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HOW INDOOR PLANTS IMPROVE HEALTH AND WELLBEING
RESEARCH UPDATE
July 2009
Margaret Burchett, Fraser Torpy & Jason Brennan
Plants and Indoor Environmental Quality Group. Faculty of Science, UTS
Margaret.Burchett@uts.edu.au
As in much of the developed world, 80% of Australians live in urban areas, and spend 90% of our time indoors
(Environ. Aust., 2003), so the quality of the indoor environment is critical to our health and wellbeing.
International research, including our own at UTS, has demonstrated that indoor plants improve many aspects of
indoor environmental quality (IEQ) - both physicochemical benefits to air quality (IAQ) and directly measurable
benefits to health and wellbeing of building occupants.
Indoor plants benefit indoor air quality
Outdoor urban air pollution (UAP) is derived mainly from fossil fuel emissions (CO 2, CO, oxides of nitrogen
and sulfur, volatile organic compounds [VOCs], ozone, etc). And - indoor air pollution is almost always higher
than outdoors, even in the CBD, because as air moves indoors it mixes with pollution from indoor sources, eg
more CO2, and more VOCs from plastics/synthetics. Australian UAP health costs are about $12 B p.a. (CSIRO
2003), and kills about 1,400 people p.a. in Sydney alone (EPA NSW 2006). Worldwide, UAP accounts for
about 3 M deaths p.a. (WHO 2002). In 2000, WHO predicted that by 2010 building managers would start
becoming responsible for IAQ. International studies show that plants, including ‘indoor’ species, absorb all
types of urban air pollutants.
UTS studies - plants to improve IAQ
In these studies we use the standard approach for environmental risk assessment (ERA) for management
decision-making - the triad approach: field investigations; laboratory uptake/toxicity validation trials; and
chemical or other analyses; to reveal mechanisms, and hence remediation strategies.
UTS ‘field’ studies
VOCs
Our first office study, in 3 UTS buildings (2 air-conditioned [AC], 1 not), using 60 offices (12-15 m2),
measured effects of pot-plants on total VOCs (TVOC loads), CO2 and CO. In no-plant offices, TVOCs ranged
from ~80–400 ppb (Aust indoor TVOC max. – 500 ppb, ie 0.5 ppm), whereas with 3 or 6 plants, loads were
kept below 100 ppb (negligible respiratory health risk). So, minimum pot number needed to cleanse air of
VOCs in offices of this size-range is less than three. All treatments worked equally well + AC. Also, CO2
was reduced by 10% (+ AC) and 25% (- AC); and CO by 90%. However, our 2 nd office study, in 2 newer
buildings, showed much lower removal rates of CO2 and CO, because of more efficient ACs, (discussed
below).
UTS Laboratory studies
VOCs We have tested 12 plant species* (in 200 mm pots), in test-chambers, tracking removal rates with
repeated top-up doses, with test VOCs, in light and dark. Our findings have greatly extended and modified
those of Wolverton et al. We have demonstrated that all species are about equally good at VOC removal;
removal rates are stimulated by the first dose, and when fully adapted, can remove increasing doses
within 24 h; they are equally effective in light or dark; potting-mix bacteria are the main removal agents;
plant roots nourish their root-zone microorganisms, so removal is achieved by the plant/potting-mix
symbiotic microcosm.
We conclude any indoor species is likely to work just as well.
Does pot/plant size matter? The Green Building Council’s Green Star Ratings provide 1 pt. per 1 Large or 2
Small plants / 30m2 NLA; or 2 pts. per 1 Large / 2 Small plants /15m2 NLA (based on surface areas; L, 300 mm
pot, being twice that of a S, 200 mm pot). To test this, we measured VOC reduction rates under ‘heavy
pollution’ or ‘industrial’ conditions, with 4 pot sizes, 125, 200, 250 and 300 mm, with 3 doses of 5 ppm + 1
dose 25 ppm benzene. The 5 mm dosage is the Aust. Maximum allowable 8-hr averaged occupational exposure
concentration for benzene. Species tested were Zanzibar, Sansavieria and Pothos.
With all 3 species, removal rates with 200 - 300 mm pots were equally fast – the 3rd 5 ppm dose was
removed in 23 h. (Rates rose further with a 25 ppm dose). But the 125 mm pots showed rates half or less
than the other 3 sizes.
So, 200 mm pots are as good as 300 mm for VOC reduction, even under ‘industrial’ conditions
We then tested Sansevieria under ‘office/home’ conditions, using 1, 2, 3 or 4 x 125 mm pots, compared with 1
x 200 mm pot. (Area of 3 x 125 mm pots = 1x 200 mm pot). Dosage was 3 doses 0.5 ppm and 1 x 5 ppm
benzene..
Results with the 3rd 0.5 ppm dose, times for removal were as follows:
1x 125 mm pot – 31h; 2 pots – 24 h; 3 pots – 17 h; 4 pots – 17 h; 1 x 200 mm – 13 h.
That is, 3 x 125 mm pots were about as good as 1 x 200 mm pot under normal office/home conditions; so
plant walls, towers, clusters, of small pots, work well also.
CO2 removal Getting enough light inside a building to support effective CO 2 reduction is often problematic.
Adequate light is needed for photosynthesis, and both plants and potting mix microorganisms also respire. CO 2
reduction varies with: light/shade tolerance of species; foliage area; plant age and acclimatisation; lighting levels
at pot-position; humidity; moisture level in potting mix; surrounding CO 2 levels.
Research on these issues is minimal, but general principles apply –
place plants according to known light/shade tolerances; and - the more foliage area the better!
We are commencing to profile light and associated requirements in three species.
Direct wellbeing benefits of indoor plants
Reductions in adverse health symptoms with indoor plant presence have been reported from a number of
studies, eg reductions in: coughing and fatigue - 37%; ear, nose and throat symptoms - 23%; sick-leave down over 60%; sick-leave down in primary pupils; perception of pain; blood pressure; feelings of anxiety, depression
and hostility; and intentions to quit.
Improvements in wellbeing (performance) have been reported, on: computer tests; item sorting tasks; creative
thinking exercises; examination scores; job satisfaction; interest and mood in dementia patients; classroom
behaviour, junior high school. A recent large on-line survey (540 respondents) found work satisfaction scores
on all 10 criteria investigated were raised more by indoor plant presence than by green window views.
Psychologists consider that direct wellbeing benefits of plants can result from simply glancing at foliage from
time to time during the day. This relieves ‘attention fatigue’, gives feelings of ‘temporary awayness’, and ‘being
part of a greater whole’, and thus resets a calming response in the brain.
UTS results- psychological responses: We administered 2 sets of surveys twice during our 2nd office study,
once before, and once 10 weeks after, plants were installed. We found significant reductions in stress and
overall depressive mood states with plant presence, including specific scores for tension, depression,
anger, fatigue and confusion, plus increases in vigour, compared with participants without plants.
Research directions
To help ensure the goal of producing sustainable urban communities, satisfying the ‘triple bottom line’ of
environmental, social and economic considerations, interior plants should become standard elements of urban
facility ecology. However, to achieve this aim, we need to investigate, among other aspects, the use of indoor
plants for CO2 and hence reduced energy consumption in city buildings. There is strong evidence now that
indoor plants are not just ‘pretty faces’, but also a portable, flexible, affordable, self-regulating, air-filtration
system, and a spirit-lifting oasis that improves job satisfaction, work performance and productivity, that will
more than repay the cost of their presence in the built environment.
Acknowledgements: We thanks our industry funding/collaborators, Ambius Tropical Plants, NIPA,Hort.Aust.
Ltd (HAL) The Container Connection; Prof A Craig (Univ. Syd); and UTS colleagues, Drs A Pulkownik, J
Tarran , A Leigh, Drs R Wood & R Orwell, and many others, including participants in 2 office studies.
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*Species tested; Aglaonema modestum; Chamaedorea elegan; Dracaena ‘Janet Craig’; D. marginata; Howea
forsteriana (Kentia); Epipremnum aureum (Pothos; Devil’s Ivy); Philodendron ‘Congo’; Sansevieria trifasciata
(Mother-in-law’s tongue); Schefflera ‘Amate’ (Qld. Umbrella Tree); Spathiphyllum ‘Petite’ (Peace Lily); S.
‘Sensation; Zamioculcas zamiifilia (Zanzibar, ZZ).