Get the Lead Out – Sunflowers love Heavy Metal

Dumbfounded, I watched the toxic sunflowers sail over the fence — seeds, heads, stalks, and all. It was one more comic moment in the struggle to bring phytoremediation, the use of green plants to clean up toxic soil, out of the laboratory and into the hands of backyard and community gardeners. I hopped the fence, collected the plants from the empty lot, and routed them towards their proper new home, Milwaukee’s lined landfill.

Using sunflowers to clean lead out of soil has become popular in activist gardener circles, thanks in part to widely-publicized efforts by Common Ground volunteers in post-Katrina New Orleans. This past fall I visited two current phytoremediation (“fido-ree-mee-diation”) projects, and spoke with one of the founders of the 2006 Common Ground sunflower campaign. These activists are tackling soil toxicity head-on by growing sunflowers in lead-contaminated soil, harvesting them after the plants have sucked up some of the heavy metal, and disposing of them like hazardous waste. With every crop the soil gets cleaner.

Low-tech, low-cost tools for Do-It-Yourself soil remediation are desperately needed, and bioremediation might be the key: many plants, mushrooms, and bacteria can be used to take up toxic metals like arsenic and mercury, and break down organic chemicals like pesticides and diesel fuel. Traditional cleanup methods include removing toxic soil and putting it in a landfill or chemically washing it, techniques that are expensive, wasteful, and rarely benefit poor people. Lead in particular is a problem in urban areas where as much as twenty percent of children might face lower IQ’s, attention deficit disorders, and behavioral problems from high exposure. Furthermore, communities organizing to build food security need to restore soils full of leaded house paint, gasoline, and battery remains.

Phytoremediation is not new, but transferring the available research into good guidelines for smaller, DIY projects is tricky. For more than 20 years, capitalist heavyweights like the United States Military, Dow Chemical, Chevron, and Ford have been investing in the field. Most research has been done in controlled laboratory conditions, not in field experiments that reflect nature’s great variety. The published case studies that do exist are mostly industrial scale and report mixed results. Lead cleanup with sunflowers is chemistry, not magic; the process is affected by numerous variables, including soil pH, the form of lead in the soil, and the variety of sunflower used. Since phytoremediation is still experimental, soil testing is an important part of knowing whether it’s working. Although soil lead tests are cheaper than others, the expense of repeated testing is a common hurdle for low-income projects.

Despite the difficulties, sunflowers are a promising tool enabling people to take soil clean up into their own hands. Several positive, field-based test studies have been published recently in scientific journals, and one of the groups I interviewed for this article is doing their own New Orleans-specific experiment. Using phytoremediation safely doesn’t hurt the soil and probably helps, as Scott Kellogg and Stacy Pettigrew point out in their recently-published book, Toolbox for Sustainable City Living, which includes excellent guidelines for soil cleanup.

Milwaukee mix-up

I heard through the grapevine that an old friend of mine was working at a community health clinic in Milwaukee, WI, and was a part of a project using sunflowers to remediate the soil in the clinic’s garden for chronic care patients. I stopped by for a visit, excited to learn something from their project.

When I arrived, my friend told me that we could certainly visit the clinic garden, but there wasn’t much to see because the sunflowers were already harvested and in the compost pile. “What?” I replied, “You can’t put those sunflowers in the compost pile- they might be full of heavy metals!” A little knowledge can be dangerous, I realized. We got in touch with the head gardener and arranged to pull the contaminated plants out of the hopefully not-yet-frozen compost pile and put them in the dumpster.

On the next garden workday we biked the 8 miles under grey November skies down to the clinic. The clinic was sited on an old industrial site and the factory rubble had been topped with a thin layer of topsoil and sod. The garden beds were all raised, but sunflowers had been planted around them to clean up the soil around the beds. The paths were covered in woodchip in an effort to add organic matter and keep the potentially contaminated dust off the vegetables and away from children’s hands. I also learned that while they had researched the history of the site to understand the past soil contamination, they had not done any soil testing to see what was actually in the layer of topsoil, rendering their sunflower-based cleanup essentially a good-faith effort. Quite possibly the topsoil was clean since it had been brought in to cap the site.

Let’s be clear: lead is a heavy metal, an element, by definition something that cannot be broken down by plants. As we worked, we discussed the basics of phytoremediation. Some plants accumulate toxic elements like lead, cadmium, mercury, and arsenic, requiring that the plant be harvested and disposed of in some appropriate manner. Other contaminants, like diesel fuel, pesticides, and fertilizers — which are organic compounds made of chains of carbon, hydrogen, oxygen, and possibly other atoms like chlorine — can be broken down into harmless carbon-based compounds by secreted root enzymes and microbial activity hosted by some roots, as well as by some mushrooms. When the clinic gardeners put the sunflowers in the compost pile, they were essentially adding heavy metals to the compost that would later be mixed into the raised beds.

There is quite a bit of debate about what to do with harvested toxic plants, especially in the DIY community. Industrially, plants may be incinerated, composted, or chemically treated to leach out the heavy metals. If you don’t live near an old mine shaft, appropriate disposal means at the very least making sure the bagged plant material goes to a lined landfill, or possibly taking it to household hazardous waste sites. It could also be carefully composted before disposal, but only in a separate, enclosed area, to prevent the lead from leaching out as the plants break down.

At the clinic, the sunflowers heads were still fully seeded even though it was late fall. We wondered if the plants transmitted any heavy metal load into the seeds, and if animals had shied away from the seeds due to a potential bad taste. I later read that there is some evidence suggesting that seeds of sunflower plants used for remediation have an almost negligible amount of heavy metals, which would still make it a bad idea to eat them, but would allow the oil to be used for industrial purposes (Madejon et al). I also read that animals do seem to avoid plants naturally high in heavy metals due to their bad taste (Henry). When I saw my friend’s co-worker throwing the plants over the fence in that misguided attempt to seed sunflowers in the empty lot, I realized again how complicated the issue is. Safe phytoremediation means posting signs advising against eating the plants, and emphasizing that the plants are toxic once they’ve done their job.

Old toxins, new energy

Hurricane Katrina didn’t necessarily bring more lead to New Orleans’ already toxic soil. It did, however, bring a flood of volunteer energy geared towards finding creative, accessible techniques for cleaning up the city at the mouth of the entire Mississippi basin. One of the projects started by Common Ground Relief volunteers was the Meg Perry Healthy Soil Project, which ran a sunflower-planting campaign in 2006. After I witnessed the confusion around bioremediation in Milwaukee, I wanted to find out more about one of the first well-publicized activist uses of sunflowers for lead cleanup.
I tracked down Emily Posner, one of the founders of the project along with veteran gardeners Starhawk, Lisa Fithian, and Scott Kellogg of the Austin-based Rhizome Collective.

One of the first things Healthy Soil Project volunteers did was independently verify the post-Katrina soil analysis done by the EPA and the Natural Resources Defense Council. Already-high lead concentrations had been spread around by the floodwaters. In 2006, forty percent of New Orleans properties were in areas with soil lead content over the EPA residential limit of 400 mg Pb/kg soil. Common Ground recommends following lower limits: the Canadian standard for children’s play areas is 140 mg/kg soil lead, while the agricultural soil lead limit is 11 mg/kg!

The sunflower project really got off the ground during Spring Break when volunteers planted sunflowers in people’s yards and adjacent empty lots. There are a number of plants that accumulate lead, including Indian and Japanese mustard, scented geraniums, corn, penny cress, and sunflowers. Emily said they chose sunflowers for the summer project because “sunflowers can grow much better than Indian mustard down here in the summer time. You can’t really use Indian mustard because it’s too hot; they’re a brassica.” Eventually they used Indian mustard during the cooler winter months, in a two-pronged approach.

The Healthy Soil project chose Giant sunflowers because of their prolific roots systems. Wide-spread root systems are important for two reasons. First, experiments are still being done to determine where exactly the lead ends up in a sunflower plant. While it’s more desirable for the lead to be transported up into the stalk and leaves, making it easier to harvest the sunflowers without worrying about pulling up the roots, I found several studies indicating that a generous portion of lead remains in sunflower roots (Nehnevajova et al 2007; Rock 2003). Sunflowers have a strong tap root that can penetrate down 6.5 ft, and an extensive lateral spread of root near the surface. Phytoremediation is only effective in the root zone, which typically includes 8-10 inches of soil below the surface, where most soil contamination usually is. Perhaps sunflowers are effective at removing lead from deeper soil horizons with their branched taproot. Pulling up a long taproot is not realistic, but it is important to include as many roots as possible when the plants are harvested.

Extensive root systems also help combat potential groundwater contamination during cleanup efforts. One challenge with lead is that it is “molecularly sticky”: lead wants to be attached to something, whether it’s joining with soil organic matter, clay particles, or forming complexes with carbonates, phosphates, and other soil molecules. There are very few free lead cations (Pb2+) available in the soil for plants to uptake. What lead the plant does absorb tends to complex with plant nutrients in the roots, instead of traveling up into the plant shoots. In other words, lead is not very bioavailable.

Fortunately, soil amendments can be added to make the soil more acidic, ideally with a pH around 5.0, which makes the lead more soluble while still allowing plant growth. Backyard gardeners can add sulfur, coffee grounds, or pine needles. Many published case studies and industrial operations use synthetic chelating agents like EDTA (ethylene-diamine tetraacetic acid), which are organic compounds that surround metals to inactivate them, preventing metal atoms from precipitating with soil molecules, for example. One of the great quandaries of metal phytoremediation is that soluble lead that is bioavailable to plants is also bioavailable to humans, and available to contaminate groundwater. It is particularly easy to add too much EDTA and essentially just leach all the lead into the groundwater, instead of making it gradually available to plants at the rate they can absorb it.

“Everyone recommends adjusting the pH. We tried to do that with sulfur,” Emily said. “One strategy we used to try to confront [groundwater contamination] was that we did a massive, almost scatterseed project so the root systems of the sunflowers really dominated the plots of land.”

In late summer 2006 they harvested the sunflowers with machetes, making sure to get the whole plant including the roots, and chose to contain the potentially contaminated plants in plastic bags and dispose of the bags in a lined landfill. “That’s a huge debate, what to do with the plants now that they’ve accumulated lead,” Emily noted. “Our solution isn’t the best solution but we had no other choice really. Some folks would say you should do some composting [of the contaminated plants in an isolated pile] and then contain the lead in that spot. But resource and space-wise we thought it would be best for us to have it contained with all the other toxic shit that’s in landfills.”

A major part of any clean-up project is follow-up soil testing, but it was hard for the Healthy Soil project to accomplish this due to issues with funding and personnel. “One of the mistakes I learned was that . . . gardens are long term. . . . You put a seed in the ground and you have to wait 40 to 120 days for it to produce, and you have to take care of it the whole time. It’s a constant project; it’s hard to have that kind of sustained interest. But the financial thing was also a huge barrier. It was hard to keep going when we were having trouble doing follow-up testing. We couldn’t necessarily produce our results. . . . Our biggest impediment is . . . develop[ing] a more scientific understanding of what’s going on. Some people say that it works and some say that it doesn’t, and I can’t necessarily answer that question based off of our experience, …because soil testing is so expensive.” With a soil heavy metal test running $30 at the well-respected UMASS Amherst soil testing laboratory, for example, it is easy to see how the repeated testing needed to build a good foundation of data could have been cost-prohibitive.

Critics of the Common Ground project with whom I spoke in New Orleans felt Common Ground’s efforts channeling outside volunteers into solidarity relief efforts made the project less interesting and accessible to city residents, who might have had the long-term commitment necessary to help the project reach a fuller potential. Although the sunflower project is long over, local involvement is something the Healthy Soil Project is addressing with their new focus on community gardens. An active member of the Lower Ninth Ward Urban Farming Coalition, they still provide soil testing to residents looking to start gardens.

Despite the fact that the amount of lead removed from the soil remains unknown, Emily counts the project a success. “Whether it removed a ton of lead or it didn’t, it certainly added to the regeneration of soil by adding to the microbial life through the compost tea that we added, and by turning the soil and getting it uncompacted. Based off of scientific evidence I know we were adding some more life to the soil, as well as adding more life to the community. We were planting some of these lots in places that were so destroyed and devastated; for people to come across lots in places that were filled with sunflowers in bloom I think was a really powerful experience. . . . This type of activity adds life and proves that life can come in some of the most unusual places. I think that was a good stepping-stone for us to establish ourselves, our roots metaphorically and the fact that we do care about healthy soil and we care about having food access. Now we have an opening to be able to work under the guidance of local people who are taking care of some of this land. It’s been a really good experience in that way.”

Filling in research gaps

Across town from the Lower Ninth Ward where Common Ground Relief is based, a community coalition is attempting to answer some of the questions surrounding the efficacy of using sunflowers for lead cleanup. On a sunny afternoon in early December I met Bric
e White, one of the coalition members, at a test plot on a street corner a mile west of Downtown. Brice is the Operations Manager for the People’s Environmental Center (PEC), an organization started after the storm with the goal of making soil testing accessible to the people of New Orleans. Like many groups started in the post-hurricane ferment of 2005-6, PEC has gone through many changes; now their main focus is supporting this sunflower experiment along with students from Dillard University, where the Director of PEC, Dr. Lovell Agwarmgbo, teaches chemistry; students from Delgado Community College; and the New Orleans Food and Farm Network.

Thanks to New Orleans’ long growing season, all the sunflowers had been harvested mere weeks before I visited, and were in the lab awaiting analysis. The project, started this past spring, is the next logical step in Katrina clean-up: “Everybody was talking about remediation after the storm, what the contaminants were, and doing a lot of testing. . . . We decided to find a place were we could test out sunflowers to see if they actually worked. Sunflowers became the thing for everybody to use, to talk about and plant,” Brice explained. “I was discouraged . . . with people coming from the radical hippie punk thing, where they’re like, ‘If you plant the plants it gets rid of the lead!’ But when you look at lead, which is a metal, it doesn’t go anywhere. People don’t even think that far, they just think ‘sunflowers get rid of lead.'”

Brice eventually developed a positive working relationship with Healthy Soil Project phytoremediators, although initially he shared Emily’s concerns about Common Ground’s approach to the sunflower campaign. “I had a lot of backlash against Common Ground . . . for several reasons, about this sort of North-South divide, liberal people coming down to say they know what to do — it’s kind of a classic, too. Some of those people didn’t mean that, but they didn’t stay here long enough to really see projects through. A lot of it’s an organizational problem. But for whatever reason, a lot of sunflowers got planted in New Orleans after Katrina…” This was fine, he pointed out, but any phytoremediation project needs a caveat: “If you’re actually trying to remediate, there’s just not much data. …You can’t plant sunflowers and then say that somehow there’s less lead . . . if you haven’t done testing to at least get a sense of what it does.”

PEC and other coalition members saw an opportunity to fill in some of the research gaps when a donation of sunflower Seedballz arrived. The gift was a trademarked version of a standard seedball with sunflower seeds rolled into a ball of clay to make them easy to grow. Through their connections with Dillard University, the coalition has the testing facilities that the Healthy Soil Project struggled to access.

The test plot is a corner lot on Oretha Castle Haley Boulevard that was donated to CafĂ© Reconcile, a job-training organization for young people. In exchange for upkeep, they were happy to have the lot used as a test site. With a history of several houses now torn down, illegally parked vehicles, and illegal dumping of house foundation material, the lot is typical of New Orleans. Because the study hasn’t yet been published, Brice couldn’t tell me any specific lead content numbers, but presumably they reflect the fairly high background levels of lead in the city.

One early lesson learned was that community-oriented science isn’t easy. Brice and his fellow coalition members encountered numerous difficulties in the process of turning the rubble-filled lot into a functioning field experiment. After trying to till it themselves, they were forced to hire a bulldozer to level the lot. Despite the addition of weed fabric, it was hard to control weeds in the nine experiment plots in the voracious New Orleans environment. The Seedballz didn’t perform well; the hot summer sun baked the clay into a hard ball, and birds picked out the seeds as the balls sat on top of the soil. “Figuring out how to get them to germinate was the real success,” noted Brice. Eventually they ended up burying the seedballs and also planting a crop of black oil sunflower seeds in an effort to not tie the project to one specific patented product, one donation.

Additionally, there was no record of the type of sunflowers in the Seedballz, and type of sunflower does seem to be an important variable in lead uptake. Researchers in Zurich, Switzerland examined the toxic metal accumulation in fifteen sunflower cultivars grown in a field contaminated with sewage sludge (Nehnevajova et. al). Because some metal uptake also varies with the kind of fertilizer used to reduce the pH, they used two different soil amendments, ammonium sulfate and ammonium nitrate. Surprisingly, they reported a wide variety in lead accumulation — almost 10 percent. The most lead, 26.5 mg/kg Dry Weight, accumulated in the Salut cultivar, when the plants were fertilized with ammonium sulfate, while the least amount of lead, only 2.8 mg/kg Dry Weight, was found in the cultivar Alzan, also grown with ammonium sulfate. To make matters more confusing, some cultivars accumulated more lead with the ammonium nitrate fertilizer than they did with ammonium sulfate. Neither of the varieties used in New Orleans, the Giant and Black Oil sunflowers, were included in the study, which used varieties widely available in Switzerland.

Despite the difficulties and multiple variables in the project, Brice said their preliminary results indicate a promising reduction in soil lead content. The study opens the door for future research with a New Orleans, community-based focus. “A lot of people have said they don’t want to use phytoremediation because they say it’s too slow,” he pointed out, “but we thought the results from 1-2 crops were promising enough to possibly use it. Also, the growing season here is longer than a lot of places. If you started first thing in the spring, you could maybe get four crops of sunflowers in. But in a place in the Northeast where they said it was too slow, they probably only got one crop in. All these things are things to look into in the future.” There are other questions as well: “When do you harvest them to get optimum efficiency? Is there lead in the seeds? Are animals eating the seeds, are people eating the seeds?… The simple thing we want to know is, did it take the lead out, and if so, is the first step that you can plant [sunflowers] and harvest them, and make sure you throw them away. Maybe that is a good start. Like all the Common Ground stuff — if they actually knew there was lead, and they planted all these sunflowers and then harvested them, they certainly didn’t hurt anything, and they probably made it better.”

Community-oriented science

In addition to providing valuable data on sunflowers, this project is a good exercise in community-oriented science. I salute Emily, Brice, and all the other intrepid gardeners who are vastly expanding the field conditions under which phytoremediation is used experimentally. By keeping track of what works under what conditions, and doing soil testing when it’s available, we can turn our DIY efforts into a solid body of knowledge created by the communities it serves. This is an excellent example of science working for the people. While we build bridges with sympathetic members of the scientific establishment, we can work towards organizing our own radical science infrastructure, like accessible soil testing labs. Let’s free bioremediation from the clutches of bureaucracy and academia! Bioremediation is a natural chemical process. No doubt there are other tools in the ground that we can use to repair the effects of industrialization, if we take the time to understand them.

Thank you to Emily and Brice for the interviews!


Toolbox for Sustainable City Living, Scott Kellogg and Stacy Pettigrew, South End Press

Gardener’s Remediation Guide, EPA (just being published; contact

ommon Ground Relief,

People’s Environmental Center, Brice White, Operations Manager,


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