Biofiltration for the removal and ‘detoxification’ of a complex mixture of volatile organic compounds

A study was performed to determine the effectiveness of using biofiltration for the removal of a complex mixture of volatile organic compounds (VOCs) air-stripped from petroleum hydrocarbons. A biofilter was constructed which contained 264 cm³ of packing material (Celite^? R-635). The unit was inoculated with a mixed culture containing a hydrocarbon-degrading Pseudomonas sp and an Alcaligenes sp. Several of the major compounds in the VOC mixture were monitored individually, along with the total VOCs, using gas chromatography. The average influent concentration of the VOC mixture was 320 ppmv and the average total VOC removal rate was over 56%, with the average removal rate of the monitored individual compounds ranging from 49–90%. After 30 days of operation the average overall removal rate was 69% and the removal of the major compounds averaged 92%. The toxicity and mutagenicity of the air stream was monitored using the Microtox and Ames assays, respectively. These data show marked decreases in toxicity and mutagenicity of the air stream as a result of the biofiltration treatment. The biofiltration system, therefore, was not only effective in removing VOCs from the air stream over an extended time-period, but was also effective in greatly reducing the toxicity and mutagenicity associated with the remaining VOCs. Received 03 July 1997/ Accepted in revised form 25 November 1997     

Volatile organic compounds produced by Saccharomyces cerevisiae inhibit the in vitro development of Guignardia citricarpa,the causal agent of citrus black spot

Due to the low chemical control effectiveness of citrus black spot, caused by the fungus Guignardia citricarpa at postharvest, and to the search for alternative control methods, this study aimed to evaluate the in vitro effect of volatile organic compounds (VOCs), produced by yeast Saccharomyces cerevisiae, on G. citricarpa. It was observed that the yeast strains evaluated acted as antagonists by VOC production, whose maximum inhibitory capacity was as high as 87.2%. The presence of fermentable carbon sources in the medium was essential for the bioactive VOC production by the yeast. The analysis of VOCs produced in PDA medium by SPME–GC–MS indicated the presence of high quantities of alcohols as well as esters. An artificial VOC mixture prepared on the basis of the composition of the VOCs mimicked the inhibitory effects of the natural VOCs released by S. cerevisiae. Thus, the VOCs produced by the yeast or the artificial mixtures can be a promising control method for citrus black spot or others postharvest diseases.     

Comparison of the Decomposition VOC Profile during Winter and Summer in a Moist,Mid-Latitude (Cfb) Climate

The investigation of volatile organic compounds (VOCs) associated with decomposition is an emerging field in forensic taphonomy due to their importance in locating human remains using biological detectors such as insects and canines. A consistent decomposition VOC profile has not yet been elucidated due to the intrinsic impact of the environment on the decomposition process in different climatic zones. The study of decomposition VOCs has typically occurred during the warmer months to enable chemical profiling of all decomposition stages. The present study investigated the decomposition VOC profile in air during both warmer and cooler months in a moist, mid-latitude (Cfb) climate as decomposition occurs year-round in this environment. Pig carcasses (Sus scrofa domesticus L.) were placed on a soil surface to decompose naturally and their VOC profile was monitored during the winter and summer months. Corresponding control sites were also monitored to determine the natural VOC profile of the surrounding soil and vegetation. VOC samples were collected onto sorbent tubes and analyzed using comprehensive two-dimensional gas chromatography – time-of-flight mass spectrometry (GC×GC-TOFMS). The summer months were characterized by higher temperatures and solar radiation, greater rainfall accumulation, and comparable humidity when compared to the winter months. The rate of decomposition was faster and the number and abundance of VOCs was proportionally higher in summer. However, a similar trend was observed in winter and summer demonstrating a rapid increase in VOC abundance during active decay with a second increase in abundance occurring later in the decomposition process. Sulfur-containing compounds, alcohols and ketones represented the most abundant classes of compounds in both seasons, although almost all 10 compound classes identified contributed to discriminating the stages of decomposition throughout both seasons. The advantages of GC×GC-TOFMS were demonstrated for detecting and identifying trace levels of VOCs, particularly ethers, which are rarely reported as decomposition VOCs.     

Microbial compositions and metabolic interactions in one- and two-phase partitioning airlift bioreactors treating a complex VOC mixture

Engineered microbial ecosystems in bioscrubbers for the treatment of volatile organic compounds (VOCs) have been complicated by complex VOC mixtures from various industrial emissions. Microbial associations with VOC removal performance of the bioscrubbers are still not definitive. Here, one- and two-phase partitioning airlift bioreactors were used for the treatment of a complex VOC mixture. Microbial characteristics in both bioreactors were uncovered by high-throughput metagenomics sequencing. Results showed that dominant species with specialized VOC biodegradability were mainly responsible for high removal efficiency of relative individual VOC. Competitive enzyme inhibitions among the VOC mixture were closely related to the deterioration of removal performance for individual VOC. Relative to the mass transfer resistance, the specialized biodegrading functions of microbial inoculations and enzymatic interactions among individual VOC biodegradation also must be carefully evaluated to optimize the treatment of complex VOC mixtures in bioreactors.     

Fusarium infection in maize: volatile induction of infected and neighboring uninfected plants has the potential to attract a pest cereal leaf beetle, Oulema melanopus

Fusarium infection of maize leaves and/or roots through the soil can stimulate the emission of volatile organic compounds (VOCs). It is also well known that VOC emission from maize plants can repel or attract pests. In our experiments, we studied VOC induction responses of Zea mays L. ssp. mays cv. ‘Prosna’ having Fusarium infection (mix of four species) in leaves or roots, then tested for VOC induction of uninfected neighboring plants, and finally examined wind-tunnel behavioral responses of the adult cereal leaf beetle, Oulema melanopus L. (Chrysomelidae: Coleoptera) behavior to four induced VOCs. In the first part of our experiment, we confirmed that several green leaf volatiles (GLVs; (Z)-3-hexenal, (E)-2-hexenal, (Z)-3-hexen-1-ol, (E)-2-hexen-1-ol, (Z)-3-hexen-1-yl acetate, 1-hexyl acetate), terpenes (β-pinene, β-myrcene, Z-ocimene, linalool, β-caryophyllene), and shikimic acid pathway derivatives (benzyl acetate, methyl salicylate, indole) were positively induced from maize plants infected by Fusarium spp. The quantities of induced VOCs were higher at 7 d than 3 d post-infection and greater when plants were infected with Fusarium on leaves rather than through soil. In the second part of our experiment, uninfected maize plants also showed significantly positive induction of several VOCs when neighboring an infected plant where the degree of induction was negatively related to the distance from the infected plant. In the third part of our experiment, a Y-tube bioassay was used to evaluate upwind orientation of adult cereal leaf beetles to four individual VOCs. Female and male O. melanopus were significantly attracted to the GLVs (Z)-3-hexenal and (Z)-3-hexenyl acetate, and the terpenes linalool and β-caryophyllene. Our results indicate that a pathogen can induce several VOCs in maize plants that also induce VOCs in neighboring uninfected plants, though VOC induction could increase the range at which an insect pest species is attracted to VOC inducing plants.     

Volatile organic compounds produced by Lysinibacillus sp. FJAT-4748 possess antifungal activity against Colletotrichum acutatum

FJAT-4748 is a bacterial strain isolated from forest soil samples taken from Dongba Valley, Lijiang, Kunming, Yunnan Province, PR China. This strain was identified as Lysinibacillus sp. based on a 16S rRNA gene sequence analysis. FJAT-4748 has been shown to possess antifungal activity against different fungi, including Colletotrichum acutatum, Aspergillus niger, Fusarium solani, Fusarium moniliforme and Fusarium oxysporum. The results of the present study indicate that this antifungal activity results from volatile organic compounds (VOCs) produced by this strain. The observed inhibition rates of VOCs from FJAT-4748 against these fungi were 100%, 100%, 37.20%, 18.94% and 7.64%, respectively. GC-MS analysis identified 24 VOCs from FJAT-4748, which included different categories of compounds, such as aldehydes, ketones, alcohols, aromatic hydrocarbons and alkanes. Of these 24 VOCs, the most abundant compound was 2-ethyl-1-hexanol, which constituted 36.24% of the total VOCs based on the relative peak area. In the in vitro C. acutatum mycelial growth assay, 2-ethyl-1-hexanol exhibited the strongest activity, with an inhibitory rate of 100% using 10?µL/plate of this VOC. The activity of benzaldehyde was lower. 2-decanone showed the weakest activity among the compounds tested. The inhibitory activity of an artificial mixture of three VOCs against the C. acutatum increased with the amount of artificial mixture used. The inhibition rate reached 100% using 30?µL/plate of this artificial mixture in the plate test. Taken together, these results show that the antifungal VOCs produced by Lysinibacillus sp. FJAT-4748 are potentially useful as agents for controlling anthracnose caused by Colletotrichum acutatum.     

Drought effects on volatile organic compound emissions from Scots pine stems

Tree stems have been identified as sources of volatile organic compounds (VOCs) that play important roles in tree defence and atmospheric chemistry. Yet, we lack understanding on the magnitude and environmental drivers of stem VOC emissions in various forest ecosystems. Due to the increasing importance of extreme drought, we studied drought effects on the VOC emissions from mature Scots pine (Pinus sylvestris L.) stems. We measured monoterpenes, acetone, acetaldehyde and methanol emissions with custom-made stem chambers, online PTR-MS and adsorbent sampling in a drought-prone forest over the hot-dry summer of 2018 and compared the emission rates and dynamics between trees in naturally dry conditions and under long-term irrigation (drought release). The pine stems were significant monoterpene sources. The stem monoterpene emissions potentially originated from resin, based on their similar monoterpene spectra. The emission dynamics of all VOCs followed temperature at a daily scale, but monoterpene and acetaldehyde emission rates decreased nonlinearly with drought over the summer. Despite the dry conditions, large peaks of monoterpene, acetaldehyde and acetone emissions occurred in late summer potentially due to abiotic or biotic stressors. Our results highlight the potential importance of stem emissions in the ecosystem VOC budget, encouraging further studies in diverse environments.     

Emission of volatile organic compounds by apple trees under spider mite attack and attraction of predatory mites

Emission rates of volatile organic compounds (VOCs) from Pirus malus L. subsp. mitis (Wallr.) var. Golden Delicious and var. Starking attacked by the phytophagous mite Panonychus ulmi Koch, and their attractiveness to the predatory mites Amblyseius andersoni Chant and Amblyseius californicus McGregor, were studied during three years. A large variability was found in the emission of individual VOCs depending on the infestation, the apple tree variety and the date. There were larger total VOC emission rates and larger total VOC leaf concentrations in apple trees attacked by phytophagous mites, especially in the var. Starking. In infested trees of this variety, there were also more predatory mites. An olfactometer assay showed that predatory mites preferentially chose branches infested by Panonychus ulmi (85% went to infested branches vs 15% to uninfested control branches) indicating that volatiles may be used as cues to find their prey.     

On-line monitoring of microbial volatile metabolites by proton transfer reaction-mass spectrometry

A method for analysis of volatile organic compounds (VOCs) from microbial cultures was established using proton transfer reaction-mass spectrometry (PTR-MS). A newly developed sampling system was coupled to a PTR-MS instrument to allow on-line monitoring of VOCs in the dynamic headspaces of microbial cultures. The novel PTR-MS method was evaluated for four reference organisms: Escherichia coli, Shigella flexneri, Salmonella enterica, and Candida tropicalis. Headspace VOCs in sampling bottles containing actively growing cultures and uninoculated culture medium controls were sequentially analyzed by PTR-MS. Characteristic marker ions were found for certain microbial cultures: C. tropicalis could be identified by several unique markers compared with the other three organisms, and E. coli and S. enterica were distinguishable from each other and from S. flexneri by specific marker ions, demonstrating the potential of this method to differentiate between even closely related microorganisms. Although the temporal profiles of some VOCs were similar to the growth dynamics of the microbial cultures, most VOCs showed a different temporal profile, characterized by constant or decreasing VOC levels or by single or multiple peaks over 24 h of incubation. These findings strongly indicate that the temporal evolution of VOC emissions during growth must be considered if characterization or differentiation based on microbial VOC emissions is attempted. Our study may help to establish the analysis of VOCs by on-line PTR-MS as a routine method in microbiology and as a tool for monitoring environmental and biotechnological processes.     

Volatile organic compounds cytotoxicity and expression of HSP72, HSP90 and GRP78 stress proteins in cultured human cells

The aim of this study was to determine whether overexpression of stress proteins (SPs) could be a sensitive biomarker for cell injury due to exposure to low doses of volatile organic compounds (VOCs) such as benzene, ethylbenzene, toluene, xylene, and chlorinated derivatives (ClB). Sublethal and cytotoxic threshold concentrations of the VOCs were determined by studying the growth rate of normal (fibroblasts) or tumor-derived human cell lines (A549, HepG2) exposed for 4 days to VOCs. Changes in SP expression as a function of concentrations were investigated by Western blotting.VOC toxicity was found to be correlated with their degree of chlorination and their hydrophobicity. Cytotoxic threshold concentrations (no-observed effect concentration, NOEC) were found to be similar for the three cell lines. It was observed that using a mixture of VOCs, each of them at concentration below the NOEC, resulted in an actual toxicity to the cells. This finding reveals a synergistic effect and should be taken into account when assessing threshold risk and exposure limit values in the worker's environment when several pollutants may be present. HSP72 and HSP90 expression levels were not affected whereas GRP78 expression was increased by all the VOCs. Taking into account the specific molecular function of GRP78, it suggests that VOC exposure results in misfolded or underglycosylated protein accumulation in the endoplasmic reticulum. GRP78 overexpression was closely related to the magnitude of growth inhibition due to increasing concentrations of each VOC. The overexpression was found to be significant for concentrations 5 to 30 times higher than NOEC, indicating that, under our experimental conditions, GRP78 expression cannot be considered as a sensitive biomarker of exposure to environmental VOCs.     

Improving Biodegradation of VOCs in Soil by Controlling Volatilization

The use of microbial inoculum and a hydrocarbon adsorbent as a soil amendment was examined to improve bioremediation efficacy of soil contaminated by volatile hydrocarbons. Biodegradation and volatilization losses of VOCs were assessed under contained composting in the laboratory and technical scales. Rhodococcus opacus GM-14, a degrader of a multitude of different hydrocarbons was used as an inoculum and activated carbon as a VOC adsorbent on a laboratory scale. Inoculating soil with R. opacus (0.02 mg R. opacus biomass per 1 mg of benzene) reduced volatilization of benzene from 80% to 40%. Amending the soil with activated carbon reduced volatilization of benzene to 15% and further to 4% when used together with R. opacus. Both amendments promoted mineralization when used separately but slowed down the mineralization when combined. Activated carbon improved the biodegradation of VOCs also during technical scale compostings (700-1100 kg of soil with 1.6-2.4 kg of VOC) from 30-40% to 86% and reduced volatilization from 40-50% to 2-5%. Reduction of VOC volatilization by use of the activated carbon improved the efficiency of VOC biodegradation on a technical scale. The activated carbon addition improves the occupational safety at the contaminated site and during transport.     

Performance and Microbial Diversity of a Trickle‐Bed Air Biofilter under Interchanging Contaminants

A trickle‐bed air biofilter (TBAB) was evaluated under conditions of interchanging the feed volatile organic compounds (VOCs) in the sequence methyl ethyl ketone (MEK), toluene, methyl isobutyl ketone (MIBK), styrene, and then back to MEK. The obtained performance results revealed that the biofilter provided high removal efficiency within the critical loading of each VOC, which was previously defined in the non‐interchanging VOC fed biofilter. The biofilter easily acclimated to the oxygenated compounds (MEK and MIBK), but re‐acclimation was delayed for the aromatic compounds (toluene and styrene). Ratios of the molar mass of CO₂ produced per molar mass of VOC removed were investigated. It has been found that the ratios for the aromatic compounds closely resembled the theoretical complete chemical oxidation based ratios while larger differences were encountered with the oxygenated compounds. Denaturing gradient gel electrophoresis (DGGE) analysis of 16S rRNA genes was used to assess the impact of interchanging VOCs on the bacterial community structure in the biofilter. The results from denaturing gradient gel electrophoresis (DGGE) showed that the structure of the microbial community in the biofilter was different after each interchange of VOCs.     

Study of the Vapor Phase Over Fusarium Fungi Cultured on Various Substrates

The compositions of volatile organic compounds (VOCs) emitted by Fusarium fungi (F. langsethiae, F. sibiricum, F. poae, and F. sporotrichioides) grown on two nutritive substrates: potato sucrose agar (PSA) and autoclaved wheat kernels (WK) were investigated. The culturing of fungi and study of their VOC emissions were performed in chromatographic vials at room temperature (23 – 24 °C) and the VOCs were sampled by a solid‐phase microextraction on a 85 μm carboxen/polydimethylsiloxane fiber. GC/MS was performed using a 60‐m HP‐5 capillary column. Components of the VOC mixture were identified by electron impact mass spectra and chromatographic retention indices (RIs). The most abundant components of the VOC mixture emitted by Fusarium fungi are EtOH, AcOH, ⁱBuOH, 3‐methylbutan‐1‐ol, 2‐methylbutan‐1‐ol, ethyl 3‐methylbutanoate, terpenes with M 136, sesquiterpenes with M 204 (a total of about 25), and trichodiene. It was found that the strains grown on PSA emit a wider spectrum and larger amount of VOCs compared with those grown on wheat kernels. F. langsethiae strain is the most active VOC producer on both substrates. The use of SPME and GC/MS also offers the potential for differentiation of fungal species and strains.     

Reduced levels of volatile emissions in jasmonate-deficient spr2 tomato mutants favour oviposition by insect herbivores

Tomato plants release volatile organic compounds (VOCs) following insect or mechanical damage. In this study, the constitutive and wound-induced emission levels of VOCs in suppressor of prosystemin-mediated responses2 (spr2) mutant plants, compromised in linolenic acid (LA) and jasmonic acid (JA) synthesis, and in 35S::prosystemin (35S::prosys) plants, having upregulated direct defence responses, were compared. The spr2 mutants produced constitutively lower levels of VOCs, which were nonetheless increased in response to (a)biotic damage, although at lower levels than wild-type (Wt) and 35S::prosys plants. No significant differences in VOC emissions were detected between the latter two genotypes, thereby suggesting that systemin does not regulate indirect defence responses, whereas differences in fatty acid composition in spr2 plants led to the predominant emission of saturated C6 volatiles in response to wounding. The expression of 1-deoxy-D-xylulose 5-phosphate synthase (DXS2), a key gene involved in VOC synthesis in the chloroplast, was only upregulated in Manduca sexta L.-damaged Wt and 35S::prosys plants. However, its expression was restored in spr2 plants by exogenous LA or JA, suggesting that abated VOC emissions in spr2 plants are correlated with lowered DXS2 expression. Bioassays with two different insects showed that adult females significantly preferred spr2 plants, indicating that lowered levels of VOCs in tomato influence plant selection by insects during oviposition.     

Plant growth-promoting rhizobacteria modulate root-system architecture in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> through volatile organic compound emission

Extensive communication occurs between plants and microorganisms during different stages of plant development in which signaling molecules from the two partners play an important role. Volatile organic compounds (VOCs) emission by certain plant-growth promoting rhizobacteria (PGPR) has been found to be involved in plant growth. However, little is known about the role of bacterial VOCs in plant developmental processes. In this work, we investigated the effects of inoculation with twelve bacterial strains isolated from the rhizosphere of lemon plants (Citrus aurantifolia) on growth and development of Arabidopsis thaliana seedlings. Several bacterial strains showed a plant growth promoting effect stimulating biomass production, which was related to differential modulation of root-system architecture. The isolates L263, L266, and L272a stimulated primary root growth and lateral root development, while L254, L265a and L265b did not significantly alter primary root growth but strongly promoted lateral root formation. VOC emission analysis by SPME-GC-MS identified aldehydes, ketones and alcohols as the most abundant compounds common to most rhizobacteria. Other VOCs, including 1-octen-3-ol and butyrolactone were strain specific. Characterization of L254, L266 and L272a bacterial isolates by 16S rDNA analysis revealed the identity of these strains as Bacillus cereus, Bacillus simplex and Bacillus sp, respectively. Taken together, our data suggest that rhizospheric bacterial strains can modulate both plant growth promotion and root-system architecture by differential VOC emission.     

Headspace measurements of irradiated in vitro cultured cells using PTR-MS

A pilot study was performed to evaluate a new concept for a radiation biodosimetry method. Proton transfer reaction-mass spectrometry (PTR-MS) was used to find out whether radiation induces changes in the composition of volatile organic compounds (VOCs) in the headspace of in vitro cultured cells. Two different cell lines, retinal pigment epithelium cells hTERT-RPE1 and lung epithelium cells A-549, were irradiated with gamma radiation at doses of 4 Gy and 8 Gy. For measuring the cell-specific effects, the VOC concentrations in the headspace of flasks containing cells plus medium, as well as of flasks containing pure medium were analyzed for changes before and after irradiation. No significant radiation-induced alterations in VOC concentrations in the headspace could be observed after irradiation.     

An endophytic/pathogenic Phoma sp. from creosote bush producing biologically active volatile compounds having fuel potential

A Phoma sp. was isolated and characterized as endophytic and as a pathogen of Larrea tridentata (creosote bush) growing in the desert region of southern Utah, USA. This fungus produces a unique mixture of volatile organic compounds (VOCs), including a series of sesquiterpenoids, some alcohols and several reduced naphthalene derivatives. Trans-caryophyllene, a product in the fungal VOCs, was also noted in the VOCs of this pungent plant. The gases of Phoma sp. possess antifungal properties and is markedly similar to that of a methanolic extract of the host plant. Some of the test organisms with the greatest sensitivity to the Phoma sp. VOCs were Verticillium, Ceratocystis, Cercospora and Sclerotinia while those being the least sensitive were Trichoderma, Colletotrichum and Aspergillus. We discuss the possible involvement of VOC production by the fungus and its role in the biology/ecology of the fungus/plant/environmental relationship with implications for utilization as an energy source.     

Decomposition Odour Profiling in the Air and Soil Surrounding Vertebrate Carrion

Chemical profiling of decomposition odour is conducted in the environmental sciences to detect malodourous target sources in air, water or soil. More recently decomposition odour profiling has been employed in the forensic sciences to generate a profile of the volatile organic compounds (VOCs) produced by decomposed remains. The chemical profile of decomposition odour is still being debated with variations in the VOC profile attributed to the sample collection technique, method of chemical analysis, and environment in which decomposition occurred. To date, little consideration has been given to the partitioning of odour between different matrices and the impact this has on developing an accurate VOC profile. The purpose of this research was to investigate the decomposition odour profile surrounding vertebrate carrion to determine how VOCs partition between soil and air. Four pig carcasses (Sus scrofa domesticus L.) were placed on a soil surface to decompose naturally and their odour profile monitored over a period of two months. Corresponding control sites were also monitored to determine the VOC profile of the surrounding environment. Samples were collected from the soil below and the air (headspace) above the decomposed remains using sorbent tubes and analysed using gas chromatography-mass spectrometry. A total of 249 compounds were identified but only 58 compounds were common to both air and soil samples. This study has demonstrated that soil and air samples produce distinct subsets of VOCs that contribute to the overall decomposition odour. Sample collection from only one matrix will reduce the likelihood of detecting the complete spectrum of VOCs, which further confounds the issue of determining a complete and accurate decomposition odour profile. Confirmation of this profile will enhance the performance of cadaver-detection dogs that are tasked with detecting decomposition odour in both soil and air to locate victim remains.