Get the Lead Out of Your Garden
Q. I have lived and gardened in my current home for the past 18 years. My vegetable garden is about 20 feet away from my 120-year-old house. I had never bothered to have a soil test done until this year, when a college student who was doing a gardening project asked me to get one. To my utter dismay, I learned that a new garden I put in this year adjacent to the house was highly contaminated with lead; a larger garden, 20 feet away from the house, has a lead rating in the "medium" range. We were told to grow nothing but flowers or grass in the garden with "high" contamination. The soil test results, from Penn State, gave instructions on how to improve the "medium" range soil so that we could safely grow flowering vegetable plants, such as tomatoes, peppers, peas and beans there—but no green leafy vegetables, as they retain lead to a higher degree, and can be eaten only if there's a "low" level of lead in the soil. My family has been eating out of this larger garden all the time we've lived here—including lots of leafy greens—and we never suspected that old lead paint from the house had infiltrated the soil. We plan to get ourselves tested for lead. Is this common knowledge - that somehow passed us by - that you should get your soil tested for lead if your garden is in the vicinity of old houses? I hope other people are more aware of this than we were.
- ---Ceal in Malvern, PA
A. Some are and some aren't, Ceal; some states and cities are better about getting the word out than others. But any soil near structures that pre-date 1978 (when lead was eliminated from house paint) should be tested before being used as a garden. Many states have a program that can perform these tests. Your state of Pennsylvania currently charges $27 for a lead test alone; $65 for lead and five other dangerous metals.
But every state is different. While all states have a county agricultural cooperative extension program, not all states support a soil test lab at their parent, 'land grant' University. States that do have a lab generally offer basic tests (like the pH of your soil and levels of selected soil nutrients) for a nominal fee (PA charges $9; a typical price). Some states—like Maine, Rhode Island and Massachusetts—include a lead screen in their basic test, and last time I checked, all three of those accepted out-of-state samples. A real deal!
Readers/listeners: See what your state offers first. Type the phrase 'soil test' and your state into a search engine. If your state has a lab, read through their prices and offerings. If they don't, check nearby states; just make sure they accept out of state samples—some do, some don't. And remember—you always have those great options in New England.
Oh, and ask the experts at your local extension office if the city, county, state or feds offer a lead testing program; it might be less expensive—or even free.
Q. I've tested my soil and learned the lead content is high, almost 700 mg/kg. I'm wondering what you think of this plan for a small (two by six foot) raised bed: I've removed the top eight to nine inches of soil and am considering lining it with denim (available at our local fabric outlet), then covering the denim with pieces of broken sidewalk concrete (to help water drain); then adding six or so inches of compost and a peat moss/vermiculite mix. But perhaps the fabric and rocks aren't needed? Would just adding new soil be enough?
- ---Lynn in the Mt. Airy section of Philly
A. Well, first I have to say that I hope you disposed of that contaminated soil properly. Soil that contains more than 500 parts per million of lead is considered hazardous waste by the EPA. ('Milligrams per kilogram' [abbreviated mg/kg] are the same as 'parts per million [or ppm].')
You and any others in your household should have your blood checked for lead. Although you can develop excessive amounts of lead in your blood by eating salads, potatoes and such grown in contaminated soil (the EPA says not to eat leafy or root vegetables if your soil lead levels exceed 20 ppm), the biggest danger is in working the soil and absorbing the lead through bare skin and/or by breathing in the dust. Lead dust is also easily tracked into the house; many carpets have tested high in lead from tracked-in dirt.
So be careful! If you're working in soil that has—or could have—lead problems, wear a dust mask, good gloves and leave your dirty shoes outside.
Now, the expert advice is not to mess with contaminated soil yourself; so I would not have advised you removing it unprofessionally. I generally recommend that people just seal off the contaminated soil with several layers of thick cardboard and then build deep raised beds on top of that barrier, filled with a clean mix of yard waste compost, screened dark high-quality topsoil and some professional mix/potting soil (kind of like your peat moss and perlite, but pH balanced). Forget the rocks and denim.
And try and keep the pH of all your soils out of the acidic range by adding wood ashes or lime if a pH test shows that they're necessary to bring things up to neutral. Lead becomes much more easily 'available' at a pH below 6.5.