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While I was shopping for a house, a good friend was living in the  
hospital with her son, who was being treated for lead poisoning.  There  
is excellent evidence that he was poisoned by lead in the mud he played  
in, and not dust inside the house.  Because of this, I did soil tests  
for lead at every house I seriously (or semi-seriously) considered,  
which was a fair number of houses.  Here's what I found:

1)  Lead from paint on houses mostly stays close to the house.  The  
dirt right around the base of the house is contaminated, but the levels  
drop off very rapidly as you move away.  If you have shrubbery at the  
base of the house, the soil outside the shrubbery is probably not too  
bad (at least, from the paint).  There are exceptions, such as my  
friend's house, where the lead paint had been illegally sandblasted and  
had dispersed over the yard, but that's unusual.  The amount of lead  
near a house is also pretty well correlated with the age of the house.   
Old houses are worse.  I wouldn't grow herbs to eat right by the door  
of an old house, but I'd be comfortable growing fruits (botanically  
speaking - so that includes cukes, tomatoes, etc.) a few feet away.

2)  Lead from gasoline fumes is more prevalent than I would have  
guessed.  I nearly bought one house that bordered a semi-major road.   
(Not a highway, but a town road with traffic most of the day.)  There  
was a striking gradient across the yard.  The gradient isn't nearly as  
steep as with paint - obviously, fumes travel farther than chips.   
Right by the road the levels were about 500 ppm which is high enough  
that I'd prefer not to grow edible leaves, and maybe not edible roots.   
Edible fruits would probably be okay, though.  100 feet from the road  
the levels were down to perhaps 100-200 ppm (I don't remember exactly,)

3)  There are unexpected blips, too.  Some are due to land containing  
fill - fill can have all sorts of nasty stuff in it.

4)  Covering the soil with mulch works pretty well to keep the lead out  
of reach.  I was thinking more of children playing than of what plant  
roots might be picking up, but I was impressed with the low levels of  
lead I found in deep mulch, even right up against older houses.  I  
think this means that lead isn't very mobile in soil.  The corollary  
would be that if you are worried about lead, dumping a modest amount of  
clean soil for the plants to grow in will probably work pretty well to  
protect you - just make sure the patch of clean soil is large enough to  
contain the roots.

I ultimately bought a house with very low levels of lead in the yard,  
not primarily for that reason, but it didn't hurt.  But I mostly grow  
fruit, so it probably doesn't matter.

One hypothesis:  Lead in plants seems to show up in the same places as  
calcium.  So "green leafy vegetables" are the most dangerous, and  
fruits the least dangerous.  I don't know this for sure, but if I was  
growing veggies in modestly contaminated soil, I would avoid the ones  
that are supposed to be good calcium sources.

Cheers,
Ginda

On Nov 10, 2003, at 9:13 AM, mIEKAL aND wrote:

> Lead takes root in urban gardens
> Hazard: A new study suggests that plants from city residential plots  
> might contain harmful levels of the toxic metal.
>
> By David Kohn
> Sun Staff
> Originally published November 10, 2003
>
> It seems like such a wholesome undertaking: tending your own little  
> urban garden filled with fresh vegetables and herbs.
>
> But some of those homegrown plants might contain potentially dangerous  
> levels of lead, according to a new study of Chicago residential  
> gardens.
>
> The greatest hazard was associated with leafy green vegetables and  
> herbs. Researchers found traces of the toxic metal in some of the  
> plants' leaves - the part people normally eat.
>
> Exposure to lead causes a variety of health problems, particularly in  
> children. It can damage the brain, retard growth, impair hearing, and  
> trigger mood swings and headaches.
>
> The plants in the study absorbed lead from soil that contained high  
> levels of the metal. The study, which appears in the latest edition of  
> the journal The Science of the Total Environment, found that lead  
> levels were highest in the roots, but in some plants it migrated  
> further into the leaves.
>
> "If you grow leafy vegetables and herbs in soil contaminated with  
> lead, it's highly likely that those vegetables will be contaminated  
> with lead," said Northwestern University environmental engineer  
> Kimberly Gray, who oversaw the study.
>
> Root vegetables such as carrots are also likely to absorb high levels  
> of lead, she said. But the study tested very few such plants - not  
> enough to produce a conclusion.
>
> Although the study was small, it suggests that many urban gardens  
> might be producing contaminated plants, said Northwestern researcher  
> Mary Finster, a co-author.
>
> She and her colleagues collected 87 vegetables, fruits and herbs from  
> 17 gardens in an urban neighborhood in Chicago. The scientists looked  
> at four kinds of plants: fruiting plants, leafy greens, herbs and root  
> vegetables.
>
> To find out how much lead was likely to be ingested by humans, the  
> scientists washed the plants before measuring lead. Even after  
> washing, some leafy greens and herbs had measurable lead, indicating  
> that the metal was absorbed into plant tissue.
>
> The researchers also tried to calculate whether eating normal amounts  
> of the contaminated plants could affect human lead levels.
>
> In some plants, the theoretical amounts of ingested lead exceeded the  
> U.S. Food and Drug Administration's safe daily maximum. A tablespoon  
> of one sample of dried cilantro contained more than 85 micrograms of  
> lead, over 10 times the limit for children under six.
>
> These levels could contribute to health problems, Gray said -  
> especially in children, who can be harmed by much lower amounts than  
> adults. Women of childbearing age are also at risk because lead can be  
> transferred to a fetus.
>
> Nearly all fruits and vegetables showed no signs of lead. While the  
> roots of strawberry and tomato plants had high lead levels, the fruits  
> had no measurable amount.
>
> The researchers also measured lead in the soil. All samples from yards  
> exceeded 400 parts per million (ppm), the Environmental Protection  
> Agency's safe limit for children's play areas. Some soils had  
> extraordinary amounts, as high as 55,000 ppm.
>
> To minimize contamination risk, Gray recommends planting gardens far  
> from lead-painted houses or other buildings - paint particles tend to  
> settle close to the structures. She also suggests testing soil for  
> lead and, if necessary, replacing it with uncontaminated soil.
>
> Lead contaminates soil mainly through lead paint, which was banned in  
> 1978, and leaded gasoline. In the century before it was outlawed in  
> 1986, leaded gasoline deposited about 6 million tons of the metal  
> across the country, much of it in heavily trafficked cities such as  
> Chicago and Baltimore.
>
> A 1983 study of Baltimore yards, for instance, found lead levels as  
> high as 10,900 parts per million. "Urban areas are likely to have high  
> levels of lead in yards," said Xavier University toxicologist Howard  
> Mielke, who did the Baltimore study.
>
> A leading expert on lead in soil, Mielke wasn't surprised by the  
> results of the recent Chicago study. He said it underscored a larger  
> point - that lead continues to saturate the environment in many large  
> cities.
>
> "It has accumulated over the years," he said. "And it's still just  
> sitting there."
>
> http://www.sunspot.net/news/nationworld/bal- 
> te.lead10nov10001546,0,2651411.story
>
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