Healthy Soil: When Tests Find Excess Lead in the Ground, Experts Advise Taking Precautions
Canillas Community Garden volunteer director Pat McGovern, center, listens to Matt Stewart, left, who teaches a food science class at Ledyard Charter School, talk about the value of gardening and eating locally at the community garden in Lebanon on September 11, 2013. The class will garden a small raised bed over the course of the year. Valley News - Elijah Nouvelage Purchase photo reprints »
Raised beds are seen at the Canillas Community Garden in Lebanon on September 7, 2013. Community garden organizers discovered that the area had previously been a dump site and that the ground was contaminated with lead. Their solution was to install raised beds with protective layers between the new and old soil. Valley News - Elijah Nouvelage Purchase photo reprints »
Before my husband and I moved to Lebanon from South Carolina six years ago, I was a would-be gardener. Compared to the hard, red clay that passed for a yard in Greenville, the rich, if rocky, soil at our new place seemed perfect for planting. I staked out a spot behind the garage, grabbed a shovel, and dug up the ground that’s come to provide about a third of our vegetables. It’s been a lot of fun, growing everything from asparagus to zucchini, but after a recent soil test found “moderate” lead contamination, I’ll be putting that plot to bed for good.
Raised gardens, here I come.
Maybe it was the junk I found in the dirt — shards of old pottery and funky metal objects bent beyond recognition. Or maybe it’s because our house is more than a century old.
Now and again, I’d wondered whether the soil might contain lead. So when a friend taking a master gardener class suggested I get it tested for nutrients, I went for it, and tacked on a metals test as well.
I mailed $24 and a cup of dirt from throughout my garden to the University of Vermont and received the results a few weeks later. In terms of nutrients and pH, the soil is pretty much perfect for growing food. Unfortunately, it’s also contaminated with lead. The initial results automatically triggered a free second test, which found 440 parts per million, more than enough to merit concern.
For contrast, the letter from UVM noted that lead paint chips, a common source of lead poisoning in children, contain as much as 30,000 to 50,000 parts per million. Eating unwashed produce grown in heavily contaminated soil, or working or playing in the soil, can “significantly add” to one’s total intake of lead, it said.
Lead exposure can lead to serious, permanent health problems, and children are especially vulnerable. In the past, a certain level of lead in a child’s blood was considered acceptable. But that’s changed.
“We know that extremely high levels can cause death and brain damage,” said Dr. Lou DiNicola, a pediatrician at Gifford Medical Center for 37 years. But over the decades, research has shown that IQs in children with no outward signs of lead poisoning and low blood lead levels can be “significantly depressed,” by 10 or so points, DiNicola said.
The majority of lead exposure comes from paint chips and dust, often stirred up during renovations and repairs in old houses, said Michael Dumond, bureau chief for the Bureau of Public Health Protection in the New Hampshire Division of Public Health Services.
In terms of lead, it’s not hard for a house to qualify as old — lead-based paints were not banned in the U.S. until 1978. According to the Centers for Disease Control and Prevention, all houses built before that time are likely to contain some lead-based paint.
But when it comes to accidental ingestion, paint is not the only culprit. DiNicola, who’s served on the executive board of the Vermont chapter of the American Academy of Pediatrics for more than two decades, has seen cases where children living in new houses test high for other reasons, such as chewing on antique furniture decorated with lead paint or drinking water piped through plumbing that contains lead. And, Dumond said, there have been cases of high lead levels resulting from exposure to contaminated soil.
For those working or playing in soil that contains lead, the main risks are ingestion and inhalation.
“Unless your soil (lead) levels are really high, like in the hundreds of parts per million, plants don’t take up very much,” said Joel Tilley, a research specialist with UVM’s Agricultural and Environmental Testing Lab. Instead, exposure usually comes from eating soil trapped in the crevices of leafy greens or root vegetables, or when children play in the dirt, and then stick their fingers in their mouths.
Safety recommendations vary, depending on how much lead is present. But even for soil with “slight” contamination, recommendations include washing all produce, peeling root vegetables, and moving play equipment away from the affected area.
“You wouldn’t want to have a playground swingset that would be raising a lot of dust,” Tilley said.
In my case, where the lead level is considered moderate, recommendations include having blood lead levels tested and growing only fruiting vegetables, such as peppers, squash and tomatoes. Leafy vegetables and root crops should be avoided. The soil pH should be kept between 6.5-7.0, as lead is less soluble in a neutral environment, and manure and compost should be added every year. Adding organic matter helps bind the lead atoms to the soil, reducing the risk that plants will take up metals, Tilley said.
Suggestions for heavily contaminated areas include covering the soil with a barrier, such as grass or mulch, and bringing in clean fill for gardening.
By far the most common source of lead in soil is old paint chips, although land alongside busy roads can have fairly high lead levels from the days when it was an ingredient in gasoline, Tilley said. Other less common sources include old junkyards or garages, where scrap metal or batteries were dumped.
He recommends soil testing for those who suspect they may have contamination or whose gardens are very close to an old house. “About 10 to 15 percent of those who ask for lead results have something above normal background level of 10 to 20 parts per million,” he said.
For those who live in old homes, DiNicola generally cautions against gardening within a 10-foot radius of the house. But, he pointed out, homeowners may not be aware of old dump sites or remains of buildings.
“It’s a great idea to have your soil tested,” he said.
I don’t want to give up on greens and root vegetables, so next spring, I plan to build raised beds. For suggestions, I contacted Canillas Community Garden in Lebanon, where organizers tackled the lead question when they were first starting out.
The organic garden is a collection of 35 raised beds on land owned by the Carter Community Building Association. It provides fresh produce for dozens of families, and lanky sunflowers add a bright splash of color to the neighborhood. But getting it going was a challenge, said Pat McGovern, who serves on the garden committee.
The hard, gray-colored soil was shot through with old bottles, coal ash, irons and pitchforks, she said. “We couldn’t even get a stake under the sod.”
As it turns out, the spot was a former dump site, likely from the early 1900s.
“It was kind of a treasure trove, but it was not good for a garden,” McGovern said with a chuckle. They contacted Grafton County’s UNH Cooperative Extension office about soil testing, and when lead was discovered, for advice about raised beds.
To prevent contact with the contaminated soil, they built frames from rough-sawn hemlock, which they lined with landscape fabric and filled with a blend of topsoil and compost. The original plots are 10 inches high, but recently, with the help of Upper Valley Healthy Eating Active Living, they added two 20-inch high beds. The taller beds, which require less stooping, have proved popular, McGovern said.
Most of the people I talked to advised against using pressure-treated lumber, due to its chemical content, and recommended rot-resistant wood, such as cedar or hemlock.
It won’t be cheap. I’ve just started shopping around, but so far, I estimate the material to build and fill three 4-by-6-foot beds will set me back about $300. But considering the annual returns: fresh red lettuce, mounds of sweet, crunchy carrots and a freezer full of kale, I figure it’s a solid investment.
Information about soil testing is available at extension.unh.edu/Soil-Testing and pss.uvm.edu/ag_testing/. For more information about lead testing, go to www.dhhs.nh.gov or healthvermont.gov/index.aspx.
Aimee Caruso can be reached at firstname.lastname@example.org or 603-727-3210.