Subject: Lead contamination

From: [email-masked] (Jim Mcnelly)
Date: Thu, 29 Dec 1994 02:51:00 +0600

C> my concerns are about lead contamination.  our soil has been tested
C> and lead levels range from 140 to 600 ppm.

C> Does anyone know the following?

C> 1. does lead naturally occur in soil and at what levels? 

I used to manage lead clean up projects in the 80's, and might take a 
stab at some of your questions. I have seen background lead levels 
range from 10 PPM up to 250 PPM, with 50 being fairly typical. Your 
levels are fairly high, and characteristic of soils near traffic ways 
in urban settings.

2. Can lead be removed by growing a cover crop and disposing of it rather
C> than composting it? 

Lead, as I understand it, is not uptaken by leaves, stems, or fruits, 
or for that matter, most plants. Its problem is associated with the 
soil itself, meaning that it attaches itself to roots, which are then 
ingested. It is also a problem with the "pica" phenomenon of children 
eating the soil, which another pathway of ingestion. Finally it is a 
concern for the soil worker, in the form of dirt on the skin, dust 
which is breathed, or dust on the skin. Lead is easily absorbed 
through the skin.

Composting does not "treat" lead or other metals. If anything, it 
might dilute the metal a bit. Composting is used for treating 
explosives, petrochemicals, oil, gasoline, diesel, and some herbicides 
and pesticides. But microbes are not alchemists. They can not convert 
base minerals into other minerals.

3. What methods can be used to remove lead from soils? 

The only two methods I am aware of are to dig up the soil and remove 
it or to put a new layer of soil on top of the old.

4. What is considered a safe level of lead in the soil? 

Well, the EPA hazardous level I worked with in the 80's was 5,000 PPM. 
In sewage sludge and compost, the levels are set around 250 PPM as a 
maximum. Added over the years, since lead does not break down into 
anything else, even a 250 PPM compost or sludge could bring the soil 
lead levels up to 250 PPM if it started at 50 PPM.

Personally, If I had soils over 300 PPM, I would avoid growing or 
eating root vegetables. Over 500 PPM, I would keep kids from playing 
in the soil and would be concerned with skin exposure.

5. I
C> understand that tomatoes, eggpplant etc. are better to grow in lead
C> contaminated soils than leafy greens because the leaves absorb ythe
C> lead.  Is this correct?

Not to my knowledge, although there might be new data showing lead 
uptake that I am not aware of. Leaf uptake is typically associated 
with cadmium.  Root vegetables are the concern. Much of the issue is 
related also to the pH of the soil. The more acid the soil, the more 
likely a metal can get absorbed, the more alkaline, the less likely 
metals will leach.

C> any help/ advice that you can offer me to help remediate this
C> problem would be very appreciatted.  I would like to rehabilitate
C> the soil as much as possible rather than just using raised beds.

 * RM 1.3 02460 * What profit to gain the world and lose your soil?

------------------============<>=============-----------------
   Granite City Connection (612) 654-8372 28.8K 3 Lines
   Email: [email-masked] (Jim Mcnelly)
------------------============<>=============-----------------

---

From: "Thomas Hansmeyer" <[email-masked]>
Date: Thu, 29 Dec 1994 16:13:55 GMT

>Does anyone know the following?
>
>1. does lead naturally occur in soil and at what levels?
>2. Can lead be removed by growing a cover crop and disposing of it
>rather than composting it?
>5. I understand that tomatoes, eggpplant etc. are better to 
>grow in lead contaminated soils than leafy greens because the leaves
>absorb ythe lead.  Is this correct?
>

Something you should research is the pH ofyour soil.  I understand that 
lead will only become available to plants when the soil in more acidic.  I 
am not sure whether this applies to leafy vegetables.  As far as removeing 
the lead from the soil, a big problem.  You might be better off building 
beds with a soil compost mixture.  Getting back to the availability of lead 
to plants, a soil fertility text book would present the effect of pH on 
lead availabilty.  Contact me if you are not able to locate it.
-- 
              Thomas Hansmeyer
              USDA-ARS
              St. Paul MN
              [email-masked]