Greetings all, For my masters thesis on community gardening, I've dipped into research on soil contamination and strategies for dealing with it. I agree with Robin's inclination to skip soil testing and remediation due to the cost of doing so, and to build raised beds with a barrier between the existing and the imported soil. I gather that there are two reasons for doing this: to prevent plant roots from growing down into the existing soil AND to prevent gardeners (and worms?) from mixing the two soils when cultivating the garden.
I'm interested in the biochar fermentation technique Diann suggested, but I wonder which toxins this method works on. On the website you referenced, I found research on bokashi in composting and impacts on plant growth, but I don't see anything about remediation-- Diann, can you tell us more about your experience? I also wonder whether this technique would be affordable- Diann, what's your experience with the cost of this method? How big of an area have you used it on? I haven't tried this, but I have read about using layer of clean gravel a few inches thick between the existing soil and the imported soil. This allows for good drainage, won't break down over time, and will discourage gardeners from mixing the two layers of soil. I also imagine that the roots of annual plants that have adequate moisture within the imported soil would not reach through the gravel, and that worms would not migrate up through the gravel, but I'm not sure about these last two points. Robin, I imagine you already know this, but you do want to make sure that the imported soil is not contaminated. If you can't afford testing and you're in an urban area, you might not want to take soil donations unless they are from a source that does regular testing/quality control. You also want to make sure you are not using materials for the raised bed walls that would leach toxins. Best of luck! Please let us know what you decide to do and how it works out. Sincerely, Katherine Jacobs On Thu, Apr 4, 2013 at 2:50 PM, Chris Reid <[email protected]> wrote: > On the chance that lead is an issue, here is a quote and link from a > Cornell University piece by Nina Bassuk: (link: > http://counties.cce.cornell.edu/schenectady/new/pdf/ag%20fact%20sheets/vegetables/Lead%20in%20Urban%20grown%20veggies.pdf > > "By far the most important factor was the amount of organic matter in the > soil. Lettuce plants grown in soils with low levels of organic matter took > up much more lead than those grown on soils with high levels (greater than > 25%). With soils of very high organic matter content (40-50% or greater), > no lead uptake was found even if the lead present in the soil was as high > as 3,000 ppm. > > Decomposed forms of organic matter seemed to be better able to bind the > lead in the soil and thus make it insoluble to plant roots. The addition of > organic soils (muck soils) or well-rotted manure-to-mineral soils > containing high lead stopped lead uptake by lettuce plants better than the > addition of fibrous peat moss or un-composted ground up leaves. > > The addition of phosphorus to high lead soils also stopped the uptake of > lead by lettuce plants. The level of phosphorus necessary to accomplish > this, however (200 ppm), was more than is required by plants for normal > growth; whereas, increasing the organic matter percentage in soils benefits > soil structure and water holding capacity. Organic matter can also be > acquired inexpensively by urban residents. > > Other than phosphorus or organic matter, a third soil variable that can > influence lead uptake is soil pH. With another heavy metal, cadmium, soil > pH levels above 6.5 effectively inhibit cadmium uptake by plant roots. With > lead also, low soil pH (under 6.0) increases lead uptake, but unlike > cadmium, higher pH levels, (most often found in urban soils), do not > prevent its uptake." > > It is well worth your while to get the soil tested at least for common > urban contaminants. Otherwise, how does a group know ifitis wasting time > and effort on a severely contaminated site that maose a danger to the > gardeners, or especially to children? > > Lead can contaminate though unwashed soil laden hands, unwashed clean > looking veggies that have dust blown onto them, veggies contaminated by > soil uptake, or dust blown around from exposed contaminated soil on a > contaminated site, whether the actual garden site or the site next door. > > i read a description that makes it easier to appreciate how little lead > it takes to disrupt a childs brain: > > The total tolerable intake of lead for a child 5 years old or younger is 6 > micrograms per day. To put that in perspective, a packet of artificial > sweetener usually contains 1 gram of sweetener. Six micrograms is equal to > six-millionths of the content of that packet, so not all that much. > > "It is easy for a child to obtain more than 6 micrograms of lead per day > in a contaminated environment," said Howard Mielke, a toxicologist at > Tulane University in New Orleans, who also spoke at the AAAS conference. > > link for above quote: > > > > http://www.myhealthnewsdaily.com/3574-produce-from-urban-gardens-could-contain-lead.html > > thus, it is not just absorption by the food that contaminates, it is > contact with the soil itself through dirty hands (wear gloves), and also > blowing dust from areas surrounding the carefully made raised beds ( you > can lay down 6 layers of newspaper and heavily mulch exposed soil with wood > chips obtained free from tree companies), the paper lasts me a year). > > > Coming back to comment about organic matter in soil, it looks important > to remember to top off and mix in new compost each year, because the beds > will drop in height over time as organic matter decomposes. keeping aware > of why you are doing this will help prevent e.g. filling and topping off > with incompletely composted materials or plain soil. > > Hope that helps. The clearer we can be about what is in our urban soil, > the more effective we can be in addressing it. > > Chris Reid > southwestern Connecticut > > By the way, Tanya mentioned using radish seeds for testing for > "pesticides". It is my understanding that the germination tests would > identify high levels of herbicides, but e.g. not something like rat poison > or termite control chemi als. > > > > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: < > http://list.communitygarden.org/pipermail/community_garden_list.communitygarden.org/attachments/20130404/fd4450e5/attachment.html > > > _______________________________________________ > The American Community Gardening Association listserve is only one of > ACGA's services to community gardeners. To learn more about the ACGA and to > find out how to join, please go to http://www.communitygarden.org > > To post an e-mail to the list: [email protected] > > To subscribe, unsubscribe or change your subscription: > http://list.communitygarden.org/mailman/listinfo/community_garden_list.communitygarden.org > -- *Katherine Jacobs, SEED * 732-947-0273 -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://list.communitygarden.org/pipermail/community_garden_list.communitygarden.org/attachments/20130404/11506002/attachment.html> _______________________________________________ The American Community Gardening Association listserve is only one of ACGA's services to community gardeners. To learn more about the ACGA and to find out how to join, please go to http://www.communitygarden.org To post an e-mail to the list: [email protected] To subscribe, unsubscribe or change your subscription: http://list.communitygarden.org/mailman/listinfo/community_garden_list.communitygarden.org
