How Pumpkins Pull Up Pollutants

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In a more recent unpublished study, the researchers found that pumpkins may also be useful in cleaning up soils contaminated with PCBs — another widespread pollutant that persists in the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

4 thoughts on “How Pumpkins Pull Up Pollutants”

  1. I learn something every day.   I’ve never heard of Milloy and just put up that DDT link because it was one of the ones that popped up at the top of a Google DDT search.  Guess you didn’t want to hear THAT.  I actually thought that the junkscience take on DDT was certainly not the norm, but I was just skimming like I do on lots of the links I post, and I’m all for airing different viewpoints, so I linked it.  Now I know to look at this one a little more closely.  Thanks.

  2. The internet’s greatest strength is also its greatest weakness… anybody can publish anything.

    That’s quite an impressive list of facts he’s got there… carefully selected I’m sure. “Politically unpopular” indeed :-)

  3. It really is mind-boggling the things plants can do. I actually did a report on bio-remediation for a tech writing class, although focussing more on heavy metal fixing than organic contaminants. There’s a huge range of plants that’ll pull contaminants out of soil.

    Problem is, and this was only mentioned in passing at the end of the article, is that one of the big problems with pollutants in the soil isn’t that they’re in the soil. The problem is that the plants pull them out of the soil and they get a little more concentrated. Then herbivores eat the plants and the pollutant gets a little more concentrated – sometimes a lot more, depending on how much contaminated plant matter the animals eat. Then carnivores eat the herbivores and the pollutant gets even more concentrated. Creatures at the top of the food chain (like us humans) get the most concentrated dose of this crap! So if the plant is edible to any local creatures, it has to be protected from those animals. We don’t want it getting into the food chain…

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