Can plants get rid of pollutants? Jury is still out

Can indoor plants remove pollutants inside your home? Prompted by WhatsApp messages advocating certain plants as air purifiers, consumers are investing in these plants in the hope of keeping at least their homes free of toxins, even as outside pollution levels hover between ‘very unsafe’ to ‘hazardous’.

Since a couple of WhatsApp messages listed plants certified as ‘air purifiers’ by the American National Aeronautics and Space Administration ( NASA), I decided to check the veracity of these claims and was amazed at the number of studies on the role of house plants in cleaning indoor air.

The trigger was probably the research supported by NASA office of Commercial Programmes and the Associated Landscape Contractors of America and published in 1989. Titled “Interior Landscape Plants for Indoor Air Pollution Abatement”, the research confirmed the role of 12 plants used in the study in removing toxins in the air. However, the two-year research in controlled laboratory environment did not look at atmospheric pollutants like particulate matter (PM 10 and 2.5), nitrogen dioxide, sulphur dioxide, ozone , carbon monoxide or sulphur dioxide that we are grappling with.

The study was limited to three volatile organic compounds –benzene, trichloroethylene and formaldehyde - released by paints, modern furnishings, particle boards, high tech equipment , common cleaning agents, in insulated, energy efficient, modern buildings in the United States, causing what is known as ‘sick home syndrome’.

This work generated lot of interest in the subject and there have been a number of studies on the topic. Researchers at the University of Georgia, for example, screened 28 ornamental house plants for their capacity to absorb and rid indoor air of five different volatile organic compounds (VOC)— benzene, toluene, octane, trichloroethylene and a.pinene and identified five species as having the highest rate of contaminant removal . But the researchers concluded that there was need for further studies to understand the phytoremediation potential of a diverse range of indoor plants. “The variation in removal efficiency among species indicates that for maximum improvement of indoor air quality, multiple species are needed. The number and type of plants should be tailored to the type of VOCs present and their rates of emanation at each specific indoor location”, the research paper titled “Screening indoor plants for volatile organic pollutant removal efficiency,” published in 2009 said. .

Similarly, a study conducted in a primary school in Aveiro, Portugal (Could household plants improve indoor air quality in schools, Department of Environment, University of Aveiro, 2012) said plants might improve indoor air and make interior breathing spaces healthier. It said that plants could lower PM 2.5 and PM 10 .

However, there are also published papers pointing out that while in closed test chambers, plants purified the air, in real-life situations or in buildings, the results have been modest or nil, raising questions on whether a few plants can really purify the air in homes or offices.

Scientists also point out that in laboratory studies, plants are exposed to adequate light – this maximizes photosynthesis and enhances their capacity to absorbs toxins. But the results could vary in homes with inadequate light. Besides, different plants have been found to absorb different pollutants and so you would need a large number of a wide variety of plants to clean the indoor air, not really practical. And most studies have so far dealt only with limited number of indoor pollutants.

The latest article, a critical review of data from a dozen studies , published on November 6 this year in the Journal of Exposure Science and Environmental Epidemiology , reiterates that plants cannot clean air quickly enough to have an effect on the indoor air quality (“Potted plants do not improve indoor air quality: a review and analysis of reported VOC removal efficiencies” )

So the jury is still out on the topic.