Characterisation of fungal and bacterial dynamics in an active green wall used for indoor air pollutant removal
Graphical abstract
Introduction
In modern societies, humans spend up to 80% of their time indoors [1], where air quality is often more polluted than outdoors [2,3]. Due to the accumulation of air pollutants, and the extended duration of exposure associated with an indoor lifestyle [4], domestic and commercial indoor air pollution is responsible for up to 5% of the global disease burden [5], equating to costs of approximately US$90 billion annually [6].
Since the 1980s, the use of plants in interior spaces to phytoremediate air pollution has grown considerably in popularity [7,8]. The efficiency of botanical systems in improving indoor air quality has been significantly enhanced by the development of active botanical biofiltration, or active green wall systems [9]. Active green walls use ornamental plants grown along a vertical plane with the addition of mechanical air induction to actively draw polluted air through the plant growth substrate and foliage [10]. During this process, air pollutants are delivered directly to the rhizosphere where they may be metabolised/sequestered by microbes, the predominant mechanism for contaminant degradation [[11], [12], [13]]. Additionally, particulate matter (PM) may be filtered by the substrate and root structures [14].
While botanical biofiltration is still an emerging technology, there is substantial evidence for its practical potential, along with growing commercial interest [[15], [16], [17], [18], [19]]. In their current state, botanical biofilters have comparable removal efficiencies to those of conventional indoor technologies such as MERV (minimum efficiency reporting value) 4, 6, 10, 11 and 13 filters for the removal of PM (PM10 and PM2.5) [20]. In addition, botanical biofilters are capable of reducing indoor concentrations of volatile organic compounds (VOCs) and other pollutants such as CO and CO2 [[21], [22], [23], [24], [25]], which cannot be removed by most conventional systems, other than by dilution [26].
Despite the benefits of active green wall technologies, there is a potential for systems that use active airflow through biologically active substrates to emit bioaerosols into the surrounding environment [27]. It has indeed been proposed that active green walls may provide a favourable environment for the proliferation of pathogenic fungal or bacterial species, with the use of mechanically assisted air flow increasing the risk of the aerosolisation of water containing microbial bioaerosols. Currently, research which has assessed bioaerosol emissions from active green walls are limited to assessments of total fungal and bacterial loading. While there are no documented cases where harmful levels of fungal [[28], [29], [30], [31]] or bacterial aerosols [20,28,31,32] have been detected in active green wall emissions, there is a paucity of research that has comprehensively characterised bioaerosol emissions, and we propose that assessments of this kind are essential to fully understand the implications of biowall systems for indoor air quality (IAQ).
Limited research has specifically investigated the aerosolised release of pathogenic bacteria from green walls [33], such as the ubiquitous bacterial genus Legionella. Legionella are free-living motile bacteria that can infect other microorganisms or form chemo-resistant biofilms [[34], [35], [36]], and several species are the causative agents of legionellosis [[36], [37], [38]]. L. pneumophila serogroup 1 is responsible for up to 90% of infections worldwide, with the exception of in Australia, New Zealand and Thailand, where L. longbeachae is the dominant pathogen, and is responsible for up to 40% of infection [[39], [40], [41], [42]]. The dispersal mechanisms of these two species vary significantly [33,43]. Where L. pneumophila requires aerosolisation through water droplets for infection to occur [33,37,38,44], L. longbeachae requires physical contact from contaminated soils with the eyes or mouth [42,43]. Due to the nature of the components used in active green walls, there is some concern that Legionella spp. may proliferate within irrigation systems and botanical substrates and become aerosolised in the event of over-watering or physical disturbance.
In this study, we aimed to determine whether an established active green wall in a modern urban office building contributed significantly to the release of fungal and bacterial aerosols, with specific focus on bioaerosols that have implications for IAQ and human health. We assessed the culturable indoor aeromycota, characterised the bacterial community composition using 16S rRNA amplicon sequencing approaches, and performed targeted enumeration of the pathogen Legionella spp. to examine potential risks to public health.
Section snippets
Site description
Aerosol sampling was conducted on four floors (levels 12–14 and 17) of a newly built commercial office building, made of steel and glass near Sydney's Central Business District. The building featured standard heating, ventilation and air conditioning (HVAC) systems with no additional filtration technology. One active and one passive green wall span the interior of two stories (levels 13 and 14), each covering 60 m2, in a semi-open plan café and meeting/reception space, with a floor space of
Fungal bioaerosol assessment
Active and passive green wall sites featured significantly higher fungal densities than the reference sites across the three-month sampling period (p = 0.001 and p = 0.009 respectively; Fig. 2). Temporal differences in fungal density were not significant, nor were interactions amongst factors or with foot traffic (p > 0.05). Despite elevated concentrations of aerosolised fungal propagules, total concentrations remained well below the World Health Organisation guideline for indoor air [61] of
In situ bioaerosol analysis
While potting soils have been implicated as a source of human pathogens [[62], [63], [64], [65]], studies documenting the dispersal of aerosolised fungal pathogens from indoor contaminated soils is limited [66]. Several studies have found that neither potted plants nor complex biowall structures contribute significantly to allergenic or pathogenic airborne fungal density [[66], [67], [68], [69], [70]], unless considerable physical disturbance or agitation occurs [71]. Nonetheless, as active
Summary and conclusion
Fungi are ubiquitous soil inhabitants and have strong associations with plants. The installation of botanical material indoors, either as simple potted plants or complex active green walls, is likely to contribute to the ambient fungal load [29,70,103,104]. Fungal aerosols in the ambient indoor environment proximal to active and passive green walls remained well below WHO guidelines and the systems did not release detectable harmful fungal bioaerosols. The concentrations detected were
Authors' contributions
RF, PJI and FT designed the study; RF collected samples; RF and PJI analysed fungal samples; RF and NW analysed bacterial samples; RG and RF analysed the data; RF interpreted data; RF, TP, RG, PJI, FT and JS drafted the manuscript.
We would like to acknowledge and express our gratitude to Production Design Engineer Laura Dominici from the Department of Environment, Land and Infrastructure Engineering (DIATI), Politecnico di Torino (Italy), for the contribution of “Fig. 1: Schematic
Declaration of competing interest
We state that there was no conflict of interest.
References (104)
- et al.
Analysis of industrial contaminants in indoor air: Part 1. Volatile organic compounds, carbonyl compounds, polycyclic aromatic hydrocarbons and polychlorinated biphenyls
J. Chromatogr., A
(2009) - et al.
Estimates and 25-year trends of the global burden of disease attributable to ambient air pollution: an analysis of data from the Global Burden of Diseases Study 2015
Lancet
(2017) - et al.
The botanical biofiltration of VOCs with active airflow: is removal efficiency related to chemical properties?
Atmos. Environ.
(2019) - et al.
Effect of plant traits and substrate moisture on the thermal performance of different plant species in vertical greenery systems
Build. Environ.
(2020) - et al.
Botanical biofilter for indoor toluene removal and reduction of carbon dioxide emission under low light intensity by using mixed C3 and CAM plants
J. Clean. Prod.
(2018) - et al.
Do the plants in functional green walls contribute to their ability to filter particulate matter?
Build. Environ.
(2017) - et al.
Towards practical indoor air phytoremediation: a review
Chemosphere
(2018) - et al.
An assessment of the atmospheric particle removal efficiency of an in-room botanical biofilter system
Build. Environ.
(2017) - et al.
Health and wellness in commercial buildings: systematic review of sustainable building rating systems and alignment with contemporary research
Build. Environ.
(2020) - et al.
Profiling indoor plants for the amelioration of high CO 2 concentrations
Urban For. Urban Green. Urban Green.
(2014)
Indoor air pollutants in occupational buildings in a sub-tropical climate: comparison among ventilation types
Build. Environ.
Botanical biofiltration for reducing indoor air pollution
Indoor and outdoor airborne bacterial and fungal air quality in kindergartens: seasonal distribution, genera, levels, and factors influencing their concentration
Build. Environ.
The effect of an indoor living wall system on humidity, mould spores and CO2-concentration
Energy Build.
Ten questions concerning the aerosolization and transmission of Legionella in the built environment
Build. Environ.
Risk of infection from Legionella associated with spray irrigation of reclaimed water
Water Res.
A survey on the pathogenic fungi in soil samples of potted plants from Sari hospitals, Iran
J. Hosp. Infect.
Aspergillus terreus infections in haematological malignancies: molecular epidemiology suggests association with in-hospital plants
J. Hosp. Infect.
Childhood hypersensitivity pneumonitis associated with fungal contamination of indoor hydroponics
Int. J. Hyg Environ. Health
An assessment of the potential fungal bioaerosol production from an active living wall
Build. Environ.
Evaluation of indoor plantings as allergen exposure sources
J. Allergy Clin. Immunol.
Actinobacteria: current research and perspectives for bioremediation of pesticides and heavy metals
Chemosphere
Multi-resistant plant growth-promoting actinobacteria and plant root exudates influence Cr(VI) and lindane dissipation
Chemosphere
Indoor-biofilter growth and exposure to airborne chemicals drive similar changes in plant root bacterial communities
Appl. Environ. Microbiol.
The National Human Activity Pattern Survey (NHAPS): a resource for assessing exposure to environmental pollutants
J. Expo. Anal. Environ. Epidemiol.
Particulate matter air pollution and cardiovascular disease: an update to the scientific statement from the american heart association
Circulation
Air Pollution: Global Damage Costs from 1900 to 2050
Foliage plants for removing indoor air pollutants from energy-efficient homes
Econ. Bot.
Interior Landscape Plants for Indoor Air Pollution Abatement
Biofiltration of airborne VOCs with green wall systems—microbial and chemical dynamics
Indoor Air
Testing the single-pass VOC removal efficiency of an active green wall using methyl ethyl ketone (MEK)
Air Qual. Atmos. Health
A review of green systems within the indoor environment
Indoor Built Environ.
The design of the botanical indoor air biofilter system for the atmospheric particle removal
MATEC Web Conf.
The phytoremediation of indoor air pollution: a review on the technology development from the potted plant through to functional green wall biofilters
Rev. Environ. Sci. Bio Technol.
Use of living pot-plants to cleanse indoor air - research review
Phylloremediation of air pollutants: exploiting the potential of plant leaves and leaf-associated microbes
Front. Plant Sci.
The removal of carbon monoxide by botanical systems
SAE Tech. Pap. Ser.
Bioaerosol production from indoor air biofilters
Indoor Air
Implementing green walls in schools
Front. Psychol.
Impact of Interior Living Walls on Indoor Air Quality : Study in a Dynamic Environment by
Reducing indoor air pollutants through biotechnology
Biotechnol. Biomimetic Civ. Eng.
Factors mediating environmental biofilm formation by Legionella pneumophila
Front. Cell. Infect. Microbiol.
Effect of disinfectant, water age, and pipe materials on bacterial and eukaryotic community structure in drinking water biofilm
Environ. Sci. Technol.
Legionella pneumophila: an environmental organism and accidental pathogen
Int. J. Sci. Technol.
Rolling epidemic of Legionnaires' disease outbreaks in small geographic areas article, Emerg
Microb. Infect.
Clinical and environmental distributions of Legionella strains in France are different
J. Clin. Microbiol.
Distribution of legionella species from environmental water sources of public facilities and genetic diversity of L. pneumophila serogroup 1 in South Korea
Appl. Environ. Microbiol.
Presence and persistence of viable, clinically relevant Legionella pneumophila bacteria in garden soil in The Netherlands, Appl
Environ. Microbiol.
NSW health notifiable conditions information management system (NCIMS)
Commun. Dis. Branch Cent. Epidemiol. Evid.
Legionella longbeachae and legionellosis
Emerg. Infect. Dis.
Cited by (28)
Phytoremediation of indoor air pollutants from construction and transport by a moveable active green wall system
2023, Atmospheric Pollution ResearchHempcrete as a substrate for fungal growth under high humidity and variable temperature conditions
2023, Construction and Building MaterialsMicrobially-assisted phytoremediation toward air pollutants: Current trends and future directions
2023, Environmental Technology and InnovationCooling, CO<inf>2</inf> reduction, and energy-saving benefits of a green-living wall in an actual workplace
2023, Building and Environment