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Urban gardens & heavy metals  RSS feed

 
            
Posts: 32
Location: Louisville, KY
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I'm wondering if there are any folks out there who have had their urban garden plots tested for heavy metals?  I'm especially curious about plots that seem to have no history of being in an industrial area. 

I ask because I would like to get a clearer idea of what kind of soil in an urban area may be heavily polluted.  As it is, I assume it is "guilty until proven innocent." I assume that the most harmless looking piece of property in an urban area could have who-knows-what buried in it: lead-based paint, battery acid, toxic building materials, and so on.  I've never been able to test a garden plot as throughly as I would like (sending off multiple samples to one of the few labs that test for heavy metals), usually for financial reasons.

I'd love to hear back from a number of people who all say they have had their plots tested and found no traces of heavy metals and that I am worrying about nothing at all, but I wonder if that's the case. 

(BTW: My understanding about the way plants accumulate heavy metals is that heavy metals generally accumulate first in the leaves, second in the flower, and that the fruits are most free of toxins.  Feel free to set me straight on this point.)
 
Joel Hollingsworth
pollinator
Posts: 2103
Location: Oakland, CA
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Kellogg & Pettigrew's book Toolbox for Sustainable City Living discusses industrial contamination in depth: varieties of it, how to research the history of the property to get an educated guess at how much testing might be necessary, and how to deal with it if you find it.

They rehabilitated a brownfield that had been a legal landfill, and then an illegal dump. They've done pioneering work in low-budget bioremediation, and managed to get funding to test for various sorts of contamination in New Orleans: money was mostly related to contamination from floods due to Katrina, but some of the suspect properties had needed funding for testing for decades prior.
 
                    
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watch the shrooms that come up. Many shrooms are accumulators of HM's and other toxins- so much so that that species like coprinus is often associated with lead, and boletes with murcury, etc.

watch the shrooms and get them tested for the most likely suspects- Stamets Mycellium Running covers this in enough depth that it is a reliable leap off point for anyone with this kind of concern for Pb, Cd, Hg As, etc.

im working with a group on Vashon Island WA right now that is diving into this. very neat to do soil remediation with the goal fo growing food in the reclaimed soils. Also, scary..
 
Leila Rich
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Posts: 3999
Location: Wellington, New Zealand. Temperate, coastal, sandy, windy,
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Will, I wanted to turn front my lawn/yard into a productive garden.
My house is over a 100 years old, so a major candidate for lead paint contamination.
I sent samples off to my regular lab, with instructions to test for lead, and if it was considered 'safe', do a regular soil test after.
I purposely took samples from round the houses' 'dripline' where the heaviest contamination would be.  A high result wouldn't be particularly representative, but I'd get a good picture of the worst case scenario...
My test came back over seven times higher than the highest 'safe' level. Good to know!
I have a good garden out the back, so I'm not growing edibles out the front. 
As far as I'm aware, heavy metal contamination is worst in the roots, bad in leaves and not such a problem in fruit/flowers/nuts etc.
From what I've read, remediation is a very slow and challenging process; I was recommended to get raised beds if I must grow edible plants there.
Raised beds on sand suck (literally).
 
Paula Edwards
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There are plants which accumulate heavy metals more than others. I read ages ago that parsley accumulates very much whereas wine grapes are safe.
 
Tyler Ludens
pollinator
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Location: Central Texas USA Latitude 30 Zone 8
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Sunflowers will accumulate heavy metals.  If you're trying to clean the soil of heavy metals you can grow sunflowers very densely for a year or more, burn them, and landfill or toxic waste dump the ashes.

Whatever organism you use to remove heavy metals, remember you can't eat or compost the organism, you must remove it from the garden.

http://www.metrojacksonville.com/article/2010-jun-sunflowers-for-lead-spider-plants-for-arsenic

 
            
Posts: 32
Location: Louisville, KY
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Thanks for your responses, they'll give me food for thought while planning the site this winter.  It sounds like the material in Toolbox for Sustainable City Living is just what I'm looking for. 

And Leila, I hadn't thought about using the riskiest areas for the sample spot: makes sense.  & thanks for the additional info on root accumulation.

And Ludi's comment reminds me about a comment I heard once but have not been able to verify: that there is a group or a company that is able to mine metals from contaminated spots by accumulating them in plants.  Too bad urban sites aren't usually contaminated with gold.


 
Tyler Ludens
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Location: Central Texas USA Latitude 30 Zone 8
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It would make the most sense to refine the contaminated ashes to retrieve the metals - but unless you can find a company that will take your ashes to refine them, you'll probably end up having to send them to toxic waste facility. 

 
                    
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most toxins are rated in parts per million or parts per billion. refining from even a several cubic feet of plant matter wont get you much return.

most companies aimed at this are collecting phytomass from landscape scale projects, like abandoned surface mines and industrial parks. its likely your best bet is to send the material to a waste facility...
 
Tyler Ludens
pollinator
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Yeah, that's what I think ,Deston, there just isn't going to be enough material to justify refining it.  In a perfect world there would be, but that's not what we're living in...
 
Travis Philp
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Posts: 965
Location: ZONE 5a Lindsay Ontario Canada
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Anyone heard of growing carrots in a bed to remove contamination? As Ludi said with the sunflowers, you burn them after harvest.

I wonder about feeding the contaminated plant material to urban gulls instead of burning it and having it go to complete waste in a landfill. I'm guessing those birds aren't exactly toxin free.
 
                                          
Posts: 95
Location: Ferndale, MI- Zone 5b
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^^^ wouldn't those birds shitting that toxic stuff all over kind of nullify the original point?

this is interesting stuff about soil remediation.  i suppose i ought to get the beds around my house tested.
 
Travis Philp
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I didn't imagine that most people have a lot of gulls hanging around their house. My thinking was that you take the carrots with you when you go to an amusement park, or your next dump run. Wherever they tend to congregate to eat toxic crap anyhow.
 
Tyler Ludens
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Location: Central Texas USA Latitude 30 Zone 8
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Doesn't make a whole lot of sense to me to go to the trouble to retrieve the toxins only to spread them around again....

 
Travis Philp
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I figured that burning them puts the toxins in the air to some degree, and taking the ashes to the dump will only temporarily keep them out of the environment.
 
Leila Rich
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Location: Wellington, New Zealand. Temperate, coastal, sandy, windy,
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Will, it's all theory until you get a test. Keep in mind that back/front/distance from house could have a major effect on your results, so you might need to get a few separate tests.
If your place is like mine and contaminated in some areas, there's nothing stopping you growing plants, just avoid edible ones in those areas! I started to freak out about birds and insects eating lead-contaminated pollen, nectar etc, but decided that was getting carried away.
Feeding the soil with organic matter helps to tie up lead, I also put a massive layer of mulch on to keep the lead away from the surface.
My research gave the impression that even using the most effective plants, phytoremediation could take centuries to clean the soil. Centuries!
Then of course you have the issue of dumping your toxic waste for someone else to clean up...
Nightmare. At least with the tests, you'll know what you're in for, and it might be pristine!
 
Delilah Gill
Posts: 35
Location: Southern Georgia
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It was very smart to get testing done. It does take a long time for reclamination of soils from heavy metals according to some of the compost forums I've read including the US Composting Council reviews. Lol, some soils are contaminated with gold, or tailing from old gold mines (see Charlotte, NC).
I agree, use raised beds for now.
Your local soil and water conservation agency can help by supplying maps of the properties that can show the history of a specific property, but urban soils have been moved around a great deal, so many times they are not as effective as one may wish.
There are several plants including trees that do take up heavy metals. You may wish to check out some of the stormwater reclaimation websites (Raingarden) too learn what your local cities and towns may be doing to assist with this issue.
 
Paul Cereghino
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Location: South Puget Sound, Salish Sea, Cascadia, North America
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Regarding hyperaccumulators... some elements are easier then others...

Here is a pretty good list of hyperaccumulators.
http://en.wikipedia.org/wiki/Phytoremediation,_Hyperaccumulators

We get lead and arsenic around here from smelter fallout... lead from paint, and near roads (leaded gasoline).
 
Joel Hollingsworth
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Location: Oakland, CA
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Travis Philp wrote:
I figured that burning them puts the toxins in the air to some degree, and taking the ashes to the dump will only temporarily keep them out of the environment.


For cadmium, mercury, and zinc, it absolutely would put them into the air. Some toxic metals are a lot less volatile.

If I were producing ashes rich in heavy metals, I'd contact a local glassblower or potter about collaboration on an art project. Not everyone is familiar with vitrification (glass/glaze making) as a method of rendering waste safe, but it has a good track record for many varieties of waste.

Concrete is another good way to immobilize heavy metals: many of the worst ones are less soluble in alkali situations than acidic ones, and compete with calcium in most sorts of metabolism, and so combining them with lime renders them safer in two ways.
 
                    
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I read a report a few years back about HM rendered in concrete. It was very discouraging, they continue to leach for years as the concrete weathers. In urban areas concrete in streams is a major source of HM leachate. at one point i was going to bring a bunch of urbanite to my site, as it was cheaper than stone, and was recycled, not mined. That report- which I believe David Eisenberg of DCAT had brought to a natural builders event in portland oregon - changed my mind. Might be cheap to bring in urbanite, but I don't need to bring more toxins home...

DCAT:http://www.dcat.net/
 
Tyler Ludens
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Travis Philp wrote:
I figured that burning them puts the toxins in the air to some degree, and taking the ashes to the dump will only temporarily keep them out of the environment.


Yep, that's true.  It's a real problem. 
 
Paula Edwards
Posts: 411
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The whole world is not pristine anymore. If you buy your veggies, do you know if the farmer got his soil tested? Petrol used to have lead in it.
As for the paint, I would definitively keep a strip clear from any plantings, pave it or whatever. Plants and houses are not good companions. I guess that most dust from lead paint would fall within a meter or so.
It is important that you keep your chicken out of contaminated zones too.
 
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