Indoor plants have the ability to remove various volatile organic compounds (VOCs) (Table 1) and may be useful for remediating the air in homes and offices, reducing the potential deleterious health effects on persons exposed. The phytoremediation effect is the result of both the plant and associated microorganisms in the media (Chun et al., 2010; Orwell et al., 2004; Son et al., 2000; Wolverton, 1986; Wolverton and Wolverton, 1993; Wood et al., 2002), the latter being the primary contributor to VOC removal during the night (Kim et al., 2008). Removal efficiency is known to vary widely among plant species, the VOC in question, and other factors (Kays, 2011).
Volatile organic compounds that have been shown to be removed from air by plants.
The U.S. Environmental Protection Agency (EPA) reported detection of more than 900 VOCs in the air of public buildings (EPA, 1989) and in a Finnish study (Kostiainen, 1995), over 200 VOCs were identified in each of 26 homes. Toluene is a highly toxic VOC commonly found as a component of indoor air, the presence of which can represent a serious health hazard. It is readily absorbed through the respiratory tract and to a lesser extent through the skin (EPA, 1990). Exposure to high levels is known to affect the kidneys, nervous system, liver, brain, and heart. Short-term exposure of humans to toluene (100 ppm v/v or greater) has elicited central nervous system effects such as fatigue, confusion, poor coordination, impairment of reaction time, perception, and motor control and function (NTP, 2000) in addition to poor performance on cognitive tests and eye and upper respiratory tract irritation (ATSDR, 1989).
We recently demonstrated that the removal efficiency of plants for toluene increased rapidly and markedly with their exposure to the gas (1.3 ppm for 18 h) (Kim et al., 2011). Of the 28 crops tested, 27 displayed an increase in toluene removal efficiency after the initial exposure with the greatest increase occurring after the first exposure. 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 Siebold & Zacc. to –16.6 in Salvia elegans Vahl (mean for all crops, 156 μg·m−3·h−1·m−2) with a maximum increase of over 600%.
Increasing the efficiency of toluene removal in particular and VOCs in general from indoor air is highly advantageous and could facilitate developing a horticultural solution to a serious health problem. Because a better understanding of the mechanism(s) involved may improve use of the response for practical applications, we determined the duration of the toluene stimulation effect on phytoremediation efficiency.
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