Urban agriculture and urban gardening are hot media topics. Crop mobs roam our cities; spade forks and rakes in hand, searching for a piece of available land to churn. Dig they must but do they know the risks. I think not.
Following is a recent thread from the American Community Gardening Association listserv that turned up in my RSS reader.
Names have been removed but there is no further editing. This conversation illustrates a significant problem that is largely swept under the rug by both the USDA extension program and other gardening organizations including the National Gardening Association.
The following quote is by the person in Canada who initiated the thread. No one on the list questioned her conclusion, nor do I.
"What is evident from this conversation today is that a few of us have some knowledge about soil toxins, but most of us, (I include myself) don't know very much."
Not only do most gardening sites under publicize the threat of urban soil contamination, they also ignore what is arguably the safest solution. Portable micro gardens (aka sub-irrigated planter systems (SIPS) are the most hygienic way to grow food in the city. They also save water and provide in the range of 50% greater productivity than in-ground growing.
While soil remediation may be a longer term answer in some situations, the best and safest quick fix is to grow food in portable micro gardens.
From the ACGA listserv:
Fri, 04 Mar 2011 04:24:06 -0800
Last year the ACGA partnered with the food movement people for a telephone conference on Brownfields. I just listened to it last night. Ann Carroll from the EPA (wish we had an EPA in Canada) talked about gardens on urban soils and the suites of contaminants which might possibly be in urban soils. There are lots of them. But any of you who haven't thought about the use of the land you garden on before you started your garden, please think about that. We know that air is polluted and that water is polluted too, why don't we think that soil could be polluted as well... I have contacted Ann and asked her to provide me with a list of chemicals as well as the other stuff that could be in soils. I will share these when I receive a reply from her. Gardening has become a big venue for the poverty industry here in Manitoba and it is managed by people who have degrees in people management. They understand very little, if anything about science, and chemistry, botany etc scare them alot, so they are sticking their heads in the sand about contaminated soils. They broadcast far and wide about how they are helping poor people with nutrition, but do not want to even consider the possibility that they are poisoning people with veg grown in toxic soils. I know that in a few jurisdictions governments are aware of this and have tried to educate gardeners. If you are from one of these jurisdictions could you please share? Denver was mentioned as a best practice type of place for site selection for community gardens. Denverites , could you share? Thanks,
Fri, 04 Mar 2011 04:47:37 -0800
In New York City, many, if not most of the community gardens are located on sites of buildings that have either burned down or been torn down. A major soil contaminant, here, is residual lead that came from lead paint in the building debris that filtered into the soil. There has been a major initiative among the various community gardening entities - New York City GreenThumb, The Trust for Public Land and New York Restoration Project - to test the soil in the community gardens for lead and other heavy metals (as well as general pH and nutrients, etc.). Gardeners are encouraged to remediate any problem areas with heavy applications of compost and/or avoid planting edible crops on contaminated soils. Traditionally, community gardens on City-owned property were required to plant only in raised beds with fresh soil/compost to try to avoid contact with potentially lead-contaminated soil.
Fri, 04 Mar 2011 07:02:14 -0800
Hi, Lead paint is going to be an issue for most locations that had structures predating 1978 or so (I don't remember exactly when they were phased out). Other issues you may face can include volatile organic compounds (VOCs) that were dumped in an area before environmental regulations, such as the massive Superfund site in the Greenpoint section of Brooklyn, NY, or for example, any location that might formerly have been a gas station. I know of one community farm in Baltimore that uses mostly raised beds overlying geotextile because they don't trust the underlying soil, but that wouldn't be of much use against said VOCs. I personally can't tell you offhand what needs to be tested beyond heavy metals in soils- the tests are specific and not all-encompassing. If anyone does know then that would be a great resource.
Fri, 04 Mar 2011 12:06:40 -0800
There is a fascinating field of research called phytoremediation. While it isn't something your garden wants to take on, members of your community who are patient and committed to cleaning up the community might be willing. Grass roots cleanup campaigns are fairly common, and I was part of one involved with PAH (a byproduct of combustion), asbestos, mercury, lead, and uranium. The cleanup successfully converted the site to a children's museum and outdoor play area. Although we did not use the phytoremediation method, which takes years, it is an important new cleanup strategy.
Basically, the site is planted with species known as hyperaccumulators. These plants exceed other plants in their uptake of heavy metals and/or the conversion of large toxic molecules to smaller harmless molecules, such as CO2, H20 and NH4. Plants used include sunflower, amaranthus, ragweed, poplar, brassicas, sugar beets, barley and other grasses and grains, and many more. You raise the plants, cut them down, and take the plant material to the land fill for disposal. The plants can't be burned or you would just return the toxin the local environment. Plants can clean up about 15% of the toxins in 3 years ... so you can see 100% cleanup is several years down the road (over a dozen). Also, plants can't clean up deep soils (below their roots).
A long list of phytoremediation plants can be found here: http://en.wikipedia.org/wiki/Phytoremediation,_Hyperaccumulators
This email is probably off subject, but the point I'm trying to make is the ability of plants to uptake toxins means you can't immediately raise a vegetable garden on a toxic site, but the same capacity of plants can be used for nondestructive environmental cleanup by a patient group of environmental stewards.
I would recommend you find out what you are truly dealing with by taking multiple samples of soil across the site, mix them thoroughly together in a bucket, put a couple spoonfuls in a plastic bag, and deliver the sample to an environmental analysis lab. Each toxin you test has its own charge, so you should inquire about the prices first. Also I was able to borrow a geiger counter from the county health department since we suspected uranium (and were correct). I found the state and county health departments to be great allies in the cleanup effort.
Fri, 04 Mar 2011 12:16:14 -0800
Thanks sooooooooo much for your thoughtful comments and link to info about phytoremediation. I'd heard a little about that, but I'm so glad that you brought up the topic and let us know a little more about it and your experience. I've read some info about phytoremediation being used for removing toxins from water, but forgot about it being used for soil, even though it's a long-term project. Not off-topic at all, imho. This is what I love about this group....lots of very helpful, practical, first-hand shared knowledge. BTW, our gardens are doing soil tests in multiple sites, combining them, etc. and sending them to University of Massachusetts for analysis. They are very thorough and reasonable cost.
Fri, 04 Mar 2011 12:28:19 -0800
Good suggestion about using the university's lab.
The nice thing about dirty sites is they are often nearly free of charge. No one wants to clean them up, even if they are well located. Ours was owned by the city and they repeatedly tried to sell it without success. No one wanted to pay for the cleanup. That' why we got involved. They agreed to give us a free building site if we cleaned it up.
I suppose a community garden could take on a brownfield with a similar strategy. Commit half of the space to phytoremediation, and half the space to raised, protected beds. Then after a dozen or so years of phytoremediation, switch sides.
Grant agencies just love feel-good projects like that.
Fri, 04 Mar 2011 13:08:54 -0800
There are different plants that will clean up certain chemicals. Takes only a season or two. I do not have the data.
Fri, 04 Mar 2011 13:58:38 -0800
I think they use mainly bacteria for the breakdown of polyaromatic hydrocarbons (PAHs) and other VOICEs- the plants would be ideal for removing heavy metals and radioactive materials. As for asbestos and other fibrous minerals, I don't know what you can do beyond keeping the soil as undisturbed as possible. Asbestiform minerals are naturally occurring (they could be present in your soil naturally, depending on the local geology), so the best strategy I can think of is to get them aggregated with other soil particles by minimizing unnecessary tillage operations and building the soils organic matter content (see other emails regarding no-till agriculture). Also, be aware that removal rates may not change with time. This means that you'll need to calculate it using a half-life approach. If it takes a given chemical a given time t to decrease to half, then a 2t the concentration will be a quarter, at 3t one eighth, at 4t one sixteenth, etc.
Fri, 04 Mar 2011 17:18:01 -0800
I think you are right, bacteria break down poly aromatic hydrocarbons, but these bacteria are not everywhere. What is evident from this conversation today is that a few of us have some knowledge about soil toxins, but most of us, (I include myself) don't know very much. I would like to point you back to the Teleconference of 2010 with Ann Carroll from the Brownfields Remediation section of the Environmental Protection Agency. She mentioned alot of things which are worth going into. For instance that if a landowner gets soils tested, then they are legally liable for damages, so the owner does not like to do this. But the EPA will do it and also has a grant for remediation and they will help you. Denver was mentioned as having a state of the art site selection programme for community gardens. The first phase involves determining what is there. Ann also talked about 'clean' soil and what 'clean soil' means. I guess I threw this out to the list serve because I am writing a resolution for a Women's Council and well, here it is... the thing is I have to write a backgrounder. So I went to listen to the Brownfields Teleconference from last year (I do get around to things, given enough time) and I got a eye opener, there is alot more than heavy metals causing unhealthy soils. Asbestos for one. And if you have that in your soil it won't make any sense to do the gardens by half. So I thought I should go back and re write the resolution. There are whole suites of toxins to be aware of. Ann Carroll also mentioned that Cornell has done two papers on community garden soils so I will hunt them up. Cornell is just such a resource. We have nothing like it in Canada, well Guelph in a way, maybe. But what burns my you know what is that it is poor people mostly who are gardening in community gardens and as if they don't have enough on their plate, adding a load of toxins to it is just too much, it is an offence to justice. I've got to make this about more than heavy metals. God invented winter so gardeners could do other things. We are still up to our necks in snow. And in other parts of the world the witch hazel is flowering. Sigh...If anybody has the time to read the attached and comment, I would really appreciate.