measured benzene levels, but indicated no risk of contracting respiratory and cardiovascular diseases due to inhalation of BTEX. The results suggest the need for BTEX emissions reduction policies in the study area, as well as the establishment of a Mexican standard that regulates the maximum permissible limit of these pollutants in ambient air in order to protect the health of the population.

Air quality policy in the Los Angeles megacity is a guidepost for other megacities. Over the last 2 decades, the policy has substantially reduced aerosol (OA) concentrations and the frequency of high aerosol events in the region. During this time, the emissions contributing to, and the temperature associated with, high aerosol events have changed. Early in the record, aerosol concentrations responded to a variety of different sources. We show that emission control has been effective with a strong decrease in temperature-independent sources. As a result, the response of aerosol to temperature has become a dominant feature of high aerosol events in the basin. The organic fraction of the aerosol (OA) increases with the temperature approaching 35% at 40 °C. We describe a simple conceptual model of aerosol in Los Angeles, illustrating how benzene, toluene, ethylbenzene, and xylenes (BTEX) and isoprene, along with molecules for which these are plausible surrogates such as monoterpenes, are sufficient to explain the observed temperature dependence of PM 2.5.

Exposure to benzene, toluene, ethylbenzene, and xylene (BTEX) and styrene have been reported in tire manufacturing. This research was designed to evaluate the exposure to BTEX and styrene and their...

The purpose of this research work was to evaluate the Benzene, toluene, ethylbenzene and xylene (BTEX) emissions from a Bamroli sewage-treatment plant (STP) in Surat City, India. Tiger handheld gas detector was utilised to measure emissions of BTEX during three periods of monitoring, and sewage samples were collected to determine the characteristics of sewage. The spatial variation of BTEX was determined at various treatment units of the STP during the months of November and April and represented as interpolation maps using ArcGIS. Box charts were plotted to represent the temporal variation of BTEX, which categorise the resultant data on the basis of their frequency. It has been noticed from the interpolation maps that the concentration of BTEX decreases as sewage travels from the inlet to subsequent units. Approximately 50% of all readings obtained of BTEX concentration fall within 0.5 parts per million, which exceeds the limits stipulated by the National Ambient Air Quality Standards, 5 μg/m3 for benzene. It can be concluded that more vent pipes have to be provided for the dispersion of these compounds in transmission lines. Also, some safety aids such as face masks have to be utilised by labourers who are continuously subjected to these compounds.

In China, due to the high density of population and vehicles in megacities, the commercial center and high-rise residential buildings have been widely equipped with large underground parking garages (UPGs). Volatile organic compounds (VOCs) and particulate matters (PM) have been confirmed as major pollutants in underground parking garages. And therefore, exposure to these air pollutants, especially ultrafine particles and BTEX (benzene, toluene, ethylbenzene, and xylenes), is closely associated with the health of the car owners or the garage workers. This study sampled or online monitored the concentrations of benzene, toluene, xylenes, formaldehyde, TVOC (total volatile organic compounds), PM2.5, and PM10 in the underground garage of three commercial center and high-rise residential buildings. The time-weighted average (TWA) concentrations of pollutants in the underground garage in the commercial center/high-rise residential buildings were as follows: benzene 0.12/0.11 mg·m−3, toluene 0.33/0.31 mg·m−3, xylenes 0.23/0.20 mg·m−3, TVOC 1.04/1.19 mg·m−3, PM2.5 0.20/0.19 mg·m−3, and PM10 0.24/0.22 mg·m−3. Indoor PM concentrations were slightly higher than outdoor PM concentrations, and there was a significant positive relationship between the difference of I/O PM concentrations and traffic volume. This paper also compared and analyzed BTEX concentration ratios (e.g., toluene/benzene and xylenes/benzene) at every sampling point of different underground garages. These ratios were compared and analyzed to evaluate the influence of vehicle emissions and outdoor air quality on the spatial distribution of indoor air quality quantitatively.

Based on 2016 fuel consumption and utilizing US-EPA AP-42 emission factors, emissions from the burning fuel facilities for energy production in Kuwait were calculated. The total emissions for criteria pollutants were 1.89E+01, 6.97E+02, 1.05E+02, 8.05E+00, 8.54E+00, and 1.60E−03 Gg of CO, SO2, NOx, PM10, PM2.5, and Pb, respectively. For benzene, ethylbenzene, toluene, xylenes, and BTEX, they were 2.27E−03, 3.11E−03, 1.91E−02, 6.21E−03, and 3.07E−02 Gg, respectively. In addition to ranking the power plants based on emission quantities, the ratio of the mass emitted from each compound to the released thermal energy (R) was calculated. The significance of R is that a power plant with a higher R value is considered to have more polluting effect if it was to have the same amount of thermal released energy. This concept was further extended to calculate the fuel-specific R using a system of 4 simultaneous equations. Zour South Power Station (PS) contributed most toward CO, SO2, and Pb emissions, while Sabiya PS had contributed most to NOx, PM10, and PM2.5 emissions. Boilers had the highest contribution to CO, SO2, NOx and Pb emissions, while gas turbines’ emissions of PM10 and PM2.5 exceeded those from boilers. Burning heavy fuel oil resulted in 89%, 90%, and 43% of the SO2, Pb, and NOx emissions. Gas oil contributed to 72% of CO emissions, while natural gas contributed to over 90% of PM10 and PM2.5 emissions. Shuwaikh Desalination Plant, which is about 1 km from urban areas, had the lowest contribution to BTEX and criteria pollutant emissions.

Natural gas processing involves the removal of acidic gases, followed by dehydration. The dehydration process is primarily carried out through absorption in triethylene glycol (TEG). During the dehydration process, volatile organic compounds (VOCs) including benzene, toluene, ethylbenzene, and isomers of xylene together known as BTEX present in natural gas are absorbed into the glycol solvent. During the thermal regeneration process of TEG, a substantial amount of BTEX and VOCs are emitted resulting in adverse environmental and health impacts, leading to the need for strict regulations. Effective mitigation of emission is essential for the natural gas industry. There are several process parameters associated with major equipment that may impact BTEX emission. Regulation of some of these parameters is found to have an adverse impact on the dehydration process as well. In this work, a multi-objective optimization is performed in order to find the optimal operating conditions related to the process parameters to mitigate BTEX emission. It is also essential to select the most important parameters from a larger set so that a reliable analysis can be performed using the reduced set of parameters. The analysis is performed using data-driven modeling using machine-learning algorithms, followed by optimization with a probabilistic technique. The least absolute shrinkage and selection operator (lasso) method is used for variable selection; support vector regression (SVR) is used for metamodeling; and a novel metaheuristic optimization algorithm, efficient ant colony optimization (EACO), is used for optimization. The surrogate or metamodel is generated with data obtained from process simulation carried out using ProMax. Using the lasso–SVR–EACO strategy, different optimized sets of operating conditions that minimize the BTEX emission for a stipulated dry gas water content, were obtained. The results show that BTEX released from the dehydration process can be mitigated by optimally choosing the TEG circulation rate, reboiler temperature, stripping gas flow rate, and absorber pressure.

This study reports on BTEX concentrations in one of the largest parking garages in Iran with a peak traffic flow reaching up to ~9300 vehicles in the last few days of the Nowruz holidays. Samples were obtained on different days of the week at three main locations in the Zaer Parking Garage. A novel wavelet-based random forest model (WRF) was trained to estimate BTEX concentrations by decomposing temperature, day of the week, sampling location, and relative humidity data with a maximal overlap discrete wavelet transform (MODWT) function and subsequently inputted into the WRF model. The results suggested that the WRF model can reasonably estimate BTEX trends and variations based on high R2 values of 0.96, 0.95, and 0.98 for training, validation, and test data subsets, respectively. The carcinogenic (LTCR) and non-carcinogenic health risk (HI) assessment results indicated a definite carcinogenic risk of benzene (LTCR = 2.22 × 10−4) and high non-carcinogenic risk (HI = 4.51) of BTEX emissions. The results of this study point to the importance of BTEX accumulation in poorly ventilated areas and the utility of machine learning in forecasting air pollution in diverse airsheds such as parking garages.

This study was conducted to determine if the thermal degradation of various plastic drinking water pipes (i.e., PEX, HDPE, PP, PVC, and CPVC) may be a source of drinking water contamination. Widespread volatile organic compound (VOC) contamination was found in water distribution systems following three wildfires in California. A potential source of this contamination was thought to be due to the degradation of plastic components in drinking water distribution systems. Eleven plastic drinking water pipes, across eight brands, were exposed to elevated temperatures (200 °C to 400 °C), and subsequently submerged in water or in n-hexane to observe the extent of VOC leaching. Results indicated that thermally damaged drinking water pipes can be sources of VOC leaching, with ten of the eleven materials leaching benzene, a carcinogen, into water. As exposure temperature increased, an increase in VOC leaching was observed in the polyethylene materials. Conversely, in the vinyl materials the significant mass loss associated with high exposure temperature was inversely proportional to the amount of BTEX leaching that was observed. Additional tentatively identified compounds (TICs), consisting primarily of aliphatic hydrocarbons, saturated ketones, or aromatic compounds, were found in the water (22 TICs) and n-hexane (134 TICs) leachate of burned plastics. This study has significant implications for both wildfire and structure fire recovery as plastic materials are increasingly being used in buried and building plumbing, and visual inspection is not a sufficient indicator of contamination risk.

Hydrocarbon storage tanks are important sources of emission of volatile organic compounds (VOCs) which have unfavorable effects on atmospheric chemistry and human health. The aim of this study is to calculate the emission of VOCs with emphasis on benzene, toluene, ethylbenzene, and xylene (BTEX) from storage tanks in the export port of Abadan petroleum refinery company in Mahshahr, Iran. The rate of VOCs emission from 32 external floating roof storage tanks containing 7 different types of organic liquids was calculated using TANKs 4.0.9d software in hot and cold seasons. Then, the dispersion of these pollutants was analyzed by implementing AERMOD model. Field measurement was performed in 6 points in the study area in hot and cold seasons to validate AERMOD modeling results. Results show that maximum quantities of benzene (0.0649 g/s) and ethylbenzene (0.0189 g/s) were emitted from light naphtha storage tanks, and maximum quantities of toluene (0.1635 g/s) and xylene (0.0593 g/s) were emitted from gasoline storage tanks in the hot season. Also, in the cold season, maximum emission of benzene (0.0335 g/s) observed from jet naphtha storage tanks, ethylbenzene (0.0093 g/s) from light naphtha storage tanks, and toluene (0.0826 g/s) and xylene (0.0314 g/s) from gasoline storage tanks. In 8-h and 24-h emissions of BTEX pollutants in the export port area, the most polluted points were identified as points 5 and 6 in the hot season and points 2 and 4 in the cold season. The highest BTEX emission rate was related to gasoline tank #14 with 0.2927 g/s in the hot season and 0.1497 g/s in the cold season. Comparison of predictions of the model with the measurements showed that mean value of absolute average relative deviation (AARD) was between 7-16% which indicates that an acceptable modeling was performed.

Volatile organic compounds (VOCs) encompass hundreds of high production volume chemicals that have been used in a wide range of household and industrial products. Widespread use of products that contain VOCs resulted in their ubiquitous occurrence in the environment, with elevated concentrations frequently found in indoor environments. Human exposure to VOCs is pervasive and has been a topic of concern, due to the mutagenic, neurotoxic, genotoxic, and carcinogenic potentials of these chemicals. Although several previous articles described toxic effects of VOCs, relatively less is known on their human exposure and body burdens. VOCs have been determined in human breath condensate, blood, feces, and urine. This review updates the information on the environmental occurrence, toxicity, sources and pathways of human exposure, metabolism and elimination, and biomonitoring of exposure to VOCs. Indoor air is a major source of human exposure to VOCs. Higher atmospheric concentrations of VOCs have been reported in Asian countries than in North American and European countries. Elevated concentrations of four widely studied VOCs namely, benzene, toluene, ethylbenzene and xylene (BTEX) were reported in air from newly constructed or renovated homes (1.3–350 μg/m3) and e-waste workshops (2.45–3,10,000 μg/m3). BTEX were also found in consumer products such as shoe polish, whiteout, leather cleaner and ink at notable concentrations (e.g., ~92,600 μg/g). Traditional methods of exposure assessment of VOCs entailed measurement of these chemicals in indoor air and determination of inhalation exposure dose. SStudies on VOC exposure assessment mainly focused on occupationally exposed individuals. Recent developments in biomonitoring of urinary metabolites of VOCs present accurate assessment of exposures and internal body burdens. Biomonitoring studies of VOCs offer novel biomarkers for the assessment of airway inflammation, lung injury, neurological disorders, immune dysfunction and cancers in populations. Considering the very high production volume (at billions of pounds annually), known toxicity, and widespread human exposures, significance of VOCs in eliciting adverse health effects in populations will be a subject of increasing public health concern for years to come.

Benzene, toluene, ethylbenzene, and xylene (BTEX) are a group of volatile organic compounds that human exposure to them may result in the development of some diseases, including cancer. Biological monitoring plays an important role in exposure assessment of workers occupationally exposed to chemicals. Several metabolites have been proposed for biological monitoring of individuals who are exposed to BTEX. There are a variety of extraction methods and analytical techniques for the determination of unmetabolized BTEX in exhaled air and their urinary metabolites. The present study aimed to summarize and review the toxicokinetics of BTEX and sample preparation and analytical methods for their measurement. Metabolites of BTEX are discussed to find out reliable ones for biological monitoring of workers exposed to these chemicals. In addition, analytical methods for unmetabolized BTEX in exhaled air and their metabolites were reviewed in order to obtain a comparison between them in term of selectivity, sensitivity, simplicity, time, environmental-friendly and cost. Given the recent trends in sample preparation, including miniaturization, automation, high-throughput performance, and on-line coupling with analytical instrument, it seems that microextraction techniques, especially microextraction by packed sorbents are the methods of choice for the determination of the BTEX metabolites.

The present study evaluated the concentrations, spatial distribution, seasonal variations, potential sources, and risk assessment of organic/inorganic pollutants in ambient air of Tehran city. Totally, 180 air samples were taken from 9 sampling stations from March 2018 to March 2019 and were analyzed to determine the concentrations of organic pollutants (BTEX compounds and PM2.5-bound PAHs) plus inorganic pollutants (PM2.5-bound metals and asbestos fibers). The results revealed that the mean concentrations of ∑ PAHs, BTEX, ∑ heavy metals, and asbestos fibers were 5.34 ng/m3, 60.55 µg/m3, 8585.12 ng/m3, and 4.13 fiber/ml in the cold season, respectively, and 3.88 ng/m3, 33.86 µg/m3, 5682.61 ng/m3, and 3.21 fiber/ml in the warm season, respectively. Source apportionment of emission of the air pollutants showed that PAHs are emitted from diesel vehicles and industrial activities. BTEX and asbestos are also released mainly by vehicles. The results of the inhalation-based risk assessment indicated that the carcinogenic risk of PAHs, BTEX, and asbestos exceeded the recommended limit by The US environmental protection agency (US EPA) and WHO (1 × 10–4). The risk of carcinogenesis of heavy metal of lead and chromium also exceeded the recommended limit. Thus, proper management strategies are required to control the concentration of these pollutants in Tehran's ambient air in order to maintain the health of Tehran’s citizens.

Based on the context of extensive petroleum hydrocarbon pollution in southern Nigeria, the concentrations of benzene, toluene, ethylbenzene and xylene (BTEX) in seafood were determined, and the health risks of these compounds were evaluated. Biota samples (Crayfish, Goby fish, Moonfish, Mudskipper, Mullet, Sardine and Tilapia) were collected from the Bonny Estuary from 2016 to 2018 and analyzed according to US EPA method 5030/8260C to determine the concentrations of BTEX. Risk assessment of BTEX to humans through the dietary route was conducted based on the lifetime cancer risk (LTCR) for benzene and the hazard quotient (HQ) for BTEX. The following BTEX concentration ranges were observed: benzene

This work focuses on the concentration and health effects of volatile organic compounds (VOCs) at an intercity bus terminal in Taipei City, Taiwan. In this study, 36 VOCs were detected in the bus terminal, including 19 hazardous air pollutants. The measurement results indicate that ethanol, acetone, toluene, and methyl tert-butyl ether (MTBE) were the main VOCs dominating this bus terminal. Moreover, the average concentration of benzene, toluene, ethylbenzene, and xylene (BTEX) compounds was 106.0 μg/m3 inside the bus terminal, contributing to approximately 70% of the hazardous air pollutants. The measurement results suggest that traffic emissions, especially from diesel buses, were the major pollution sources in the bus terminal. The cancer risk for 1,3-butadiene, benzene, ethylbenzene, and naphthalene exceeded the suggested value by the U.S. EPA. In addition, the individual chronic hazard quotient of benzene was higher than the recommended level. The findings of this work imply that bus terminal workers face a potential health risk, which is a matter of concern.

In complex atmospheric emission environments such as urban agglomerates, multiple sources control the ambient chemical composition driving air quality and regional climate. In contrast to pristine sites, where reliance on single or a few chemical tracers is often adequate for resolving pollution plumes and source influences, the comprehensive chemical fingerprinting of sources using non-methane hydrocarbons (NMHCs) and the identification of suitable tracer molecules and emission ratios becomes necessary. Here, we characterise and present chemical fingerprints of some major urban and agricultural emission sources active in South Asia, such as paddy stubble burning, garbage burning, idling vehicular exhaust and evaporative fuel emissions. A total of 121 whole air samples were actively collected from the different emission sources in passivated air sampling steel canisters and then analysed for 49 NMHCs (22 alkanes, 16 aromatics, 10 alkenes and one alkyne) using thermal desorption gas chromatography flame ionisation detection. Several new insights were obtained. Propane was found to be present in paddy stubble fire emissions (8 %), and therefore, for an environment impacted by crop residue fires, the use of propane as a fugitive liquefied petroleum gas (LPG) emission tracer must be done with caution. Propene was found to be ∼ 1.6 times greater (by weight) than ethene in smouldering paddy fires. Compositional differences were observed between evaporative emissions of domestic LPG and commercial LPG, which are used in South Asia. While the domestic LPG vapours had more propane (40 ± 6 %) than n-butane (19 ± 2 %), the converse was true for commercial LPG vapours (7 ± 6 % and 37 ± 4 %, respectively). Isoprene was identified as a new tracer for distinguishing paddy stubble and garbage burning in the absence of isoprene emissions at night from biogenic sources. Analyses of source-specific inter-NMHC molar ratios revealed that toluene/benzene ratios can be used to distinguish among paddy stubble fire emissions in the flaming (0.38 ± 0.11) and smouldering stages (1.40 ± 0.10), garbage burning flaming (0.26 ± 0.07) and smouldering emissions (0.59 ± 0.16), and traffic emissions (3.54 ± 0.21), whereas i-pentane ∕ n-pentane can be used to distinguish biomass burning emissions (0.06–1.46) from the petrol-dominated traffic and fossil fuel emissions (2.83–4.13). i-butane ∕ n-butane ratios were similar (0.20–0.30) for many sources and could be used as a tracer for photochemical ageing. In agreement with previous studies, i-pentane, propane and acetylene were identified as suitable chemical tracers for petrol vehicular and evaporative emissions, LPG evaporative and vehicular emissions and flaming-stage biomass fires, respectively. The secondary pollutant formation potential and human health impact of the sources was also assessed in terms of their hydroxyl radical (OH) reactivity (s−1), ozone formation potential (OFP; gO3/gNMHC) and fractional benzene, toluene, ethylbenzene and xylenes (BTEX) content. Petrol vehicular emissions, paddy stubble fires and garbage fires were found to have a higher pollution potential (at ≥95 % confidence interval) relative to the other sources studied in this work. Thus, many results of this study provide a new foundational framework for quantitative source apportionment studies in complex emission environments.

The municipal solid waste transfer stations (MSWTSs) affects both the environment and human health. The present study aimed to investigatethe Concentrations of BTEX (benzene, toluene, ethylbenzene ...

Oil leakage from gas stations in Taiwan is commonly caused by the corrosion of oil tanks or loose pipeline joints, contaminating the soil and groundwater near the gas station. Wine-processing waste sludge (WPWS) does not contain toxic substances and has a high organic matter content. Thus, it has high affinity for methyl tert-butyl ether (MTBE) and benzene, toluene, ethylbenzene, and xylenes (BTEX), being suitable for application in preventing and controlling groundwater pollution. In this study, a permeable reaction barrier (PRB) constructed utilizing WPWS in a large water tank was designed to simulate the diffusion and blockage of gasoline plumes in an aquifer. The constructed WPWS PRB had a rectangular shape with a thickness and height of 9 and 60 cm, respectively. The depth in the aquifer was adjusted to 50 cm. MTBE was detected in the aquifer downstream of the WPWS PRB every day during the experiment; however, the maximum concentration detected was only 5.33 ppb. BTEX were only detected on 3 days during the experiment and had maximum concentrations of 1.76, 2.28, 0.34, and 0.60 ppb, which are below the water quality control standards.

Urinary benzene, toluene, ethylbenzene, and xylenes (BTEX) can be used as a reliable biomarker of exposure to these pollutants. This cross-sectional study aimed to employ biomonitoring to assess BTEX exposure among South Pars Gas Field (SPGF) workers in Assaluyeh, Iran. Forty employees who were working on the site were recruited as the case group. Besides, 31 administrative employees were recruited as the control group. Pre-shift and post-shift spot urine samples were collected from the subjects in the case group, while the subjects in the control group provided mid-morning urine samples. Overall, 111 urine samples, including 80 samples from the case group and 31 samples from the controls, were collected. Gas chromatography-mass spectrometry (GC/MS) was used to determine the urinary levels of BTEX compounds. The median urinary levels of benzene, toluene, ethylbenzene, m,p-xylene, and o-xylene in the post-shift samples of the exposed group were 1.24, 2.28, 0.5, 1.32, and 1.5 μg/l, respectively. Significant differences were observed in urinary BTEX levels among smokers and non-smokers in both studied groups (p

Benzene, toluene, ethylbenzene and xylene (BTEX) are monoaromatic hydrocarbons found frequently in petroleum and its derivatives; and they are among the most important pollutants of soil and groundwater. This study focused on harnessing the enzymatic capabilities of filamentous fungi Gliocladium sp. and Aspergillus terreus, dwelling in a petroleum-contaminated soil to degrade benzene, toluene, ethylbenzene and xylene (BTEX) compounds. The biodegradation experiment was carried out using the fungi individually and in consortium in a batch culture containing mineral salts medium supplemented with 1% v/v BTEX. The experiments were carried out in triplicates at room temperature on a rotary shaker (180rpm) for twenty five days and aliquots were taken on a five day interval to determine the hydrocarbon utilizing fungal (HUF) count and residual BTEX in order to monitor the rate of biodegradation. The hydrocarbon utilizing fungal counts were determined by direct counting using a Neubauer Haemocytometer while, the residual BTEX was determined using absorbance values measured using a spectrophotometer and the corresponding concentrations determined from a standard curve. The highest percentage degradation of BTEX was observed with Aspergillus terreus (89.1%) while, the least was observed with Gliocladium sp. (84.4%). The growth peak was attained on the 15th day in all treatments after which the HUF counts declined. Statistical analysis showed no significant difference (P>0.05) in the mean amounts of BTEX degraded and hydrocarbon-utilizing fungal counts between the treatments. The strains of Gliocladium sp. and Aspergillus terreus used in this study showed high ability for BTEX degradation thus, they are potential candidates for bioremediation of soils contaminated with monoaromatic hydrocarbons. Keywords: Biodegradation, BTEX, Gliocladium sp., Aspergillus terreus, Monoaromatic hydrocarbons

The present study aimed to assess BTEX (benzene, toluene, ethylbenzene, and xylenes) concentrations, their sources and health risk estimates in Shiraz, the fifth-most populous city in Iran. Air samples were collected from 19 sampling stations across Shiraz using passive samplers. Identification and quantification of BTEX were conducted by a Gas Chromatography–Mass Spectrometry (GC–MS). Spatial distribution of BTEX compounds were mapped by inverse distance weighting (IDW) procedure. Monte Carlo simulation was employed to assess the corresponding carcinogenic and non-carcinogenic risks of BTEX concentrations. BTEX concentrations were higher than current levels in Western countries but lower than concentrations measured in East Asia. Analysis of individual BTEX ratios and their strong correlation indicated that fresh traffic emissions were the main contributor to these compounds in Shiraz, with additional sources contributing to toluene (e.g. industrial solvent use) and benzene (e.g. evaporative emissions). The incremental lifetime cancer risk (ILCR) for benzene and ethylbenzene were estimated to be 6.49 × 10−7- 1.27 × 10-5 and 1.21 × 10−7- 2.37 × 10-6, respectively, exceeding the WHO and EPA recommendations. The current evaluation of BTEX sources and associated health risks will assist policymakers to define action plans to minimize BTEX exposure in Shiraz and similar cities in the Middle East.

The toxic air pollutants such as benzene, toluene, ethylbenzene and xylene (BTEX) as well as asbestos are considered hazardous because of their role in adverse impacts on human health. Accordingly,...

This study was aimed to evaluate urinary benzene, toluene, ethylbenzene, m + p-xylene, o-xylene (BTEX), as biomarkers of exposure to BTEX. Total of 76 first-morning void urine samples were collecte...

A new Pseudomonas putida strain (AQ8) was isolated from a decommissioned oil refinery's soil in Italy and characterized for its ability to degrade BTEX. The draft genome of the new strain was sequenced and annotated for genes that encode enzymes putatively involved in BTEX degradation and quorum sensing. The strain was transformed with a plasmid expressing lactonase, which cleaves the autoinducer quorum sensing signal molecule, the acyl-homoserine lactone, to obtain a quorum sensing minus strain. P. putida AQ8 depleted the 40% on average of all the components of the initial BTEX concentration in 36 h. The quorum sensing minus strain, in the same time interval, depleted only the 10% of the initial BTEX concentration. The role of quorum sensing in regulating the expression of the annotated benzene/toluene dioxygenase gene (benzA) and biphenyl/toluene/benzene dioxygenase (bphA) genes, which are involved in BTEX degradation, was studied by quantitative RT-real-time quantitative (q)PCR analysis. The qPCR data showed decreased levels of expression of the benzA and bphA genes in the quorum sensing minus strain. Our results showed, for the first time, quorum sensing modulation of the level of transcription of dioxygenase genes in the upper BTEX oxidation pathway.

Release of analytes from their native matrix and diffusion into the gas phase is the rate-limiting step for the sampling of volatiles in complex solid samples. This limitation is more serious in the solvent-less and solvent-free microextraction sampling strategies. In this research, a three-stage reinforced sampling strategy including high-pressure/sonication/low-pressure was introduced for fast and efficient release of analytes in soil samples. For this purpose, a novel ultrasound-assisted pressure-regulated solid-phase microextraction (UA-PR-SPME) device was developed. It was coupled with gas chromatography-flame ionization detection (GC-FID) and carried out for the determination of benzene, toluene, ethylbenzene, and xylenes (BTEX, as the model analytes) in complex solid samples. Graphene oxide/3-aminopropyltriethoxysilane (GO-APTES) nanocomposite was synthesized and used as the SPME fiber coating. Under optimal conditions, the limits of detection (LODs) were obtained 0.1-0.4 ng/g. The calibration curves were linear over the range of 2.4-5000 ng/g. Relative standard deviations (RSDs%) were calculated 5.1-7.0% (n = 6). The developed technique was employed for the analysis of BTEX in contaminated soil samples.

Select volatile organic compounds (VOCs) were measured in the vicinity of chemical facilities and other operations in the Rubbertown industrial area of Louisville, Kentucky (USA) using modified EPA Methods 325A/B passive sampler tubes. Two-week, time-integrated passive samplers were deployed at ten sites which were aggregated into three site groups of varying distances from the Rubbertown area facilities. In comparison to canister data from 2001 to 2005, two of the sites suggested generally lower current VOC levels. Good precision was obtained from the duplicate tubes (≤ 12%) for benzene, toluene, ethylbenzene, and xylene isomers (BTEX), styrene, 1,3-butadiene, perchloroethylene, and other trace VOCs. BTEX, styrene, and 1,3-butadiene concentrations were statistically significantly higher at two site groups near Rubbertown sources than the site group farther away. As found in a similar study in South Philadelphia, BTEX concentrations were also lower for sites farther from a source, though the decline was less pronounced on a percentage basis in Rubbertown. These results suggest that EPA Methods 325A/B can be useful to assess VOC gradients for emissions from chemical facilities besides fenceline benzene levels from refineries.

The primary aims of this present study were to evaluate the effect of oxygen limitation on the bacterial community structure of enrichment cultures degrading either benzene or toluene and to clarify the role of Malikia-related bacteria in the aerobic degradation of BTEX compounds. Accordingly, parallel aerobic and microaerobic enrichment cultures were set up and the bacterial communities were investigated through cultivation and 16S rDNA Illumina amplicon sequencing. In the aerobic benzene-degrading enrichment cultures, the overwhelming dominance of Malikia spinosa was observed and it was abundant in the aerobic toluene-degrading enrichment cultures as well. Successful isolation of a Malikia spinosa strain shed light on the fact that this bacterium harbours a catechol 2,3-dioxygenase (C23O) gene encoding a subfamily I.2.C-type extradiol dioxygenase and it is able to degrade benzene, toluene and ethylbenzene under clear aerobic conditions. While quick degradation of the aromatic substrates was observable in the case of the aerobic enrichments, no significant benzene degradation, and the slow degradation of toluene was observed in the microaerobic enrichments. Despite harbouring a subfamily I.2.C-type C23O gene, Malikia spinosa was not found in the microaerobic enrichments; instead, members of the Pseudomonas veronii/extremaustralis lineage dominated these communities. Whole-genome analysis of M. spinosa strain AB6 revealed that the C23O gene was part of a phenol-degrading gene cluster, which was acquired by the strain through a horizontal gene transfer event. Results of the present study revealed that bacteria, which encode subfamily I.2.C-type extradiol dioxygenase enzyme, will not be automatically able to degrade monoaromatic hydrocarbons under microaerobic conditions.

The combination of persulfate (PS) oxidation with enhanced bioremediation (EBR) is a potential trend in remediating organic-contaminated groundwater. However, the impacts of PS on EBR presented in the transition zone between PS oxidation zone and EBR zone need further study. To better characterize the impacts and provide available indicators, PS oxidation and EBR with nitrate amended were performed through the microcosm experiments to remove dissolved benzene, toluene, ethylbenzene and xylene (denoted as BTEX) in gasoline-saturated groundwater. The results indicated that PS oxidation combined with EBR almost completely removed BTEX with the ratio of > 93% over the experiments, which is better than PS oxidation (54–97%) but still worse than EBR (100%). The removal velocities of BTEX in EBR, PS oxidation, and PS oxidation combined with EBR were 0.94, 0.1–0.16, and 0.1–0.54 mg/L/d, respectively. High concentration of PS, along with high-strength activation, made the pH decrease to 3.3–4.4 and the Eh increase to 141–203 mV, thus greatly inhibited microbial activities as well. In such circumstances, oxygen and nitrate could not be significantly used as electron acceptors by microbials. To reduce the impacts of PS oxidation on EBR, the PS/BTEX molar ratio of 1 may be appropriate in transition zone. The hydro-chemical indicators, including pH, Eh, and availability of electron acceptors such as oxygen and nitrate, could reflect the impacts of PS oxidation on bioprocesses. During in-situ chemical oxidation (ISCO), PS injection and PS activation by Fe2+ should be managed for decreasing the impacts on EBR, based on the PS/BTEX and PS/Fe2+ molar ratios.

Persistent organic pollutants (POPs), such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and pesticides were measured in water samples from six sites on the Aoos Riv...

To assess the ecological risk resulting from an accidental gasoline spill upstream from a wetland, groundwater and sediment sampling was carried out during two campaigns at the 48th and 52nd months after the spill had occurred. In total, 21 groundwater monitoring wells in the affected area were sampled plus an additional reference well located upstream from the accident location. Seven sediment sampling points were selected inside the wetland, plus a reference point upstream from the accident. Physicochemical parameters, BTEX (benzene, toluene, ethylbenzene, m-xylene, p-xylene and o-xylene) and metal concentrations were analysed to estimate the chemical risk. Acute (Allivibrio fischeri, Daphnia similis, Hyalella azteca) and chronic (Artemia salina and Desmodesmus subspicatus) toxicity assays were performed with groundwater and sediments elutriate to determine the ecotoxicological risk. Results from groundwater indicated an extreme chemical level of risk in14 out of 21 monitoring wells. These 14 wells also exhibited free-phase gasoline and lead (Pb) concentrations above the threshold values adopted by this study. The presence of Pb, however, could not be associated with the gasoline accident. High acute and chronic toxicities were reported for the majority of wells. Conversely, the risks associated with the sediments were considered low in most sampling points, and the ecotoxicity found could not be related to the presence of gasoline. Groundwater flow modelling results have evidenced the migration of the contamination plume towards the wetland. Thus, to prevent contamination from reaching the protected area, more effective groundwater clean-up techniques are still required.

The health risk assessment of benzene, toluene, ethylbenzene and xylenes (BTEX) associated with the combustion of gas in gas flares of one of the largest gas refinery complex in Iran (South Pars gas complex in Asalouyeh, 1–10 phases) has been conducted based on Office of Environmental Health Hazard Assessment’s (OEHHA) method. In this regard, AERMOD dispersion model coupled with WRF model has been used to predict the ground level concentration of pollutants emitted from gas flares. The accuracy of the dispersion model has been verified with measured ambient SO2 data. The risk assessment results have shown that the chronic noncarcinogenic risk of BTEX emitted from gas flares is in the acceptable range in the residential area and most of refineries site. Regarding acute noncarcinogenic risk, the hazard indices (HIs) are only greater than one in refineries sites and are less than permitted level elsewhere in the study area. For carcinogenic risk, the cumulative risk of benzene and ethylbenzene are greater than 10−6 in refineries sites and two cities (Asalouyeh and Nakhl Taghi), but in two camps nearby the gas flaring sites, the value is less than the allowable limit. Besides, the relative contribution of gas flaring in health risk assessment of BTEX is accomplished by calculating the health risk parameters with the measured BTEX concentrations at 10 receptors, which reveal the cumulative effects of all potential sources of BTEX throughout the study area. The comparison of health risk parameters has shown that the health risk of BTEX associated with flaring is in average 42 %, 2.6 % and 10.8 % of the overall health risk of BTEX in industrial areas, two cities and camps, respectively. It can be concluded that the contribution of gas flaring in industrial areas is noticeable and application of emission reduction policies at gas flaring, has a major effect on industrial areas and maybe has minor effects on the air quality of the residential areas.

Background & Aims of the Study: The benzene, toluene, ethylbenzene, and xylene (BTEX) compounds are the most abundant volatile organic compounds in the urban atmosphere. This study aimed to investigate and monitor the ambient BTEX compounds in Ahvaz, Iran. Materials and Methods: The atmospheric concentrations of the BTEX were measured using the Air Quality Monitoring Station in the center of Ahvaz. Hourly mean concentration data of the BTEX compounds from March 21, 2017, until November 21, 2017, were obtained from the environmental protection organization of Khuzestan province. Results: Mean concentrations of the BTEX compounds were 0.80±0.04, 2.55±0.10, 0.54±0.03, and 1.26±0.07 µg/m3, respectively, and these concentrations were lower in the summer, compared to other seasons. A significant relationship between benzene and other BTEX compounds indicates that BTEX release from certain sources, such as gasoline vehicles. Moreover, the mean toluene/benzene ratio was estimated at 3.29±0.84, and this ratio shows that the highest concentrations of pollutant emissions were emitted from the activity traffic. Carcinogen risk assessment of Ahvazi people exposure to benzene showed that the mean cancer risk value for benzene exposure was 0.89×10−6, which was lower than the unit cancer risk value (i.e., 1×10-6). Hazard quotient's calculation showed that the mean non-carcinogenic risk values for exposure to BTEX compounds were 3.84, 0.074, 0.077, and 1.76, respectively. The mean hazard index (HI) for exposure to BTEX compounds was 5.75, which was considerably higher than the unit value of 1. Conclusion: Based on the findings, the necessity of controlling BTEX emissions, especially benzene and identifying the sources of these compounds can be a useful tool for the management of connected control strategies.

This study aims to determine BTEX concentrations in the Metropolitan Region of Rio de Janeiro (MRRJ, Brazil) and evaluate potential health risks of benzene and ethylbenzene exposure based on the collected data, in 2015, the year before the Rio 2016 Olympic Games. Samples were collected and analyzed following method TO-15 (U.S.EPA). Toluene was the most abundant compound in all samples (mean concentration 16.72 ± 15.70 µg m−3). The average benzene concentration in ambient air (3.44 ± 3.14 µg m−3) was slightly lower than the yearly average “upper assessment threshold”, 3.5 µg m−3, established by EU Directive 2008/50/EC. The calculated cancer risk values were > 1 × 10−6 for all samples, clearly indicating a potential cancer risk and the importance of fixed measurements by the monitoring stations to assess ambient air quality in the urban areas of the MRRJ. Calculated ratios for the BTEX species indicate that these compounds are predominantly emitted from vehicular sources with a contribution from industrial sources.

In this study, nano-CaO2 (nCaO2 ) was successfully synthesized and constituted the nCaO2 /Fe(II) system applying to remediate BTEX, which are typical mixed pollutants in contaminated groundwater. The particle size of the synthesized nCaO2 was 108.91 nm, and it displayed better BTEX remediation performance than that of commercial CaO2 . The innovative generation pattern of hydroxyl radicals ( HO · ) in the nCaO2 /Fe(II) system has been investigated using benzoic acid as the HO · probe, and the proper molar ratio of nCaO2 /Fe(II) was optimized as 1/1. Over 90% of BTEX was removed in 180 min with the nCaO2 /Fe(II)/BTEX molar ratio of 40/40/1. Further experiments evaluated the influence of co-existence of mixed pollutants chlorinated hydrocarbon compounds (CHCs) or surfactant constituents on BTEX remediation performance. The experimental results suggested that CHCs have limited influence on BTEX removal rate and surfactants have negative effects on BTEX remediation performance in the experimental conditions. In conclusion, the findings in this study could give some inspirations to apply the nCaO2 /Fe(II) process in remediating co-existing pollutants in contaminated groundwater. PRACTITIONER POINTS: nCaO2 /Fe(II) system applied to remediate mixed contaminants. HO · generation pattern of the nCaO2 /Fe(II) system has been investigated. The influence of chloride hydrocarbon compounds have been studied. The effects of surfactants were evaluated.