Removal ratio of gaseous toluene and xylene transported from air to root zone via the stem by indoor plants

Abstract

This work was designed to investigate the removal efficiency as well as the ratios of toluene and xylene transported from air to root zone via the stem and by direct diffusion from the air into the medium. Indoor plants (Schefflera actinophylla and Ficus benghalensis) were placed in a sealed test chamber. Shoot or root zone were sealed with a Teflon bag, and gaseous toluene and xylene were exposed. Removal efficiency of toluene and total xylene (m, p, o) was 13.3 and 7.0 μg·m(-3)·m(-2) leaf area over a 24-h period in S. actinophylla, and was 13.0 and 7.3 μg·m(-3)·m(-2) leaf area in F. benghalensis. Gaseous toluene and xylene in a chamber were absorbed through leaf and transported via the stem, and finally reached to root zone, and also transported by direct diffusion from the air into the medium. Toluene and xylene transported via the stem was decreased with time after exposure. Xylene transported via the stem was higher than that by direct diffusion from the air into the medium over a 24-h period. The ratios of toluene transported via the stem versus direct diffusion from the air into the medium were 46.3 and 53.7% in S. actinophylla, and 46.9 and 53.1% in F. benghalensis, for an average of 47 and 53% for both species. The ratios of m,p-xylene transported over 3 to 9 h via the stem versus direct diffusion from the air into the medium was 58.5 and 41.5% in S. actinophylla, and 60.7 and 39.3% in F. benghalensis, for an average of 60 and 40% for both species, whereas the ratios of o-xylene transported via the stem versus direct diffusion from the air into the medium were 61 and 39%. Both S. actinophylla and F. benghalensis removed toluene and xylene from the air. The ratios of toluene and xylene transported from air to root zone via the stem were 47 and 60 %, respectively. This result suggests that root zone is a significant contributor to gaseous toluene and xylene removal, and transported via the stem plays an important role in this process.

Does plant species selection in functional active green walls influence VOC phytoremediation efficiency?

“…VOCs (Ugrekhelidze et al 1997, Kim and Jeon 2009, Sriprapat and Thiravetyan 2013, Dela Cruz et al 2014, Kim et al 2016, Hörmann et al 2018. However, it is known that the efficiency of VOC removal varies substantially both among plant species (Kim et al 2018, Yoo et al 2006, and with the molecular characteristics of individual compounds.…”

Potted plants do not improve indoor air quality: a review and analysis of reported VOC removal efficiencies

“…Given the leaf area of all plant species and an initial concentration in the chamber, conversion to CADR p was possible. Kim et al [46] plotted concentration over time for two distinct plant species removing three different VOCs. The CADR p results for these studies are detailed in Table S2.…”

“…This figure thus explores the possibility of constraining CADR p for each VOC. Some of the data preliminarily indicates that certain VOCs may be more efficiently removed by potted plants; for instance, Kim et al [44][45][46] observed better formaldehyde removal than for xylene, and Wolverton et al [49] observed a much lower TCE removal than for formaldehyde and benzene. However, these trends are not consistent throughout all studies; for instance, Yang et al [50] observed similar removal of TCE, benzene, and toluene.…”

“…More notably, however, the variance of CADR p values belonging to a particular study is much smaller than the variance of the dataset as a whole (intra-study values range 1-2 orders of magnitude, as compared to the total CADR p range of~4 orders of magnitude). For example, of the 46 CADR p values calculated from Kim et al [44][45][46], 32 of them (70%) reside above 0.1 m 3 h −1 plant −1 , making up 84% of the total 38 CADR p greater than 0.1 m 3 h −1 plant −1 . On the other end of this spectrum, all CADR p values belonging to Irga et al [43] and Yang et al [50] were less than 0.001 m 3 h −1 plant −1 , making up all but one other CADR p below 0.001 m 3 h −1 plant −1 .…”

“…However, the experimental results of the underlying scientific works are often reported in ways such that they cannot simply be extrapolated into impacts in real indoor environments. Typical for these studies, a potted plant was placed in a sealed chamber (often with volume of 1 m 3 ), into which a single VOC was injected, and its decay was tracked over the course of many hours or days [42][43][44][45][46][47][48][49][50][51][52]. In contrast, building volumes are much larger than that of an experimental chamber, and VOC emissions are persistent.…”