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.

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    19 Comments

    1. I think technology should be used to determine how nature works and how nature works best. I think then, technology should be used to helps us utilize natural practices to the best balance for our needs and natural needs. An example, we have many medicines that are synthesized from natural plant essences/extracts/enzymes. Technology is used to study herbal remedies and find the scientific data to authenticate them and synthesize or extract them for our use. This is an appropriate use of our technological advances in balance with nature. If we had paid attention to years of accumulated data on lead, our technology should have led us to using alternatives. Unfortunately, technology use needs a more common sense approach and less a greed approach. I am not sure that change is going to be universal any time soon.

    2. as a curiousity, since you have high phosphate levels in your soil along with the lead, did you test any of your plants to see if they were indeed uptaking that lead??

      • It’s something that I’d like to do when my budget will allow. The Wallace Lab report, incidentally, measures “plant available” lead. The levels were high. The next time I talk to Wallace I ask him about this issue.

    3. One other solution is removal. I have worked a few jobs where we literally removed all of the soil on site down about 3 feet and replaced it with uncontaminated soil. This is not usually financially feasible in an urban area, but if you live in a rural setting and have enough land to source your own clean soil it might be an option.

    4. I can’t remember from previous posts what your lead count was. At our community garden the lead test came in at 22 ppm – in the normal range, yet above average, so I’m told. I’m fuzzy on phosphate vs phosphorus, but our phosphate levels were also low. I hadn’t considered the relationship between phosphate and lead. Is there a land-based amendment high in phosphates (we’re in the Midwest)? We’ve just been adding lots of organic matter (manure, leaf mold, mushroom compost, wood chips) and hoping it’s ok…I’ve heard that fruit trees are safe in contaminated soils b/c the fruit won’t absorb these nutrients, can anyone here confirm this?

      • Fruit trees–in fact most everything that has fruit, including tomatoes, are safe. Adding organic matter is good. Our lead levels are around 500 ppm–a lot higher than yours. Personally, I wouldn’t worry about your low levels.

      • If all fruit is safe, why are you growing in raised beds? Are you using “fruit” as the product of the plant? (Squash, a vegetable, could still be called the “fruit” of the plant.) Would leaves like spinach or root crops like carrots be contaminated with lead? How about pecans or other nuts?

        My hens take long dust baths in soil outside my home that is 112-years-old. Could your hens or mine be exposed to a degree that would harm them? Would the eggs or meat be contaminated?

        Moving into a newer home might still leave a homeowner with lead in the soil since many older houses and buildings are razed for newer subdivisions.

      • I’m growing fruit in the ground and vegetables in raised beds. Leaf crops are the ones to worry about in lead soil–especially spinach.

        Not sure about the hens.

        And you’re right about new homes–you never know what was there before.

    5. So what I’m not sure about is how much dirt to sample, how deep to dig it, etc. Surely some parts of the yard might have more lead (or less!!) than others? Do they ask you to send in samples from all over the yard?

      • Hey Birdzilla,

        All of the labs I linked to have detailed instructions on how to take the samples. If you know where you want to put your vegetable garden I would take a couple of samples from that area and mix them up. Or you can take a bunch of samples from all over the yard and do an average. Then, if there’s a problem, go back and test specific areas. In our case I found basically the same elevated levels in the entire yard no matter where I sampled.

      • That’s an interesting one– Apparently they think the worms might isolate the lead from the soil and hold it in their bodies.

        How you manage the system is less clear. I guess you’d have to set up some kind of soil processing system full of sacrificial worms that you “harvest” Logan’s Run-style every so often, and take to toxic waste disposal. Thing is, once a worm dies it gets reabsorbed into the bin really fast, so worms that die with lead in their bellies (ha! like cowboys!) would return that lead to the bin. Would it get picked up again? Tricky. But interesting.

    6. Hey everyone, I recently heard Dick Chaney, USDA “soil contaminant expert” talk here in Baltimore regarding urban gardening and lead contamination. Just like Mr. Homegrown said, Chaney refuted the validity of the Umass soil lead test and recommended instead Penn State’s test, which seems to be one of the cheaper options at $27. See http://www.aasl.psu.edu/EnvirSoilTests.HTM

      Additionally, he warned that some root crops do actually uptake lead in their xylem, especially carrots, but also beets, radishes, turnips, etc. He joked that urban growers may just have to give up growing carrots. Additionally he warned that the main risk from growing leafy vegetables is actually digesting soil that adheres to leaf as opposed to the plant actually taking up the lead.

      Lastly, he stated that if your lead levels are under 400 ppm you are pretty much safe to grow whatever you please (carrots still questionable!), which fits with what the US EPA recommends. However ,I find it interesting that countries that actually have ESTABLISHED agricultural soil standards have much more conservative recommendations. In Canada, soils that are over 70 ppm lead are considered unsafe for agriculture practices….gotta love the good ol’ USA.

    7. I’ve been following your ordeal with lead and it really gave me a push to test the soil in the new (nonraised) beds around our 1850 house. All three beds were contaminated, one with 1000 ppm! Needless to say, we put an end to the edible growing in that one. Any advice for what to do with prunings from shrubs growing in that highly contaminated soil? Bag them and trash them?
      Thank you so much for sharing your story…I really hear very little about lead contaminated soil and yet I see so much about urban foraging, urban gardening etc. I do worry for folks.

    8. Still… I wonder how food homegrown in lead-contaminated soil compares, health-wise, to the same food store-bought? Even organic?

      I’m curious to know what soil you settle on for your beds. I’m not happy with the soil I chose. Lifeless, after 6 months and a less-than-bumper crop (no worms, no bugs). I’m hoping mixing in a generous dose of horse poop will bring some life and a better crop. I’m not sure what else to do.

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