Screening Indoor Plants for Volatile Organic Pollutant Removal Efficiency

Twenty-eight ornamental species commonly used for interior plantscapes were screened for their ability to remove five volatile indoor pollutants: aromatic hydrocarbons (benzene and toluene), aliphatic hydrocarbon (octane), halogenated hydrocarbon [trichloroethylene (TCE)], and terpene (a-pinene). Individual plants were placed in 10.5-L gas-tight glass jars and exposed to ’10 ppm (31.9, 53.7, 37.7, 46.7, and 55.7 mg m) of benzene, TCE, toluene, octane, and a-pinene, respectively. Air samples (1.0 mL) within the glass containers were analyzed by gas chromatography–mass spectroscopy 3 and 6 h after exposure to the test pollutants to determine removal efficiency by monitoring the decline in concentration over 6 h within sealed glass containers. To determine removal by the plant, removal by other means (glass, plant pot, media) was subtracted. The removal efficiency, expressed on a leaf area basis for each volatile organic compound (VOC), varied with plant species. Of the 28 species tested, Hemigraphis alternata, Hedera helix, Hoya carnosa, and Asparagus densiflorus had the highest removal efficiencies for all pollutants; Tradescantia pallida displayed superior removal efficiency for four of the five VOCs (i.e., benzene, toluene, TCE, and a-pinene). The five species ranged in their removal efficiency from 26.08 to 44.04 mg m m h of the total VOCs. Fittonia argyroneura effectively removed benzene, toluene, and TCE. Ficus benjamina effectively removed octane and a-pinene, whereas Polyscias fruticosa effectively removed octane. The variation in removal efficiency among species indicates that for maximum improvement of indoor air quality, multiple species are needed. The number and type of plants should be tailored to the type of VOCs present and their rates of emanation at each specific indoor location. The importance of indoor air quality to human health has become of increasing interest in developed countries where inhabitants often spend over 90% of their time indoors (Jenkins et al., 1992; Snyder, 1990). Indoor air has been reported to be as much as 12 times more polluted than that outdoors (Ingrosso, 2002; Orwell et al., 2004; Zabiega1a, 2006). Indoor air pollutants primarily originate from building product emissions, human activities inside the building, and infiltration of outdoor air (Wolkoff and Nielsen, 2001; Zabiega1a, 2006) and have increased as a result of the lower gas exchange rates of newer, more energy-efficient buildings (Cohen, 1996). Indoor air pollutants include volatile organic compounds (VOCs), particulate matter, ozone, radon, lead, and biological contaminants (Destaillats et al., 2008). Exposure can cause acute illnesses (e.g., asthma, nausea) and chronic diseases (e.g., cancer, immunologic, neurologic, reproductive, developmental, and respiratory disorders) (Suh et al., 2000). VOCs emanating from paints, varnishes, adhesives, furnishings, clothing, solvents, building materials, combustion appliances, and potable water (Jones, 1999; Maroni et al., 1995; Zabiega1a, 2006) have a negative effect on indoor air quality (Darlington et al., 2000). VOCs are generally classified as aromatic hydrocarbons (e.g., benzene, toluene, ethylbenzene, xylene), aliphatic hydrocarbons (e.g., hexane, heptane, octane, decane), halogenated hydrocarbons [e.g., trichloroethylene (TCE), methylene chloride], and terpenes (e.g., a-pinene, d-limonene) (Jones, 1999; Suh et al., 2000; Wolkoff and Nielsen, 2001; Won et al., 2005; Zabiega1a, 2006). Benzene and toluene, octane, TCE, and a-pinene are representative VOCs from each class (i.e., aromatic hydrocarbons, aliphatic hydrocarbons, halogenated hydrocarbons, and terpenes, respectively) and are considered to be important indoor air pollutants as a result of their toxicity (Liu et al., 2007; Newman et al., 1997; Orwell et al., 2006). Plants remove VOCs from indoor air through stomatal uptake, absorption, and adsorption to plant surfaces (Beattie and Seibel, 2007; Korte et al., 2000; Sandhu et al., 2007). Several indoor species have been screened for their ability to remove benzene (Liu et al., 2007), some of which could remove 40 to 88 mg m d (Orwell et al., 2004), in addition to other VOCs (e.g., toluene, TCE, m-xylene, hexane) (Cornejo et al., 1999; Orwell et al., 2006; Wood et al., 2002; Yoo et al., 2006). The efficiency of VOC removal varies substantially among species (Yoo et al., 2006) and with the molecular characteristics of each compound. To date, only a limited number of indoor species have been tested for their phytoremediation potential and the range of pollutants assessed is even more limited (Cornejo et al., 1999; Ugrekhelidze et al., 1997; Wolverton et al., 1989; Wood et al., 2002). It is evident that a better understanding of the phytoremediation potential of a diverse range of indoor plants is needed. In this study, a cross-section of indoor plants (28 species) was screened for their ability to remove five important VOCs with differing chemistries (benzene, toluene, octane, TCE, and a-pinene). Materials and Methods Plant material. Twenty-eight species of popular indoor ornamental plants available in the southeastern United States, which represented 26 genera and 15 botanical families (Table 1), were obtained from commercial sources. After the media was washed from the roots, the plants were repotted in 10-cm (500-cc) pots using a growing media comprised of peatmoss, pine bark, and perlite/ vermiculite (2:1:1, v/v) (Fafard 3B; Fafard, Anderson, SC) and grown in a shade house for 8 weeks before acclimatization for 12 weeks under indoor conditions, 22 ± 1 C, 50% relative humidity, and 5.45 mmol m s photosynthetically active radiation (PAR) (LI-COR LI-189 light meter with a line quantum sensor; LI-COR, Lincoln, NE). The plants were watered as needed during growth and acclimatization periods. At the end of the experiment, the leaf areas were determined using a LI-3100c leaf area meter (LI-COR) to allow expressing the removal efficiency on a leaf area basis. Introduction of volatile organic compounds. Plants were placed in 10.5-L gas-tight glass jars (one plant/jar) with the lid fitted with welded stainless steel tubing inlet and outlet ports. To facilitate a uniform distribution of the gases in the jar, the inlet tubing extended downward within the jar following the contour of the side of the jar, three-fourths of the distance to the base. The lids were sealed using specially constructed 11.8 cm o.d.· 9.8 cm i.d. Received for publication 14 Nov. 2008. Accepted for publication 7 Jan. 2009. To whom reprint requests should be addressed; e-mail [email protected]. HORTSCIENCE VOL. 44(5) AUGUST 2009 1377 POSTHARVEST BIOLOGY AND TECHNOLOGY