Readers, thank you for your concern. Rest assured, I have not developed abdominal cramps, headaches, aggressive behavior, or any other symptoms of lead poisoning (although I suppose it might be too soon to tell). I've been eating lustily from my garden, both from the beds that are properly raised (a foot off the ground) and also those that are only slightly raised (four to six inches).
What's up with that? you might ask. I thought you were living on a bed of lead! Well, it's not quite as bad as I feared. It's true, there is a lot of lead in the soil next to my flaky old garage and house. The worst of the results I got back from the lab showed levels of 5600 parts per million—14 times the recommended limit for growing edible plants. The good news, though, is that as long as I take some precautions, this lead is not very likely to make it into my body (or yours, if you come over for dinner).
When I got the dreaded results back from the lab, the first thing I did was to dash off a rather anxious email to my friend and neighbor Grace Troccolo Rink, an environmental consultant and the former Assistant Commissioner for the Division of Natural Resources at the City of Chicago's Department of the Environment. Grace knew something about soil contamination from her days working with Greencorps, a city program that supports community gardens. Lead was a hot topic down there.
Lead is everywhere in Chicago, she said. It has three main sources:
1. old house paint (pre-1978)
2. industrial, railway, or commercial waste
3. leaded gasoline in cars
The city's position, she said, is this: assume that your soil has more lead than is safe to eat from. Raise edible plants in raised beds lined with permeable garden fabric and filled with virgin soil.
She discouraged me from trying to fix the soil, saying that it would be either very expensive and full of bureaucratic hurdles or very slow and only marginally effective. And anyway, she said, you can't really get away from it. Even if you manage to clean up your own soil, your neighbors' soil surely has the same problem, and the leaded dust is always going to be blowing through. Best to leave the lead where it is and bring in fresh dirt for your vegetables.
She suggested I talk to Aaron Durnbaugh, the city's current Deputy Commissioner for the Division of Natural Resources and Water Quality. He also lives in the neighborhood and had hosted conferences on lead contamination of soil.
Aaron agreed to walk over after work one evening. He came with his two-year-old son in tow and took a look around the back yard. I told him about my test results. I took comfort from the fact that he did not shake his head gravely or, worse, leave immediately, saying that my yard was an unsafe place for his child. In fact, he did not seem terribly surprised or alarmed. He repeated what Grace had told me, that the city line on best safe gardening practices is to put all of your edible plants in raised beds with fresh soil.
In fact, he said, Greencorps won't support community gardens that put edible plants directly in the ground. He talked of encounters with veteran community gardeners who scoffed at the idea of raised beds: "We walk away from them."
He acknowledged that it's not easy to verify the cleanness of topsoil that you buy; some landscape supply companies test for lead or other contaminants, some don't. Most topsoil, he said, comes from regional farmland that's being developed; farming has not typically involved lead (although it may well have involved pesticides), so there's a good bet that it's safer than city soil in that regard, but you won't know for sure unless it's tested. Compost is more likely to be tested than topsoil.
Of all the possible soil contaminants (and there are many), he said, "I worry about lead. It's the most insidious."
That said, he admitted that it is usually not taken up by plants. This surprised me. If that's the case, then what is all the fuss about? As long as we don't eat the dirt itself (not to be taken for granted with small children), shouldn't we be fine? The problem is, he said, there's not a lot of data on the subject, so the government and other authorities are inclined to err on the safe side when issuing guidelines and advice.
He pointed me to a series of articles and presentation documents from a soil safety conference he organized in 2005. At the time, he was the president of GreenNet, a coalition of nonprofit and government organizations devoted to community gardens and other greening projects. GreenNet hosted the conference, called Gardening Safely in Urban Soils; some of the documents from that conference are posted on their web page about safe gardening.
From these documents and other sources, I gleaned answers to some of my questions:
Why is Lead So Dangerous?
Lead poisoning can cause a host of ailments in adults, including fatigue, nervous system disorders, abdominal cramping, sterility in men and miscarriage or premature birth in pregnant women. The real danger, though, is for children, who can suffer from similar symptoms as adults, but also from learning and developmental delays.
While a high dose of lead can lead to emergency symptoms, the greater danger to children is the accumulation of lead over time. This is what typically leads to the impairment of brain development. The younger the child, the greater the risk, with fetuses being the most vulnerable. This means that pregnant women should be especially careful, as well as women who may someday become pregnant, as lead can stay in your bones and be released during gestation, which is a real pisser.
How Do You Get Lead Poisoning?
Through eating lead or inhaling lead dust. The sources of lead poisoning that have caused the most concern are paint chips and dust in old houses as well as lead paint on toys made outside the U.S. There is also lead in our plumbing, in some vintage housewares, and, as we now know, in our soil.
How Much Lead is Too Much?
I have not found a really useful answer to this question. The FDA's Provisional Total Tolerable Intake Levels (say that ten times fast) is this:
Children up to 6 years old: 6 micrograms/day
Children 7 years and older: 15 micrograms/day
Pregnant women: 25 micrograms/day
Other adults: 75 micrograms/day
This information is pretty meaningless if you don't have a handheld Lead-O-Meter, but it's the best I can do. It may be some comfort to know that we do not even absorb all of the lead that we ingest: adults absorb about 11% of it and children can absorb anywhere from 30–75%.
What Happens to Edible Plants in Lead-Contaminated Soil?
In general, fruiting plants (beans, tomatoes, watermelons) are safest, as any lead that leaches into plants tends to stick in the roots or the leaves. The greatest danger is with leafy greens and herbs, which are morely likely to hold lead inside the leaves but also in the dust that floats up from the ground. In fact, it seems that simply washing all of your vegetables with detergent (or a vinegar-water solution) will take care of the worst of it.
Although there's not a lot of data on this, there was a 2003 study done at Northwestern that examined vegetables grown in two areas in Chicago's West Town neighborhood. In the samples from that study, the some of the worst-offending vegetables were cilantro, collard greens, coriander, mint, rhubarb, swiss chard, onions, and cucumbers. (It's hard to explain the cucumbers, although it should be noted that these were one among seven batches of cukes, the rest of which were perfectly fine, even though some were grown in even worse soil. Here, too, detergent seems to help.)
As with so many aspects of our natural world, it's hard to get a real handle on the impact of lead in our garden soil. As Aaron Durnbaugh said, you take the information you can find and do the best you can. As a private citizen, he admitted that he plants his own tomatoes directly in the ground, albeit in the middle of the yard, where they're removed from the lead halo that tends to accumulate around old buildings.
Initially, I was frustrated, even irritated, at the lack of more precise guidelines and information. What's a conscientious city gardener to do? I thought. Do I have to move to the virgin wilderness? How would I file my NEST postings without an internet connection?
But then I realized that this is no different than so many other issues I deal with regarding food safety: I do the best I can to avoid food contaminated with pesticides, growth hormones, and icky plastic chemicals. Do I know these things are unhealthy in certain quantities? Yes. Do I know the precise ratio between contamination and ill effect? No.
Ultimately, I'll weigh this against all of the other things I have to worry about and decide how much energy I'm willing to devote to it. Although I know I won't be able to remove every trace of lead from my home-grown diet, I can follow certain best practices and that will minimize the risk. In the mean time, I will trust that the countless other benefits of home gardening will far outweigh the disadvantages.
So what did I decide to do about the raspberries? Stay tuned for Speaking of Lead Part 3: the Solution.
LINKS
GreenNet: Gardening Safely in the City Here you will find links to presentation documents from the 2005 conference, "Gardening Safely in Urban Soils," as well as to the NU study, "Lead levels of edibles grown in contaminated residential soils: a field survey," by Finster, Grey, and Binns. These documents are full of wonderful information.
Lead Safe Chicago The City of Chicago's Childhood Lead Poisoning Prevention Program
Lead Contamination in Gardens by the Ohio Department of Health
Mayo Clinic's article on lead poisoning
Medline Plus article on lead poisoning Medline Plus is a service of the National Library of Medicine and the National Institute of Health.
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