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Lead and Soil
The more you know the less it can hurt you.

By Lee Reich

kids playing
Old lead-based paint can leach lead into the surrounding soil via improper removal methods or exposure to the elements over time. The health risks can be considerable—especially to children.

Photo Courtesy of Lee Reich.

My friend Linda was understandably enthusiastic about moving. Her "new" home was an older, country house in a bucolic setting where she and her husband could raise homegrown vegetables, a few chickens, and their new baby, Adam. Two years later, the family was moving again. The reason for the dramatic turnaround was lead, but the source of the problem wasn’t interior paint—a common issue in older homes, and one that’s been widely publicized for the dangers it poses to children. Linda's lead was in the soil around her house.

Lead can damage almost every organ in the body, and children are most susceptible to its adverse effects because they incorporate the element into their growing bodies. As nearly every old-house owner knows, lead poisoning in children can cause learning disabilities, stunted growth, and even death. What they may not realize is that, like lead in interior finishes, lead in soil may also pose health problems—when kids eat it, for example, or don’t wash up well enough after playing outdoors. Fortunately, applying some straightforward methods for evaluating and mitigating lead-in-soil conditions can go a long way in reducing the potential for problems.

Understanding the Problem
At Adam’s one-year checkup, Linda's pediatrician discovered elevated lead levels in the boy’s blood, prompting him to ask about the age and nature of Linda’s house. In testing the building, the high readings near the entrance pointed to the soil outside as the source, and when the soil was tested, it was shown to harbor lead levels of more than 2,000 ppm (parts per million)—much higher than the 10 to 50 ppm found naturally.

Elevated levels of lead in soil stem from decades of the element’s use in paints, pesticides, and gasoline. Because lead pretty much stays put in soil, it remains in the ground around some houses despite the fact that lead-containing products have been banned for decades. Certain situations warrant testing for lead. Any house built before 1978 (the date after which lead pigments were eliminated in common paints) may hold lead in surrounding soil from exterior paint that was scraped off, or that flaked or washed away over time. Houses on or near old farms that once grew fruits, vegetables, or cotton also are at increased risk because lead arsenate was commonly used as an insecticide in the early 20th century. In addition, houses close to busy roads can harbor elevated levels from automobile exhausts that formerly spewed combustion by-products of leaded gasoline. Even some new houses can be prone to soil lead if they were built over a previous home site, like the McMansions sprouting nationwide over tear-downs of more modest old houses.

Because lead in soil does not tend to migrate, it is important to test each potential problem area separately. For example, if exterior lead paint is one potential source of the problem, take soil samples at varying distances from the house—in the first 3’, between 3’ and 15’, and at 30’. Draw several samples at each distance, combine and mix them (to equalize any variations), then take from this composited sample the amount needed for testing. If there’s evidence of an orchard too, then follow the same procedure around the trees at varying distances as well. It’s also a good idea to test the soil’s pH, because acidity can influence how much ingested lead reaches the bloodstream. Many private soil testing laboratories, as well as state laboratories (located at state universities), test for lead in soil.

Taking Action
How do you deal with a home that has high levels of lead in surrounding soil? Moving, as Linda did, is one way, but certainly not the only way. The approach you take should factor in the level of contamination and the individuals at risk. Because kids play in soil, homes with children face the most stringent guidelines. HUD and EPA both allow an uppermost limit of 400 ppm of lead in bare soil where children play, 1,200 ppm otherwise. Emotions run high on the subject of lead contamination, but remember:

There is no automatic relationship between environmental lead levels and those found in children because several mitigating factors—like good nutrition and hand washing—reduce lead’s absorption or uptake.

There are a number of approaches you can take for dealing with lead levels above the 400 ppm guideline. For levels between 400 and 1,200 ppm, keeping soil in place or putting some sort of barrier between small, human hands (or clothes) and the soil is a viable safeguard. Establishing a dense lawn, for example, keeps contaminated soil from being tracked indoors on shoes and also acts as a barrier to small hands. In areas where trees create too much shade and root competition for a solid lawn, you can substitute a thick, shade-loving groundcover like pachysandra. You can also lay landscape fabric, topped with wood chips, on the ground to establish a barrier in sun or shade. In flower and shrub beds, maintaining a permanent mulch of leaves, straw, or other organic material is also effective. Avoid any tillage. If elevated lead levels are confined to certain areas—near house walls, for example, from past use of lead paint—you can exclude children from those places with fencing or by planting prickly shrubs.

Lead is not a plant nutrient, so roots take up very little of the metal. The hazard from growing edible plants in lead-rich soil comes from earth that clings to root vegetables or adheres to the leaves of lettuce and leafy greens. Eating vegetables, fruits, or herbs grown in soils with lead levels as high as 1,000 ppm shouldn’t present a hazard as long as root vegetables are well-scrubbed or peeled, and leafy vegetables are washed well. Even soil lead levels above 3,000 ppm shouldn’t pose a risk for fruits and vegetables that grow tall or that have smooth skins, which limit the chances of holding airborne particles. (Nonetheless, bringing this soil indoors on clothes, shoes, and hands still presents a hazard.) An alternate gardening approach appropriate for any level of lead in soil is to construct raised vegetable beds and fill them with new, uncontaminated soil. Avoid deep tillage, which would bring lead-rich soil to the surface.

Lead can exist in more than one form in the soil, and all forms aren’t equally able to find their way into our bloodstreams when ingested. Dr. Rufus Chaney, along with co-workers at the U.S. Department of Agriculture, has developed a method of "deactivating" soil lead. This bioremediation entails tilling large amounts of compost rich in both iron and phosphorus into the soil. You need about five pounds of compost per square foot, or an 8” depth, plus you must add limestone or wood ashes to make the soil more alkaline. These treatments have reduced lead bioavailability by more than 50 percent and work in soil with lead levels up to 2,000 ppm. Granted, this bioremediation requires a large amount of compost, but the process is a one-time deal. In addition to deactivating the lead, it also creates a very rich soil that, in turn, nourishes dense grass growth that helps keep the soil in place.

Dr. Chaney is exploring the possibility of specially formulating composts for lead remediation. Municipal composts from sewage treatment plants work well because iron is added during processing to separate phosphorus and prevent it from entering waterways; your backyard compost isn’t rich enough in iron and phosphorus to effect this level of lead remediation.

One final way to deal with lead in soil is to remove all the surface soil and replace it with a clean layer—what I call the Herculean Approach because it’s so labor-intensive. Thankfully, there are many other options to consider before this act of last resort—or moving like Linda did.

Lee Reich, PhD, gardens around an old house in New Paltz, New York, and is the author of Uncommon Fruits for Every Garden (Timber Press, 2004) and Weedless Gardening (Workman Publishing, 2001).

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Looking Out for Lead Paint.

Best Ways to Test

Getting accurate soil samples can be a challenge because, even for a modest-sized problem area of 100 square feet, the amount of soil used for a test will only be about two cups’ worth—or representative of about .002 percent of the top 6” of the ground. When you think of it this way, it’s easy to understand why it’s so important to composite the samples you take in each area in order to get accurate results.

A test area should be relatively uniform. Where obvious differences in soil or topography exist, you should subdivide these spots into separate testing areas. To avoid non-representative samples, take a half-dozen specimens from random spots within the designated area. Remove surface debris like compost, sod, or plant residues, then make a hole to sampling depth—for lead you should sample the top inch, then the top 6” of soil, separately—but don’t use this first bit of soil for your specimen. Instead, take a slice, uniformly thick from top to bottom, from along the edge of the hole you just made. You could also use a soil probe.

Gather specimens from each test area and depth into a separate clean plastic bucket. Thoroughly mix them together, crumbling the soil while discarding stones, sticks, insects, and other debris. Spread the soil out on a clean baking pan to air dry for a day, then remove two cups for testing. Throughout sample preparation, it’s important to avoid contamination from either your hands or dirty utensils. Follow any packing instructions supplied by the testing laboratory, and label the 1” and 6” depth samples from each area—making a note for yourself of their location on your property.


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