Environmental Contaminants in Urban Gardens

The American Community Garden Association (ACGA) held its annual conference in Atlanta recently.  I attended (and much anticipated) a workshop with the title of this blog, given by Patrick Shaw, a Johns Hopkins grad student.  I was very much hoping my long-standing questions to urban soil pollution would be addressed.

When I founded Sugar Creek garden, urban soil contaminants were of particular concern because of the proximity to Sugar Creek- a concrete swale with the potential to deliver unabated metals and chemicals onto our site, its floodplain, given any big storm.  This is one of the main reasons we now know not to turn our streams into concrete.  Natural streams contain vegetation and soils which trap and break down potential garden contaminants, as well as slowing floodwater that causes stream bed erosion.

So I was concerned, about past flooding, about what might be upstream from us and what has been deposited into the soil of our garden.  But with all the research I did on the subject- asking other urban gardeners, reading and even calling the best labs in the country- I could find very little information.  There is not, for example, any standard soil test for urban gardens that gives chemical or metal levels!  Again, there is no test that one can buy to cover the most common pollutants that may occur in urban soil.  I was amazed to discover this.

This was confirmed by Mr Shaw in our conference discussion and in response to my question;  he noted the chemical pollutants are just too numerous to approach with one test and the research only in its infancy.  In short, we dont know what kind of SH*T we've put into our environment and we have no way of tracking it.  Excellent.  I was fortunate to discover, with Sugar Creek, that our site, the engineered floodplain, somehow rarely flooded and thus we have little risk of exposure.  As well, we have 'natural' stream channels above the garden that would intercept any industry or golf course farther upstream.  Still, these relevant concerns about pollution in urban gardening stuck in my mind.

As for metals, he gave us a list of elements-see your periodic table- and advised us to test for all of them.  Of interest, he noted that sites with burned-down houses were particularly contaminated with lead, but lead doesnt readily uptake into our food to toxic levels (except grains). "It's heavy" as a friend of mine pointed out.   Fruit is fire, or light.... i'll have to reference the biodynamic calendar on that one.  So gardening in toxic urban soils, you are much more likely to get poisoned from the air-borne metals (this is where I should have asked my friend, "but if its light how does it get caught by wind"), or through direct contact with your hands in the soil, than you would through eating the food produced on such soil.  News to me.  Wear gloves.  There's also a method of 'engineered raised beds' which allows you to grow on a toxic site without the toxins leaching into your grow area.  But why would you want to be on a 'toxic' site if wind contamination was such a problem?

Someone mentioned post-Katrina waste being ground up and sold as "mulch" and this of course has very high levels of metals from construction debris and sewage...... what?!   The room was peppered with all kinds of questions and comments about the possibilities of environmental toxins in urban gardening.  Doesnt make one feel good about environmental or human health......

On the sewage containing metals, if you use your municipal compost, make sure it is Type A, not containing MSW (mechanically separated waste or Municipal solid waste).  The other options are Type B or untested... or the guy on the phone at the landfill probably doesn't know.

Soil sampling was covered and Mr Shaw mentioned that UMass will test an array of heavy metals, as opposed to most labs which charge separately for each metal.  Also, you could contact profs at different universities and ask them if they have the right equipment to do appropriate samples.... none of which I can remember.  That all sounded a bit..... like i dont have all day everyday to look into this stuff.

He mentioned creosote was actually 'undetermined' as a toxin, but that rail road ties shouldnt be used in your veggie garden because they've picked up so much else from trains over the years.  Creosote may be 'undetermined' but my eyes and nose tell me its coming no where near my garden.  That stuff is nasty!

Phytoremediation.  Plants that help uptake these pollutants, thus healing our soils.  Brassica juncea remove lead and cadmium, Pteris vittata removes arsenie, Salix viminalis takes up cadmium, copper, and zinc.  All these plants store metals in the foliage and should be removed (with gloves) and discarded (in a landfill).  Its sufficient to harvest them from the stem up, and allow the root stock to continue and the plants will grow and continue to remediate the soil.  Im a big fan of phytoremediation possibilities, especially in a wetlands setting.  I'd like to see a constructed wetland where Sugar Creek joins its neighboring creek at the South end of the property.  There are many other wetland plants that remediate pollutants- cattail is one, but its borderline invasive here in Atlanta.....

I dont know how to wrap this up.  There's no punctuating note to pollutants in urban soil, except perhaps- we sure have put a whole lot out there and know very, very little about what it's actually doing to affect us and the rest of the environment.....

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