Unleaded For My Garden, Please!

A Reader Writes The Green Guide:

I have a question about heavy metal or pesticide residues in garden soil used for growing vegetables. I live in a house built in the 1950's and want to redevelop my backyard to include an area for growing fruits (such as raspberries, saskatoons, nanking cherries, rhubarb etc.) and vegetables. We plan to remove a layer of topsoil and replace with organic soil in the areas I want to grow edible plants. I have no idea of the history of the house over the last 50 years and am wondering if I should be testing the soil that will remain. Testing for a broad spread of heavy metals is expensive and testing for a broad spread of pesticides is even more so.

1. Can you advise which are the most likely and/or the most toxic heavy metals I might need to test for?

2. Can you please advise which are the most likely and/or the most toxic pesticides to test for?

3. If I remove and replace enough depth of soil in these areas would the risk be minimal enough that there would be no need to test? What depth do you think I would need to remove?

It would be lovely to eat from the garden, but I do not wish to inadvertently poison my kids!!!

The Green Guide Responds:

It's wise to consider the condition of soil when children are involved. Lead poisoning in children, for example, can lead to a host of health concerns, such as behavior and learning problems or slow growth, if left untreated. However, there are many things you can do to minimize risk and protect your family's health.

Surprisingly enough your children are less at risk eating vegetables grown in lead contaminated soil than they are from playing in that soil. Research shows that fruits of plants as opposed to the roots and leaves don't tend to absorb much lead, which can penetrate soil from exterior paint and leaded gas in cars. You'd also have to eat a lot of fruit for it to become an issue. Young children are more likely to put dirty hands in their mouths and their small bodies are much more susceptible to its impact. "Children playing in soil contaminated with lead or cadmium is more of an issue than growing plants in it and eating the produce," says Nina Bassuk, professor of Urban Horticulture, at Cornell University's Department of Horticulture. According to Bassuk your two greatest heavy metal concerns should be lead and cadmium. Chances are residential pesticides are not an issue if there has been a house on the land for a long time.

Since you are replacing the topsoil it may be unnecessary to test the soil for lead or cadmium because heavy metals don't migrate very easily. If there are heavy metals in your soil it won't contaminate new soil. Bassuk recommends taking at least six inches off and replacing it with uncontaminated soil if you want to grow vegetables. If you want to test your soil for peace of mind, you can send it to Cornell's lab for analysis (see below for details). You may want to test the area where your kids play if they can easily get dirt on their hands.

Another good way to protect your soil is to keep it slightly alkaline. Keeping your pH level above 7 binds the lead in the soil which helps prevent it from being absorbed by plants, says Bassuk. You can test your pH level with a simple home kit (see below). Adding well composted organic matter, notes Bassuk, is another good way to help bind heavy metals to the soil so they are not available for plant uptake.

It's also possible for lead particles from car exhaust to land on plants through the air so if possible try to keep your garden away from heavily trafficked streets. You can also wash your vegetables in either of the following two solutions according to Cornell a 1% vinegar (1 part vinegar to 99 parts water, about 1 tablespoon of vinegar dissolved in 1 1/2 quarts of water) or a 0.5% dishwashing liquid solution (1/2 tablespoon of dishwashing liquid dissolved in 1 1/2 quarts of water).

If you take these precautions it should be safe to grow fruits and vegetables in your garden. Just make sure your kids are eating the produce and not the dirt!

How to get your soil tested

Take samples from 3 to 4 areas, by digging about 2 to 8 inches down. Mix your samples well. Take 1 to 2 cups of mixture and send it to Cornell's laboratory. Make sure it is very dry and send it in a paper bag, to avoid mold. It costs $66 to test your soil for 18 elements, lead and cadmium are included. Include your check to Cornell University along with your name, address, phone number, and e-mail address. You also need to write a brief note indicating what elements you are concerned about. In your case tell them you are worried about lead and cadmium.

Send your samples to:

ICP Analytical Lab
Department of Horticulture
135A Plant Science
Cornell University
Ithaca, NY 1853

For additional information or instructions please call 607-255-1785.

Testing your pH levels

You can buy pH test kits through your Local Cooperative Extension Office. Go to www.csrees.usda.gov to locate it. If you live in New York you can buy a kit from Cornell for $15.00. Just call 607-255-4540 or fill out the form online, www.css.cornell.edu/soiltest.

Additional Resources

Cornell University's gardening web site, www.hort.cornell.edu/gardening

National Lead Information Center, 1-800-424-5323, www.epa.gov/lead/nlic.htm

Environmental Protection Agency, www.epa.gov/lead/leadinfo.htm#health

Testing Your Home For Lead In Paint, Dust, And Soil, published by the EPA, www.epa.gov/lead/leadtest.pdf