How Indoor Plants Improve

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

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 (CO2, 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 2nd 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

VOCsWe 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 CO2 reduction is often problematic. Adequate light is needed for photosynthesis, and both plants and potting mix microorganisms also respire. CO2 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 CO2 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).