From what I have learned, most of the lead in food comes from two sources, old paint peeling off old buildings, and soil within several feet of roads where many years of leaded gasoline has contaminated the soil.
If you suspect lead, contact your Cooperative Extension Service [find yours here: http://www.csrees.usda.gov/Extension/] and ask who tests soil for that, and then call the lab and ask how to collect a soil sample properly.
If you have young children (esp under 8), the lead should be less than 100 parts per million (ppm). For adults, anything less than 300 ppm should be okay unless you've got a family member that eats soil with a spoon. Over 300 ppm (or 100 ppm for children), you'll need to take a bit more care.
Leafy greens like lettuce, spinach, kale, etc, take up the most lead of all plants. Depending on your soil lead levels, you may want to grow these as far from the contaminated sites as you can, or in tubs or barrels or raised beds, all filled with clean soil.
Root crops are contaminated by the soil that clings to the outside of their roots, so you should peel them and wash them thoroughly. They apparently don't absorb lead.
Other crops like squashes, melons, corn, tomatoes, beans, peas, tree fruits and shrub fruits (raspberries, blackberries, etc) just don't take up much lead. The biggest danger with them even in areas of soil with lead is the dust on them, so just wash them thoroughly before eating (no grazing).
Lead likes acid soils, so adding lime to raise the pH to 6.5 or 7 (no higher) will make the plants unable to absorb the lead. Good phosphorus levels in the soil will help to do the same thing, as will organic matter that isn’t acidic. Oak leaves and peat moss are usually acidic, so try to avoid those as mulches or compost.
And that seems to be it. It really isn't as bad as I had thought. The worst lead toxicity with children seems to be the hand-to-mouth contamination, or eating dirt (pica).
Sue
Edited by Susan (01/01/10 08:41 PM)
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