Article

Greatly Enhanced Removal of Volatile Organic Carcinogens by a Genetically Modified Houseplant, Pothos Ivy ( Epipremnum aureum ) Expressing the Mammalian Cytochrome P450 2e1 Gene

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Abstract

The indoor air in urban homes of developed countries is usually contaminated with significant levels of volatile organic carcinogens (VOCs), such as formaldehyde, benzene, and chloroform. There is a need for a practical, sustainable technology for the removal of VOCs in homes. Here we show that a detoxifying transgene, mammalian cytochrome P450 2e1 can be expressed in a houseplant, Epipremnum aureum, pothos ivy, and that the resulting genetically modified plant has sufficient detoxifying activity against benzene and chloroform to suggest that biofilters using transgenic plants could remove VOCs from home air at useful rates.

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... However, the experimental results of the underlying scientific works are often reported in ways such that they cannot simply be extrapolated into impacts in real indoor environments. Typical for these studies, a potted plant was placed in a sealed chamber (often with volume of 1 m 3 ), into which a single VOC was injected, and its decay was tracked over the course of many hours or days [42][43][44][45][46][47][48][49][50][51][52]. In contrast, building volumes are much larger than that of an experimental chamber, and VOC emissions are persistent. ...
... (1) A sealed chamber (setup I) presenting only initial and final concentration measurements (or their ratios), for a certain duration of time. [50] 0.011 -33 a,c Yoo et al. [51] 0.287 -8 a,c Zhang et al. [52] 0.040 -1 b Category 2 (see Table S2) Irga (2) A sealed chamber (setup I) presenting a timeseries of concentration measurements. (3) A flow-through chamber (setup II) presenting C inlet and C outlet measurements. ...
... Yang et al. [50] presented results similarly for five VOCs across several plant species organized qualitatively by performance (i.e., "superior," "intermediate," and "poor" performing plants). Zhang et al. [52] used a genetically modified version of Pothos Ivy, designed to enhance VOC uptake, and provided a percent reduction of concentration achieved over the timespan of days. The CADR p results for these studies are detailed in Table S1. ...
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Potted plants have demonstrated abilities to remove airborne volatile organic compounds (VOC) in small, sealed chambers over timescales of many hours or days. Claims have subsequently been made suggesting that potted plants may reduce indoor VOC concentrations. These potted plant chamber studies reported outcomes using various metrics, often not directly applicable to contextualizing plants' impacts on indoor VOC loads. To assess potential impacts, 12 published studies of chamber experiments were reviewed, and 196 experimental results were translated into clean air delivery rates (CADR, m3/h), which is an air cleaner metric that can be normalized by volume to parameterize first-order loss indoors. The distribution of single-plant CADR spanned orders of magnitude, with a median of 0.023 m3/h, necessitating the placement of 10-1000 plants/m2 of a building's floor space for the combined VOC-removing ability by potted plants to achieve the same removal rate that outdoor-to-indoor air exchange already provides in typical buildings (~1 h-1). Future experiments should shift the focus from potted plants' (in)abilities to passively clean indoor air, and instead investigate VOC uptake mechanisms, alternative biofiltration technologies, biophilic productivity and well-being benefits, or negative impacts of other plant-sourced emissions, which must be assessed by rigorous field work accounting for important indoor processes.
... Volatile organic compounds (VOCs) such as formaldehyde (FA), acetone, ethyl acetate, benzene, and chloroform are common indoor pollutants [1]. Some VOCs, including FA, are carcinogenic, damage the nervous and circulatory system [2], and cause allergies, skin irritation, and respiratory diseases [3]. ...
Article
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Air pollution with formaldehyde (FA) has been an emerging concern over recent years. This study was aimed at evaluating the contribution of green wall system-derived expanded clay pellets (ECP) and biofilms to FA removal in liquid phase. The effects of four plant species on this process were compared. An inhibition of the fluorescein diacetate hydrolysis activity of biofilm-derived microorganisms was detected during the exposure to FA in both air and liquid phases, and this effect was plant-species-specific. Liquid chromatography with a UV detector was applied for the quantification of FA. The FA removal activity of ECP in the liquid phase was 76.5 mg ECP−1 after a 24 h incubation in the presence of 100 mg/L FA, while the removal activity of the biofilm differed depending on the plant species used, with the highest values detected in the set with Mentha aquatica, i.e., 59.2 mg ECP−1. The overall FA removal from the liquid phase during 24 h varied in the range from 63% to 82% with the initial FA concentration of 100 mg/L. Differences in biofilm formation upon ECP enrichment were detected by using confocal laser scanning microscopy. These results contribute to the understanding of air biofiltration mechanisms in hydroponic systems.
... Researchers have worked out that the detoxification ability of the plants can be improved by the expression of the mammalian gene(s). Stuart strand and colleagues introduced a rabbit gene (CYP2E1) into a common houseplant, pothos ivy (Epipremnum aureum), and resultant plants were able to remove injected chloroform and benzene from the vial containing transgenic ivy plants [16]. ...
... www.nature.com/scientificreports/ same time, VOCs absorbed into the blood could inhibit the metabolism of cotinine by cytochrome P450 [14][15][16][17] . It showed that when the body absorbed the above two at the same time, there could be a synergistic effect. ...
Article
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Although people all know that nicotine in tobacco smoke is the key to cause health damage, they ignore the synergistic effect of a large number of Volatile Organic Compounds (VOCs) produced by incomplete tobacco combustion on nicotine or cotinine metabolism. Our aim is to investigate the association between serum VOCs and cotinine in smokers infected with HIV, HBV or HCV. National Health and Nutrition Examination Survey (NHANES 2005–2018) database, including 13,652 nationally representative subjects’ sociodemographic characteristics and serological indicators, was used in this study. Smokers living with human immunodeficiency virus (HIV), hepatitis B virus (HBV) or hepatitis C virus (HCV) were compared to non-infected population. The correlation between VOCs and cotinine as well as the effects of VOCs on cotinine metabolism were analyzed by Spearman correlation analysis and multivariable logistic regression analysis, respectively. Among HIV, HBV, or HCV infected smokers with the largest exposure dose to tobacco, the intensity of the association between VOCs and cotinine was the strongest. The results of multivariable binary logistic regression showed that high concentrations of 1,2-Dichlorobenzene (OR:1.036, CI:1.009–1.124), Benzene (OR:1.478, CI:1.036–2.292), Carbon Tetrachloride (OR:1.576, CI:1.275–2.085) and 2,5-Dimethylfuran (OR:1.091, CI:1.030–1.157) in blood might be independent risk factors leading to the increase of serum metabolite cotinine in smokers.
... Incorporation of mammalian cytochrome P450 2e1 (rabbit CYP2E1) in pothos ivy boosted its ability to detoxify the abovementioned hazardous molecules. The engineered plants were able to detoxify chloroform and benzene in the closed vials within 8 days of culture, thus showing great potential to detoxify the undesired molecules [45]. Likewise, sulfur metabolism can be engineered to improve resistance to SO 2 . ...
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Tropical plants are an integral part of the ecosystem and are of significance for the well-being of humanity. Since their domestication in 10,000 BC, conventional breeding has played a crucial role in their conservation and widespread adaptation worldwide. Advancements in multi-omics approaches, that is, genomics, metabolomics, transcriptomics, proteomics, whole genome sequencing, and annotation, have led to the identification of novel genes involved in crucial metabolic pathways, thus helping to develop tropical plant varieties with desirable traits. Information retrieved from the pan-genome, super-pan-genome, and pan-transcriptome has further uplifted marker-assisted selection and molecular breeding. Tissue culture techniques have not only helped to conserve endangered plant species but have also opened up new avenues in terms of mass-scale propagation of ornamental plants. Transgenic technology is increasingly contributing to the betterment of tropical plants, and different plant species have been engineered for valuable traits. Likewise, genome editing is appearing to be a promising tool to develop tropical plants having the potential to fulfill future needs. Hence, this chapter highlights the importance of conventional and modern scientific approaches for the conservation and improvement of tropical plant species.
... Plants have been widely used in indoor environments for psychological and physiological benefits (Mcsweeney et al., 2015;Chorong et al., 2016;Lee, 2020;Aydogan and Cerone, 2021). Epipremnum aureum is the most common plant in the indoor environment (Lee, 2020), removing volatile organic carcinogens at a reasonable rate (Zhang et al., 2019). Interaction with plants has been observed to link with suppressing sympathetic nervous system activity and diastolic blood pressure, promoting comfortable, soothed, and natural feelings (Lee et al., 2015). ...
Article
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Owing to the COVID-19 pandemic, working from home promotes the importance of indoor environment qualities. With the settings and functions of home offices, an experiment was carried out to determine the interaction effects between indoor plants and traffic noise levels (TNLs) on the performance and environmental evaluations of English reading comprehension tasks (ERCTs) and the performance of short-term breaks. A sample of 22 Chinese university students (12 males and 10 females) took part in the experiment. Two visual conditions (with and without plants) and five TNLs (i.e., 35, 45, 50, 55, and 60 dBA TNL) were included. Participants’ accuracy rates, eye movements, mental workload, and feelings about the environment were collected. The mental fatigue recovery (MFR), visual fatigue recovery (VFR), anxiety recovery (AR), and unfriendly recovery (UR) were measured for the analysis of a 5-min short-term break. The results demonstrate (1) plants have significant effects on ERCTs and short-term breaks, especially at 45 and 50 dBA TNL; (2) the effects of TNLs on ERCTs’ eye movements and work environment satisfaction differ by the presence of plants, e.g., the average pupil diameter (APD), lighting and layout satisfaction; (3) The effects of indoor plants on ERCT differ by the range of TNLs. In conclusion, indoor plants are beneficial to home workers engaged in ERCT when TNL does not exceed 50 dBA. The current data highlight the importance of audio-visual interaction in home offices and provide insights into the interaction mechanism between indoor plants and traffic noise.
... Smoking, a social behavior, leads to the absorption of nicotine and VOCs. At the same time, VOCs absorbed into the blood may inhibit the metabolism of cotinine by cytochrome P450 [14][15][16][17] . This shows that when the body absorbs the above two at the same time, there may be a synergistic effect. ...
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Objectives: To identify the unilateral effect of VOCs on cotinine metabolism. Methods: Measurements of 13,652 participants included sociodemographic characteristics and serological indicators (VOCs and cotinine). Correlation between VOCs and cotinine and the effect of VOCs on cotinine metabolism were analyzed by Spearman analysis and multivariable logistic regression analysis. Results: Among smokers infected with HIV | HBV | HCV with the largest exposure dose to tobacco, the intensity of the association between VOCs and cotinine was the strongest. High concentrations of 1,2-Dichlorobenzene (OR: 1.101, CI: 1.069–1.134), Benzene (OR: 1.354, CI: 1.123–1.632), 2,5-Dimethylfuran (OR: 1.054, CI: 1.027–1.082) and Nitrobenzene (OR: 1.347, CI: 1.039–1.746) and low concentration of Carbon Tetrachloride (OR: 0.760, CI: 0.661–0.873) in blood might be independent risk factors leading to the increase of serum metabolite cotinine. Conclusions: The influence intensity of four VOCs (including 1,2-dichlorobenzene, benzene, carbon tetrachloride, 2,5-dimethylfuran and nitrobenzene) on serum cotinine metabolism has a dose-response relationship, that is, the higher the tobacco exposure, the stronger the influence intensity. In addition, this study used molecular epidemiology to indirectly provide new ideas and views on the harm of smoking for smokers.
... This new level of understanding may lead to the development of transgenic and hybrid plants with improved tolerance to xenobiotics, extraction capabilities, growth rate, root depth, and other favorable characteristics for remediation. For example, the expression of the mammalian Cytochrome P450 2E1, a gene involved in the metabolism of xenobiotics in the liver, has been expressed in numerous genetically engineered plants, drastically increasing the plants ability to degrade xenobiotic compounds such as carcinogenic VOCs (Doty et al. 2007(Doty et al. , 2000James et al. 2008;Legault et al. 2017;Zhang et al. 2019). Plants use pathways and enzymes similar to livers in mammalian systems; however, plants lack enzymes capable of mineralizing organic compounds due to the fact that plants do not utilize organic compounds for their energy and Content courtesy of Springer Nature, terms of use apply. ...
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... In general, the average air quality improvement (only accounting for the major air pollutants: O 3 , PM 10 , NO 2 , SO 2 , and CO) due to plants is estimated to be relatively low at around 1% (Nowak et al., 2006). However, the ease by which microbial genomes and plant microbiomes may be manipulated (Zhang et al., 2019), and the capacities for pollutant removal of these complex matrices demonstrated in the laboratory, indicates that the plantÀmicroorganism system is a promising tool for the management of air quality in the future (Doty et al., 2007). ...
... Findings from a recent study undertaken by Zhang et al. 119 indicate that genetic modification may enable the selection and enhancement of micromorphological features for air pollution removal, as previously suggested by Lawson and Blatt 116 . Due to their complex leaf surface micromorphology, broadleaf species are more effective for deposition than coniferous species per leaf area, whereas coniferous species are more effective at tree scale due to a larger total leaf area 110,115 . ...
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Vegetation can form a barrier between traffic emissions and adjacent areas, but the optimal configuration and plant composition of such green infrastructure (GI) are currently unclear. We examined the literature on aspects of GI that influence ambient air quality, with a particular focus on vegetation barriers in open-road environments. Findings were critically evaluated in order to identify principles for effective barrier design, and recommendations regarding plant selection were established with reference to relevant spatial scales. As an initial investigation into viable species for UK urban GI, we compiled data on 12 influential traits for 61 tree species, and created a supplementary plant selection framework. We found that if the scale of the intervention, the context and conditions of the site and the target air pollutant type are appreciated, the selection of plants that exhibit certain biophysical traits can enhance air pollution mitigation. For super-micrometre particles, advantageous leaf micromorphological traits include the presence of trichomes and ridges or grooves. Stomatal characteristics are more significant for sub-micrometre particle and gaseous pollutant uptake, although we found a comparative dearth of studies into such pollutants. Generally advantageous macromorphological traits include small leaf size and high leaf complexity, but optimal vegetation height, form and density depend on planting configuration with respect to the immediate physical environment. Biogenic volatile organic compound and pollen emissions can be minimised by appropriate species selection, although their significance varies with scale and context. While this review assembled evidence-based recommendations for practitioners, several important areas for future research were identified.
... GM pothos ivy removes chloroform and benzene from the air. Both benzene and chloroform exposure have been linked to cancer (Zhang et al. 2019). Pothos ivy does not flower in temperate climates, so the GM plants will not spread via pollen. ...
Chapter
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Objectives: To report a novel case of Epipremnum aureum toxicity masquerading as bilateral infectious keratitis and review the literature on ocular manifestations of Epipremnum exposure. Methods: Case report and literature review. Results: A 70-year-old man with a history of photorefractive keratectomy presented with a 3-day history of bilateral eye pain. The patient reported exposure to plant debris while performing yard work and also water exposure while cleaning his coral fish tanks. Clinical examination revealed bilateral epitheliopathy progressing to frank epithelial defects with underlying stromal necrosis 6 days after exposure. Empiric topical antibiotic drops were initiated, but multiple cultures, corneal biopsy, and confocal microscopy were all negative for an infectious agent. Over a 2-week period, the epithelial defects worsened and a suspicion for a toxic etiology was raised. The patient later recalled rubbing his eyes after exposure to Epipremnum aureum (Golden Pothos/Devils Ivy) sap. He was thus treated conservatively with artificial tears, topical corticosteroids, and amniotic membrane. After 3 months, the epithelial defects resolved, but with corneal scarring, prominently in the left eye and underwent penetrating keratoplasty. Five years after presentation, best-corrected visual acuity with hard contact lenses was 20/25 in the right eye and 20/20 in the left eye. Conclusion: Epipremnum aureum toxicity is a rare cause of keratitis. It can mimic acanthamoeba keratitis or anesthetic abuse and should be considered in cases of culture negative nonhealing corneal ulcerations. Eliciting a history of plant sap exposure can facilitate appropriate supportive care for this toxic keratitis.
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The application of tandem catalysis is rarely investigated in degrading organic pollutants in environment. Herein, a tandem catalyst on single platinum (Pt) nanoparticles (Pt0 NPs) is prepared for sequential degrading formaldehyde (HCHO) to carbon dioxide gas (CO2(g)) at room temperature. The synthesis approach includes coating of uniform Pt NPs on SrBi2Ta2O9 platelets using a photoreduction process, followed by calcination of the sample in atmosphere to tune partial transformation of Pt0 atoms to Pt2+ ions in the tandem catalyst. The conversion of HCHO to CO2(g) is monitored by in situ Fourier transform infrared spectroscopy, which shows first conversion of HCHO to CO32- ions onto Pt0 active sites and subsequently the conversion of CO32- ions to CO2(g) by neighboring Pt2+ species of the catalyst. The later process by Pt2+ species do not allow CO32- poisoning of the catalyst. The enhanced activity of the prepared tandem catalyst to oxidize HCHO is maintained continuously for 680 min. Comparatively, the catalyst without Pt2+ shows the activity only for 40 min. Additionally, the tandem catalyst presented in this paper has better performance than Pt/titanium dioxide (TiO2) catalyst to degrade HCHO. Overall, the tandem catalyst may be applied to degrade organic pollutants efficiently.
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The deposition of toxic munitions compounds, such as hexahydro-1, 3, 5-triniitro-1, 3, 5-trizaine (RDX), on soils around targets in live-fire-training ranges is an important source of groundwater contamination. Plants take up RDX but do not significantly degrade it. Reported here is the transformation of two perennial grass species, switchgrass (Panicum virgatum) and creeping bentgrass (Agrostis stolonifera), with the genes for degradation of RDX. These species possess a number of agronomic traits making them well-equipped for the uptake and removal of RDX from root zone leachates. Transformation vectors were constructed with xplA and xplB, which confer the ability to degrade RDX, and nfsI, which encodes a nitroreductase for the detoxification of the co-contaminating explosive 2, 4, 6-trinitrotoluene (TNT). The vectors were transformed into the grass species using Agrobacterium tumefaciens infection. All transformed grass lines showing high transgene expression levels removed significantly more RDX from hydroponic solutions and retained significantly less RDX in their leaf tissues than wild type plants. Soil columns planted with the best-performing switchgrass line were able to prevent leaching of RDX through a 0.5 m root zone. These plants represent a promising plant biotechnology to sustainably remove RDX from training range soil, thus preventing contamination of groundwater. This article is protected by copyright. All rights reserved.
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The "ASHRAE Position Document on Filtration and Air Cleaning" provides Society members and other stakeholders with information on these technologies and their application. This column answers a few questions about the main positions and statements formulated in the position document (http://tinyurl.com/ashraeiaq).
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Leaf and petiole explants of monocotyledonous pothos (Epipremnum aureum) ‘Jade’ were cultured on Murashige and Skoog basal medium supplemented with N-(2-chloro-4-pyridl)-N′-phenylurea (CPPU) or N-phenyl-N′-1,2,3-thiadiazol-5-ylurea (TDZ) with α-naphthalene acetic acid (NAA). Somatic embryos appeared directly from explants after 4–8 weeks of culture; 9.1 μM TDZ with 1.1 μM NAA induced 61.1 % leaf discs and 94.4 % of petiole segments to produce plantlets through embryo conversion. Using this established regeneration method and an enhanced green fluorescent protein (GFP) gene (egfp) as a reporter marker, an Agrobacterium-mediated transformation procedure was developed. Leaf discs and petiole segments were inoculated with Agrobacterium tumefaciens strain EHA105 harboring a binary vector pLC902 that contains novel bi-directional duplex promoters driving the egfp gene and hygromycin phosphotransferase gene (hpt), respectively. The explants were co-cultivated with strain EHA105 for 3, 5, and 7 days, respectively prior to selective culture with 25 mg l−1 hygromycin. A 5-day co-cultivation led to 100 % of leaf discs to show transient GFP expression and 23.8 % of the discs to produce stable GFP-expressing somatic embryos. A 7-day co-cultivation of petiole explants resulted in the corresponding responses at 100 and 14.3 %, respectively. A total of 237 transgenic plants were obtained, and GFP fluorescence was observed in all plant organs. Regular PCR and quantitative real-time PCR analyses confirmed the presence of 1 or 2 copies of the egfp gene in analyzed plants. The highly efficient regeneration and transformation systems established in this study may enable genetic improvement of this vegetatively propagated species through biotechnological means.
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To establish a procedure for Agrobacterium tumefaciens-mediated transformation of golden pothos (Epipremnum aureum) plants, the effects of selection antibiotics and the preculture period of stem explants before A. tumefaciens infection were examined. Explants were co-cultivated with A. tumefaciens EHA105, harboring the plasmid pGWB2/cGUS, on a somatic embryo-inducing medium supplemented with acetosyringone. Resulting transgenic somatic embryos were screened on an antibiotic selection medium, and the transgenic pothos plants were regenerated on a germination medium. Hygromycin was the optimum selection antibiotic tested. The preculture period significantly affected the transformation efficiency, with explants precultured for one-day showing the best efficiency (5–30%). Both transformed hygromycin-resistant embryos and regenerated plants showed β-glucuronidase activity. Southern blot analysis confirmed transgene integration into the pothos genome. This reproducible transformation system for golden pothos may enable the molecular breeding of this very common indoor plant.
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Chlorinated solvents, especially trichloroethylene (TCE), are the most widespread groundwater contaminants in the United States. Existing methods of pumping and treating are expensive and laborious. Phytoremediation, the use of plants for remediation of soil and groundwater pollution, is less expensive and has low maintenance; however, it requires large land areas and there are a limited number of suitable plants that are known to combine adaptation to a particular environment with efficient metabolism of the contaminant. In this work, we have engineered plants with a profound increase in metabolism of the most common contaminant, TCE, by introducing the mammalian cytochrome P450 2E1. This enzyme oxidizes a wide range of important pollutants, including TCE, ethylene dibromide, carbon tetrachloride, chloroform, and vinyl chloride. The transgenic plants had a dramatic enhancement in metabolism of TCE of up to 640-fold as compared with null vector control plants. The transgenic plants also showed an increased uptake and debromination of ethylene dibromide. Therefore, transgenic plants with this enzyme could be used for more efficient remediation of many sites contaminated with halogenated hydrocarbons.
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The phytotoxicity of formaldehyde for spider plants (Chlorophytum comosum L.), tobacco plants (Nicotiana tabacum L. cv Bel B and Bel W3), and soybean (Glycine max L.) cell-suspension cultures was found to be low enough to allow metabolic studies. Spider plant shoots were exposed to 7.1 [mu]L L-1 (8.5 mg m-3) gaseous [14C]-formaldehyde over 24 h. Approximately 88% of the recovered radioactivity was plant associated and was found to be incorporated into organic acids, amino acids, free sugars, and lipids as well as cell-wall components. Similar results were obtained upon feeding [14C]formaldehyde from aqueous solution to aseptic soybean cell-suspension cultures. Serine and phosphatidylcholine were identified as major metabolic products. Spider plant enzyme extracts contained two NAS+-dependent formaldehyde dehydrogenase activities with molecular mass values of about 129 and 79 kD. Only the latter enzyme activity required glutathione as an obligatory second cofactor. It had an apparent Km value of 30 [mu]M for formaldehyde and an isoelectric point at pH 5.4. Total cell-free dehydrogenase activity corresponded to 13 [mu]g formaldehyde oxidized h-1 g-1 leaf fresh weight. Glutathione-dependent formaldehyde dehydrogenases were also isolated from shoots and leaves of Equisetum telmateia and from cell-suspension cultures of wheat (Triticum aestivum L.) and maize (Zea mays L.). The results obtained are consistent with the concept of indoor air decontamination with common room plants such as the spider plant. Formaldehyde appears to be efficiently detoxified by oxidation and subsequent C1 metabolism.
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We describe a protocol for Agrobacterium-mediated genetic transformation of Theobroma cacao L. using cotyledonary explants from primary somatic embryos (SEs) and A. tumefaciens strain AGL1. Transgenic plants carrying the visible marker, gene green fluorescent protein ( EGFP), the selectable marker gene neomycin phosphotransferase II ( NPTII), the class I chitinase gene from cacao ( Chi), and tobacco nuclear matrix attachment regions (MARs) in different combinations were successfully produced via regeneration of secondary SEs. The presence of the Chi gene or MARs did not influence the number of transgenic plants produced compared to the marker genes alone. However, the inclusion of MARs contributed to increased mean GFP expression in the population of transgenics. Additionally, the presence of MARs reduced the occurrence of gene silencing and stabilized high levels of GFP expression in lines of transgenic plants multiplied via reiterative somatic embryogenesis. Ninety-four transgenic plants were acclimated in a greenhouse and grown to maturity. Detailed growth analysis indicated that there were no differences in various growth parameters between transgenic and non-transgenic SE-derived plants. Seeds produced from two genetic crosses with one of the transgenic lines were analyzed for EGFP expression-a near-perfect 1:1 segregation was observed, indicating that this line resulted from the insertion of a single locus of T-DNA.
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The ADH2 gene codes for the Arabidopsis glutathione-dependent formaldehyde dehydrogenase (FALDH), an enzyme involved in formaldehyde metabolism in eukaryotes. In the present work, we have investigated the potential role of FALDH in detoxification of exogenous formaldehyde. We have generated a yeast (Saccharomyces cerevisiae) mutant strain (sfa1Delta) by in vivo deletion of the SFA1 gene that codes for the endogenous FALDH. Overexpression of Arabidopsis FALDH in this mutant confers high resistance to formaldehyde added exogenously, which demonstrates the functional conservation of the enzyme through evolution and supports its essential role in formaldehyde metabolism. To investigate the role of the enzyme in plants, we have generated Arabidopsis transgenic lines with modified levels of FALDH. Plants overexpressing the enzyme show a 25% increase in their efficiency to take up exogenous formaldehyde, whereas plants with reduced levels of FALDH (due to either a cosuppression phenotype or to the expression of an antisense construct) show a marked slower rate and reduced ability for formaldehyde detoxification as compared with the wild-type Arabidopsis. These results show that the capacity to take up and detoxify high concentrations of formaldehyde is proportionally related to the FALDH activity in the plant, revealing the essential role of this enzyme in formaldehyde detoxification.
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In this study we compared cancer risks from organic hazardous air pollutants (HAPs) based on total personal exposure summed across different microenvironments and exposure pathways. We developed distributions of personal exposure concentrations using field monitoring and modeling data for inhalation and, where relevant, ingestion pathways. We calculated risks for a nonoccupationally exposed and nonsmoking population using U.S. Environmental Protection Agency (EPA) and California Office of Environmental Health and Hazard Assessment (OEHHA) unit risks. We determined the contribution to risk from indoor versus outdoor sources using indoor/outdoor ratios for gaseous compounds and the infiltration factor for particle-bound compounds. With OEHHA's unit risks, the highest ranking compounds based on the population median are 1,3-butadiene, formaldehyde, benzene, and dioxin, with risks on the order of 10(-4)-10(-5). The highest risk compounds with the U.S. EPA unit risks were dioxin, benzene, formaldehyde, and chloroform, with risks on a similar order of magnitude. Although indoor exposures are responsible for nearly 70% of risk using OEHHA's unit risks, when infiltration is accounted for, inhalation of outdoor sources contributed 50% to total risk, on average. Additionally, 15% of risk resulted from exposures through food, mainly due to dioxin. Most of the polycyclic aromatic hydrocarbon, benzene, acetaldehyde, and 1,3-butadiene risk came from outdoor sources, whereas indoor sources were primarily responsible for chloroform, formaldehyde, and naphthalene risks. The infiltration of outdoor pollution into buildings, emissions from indoor sources, and uptake through food are all important to consider in reducing overall personal risk to HAPs.
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Small, volatile hydrocarbons, including trichloroethylene, vinyl chloride, carbon tetrachloride, benzene, and chloroform, are common environmental pollutants that pose serious health effects. We have developed transgenic poplar (Populus tremula × Populus alba) plants with greatly increased rates of metabolism and removal of these pollutants through the overexpression of cytochrome P450 2E1, a key enzyme in the metabolism of a variety of halogenated compounds. The transgenic poplar plants exhibited increased removal rates of these pollutants from hydroponic solution. When the plants were exposed to gaseous trichloroethylene, chloroform, and benzene, they also demonstrated superior removal of the pollutants from the air. In view of their large size and extensive root systems, these transgenic poplars may provide the means to effectively remediate sites contaminated with a variety of pollutants at much faster rates and at lower costs than can be achieved with current conventional techniques. • CYP2E1 • P450 • poplar • trichloroethylene • carbon tetrachloride
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All across Europe, people live and work in indoor environments. On average, people spend around 90% of their time indoors (homes, workplaces, cars and public transport means, etc.) and are exposed to a complex mixture of pollutants at concentration levels that are often several times higher than outdoors. These pollutants are emitted by different sources indoors and outdoors and include volatile organic compounds (VOCs), carbonyls (aldehydes and ketones) and other chemical substances often adsorbed on particles. Moreover, legal obligations opposed by legislations, such as the European Union's General Product Safety Directive (GPSD) and Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH), increasingly require detailed understanding of where and how chemical substances are used throughout their life-cycle and require better characterisation of their emissions and exposure. This information is essential to be able to control emissions from sources aiming at a reduction of adverse health effects. Scientifically sound human risk assessment procedures based on qualitative and quantitative human exposure information allows a better characterisation of population exposures to chemical substances. In this context, the current paper compares inhalation exposures to three health-based EU priority substances, i.e. benzene, formaldehyde and acetaldehyde. Distributions of urban population inhalation exposures, indoor and outdoor concentrations were created on the basis of measured AIRMEX data in 12 European cities and compared to results from existing European population exposure studies published within the scientific literature. By pooling all EU city personal exposure, indoor and outdoor concentration means, representative EU city cumulative frequency distributions were created. Population exposures were modelled with a microenvironment model using the time spent and concentrations in four microenvironments, i.e. indoors at home and at work, outdoors at work and in transit, as input parameters. Pooled EU city inhalation exposures were compared to modelled population exposures. The contributions of these microenvironments to the total daily inhalation exposure of formaldehyde, benzene and acetaldehyde were estimated. Inhalation exposures were compared to the EU annual ambient benzene air quality guideline (5 microg/m3-to be met by 2010) and the recommended (based on the INDEX project) 30-min average formaldehyde limit value (30 microg/m3). Indoor inhalation exposure contributions are much higher compared to the outdoor or in-transit microenvironment contributions, accounting for almost 99% in the case of formaldehyde. The highest in-transit exposure contribution was found for benzene; 29.4% of the total inhalation exposure contribution. Comparing the pooled AIRMEX EU city inhalation exposures with the modelled exposures, benzene, formaldehyde and acetaldehyde exposures are 5.1, 17.3 and 11.8 microg/m3 vs. 5.1, 20.1 and 10.2 microg/m3, respectively. Together with the fact that a dominating fraction of time is spent indoors (>90%), the total inhalation exposure is mostly driven by the time spent indoors. The approach used in this paper faced three challenges concerning exposure and time-activity data, comparability and scarce or missing in-transit data inducing careful interpretation of the results. The results obtained by AIRMEX underline that many European urban populations are still exposed to elevated levels of benzene and formaldehyde in the inhaled air. It is still likely that the annual ambient benzene air quality guideline of 5 microg/m3 in the EU and recommended formaldehyde 30-min average limit value of 30 microg/m3 are exceeded by a substantial part of populations living in urban areas. Considering multimedia and multi-pathway exposure to acetaldehyde, the biggest exposure contribution was found to be related to dietary behaviour rather than to inhalation. In the present study, inhalation exposures of urban populations were assessed on the basis of novel and existing exposure data. The indoor residential microenvironment contributed most to the total daily urban population inhalation exposure. The results presented in this paper suggest that a significant part of the populations living in European cities exceed the annual ambient benzene air quality guideline of 5 microg/m3 in the EU and recommended (INDEX project) formaldehyde 30-min average limit value of 30 microg/m3. To reduce exposures and consequent health effects, adequate measures must be taken to diminish emissions from sources such as materials and products that especially emit benzene and formaldehyde in indoor air. In parallel, measures can be taken aiming at reducing the outdoor pollution contribution indoors. Besides emission reduction, mechanisms to effectively monitor and manage the indoor air quality should be established. These mechanisms could be developed by setting up appropriate EU indoor air guidelines.
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A controlled field study was performed to evaluate the effectiveness of transgenic poplars for phytoremediation in a field setting. Three hydraulically contained test beds were planted with twelve transgenic poplars, twelve wild type (WT) poplars, or left unplanted, and dosed with equivalent amounts of trichloroethylene (TCE). Degradation of TCE was enhanced in the transgenic tree bed, but not to the extent of the enhanced removal observed in laboratory studies. Total chlorinated ethene removal was 87% in the CYP2E1 bed, 85% in the WT bed, and 34% in the unplanted bed in 2012. Evapotranspiration of TCE from transgenic leaves was reduced by 80% and diffusion of TCE from transgenic stems was reduced by 90% compared to WT. Cis-dichloroethene and vinyl chloride levels were reduced in the transgenic tree bed. Chloride ion accumulated in the planted beds corresponding to the TCE loss, suggesting that contaminant dehalogenation was the primary loss fate. Modeling of TCE in the plant indicated that the enhanced rate of metabolism in CYPE1 roots was insufficient to substantially increase uptake of TCE in a field setting.
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Removal rates of benzene and formaldehyde gas by houseplants reported by several laboratories varied by several orders of magnitude. We hypothesized that these variations were caused by differential responses of soil microbial populations to the high levels of pollutant used in the studies, and tested responses to benzene by plants and soils separately. Five houseplant species and tobacco were exposed to benzene under hydroponic conditions and the uptake rates compared. Among the test plants, Syngonium podophyllum and Chlorophytum comosum and Epipremnum aureum had the highest benzene removal rates. The effects of benzene addition on populations of soil bacteria were determined using reverse transcription quantitative PCR (RT-qPCR) assays targeting microbial genes involved in benzene degradation. The total bacterial population increased as shown by increases in the levels of eubacteria 16S rRNA, which was significantly higher in the high benzene incubations than in the low benzene incubations. Transcripts (mRNA) of genes encoding phenol monooxygenases, catechol-2,3-dioxygenase and the housekeeping gene rpoB increased in all soils incubated with high benzene concentrations. Therefore the enrichment of soils with benzene gas levels typical of experiments with houseplants in the literature artificially increased the levels of total soil bacterial populations, and especially the levels and activities of benzene-degrading bacteria.
Article
The faldh gene coding for a putative Brevibacillus brevis formaldehyde dehydrogenase (FALDH) was isolated and then transformed into tobacco. A total of three lines of transgenic plants were generated, with each showing 2- to 3-fold higher specific formaldehyde dehydrogenase activities than wild-type tobacco, a result that demonstrates the functional activity of the enzyme in formaldehyde (HCHO) oxidation. Overexpression of faldh in tobacco confers a high tolerance to exogenous HCHO and an increased ability to take up HCHO. A (13)C-nuclear magnetic resonance technique revealed that the transgenic plants were able to oxidize more aqueous HCHO to formate than the wild-type (WT) plants. When treated with gaseous HCHO, the transgenic tobacco exhibited an enhanced ability to transform more HCHO into formate, citrate acid, and malate but less glycine than the WT plants. These results indicate that the increased capacity of the transgenic tobacco to take up, tolerate, and metabolize higher concentrations of HCHO was due to the overexpression of B. brevis FALDH, revealing the essential function of this enzyme in HCHO detoxification. Our results provide a potential genetic engineering strategy for improving the phytoremediation of HCHO pollution.
Article
Uptake, translocation and metabolism of 14C-labelled formaldehyde in the leaves of Epipremnum aureum (Golden Potho) and Ficus benjamina (Weeping Fig) were investigated. Plants were exposed in light and dark to 14C-formaldehyde (500 μg m−3) in gas exposure chambers. The amount of 14C-incorporation into the soluble (water-extractable) and insoluble fractions of leaves, stem sections and roots was determined. The soluble 14C-activity was fractionated by ion exchange chromatography followed by thin-layer chromatography/autoradiography. Approximately 60–70% of the applied 14C-formaldehyde was recovered from the plants. In the light about five times more 14C-formaldehyde was assimilated than in the dark. The amount of 14C-label derived from 14C-formaldehyde, which was incorporated into acid-stable metabolites, was enhanced to an even larger extent in the light. The 14C-activity pattern closely resembled the general labelling spectrum of photosynthates, obtained after a 14CO2 exposure. A substantial amount of labelled material, mostly sucrose, was translocated into the stems and roots. Our results suggest that in the light 14C enters the Calvin cycle after an enzymatic two-step oxidation process of 14C-formaldehyde to 14CO2. The activities of the respective enzymes, formaldehyde dehydrogenase and formate dehydrogenase, were determined. Among 27 ‘leafy’ indoor decorative plants, a screening experiment revealed no outstanding species with regard to its capacity for metabolism of formaldehyde, and rate of uptake through stomata was too low to justify claims that plants contribute usefully to indoor air purification.
Article
A sealed, Plexiglas chamber with temperature and humidity control and illuminated externally with wide spectrum grow lights was used to evaluate the ability of golden pothos (Scindapsus aureus), nephthytis (Syngonium podophyllum), and spider plant (Chlorophytum elatum var.vittatum) to effect the removal of formaldehyde from contaminated air at initial concentrations of 15–37 ppm. Under the conditions of this study, the spider plant proved most efficient by sorbing and/ or effecting the removal of up to 2.27 fig formaldehyde per cm2 leaf surface area in 6 h of exposure. The immediate application of this new botanical air-purification system should be in energy-efficient homes that have a high risk of this organic concentrating in the air, due to outgassing of urea-formaldehyde foam insulation, particleboard, fabrics and various other synthetic materials.
Article
The California Air Resources Board funded a statewide survey of activity patterns of Californians over 11 years of age in order to improve the accuracy of exposure assessments for air pollutants. Telephone interviews were conducted with 1762 respondents over the four seasons from fall 1987 through summer 1988. In addition to completing a 24-h recall diary of activities and locations, participants also responded to questions about their use of and proximity to potential pollutant sources. Results are presented regarding time spent by Californians in different activities and locations relevant to pollutant exposure, and their frequency of use of or proximity to pollutant sources including cigarettes, consumer products such as paints and deodorizers, combustion appliances and motor vehicles. The results show that Californians spend, on average, 87% of their time indoors, 7% in enclosed transit and 6% outdoors. At least 62% of the population over 11 years of age and 46% of nonsmokers are near others' tobacco smoke at some time during the day. Potential exposure to different pollutant sources appears to vary among different gender and age groups. For example, women are more likely to use or be near personal care products and household cleaning agents, while men are more likely to be exposed to environmental tobacco smoke, solvents and paints. Data from this study can be used to reduce significantly the uncertainty associated with risk assessments for many pollutants.
Article
Switchgrass (Panicum virgatum L.) is a C4 perennial grass and has been identified as a potential bioenergy crop for cellulosic ethanol because of its rapid growth rate, nutrient use efficiency and widespread distribution throughout North America. The improvement of bioenergy feedstocks is needed to make cellulosic ethanol economically feasible, and genetic engineering of switchgrass is a promising approach towards this goal. A crucial component of creating transgenic switchgrass is having the capability of transforming the explants with DNA sequences of interest using vector constructs. However, there are limited options with the monocot plant vectors currently available. With this in mind, a versatile set of Gateway-compatible destination vectors (termed pANIC) was constructed to be used in monocot plants for transgenic crop improvement. The pANIC vectors can be used for transgene overexpression or RNAi-mediated gene suppression. The pANIC vector set includes vectors that can be utilized for particle bombardment or Agrobacterium-mediated transformation. All the vectors contain (i) a Gateway cassette for overexpression or silencing of the target sequence, (ii) a plant selection cassette and (iii) a visual reporter cassette. The pANIC vector set was functionally validated in switchgrass and rice and allows for high-throughput screening of sequences of interest in other monocot species as well.
Article
Cooking emission samples collected in two residential kitchens were compared where towngas (denoted as dwelling A) and liquefied petroleum gas (LPG) (denoted as dwelling B) were used as cooking fuels. A total of 50 different volatile organic compounds (VOCs) were quantified during the 90 min cooking periods. None of any carcinogenic compounds like formaldehyde, acetaldehyde or benzene are detected in the raw fuels, confirming that those are almost entirely derived due to cooking activity alone. Alkenes accounted for approximately 53% of the total measured VOCs collected at dwelling A, while alkanes contributed approximately 95% of the VOCs at dwelling B during the cooking periods. The concentration of aromatic hydrocarbons such as benzene and toluene also increased during the cooking periods. The total amount of carbonyls emitted from the cooking processes at dwelling A (2708 μg) is three times higher than that at dwelling B (793 μg). Acetaldehyde was the most abundant carbonyl at the dwelling A but its emission was insignificant at the dwelling B. Carcinogenic risks on chronic exposure to formaldehyde, acetaldehyde, and benzene for housewives and domestic helpers were evaluated. Formaldehyde accounts for 68% and close to 100% of lifetime cancer risks at dwelling A and B, respectively.
Article
Previously, preliminary data on the ability of a group of common indoor plants to remove organic chemical from indoor air was presented. The group of plants chosen for this study was determined by joint agreement between NASA and the Associated Landscape Contractors of America. The chemicals chosen for study were benzene, trichloroethylene, and formaldehyde. The results show that plants can play a major role in removal of organic chemicals from indoor air.
Article
Xenobiotic metabolism in plants resembles that in animal liver on the levels of metabolite patterns, enzyme classes and cDNA sequences. Historical and current evidence for the 'green liver' concept of xenobiotic plant metabolism is presented. Xenobiotic residues resulting from phase I (transformation) and phase II (conjugation) are usually stored in the plant tissue in phase III (compartmentation). The following topics are discussed: residue toxicology, metabolic modelling, enzyme inducibility and enzyme evolution.
Article
Freeze-thaw transformation provides a simple and rapid method to transform Agrobacterium tumefaciens directly with plasmid DNA. Competent A. tumefaciens cells of strains LBA4404, GV3850 and EHA101 were transformed with four to nine plasmids differing in size, size of insert and in some cases sensitivity to antibiotics. A threefold to fourfold increase in transformed colonies per microgram of DNA was obtained by freezing cells with liquid nitrogen vs. dry ice/ethanol. Freezing cells in liquid nitrogen followed by incubation of transformed cells in a low concentration of appropriate antibiotics prior to plating resulted in a ninefold increase in colonies obtained compared with the procedure of freezing cells in dry ice/ethanol without the incubation period in the low concentration of antibiotics prior to plating. Restriction fragments of the expected sizes from the plasmids indicated that the procedural modifications did not cause apparent recombinations in the region of the inserts.
Article
We have used the maize ubiquitin 1 promoter, first exon and first intron (UBI) for rice (Oryza sativa L. cv. Taipei 309) transformation experiments and studied its expression in transgenic calli and plants. UBI directed significantly higher levels of transient gene expression than other promoter/intron combinations used for rice transformation. We exploited these high levels of expression to identify stable transformants obtained from callus-derived protoplasts co-transfected with two chimeric genes. The genes consisted of UBI fused to the coding regions of the uidA and bar marker genes (UBI:GUS and UBI:BAR). UBI:GUS expression increased in response to thermal stress in both transfected protoplasts and transgenic rice calli. Histochemical localization of GUS activity revealed that UBI was most active in rapidly dividing cells. This promoter is expressed in many, but not all, rice tissues and undergoes important changes in activity during the development of transgenic rice plants.
Article
The green fluorescent protein (GFP) from the jellyfish Aequorea victoria has become an important marker of gene expression. However, the sensitivity of wild-type GFP has been below that of standard reporter proteins, such as beta-galactosidase, which utilize enzymatic amplification. To improve the detection of GFP in transfected mammalian cells, we have constructed a unique GFP variant which contains chromophore mutations that make the protein 35 times brighter than wild-type GFP, and is codon-optimized for higher expression in mammalian cells. These changes in the GFP coding sequence provide an enhanced GFP (EGFP) that greatly increases the sensitivity of the reporter protein. We show that the EGFP expression vector delivered into mammalian cells gives rise to bright fluorescence that is readily detectable following a 16-24 hr transfection interval. Visual detection of transfected cells with EGFP appears to be more sensitive than equivalent measurements with beta-galactosidase catalyzed conversion of the X-gal substrate. We conclude that EGFP allows sensitive and convenient detection of gene transfer in mammalian cells.
Article
The use of transgenic crops has generated concerns about transgene movement to unintended hosts and the associated ecological consequences. Moreover, the in-field monitoring of transgene expression is of practical concern (e.g., the underexpression of an herbicide tolerance gene in crop plants that are due to be sprayed with herbicide). A solution to these potential problems is to monitor the presence and expression of an agronomically important gene by linking it to a marker gene, such as GFP. Here we show that GFP fluorescence can indicate expression of the Bacillus thuringiensus cry1Ac gene when co-introduced into tobacco and oilseed rape, as demonstrated by insect bioassays and western blot analysis. Furthermore we conducted two seasons of field experiments to characterize the performance of three different GFP genes in transgenic tobacco. The best gene tested was mGFP5er, a mutagenized GFP gene that is targeted to the endoplasmic reticulum. We also demonstrated that host plants synthesizing GFP in the field suffered no fitness costs.
Article
Formaldehyde is a toxic substance with adverse health effects detectable at low concentrations. Formaldehyde causes irritation of the eyes, skin and respiratory tract, wheezing, nausea, coughing, diarrhoea, vomiting, dizziness and lethargy at levels as low as 50 parts per billion (ppb) (0.05 ppm) (Horvath et al, 1988). Formaldehyde has also been associated with aggravation of asthma, emphysema, hayfever and allergy problems at low levels (EPA, 1987). Formaldehyde is currently considered a potential carcinogen to humans (EPA, 1987). Formaldehyde is a ubiquitous gas found in elevated concentrations in indoor environments. Concentrations of formaldehyde are typically an order of magnitude greater inside buildings compared to outdoor air (Godish, 1990). Formaldehyde concentrations are particularly high in portable buildings due to the presence of more formaldehyde emitting materials and the relatively smaller interior volumes of air (Sexton et al, 1983). Major sources of formaldehyde indoors are pressed wood products, such as particle board and plywood (Elbert, 1995: Myer and Hermans, 1985), and urea formaldehyde foam insulation (Spengler and Sexton, 1983). Other sources include carpets, curtains, floor linings, paper products, cosmetics and soaps, tobacco smoke and gas combustion (Spengler and Sexton, 1983: Godish, 1990). Methods to reduce indoor formaldehyde include source removal or use of non- polluting materials, emission reduction through physical or chemical treatments and dilution through ventilation and air purification. While most solutions involve dilution through ventilation, increased interest in the scientific literature (Wolverton et al, 1989: Godish and Guindon, 1989) as well as in the popular media has been given to the use of plants to purify air in buildings . Most studies however, have been conducted in the laboratory (Levin J, 1992: Godish T and Guindon C, 1989) and are difficult to extrapolate to real life situations (Wolverton et al, 1989: Godish and Guindon, 1989).
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The lifetime cancer risks of exposure of cooks and food service workers, office workers, housewives, and schoolchildren in Hong Kong to volatile organic compounds (VOCs) in their respective indoor premises during normal indoor activities were assessed. The estimated cancer risk for housewives was the highest, and the second-highest lifetime cancer risk to VOC exposure was for the groups of food service and office workers. Within a certain group of the population, the lifetime cancer risk of the home living room was one to two orders of magnitude higher than that in other indoor environments. The estimated lifetime risks of food service workers were about two times that of office workers. Furthermore, the cancer risks of working in kitchen environments were approximately two times higher than the risks arising from studying in air-conditioned classrooms. The bus riders had higher average lifetime cancer risks than those travelling by Mass Transit Railway. For all target groups of people, the findings of this study show that the exposures to VOCs may lead to lifetime risks higher than 1 x 10(-6). Seven indoor environments were selected for the measurement of human exposure and the estimation of the corresponding lifetime cancer risks. The lifetime risks with 8-h average daily exposures to individual VOCs in individual environments were compared. People in a smoking home had the highest cancer risk, while students in an air-conditioned classroom had the lowest risk of cancer. Benzene accounted for about or more than 40% of the lifetime cancer risks for each category of indoor environment. Nonsmoking and smoking residences in Hong Kong had cancer risks associated with 8-h exposures of benzene above 1.8 x 10(-5) and 8.0 x 10(-5), respectively. The cancer risks associated with 1,1-dichloroethene, chloroform, methylene chloride, trichloroethene, and tetrachloroethene became more significant at selected homes and restaurants. Higher lifetime cancer risks due to exposure to styrene were only observed in the administrative and printing offices and air-conditioned classrooms. Higher lifetime cancer risks related to chloroform exposures were observed at the restaurant and the canteen.
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This study was designed to determine the effectiveness of spider plants (Clorophytum elatum var. vittatium) as a botanical air purification measure for formaldehyde under dynamic laboratory chamber conditions. Significant reductions in chamber formaldehyde levels were observed when spider plants were placed in experimental chambers. However, highest reductions occurred when spider plants were defoliated. Observed reductions in formaldehyde levels appeared to have been associated with soil medium factors and a source moisture storage phenomenon associated with the use of particleboard as a formaldehyde source inside the chambers. The results of this study do not support the conclusions of previous studies which suggest that botanical air purification using only plant leaves is an effective means of reducing residential formaldehyde levels.
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Today, cloning vectors that have been specifically designed to facilitate the fusion, overexpression or down-regulation of a variety of genes in plant cells are available from various sources. In most cases, their basic design allows the cloning of a single target gene, typically under a specific promoter, in parallel with the expression of selection and/or marker genes from the same vector. However, new and versatile systems now exist that expand the user's choice to a large number of promoters and terminators, and various autofluorescent tags confer the ability to express multiple genes from a single transformation vector.
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The use of portable air cleaning devices in residential settings has been steadily growing over the last 10 years. Three out of every 10 households now contain a portable air cleaning device. This increased use of air cleaners is accompanied by, if not influenced by, a fundamental belief by consumers that the air cleaners are providing an improved indoor air environment. However, there is a wide variation in the performance of air cleaners that is dependent on the specific air cleaner design and various indoor factors. The most widely used method in the United States to assess the performance of new air cleaners is the procedure described in the American National Standards Institute (ANSI)/Association of Home Appliance Manufacturers (AHAM) AC-1-2002. This method describes both the test conditions and the testing protocol. The protocol yields a performance metric that is based on the measured decay rate of contaminant concentrations with the air cleaner operating compared with the measured decay rate with the air cleaner turned off. The resulting metric, the clean air delivery rate (CADR), permits both an intercomparison of performance among various air cleaners and a comparison of air cleaner operation to other contaminant removal processes. In this article, we comment on the testing process, discuss its applicability to various contaminants, and evaluate the resulting performance metrics for effective air cleaning.
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