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  • Author or Editor: Kwang Jin Kim x
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Begonia maculata, Ardisia crenata, and Ardisia japonica plants exposed to 3.5 ppm toluene in air for 12 h displayed a pronounced stimulation (358%, 318%, and 252%, respectively) in subsequent toluene removal potential. The duration of the stimulation effect, monitored over 3 weeks, was short-lived decaying to prestimulation levels within 1 to 7 days depending on species. Elevated phytoremediation rate was dependent on the continued presence of toluene. The rapid rate of increase in phytoremediation and subsequent decay points toward a response mediated by changes in gene expression by the plant, microorganisms within the media, or both rather than an alteration in microbe population. A better understanding of the stimulation response may facilitate the use of plants for indoor air remediation in homes and offices.

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Volatile organic compounds (VOCs) in homes and offices represent a potentially serious health problem for exposed individuals. While certain indoor plants have been shown to remove VOCs in small test chambers, the results have not consistently translated to larger, more complex structures. We report the results of a mathematical model that assesses the effect of plants on the removal of benzene or other VOCs in buildings, incorporating the primary variables modulating indoor air VOC concentration. Building air volume, amount of plant material, VOC concentration and air exchange, VOC emanation, and plant phytoremediation rates can be altered over ranges reported in the literature, clarifying the relationship among these parameters and thereby identifying the most appropriate interior air remediation options. The results indicate existing published phytoremediation rates determined using small test chambers are far higher than can be achieved with static potted plants in buildings, and facilitated air movement through the plant media will most likely be essential for phytoremediation to be a viable means of improving indoor air quality.

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Phytoremediation of volatile organic compounds in indoor air involves both the plant and microbes in the media; however, removal rate is typically expressed on a leaf area basis. We determined the effect of root media volume on phytoremediation rate of volatile toluene and xylene to determine if there is a change in phytoremediation efficiency. Phytoremediation rate was calculated based on the aboveground space occupied by the plant and on the leaf area. Foliage plants of Fatsia japonica and Draceana fragrans ‘Massangeana’ were grown in different-sized pots (1, 2, 4, 6, and 12 L) that gave aerial plant to root zone volume ratios of 21:1, 21:2, 21:3, and 21:6. Total root volume and root fresh weight increased in D. fragrans with increasing media volume, whereas root density per unit of media volume decreased in both species. The efficiency of volatile toluene and xylene removal by the plants was increased as the root zone volume increased, whereas removal efficiency per unit media volume increased and then decreased. The highest volatile toluene and xylene removal efficiency was at a ratio of 21:3 (aerial plant:root zone volume) in F. japonica and 21:2 in D. fragrans. When phytoremediation efficiency was expressed on a leaf area basis, the phytoremediation rate for toluene and xylene increased progressively for both species with increasing media volume and as root volume increased. Calculating the amount of plant material needed within a home or office to obtain sufficient volatile organic compound (VOC) removal cannot be accurately predicted base solely on a leaf area (LA) or aboveground volume basis.

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Changes in phytoremediation efficiency after repeated exposures (three) to toluene (1.3 ppm) were assessed in 26 species and two additional cultivars of indoor plants. There was a rapid increase in toluene removal efficiency in 27 of the 28 crops with the greatest increase between the first and second exposure (i.e., after 3 days). The increase in efficiency between the first and third exposure ranged from 378 μg·m−3·h−1·m−2 leaf area in Pinus densiflora to –16.6 in Salvia elegans with a mean of 156 for all crops. Percent change ranged from 614 (Pittosporum tobira) to –8 (Salvia elegans) but was not necessarily indicative of phytoremediation value of a species. Rapid changes in phytoremediation efficiency in response to exposure to toluene appear to be widespread in plants and may be the result of an effect on gene expression in the plant and/or certain soil microbes or changes in the population density of toluene-metabolizing microbes. Increasing toluene removal efficiency is advantageous and as a consequence, a better understanding of the mechanism(s) operative may improve use of the response for practical applications.

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The efficiency of volatile formaldehyde removal was assessed in 86 species of plants representing five general classes (ferns, woody foliage plants, herbaceous foliage plants, Korean native plants, and herbs). Phytoremediation potential was assessed by exposing the plants to gaseous formaldehyde (2.0 μL·L−1) in airtight chambers (1.0 m3) constructed of inert materials and measuring the rate of removal. Osmunda japonica, Selaginella tamariscina, Davallia mariesii, Polypodium formosanum, Psidium guajava, Lavandula spp., Pteris dispar, Pteris multifida, and Pelargonium spp. were the most effective species tested, removing more than 1.87 μg·m−3·cm−2 over 5 h. Ferns had the highest formaldehyde removal efficiency of the classes of plants tested with O. japonica the most effective of the 86 species (i.e., 6.64 μg·m−3·cm−2 leaf area over 5 h). The most effective species in individual classes were: ferns—Osmunda japonica, Selaginella tamariscina, and Davallia mariesii; woody foliage plants—Psidium guajava, Rhapis excels, and Zamia pumila; herbaceous foliage plants—Chlorophytum bichetii, Dieffenbachia ‘Marianne’, Tillandsia cyanea, and Anthurium andraeanum; Korean native plants—Nandina domestica; and herbs—Lavandula spp., Pelargonium spp., and Rosmarinus officinalis. The species were separated into three general groups based on their formaldehyde removal efficiency: excellent (greater than 1.2 μg·m−3 formaldehyde per cm2 of leaf area over 5 h), intermediate (1.2 or less to 0.6), and poor (less than 0.6). Species classified as excellent are considered viable phytoremediation candidates for homes and offices where volatile formaldehyde is a concern.

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