The 'green' side of pumpkins — purging pollution from contaminated soils

While parents and youngsters are busy carving jack-o-lanterns in preparation for Halloween, Canadian scientists are hard at work on another way to use the popular yellow-orange plant. New research shows that pumpkins can clean up soil contaminated with DDT and other pollutants.

In a greenhouse study, members of the Cucurbita pepo species — including pumpkin and zucchini — demonstrated the ability to remove DDT from soil, suggesting a potential "green" technique for cleaning up sites contaminated with DDT, PCBs and other harmful compounds.

The report is scheduled to appear in the Nov. 15 edition of Environmental Science & Technology, a peer-reviewed journal of the American Chemical Society, the world’s largest scientific society.

DDT was applied widely as an insecticide in North America until it was banned in 1972. Some developing nations still use DDT for protection against typhus and malaria, and it endures for long periods of time in the environment, posing a potential health threat to humans and animals.

"Persistent organic pollutants" like DDT, PCBs and dioxins are difficult to remove from soils because they are not water soluble, and the difficulty increases with the passage of time. To clean up contaminated sites, it is typically necessary to excavate the soil and place it in a landfill or burn it in a high-temperature incinerator.

"Phytoremediation offers a ‘green’ solution to cleaning up contaminated sites," says Ken Reimer, Ph.D., a chemist at the Royal Military College of Canada and corresponding author of the paper.

Phytoremediation broadly refers to the use of plants to take up contaminants from the soil. In the case of pumpkins, rather than being eaten, both the plants and their vines would be cut down after they ripen and then composted to reduce their volume before being disposed of in landfills or incinerated.

"Our research has shown that members of the Cucurbita pepo species, including pumpkins, are particularly effective in this regard," Reimer says.

Reimer and his coworkers, Alissa Lunney and Barbara Zeeb, conducted a greenhouse study of five plant species: rye grass, tall fescue, alfalfa, zucchini and pumpkin. The researchers used soil from a site in the Canadian Arctic where DDT had been sprayed to protect workers from mosquitoes.

"The cold temperatures meant that the contamination was virtually identical to the technical grade DDT mixture that had originally been used," Reimer says. "We could therefore examine the ability of [the plants] to ‘suck’ the DDT out of the soil that had been contaminated with DDT for several decades."

Pumpkins took up the largest amount of DDT, while another member of the Cucurbita pepo species — zucchini — came in second at about half the pumpkins’ accumulation. This success could be due to the large mass and volume found in members of this species, the researchers suggest.

Phytoremediation with pumpkins would be most useful at small sites where cleanup is less urgent, Reimer says. Ideally, the plants would grow undisturbed until they are harvested — for disposal rather than for food — at the end of the season, and the process could be repeated for several planting cycles.

While the technique is not likely to replace traditional methods any time soon, phytoremediation could offer an inexpensive and environmentally friendly alternative, especially in small communities and developing countries where money is a major obstacle, Reimer says.

In a more recent unpublished study, the researchers found that pumpkins may also be useful in cleaning up soils contaminated with PCBs — another widespread pollutant that persists in the environment.

Reimer and his colleagues are also trying to identify other plants that can do the same job, including non-edible crops to help ensure that local wildlife don’t eat the contaminated plants.

20-oct-2004