Urban roadside aromatic hydrocarbons in three cities of the Pearl River Delta,People's Republic of China

Urban roadside levels of benzene, toluene, ethylbenzene and xylenes (BTEX) were investigated in three typical cities (Guangzhou, Macau and Nanhai) in the Pearl River Delta Region of south China. Air samples were collected at typical ground level microenvironments by multi-bed adsorbent tubes. The BTEX concentrations were determined by thermal desorption–gas chromatography–mass selective detector (TD–GC–MSD) technique. The mean concentrations of benzene, toluene, ethylbenzene and xylenes were, respectively, 51.5, 77.3, 17.8 and 81.6 μg/m³ in Guangzhou, 34.9, 85.9, 24.1, 95.6 μg/m³ in Macau, and 20.0, 39.1, 3.0 and 14.2 μg/m³ in Nanhai. The relative concentration distribution pattern and mutual correlation analysis indicated that in Macau BTEX were predominantly traffic-related while in Guangzhou benzene had sources other than vehicle emission. In Nanhai, both benzene and toluene had different sources other than vehicle emission. The samples collected from Guangzhou showed that BTEX had significant higher concentrations in November than those in July.     

High occurrence of BTEX around major industrial plants in Kaohsiung,Taiwan

The Houjing River, which flows by large industrial complexes in southwestern Taiwan, has been seriously polluted with benzene, toluene, ethylbenzene, and xylene (BTEX). Using Spearman’s analysis of BTEX concentrations measured at different sites along the river, we identified the main sources of this pollution to be the Dashe and Renwu Industrial Parks. Maximum concentrations of benzene and toluene (402 and 143.19 µg/L, respectively) were considerably higher than those reported in similar studies and regulatory limits. We compared these findings with those of positive matrix factorization (PMF) modelling. PMF also identified the two industrial parks as being sources of BTEX, most likely originating from petrochemical activities that occur there. This study can serve as an important reference for future watershed management and pollution control plans for Kaohsiung, the most industrialized city in Taiwan. PMF proved to be a reliable computer modelling program for source apportionment and environmental forensic studies.     

Risk factors for increased BTEX exposure in four Australian cities

Benzene, toluene, ethylbenzene and xylenes (BTEX) are common volatile organic compounds (VOCs) found in urban airsheds. Elevated levels of VOCs have been reported in many airsheds at many locations, particularly those associated with industrial activity, wood heater use and heavy traffic. Exposure to some VOCs has been associated with health risks. There have been limited investigations into community exposures to BTEX using personal monitoring to elucidate the concentrations to which members of the community may be exposed and the main contributors to that exposure. In this cross sectional study we investigated BTEX exposure of 204 non-smoking, non-occupationally exposed people from four Australian cities. Each participant wore a passive BTEX sampler over 24h on five consecutive days in both winter and summer and completed an exposure source questionnaire for each season and a diary for each day of monitoring. The geometric mean (GM) and range of daily BTEX concentrations recorded for the study population were benzene 0.80 (0.04-23.8 ppb); toluene 2.83 (0.03-2120 ppb); ethylbenzene 0.49 (0.03-119 ppb); and xylenes 2.36 (0.04-697 ppb). A generalised linear model was used to investigate significant risk factors for increased BTEX exposure. Activities and locations found to increase personal exposure included vehicle repair and machinery use, refuelling of motor vehicles, being in an enclosed car park and time spent undertaking arts and crafts. A highly significant difference was found between the mean exposures in each of the four cities, which may be explained by differences in fuel composition, differences in the mix and density of industry, density of motor vehicles and air pollution meteorology.     

Assessment of indoor air concentrations of VOCs and their associated health risks in the library of Jawaharlal Nehru University,New Delhi

The present work investigated the levels of total volatile organic compounds (TVOC) and benzene, toluene, ethylbenzene, m/p-xylene, and o-xylene (BTEX) in different microenvironments in the library of Jawaharlal Nehru University in summer and winter during 2011–2012. Carcinogenic and non-carcinogenic health risks due to organic compounds were also evaluated using US Environmental Protection Agency (USEPA) conventional approaches. Real-time monitoring was done for TVOC using a data-logging photo-ionization detector. For BTEX measurements, the National Institute for Occupational Safety and Health (NIOSH) standard method which consists of active sampling of air through activated charcoal, followed by analysis with gas chromatography, was performed. Simultaneously, outdoor measurements for TVOC and BTEX were carried out. Indoor concentrations of TVOC and BTEX (except benzene) were higher as compared to the outdoor for both seasons. Toluene and m/p-xylene were the most abundant organic contaminant observed in this study. Indoor to outdoor (I/O) ratios of BTEX compounds were generally greater than unity and ranged from 0.2 to 8.7 and 0.2 to 4.3 in winter and summer, respectively. Statistical analysis and I/O ratios showed that the dominant pollution sources mainly came from indoors. The observed mean concentrations of TVOC lie within the second group of the Molhave criteria of indoor air quality, indicating a multifactorial exposure range. The estimated lifetime cancer risk (LCR) due to benzene in this study exceeded the value of 1?×?10^?6 recommended by USEPA, and the hazard quotient (HQ) of non-cancer risk came under an acceptable range.     

Indoor pollution and burning practices in wood stove management

This study evaluates effects of good burning practice and correct installation and management of wood heaters on indoor air pollution in an Italian rural area. The same study attests the role of education in mitigating wood smoke pollution. In August 2007 and winters of 2007 and 2008, in a little mountain village of Liguria Apennines (Italy), indoor and outdoor benzene, toluene, ethylbenzene, and xylene (BTEX) concentrations were measured in nine wood-heated houses. During the first sampling, several mistakes in heating plant installations and management were found in all houses. Indoor BTEX concentrations increased during use of wood burning. Low toluene/benzene ratios were in agreement with wood smoke as main indoor and outdoor pollution source. Other BTEX sources were identified as the indoor use of solvents and paints and incense burning. Results obtained during 2007 were presented and discussed with homeowners. Following this preventive intervention, in the second winter sampling all indoor BTEX concentrations decreased, in spite of the colder outdoor air temperatures. Information provided to families has induced the adoption of effective good practices in stoves and fire management. These results highlight the importance of education, supported by reliable data on air pollution, as an effective method to reduce wood smoke exposures.

Implications:Information about burning practices and correct installation and management of wood heaters, supported by reliable data on indoor and outdoor pollution, may help to identify and remove indoor pollution sources. This can be an effective strategy in mitigate wood smoke pollution.     

Response of a solid-liquid two-phase partitioning bioreactor to transient BTEX loadings

A two-phase partitioning bioreactor (TPPB) consisting of an aqueous phase containing a bacterial consortium and a polymeric phase of silicone rubber pellets (solid volume fraction 0.1) was used to treat a gaseous waste stream containing benzene, toluene, ethylbenzene and o-xylene (BTEX). The function of the solid polymer phase was to absorb/desorb the gaseous volatile organic compounds providing a buffering effect to protect the cells from high transient loadings and to sequester the BTEX for subsequent degradation. The TPPB was subjected to high and fluctuating inlet loadings of BTEX in the form of 4h step changes of 2, 4, 6 and 10 times the nominal inlet loading of 60 gm(-3) h(-1) total BTEX in approximately equal amounts, and removal efficiencies and elimination capacities were determined. It was found that overall removal efficiencies of greater than 95% can be achieved while obtaining overall elimination capacities of up to 282 gm(-3) h(-1) during transient operation and TPPB operation succumbs to toxic substrate levels between step changes of 6 and 10 times the nominal loading value (360-600 gm(-3) h(-1)). BTEX concentrations in the aqueous phase and the polymer phase of the TPPB were monitored throughout the imposed step changes to determine the extent to which the sequestering phase can buffer the aqueous phase from BTEX. With the polymer phase comprising only 10% of the total working volume of the reactor, the polymer beads accounted for up to 93%, 91% and 70% of the total BTEX present in the working volume for step changes of 2, 4 and 6 times the nominal loading, respectively.     

Spatial and seasonal variations of atmospheric BTEX,sulfur dioxide,nitrogen dioxide,and ozone concentrations in Istanbul,and health risk assessment of BTEX

Volatile organic compounds (VOCs) such as benzene, toluene, ethylbenzene, and xylene (BTEX) along with inorganic gases such as sulfur dioxide (SO₂), nitrogen dioxide (NO₂), and ozone (O₃) levels were found in the atmosphere of the Kemerburgaz region where environmental issues became a major concern due to nearby incineration plant and waste disposal facility in Istanbul. Ten sampling locations were selected considering possible sources in the study area. The sampling areas were classified as suburban, industrial, rural, and background regions. Sampling campaigns were carried out for four-week periods from March 2011 to August 2012 in all locations. Elevated concentrations of BTEX around roads and the industrial locations indicated that vehicle exhaust and industrial activities were the main sources of these pollutants in the region. Concentrations of NO₂ were also high around roads. A much more uniform distribution was observed for SO₂ during sampling periods. However higher levels were observed at suburban locations due to the use of coal for local heating especially during winter. Ozone concentrations were low at the industrial locations and roadsides, but high in suburban and rural locations downwind from the sources. The results of these organic and inorganic gases meet the national limit values. Furthermore, a lifetime risk assessment methodology was used to evaluate the potential adverse health effects of BTEX. The mean cancer risk level for benzene was estimated to be 7.71E-07 that is lower than assigned acceptable risk level of 1.0E-04. Toluene, ethylbenzene, and xylenes were lower than the specified level of 1.0 with respect to mean non-carcinogenic risks. The findings reveal that determined BTEX emissions do not pose a health threat to residents in the studied region.     

The variability and intrinsic remediation of a BTEX plume in anaerobic sulphate-rich groundwater

Data from long-term groundwater sampling, limited coring, and associated studies are synthesised to assess the variability and intrinsic remediation/natural attenuation of a dissolved hydrocarbon plume in sulphate-rich anaerobic groundwater. Fine vertical scale (0.25- and 0.5-m depth intervals) and horizontal plume-scale (>400 m) characteristics of the plume were mapped over a 5-year period from 1991 to 1996. The plume of dissolved BTEX (benzene, toluene, ethylbenzene, xylene) and other organic compounds originated from leakage of gasoline from a subsurface fuel storage tank. The plume was up to 420 m long, less than 50 m wide and 3 m thick. In the first few years of monitoring, BTEX concentrations near the point of leakage were in approximate equilibrium with non-aqueous phase liquid (NAPL) gasoline. NAPL composition of core material and long-term trends in ratios of BTEX concentrations in groundwater indicated significant depletion (water washing, volatilisation and possibly biodegradation) of benzene from residual NAPL after 1992. Large fluctuations in BTEX concentrations in individual boreholes were shown to be largely attributable to seasonal groundwater flow variations. A combination of temporal and spatial groundwater quality data was required to adequately assess the stationarity of plumes, so as to allow inference of intrinsic remediation. Contoured concentration data for the period 1991 to 1996 indicated that plumes of toluene and o-xylene were, at best, only partially steady state (pseudo-steady state) due to seasonal groundwater flow changes. From this analysis, it was inferred that significant remediation by natural biodegradation was occurring for BTEX component plumes such as toluene and o-xylene, but provided no conclusive evidence of benzene biodegradation. Issues associated with field quantification of intrinsic remediation from groundwater sampling are highlighted. Preferential intrinsic biodegradation of selected organic compounds within the BTEX plume was shown to be occurring, in parallel with sulphate reduction and bicarbonate production. Ratios of average hydrocarbon concentrations to benzene for the period 1991 to 1992 were used to estimate degradation rates (half-lives) at various distances along the plume. The estimates varied with distance, the narrowest range being, for toluene, 110 to 260 days. These estimates were comparable to rates determined previously from an in situ tracer test and from plume-scale modelling.     

Removal of BTEX vapor from waste gases by a trickle bed biofilter

The system performance of a trickle bed biofilter for treating single and mixed benzene, toluene, ethylbenzene, and o-xylene (BTEX) vapors from waste gases was investigated under different gas flow rates and influent BTEX concentrations. When a single substrate was fed, removal efficiencies of greater than 90% could be achieved for the loads below 64 g benzene/m3/hr, 110 g toluene/m3/hr, 53 g ethylbenzene/m3/hr, and 55 g o-xylene/m3/hr. When a mixed substrate was fed, removal efficiencies of each compound could be above 90% at BTEX loads below 96 g/m3/hr. The trickle bed biofilter appears to be an effective treatment process for removing both single and mixed BTEX vapors with low to high loads. Under similar substrate loads, BTEX vapors were preferentially biodegraded in the order of toluene, benzene, o-xylene, and ethylbenzene. The volumetric removal rates (elimination capacities) of BTEX vapors for a single-substrate feed were higher than those for a mixed-substrate feed under similar substrate loads; these differences were enhanced at higher substrate loads and less significant for a preferred substrate.     

Aromatic hydrocarbons in the atmospheric environment. Part III: personal monitoring

As part of a larger study, personal sampling of the aromatic hydrocarbons benzene, toluene, ethylbenzene and the isomeric xylenes (BTEX) was carried out by 55 nonsmoking volunteers for a period of 14 days. Thirty-nine persons lived in a rural area near Hannover (Germany) with hardly any traffic at all, while 16 persons lived in a high-traffic city street in Hannover. The personal exposure level of the persons in the rural area (some commuting to Hannover) was: 2.9, 24.8, 2.4 and 7.7 μg m⁻³ for benzene, toluene, ethylbenzene and the sum of xylenes, respectively, while the corresponding data for the high traffic city streets were 4.0, 22.2, 2.8 and 9.7 μg m⁻³ (geometric means). Four microenvironments have been monitored which contribute to the total exposure to BTEX, i.e. the home, the outdoor air, the workplace and the car cabin. The most important microenvironment for non-working persons is the private home. The concentration of most BTEX in the private home is almost equal to the personal exposure level, demonstrating that the indoor pollution in the home makes by far the highest contribution to the total exposure. For working people (mostly office workers), the workplace is the second most important microenvironment contributing to the total BTEX exposure. Taking all working persons into consideration (independent of the location of their private home) the personal exposure level is higher by a factor of 1.2–1.4 than that of the workplace (for toluene this factor is 2.2). As already found by others, very high BTEX concentrations may be found in car cabins, in particular, if the engine is gasoline-driven. In the cabin of 44 cars in the rural/urban area average benzene concentrations (geometric mean) of 12/14 μg m⁻³ and a maximum value of ∼550 μg m⁻³ were found. On average, the participating volunteers drove their car for 45 min day⁻¹ (i.e. 3% of the day). Nevertheless, the car cabin constitutes about 10% of the total benzene exposure. Refueling of the car during the 14-day sampling period has only a small effect on the personal exposure level.     

Ambient levels of volatile organic compounds in the atmosphere of Greater Cairo

Ambient volatile organic compounds (VOCs) samples were collected at three locations, two in urban areas in Greater Cairo (Ramsis and Haram) and background one in rural area in Menofiya province (Kafr El-Akram), during the period of June, 2004–August, 2004. The highest concentrations of VOCs were found in Ramsis, whereas the lowest concentrations were detected in Kafr El-Akram, and the difference in mean concentrations were statistically significant (p<0.001). Among all of the measured VOCs species, the contribution of individual VOC to the total VOCs concentration were very similar in Ramsis and Haram locations, toluene was the most abundant compound followed by (m, p)-xylene. This similarity implies a similar emission sources of VOCs in both urban locations, vehicle exhausts are the dominant one. Greater Cairo has high levels of volatile aromatic hydrocarbons compared with many polluted cities in the world. The BTEX (benzene: toluene: ethylbenzene: xylenes) concentration ratios were (2.01:4.94:1:4.95), (2.03:4.91:1:4.87) and (2.31:2.98:1:2.59) in Ramsis, Haram and Kafr El-Akram, respectively. The average toluene/benzene (T/B), (m, p)-xylene/benzene ((m, p)-X/B) and o-xylene/benzene (o-X/B) concentration ratios were 2.45, 1.61and 0.85, respectively in Ramsis and 2.42, 1.61 and 0.78, respectively in Haram. The ratios in both urban locations were of the same magnitude and close to those obtained from automotive exhausts, indicating that the ambient BTEX originate mainly from motor vehicle emissions. However, the (T/B), ((m, p)-X/B) and (o-X/B) concentration ratios were 1.29, 0.71 and 0.41 in Kafr El-Akram, respectively. These ratios were lower than those found in Ramsis and Haram locations and in automotive exhaust, suggesting that the BTEX in Kafr El-Akram do not come from a local source and are exclusively results from the diffusion and dispersion of VOCs produced from the traffic density in the surrounding cities. Significant positive correlation coefficients (p<0.001) were found between the concentrations of BTEX compounds at the three sampling locations. The diurnal variation of VOCs concentrations in Ramsis location showed two daily peaks linked to traffic density.     

Benzene, toluene, ethyl benzene and xylenes in ambient air and Pinus sylvestris L. needles: a comparative study between Belgium, Hungary and Latvia

Concentrations of benzene, toluene, ethyl benzene and xylenes (BTEX) in ambient air and in 1 yr old Pinus sylvestris pine needles were monitored along a busy road, petrol station and rural area of Belgium, Hungary and Latvia in a 1 yr period. To test P. sylvestris as a possible biomonitor for the BTEX concentrations, samples were taken in the four seasons. As the distribution of data was not normal, the level of pollution on different sites and seasons was compared and evaluated by non-parametric tests. The measured air concentrations did not differ significantly from one season to another throughout the year. There were, however, differences between sampling places. The C₂-alkylbenzene and toluene concentrations in the needles were similar in the autumn/winter and spring/summer periods but a significant decrease in their concentration was observed in every place between winter and spring. This effect was less obvious for toluene.     

Petroleum mass removal from low permeability sediment using air sparging/soil vapor extraction: impact of continuous or pulsed operation

Air sparging and soil vapor extraction (AS/SVE) are innovative remediation techniques that utilize volatilization and microbial degradation to remediate petroleum spills from soils and groundwater. This in situ study investigated the use of AS/SVE to remediate a gasoline spill from a leaking underground storage tank (UST) in the low permeability, clayey soil of the Appalachian Piedmont. The objectives of this study were to evaluate AS/SVE in low permeability soils by quantifying petroleum mass removal rates, monitoring vadose zone contaminant levels, and comparing the mass extraction rates of continuous AS/SVE to 8 and 24 h pulsed operation. The objectives were met by collecting AS/SVE exhaust gas samples and vadose zone air from multi-depth soil vapor probes. Samples were analyzed for O₂, CO₂, BTEX (benzene, toluene, ethylbenzene, xylene), and total combustible hydrocarbon (TCH) concentrations using portable hand meters and gas chromatography. Continuous AS/SVE was effective in removing 608 kg of petroleum hydrocarbons from low permeability soil in 44 days (14.3 kg day⁻¹). Mass removal rates ranged from 2.6 times higher to 5.1 times lower than other AS/SVE studies performed in sandy sediments. BTEX levels in the vadose zone were reduced from about 5 ppm to 1 ppm. Ten pulsed AS/SVE tests removed 78 kg in 23 days and the mean mass removal rate (17.6 kg day⁻¹) was significantly higher than the last 15 days of continuous extraction. Pulsed operation may be preferable to continuous operation because of increased mass removal and decreased energy consumption.     

Construction and comparison of fluorescence and bioluminescence bacterial biosensors for the detection of bioavailable toluene and related compounds

Environmental pollution with petroleum products such as benzene, toluene, ethylbenzene, and xylenes (BTEX) has garnered increasing awareness because of its serious consequences for human health and the environment. We have constructed toluene bacterial biosensors comprised of two reporter genes, gfp and luxCDABE, characterized by green fluorescence and luminescence, respectively, and compared their abilities to detect bioavailable toluene and related compounds. The bacterial luminescence biosensor allowed faster and more-sensitive detection of toluene; the fluorescence biosensor strain was much more stable and thus more applicable for long-term exposure. Both luminescence and fluorescence biosensors were field-tested to measure the relative bioavailability of BTEX in contaminated groundwater and soil samples. The estimated BTEX concentrations determined by the luminescence and fluorescence bacterial biosensors were closely comparable to each other. Our results demonstrate that both bacterial luminescence and fluorescence biosensors are useful in determining the presence and the bioavailable fractions of BTEX in the environment.     

Inverse modeling of BTEX dissolution and biodegradation at the Bemidji, MN crude-oil spill site

The U.S. Geological Survey (USGS) solute transport and biodegradation code BIOMOC was used in conjunction with the USGS universal inverse modeling code UCODE to quantify field-scale hydrocarbon dissolution and biodegradation at the USGS Toxic Substances Hydrology Program crude-oil spill research site located near Bemidji, MN. This inverse modeling effort used the extensive historical data compiled at the Bemidji site from 1986 to 1997 and incorporated a multicomponent transport and biodegradation model. Inverse modeling was successful when coupled transport and degradation processes were incorporated into the model and a single dissolution rate coefficient was used for all BTEX components. Assuming a stationary oil body, we simulated benzene, toluene, ethylbenzene, m,p-xylene, and o-xylene (BTEX) concentrations in the oil and ground water, respectively, as well as dissolved oxygen. Dissolution from the oil phase and aerobic and anaerobic degradation processes were represented. The parameters estimated were the recharge rate, hydraulic conductivity, dissolution rate coefficient, individual first-order BTEX anaerobic degradation rates, and transverse dispersivity. Results were similar for simulations obtained using several alternative conceptual models of the hydrologic system and biodegradation processes. The dissolved BTEX concentration data were not sufficient to discriminate between these conceptual models. The calibrated simulations reproduced the general large-scale evolution of the plume, but did not reproduce the observed small-scale spatial and temporal variability in concentrations. The estimated anaerobic biodegradation rates for toluene and o-xylene were greater than the dissolution rate coefficient. However, the estimated anaerobic biodegradation rates for benzene, ethylbenzene, and m,p-xylene were less than the dissolution rate coefficient. The calibrated model was used to determine the BTEX mass balance in the oil body and groundwater plume. Dissolution from the oil body was greatest for compounds with large effective solubilities (benzene) and with large degradation rates (toluene and o-xylene). Anaerobic degradation removed 77% of the BTEX that dissolved into the water phase and aerobic degradation removed 17%. Although goodness-of-fit measures for the alternative conceptual models were not significantly different, predictions made with the models were quite variable.     

Determination of benzene, toluene, ethylbenzene, xylenes in water at sub-ng l-1 levels by solid-phase microextraction coupled to cryo-trap gas chromatography-mass spectrometry

A trace analytical method of benzene, toluene, ethylbenzene and xylenes (BTEX) in water has been developed by using headspace solid-phase microextraction (HS-SPME) coupled to cryo-trap gas chromatography-mass spectrometry (GC-MS). The chromatographic peak shape for BTEX was improved by using cryo-trap equipment. The HS-SPME experimental procedures to extract BTEX from water were optimized with a 75 microm carboxen/polydimethylsiloxane (CAR/PDMS)-coated fiber at a sodium chloride concentration of 267 g l(-1), extraction for 15 min at 25 degrees C and desorption at 290 degrees C for 2 min. Good linearity was verified in a range of 0.0001-50 microg l(-1) for each analyte (r(2)=0.996-0.999). The limits of detection (LODs) of BTEX in water reached at sub-ng l(-1) levels. LODs of benzene, toluene, ethylbenzene, m/p-xylene and o-xylene were 0.04, 0.02, 0.05, 0.01 and 0.02 ng l(-1), respectively. The proposed analytical method was successfully used for the quantification of trace BTEX in ground water. The results indicate that HS-SPME coupled to cryo-trap GC-MS is an effective tool for analysis of BTEX in water samples at the sub-ng l(-1) level.     

Measurement of BTEX (benzene,toluene, ethybenzene,and xylene) levels at urban and semirural areas of Algiers City using passive air samplers

The study presents the levels of air pollution by aromatic organic compounds BTEX (benzene, toluene, ethylbenzene, o-, m-, and p-xylenes) in the city of Algiers. The sampling was carried out using Radiello passive sampler. Three sampling campaigns were carried out in roadside, tunnel, urban background, and semirural sites in Algiers. In order to determine the diurnal mean levels of air pollution by BTEX to which people are exposed, a modified passive sampler was used for the first time. In addition, monitoring of pollution inside vehicles was also made. In the spring of 2009, more than 27 samplings were carried out. In the background and road traffic sites the Radiello sampler was exposed for 7 days, whereas the time exposure was reduced to 1 day in the case of the vehicle as well as the tunnel. The results indicate that average benzene concentrations in the roadside and inside vehicle exceed largely the limit value of 5 μg m^?3 established by the European Community (EC). On the other hand, it has been noticed that the concentration levels of other BTEX are relatively high. Also, in order to identify the origin of emission sources, ratios and correlations between the BTEX species have been highlighted. This study shows that road traffic remains the main source of many local emission in Algiers.

Implications The vehicle fleet in Algeria is growing rapidly since the 1990s following economic growth and is responsible for the increasing air pollution in large cities. Because there are no data collection of BTEX carried out by national air quality network, all environmental and transportation policies are based on European emissions standards, but national emission standards are currently not in place. This work will contribute to the analysis of real emissions of BTEX in Algiers, for the development of management and for assessment of population exposure variation depending on the location in the city of Algiers.     

Degradation characteristics of toluene,benzene, ethylbenzene,and xylene by Stenotrophomonas maltophilia T3-c

Stenotrophomonas maltophilia T3-c, isolated from a biofilter for the removal of benzene, toluene, ethylbenzene, and xylene (BTEX), could grow in a mineral salt medium containing toluene, benzene, or ethylbenzene as the sole source of carbon. The effect of environmental factors such as initial toluene mass, medium pH, and temperature on the degradation rate of toluene was investigated. The cosubstrate interactions in the BTEX mixture by the isolate were also studied. Within the range of initial toluene mass (from 23 to 70 pmol), an increased substrate concentration increased the specific degradation of toluene by S. maltophilia T3-c. The toluene degradation activity of S. maltophilia T3-c could be maintained at a broad pH range from 5 to 8. The rates at 20 and 40 degrees C were 43 and 83%, respectively, of the rate at 30 degrees C. The specific degradation rates of toluene, benzene, and ethylbenzene by strain T3-c were 2.38, 4.25, and 2.06 micromol/g-DCW/hr. While xylene could not be utilized as a growth substrate by S. maltophilia T3-c, the presence of toluene resulted in the cometabolic degradation of xylene. The specific degradation rate of toluene was increased by the presence of benzene, ethylbenzene, or xylene in binary mixtures. The presence of toluene or xylene in binary mixtures with benzene increased the specific degradation rate of benzene. The presence of ethylbenzene in binary mixtures with benzene inhibited benzene degradation. The presence of more than three kinds of substrates inhibited the specific degradation rate of benzene. All BTEX mixtures, except tri-mixtures of benzene, ethylbenzene, and xylene or mixtures of all four substrates, had little effect on the degradation of ethylbenzene by S. maltophilia T3-c. The utilization preference of the substrates by S. maltophilia T3-c was as follows: ethylbenzene was degraded fastest, followed by toluene and benzene. However, the specific degradation rates of substrates, in order, were benzene, toluene, and ethylbenzene.     

Nitrate-enhanced bioremediation of BTEX-contaminated groundwater: parameter estimation from natural-gradient tracer experiments

Two natural-gradient pulse tracer tests were conducted in a petroleum-contaminated aquifer to evaluate the potential for benzene, toluene, ethylbenzene, and xylenes (BTEX) biodegradation under enhanced nitrate-reducing conditions. Addition of nitrate resulted in loss of toluene, ethylbenzene, and m,p-xylenes (TEX) after an initial lag period of approximately 9 days. Losses of benzene were not observed over the 60-day monitoring period. Tracer breakthrough curves (BTCs) were analyzed to derive transport and biodegradation parameters, including advective velocities, retardation factors, dispersion coefficients, biodegradation rate constants, and nitrate utilization ratios. Using the parameters derived from the BTC analysis, numerical simulations of one of the tracer experiments were conducted using BIONAPL/3D [Molson, J., BIONAPL/3D User Guide, A 3D Coupled Flow and Multi-Component Reactive transport model. University of Waterloo, Waterloo, Ontario, Canada]. Simulations using the BTC-derived transport and biodegradation parameters successfully reproduced benzene, TEX, and nitrate concentrations measured during the tracer experiment. Comparisons of observed and simulated nitrate concentrations indicate that the mass ratio of nitrate-N utilized to TEX degraded increased over time during the experiment, reaching values many times that expected based on stoichiometry of TEX oxidation coupled to nitrate reduction. Excess nitrate loss is likely due to oxidation of other organics in addition to TEX.     

Volatile organic compounds (VOCs) in urban atmosphere of Hong Kong

The assessment of volatile organic compounds (VOCs) has become a major issue of air quality network monitoring in Hong Kong. This study is aimed to identify, quantify and characterize volatile organic compounds (VOCs) in different urban areas in Hong Kong. The spatial distribution, temporal variation as well as correlations of VOCs at five roadside sampling sites were discussed. Twelve VOCs were routinely detected in urban areas (Mong Kok, Kwai Chung, Yuen Long and Causeway Bay). The concentrations of VOCs ranged from undetectable to 1396 microg/m3. Among all of the VOC species, toluene has the highest concentration. Benzene, toluene, ethylbenzene and xylenes (BTEX) were the major constituents (more than 60% in composition of total VOC detected), mainly contributed from mobile sources. Similar to other Asian cities, the VOC levels measured in urban areas in Hong Kong were affected both by automobile exhaust and industrial emissions. High toluene to benzene ratios (average T/B ratio = 5) was also found in Hong Kong as in other Asian cities. In general, VOC concentrations in the winter were higher than those measured in the summer (winter to summer ratio > 1). As toluene and benzene were the major pollutants from vehicle exhausts, there is a necessity to tighten automobile emission standards in Hong Kong.