Low Concentrations Of Benzene Research Articles

Microbial diversity and metabolic pathways linked to benzene degradation in petrochemical-polluted groundwater

The rapid advance in shotgun metagenome sequencing has enabled us to identify uncultivated functional microorganisms in polluted environments. While aerobic petrochemical-degrading pathways have been extensively studied, the anaerobic mechanisms remain less explored. Here, we conducted a study at a petrochemical-polluted groundwater site in Henan Province, Central China. A total of twelve groundwater monitoring wells were installed to collect groundwater samples. Benzene appeared to be the predominant pollutant, detected in 10 out of 12 samples, with concentrations ranging from 1.4 μg/L to 5,280 μg/L. Due to the low aquifer permeability, pollutant migration occurred slowly, resulting in relatively low benzene concentrations downstream within the heavily polluted area. Deep metagenome sequencing revealed Proteobacteria as the dominant phylum, accounting for over 63 % of total abundances. Microbial α-diversity was low in heavily polluted samples, with community compositions substantially differing from those in lightly polluted samples. dmpK encoding the phenol/toluene 2-monooxygenase was detected across all samples, while the dioxygenase bedC1 was not detected, suggesting that aerobic benzene degradation might occur through monooxygenation. Sequence assembly and binning yielded 350 high-quality metagenome-assembled genomes (MAGs), with 30 MAGs harboring functional genes associated with aerobic or anaerobic benzene degradation. About 80 % of MAGs harboring functional genes associated with anaerobic benzene degradation remained taxonomically unclassified at the genus level, suggesting that our current database coverage of anaerobic benzene-degrading microorganisms is very limited. Furthermore, two genes integral to anaerobic benzene metabolism, i.e, benzoyl-CoA reductase (bamB) and glutaryl-CoA dehydrogenase (acd), were not annotated by metagenome functional analyses but were identified within the MAGs, signifying the importance of integrating both contig-based and MAG-based approaches. Together, our efforts of functional annotation and metagenome binning generate a robust blueprint of microbial functional potentials in petrochemical-polluted groundwater, which is crucial for designing proficient bioremediation strategies.

Single and Binary Adsorption of Benzene, Phenol, and p‐Nitrophenol: Effect of Physical Interactions

AbstractThis work aims at emphasizing the impact of different physical interactions such as intermolecular ones between co‐adsorbed molecules on the adsorption mechanisms in the liquid phase. Thus, the adsorption of a low concentration (5 ppm) of benzene, phenol, and p‐nitrophenol from aqueous medium in single and binary mixture solutions is studied. Two activated carbons were prepared from two different activating agents and used in this regard. The adsorbed amounts are determined by high‐performance liquid chromatography. The results showed the great importance of the aforementioned interactions in the adsorption of phenol, particularly the interactions with the co‐adsorbed compounds. Indeed, phenol was remarkably better retained in binary mixture solutions than in a single one.

Long-Term Exposure to Low Concentrations of Ambient Benzene and Mortality in a National English Cohort.

Background: Benzene affects human health through environmental exposure in addition to occupational contact. However, few studies have examined the associations between long-term exposure to low concentrations of ambient benzene and mortality risks in nonoccupational settings.Methods: This prospective cohort study consists of 393,042 participants without stroke, myocardial infarction, or cancer at baseline from the UK Biobank. Annual average concentrations of benzene for each year during follow-up were measured using air dispersion models. The main outcomes were all-cause mortality and mortality from specific causes. Cox proportional-hazards models with time-varying exposure measurements were used to estimate the hazard ratios and 95% confidence intervals (CIs) for mortality risks. Restricted cubic spline models were used to estimate exposure-response relationships.Measurements and Main Results: With each interquartile range increase in the average annual concentration of benzene, the adjusted hazard ratios of mortality risk from all causes, cardiovascular disease, cancer, and respiratory disease were 1.26 (95% CI, 1.24-1.27), 1.24 (95% CI, 1.21-1.28), 1.27 (95% CI, 1.25-1.29), and 1.25 (95% CI, 1.20-1.30), respectively. The monotonically increasing exposure-response curves showed no threshold and plateau within the observed concentration range. Furthermore, the effect of benzene exposure on mortality persisted across different subgroups and was somewhat stronger in younger and White people (P for interaction < 0.05).Conclusions: Long-term exposure to low concentrations of ambient benzene significantly increases mortality risk in the general population. Ambient benzene represents a potential threat to public health, and further investigations are needed to support timely pollution regulation and health protection.

High sensitive phosphorene and molecular imprinted polymers electrochemical sensor to determine benzene in oilfield-produced water

A new electrochemical sensor based on a carbon screen-printed electrode (CSPE) modified with phosphorene (BP) and PEDOT:PSS (BP-PEDOT:PSS) and molecularly imprinted polymers (MIPs) composed of poly(o-phenylenediamine) has been developed and applied to determine low benzene concentrations in oilfield-produced water (OPW). Morphological and electrochemical characterization of the sensor confirmed that the CSPE surface was modified with BP-PEDOT:PSS and MIPs. CSPE modification with BP-PEDOT:PSS increased the electrochemical current by 24.8%. Under optimized conditions, the sensor presented analytical curves with two linear ranges from 4.0 × 10−8 to 1.0 × 10−7 mol L−1 and from 2.0 × 10−7 to 1.0 × 10−6 mol L−1. The limit of detection, limit of quantification, and sensitivity were 7.4 × 10−9 mol L−1, 2.3 × 10−8 mol L−1, and 36.4 A L mol−1 (n = 3), respectively. The sensor showed good interday and intraday repeatability, with RSD values of 3.4% and 4.9%, respectively. Its stability was excellent, preserving 90.7% of its initial current after storage at room temperature and in contact with the ambient atmosphere for 15 days. The sensor also displayed excellent selectivity for the benzene molecule in the presence of interferents (o-xylene, m-xylene, phenol, and toluene). The proposed method was validated by comparison using the technique of gas chromatography coupled to flame injection detection (GC-FID) and successfully applied to determine benzene in an OPW sample.

A novel MOF-based hollow carbon nanofiber mat with hierarchical apertures for efficient adsorption of low concentration benzene under high humidity

An ultraporous metal-organic framework (MOF)-based carbon nanofiber mat (CNFM4) with two types of hollow structure was prepared by electrospinning the mixed solution with polyacrylonitrile, polymethyl methacrylate and ZIF-8, followed by carbonization. The self-supporting CNFM4 has a higher Brunauer-Emmett-Teller (BET) specific surface area (SBET) (935.5 m2/g) and total pore volume (Vtotal) (0.69 cm3 g−1) than the PAN, PAN/PMMA, PAN/ZIF-8-derived carbon nanofiber mats (CNFMs). Static adsorption experiment showed CNFM4 had a high benzene adsorption capacity of about 12 mmol g−1 at saturated vapor pressure at 298 K, due to its high Vtotal. And even at low pressure of 0.1 kPa, its adsorption capacity still reached 2.75 mmol g−1, owing to its high SBET and rich micropore. The dynamic adsorption study showed CNFM4 has a breakthrough and saturation adsorption amount of 0.4902 and 0.5714 mmol g−1 at dry gas, respectively, and even at 60 RH%, they still can keep 0.2620 and 0.3642 mmol g−1, respectively, suggesting its application potential under the actual environment. The dynamic adsorption study also proves the important role of hollow structure at improving adsorption rate. This work provides a new idea for preparing the ultraporous MOF-based hollow CNFMs, and broadens the application of MOF-based CNFMs for VOCs removal.

Combined effects of arsenate and benzene on Microcystis aeruginosa growth and arsenic metabolism

To comprehensively understand the ecological risks of the coexistence of organic pollutants benzene and inorganic arsenate (As(V)) in the aquatic environment, Microcystis aeruginosa, one of the dominant algal species in eutrophic waters, was taken as the experimental alga to explore their growth response, arsenic (As) metabolism and the dissolved organic matter (DOM) changes in water under individual and combined pollution for benzene and As, respectively. The results showed that the algal cells of M. aeruginosa could proliferate normally. No significant differences were found among treatments after 96 h exposure to benzene and As(V) individual or combined. Intracellular As(V) accumulation was the main metabolism path for this alga and was significantly correlated to As(V) concentration but not benzene in the environment under different treatments. Benzene could promote As accumulation in algae and the total As metabolism amount in an individual algal cell at low As(V) levels. Meanwhile, only low benzene concentration showed As accumulation promotion at high As(V) levels. Microcystins (MCs) release in media affected by As(V) was different with benzene concentrations. There were no significant differences of UV254 in media among different treatments which represented macromolecular organic matters and aromatic compounds containing CC and CO bonds. Total organic carbon (TOC) was relatively higher in benzene media than in other treatments. The infrared spectrum characteristics of dissolved organic matter (DOM) confirmed that benzene was degraded and converted obviously at high levels in media by algal cells. Meanwhile, the three-dimensional fluorescence spectrum analysis showed that benzene in media could restrict proteins released in DOM caused by algae cells. The results are of great significance to the application of microalgae in water bioremediation and the comprehensive understanding of the ecological effects and risks in aquatic ecosystems.

Hierarchical porous carbon with tunable apertures and nitrogen/oxygen heteroatoms for efficient adsorption and separation of VOCs

Porous carbon materials are good adsorbent candidates for removing volatile organic compounds (VOCs) due to their reliability and cost-effectiveness. Especially, the pore size distribution (PSD) of porous carbon materials plays a critical role in VOCs adsorption and separation. In this study, we present benzimidazole-derived porous carbons (BICs) with controllable pore size and oxygen/nitrogen heteroatoms. The pore size is controlled by adjusting the reaction degree of inorganic salt (K2CO3) and nitrogen-containing groups in the system. The tunable pore size distribution makes BICs highly efficient for the adsorption and separation of VOCs. BIC-3-900 exhibits a dominant pore size distribution of 3.0–4.0 nm and an exceptionally high total pore volume of 2.42 cm3/g, leading to ultra-high adsorption capacities for benzene and methanol (22.19 and 52.65 mmol/g, respectively) at 293 K. In addition, BIC-1-700 dominated by the micropore size is more favorable for adsorbing low-concentration small molecule VOCs (with a dynamic adsorption capacity of 4.21 mmol/g for methanol at 3800 ppm). In terms of the adsorptive separation performance, BIC-1-900 has an efficient benzene/methanol selectivity (∼30.13) due to its PSD (1.2–2.0 nm) which was more favorable for capturing low-concentration benzene. Moreover, both experimental and simulation (GCMC and DFT) results demonstrate that the abundant N/O heteroatoms doping in BIC-1-700 results in charge heterogeneity and stronger electrostatic affinity for polar VOCs molecules. Herein, our findings suggest that BICs with controllable pore size and oxygen/nitrogen heteroatoms have significant potential in practical VOCs capture and separation.

55 Validation of Diffusive Sampling Methods for Accurate Low-Dose Benzene Exposure Assessment, Inhalation Monitoring

Abstract The present research project is aimed at providing an accurate low-dose benzene exposure assessment method, by validating diffusive monitoring techniques for benzene personal exposure measurements at workplaces where low benzene concentrations are expected. The experiments have been conducted following the EN 838:2010 standard in the range of 16 to 320 µg/m3 (0.005 to 0.1 ppm). The study is part of the Concawe project on “accurate low-dose benzene exposure assessment, dose-specific metabolism and potential early markers” aiming at developing a methodology to monitor benzene exposures at low levels in environments typical of the petroleum industry. Diffusive sampling offers a reliable alternative to pumped sampling methods, intrinsic safety in potentially explosive atmospheres, lightness and ease of use. The tested diffusive sampler is radiello™, two alternative configurations of the sampler can be used: RAD130, packed with activated charcoal, suitable for solvent desorption and analysis by HRGC-FID, and RAD145, packed with graphitised charcoal, suitable for thermal desorption and analysis by HRGC-MS. For both configurations the sampler performances have fulfilled all requisites of the EN 838:2010 standard, in particular: bias due to the selection of a non-ideal sorbent is lower than 10% (no significant back diffusion of benzene due to concentration change in the atmosphere); bias due to storage of samples for up to 2 months is lower than 10%; nominal uptake rate for benzene on RAD130 is 74.6 ml/min and on RAD145 is 32.3 ml/min; expanded uncertainty of the sampling and analytical method is 20.2% on RAD130 and 26.1% on RAD145.

Low-level occupational exposure to BTEX and dyschromatopsia: a systematic review and meta-analysis

Objectives. The present study aimed to assess whether occupational exposure to low concentrations of benzene, toluene, ethylbenzene and xylene (BTEX) is associated with color vision impairment. Methods. We queried PubMed, Scopus, Embase, Web of Science and ProQuest as the main databases, as well as gray literature such as Google Scholar. A random-effects model was used to assess relative risk. A funnel plot was created to assess publication bias. Meta-regression analysis was applied to identify variables that explain the between-study variation in the reported risk estimate. Results. An overall standardized mean difference of 0.529 (95% confidence interval [0.269, 0.788]; p < 0.0001) was obtained in the random-effects model, which corresponded to a medium-size effect. Duration and the levels of exposure to benzene, toluene and xylene were the significant predictors of the magnitude of the combined risk estimate. Chronic exposure to low levels of BTEX was associated with dyschromatopsia determined by the color confusion index. Conclusions. The impairments can occur even at exposures lower than the occupational exposure limits of BTEX. However, there are several flaws in the determination of workers’ exposure, which did not allow to establish how low a level of these chemicals can cause color vision impairment.

Metabolomic Study of Urine from Workers Exposed to Low Concentrations of Benzene by UHPLC-ESI-QToF-MS Reveals Potential Biomarkers Associated with Oxidative Stress and Genotoxicity.

Benzene is a human carcinogen whose exposure to concentrations below 1 ppm (3.19 mg·m−3) is associated with myelotoxic effects. The determination of biomarkers such as trans-trans muconic acid (AttM) and S-phenylmercapturic acid (SPMA) show exposure without reflecting the toxic effects of benzene. For this reason, in this study, the urinary metabolome of individuals exposed to low concentrations of benzene was investigated, with the aim of understanding the biological response to exposure to this xenobiotic and identifying metabolites correlated with the toxic effects induced by it. Ultra-efficient liquid chromatography coupled to a quadrupole-time-of-flight mass spectrometer (UHPLC-ESI-Q-ToF-MS) was used to identify metabolites in the urine of environmentally (n = 28) and occupationally exposed (n = 32) to benzene (mean of 22.1 μg·m−3 and 31.8 μg·m−3, respectively). Non-targeted metabolomics analysis by PLS-DA revealed nine urinary metabolites discriminating between groups and statistically correlated with oxidative damage (MDA, thiol) and genetic material (chromosomal aberrations) induced by the hydrocarbon. The analysis of metabolic pathways revealed important alterations in lipid metabolism. These results point to the involvement of alterations in lipid metabolism in the mechanisms of cytotoxic and genotoxic action of benzene. Furthermore, this study proves the potential of metabolomics to provide relevant information to understand the biological response to exposure to xenobiotics and identify early effect biomarkers.

Engineering ZnSn(OH)6 with ternary active sites-directed hydroxyl vacancies for robust deep C6H6 photo-oxidation: Experiment and DFT calculations

The removal mechanisms of low concentration benzene series VOCs over photocatalysts are often ascribed to the surface interface charge transfer or hydroxyl radical (OH) oxidation. Typically, reactive oxygen species (ROSs) contribute to the enhanced photoactivity, however, it remains ambiguous at this stage. Herein, ZnSn(OH)6 with hydroxyl vacancies (ZHS160) is examined to identify the specific ROSs for C6H6 photo-oxidation, namely holes, electrons, H2O and O2/O2− except OH. The well-designed ZHS160 possesses ternary active sites: hydroxyl vacancies for localizing electrons and adsorbing H2O molecules, exposed Zn and Sn sites for adsorbing/activating molecular C6H6 and O2, respectively. Therefore, ZHS160 exemplifies an exceptional photo-oxidation rate of low concentration C6H6 reaching 86%, far exceeding that of pristine ZnSn(OH)6 (22%). Impressively, the formed intermediates are confirmed to gain insights into their formation, chemical and electronic features as empowered by the in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), gas chromatography-mass spectrometry (GC–MS) and density functional theory (DFT) simulations. Accordingly, a distinguishing reaction path based on the pristine ZnSn(OH)6 and ZHS160 is elucidated. As such, these results advance the mechanistic understanding of deep photo-oxidation of C6H6 to CO2 over ZnSn(OH)6 with hydroxyl vacancies.

BENZENE AND TOLUENE CONCENTRATION AT DIFFERENT TRAFFIC INTERSECTION DURING PRE-MID-POST WINTER SEASON, IN AMBIENT AIR OF ALIGARH AND ITS IMPACT ON HUMAN HEALTH

In current scenario, pollution in environment, is a big problem for all living species at around the world.We know that, Volatile Organic Compounds (VOCs) in presence of sunlight and oxides of nitrogen in atmosphere are considered as precursors for ozone production at the layer of Troposphere.Concentration of Benzene and Toluene (BT) in ambient air was measured near three major traffic sites in the city of Aligarh,India.All air samples were collected using for two times (in a month) during eight hours of normal working period time for in October – December 2020, and January - March 2021.The three selected sites used in this study represent traffic sites ( at Etah Chungi Chauraha, Quarsi Chauraha and Sootmil Chauraha, Aligarh ). In this study, real-time measurements of Benzene and Toluene concentration were performed the programmable compound specific PID detector designed to provide instantaneous exposure monitoring of a specific organic gas.It monitors a specific gas by utilizing a gas separation tube and the photo-ionization detector (PID) with a 9.8 eV gas discharge lamp (range- 50 ppb to 200 ppb) and whole data analyzed by SPSS software. The study the higher concentration 25.32 µg/m3 of Benzene in the evening shows at site 3 and lower concentration 10.22 µg/m3 of Benzene shows at site 2 in the morning.The higher concentration 22.22 µg/m3 in the evening of Toluene shows at site 1 and lower concentration 07.10 µg/m3 in the evening of Toluene shows at site 2, were observed respectively. Benzene and Toluene were widely used as a solvent in different products and petroleum. Exposure to a mixture of toluene and benzene in air led to an increase in the cytotoxic effect and DNA damage without any further repair and also its chronic effect on human health.The higher concentration of benzene and toluene co-exposure of benzene or toluene in this study.The relevance of these data on interactions for humans exposed at low benzene concentrations can be best assessed only when the mechanism of interaction is understood at a quantitative level and incorporated within a biologically based modelling framework for human health.

Influence of current density and inlet gas flow in the treatment of gaseous streams polluted with benzene by electro-absorption

This paper is focused on the evaluation of the electrochemically assisted absorption process (electro-absorption) as a treatment for volatile organic compounds contained in polluted air flows. Benzene degradation was used to test the technology, using a system consisting of a packed absorption column and a single compartment electrochemical cell equipped with boron-doped diamond (BDD) as anode and steel-steal as cathode. The influence of inlet gas flow rate and operation current intensity was evaluated by monitoring the concentration of benzene and intermediates both, in the liquid absorbent / electrolyte and in the outlet gaseous stream. Results show that steady-state values reached, during benzene absorption and electro-absorption, increase when the inlet gas flow rises from 1.5 to 6.0 L h−1 and that the bare absorption process retains benzene only up to this steady-state value of the liquid and then, it has no effect on the removal of benzene. Concentrations of benzene in the absorbent/electrolyte decreases with the increase in the current density during electrochemically assisted processes. As well, mineralization was found to be very important, as expected because of the very low concentrations of benzene into the liquid and the very high efficiencies of the electrolytic degradation with BDD electrodes, and benzoquinone and carboxylic acids were identified as the primary intermediates. These species were not detected in the outlet gas flow. The decrease in the concentration and mass flow of benzene in the outlet streams confirms that electro-absorption is a functional electrochemical application to remove benzene from gaseous streams. When current density rises (10, 50 and 100 mA cm−2), the degradation percentage increases. The values obtained were 43, 61 and 75% with 1,5 L h−1 of inlet gas flow and 10, 25 and 37 % with 6 L h−1. However, the degradation percentage relative to the energy consumption decreases when the current density rises. Results were, correspondingly, 24.7, 4.2 and 2.2 % kWh−1 with 1,5 L h−1 of inlet gas flow and 7.1, 2.1 and 1.4 % with 6 L h−1. This energy efficiency trend was explained because mass transport becomes the bottleneck in the oxidation of diluted organic solutions. These results contribute to expand the understanding of the mechanisms involved in the electro-absorption of benzene and recommend for further research in the topic, due to the relevance of the treatment results.

Remarkable performance of N-doped carbonization modified MIL-101 for low-concentration benzene adsorption

As a common volatile organic compound (VOC) species emitted from industrial production, benzene poses a severe threat to human health. Due to its ultra-high specific surface area and developed mesoporous structure, MIL-101 based metal–organic framework (MOF) materials are widely used in VOCs adsorption. However, MIL-101 has a poor ability to adsorb non-polar benzene due to its polar ligands and metal nodes. Herein, we presented a simple strategy of carbonization and nitrogen doping to modify MIL-101. The effect of various surface physicochemical properties of modified MIL-101 on its adsorptive capacity was thoroughly evaluated. The interaction mechanism between activated sites of modified MIL-101 and benzene was also deeply explored using density functional theory (DFT) calculation. The results showed that modified MIL-101 featured graphite skeletons doped with different N-containing functional groups. The adsorptive capacity of MCN-800 increased by 100% compared with that of pristine MIL-101, owing to the largest mesoporous volume and the greatest number of the pyridinic-N moiety. Moreover, both experimental and theoretical results proved that N-containing functional groups had a strong interaction with benzene through π-π interaction and N-H hydrogen bond, and pyridinic-N displayed a stronger interaction than pyrrolic-N and graphite-N. This study provides a valuable synthesis strategy of functionalized MOF adsorbents for the removal of low-concentration benzene pollution.

Surface enrichment promotes the decomposition of benzene from air

Doping TiO2 with copper can strengthen the absorption of benzene and facilitate the generation of hydroxyl radicals. It can photocatalytically remove very low concentrations of gaseous benzene (4 mg m−3) in air, even at a flow rate of 100 L min−1.

Optimization and modeling of Zn2SnO4 sensitivity as gas sensor for detection benzene in the air by using the response surface methodology

In this paper, the performance of the benzene gas detection sensor in the air is optimized by an experimental design method. So in this work, Nanostructured thin films of ZnO and Zn2SnO4 were prepared in wurtzite form via a facile atmospheric pressure chemical vapor deposition (CVD) method, using metallic zinc and tin precursors. Characterization of the gas sensor was performed by using Powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and surface area analysis (using BET method). The results show that Zn2SnO4 nanowire network exhibited good sensitivity at 299 °C temperature to low concentrations (100 ppb) of Benzene which can be potentially used as a resistive gas sensor. Ultimately modeling and optimization of Zn2SnO4 sensor performance to detect benzene by surface response method in design expert11 software has been done. Also, the effect of each parameter on the sensitivity of the sensor was analyzed by analysis of variance (ANOVA). Moreover, the performance efficiency of the Zn2SnO4 sensor is estimated with the reliable correlations obtained in the modeling. The two parameters selected to optimize the performance of the gas sensor include the operating temperature of the sensor and the concentration of the sensor. Comparison of the modeling results and the predicted values for the sensor sensitivity to benzene shows 97.60% excellent agreement.

Poly aniline (PANI) loaded hierarchical Ti1−xSbxO2 rutile phase nanocubes for selective room temperature detection of benzene vapor

Benzene is one of the aromatic yet hazardous hydrocarbons that are deceptive under their sweet odor. Even in low ppm concentration, benzene vapor in ambient surroundings have been proven to be a major human carcinogen, primarily responsible for leukemia. Often found along with traces of toluene and xylene which have similar molecular structures, selective detection of low concentration benzene, particularly at room temperature is a major challenge. In this work, using the idea that transition from uni-faceted to bi-faceted crystal growth shall induce a change in morphology from spherical to cubical; antimony doped rutile TiO2 nanocubes were synthesized and employed in benzene vapor detection. While the PANI loaded antimony doped (0.03) TiO2 nanocubes showed an enhanced 80% response to 2 ppm benzene in air at room temperature, it was selective (up to 7 times more) against 2 ppm toluene and xylene vapor. The sensors were highly stable against humidity and also reusable for a considerable span of time. The role of specificity in exposed cubical facet has been explained for eliminating cross-sensitivity in benzene detection phenomenon.

Fire and Water: Assessing Drinking Water Contamination After a Major Wildfire.

We investigated patterns of volatile organic compound (VOC) contamination in drinking water systems affected by the California 2018 Camp Fire. We performed spatial analysis of over 5000 water samples collected over a 17 month period by a local water utility, sampled tap water for VOCs in approximately 10% (N = 136) of standing homes, and conducted additional nontargeted chemical analysis of 10 samples. Benzene contamination was present in 29% of service connections to destroyed structures and 2% of service connections to standing homes. A spatial pattern was apparent. Tap water in standing homes 11 months after the fire contained low concentrations of benzene in 1% of samples, but methylene chloride was present in 19% of samples, including several above regulatory limits. Elevated methylene chloride was associated with greater distance from the water meter to the tap, longer stagnation time, and the presence of a destroyed structure on the service connection; it was inversely associated with certain trihalomethanes. Nontargeted analysis identified multiple combustion byproducts in the water at 2/10 homes. Our findings support the hypothesis that pyrolysis and smoke intrusion from depressurization contributed to the benzene contamination. Further research is needed to test the hypothesis that methylene chloride may be generated from the dehalogenation of disinfection byproducts stagnating in galvanized iron pipes.

Purification of benzene-laden air by static adsorption of benzene onto activated carbon prepared from Diplotaxis acris biomass

Activated carbon (AC) was prepared from Diplotaxis acris biomass. The change in the surface functional groups between the biomass raw material and the produced AC was detected using Fourier-transform infrared (FTIR) and Raman spectroscopy. The thermal stability of the prepared AC was determined by using thermogravimetric analysis (TGA). It has a surface area of 40.21 m2/g which gave evidence for its external porous surface. The surface porosity and the graphite properties of the prepared AC were detected by scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis, respectively. The amount of adsorbed benzene on the AC surface was determined using a gas chromatograph supported with a flame ionization detector (GC-FID) after extraction in methanol. The adsorption capacity of benzene was 5.4 mg/g at room temperature (25°C), and its removal efficiency reached 95.58% for low benzene concentration (1000 mg/m3). The obtained results were well fitted by the Langmuir isotherm model. The adsorption kinetics of benzene followed the pseudo-second-order kinetic model accompanied by the intra-particle diffusion model. The reuse of the AC samples for three consecutive cycles retained the removal efficiency by more than 75% of its original efficiency. Overall, the study revealed that the prepared AC from Diplotaxis acris biomass has a great potential in the removal of benzene from polluted air.

Investigation on occupational hazards in 20 automobile manufacturing enterprises in Shandong Province

Objective: To investigate the current situation of occupational hazards in automobile manufacturing enterprises in Shandong Province. Methods: From February to May 2019, the convenience sampling method was adopted to conduct on-site occupational health surveys with 20 automobile manufacturing enterprises in Shandong Province as the survey subjects, to detect the occupational hazard factors in the workplaces and individual exposure levels, and to analyze the occupational health check results of operators. Results: There were 13 small-sized, 4 medium-sized and 3 large-sized enterprises among the 20 automobile manufacturing enterprises. The detection results of benzene and toluene in the workplaces met the occupational exposure limits, and the detection results of welding fumes, manganese and its compounds, and xylene exceed the occupational exposure limits. The maximum short-term exposure concentration (C(STE)) of welding fume in the air of workplaces was 24.23 mg/m(3), and the over-standard rate was 11.0% (16/146) . The maximum time-weighted average concentration (C(TWA)) of welding fume of operators is 10.60 mg/m(3), and the over-standard rate was 11.0% (8/73) . The maximum C(STE) of manganese and its compounds in the air of workplaces was 0.879 mg/m(3), and the of manganese and its compounds of operators was 0.175 mg/m(3), and the over-standard rate was 5.7% (4/70) . The maximum xylene C(STE) in the air of workplaces was 230.00 mg/m(3), and the over-standard rate was 3.9% (2/51) . The maximum xylene C(TWA) of operators was 70.40 mg/m(3), the over-standard rate was 3.6% (1/28) . Among the 4775 workers exposed to occupational hazards, 38 (0.80%) were suspected of electric welder's pneumoconiosis, 27 (0.57%) were suspected of manganese poisoning and 31 (0.65%) were suspected of chronic low-concentration benzene and benzene series poisoning. The detection rates of suspected occupational diseases among workers in small and medium-sized enterprises were relatively high, 2.86% (30/1048) and 4.51% (51/1132) respectively. There was a statistically significant difference in the detection rates of suspected occupational diseases among the operators of different scale automobile manufacturers (P<0.05) . Conclusion: The exposure levels of electric welding fumes, manganese and its compounds in welding jobs and xylene exposure levels in spray painting jobsin Shandong Province's automobile manufacturing enterprises are more serious. The supervision and management of occupational hygiene should be strengthened, the working environment should be improved, and the health of welding and painting workers should be protected.