Indoor plants not only add aesthetic appeal to your living spaces but also play a crucial role in improving indoor air quality. Modern buildings often use synthetic materials that release volatile organic compounds (VOCs) into the air. These pollutants can cause various health issues, such as headaches, respiratory problems, and even cancer. Research, including studies by NASA, has demonstrated that certain indoor plants can effectively remove these harmful substances, making indoor environments healthier.
The Origin of Air-Purifying Plant Research: NASA’s Pioneering Role
The study of indoor plants’ capacity to remove air pollutants began in the late 1960s and early 1970s when NASA initiated research to improve air quality in enclosed environments such as space stations. This research was crucial for developing closed ecological systems for long-duration space missions.
Dr. B.C. Wolverton, a NASA scientist, spearheaded these efforts by studying how plants could naturally clean air by removing volatile organic compounds (VOCs). Wolverton’s experiments demonstrated that certain plants could effectively absorb and metabolize common indoor pollutants, such as benzene, formaldehyde, and trichloroethylene, through their leaves and root systems. This pioneering work not only advanced space technology but also provided a scientific foundation for using indoor plants to enhance air quality on Earth.
The book How to Grow Fresh Air: 50 Houseplants That Purify Your Home or Office, published in 1996 by Dr. B.C. Wolverton, popularized the concept of air-purifying houseplants and brought this research into mainstream awareness globally.
The Science Behind How Air-Purifying Plants Work
Plants have a remarkable ability to purify the air by removing and neutralizing pollutants through an intricate system involving their leaves, roots, soil, and associated microorganisms. This process can be understood in several detailed steps:
1. Absorption: The Role of Stomata and Cuticles
- Stomata: Plants have tiny openings on the surface (usually the underside) of their leaves called stomata. These pores play a crucial role in gas exchange, allowing the plant to take in carbon dioxide (CO₂) for photosynthesis and release oxygen (O₂). Stomata also facilitate the uptake of volatile organic compounds (VOCs) and other pollutants from the air. The size and number of stomata can vary depending on the species of plant and environmental conditions.
- Cuticles: The cuticle is a waxy layer that covers the leaves of many plants. While primarily designed to reduce water loss, the cuticle can also absorb lipophilic (fat-loving) pollutants, which can then be metabolized by the plant.
2. Translocation: Moving Pollutants Within the Plant
Once pollutants are absorbed through the stomata or cuticle, they are translocated, or moved, throughout the plant’s internal systems. This movement involves:
- Xylem and Phloem: These are the vascular tissues in plants responsible for the transport of water, nutrients, and chemicals. The xylem moves water and soluble minerals from the roots to the leaves, while the phloem transports the products of photosynthesis such as sugars and other solutes. Pollutants absorbed by the leaves can enter these transport systems and be distributed throughout the plant.
- Transpiration Stream: The continuous movement of water from the roots to the leaves, called the transpiration stream, helps carry pollutants absorbed by the roots or leaves to different parts of the plant. This process also contributes to the plant’s cooling and nutrient distribution.
3. Degradation: Breakdown by Plant Metabolism and Soil Microorganisms
- Metabolic Transformation: Within the plant, pollutants can be metabolized into less harmful compounds through various biochemical pathways. Enzymes within the plant cells can convert toxic chemicals into inert or less toxic substances that can be stored, used in cellular processes, or excreted.
- Rhizosphere Interaction: The rhizosphere is the zone of soil surrounding the plant roots, rich in microorganisms such as bacteria, fungi, and protozoa. This area is highly active biologically, as plant roots exude organic compounds that stimulate microbial growth. Pollutants translocated to the roots can be released into the rhizosphere, where soil microorganisms degrade them through:
- Biodegradation: Microorganisms break down organic pollutants into simpler, non-toxic substances. For example, bacteria in the rhizosphere can metabolize formaldehyde and benzene into carbon dioxide, water, and biomass.
- Phytoremediation: Plants and their associated microbes can work together to decontaminate soils and water. This process can include the uptake of heavy metals and their sequestration in the plant tissues, or the transformation of organic pollutants by root-associated bacteria.
4. Symbiotic Relationship: Enhancing Effectiveness
The effectiveness of plants in purifying air is enhanced by their symbiotic relationships with soil microorganisms. These relationships provide mutual benefits:
- Microbial Support: Microorganisms in the soil aid in nutrient cycling and enhance the plant’s ability to absorb essential minerals. In return, plants supply the microbes with organic compounds derived from photosynthesis.
- Adaptation and Efficiency: Over time, soil microorganisms can adapt to the presence of specific pollutants, becoming more efficient at breaking them down. This adaptation enhances the plant’s overall ability to detoxify the environment.
Additional Factors Affecting Plant Efficiency in Removing Air Pollutants
The type of houseplants used, their number, and placement in the room can have a significant effect on their effectiveness in removing VOC pollutants from the air.
1. Plant Species and Growth Conditions
Different plant species vary in their ability to absorb and degrade pollutants. Factors such as leaf structure, root exudates, and overall biomass influence their effectiveness.
Additionally, the efficiency of pollutant removal can be affected by:
- Light Intensity: Adequate light is essential for photosynthesis, which drives the plant’s metabolism and pollutant uptake.
- Humidity and Temperature: Higher humidity and appropriate temperature levels can enhance stomatal opening, increasing the plant’s ability to absorb pollutants.
- Soil Quality: Nutrient-rich soil with good microbial activity supports healthy plant growth and enhances the degradation of pollutants.
2. Integration in Indoor Environments
The placement and number of plants can impact their effectiveness in improving indoor air quality. Strategic placement near pollutant sources or in areas with poor ventilation can maximize their air-purifying benefits. Regular maintenance, such as dusting leaves and ensuring proper watering, helps keep plants healthy and effective in their role as natural air purifiers.
Common Indoor Pollutants, Their Sources and Health Effects
Indoor environments often harbor various pollutants, particularly volatile organic compounds (VOCs). These compounds can originate from everyday household items and building materials, leading to potential health risks. Understanding the sources and effects of common VOCs is crucial for improving indoor air quality.
1. Formaldehyde
Sources:
- Building Materials: Formaldehyde is commonly found in pressed wood products such as particleboard, plywood, and fiberboard. These materials are used in furniture, cabinetry, and wall panels.
- Furnishings: Upholstered furniture, drapes, and other textiles treated with formaldehyde-based resins for wrinkle resistance and stain protection.
- Household Products: Cleaning agents, disinfectants, paints, varnishes, and some personal care products release formaldehyde.
Health Effects:
- Acute Exposure: Short-term exposure can cause irritation of the eyes, nose, and throat, coughing, and skin rashes. High levels can trigger asthma symptoms.
- Chronic Exposure: Prolonged exposure is associated with an increased risk of cancer, particularly nasopharyngeal cancer and leukemia. Formaldehyde is classified as a human carcinogen by the International Agency for Research on Cancer (IARC) .
2. Benzene
Sources:
- Tobacco Smoke: Cigarette smoke is a major indoor source of benzene.
- Stored Fuels: Gasoline and other fuels stored in garages or sheds can emit benzene vapors.
- Paints and Solvents: Used in the production of paints, adhesives, and various household solvents. Also found in vehicle exhaust, which can infiltrate indoor spaces from attached garages or nearby traffic.
Health Effects:
- Acute Exposure: Can cause dizziness, headaches, tremors, confusion, and unconsciousness at high concentrations.
- Chronic Exposure: Long-term exposure is linked to bone marrow damage, leading to blood disorders such as anemia and an increased risk of leukemia. Benzene is classified as a human carcinogen by IARC .
3. Trichloroethylene (TCE)
Sources:
- Dry Cleaning: TCE is used as a solvent in the dry cleaning industry.
- Adhesives: Found in various adhesives and sealants used in construction and crafts.
- Paint Removers: Used as a solvent in paint removers and degreasers.
Health Effects:
- Acute Exposure: Can cause dizziness, headaches, drowsiness, and in severe cases, unconsciousness.
- Chronic Exposure: Linked to liver and kidney damage, immune system suppression, and an increased risk of certain cancers, including liver cancer and non-Hodgkin lymphoma .
4. Xylene and Toluene
Sources:
- Paint Thinners: Both compounds are common ingredients in paint thinners and strippers.
- Nail Polish and Adhesives: Found in nail polish, nail polish removers, and various household adhesives.
- Industrial Emissions: Emitted during the production of chemicals, rubber, and leather goods.
Health Effects:
- Acute Exposure: Short-term exposure to xylene can cause headaches, dizziness, nausea, and respiratory tract irritation. Toluene exposure can lead to similar symptoms, along with neurological effects such as memory loss and cognitive impairment.
- Chronic Exposure: Prolonged exposure to xylene can lead to liver and kidney damage. Toluene exposure may result in nervous system damage and developmental effects in fetuses when inhaled by pregnant women .
Additional Indoor Pollutants
5. Acetone
Sources:
- Nail Products: Widely used in nail polish removers and other nail care products.
- Household Products: Found in paint removers, varnishes, and adhesives.
Health Effects:
- Acute Exposure: Can cause irritation of the eyes, nose, and throat, along with headaches and dizziness.
- Chronic Exposure: Long-term exposure may lead to respiratory issues and skin dermatitis .
6. Ethylene Glycol
Sources:
- Antifreeze: Used in automotive antifreeze and de-icing solutions.
- Industrial Products: Found in some paints, plastics, and adhesives.
Health Effects:
- Acute Exposure: Can cause central nervous system depression, resulting in dizziness, headaches, and confusion.
- Chronic Exposure: Prolonged exposure can lead to kidney and liver damage .
7. Methylene Chloride
Sources:
- Paint Strippers: Commonly found in paint strippers and removers.
- Aerosol Products: Used in some aerosol products and adhesives.
Health Effects:
- Acute Exposure: Can cause dizziness, nausea, and irritation of the respiratory tract. High concentrations may result in unconsciousness.
- Chronic Exposure: Associated with liver and kidney damage and an increased risk of cancer .
8. Perchloroethylene (PCE)
Sources:
- Dry Cleaning: Widely used in dry cleaning processes.
- Industrial Solvents: Found in metal degreasers and other industrial solvents.
Health Effects:
- Acute Exposure: Can cause dizziness, fatigue, headaches, and respiratory irritation.
- Chronic Exposure: Long-term exposure is associated with liver and kidney damage and an increased risk of certain cancers .
Tips to Reduce Exposure to Indoor Pollutants
Numerous strategies can be employed to reduce indoor VOC levels, which, when combined with houseplants, can enhance their efficiency by decreasing the pollutant load they need to manage, thus accelerating the air purification process.
Additional Strategies to reduce VOC levels:
- Source Control: Remove or reduce the use of products that emit VOCs. Opt for low-VOC or VOC-free products where possible.
- Ventilation: Increase ventilation by opening windows and using exhaust fans, especially during and after activities that release VOCs.
- Air Purifiers: Use air purifiers with activated carbon filters to capture and neutralize VOCs.
The List of Most Effective Air-Purifying Plants
Selecting indoor plants for air purification involves choosing species known for their ability to remove various pollutants and thrive in indoor conditions.
Here is a list of some of the best air-purifying plants based on research from NASA and other sources, along with details about the pollutants they remove, their efficiency, light requirements, and general care tips:
1. Peace Lily (Spathiphyllum sp.)
- Pollutants Removed: Benzene, Formaldehyde, Trichloroethylene, Ammonia
- Effectiveness: High – among the top performers in NASA studies for VOC removal.
- Light Requirements: Low to bright indirect light
- Care Tips: Keep soil moist but not waterlogged. Benefits from regular misting to maintain humidity.
2. Spider Plant (Chlorophytum comosum)
- Pollutants Removed: Formaldehyde, Xylene, Toluene
- Effectiveness: High – excellent for reducing VOC levels.
- Light Requirements: Bright, indirect light
- Care Tips: Easy to grow; tolerant of occasional neglect. Requires moderate watering.
3. Snake Plant (Sansevieria trifasciata)
- Pollutants Removed: Benzene, Formaldehyde, Trichloroethylene, Xylene
- Effectiveness: High – effective even in low light and low maintenance.
- Light Requirements: Low to bright light; tolerates low light well
- Care Tips: Water sparingly; drought-tolerant. Avoid overwatering, especially in winter.
4. Boston Fern (Nephrolepis exaltata)
- Pollutants Removed: Formaldehyde, Xylene, Toluene
- Effectiveness: High – excellent for humid environments.
- Light Requirements: Indirect sunlight
- Care Tips: Prefers high humidity and consistent moisture. Mist regularly and provide well-draining soil.
5. Areca Palm (Dypsis lutescens)
- Pollutants Removed: Formaldehyde, Xylene, Toluene
- Effectiveness: High – effective in large spaces.
- Light Requirements: Bright, indirect light
- Care Tips: Requires regular watering and high humidity.
6. Rubber Plant (Ficus elastica)
- Pollutants Removed: Formaldehyde
- Effectiveness: High – strong performance in formaldehyde removal.
- Light Requirements: Bright, indirect light
- Care Tips: Keep soil moderately moist. Benefits from occasional leaf cleaning.
7. English Ivy (Hedera helix)
- Pollutants Removed: Benzene, Formaldehyde, Xylene
- Effectiveness: High – effective but requires careful maintenance.
- Light Requirements: Bright, indirect light
- Care Tips: Water regularly and maintain high humidity. Prone to spider mites; check regularly.
8. Aloe Vera (Aloe barbadensis)
- Pollutants Removed: Benzene, Formaldehyde
- Effectiveness: Moderate to High – good for removing VOCs in smaller spaces.
- Light Requirements: Bright, indirect to direct sunlight
- Care Tips: Requires infrequent watering. Allow soil to dry out completely between waterings.
9. Bamboo Palm (Chamaedorea seifrizii)
- Pollutants Removed: Formaldehyde, Benzene, Trichloroethylene
- Effectiveness: High – especially effective in filtering formaldehyde.
- Light Requirements: Low to moderate light
- Care Tips: Keep soil evenly moist. Benefits from high humidity.
10. Dracaena (Dracaena marginata and Dracaena deremensis)
- Pollutants Removed: Benzene, Formaldehyde, Trichloroethylene, Xylene
- Effectiveness: High – versatile and efficient in removing multiple VOCs.
- Light Requirements: Moderate to bright indirect light
- Care Tips: Water when the top inch of soil is dry. Avoid overwatering and direct sunlight.
11. Golden Pothos (Epipremnum aureum)
- Pollutants Removed: Formaldehyde, Benzene, Xylene, Toluene
- Effectiveness: High – easy to care for and effective in various conditions.
- Light Requirements: Low to bright indirect light
- Care Tips: Very easy to grow; tolerate low light and neglect. Allow soil to dry between waterings.
12. Philodendron (Philodendron spp.)
- Pollutants Removed: Formaldehyde
- Effectiveness: Moderate to High – particularly effective in removing formaldehyde.
- Light Requirements: Low to bright indirect light
- Care Tips: Allow the top inch of soil to dry before watering. Easy to care for and grows well in low light.
*13. Peace Lily (Spathiphyllum sp.)
- Pollutants Removed: Benzene, Formaldehyde, Trichloroethylene, Ammonia
- Effectiveness: High – among the top performers in NASA studies for VOC removal.
- Light Requirements: Low to bright indirect light
- Care Tips: Keep soil moist but not waterlogged. Benefits from regular misting to maintain humidity.
14. Weeping Fig (Ficus benjamina)
- Pollutants Removed: Formaldehyde, Xylene, Toluene
- Effectiveness: High – but sensitive to changes in environment.
- Light Requirements: Bright, indirect light
- Care Tips: Maintain consistent watering schedule and avoid drafts.
15. Chinese Evergreen (Aglaonema sp.)
- Pollutants Removed: Benzene, Formaldehyde
- Effectiveness: Moderate to High – tolerates low light and is easy to care for.
- Light Requirements: Low to moderate light
- Care Tips: Water moderately and avoid direct sunlight. Tolerates lower light conditions well.
Choosing the Best Plants
The effectiveness of these plants can vary based on their care and environmental conditions. To maximize their benefits:
- Diversity: Use a mix of plants to target a broad range of pollutants.
- Placement: Place plants near sources of pollutants or in areas with poor ventilation.
- Maintenance: Regularly dust leaves, water appropriately, and ensure adequate light and humidity to keep the plants healthy.
For the most effective air purification, it is beneficial to have a variety of plants, each targeting different pollutants, to ensure comprehensive coverage of indoor air quality improvement.
Tips for Maximizing Air Purification
- Number of Plants: NASA recommends 15 to 18 good-sized plants in 15-20 cm (6-8 in) wide pots to improve air quality in a 1,800 square-foot (approximately 167.2 square meter) house.
- Placement: Place plants in personal breathing zones, such as near desks, beds, or sitting areas, for the best effect.
- Maintenance: Regularly wipe leaves to remove dust and ensure plants are well-watered and healthy.
In conclusion, incorporating indoor plants into your living space is not only a design choice but also a health investment. By selecting plants that are known to filter out specific pollutants, you can create a cleaner, healthier indoor environment. Consider the light requirements and maintenance needs of each plant to keep them thriving and maximizing their air-purifying potential.
References
- National Cancer Institute. (2023). Formaldehyde and Cancer Risk. Retrieved from https://www.cancer.gov/about-cancer/causes-prevention/risk/substances/formaldehyde/formaldehyde-fact-sheet
- U.S. Environmental Protection Agency. (2023). Formaldehyde. Retrieved from https://www.epa.gov/formaldehyde
- International Agency for Research on Cancer. (2018). IARC Monographs on Benzene. Retrieved from https://monographs.iarc.who.int/wp-content/uploads/2018/06/mono120.pdf
- U.S. Environmental Protection Agency. (2023). Benzene. Retrieved from https://www.epa.gov/benzene
- U.S. Environmental Protection Agency. (2023). Trichloroethylene (TCE). Retrieved from https://www.epa.gov/trichloroethylene
- Agency for Toxic Substances and Disease Registry. (2021). Toxicological Profile for Trichloroethylene (TCE). Retrieved from https://www.atsdr.cdc.gov/ToxProfiles/tp19.pdf
- PubChem. (2023). Xylene. Retrieved from https://pubchem.ncbi.nlm.nih.gov/compound/xylene
- PubChem. (2023). Toluene. Retrieved from https://pubchem.ncbi.nlm.nih.gov/compound/toluene
- PubChem. (2023). Acetone. Retrieved from https://pubchem.ncbi.nlm.nih.gov/compound/acetone
- Agency for Toxic Substances and Disease Registry. (2021). Toxicological Profile for Acetone. Retrieved from https://www.atsdr.cdc.gov/ToxProfiles/tp21.pdf
- PubChem. (2023). Ethylene Glycol. Retrieved from https://pubchem.ncbi.nlm.nih.gov/compound/ethylene-glycol
- Agency for Toxic Substances and Disease Registry. (2021). Toxicological Profile for Ethylene Glycol. Retrieved from https://www.atsdr.cdc.gov/ToxProfiles/tp96.pdf
- U.S. Environmental Protection Agency. (2023). Methylene Chloride. Retrieved from https://www.epa.gov/methylene-chloride
- Agency for Toxic Substances and Disease Registry. (2021). Toxicological Profile for Methylene Chloride. Retrieved from https://www.atsdr.cdc.gov/ToxProfiles/tp14.pdf
- U.S. Environmental Protection Agency. (2023). Perchloroethylene (PCE). Retrieved from https://www.epa.gov/pce
- Agency for Toxic Substances and Disease Registry. (2021). Toxicological Profile for Tetrachloroethylene (PCE). Retrieved from https://www.atsdr.cdc.gov/ToxProfiles/tp18.pdf