Application of exogenous indole-3-acetic acid on shoots of Zamioculcas zamiifolia for enhancing toluene and formaldehyde removal Haseeb Ullah 1 & Chairat Treesubsuntorn 2 & Paitip Thiravetyan 1 Received: 10 March 2020 /Accepted: 19 March 2020 # Springer Nature B.V. 2020 Abstract Indoor air pollution is of increasing concern for human health. Amongst the volatile organic compounds (VOCs) found indoors, formaldehyde and toluene are two toxic compounds. Indoor plants have an innate capability to remediate indoor airborne pollutants. Zamioculcas zamiifolia is an ornamental plant local to Thailand reported to be very efficient for VOC removal. Indole acetic acid (IAA) was applied to shoots and roots of Z. zamiifolia to enhance the capability for removing a toluene and formaldehyde mixture. We found that 5 μM of exogenous IAA can enhance Z. zamiifolia efficiency about 20% and 40% for toluene and formaldehyde, respectively, after plant was exposed to initial toluene-formaldehyde mixture concentration 20 ppm (1:1) for 3 cycles (156 h). We found that 5 μM of exogenous IAA had a positive effect on the stomatal aperture opening and stomatal conductance. However, 10 μM of exogenous IAA had a negative effect on the opening of stomatal aperture, and thus initially decreased that remediating ability of Z. zamiifolia for formaldehyde and toluene. We investigated the formaldehyde dehydrogenase activity in shoots of Z. zamiifolia and found significantly enhanced FDH activity in plants supplied with exogenous IAA. We concluded that exogenous IAA in optimum amounts could enhance the mitigating ability of indoor plants for airborne air pollutants. However, our research indicated that the application of IAA to roots could have a negative effect on the remediating ability of Z. zamiifolia. Keywords Zamioculcas zamiifolia . Indole-3-acetic acid . Toluene . Formaldehyde . Air phytoremediation Introduction Toluene and formaldehyde are two volatile organic com- pounds (VOCs) with different chemical natures. While form- aldehyde is a polar molecule, toluene is non-polar. Both com- pounds are hazardous and can impose health concerns if pres- ent in considerable concentrations indoors (Leggat et al. 2007). Long-term exposure to formaldehyde can cause serious chronic diseases, such as lung cancer (Gupta et al. 1982). At concentrations above 0.1 ppm in air, formaldehyde can irritate the eyes and mucous membranes, resulting in watery eyes (Tang et al. 2009). Inhalation of toluene in low to moderate levels can also cause tiredness, confusion, weakness, drunkenness, memory loss, nausea, loss of appetite, hearing loss and colour vision loss (Grandjean and Landrigan 2006). Traces of aforementioned compounds can be found in the ambient air of buildings, houses and other infrastructures, and thus pose a reasonable threat to human health (Ballester et al. 2010). Formaldehyde is used in building material, car- pets, paints and other cosmetics. This compound is also ex- tensively used in chemical industries and laboratories (Khaksar et al. 2016a). Toluene is also used extensively in furniture, paints, oils, adhesives, leather tanning and disinfectants. As plants have an innate ability to absorb airborne pollut- ants, research in the area of phytoremediation has angled to- wards evaluating the ability of different indoor plant species for the remediation of a number of VOCs (Irga et al. 2017; Cruz et al. 2014; Lee and Hyunkyung 2015; Treesubsuntorn and Thiravetyan 2018; Irga et al. 2019). Many plant species show enough potential for air quality improvement. In addi- tion, air phytoremediation technology has been developed and designed for real site application such as active living, which also showed the potential to improve air quality (Torpy et al. * Paitip Thiravetyan paitip.thi@kmutt.ac.th 1 School of Bioresources and Technology, King Mongkut’ s University of Technology Thonburi, Bangkok 10150, Thailand 2 Pilot Plant Development and Training Institute, King Mongkut’ s University of Technology Thonburi, Bangkok 10150, Thailand Air Quality, Atmosphere & Health https://doi.org/10.1007/s11869-020-00820-y