Environ Sci Pollut Res DOI 10.1007/s11356-014-3240-x REVIEW ARTICLE Can ornamental potted plants remove volatile organic compounds from indoor air? — areview Majbrit Dela Cruz & Jan H. Christensen & Jane Dyrhauge Thomsen & Renate Müller Received: 7 January 2014 /Accepted: 19 June 2014 # Springer-Verlag Berlin Heidelberg 2014 Abstract Volatile organic compounds (VOCs) are found in Introduction indoor air, and many of these can affect human health (e.g. formaldehyde and benzene are carcinogenic). Plants affect the Indoor air quality has become a major issue in recent years. levels of VOCs in indoor environments, thus they represent a Danish people spend up to 90 % of their time indoors potential green solution for improving indoor air quality that (Gunnarsen et al. 2006) and factors such as exposure to at the same time can improve human health. This article volatile organic compounds (VOCs), thermal comfort and reviews scientific studies of plants’ ability to remove VOCs noise in the indoor environment have been identified as from indoor air. The focus of the review is on pathways of stressors that can cause both short- and long-term effects on VOC removal by the plants and factors affecting the efficiency humans (Bluyssen et al. 2011). VOCs in indoor air have and rate of VOC removal by plants. Laboratory based studies received appreciable attention due to their adverse health indicate that plant induced removal of VOCs is a combination effects on humans (Jones 1999). Examples are formaldehyde, of direct (e.g. absorption) and indirect (e.g. biotransformation which can cause sensory irritation and nasopharyngeal cancer by microorganisms) mechanisms. They also demonstrate that and has a 30-min average concentration guideline value of plants’ rate of reducing the level of VOCs is influenced by a 0.1 mg/m3, and benzene, which can cause blood dyscrasias number of factors such as plant species, light intensity and and where no safe level of exposure can be recommended VOC concentration. For instance, an increase in light intensity (World Health Organization 2010). has in some studies been shown to lead to an increase in In a recent study, indoor residential concentrations of removal of a pollutant. Studies conducted in real-life settings VOCs were compared to health guidelines set by a number such as offices and homes are few and show mixed results. of agencies including the World Health Organization and the United States Environmental Protection Agency (Logue et al. Keywords Indoor air . Volatile organic compounds . Plants . 2011). For 18 out of 59 VOCs the indoor concentrations were Pollutants . Removal . Purification higher than at least one guideline value (Logue et al. 2011). In addition, VOCs are often recognized as odours before they Responsible editor: Elena Maestri reach levels that can affect human health, thereby contributing to the perception of indoor air quality (Wolkoff et al. 2006). * : M. Dela Cruz ( ) R. Müller The level and composition of VOCs that a person is exposed Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, to on a daily basis varies according to personal activities and HøjbakkegårdAllé 30, 2630 Taastrup, Denmark indoor sources (Edwards et al. 2001). Furthermore, VOC e-mail: [email protected] concentrations in indoor environments vary according to sea- son and are highest in the wintertime (Rehwagen et al. 2003; J. H. Christensen Department of Plant and Environmental Sciences, Schlink et al. 2004). The main reason for this observation may Faculty of Science, University of Copenhagen, Thorvaldsensvej 40, be a reduction in air exchange rate during winter due to closed 1871 Frederiksberg C, Denmark windows (Schlink et al. 2004). VOCs are emitted from materials such as carpets, wallpa- J. D. Thomsen AgroTech A/S, Institute for Agri Technology and Food innovation, per, office chairs, and electronic equipment (Destaillats et al. HøjbakkegårdAllé 21, 2630 Taastrup, Denmark 2008; Wolkoff 1995; Yu and Crump 1998), with highest Environ Sci Pollut Res emissions when the material is new (Yu and Crump 1998). review. The literature regarding indoor VOC removal by The emission of a chemical from a certain material depends on plants is limited and studies dealing with outdoor VOC re- the concentration of the chemical in the material, the concen- moval by plants as well as removal of polycyclic aromatic tration of the chemical in the room holding the material, the hydrocarbons (PAHs) and pesticides are in some cases includ- room air exchange rate, and the total surface area of the ed to provide a more in depth analysis. However, outdoor material compared to the volume of air in the room (Yu and removal of VOCs, PAHs, and pesticides is not the focus of this Crump 1998). review. In addition, mechanical strategies to enhance indoor The level of VOCs in indoor air can be reduced by using VOC removal by plants such as drawing air through the low-emission products and dispersing and diluting the emitted potting mix of plants are not included. VOCs by means of ventilation (World Health Organization To our knowledge, no review deals only with indoor potted 2010). If further reduction of the pollution is needed, tech- plants’ ability to remove VOCs. Reviews exist on general niques such as filtration and adsorption to e.g. activated biological treatment of indoor air which include active charcoal or silica gel exist (Yu et al. 2009). An alternative biofiltration, but also deals to some extent with potted plants way to reduce the level of VOCs in indoor air is the use of (Guieysse et al. 2008; Soreanu et al. 2013). In addition, there plants. Several ornamental potted plant species have the abil- are several reviews on bioremediation and phytoremediation ity to absorb VOCs from indoor air (Yang et al. 2009). which focus on remediation of soils (Arthur et al. 2005; Thereby, the plants act as sinks and consequently reduce the Juwarkar et al. 2010; McGuinness and Dowling 2009; Salt VOC concentration in the air. In addition, decorating offices et al. 1998), as well as reviews of modelling on xenobiotic with plants can decrease levels of discomfort such as cough accumulation in edible plants (Collins and Finnegan 2010; and fatigue and improve health (Fjeld et al. 1998). These Trapp 2004; Zebrowski et al. 2004). Recently, a review has effects may in part be caused by the plants removing VOCs been published dealing with deposition of atmospheric PAHs from the air. Plants also have the advantage that they can have in plants (Desalme et al. 2013). The review by Desalme et al. psychological and social benefits for humans (Bringslimark (2013) offers valuable insight into deposition, accumulation, et al. 2009; Thomsen et al. 2011). mechanisms of transfer, and ecological and physiological The aim of the present review is to provide insight into how effects of PAHs. VOCs are removed by a potted plant and which factors affect To help the reader throughout this review, two terms for the efficiency and rate of VOC removal by plants. The review removal of VOCs are used: (1) removal rate (the amount of is organized by firstly presenting the section “Summary of VOC removed per unit time per leaf area) or (2) removal laboratory and field studies”, which is divided into four sub- efficiency (percentage of VOC removed per unit time per leaf sections. The first section (“Pathways for VOC removal”) area). There is an inconsistency in the units used in the describes how VOCs are removed by potted plants and is reviewed literature but for many purposes the conclusions divided into “Removal of VOCs by aboveground plant parts”, obtained are not affected by this. However, the terms become “Removal of VOCs by microorganisms”,and“Removal of important when evaluating effects of VOC concentration. For VOCs by growing media and roots”. The second section further help throughout the review, suggestions for botanical (“Factors affecting the efficiency and rate of VOC removal names are given in brackets following the common English by plants”) deals with how factors such as light and VOC name for those studies where it was not included by the concentration can influence VOC removal and is divided into researchers. In addition, light intensities have been converted “Plant species”, “Growing media”, “Light”, “Temperature”, from lux to μmol/m2/s (Enoch and Kimball 1986) and VOC “VOC concentration”, “VOC identity”,and“VOC mixture concentrations have been converted to μg/m3 where possible effects”. The third section (“VOC removal in real-life set- under 101,325 Pa and temperature given in the study. tings”) is a summary of studies conducted in indoor settings with the intention of evaluating if VOC removal by plants is of value in real-life situations. The fourth section (“Plant modi- Summary of laboratory and field studies fications for enhanced VOC removal”) evaluates if VOC removal can be enhanced by genetically modifying plants. More than 100 plant species have been examined to estimate At the end of the review, “Supplementary comments and their ability to remove VOCs from indoor air (see Table 1). future research needs” discusses additional information ob- The results of the reviewed literature document that plants in tained in the reviewed literature studies, the applicability of general are able to remove VOCs. As an example, seven plant laboratory studies for real-life simulations, and suggest future species removed 59–337 ppm/m2/day of benzene (Table 1), research needs. Finally, the “Conclusion” is presented. which, with a chamber size of 0.216 m3, corresponds to a The review is limited to indoor plants’ ability to remove removal rate of 43.8–205.6 mg/m2/day (Orwell et al. 2004). In VOCs including formaldehyde. This means that only organic addition, three plant species removed 3,371–4,759 μgform- pollutants that are mainly in their gas phase are the focus of the aldehyde in 7 h (Table 1) (Wolverton and Mcdonald 1982).