Is Lead Poisoning a Risk in Urban Gardens?

82-Lead-Tile

Those of you who have followed our blog over the years know that our yard is contaminated with lead. This is, most likely, due to some combination of lead paint residue and car exhaust. For years we’ve grown vegetables in raised beds because of this issue.

But if the results of a University of Washington study on lead and urban agriculture are to be believed, we might not need to be as concerned. The researchers note that most vegetables don’t take up lead and that improving soil with compost greatly reduces the bioavailability of lead.

You can read a summary of the results of this research paper here.

Thanks to Joanne Poyourow of Environmental Change Makers for tipping me off to this research.

Phytoremediation of Heavy Metals

ArtemisiaVulgaris

Mugwort (Artemisia vulgaris)

Us city slickers have fouled the sandboxes we play in. Find an open field in a big city like Los Angeles or New York and the odds are that it’s a former toxic waste dump. Here in our neighborhood we’ve got a lot of lead and zinc–lead from paint and gasoline and zinc from brake linings.

These heavy metals don’t magically go away. They are elements, and short of an alchemical transformation you have to physically remove them, cover them up, or apply phosphate so that plants don’t take them up as readily.

One promising strategy is phytoremediation, the use of plants to uptake heavy metals. City Atlas youarethecity, in New York, is experimenting with Indian mustard, mugwort, basket willow and sunflowers to remediate a contaminated garden. The results are promising with some metals down 50% in a year. Mugwort (Artimesia vulgaris) did an especially good job with a wide range of contaminants.

I should note that Garm Wallace, who runs Wallace Labs, a soil testing service, says that phytoremediation can take many years to get heavy metals down to a safe level. That being said, breeding plants specifically for heavy metal hyperaccumulation is a technology that could make up for our past transgressions.

Thanks to Michael Tortorello for the tip.

Urban Chickens and Lead

From the One More Thing To Worry About department, the New York Times has an article on lead levels in eggs laid by urban chickens “Worries About Lead for New York City’s Garden-Fresh Eggs.” According to the article, the lead levels found in New York City’s home grown eggs ranged from none to over a 100 parts per billion. Since the FDA does not have an acceptable lead level in eggs it’s difficult to interpret the results. And I have to wonder what unknown problems lurk in industrial eggs.

It’s a reminder that those of us who live in older cities and grow food need to confront the lead problem. Personally, I’d also like to see the Real Estate industry come clean on this issue beyond boiler plate disclosures buried in sales documents. But I’m not holding my breath.

Five Lessons We Learned About Lead in Soil

As regular followers of this blog may recall, we did some soil tests last year that revealed elevated levels of lead and zinc in our backyard. The cause? Most likely, paint from our 92 year old house and nearly a hundred years of auto exhaust and dust from brake linings.

Applying a little alchemy to turn lead to gold, I think the most productive thing I can do is to help get the word out about lead soil and how common this problem is in urban areas. Towards that end I though I would share five things that we learned from our backyard lead crisis:

    1. Buyer Beware. When you are shopping for a house do multiple soil tests. Once you buy the house it’s too late. Real estate contracts in California (and I suspect elsewhere) have been loaded up with disclaimers about lead and old houses. I’m no legal expert, but I suspect it would be difficult to go after the seller given the lead clauses we signed in our ignorance.
    2. The dirt on soil labs. Choose a soil lab that gives detailed results and is willing to do some phone consultation. We used to recommend the cheap tests form UMass, but their results were significantly different than Timberleaf Soil Testing and Wallace Labs, which were more in line with each other. Both Wallace and Timberleaf give you more detailed reports and are both willing to chat on the phone. They cost more but are worth it.
    3. Raised beds.  Not much else to say other than those two words if you want to grow vegetables and have a lead problem. Right now I have a big compost pile going that I made with hay, straw and horse manure. I’ll use this compost along with imported soil to fill the raised beds that I’m going to build this winter. And you can bet that I’m going to test that imported soil first.
    4. Philosophical lesson. The future health of the human species requires us to be a lot more conservative in the use of chemicals. Lead was known to be a problem since the Romans, but we went ahead and used it anyways in paint and in gasoline and the results have been tragic. Nassim Taleb has written eloquently about the need to approach complex systems like nature and the economy with an attitude of humility and admit our ignorance. When we fool around with complex systems we’re asking for trouble.
    5. Rhetorical lesson. There should be a logical fallacy called the “appeal to technology.” It’s the idea that there just has to be a technological solution to every problem. This is a very common fallacy in our age. Some people have suggested that I try phytoremediation, the process of growing plants like sunflowers that accumulate lead. At the end of their growing cycle you pull the sunflowers and send them to a toxic waste dump.  Sadly, this is just not practical in a residential yard. I would have to pull every living thing, including a mature avocado tree, and grow nothing but sunflowers for the next 20 years. Others have suggested mushrooms as a remediation technique, but they don’t grow well in this dry climate.  Lead is an element and it simply doesn’t go away. Once it’s in the ground it’s in the ground. The best way to deal with it is not to use it in the first place. The city of Oakland is trying a more practical solution to deal with lead: applying fish bone meal to lead contaminated soil. Fish bones contain phosphates which bind up lead and make it less bioavailable to plants. Our soil tests indicate that we already have lots of phosphates in our soil, so I’m not sure if adding more would help.

    Of all of these points I think the first is the most important. I’ll repeat it again, if you are shopping for property get a soil test.

    Testing the Lead Testers

    Varian ICP-MS from Wikipedia

    Dear readers,

    Excuses for a technical post here, but we need your scientific expertise. If you have experience in soil laboratory testing techniques, or know someone who does, please send us an email at rootsimple@gmail.com or leave a comment. We’re attempting to reconcile slightly different lead results from three different labs and I’d like to be able to write about soil testing methods. Two of the labs we sent samples off to (UMass and Timberleaf Soil Testing) use inductively coupled plasma mass spectrometry (ICP) to test for lead. Wallace labs uses an extractant, AB-DTPA (ammonium bicarbonate Diethylene Triamine Pentaacetic acid).

    Here’s how Wallace described their lead testing techinique,

    We use AB-DTPA (ammonium bicarbonate Diethylene Triamine Pentaacetic acid).

    It is a gentle extractant and it mimics roots in extracting minerals from the soil. Most often environmental tests are made with boiling acids which are more aggressive than roots. The AB-DTPA method is a standard testing method of the Soil Science Society of America. It is called the universal extractant. It measures the bioavailable or plant available minerals which is expected to be adsorbed by plants. Most of the background heavy metals are occluded and are unavailable to plants. Our testing does not see the occluded metals.

    Total lead is approximately 10 times higher than our AB-DTPA measured lead. We recommend that AB-DTPA lead be less than 30 parts per million for home production of edible produce.

    UMass says,

    We use a modified Morgan solution (dilute glacial acetic acid and ammonium hydroxide) to measure extractable lead (using ICP).  Total Estimated Lead is calculated using a correlation established during a study performed here at UMass that compared total digestion levels to extractable levels using 300-400 soils.

    I divided one soil sample into three parts and sent a portion to three labs. While all three labs indicated the presence of above natural levels of lead, there were enough differences between the tests to warrant a closer look at the techniques. Your assistance would be greatly appreciated and we’ll share what we find out.

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