Occurrence Of Volatile Organic Compounds Research Articles

Occurrence of Volatile Organic Compounds and Extrafloral Nectaries in Tropical Rainforest Species in Danum Valley Conservation Area, Sabah, Malaysia

Plants synthesize numerous classes of secondary metabolites that are crucial in plant defense. Two of the common but non-ubiquitous defenses are the emission of volatile organic compounds (VOCs) and production of extrafloral nectaries (EFN). This study investigates the occurrence of emission of VOC and production of EFN in forest species in Danum Valley Conservation Area, Sabah, Malaysia. From the 165 species screened, 131 species were found to emit VOC while 41 species were EFN-bearing plants. There are 34 species that are both emitting VOC and producing EFN, while 97 species were found to be emitting VOC with no EFN observed. On the other hand, there are 7 species that were EFN bearing but non-VOC emitter, while 27 species were neither emitting VOC nor producing EFN. All 12 dipterocarp species were observed to emit VOC, of these 3 are non-EFN bearing. VOC emissions were further classified into isoprene (C5) and monoterpene (C10) compounds. There are 46 species that were detected to emit both isoprene and monoterpenes, while there are more exclusive monoterpene emitters (62 species) than isoprene-only emitters (23 species). This study showcased the ability of plants to produce a wide array of secondary metabolites as plant defense making them successfully adapt to the complexities of tropical rainforest ecosystem.

Occurrence of and dermal exposure to benzene, toluene and styrene in sunscreen products marketed in the United States

Occurrence of volatile organic compounds (VOCs) such as benzene in personal care products is a topic of public health concern. Sunscreen products are extensively used to protect skin and hair from UV radiation from sun light. Nevertheless, little is known about exposure doses and risks of VOCs present in sunscreens. In this study, we determined the concentrations of and exposure to three VOCs, namely benzene, toluene and styrene, in 50 sunscreen products marketed in the United States. Benzene, toluene and styrene were found in 80 %, 92 % and 58 %, respectively, of the samples analyzed at mean concentrations of 45.8 ng/g (range: 0.007–862), 89.0 ng/g (range: 0.006–470) and 161 ng/g (range: 0.006–1650), respectively. The mean dermal exposure doses (DEDs) to benzene, toluene and styrene of children/teenagers were 68.3, 133 and 441 ng/kg-bw/d, respectively, whereas those of adults were 48.7, 94.6 and 171 ng/kg-bw/d, respectively. The lifetime cancer risk from benzene concentrations present in 22 sunscreen products (44 % of the samples) for children/teenagers and 19 sunscreen products (38 %) for adults, exceeded the acceptable benchmark risk level (1.0 × 10−6). This is the first study to comprehensively assess the concentrations of and risks to benzene, toluene and styrene present in sunscreen products.

LC-MS and GC-MS Data Fusion Metabolomics Profiling Coupled with Multivariate Analysis for the Discrimination of Different Parts of Faustrime Fruit and Evaluation of Their Antioxidant Activity

The comparative chemical composition of different part of Faustrime fruits (peels, pulp, albedo, and seeds) extracted with different solvents was determined by GC-MS and UHPLC-HRMS QTof. The obtained data were also combined for their in vitro antioxidant activity by multivariate analysis to define a complex fingerprint of the fruit. The principal component analysis model showed the significative occurrence of volatile organic compounds as α-bisabolol and α-trans-bergamotol in the pulp and albedo, hexanoic acid in the seeds, and several coumarins and phenolics in the peels. The higher radical scavenging activity of the pulp was related to the incidence of citric acid in partial least square regression.

Preliminary Assessment of Occurrence, Potential Origin, and Human Health Risk of Volatile Organic Compounds in Uncontrolled Springs, North Morocco.

In recent years, with the drastic increase in worldwide pollution rates, considerable attention has been paid to the volatile organic compounds (VOCs) that might lead to serious health problems, e.g., cancer. As there appears to be a notable lack of research on the pollution (specifically, VOCs) of water bodies in Morocco, we aimed to assess the occurrence of VOCs in some uncontrolled springs in the north of Morocco that have not been previously investigated. We also discuss the estimation of health risks posed by ingestion and dermal contact as well as the different potential origins of these pollutants. For this purpose, water samples were collected from twenty-six sampling sites and were analyzed via headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry (HS-SPME-GC-MS). Out of the 60 suspected VOCs, a total of 15 compounds belonging to five distinct groups were identified and quantified. Among them, fumigants, solvents, and gasoline hydrocarbons were the most abundant groups, with proportions of 40%, 26.7%, and 20%, respectively. A heatmap clustered the provinces based on their degree of pollution, while a dendrogram was used to classify the studied springs into six main groups. Regarding carcinogenic risk, all the samples were safe for consumption as well as for dermal contact, except for S17, S18, and S8, and S19, which might present a severe threat to inhabitants due to their contents of, respectively, naphthalene (2.1 × 10-3), chloroform (2.5 × 10-4), and cis and trans-dichlropropene (1.61 × 10-4 and 1.11 × 10-4). Our investigation revealed several anthropogenic sources of water contamination, which could aid authorities in limiting contamination spread in water bodies.

Volatile organic compounds in groundwater used for public supply across the United States: Occurrence, explanatory factors, and human-health context

This systematic assessment of occurrence for 85 volatile organic compounds (VOCs) in raw (untreated) groundwater used for public supply across the United States (U.S.), which includes 43 compounds not previously monitored by national studies, relates VOC occurrence to explanatory factors and assesses VOC detections in a human-health context. Samples were collected in 2013 through 2019 from 1537 public-supply wells in aquifers representing 78% of the volume pumped for public drinking-water supply. Laboratory detection limits for VOCs generally were less than 0.1 μg/L. Detections were reported for 36% of the sampled principal-aquifer area (38% of sampled wells) and were most common in wells in shallow, unconfined aquifers in urban areas that produce high proportions of modern-age and oxic groundwater. The disinfection by-product trichloromethane (chloroform) was the most commonly detected VOC associated primarily with anthropogenic sources (24% of the sampled area, 25% of sampled wells), followed by the gasoline oxygenate methyl tert-butyl ether (8.4% of area, 11% of wells). Carbon disulfide (12% of area, 14% of wells) was examined separately because of likely substantial contributions from natural sources. Newly monitored VOCs were each detected in <1% of the sampled area. Although detections of 1,4-dioxane in this first national study of its occurrence in raw groundwater were rare, measured concentrations exceeded the most stringent (non-enforceable) human-health benchmark in 0.5% of the sampled area (9 wells). Two wells had exceedances of enforceable benchmarks for tetrachloroethylene and trichloroethylene, and 50 wells total (representing 2.0% of the sampled area, 3.3% of sampled wells) had combined VOC concentrations exceeding 10% of benchmarks of any type. Compared with previous national findings, this study reports lower rates of VOC detection, but confirms widespread anthropogenic influence on groundwater used for public supply, with relatively few concentrations of individual VOCs or mixtures that approach or exceed human-health benchmarks.

Characteristics and Sources of Selected Halocarbon and Hydrocarbon Volatile Organic Compounds in Surface Water of the Han River Basin

Volatile organic compounds (VOCs) are ubiquitous pollutants in surface water, which is the main source of drinking water in South Korea. We investigated the behavior (concentration, distribution, and environmental risk) of eleven selected VOCs in the surface water of the Han River tributaries using purge-and-trap gas chromatography/mass spectrometry. The average concentration of VOCs was 0.29 ± 0.47 μg/L. Chloroform and trichloroethylene (TCE) were the major pollutants, accounting for approximately 64.2% and 25.6% of the total concentration, respectively, and showing that halocarbons accounted for 94%. Chloroform was positively correlated with TCE and xylenes, and TCE was positively correlated with tetrachloroethylene (PCE). No differences were observed in the temporal average concentrations of total VOCs, but the concentrations differed significantly among sub-watershed areas. The Imjin-Hantan River, Han River mainstream, and Anseong Stream watersheds had a high positive association with TCE, whereas the Bukhan and Namhan River watersheds had a strong positive link with chloroform. The contamination and detection frequency of VOCs were highest in industrial complexes, followed by urban and rural areas. Thus, point source pollution significantly contributed to VOC contamination of these tributaries. Risk quotients for most VOCs were &lt;1, suggesting negligible risk. Considering the relatively high occurrence of VOCs and their potential ecological risks, continuous environmental monitoring and study of environmental impacts based on ecotoxicity studies of domestic aquatic species are warranted.

Occurrence and health risk assessment of volatile organic compounds in the surface water of Poyang Lake in March 2017.

An investigation into the occurrence of volatile organic compounds (VOCs) in the surface water of Poyang Lake was conducted. The determination of 54 different kinds of VOCs was performed with a purge and trap-gas chromatography-mass spectrometry method at 28 sampling points. Twenty-two types of VOCs were detected; methylene chloride had the highest mean concentration of 708.19 ng L−1, followed by 1,2-dichloroethane and chloroform, with mean concentrations of 376.78 and 187.26 ng L−1, respectively. The distribution of VOCs in the areas of Poyang Lake from low to high was as follows: west and south < east and central; the highest ∑VOC concentration occurred at the sample site of Zhangsihe. The health risks of VOCs in Poyang Lake were also determined by calculating the cancer and non-cancer risk from the two exposure routes of ingestion and dermal adsorption. The results showed that VOCs have no carcinogenicity risk, while only methylene chloride has a certain carcinogenic risk to the human body.

Ethylene, xylene, toluene and hexane are major contributors of atmospheric ozone in Hangzhou, China, prior to the 2022 Asian Games

The occurrence of volatile organic compounds (VOCs) in the atmosphere is a major health issue, notably in China, because those compounds are the precursors of tropospheric ozone and sources of secondary organic aerosols. Also, some compounds are carcinogenic. Atmospheric nitrogen oxides (NOx) are also a source of tropospheric ozone, thus creating diseases in human respiratory systems. Therefore, controlling VOCs and NOx is essential for the welfare of local citizens and incoming 2022 Asian Games in Hangzhou. Here, we recorded daily average concentrations for 55 different VOCs species and NOx in 2017. For each VOC, we calculated the ozone formation potential, the propene equivalent concentration and the secondary organic aerosol formation potential. We used the Weather Research and Forecast coupled with Community Multi-scale Air Quality models to assess the regional transport and local sector contributions for VOCs and NOx. Results show that ethylene contributed over 16% of total ozone generated from VOCs, followed by M/P-xylene and toluene. M/P-Xylene, toluene and n-hexane were the top 3 VOCs species that generated ozone fastest. Benzene, toluene and ethylbenzene generated most secondary organic aerosols. The annual regional transport rate is 45% for VOCs and 22% for NOx. Local industry produced 28% VOCs, while local traffic contributed 64% NOx. Overall, ground-level ozone could be reduced by controlling VOCs emissions first and then controlling NOx emissions.

Occurrence of chlorinated volatile organic compounds (VOCs) in a sanitary sewer system: Implications for assessing vapor intrusion alternative pathways

Sewer systems have been recently recognized as potentially important exposure pathways to consider during vapor intrusion assessments; however, this pathway has not been well-characterized and there is need for additional information about the occurrence of volatile organic compounds (VOCs) in sewer systems. This paper reports the results of sewer gas sampling conducted in a sanitary sewer over the years of 2014–2017. Sewer gas samples were collected and analyzed using several different techniques, including TO-15 (grab), TO-17 (passive), Radiello® (passive) and a novel continuous monitoring technique, the Autonomous Rugged Optical Multigas Analyzer (AROMA). The applicability of each of the different approaches used in this study is discussed in the context of investigating sanitary sewers as a vapor intrusion alternative pathway. The data confirmed that trichloroethylene (TCE) concentrations in sewer gas were detected adjacent to and extending hundreds of feet away from a previously defined vapor intrusion area, where TCE was a primary contaminant. TCE concentrations detected in sewer gas ranged from non-detect to 1600μg/m3. Temporal variability was observed in TCE concentrations over timescales that ranged from minutes to months to years at discrete sampling locations. Spatial variability in sewer gas concentrations was also observed throughout the study area. Temporal and spatial variability may be caused by groundwater contamination sources in the study area, as well as sewer gas transport mechanisms.

Occurrence of Indoor VOCs in Nursery School - Case Study

Children’s exposure to air pollutants is an important public health challenge. Particular attention should be paid to preschools because younger children are more vulnerable to air pollution than higher grade children and spend more time indoors. The concentrations of volatile organic compounds (VOCs) as well as carbon dioxide (CO2) concentrations in younger and older children’s classrooms during the winter season were studied. An electronic nose based on gas chromatography was used for the analysis of individual VOCs and a photoionization detector with a UV lamp was used for the determination of total volatile organic compounds (TVOC) concentration. Continuous measurements of CO2 concentrations both inside classrooms and outside each building were performed using automatic portable monitors. Improving ventilation, decreasing the occupancy per room and completing cleaning activities following occupancy periods can contribute to alleviating high CO2 and VOCs occurrence levels.

Determination of VOCs in the Indoor Air of a New and a Renovated Apartment

Abstract This study deals with the occurrence of volatile organic compounds (VOCs) in the indoor environment of a new and a renovated apartment. Qualitative determination of VOCs was carried out with a gas chromatograph with surface acoustic wave detector (GC/SAW). Concentrations of total volatile organic compounds (TVOC) were determined by a photoionization detector with UV lamp. Simultaneously, temperature and relative humidity were monitored with a data logger. The aim of this study was to determine of TVOC concentrations, to use of GC/SAW for determination of individual VOCs in indoor air as well as to predict possible sources of VOCs in these apartments. Measurements were performed after each construction work for better resolution of the contributions of individual materials to the levels of VOC. Mean concentrations of TVOC were 624 μg/m3 in the renovated apartment and 1,686 μg/m3 in the new apartment after completion of all works. The results from the renovated apartment showed that the use of new materials can lead to lower levels of organic compounds in indoor air compared to old materials that were less environmentally friendly. Many types of VOCs were found in both apartments. After reviewing the possible sources, it seems that the main sources of these substances were applied coatings and flooring materials.

Occurrence of volatile organic compounds in shallow alluvial aquifers of a Mediterranean region: Baseline scenario and ecological implications

A regional survey of eight volatile organic compounds (VOCs), namely BTEX (benzene, toluene, ethylbenzene and p-xylene) and four chlorinated aliphatic hydrocarbons (CAHs: chloroform, 1,2-dichloroethane, trichloroethene and tetrachloroethene), was carried out at 174 sites, in 17 alluvial aquifers of Abruzzo, a Mediterranean region of southern Italy, from 2004 to 2009. Frequency of detection, concentration range, spatial distribution pattern, and temporal trend of contaminant concentration in each aquifer were analyzed as well as the relationships between VOC concentrations and the total amount of precipitation during the 90days preceding each sampling date. A review of published ecotoxicological data, providing an indication of the biological risk associated with the observed levels of VOC contamination, was presented and discussed. BTEX concentrations were under detection limits in all the investigated aquifers, indicating absence of contamination. In contrast, CAH contamination occurred in 14 out of 17 aquifers. The two most frequently detected compounds were chloroform and tetrachloroethene. No significant temporal trend was observed for chloroform and tetrachloroethene concentrations during the six years of observation, indicating the persistence of stable contaminations, except for some slightly decreasing trends observed in three out of 17 aquifers. In four aquifers chloroform and tetrachloroethene concentrations increased with precipitations in the preceding months. Spatial patterns of contamination differed among aquifers, indicating highly complex contaminant distributions at aquifer scale not related to single-plume geometries. Patterns of contamination by chloroform and tetrachloroethene in the most urbanized aquifers were likely associated with multiple sources of VOCs not clearly detectable at the scale used in this study. In five out of 17 aquifers, chloroform and tetrachloroethene co-occurred at concentrations that are lethal to groundwater-dwelling organisms under a short exposure period (four days). Future studies should therefore consider the possibility that in the other aquifers groundwater-dwelling organisms might be physiologically damaged by sublethal VOC concentrations.

Volatile organic compounds (VOCs) in soil gases from Solfatara crater (Campi Flegrei, southern Italy): Geogenic source(s) vs. biogeochemical processes

The chemical composition of volatile organic compounds (VOCs) in soil gases from the Solfatara crater (Campi Flegrei, Italy) was analyzed to investigate the effects of biogeochemical processes on gases discharged from the hydrothermal reservoir and released into the atmosphere through diffuse degassing. The chemistry of fluids from fumarolic vents, which represent preferential pathways for fluid uprising, was also reported for comparison. Oxidation–reduction and hydration–dehydration reactions, as well as microbial activity, strongly affected the composition of C4–C9 alkanes, alkenes, S-bearing compounds and alkylated aromatics, especially in those sites where the soil showed relatively low permeability to uprising fluids. Other endogenous organic compounds, such as benzene, phenol and hydrofluorocarbons were able to transit through the soil almost undisturbed, independently on the gas emission rate. Products of VOC degradation mainly consisted of aldehydes, ketones, esters, ethers and, subordinately, alcohols. Cyclic compounds revealed the occurrence of VOCs produced within sedimentary formations overlying the hydrothermal reservoir, whereas the presence of chlorofluorocarbons (CFCs) was likely related to air contamination. The results of the present study highlighted the strict control of biogeochemical processes on the behavior of hydrothermal VOCs that, at least at a local scale, may have a significant impact on air quality. This information could be improved by laboratory experiments conducted at specific chemical–physical conditions and in presence of different microbial populations.

Occurrence of volatile organic compounds in foods from the Belgian market and dietary exposure assessment

Because volatile organic compounds (VOCs) are ubiquitous in the environment and may represent health risks, it is important to know whether they are present in our diet and to identify possible sources in order to reduce daily intake. In the present study, 377 food samples from the Belgian market were screened for the presence of 21 VOCs. The most prevalent of these compounds and respective percentages of occurrence were: chloroform (97%), toluene (95%), ethyl benzene (80%), o-xylene (79%) and benzene (58%). Dietary intake by the Belgian adult population was calculated for these five most prevalent VOCs. The maximum probabilistic dietary intake was with 0.151, 0.645, 0.138, 0.066 and 0.118 μg kg bw−1day−1 for chloroform, toluene, ethyl benzene, o-xylene and benzene respectively below the minimal risk level (MRL) set for each of the VOCs for oral chronic/acute exposure and below the Reference Dose for Chronic Oral Exposure (RfD). The Margin of Exposure (MOE) for benzene was significantly larger than 100,000. Therefore, it was concluded that the dietary exposure to VOCs for the Belgian adult population does not impose health risks.

Identification of microorganisms based on headspace analysis of volatile organic compounds by gas chromatography–mass spectrometry

The identification of specific volatile organic compounds (VOCs) produced by microorganisms may assist in developing a fast and accurate methodology for the determination of pulmonary bacterial infections in exhaled air. As a first step, pulmonary bacteria were cultured and their headspace analyzed for the total amount of excreted VOCs to select those compounds which are exclusively associated with specific microorganisms. Development of a rapid, noninvasive methodology for identification of bacterial species may improve diagnostics and antibiotic therapy, ultimately leading to controlling the antibiotic resistance problem. Two hundred bacterial headspace samples from four different microorganisms (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Klebsiella pneumoniae) were analyzed by gas chromatography–mass spectrometry to detect a wide array of VOCs. Statistical analysis of these volatiles enabled the characterization of specific VOC profiles indicative for each microorganism. Differences in VOC abundance between the bacterial types were determined using ANalysis of VAriance-principal component analysis (ANOVA-PCA). These differences were visualized with PCA. Cross validation was applied to validate the results. We identified a large number of different compounds in the various headspaces, thus demonstrating a highly significant difference in VOC occurrence of bacterial cultures compared to the medium and between the cultures themselves. Additionally, a separation between a methicillin-resistant and a methicillin-sensitive isolate of S. aureus could be made due to significant differences between compounds. ANOVA-PCA analysis showed that 25 VOCs were differently profiled across the various microorganisms, whereas a PCA score plot enabled the visualization of these clear differences between the bacterial types. We demonstrated that identification of the studied microorganisms, including an antibiotic susceptible and resistant S. aureus substrain, is possible based on a selected number of compounds measured in the headspace of these cultures. These in vitro results may translate into a breath analysis approach that has the potential to be used as a diagnostic tool in medical microbiology.

Occurrence of volatile organic compounds in sugarcane silages

The main objective of this study was to describe the occurrence of VOC in sugarcane silages. Thirty-three samples of sugarcane silage were collected from farm-scale (n=25) and laboratory-scale silos (n=8). From the total, 11 silages were prepared without additives, 17 were treated with sodium benzoate and 5 were inoculated with Lactobacillus buchneri. Water extracts were prepared and analyzed for 18 fermentation end-products using HPLC and special GC techniques. The functional relationships among the fermentation end-products were established using principal component analysis. In addition to high contents of ethanol, acetic acid, and lactic acid, significant concentrations of 1,2-propanediol, ethyl lactate, acetone, 2,3-butanediol, propionic acid, n-butyric acid, ethyl acetate, 2-butanol, methanol, propanol, and iso-butyric acid were found. Ethanol was negatively associated with acetic acid and 2,3-butanediol but positively correlated with lactic acid and esters. Dry matter content determined by oven drying (DMoven) and ethanol concentration explained 0.98 of the variation in the dry matter content corrected for volatile compounds [DMcorr (g/kg as fed)=42.81+0.916 × DMoven (g/kg as fed)+0.141 × Ethanol (g/kg DMoven)], because silages with high contents of ethanol frequently also contained significant amounts of other volatile substances.

Ionic liquids versus amine solutions in biogas upgrading: the level of volatile organic compounds

Background: This article provides information related to the occurrence of volatile organic compounds before and after biogas purification, by means of both aqueous amine solutions and ionic liquids. Results & discussion: Encouraging results were obtained. Under the experimental conditions, 1-butyl-3-methylimidazolium acetate ionic liquid appeared to perform at least two-times better than aqueous amines solutions, since it captured 65 wt% of the identified volatile organic compounds, while aqueous amine solutions retained around 35 wt% only. However, in the case of octamethylcyclotetrasiloxane and dichlorobenzene, aqueous amine solutions rendered better purification performance and diminished the concentration of aforementioned compounds by a factor of five and ten, respectively. Conclusion: This paper sheds new light on ionic liquids as potential separation sorbents and contributes to the understanding of the complex science of biogas upgrading and utilization of renewable energy resources.

Volatile organic compounds in landfill odorant emissions on the island of Mallorca

This study provides data on the occurrence of volatile organic compounds (VOCs) in the biogas emission from a landfill located on the island of Mallorca (Balearic Islands, Spain), where 200,000 tonnes of urban solid wastes are dumped every year. Three different sampling cells, of differing waste ageing were investigated in August 2008, during the main tourist season and the warmest possible weather conditions. Samples were collected in Nalophan™ bags according to the standard European method EN 13725 followed by VOCs adsorption onto Carboxen 1000™ and Tenax TA™ materials prior to thermal desorption and analysis by GC-MS. In total 42 VOCs were analysed, using external standards, out of which 36 were positively identified. Detected VOCs in µg m−3 were alkanes (19–62), aldehydes (65–98), ketones (78–129), alcohols (67–78), esters (25–33), BTEX (83–106), halogenated compounds (16–39), terpens (1.4–2.4) and reduced sulphur compounds (2.6–4.2), showing different concentrations on each one of the three cells. Emitted VOCs showed some similarities with other previous studies from China and Turkey, while large differences to an Italian study. The benzene-to-toluene ratio (B:T) showed values in the range of 0.13 to 0.20 characteristic of biogas. H2S and NH3 gases emitted by the landfill were measured in-situ utilising Dräger™ Tubes for Short-Term-Measurements, showing concentration levels of ≤800 µg m−3 and <300 µg m−3, respectively, which is higher than the determined VOCs in accordance with previous studies. Samples were examined with dynamic olfactometry following standard European method EN 13725, to determine a potential statistical linear correlation between odour and VOC concentrations. Such correlations were not observed probably owing to the large number of compounds emitted from garbage which are not quantified, yet causing positive results in olfactometry.

Trends in concentrations of nitrate and total dissolved solids in public supply wells of the Bunker Hill, Lytle, Rialto, and Colton groundwater subbasins, San Bernardino County, California: Influence of legacy land use

Concentrations and temporal changes in concentrations of nitrate and total dissolved solids (TDS) in groundwater of the Bunker Hill, Lytle, Rialto, and Colton groundwater subbasins of the Upper Santa Ana Valley Groundwater Basin were evaluated to identify trends and factors that may be affecting trends. One hundred, thirty-one public-supply wells were selected for analysis based on the availability of data spanning at least 11years between the late 1980s and the 2000s.Forty-one of the 131 wells (31%) had a significant (p<0.10) increase in nitrate and 14 wells (11%) had a significant decrease in nitrate. For TDS, 46 wells (35%) had a significant increase and 8 wells (6%) had a significant decrease. Slopes for the observed significant trends ranged from −0.44 to 0.91mg/L/yr for nitrate (as N) and −8 to 13mg/L/yr for TDS.Increasing nitrate trends were associated with greater well depth, higher percentage of agricultural land use, and being closer to the distal end of the flow system. Decreasing nitrate trends were associated with the occurrence of volatile organic compounds (VOCs); VOC occurrence decreases with increasing depth.The relations of nitrate trends to depth, lateral position, and VOCs imply that increasing nitrate concentrations are associated with nitrate loading from historical agricultural land use and that more recent urban land use is generally associated with lower nitrate concentrations and greater VOC occurrence. Increasing TDS trends were associated with relatively greater current nitrate concentrations and relatively greater amounts of urban land. Decreasing TDS trends were associated with relatively greater amounts of natural land use. Trends in TDS concentrations were not related to depth, lateral position, or VOC occurrence, reflecting more complex factors affecting TDS than nitrate in the study area.

Volatile organic compounds in an urban environment: a comparison among Belgium, Vietnam and Ethiopia

The effects of urban and indoor air pollution on human health are a major environmental concern for all, but not much has been researched in the developing world. Specifically, quantitative data on the occurrence of volatile organic compounds (VOCs) – main contributors to air pollution – in Asia and Africa are scarce compared to the availability of data in the developed world. This paper presents one of the first studies focusing on the analysis and occurrence of VOCs in Vietnam and Ethiopia, which constitutes part of the novelty of this work. A spectrum of 34 VOCs was measured at eight different urban sites in Ghent (Belgium), Hanoi (Vietnam), Jimma and Addis Ababa (Ethiopia) during three sampling campaigns from September 2008 to September 2010. Sampling was done in an active way by means of sorbent tubes filled with Tenax TA. The analysis was done by TD-GC-MS using internal standard calibration. Data were interpreted and compared in terms of (i) individual, subgroup and total VOCs concentration (TVOCs), (ii) indoor-to-outdoor (I/O) concentration ratios, (iii) source identification by diagnostic ratio and/or correlation coefficients, and (iv) ozone formation potential (OFP) at outdoor sites based on up-to-date maximum incremental reactivity (MIR). I/O concentration ratios varied between 0.2 and 30, with big differences noticed with respect to the type of VOC(s) considered and the type of outdoor sampling location. The highest TVOC concentrations were measured in street samples with maximum values of 54 µg/m3 in Ghent, 507 µg/m3 in Hanoi and 318 µg/m3 in Addis Ababa illustrating the large difference in ambient air quality levels. This is also reflected in the arithmetic mean OFP values (µg/m3) of 82, 1308 and 596 in Ghent, Hanoi and Addis Ababa, respectively. Results of this study could be helpful to support formulation of national policy with regard to ambient air quality.