Toronto Master Gardener Factsheet    

• Symptoms of Sick Building Syndrome
• Sources of Indoor Air Pollution
• Experiments with Plants
• How Plants Clean The Air
• Clean Air Plants
• Number of Plants

Symptoms of Sick Building Syndrome

• Allergies
• Asthma
• Eye, nose and throat irritations
• Fatigue
• Headache
• Nervous-system disorders
• Respiratory congestion
• Sinus congestion

These are the symptoms associated with Sick Building Syndrome, a condition produced by poor indoor air quality. Since the 1980's problems with indoor air pollution have become more prevalent because, in order to conserve energy resources, many homes and office buildings are now efficiently sealed from the air outside, trapping the gases that synthetic materials emit or "off-gas" inside. In fact, indoor air pollution is now considered by many experts to be one of the major threats to health. It may be an even greater threat than outdoor pollution - primarily because of the greater length of exposure.

Sources of Indoor Air Pollution

The most common harmful airborne chemicals found in the average home or office are formaldehyde, benzene, trichloroethylene and carbon monoxide. Even in low concentrations these chemicals can cause a variety of health problems.

Formaldehyde … is found in virtually all indoor environments:

• Office or household furniture made of particle board or pressed wood products
• Consumer paper products: grocery bags, paper towels, facial tissues
• Adhesive binders in floor covering, carpet backing
• Many common household cleaning agents
• Natural gas from gas stoves and kerosene
• Tobacco smoke
• Permanent-press clothes, water repellent, fire retardants

Symptoms … include eye, nose and throat irritation, headaches, allergic dermatitis, controversial links to asthma, cancer, chronic respiratory diseases and neuropsychological problems.

Benzene … is used in:

• Commonly used solvents
• The manufacture of detergents
• Some pharmaceuticals
• Oils
• Paints
• Plastics
• Rubber
• Dyes
• Synthetic fibres
• Inks

Symptoms … include skin and eye irritation, headaches, loss of appetite, drowsiness, psychological disturbances and some blood system diseases including anemia and bone marrow disease.

Trichloroethylene … is used by the metal degreasing and dry cleaning industry and is also found in:

• Printing inks
• Paints
• Varnishes
• Adhesives
• Lacquers

It is considered to be a potent liver carcinogen.

Carbon monoxide … is found in:

• Cigarette smoke
• Fuel-fired furnaces
• Gas water heaters
• Fireplaces and woodstoves
• Gas stoves
• Gas dryers

Symptoms … Exposure to low levels can cause drowsiness and "flu-like" symptoms of dizziness, nausea and headaches.

Bioeffluents … are released during human respiration and also increase Indoor Air Quality problems. The four most prevalent bioeffluents found in a crowded classroom are: ethyl alcohol, acetone, methyl alcohol and ethyl acetate.

Other Air Quality Factors: airborne microbes such as mould spores and low relative humidity. (Healthy humidity levels range between 35 and 65%.)

Experiments with Plants

The National Aeronautics and Space Administration was instrumental in determining that house plants improve the quality of air that we breathe while they were researching ways to clean the air in space stations. Scientists discovered that there were 300 volatile organic chemicals in the air occupied by the crew. Dr. B.C. Wolverton, a research scientist, headed up a team that experimented with plants to determine which were best at purifying the air. In 1996 he published the results on 50 plants in his book "Eco Friendly House Plants". The following information is largely taken from his findings.

How Plants Clean The Air

Because most houseplants evolved in the undercanopy of tropical or subtropical forests, they have unusually high rates of photosynthesis to allow them to thrive in dim light. This trait works to our advantage when dealing with indoor environments.

The studies confirmed that houseplant leaves, roots, soil and microorganisms work together in a symbiotic relationship to removal chemical pollutants:

• Air pollutants are absorbed through microscopic openings in the leaves called stomata. Through translocation, the movement of substances through the plant to the root zone, toxins are removed from the air to the soil and broken down by microbes. Some chemicals, however, are destroyed by the plant's own biological processes without involving the action of soil microbes.
• Water vapour is emitted into the air from plant leaves through a process called transpiration. Convection air currents set up by leaf transpiration transport toxins to the root zone. Effective toxin transportation can be increased if the lower leaves of houseplants are removed so that as much soil as possible is in contact with the air.
• Soil microbes biodegrade the toxins into a source of food for the microbes and the plant. A varied population of microorganisms live in the soil. They are responsible for, among other things, making nutrients available to plants and detoxifying the soil. They are highly adaptive, having the ability to mutate to cope with environmental changes. It is important to note that, since research has shown that microorganisms become more adept at detoxification the longer they are exposed to toxins, the longer we are able to keep our houseplants, the more successful they will be as Clean Air Plants.
• While most plants photosynthesize in daylight, some plants, including most succulents, orchids and bromeliads, act in the opposite manner, opening their stomata at night. Therefore, with a well-balanced selection of houseplants, it is possible to purify continuously the indoor environment - day and night!

Clean Air Plants

The following 20 plants were given the highest ratings for removal of chemical vapours in Dr. Wolverton's Book "Eco Friendly House Plants". The book gives detailed information on all fifty plants tested.

Plant Name	Ability (out of 10) to remove chemicals	Lighting Conditions Full sun = min. 5 hrs of sun Semi-sun = 2 hrs of sun in winter Semi-shade = only indirect light	Notes
Areca Palm (Chrysalidocarpus lutescens)	8	Semi-sun	Easy to grow. Requires high humidity
Lady Palm (Rhapis excelsa)	7	Semi-sun	Easy to grow
Bamboo Palm (Chamaedorea seifrizii)	9	Semi-sun	Easy to grow
Rubber Plant (Ficus robusta)	9	Semi-shade	Easy to grow
Dracaena 'Janet Craig' (Dracaena deremensis 'Janet Craig')	8		Easy to grow
English Ivy (Hedera Helix)	9	Semi-sun Semi-shade	Requires high humidity. Parts poisonous. Prone to spider mite.
Dwarf Date Palm (Phoenix roebelenii)	9	Semi-shade
Ficus Alii (Ficus macleilandii 'Alii')	7	Full sun	Easier to grow than F. Benjamina
Boston Fern (Nephrolepis exaltata 'Bostoniensis')	9	Semi-sun Semi-shade	Requires humidity and good light
Peace Lily (Spathiphyllum sp.)	8	Semi-sun Semi-shade	Easy to grow
Corn Plant (Dracaena fragrans 'Massangeana')	8	Semi-shade	Very easy to grow
Kimberley Queen (Nephrolepis obliterata)	9	Semi-sun Semi-shade	Tolerant fern
Florist's Mum (Chrysanthemum morifolium)	9	Full sun	Easy to grow
Gerbera Daisy (Gerbera jamesonii)	9	Full sun Semi-sun
Dumb Cane (Dieffenbachia 'Exotica Compacta')	7	Full sun Semi-sun	Very easy to grow Toxic
Weeping Fig (Ficus benjamina)	8	Full sun	Requires draught-free environment
Schefflera (Brassaia actinophylla)	8	Semi-shade
Dendrobium Orchid (Dendrobium sp.)	7	Semi-sun
Tulip (Tulipa gesneriana)	7	Full sun	Bulb poisonous when eaten
Spider Plant (Chlorophytum comosum 'Vittatum')	6	Semi-sun Semi-shade	Easy to grow

Number of plants

The recommendation generated by NASA studies is to use 15 to 18 good sized houseplants in 6 inch (15 cm) to 8 inch (20 cm) containers to improve the air quality in an average 1,800 square-foot house. The more vigorously they grow, the better job they'll do.

A personal breathing zone is an area of 0.17 to 0.23 cubic metres (6-8 cubic feet) surrounding a person. These are usually areas where an individual remains for several hours working, watching TV or asleep. Plants placed within this zone can add humidity, remove bioeffluents and chemical toxins and suppress airborne microbes. Plant-filled rooms contained 50 to 60% fewer airborne moulds and bacteria than plant-less rooms.

Further Reading

• Eco Friendly House Plants, B.C. Wolverton.

 

Factsheets are produced by the Toronto Master Gardeners in association with the Toronto Botanical Garden. They provide introductory information about a broad range of horticultural topics and are intended for personal use and study purposes. Should your gardening group or organization wish to use multiple copies we ask that you inform the Toronto Botanical Garden at info@torontobotanicalgarden.ca.

Date revised: This factsheet was created prior to May 2005.