Getting the Lead Out

May 26, 2011 10:23 AM

We just got back soil test results for our new garden, and the lead levels are unfortunately pretty high (around 800 ppm). Now what?

We obviously should have tested the soil *before* starting the garden, but we now have a variety of plants growing out there, and we're not sure how concerned we should be about eating them. The research I've done has said anything from "Just wash them thoroughly" to "Don't garden if the lead is above 300 ppm". Should we kill the garden and start over with raised beds, or just eat what we have, or...?

I should note that the soils have already been remediated somewhat, and they are slightly alkaline, which is supposed to bind the lead and keep it unavailable to plants. Also, no children will be eating the food.

posted by tau_ceti to home & garden (12 answers total)

It seems like you have a medium level of lead, not particularly high according to this site at the Horticulture program of URI if your levels were for total lead and not extracted.

Having said that, the site also indicates that: vegetables and fruits can accumulate lead in their leafy green tissues, although lead accumulation will be lower in fruits. In high-risk lead areas, grow crops such as tomatoes, eggplants, peppers, squash, melons and cucumbers rather than leafy greens such as lettuce, chard, collards or spinach. Crops such as carrots, radishes, turnips, onions and potatoes can accumulate lead and should not be planted in heavily contaminated soils.

I am also a huge fan of raised beds and find that I get a much better haul from my raised beds than I ever did in the ground. Also, you can share your harvest with friends without the worry that there will be accumulated lead in their spinach salad.

Personally, I went with the raised beds.
posted by Sophie1 at 10:50 AM on May 26, 2011 [1 favorite]

If this is a hobby garden that you're going to enjoy eating the vegetables out of, go ahead and eat them. However, I wouldn't advise trying to live the whole summer eating nothing but what you've grown yourself. The lead levels in your tomatoes will probably be low but not immediately dangerous; leafy greens slightly higher. Think about making a pile of all the food you eat in a day and how much of that pile will come from your garden, and how much lead is in that garden portion according to the leaf/root/fruit (descending order of leadiness) distinction above and the fact that alkalinity and availability of other nutrients in the soil will decrease the tendency of a plant towards lead absorption. Think about the fact that it takes a couple of years for lead to leave the body once its in, so your current diet can affect your lead levels in the future. It's not 100% safe or the stupidest thing ever -a choice you've got to make for yourself for your own circumstances.

Personally I would go ahead and eat the veg as *part* of my diet, maybe replant the greens in a safer container - but that's in the absence of extenuating circumstances like planning to get pregnant in the next couple of years (the transfer of lead from mother bones to baby bones is unfortunately efficient).
posted by aimedwander at 11:04 AM on May 26, 2011

If you start over with raised beds, you may want to include a membrane (e.g. landscape cloth) to prevent your plants from sending roots into the lead-y soil.

Personally, I'd eat the veg this year (assuming a hobby garden) and plan a raised bed for next year. Washing thoroughly is good advice - I've been told that part of the reason leafy greens are a high lead risk is because of the dirft remaining on the harvested leaves.
posted by momus_window at 11:21 AM on May 26, 2011

Tau_ceti's S.O. here and trying not to threadsit too much. But to add some clarification: pregnancy's not an issue, and amending the hell out of the soil is an option, within the realm of budget. Since we're renters, cheap but time consuming options (slowly improving the soil with organic material, trucking in a few bags of clean topsoil here and there) are preferable to permanent/expensive ones when it comes to transforming the empty lot next to our house.

Right now I think we're leaning towards eating all the non-greens, and re-seeding greens and herbs in pots. But if we could till in more stuff to make the lead sufficiently biounavailable, even better.
posted by deludingmyself at 11:54 AM on May 26, 2011

Lead is bad for you and makes you stupid. I recommend dealing with it. When I had lead in my garden soil, I removed the top 12" of soil and replaced it. You'll usually use the same soil in subsequent years, and will be turning it, so you should go down 12".

You could create a new garden plot and transplant your seedlings; they won't bring much soil with them.
posted by theora55 at 12:56 PM on May 26, 2011

Have you checked in with local offices? Environmental health, extension service, etc? They may have advice and/or programs for dealing with this.

How long has your rental been there? If it's been there a while (or is right next to the road) the likely source is paint and/or auto exhaust. However, if your development is relatively new (like 80s or later), I'd be concerned about the source(s) of the lead, which could be industrial, through something like a foundry, mining operation, lead mill, or other heavy industry, or a junkyard or lumberyard. (Have you checked out your neighborhood on Geotracker, which is the CA SWQBC's database of significantly impacted sites? Any listings?) Industrial use would be a much bigger concern than just the lead alone, because there could potentially be other heavy metals or industrial contaminants. Some of those could also get into your veggies. (If it's bad enough contamination, some of them could infiltrate into your home via vapor intrusion.)

Full disclosure: I'm in the environmental industry. My personal take on lead is that ANY lead is too much lead -- it's a carcinogen, it damages your nervous system, and it's just not something it's worth being exposed to. There are some things I'm more casual about because of my industry background, but lead exposure really isn't one of them. If I were in your situation I'd be going the raised bed/container gardening route and putting a barrier between the base of the raised bed and the surface soil.
posted by pie ninja at 1:14 PM on May 26, 2011 [1 favorite]

If you've decided on not eating the leafy greens already planted (which seems wise), I would leave them there rather than pulling them up or spraying weed killer on them. When they get to harvest time, just pull them, bag them up and throw them away in the garbage. The lead they pull out of the soil is lead that you no longer have to deal with.

I'm not sure that lettuce and other edible greens are really the most efficient bio-remediators, but they're probably better than nothing.
posted by Kadin2048 at 2:50 PM on May 26, 2011

I'm with pie ninja on this one. I also work on the environmental industry, and 800 ppm is a lot of lead. Pie ninja also has a good point that this may indicate the presence of other things in the soil depending on source that you may not have analyzed for - if it's from paint there could be cadmium and chromium too for example.

Raised beds with known source soil brought in would be my suggestion.
posted by Big_B at 2:59 PM on May 26, 2011

How many samples were tested and how were they collected? Depending on the cost of the test it might be worth trying one or two more samples and see if you're getting the same sort of results. If this number is based on a single sample, it could be that your sample was a hot spot and things aren't all that bad. Or it could be that you sampled the cleanest spot out there and the reality is actually much worse.
posted by Kid Charlemagne at 3:40 PM on May 26, 2011

Back again to reply:
* The lot is next to our 1910 rental house, and clearly had some kind of construction in it. We've been cleaning out broken glass, concrete, bits of metal, shingling, tons of rocks, etc. It's hard to say what was there before, but I suspect it wasn't industrial.
* The samples were a co-mingled set of 8 taken from all the areas we might plant in the yard. They do not include any samples from 10' or closer to our house (since we assume there's more paint there).
* We did test for cadmium and aluminum (both within normal range), but didn't test for chromium.
* The tomatoes and other plants we're considering eating are planted in double-dug soil that has been amended with roughly 1 part purchased soil to 3 parts old soil. I'm basing the idea that the fruits are probably ok to eat on this article and other sources. Also, the previous tenants grew and ate a ton of tomatoes last year, and so far haven't spouted extra arms (not that that means anything).

We will contact these guys and see about working with our landlord to get the county to do an on-site assessment. Thanks for all the replies.
posted by deludingmyself at 3:57 PM on May 26, 2011

and amending the hell out of the soil is an option, within the realm of budget. Since we're renters, cheap but time consuming options (slowly improving the soil with organic material, trucking in a few bags of clean topsoil here and there) are preferable to permanent/expensive ones when it comes to transforming the empty lot next to our house.

Raised beds. No point amending the soil- with all the money you would have to spend on amendments to make a dent, you could easily build raised beds and fill them with clean topsoil. (One other consideration with amending with organic material is that it often lowers pH.) Vegetable roots can penetrate many feet: in this study, beet roots went down as far as 10 feet.* That's a single beet. However, compressing root development somewhat in a raised bed with landscape fabric on the bottom is a fine way to grow vegetables.

Keep the pH above 6.5 but below 7.5 (for best plant nutrition) and you will be fine with existing soil, especially where fruits are concerned. However, it's most important to wash everything that touches soil before it comes in your house- you are more likely to accumulate lead from soil tracked in than eating the vegetables. If your pH is high enough, the bigger worry is other vectors of soil and dust coming into your house, because the vegetables won't pick up much.



* Because of this, removing a few feet of topsoil is only feasible if the soil below is not contaminated, and lateral movement of water from adjacent contaminated soil is prevented, which is really quite difficult. If the water table rises enough during the rainy season, and excavated hole will collect lead in suspension. Again, higher pH helps immobilize the lead.
posted by oneirodynia at 4:02 PM on May 26, 2011

The lot is next to our 1910 rental house, and clearly had some kind of construction in it.

Please keep an eye out for asbestos if you're pulling crap like that out of the soil. No point avoiding the lead then giving yourself fibromyalgia.
posted by smoke at 5:15 PM on May 26, 2011