Can Plants Improve Indoor Air Quality? It Depends On Chemistry
Carmen Drahl | Forbes
Sorry IKEA. The humble houseplant gets my nod for the ultimate in multitasking decor. Houseplants not only provide a pop of color and add to a room’s ambiance, they also remove traces of harmful pollutants, such as formaldehyde, from indoor air. NASA demonstrated some plants’ air purifying abilities in a much-cited 1989 study. Since then, many other scientists have been expanding upon that work.
Indoor air pollution is a legitimate health and environmental problem. Paints, furniture, cleaning supplies and even building materials themselves contribute to buildup of what chemists call volatile organic compounds — compounds that easily evaporate to gaseous form at normal temperatures. Not every gaseous compound is harmful, but at high enough concentrations, some of them can lead to allergies and dizziness, or even have the potential to cause cancer. The indoor air quality issue came to a head in the wake of the 1970s-era oil crisis, when buildings were renovated or designed to reduce energy costs. The blueprints cut down on fresh air exchange in the name of energy efficiency, exacerbating the effects of harmful chemicals. This phenomenon has a name–sick building syndrome. Workers in some industries, such as nail salons, face far higher exposure levels to these chemicals because of the nature of their jobs.
NASA’s 1989 report showed that certain plants could complement ventilation systems to reduce indoor air pollution. Follow-up studies showed that the plants absorb and break down harmful compounds through a variety of different pathways. Niri’s goal was to compare how well plants would work to remove several different volatile organic compounds at the same time.
Niri’s team studied five commonly used houseplants in his region:
• Jade Plant (Crassula argentea)
• Spider Plant (Chlorophytum comosum)
• Bromeliad (Guzmania lingulata)
• Caribbean Tree Cactus (Consolea falcata)
• Dracaena (Dracaena fragrans)
They built sealed chambers in their lab and kept track of how well the houseplants could remove eight different gaseous compounds:
• Dichloromethane (also called methylene chloride)
• Trichloromethane (also called chloroform)
To learn more about how the plants take up the harmful chemicals, the team analyzed pollutant removal rates and removal percentages under different conditions. They tried covering the soil or leaving the soil uncovered, to distinguish pollutant removal by the roots from removal by the parts of the plant above ground. They also tested plants with and without light to mimic daytime and nighttime. Finally, they accounted for each plant’s leaf area when gauging performance.
In line with what prior studies have found, Niri’s team determined that certain plants are better than others at removing specific compounds from air. For example, although all five plants took up acetone, which is a chemical commonly found in nail polish remover, the Dracaena plant was most effective. At a press conference in August, 2016, Niri disclosed that the jade plant was best for removing toluene in his laboratory tests. The Washington Post reported August 24, 2016 that “spider plants were lightning fast – the minute one was placed inside the container, the concentration of VOCs immediately began to go down.”
The bromeliad was the all-around champ — it was good at removing a variety of compounds from the air. However, two of the target compounds, dichloromethane and trichloromethane, proved more challenging for the plants to remove. At the press conference, Niri speculated that this could be due to the chlorine atoms in these compounds’ structures — all the other compounds in the study contain only carbon, hydrogen and oxygen.
According to Bill Wolverton, who led NASA’s original studies, one thing that’s relatively new in this field is the process Niri’s team used to sample volatile organic compounds. Niri’s team used solid phase microextraction coupled with gas chromatography-mass spectrometry. The first part of this technique, solid-phase microextraction, involves a fiber that can extract target compounds from from air, in proportion to concentration, and the second part, gas chromatography-mass spectrometry, identifies and quantifies what the fiber pulled from the air. The microextraction technique lets researchers detect far lower concentrations of compounds compared to prior methods, Wolverton says.
The results reported in 2016 give scientists a better idea of which plants are good for counteracting certain kinds of pollutants, Niri says. Ultimately, though, recommendations should be based on real-world testing. That’s next on the agenda for Niri, and he plans to start by putting plants in nail salons. In this study, his team accounted for each plant’s leaf area when measuring performance. To figure out how many plants you’d need to obtain a certain drop in levels of pollutant compounds, his team will put different numbers of plants in differently-sized salons. “The ratio of [plant leaf] surface area to volume of the room is very important,” Niri said.
It’s extremely unlikely that plants alone can protect manicurists from excessive exposure to hazards. New York state is now requiring ventilation systems in nail salons following a New York Times investigation, one that nail salon owners are still criticizing over a year after its publication. (It’s worth noting that the fallout of the investigation has been complex, and that while a tiny number of critical news reports led to an important reexamination of certain details in the story, the overall thrust of the investigation isn’t being questioned.)
But Niri has a personal story that’s inspiring his research choice. Not long ago, he happened to be with his wife for a trip to the salon. “I waited inside for a while, but I couldn’t stay,” he said, because the smell of acetone positively overwhelmed him. At the time, he was working on air analysis projects, so he looked into nail salon conditions and was saddened to read about the many hazards to nail workers reported by the Occupational Safety and Health Administration and the Environmental Protection Agency. “I thought, ‘maybe I can do something about this,’” he recalls. No matter the outcome of Niri’s future tests, it’s clear that all parties would welcome a way to reduce the costs of keeping workers safe.
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