Researchers at the University of Washington have genetically modified a common houseplant — pothos ivy — to remove chloroform and benzene from the air around it.
Photo: Mark Stone/University of Washington

Burrowing into a new niche of phytoremediation, researchers at the University of Washington have added rabbit DNA to pothos ivy, enabling the plants to clean carcinogens from the air in homes.

Dr. Stuart E. Strand is research professor emeritus in the University of Washington’s Department of Civil and Environmental Engineering and author of a study in Environmental Science & Technology. He says he and his colleagues modified the houseplants, in part, because no device currently in existence is able to remove volatile organic carcinogens (VOCs) such as benzene and chloroform from the air in homes.

“No high-energy or activated carbon devices can do what our plants can,” he says.

Problematic pollutants

Pollutants that can cause cancer in humans and animals concentrate more in the air in houses and apartments than in schools and offices, Strand says.

“Many studies of homes and apartments [in] developed countries — modern cities — around the world have shown that benzene, formaldehyde, chloroform and a few other of these pollutants are at levels that in some houses, approach levels that would be regulated in an industrial setting,” Strand says.

Several household activities account for this. For instance, municipalities treat drinking water with chlorine to remove disease-causing bacteria. This makes the water safe to drink, Strand says. But when the water heats through a hot water heater for showering or washing and hits the air, the chloroform in the water releases as a gas and becomes carcinogenic to animals. It is also a suspected human carcinogen.

Benzene, meanwhile, is a proven human carcinogen, says Strand, who wrote in the study that benzene “originates from fuel storage in attached garages, outside air, and environmental tobacco smoke.”

The team behind the modified houseplants. From left to right: researchers Ryan Routsong, Long Zhang and Dr. Stuart E. Strand
Photo: Mark Stone/University of Washington

Clearing the air

Genetically modified plants are a perfect vehicle for air purification, Strand says. Much of his environmental engineering work is in phytoremediation. Plants have excess energy that allows them to acquire new genes and, subsequently, take on roles like air-pollutant removal.

Strand and his colleagues chose pothos ivy — Epipremnum aureum — for their work in part because it tolerates low light, has a large amount of foliage and grows steadily. Good for GMO biosafety, it is also gibberellin-deficient and does not flower in North America, Strand says, so in wild populations, there is no sexual transmission of genes and no pollen to spread those genes.

Before beginning their study, Strand says the researchers knew from completed work within the scientific community that pothos ivy can be transformed. So, they modified that method until they could transform the plant themselves.

Strand and his colleagues took a rabbit gene sequence that is similar to DNA found in humans and other mammals. The gene produces an enzyme that detoxifies chemicals in mammals but can create free radicals in the process, initiating cancer-causing processes. This is why the scientists placed the gene in plants.

For plants in the home to be able to effectively remove hazardous molecules from the air, they must also be placed inside an enclosure with a device that can move air past their leaves, such as a fan.
Photo: Mark Stone/University of Washington

They converted the sequence to an amino acid sequence and used the appropriate codons, or “words,” that allowed the plant to make protein, Strand says. “We’ve also put that gene under the control of synthetic promoters, which are the little pieces of DNA that sit in front of the gene, that tell the cell to transcribe that gene and make the protein from that gene,” he says. “We put promoters in there from plants that are on all the time.”

Later, the researchers placed the small GMO plants in vials with benzene and chloroform, Strand says. “We do our experiments in sterile conditions just with the plant in the vessel,” he says. “When we do that and compare them to unmodified, what we call ‘wild-type pothos ivy,’ the wild-type pothos ivy barely removes any benzene — maybe 5 percent or so. The significance of that removal is borderline in terms of the statistics of the data, whereas the genetically modified plant removes all of the benzene in the vial in about seven days.”

While unmodified pothos ivy removed roughly 5 percent of benzene, it didn’t remove any chloroform, Strand says. But the modified plants removed all of the chloroform even faster than they removed all of the benzene.

Bringing the houseplant to the house

The Canadian Food Inspection Agency (CFIA) approved the genetically modified pothos ivy for sale; frost kills pathos, and all of Canada experiences frosts. The ivy is still pending approval in the United States, as it grows outside in Southern Florida, Southern California and possibly parts of South Texas. The researchers are conducting experiments to show the USDA Animal and Plant Health Inspection Service (APHIS) that the modified ivy is not invasive or resistant to herbicides.

For Canadian markets and, if approved, U.S. markets, Strand says he would like to sell the plants with a window-sized miniature “greenhouse” with a fan blowing across it to help the air pollutants get to the plants. The ivy should be able to remove pollutants from the air with the same efficiency as particle filters, which remove most particles that pass through them, Strand says.

The University of Washington is currently looking for Canadian partners to license its plants and miniature greenhouses to, Strand says. “We want them to propagate the plants, serve as a wholesaler and make contact with home-improvement stores and the horticulture outlets … There is quite a market here if we can find someone who is willing to step up to this GMO thing,” he says.