Some people seem to think that if the ph is high (we are in Colorado, so even aside from the concrete, it will be) and the organic matter high (it will be, because we are sheet mulching to get around the rock problem) lead does not pose much of a problem. Is this so? Is there any scientific studies which show the amount of lead which actually gets into the plants from different kinds of soil?
How should I proceed? Children will be eating out of this garden, and I don't want to limit plants to fruit bearing vegetables, though I will if necessary.
The location is much "Newer" than some areas; it has not been built up as long, so there will be less total lead in the surrounding area. But I can't know where the fill came from
Gilbert Fritz wrote:Some thing I forgot to mention in my first post: what about adding phosphorus to turn lead into chloropyromorphite? Is this something which can actually be done on a field scale, or only in a laboratory beaker?
It appears they did just that in this study.
One thing you might try is to plant a cover crop of a hyperaccumulator of lead and harvest and discard that crop somewhere else (like deep in a landfill). This study claims that Chinese cabbage is a hyperaccumulator for lead.
Lead is pretty easy to test for even in the most meagerly outfitted chemistry lab. Rather than buy DIY test kits, have you thought of doing the tests completely by yourself? If you want, I'm pretty sure I could MacGyver up a lead test method for you, using commonly available ingredients.
Gilbert Fritz wrote:Hello John,
Thanks for the links. If you could give me some information on completely DIY testing, I would be interested.
First thing you have to realize is that the reason lead tests cost $50 is because of the cost and maintenance of the ICP-mass spec instrument. As the Qualitative inorganic analysis Wiki article says at the bottom: "Qualitative inorganic analysis is now used only as a pedagogical tool. Modern techniques such as atomic absorption spectroscopy and ICP-MS are able to quickly detect the presence and concentrations of elements using a very small amount of sample."
Before we get started, here is a second opinion on what you can expect from commercially available test kits.
There are still a few of us around who remember the days before ICP-MS instruments were common place and who actually had to do qualitative analysis in the chem lab.
Step 1) Take your sample and cook it in your oven as high as it can go. You want to burn all the organic matter to carbon. Don't worry, none of the metals you are going to analyze for later are going to volatilize.
Step 2) Digestion. Add a mixture of aqua regia (equal parts hydrochloric and nitric acid) to your sample and simmer it for a good while. This should dissolve all the metal compounds in the sample. Then you can pour off the liquid and use that as your sample to qualitatively analyze. At this point it is important to neutralize the acid, because you don't want ion complexes in solution, you just want hydrated metal ions to analyze for. Since we don' t care about analyzing for sodium, we can use sodium hydroxide to neutralize the excess acid.
Step 3) At this point you are ready to test for Group I ions (Pb, Ag, and Hg). Since you only really care about Pb, you could add potassium iodide solution at this point to precipitate PbI2. If you filter, dry and weigh your precipitate, you can calculate back how much lead you had in your sample.
For example, if you ended up with 461 mg of PbI2 precipitate, that's 1 millimole, meaning that the amount of lead that was in solution was 207 mg. If your original sample had a dried wight of 1kg, then the lead concentration in your soil is 0.207/1000 or 207 ppm.
This is just a rough guide as to what is involved to do the wet chemistry method. Think about this and how practical it would be for you to set up a home chem lab. In the meanwhile, I'll try to find some more rigorous protocols on line so you can revive this lost art.
the bigger hazard, compared to intake through eating veggies, is disturbing lead contaminated soils making lead dust airborne which you can breathe in and can be absorbed through the skin.
http://www.gardensalive.com/article.asp?ai=995 ---> has tips on mitigating the hazard
please excuse the question, but reading the description of the land, Im wondering why you feel there is lead contamination, lacking actual tests?
I think there might be lead because the fill appears to contain concrete rubble, suggesting that it came from old construction or demolition sites. Any building being torn down more than 37 years ago would have almost certainly had lead in it.
But maybe I am worrying to much about this. Does anyone know how concerned I should be in this situation? Has anyone dealt with a large, varied, filled, urban site?
I can't use raised beds because water is extremely expensive here, and the Urban Farming group has very little money for raised beds.
What if I just keep the pH and phosphorus and organic matter up? How much lead could this neutralize? 500 ppm? 4000 ppm? So would I be safe doing this in the worst case scenario?
all of downtown Durango was filled with uranium tailings decades ago. dont see people dropping left and right from gardening there.
its a dirty world. i would get to overly paranoid unless you have reason to believe something is truly toxic.
* I'm not recommending sewer sludge compost, maybe your own aggressive compost collection (and hey your own humanure really adds up and encourages you to collect biomass, food, market scraps to feed the thermophilic fire
The test I outlined above is simple chemistry, but it is time consuming. Which method you use really depends on time and $$.
And if you really don't want to be spending either, but still want some peace of mind, I guess the best thing you can do is plant a known bioaccumulator crop and have it carted away.
I note that you are in Denver, CO - do you know the pH of your soil? I suspect it is alkaline (i.e. greater than 7.0). If so, plants tend to take up less lead in alkaline soils (one of the bonuses of alkaline soil). You can read more here in this useful publication from UC-Davis: http://anrcatalog.ucdavis.edu/pdf/8424.pdf
Being a westerner myself (Phoenix, AZ) - I applaud you for NOT going with raised beds (even if your limiting factor was funding) simply because they are ill-suited to the climate of most of the intermountain West and shed precious rain and irrigation water instead of harvesting it. I know this flies in the face of the conventional gardening practices that we see in all the beautiful gardening books - but those books were written for humid climates where precipitation exceeds evaporation - not the situation we have where evaporation exceeds precipitation. In fact, many of us in the hot drylands use sunken beds which can also protect seedlings from dry, desiccating winds. Raised beds in alkaline soils, which often have a high salt content as well, will draw those salts to the highest point in the soil putting them right in the root zone of the plants.
Whatever you do - let us know what happens. It sounds like you have a really interesting project going on and I am always interested to hear about the progress of dryland projects especially.
Jen in Phoenix
Thanks for the link. It is much less alarmist in tone than others I have read, which is nice. I didn't know that 4 ppm in water was considered safe! But in some ways that is reassuring, as regards using this soil.
I tried to use a preexisting raised bed in my home garden, and wasn't happy with it. It dried out much too fast, and the water flowed OVER the hardening soil and through cracks in the wooden walls.
I haven't done professional testing, but I have used a home test kit. (I will be getting professional nutrient testing done in a few weeks in connection with the lead testing.) The kit showed that the soil is neutral. This is probably because the plot is in a creek bottom floodplain, and is bordered by two irrigation ditches (neither of which we are allowed to use!) So the soil is fairly moist. (The fill was probably brought in in preparation for houses which were never built.)
I have decided to divide the land into small areas and have each tested separately. This may be difficult, and will be rather expensive, but each load of fill could be very different. If lead levels are under about 500 ppm, I will use organic matter and phosphorus to tie it up, and ignore it. (We are already laying down heavy sheet mulches to get around the problem of a rocky soil, and we will be adding phosphate rock or bone meal underneath it. The phosphorus levels were medium, whereas the potassium levels were high.) If lead levels are over 500 ppm, I will prepare beds the same way, but only grow fruiting crops in them. I am not really expecting to find extremely high levels; the band of contaminated soil from a demolished building would have been diluted in the fill. (There are concrete chunks, terra-cotta drain pipe shards, etc. in the fill.)
I will be posting pictures and information about my project here as things proceed.
Gilbert Fritz wrote:I tried to use a preexisting raised bed in my home garden, and wasn't happy with it. It dried out much too fast, and the water flowed OVER the hardening soil and through cracks in the wooden walls.
This is EXACTLY what happened in the raised beds I started out with long ago before learning about climate-appropriate gardening! =) They say you have to make mistakes to learn, but must I make ALL the mistakes? Repeatedly? (I guess I do! But since I'm having fun, I don't mind too much).
I wish you the greatest success.