Q. I'm doing a whole-house remodel on an old home. It's the height of the gardening season, and the owners - knowing that many layers of lead-based paint had been scraped off the house over the years - asked me what I thought about planting tomatoes in the soil next to the south wall. Is there a danger that soil lead could be taken up into vegetables in dangerous quantities?
A. Carl Rosen, a soil scientist at the University of Minnesota, responds: In general, plants do not take up large quantities of lead even when grown in soil with elevated lead levels; however, lead levels in plants will increase as the soil lead level increases. The amount of lead taken up depends on the type of plant being grown. Lead accumulates more in leafy vegetables like lettuce and in root crops like carrots than in the fruiting part of plants like tomatoes, squash, and strawberries.
The only way to know if soil is safe for gardening is to have it tested; the homeowners can contact their local extension service for the name of a reputable lab. Some states use 500 ppm (parts per million) as the cutoff for vegetable gardens; in Minnesota we use 300 ppm.
If the soil does contain high lead levels, there are ways to reduce the risk so that the space can be used for gardening. For example, the homeowners can amend the soil with lime and organic matter to immobilize the lead, or simply make raised beds with clean soil. If they decide not to garden there, covering the soil with sod will protect children who might be playing in the area. There's a much higher risk of lead exposure through direct ingestion of contaminated soil than there is through eating plants grown in the soil.