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Lead in soil and composting: am I overthinking this?

 
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I am an urban gardener striving for permaculture.

A few years ago, I had my soil tested for contaminants (based on the principle that "urban soil is contaminated until proven otherwise"). Everything was ok, except for lead which is on the low side of concerning (170 mg/kg).

From what I've read and analyzed, I'm comfortable growing fruiting vegetables and fruit trees/shrubs in that soil, but I use raised beds with "clean" soil for leaf and root vegetables.

I've also been composting for a few years, using mostly garden material (our kitchen scraps go in the curb-side composting system). I've assumed that this compost is "unclean" (due to the presence of lead extracted from the soil into the garden residue) and thus use it only on ground soil, not in my raised beds.

On the other hand, I'm not perfectly orthodox in this: I've used branches as filler for the bottom of my beds, partially composted leaves as mulch, and compost from the municipal service which is free, but probably not entirely free of contaminants either. To make things even more complicated, we just learned that our house is considered "at risk" for borderline amounts of lead in the water source (between 5 and 10 micrograms per L. The amount that is ok for healthy adults to drink, but not recommended for pregnant women or young children). It is not a sure thing - maybe it's all clean, but we'll only know for sure in a few months/years.  I mostly water with rainwater, but sometimes supplement with municipal water, so that's another possible breach on the "lead purity" of my garden beds.

Am I over-complicating things? Or am I better to keep buying organic compost for my garden beds, even though I'd rather have a more closed input system.

(I'm also considering having a second compost bin for kitchen scraps only, but I'm limited by space. I'm also considering worm composting, but I'm not sure I'm ready to commit to that... I'd probably forget to water or feed them. )
 
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I don't believe that lead can be pulled up into plant tissue either by osmosis or capillary action (adhesion).  Thus, those trace amounts of lead in the soil would remain in the soil as plants grow.  The plant tissue is made of carbon which the plant pulls from the air through photosynthesis.  I can't imagine that compost made with plants grown in your garden would be compromised, any more than an apple or tomato grown in your soil puts you at risk for lead contamination.  But if you are concerned, you could always use that compost somewhere where it will not cause concern -- around trees or non-eatable plants.

Fungi has been shown to bind soil toxins and render them inert.  Fungal networks are part of nature's bioremediation system.  Consider ways in which you can feed soil fungal networks to help detoxify anything that might be in your soil.  Putting down a thick layer of wood chips throughout your garden/orchard/food forest every year is the simplest way to immediately jumpstart the fungi that are present.  Feed the fungi and they'll do all sorts of beneficial things for you.
 
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Hau Kena, I really like your question, it is perhaps one of the most significant things for city dwellers to think about when they want to garden.

Oyster mushrooms will help a great deal when dealing with heavy metals (lead is a heavy metal) to get the best performance from the mycelium you would need to provide some food source like hardwood chips, spent coffee grounds, dead leaves, etc.
As the mycelium contacts the heavy metals they excrete enzymes that help the mycelium create new compounds that are more stable and lock up the metal component into those compounds.
Wine caps are another fungi that help with remediation of heavy metal contamination.

To contain such contaminates you can introduce spawn (mycelium) into your garden beds, the fungi won't interfere with your plants, it will help them grow better and remove any worries about the contaminate making its way into food stuffs you grow.

Redhawk
 
Kena Landry
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Lead does get into some plants (that's how phytoremediation works. For instance, I know that brassicas are particularly good at extracting lead from soil). And it can be a problem from root vegetables, if they are in direct contact with contaminated soil and not cleaned properly.

I'm happy to hear about the fungi, though. I've pretty much covered my yard in inoculated ramial chipped wood already (not sure inoculated with what - it's a "special mix" from a local producer) and it's done wonders to my soil. I didn't know I was helping with my lead problem as well. I could probably add some more specific mycellium as well (And part of my yard is in full shade, so mushrooms were on my dream list already)
 
Bryant RedHawk
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You are very right to be concerned, as you mentioned, the brassicas are great at sucking up heavy metals (including chromium and lithium) but so are tomatoes and some of the squashes.  Fruit trees are another collector of heavy metals.
 
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The more acid the soil, the more bioavailable heavy metals are to plants. Keep the soil alkaline to minimize the risk if you can by the plant's preferences.

If you search soil ph and heavy metals you'll find a bunch of studies. I'd paste them here for ease of reference but my computer died and I'm on a little tablet and havent figured out copy and paste on this borowed device yet.  :(
 
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I have similar concerns about lead in my urban soil.
I was under the impression that lead general concentrated in the leaves and foilage of plants,  and was largely screened from the fruits.
Im not sure lead has any safe level,  and I'm not clear that conventional farming land is tested for lead.
This article cites studies that show much higher heavy metal content in organic foods than in conventional produce:
https://pursuitofresearch.org/2018/08/26/organic-food-and-heavy-metals/


This pamphlet encourages adding high amounts of plant matter, and phosphorus, to slow uptake of  lead.
https://www.google.com/url?sa=t&source=web&rct=j&url=https://anrcatalog.ucanr.edu/pdf/8424.pdf&ved=2ahUKEwioxL7vq6znAhUBUt8KHZ_VCnQQFjABegQIDhAH&usg=AOvVaw0pgH2oVJYILBMBvXndFqxY&cshid=1580422519340

All told,  I'd say you're doing fine.
You've probably  have taken more precautions than any other  producer of your food has.
 
Kena Landry
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Thanks everyone! Excellent food for thought.

My ground is naturally very alcaline (clay) so I'll keep building up a good organic layer for the fungi to thrive and let go.

At the very least, getting my soil tested immunized me forever from the temptation of straying from organic gardening. When you realize that whatever gets in the soil stays there pretty much forever (unless you literally shovel the problem off to someone else), I've been feeling more connected to my role as a stewart of my little corner of the world.
 
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>> You are very right to be concerned, as you mentioned, the brassicas are great at sucking up heavy metals (including chromium and lithium) but so are tomatoes and some of the squashes.  Fruit trees are another collector of heavy metals.

Thank you for sharing your formidable expertise on this topic.

Unfortunately I too have found out that my urban soil contains high amounts of lead. I'm attempting to bioremediate using brassica, helianthus, scented geraniums, also potash (to bind it) and diluting with mulch.

I had thought that consuming the fruit from my avocado, plum, fig trees and also the squash, would be safe because I had read that they *don't* accumulate lead into their fruits?

In your opinion Dr. Redhawk, and anyone else, should I be concerned about eating squashes and fruit from trees grown in lead contaminated soil?

Thank you for your thoughts!
 
Bryant RedHawk
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If you know the concenttration of lead or other heavy metals, you could be safe with fruits from trees. Anything over two times the limit set by the epa and remediation or having the produce tested (safest method) is the wise move.

You can remediate with oyster mushrooms or winecaps, chanterells are another good remedator fungus. Once you have the fungi well established expect to wait at lest a year before you check the soil so the fungi can work on heavy metal removal.

There are many parts of the human anatomy that lead can wreak havoc on, the brain is usually the first organ to be noticed as functions start dropping with as little as 5 ppm.

Redhawk
 
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Thank you for this excellent discussion. I'm a little confused though how somebody with high lead soil should proceed. Here's what I gather from this thread. Please correct or comment:
1. Introduce fungi such as oyster or wine cap and their food. Fungi slow the uptake of heavy metals by plants. Are the fruit bodies healthy to eat? What happens if you keep chicken in such a plot, will their eggs and meat have a higher level of heavy metals?
2. Fruit are safe to eat.
3. Phytoremediation by planting brassica and sunflower. Surely you need to dispose of the plants off site?
4. Planting vegetables in raised beds. This supposes that they root only in the brought in soil. However veg root much deeper than we suppose. Up to several metres I've read. Is that not in contradiction to point three?
 
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Biochar has also been shown in many studies to effectively immobilize heavy metals such as lead.  Soil lead immobilization by biochars

I like to add biochar to the compost pile while building it, which also helps the pile heat up faster, as well as laying some on the ground before mulching over it.  You'll find lots of posts in the biochar forum on how to make your own biochar if you're interested.  Here's a link to one of them.  With the mulching method you get to immobilize the lead with both the biochar as well as by feeding the fungi!
 
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Susan Wakeman wrote:Thank you for this excellent discussion. I'm a little confused though how somebody with high lead soil should proceed. Here's what I gather from this thread. Please correct or comment:
1. Introduce fungi such as oyster or wine cap and their food. Fungi slow the uptake of heavy metals by plants. Are the fruit bodies healthy to eat? What happens if you keep chicken in such a plot, will their eggs and meat have a higher level of heavy metals?
2. Fruit are safe to eat.
3. Phytoremediation by planting brassica and sunflower. Surely you need to dispose of the plants off site?
4. Planting vegetables in raised beds. This supposes that they root only in the brought in soil. However veg root much deeper than we suppose. Up to several metres I've read. Is that not in contradiction to point three?


My thoughts, but I'd love to hear others:

1.I would avoid the fruiting bodies of the fungi for at least a year while continuing to fees them. My understanding is that over time the mycelial network immobilizes the heavy metal. I am very curious to hear thoughts about the chicken question, I have no clue
2. Fruit from trees is safe, I believe, because the trees incorporate the heavy metals into their wood not their fruit. I don't know about softer annual fruits
3. My understanding is that you can compost these plants and use that compost around things like trees, effectively diluting the concentration of lead and trapping it in long lasting wood
4. At least for root veggies I think the main concern is the soil that the part you eat is covered in and inadvertently getting some of that soil ingested.

I used to volunteer on a farm in the city of Detroit, without a doubt that soil was very contaminated and likely by chemicals that can't reasonably even be tested for (there were factories in the area that had historically used all sorts of now banned substances as well as factories that used experimental lubricants and such over the decades). However, the farmer there approached it as a spiritual problem. He believed that the mess was ours and that it was created ultimately by our refuting natural ways, in essence that the pollution was our spiritual pollution made physical. He believed that if we put our faith back in abundant nature and fostered living systems that the land would remediate itself and return to being a source of life for human beings.

I don't advise ignoring lead contamination and applaud your desire to make the safest produce possible but I do think there is value and wisdom in his line of thinking. I also believe that robust biological systems are capable of elemental transmutation so perhaps he was literally correct too
 
Bryant RedHawk
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When you are remediating contaminated soil it is important to remember that those organisms are breaking down and making use of the contaminating chemicals and/ or minerals (lead, etc.). I would take those fungi, fruits and vegetables and compost them in hot compost heaps, consumption would not be advisable since the plants and fungi are concentrating the contaminates.  

Remediation takes some tiime to accomplish one year is just the start.

Redhawk
 
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This is a very basic article on plants that are particularly helpful in sucking up lead and other contaminants.
http://magicalchildhood.com/life/2017/07/17/seven-plants-weeds-and-flowers-that-naturally-remove-lead-from-your-property/

Several years ago I read an book from England about work being done there on old industrial sites. I believe the gist of it was that they planted plants known to absorb target materials, harvested the results and composted in a contained area which they then grew more of the same plants in, repeat until they had a smaller quantity of plants with very high concentrations of the target material and then disposed of this "high concentration" material responsibly. I seem to recall that there were situations where "responsible" was actually to have the concentrated material "harvested" and sold to companies that still use that raw material (I think it was lead - industry still uses it and reusing it from places we don't want it to be, rather than mining it, is responsible in my eyes.)
 
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Looking at the article posted by Jay Angler re plants to grow for phytoremediation, I was struck by the warnings to remove all the now contaminated plant materials at the end of the season. What they don't say is how or where to dump it. Surely the council dump would want to know about potential higher levels of lead especially if they are producing what we call in the uk green waste compost to sell back to gardeners? This is another example of focussing on the short term immediate problem without considering the wider implications!

I also have a question for anyone regarding the use of fungi. Where does the lead go that they trap so well? I thought the whole point about fungi in soil was they can transport minerals through their hyphae networks and make them available to plants to use?

 
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