Timely tips for urban gardeners concerned about lead safety

For Paula Gordon the question of why she has a garden smack dab in the middle of town, the answer is easy.

“I like growing things,” she says, as she stands in her front yard surrounded by all manner of plants, including vegetables, herbs, berries, and flowers.

But she’s quick to say that it goes further than that. “I want to know what I’m eating,” she says. “I’m skeptical about modern farming practices. Everything I grow is organic.”

When her town, Sedro-Woolley, WA, went into partial lockdown in 2020 because of Covid-19, she decided she’d grow her own food, although she had already turned her entire front yard into a garden years ago. This time, though, she would be growing more food than usual.

“It saved my sanity,” she says, referring to having a project like this to keep her busy and happy.

Gordon is not alone in this. According to Trust for Public Land neighborhood gardening statistics, there are more than 29,000 community garden plots in city parks in the 100 largest U.S. cities. And though Gordon’s garden isn’t a community garden in a city park, it represents the growing interest people have in planting gardens in their own yards.

Gordon’s garden is a bit unusual in that she grows her plants in large trash cans and other containers. By early September, she had already harvested most of her potatoes as well as greens such as lettuce and kale, although there was still a lone kale plant reaching for the sun. Large green tomatoes hang from sturdy plant branches, sweet basil is abundant and vigorous, and strawberries peek up from their containers. In her backyard, grapes and kiwis thrive.

Since the house was built in the 1920s, she’s not worried about lead or other contaminants left over from things like a parking lot or factory, or a house that has been torn down on the site, all of which could leave contaminants in the soil.

“It’s good sandy loam,” she said, referring to the soil she filled the planting containers with.

And even though she’s on city water, she washes her produce with water from a friend’s place whose water has been “super filtered.”

The soil
When it comes to planting a garden in town, or a city, there’s more to it than putting a shovel into the ground and planting some seeds or plants.

That’s because the way the land has been used in urban areas can often leave an unfortunate legacy of contaminated soils. The plot itself might have been through quite a lot of uses, and some of them can be worrisome for a gardener.

For example, sites, where there were commercial or industrial buildings, are often contaminated with lead-based paint chips, asbestos, petroleum products, dust, and debris.

Then too, vehicle exhausts can be a problem. As the result of past use of leaded gasoline, lead can also be found in the soil near major roadways or intersections.

And old houses, as charming as they may be, often have lead concentrated near their foundations. And when they’re torn down or renovated, lead dust can contaminate the soil. Another thing to consider is that if the house is 50 years or older and if it’s painted, lead paint may have chipped off the house and landed in the soil directly next to it.

Even an apple tree can be suspect simply because it could have been sprayed with an arsenic-based pesticide, year after year.

Then, too, soil in former parks and along railroad rights-of-way can harbor pesticide residues.

All of this means that urban gardeners concerned about food safety will want to have the soil tested before planting any seeds in the ground.

But because testing the soil for an array of possible toxins can be expensive, some urban gardeners remove the old soil, place an impermeable barrier on the ground, and add new topsoil. Or, like Gordon, simply put new topsoil in large barrels or tubs and plant their gardens in them. Potatoes and carrots even do well when planted this way, not to mention lettuce, greens, and an array of vegetables.

Even former First Lady Michelle Obama had to make sure that the lead levels in the ground where she wanted to plant an organic garden on the South Lawn of the White House didn’t have dangerous levels of lead in it. The initial concern was that the ground had previously been spread with biosolids, also known as sewage sludge.

Fortunately, testing showed that lead levels were far lower than what was considered to be a possible danger to human health. And with that much confirmed, the crops were planted directly into the ground. Happy kids and vegetables are galore.

The water
An urban gardener needs to consider the source of the water used to water the garden. Fortunately, most public water systems provided by cities or other municipalities should be safe. Water authorities use filtration, chlorination, and testing to make sure the water meets U.S. Environmental standards for drinking water.

But that’s not the case with untreated water from unregulated sources such as rivers, streams, irrigation ditches, ponds or wells, all of which can be contaminated with biological and chemical hazards such as lead, bacteria, viruses, domestic waste, nitrate nitrogen, combustion products from roadways, petroleum residues and heavy metals. That’s why if the garden is being irrigated with untreated water, regular testing of the water is advised.

Well water should also be tested to make sure it’s up to the Environmental Protection Agency’s standards for drinking water.

Bottomline, if you wouldn’t drink the water, don’t apply it to the edible parts of the plants.

Another problem is what is called “splash.” If the soil does contain some lead, when it rains or when the garden is watered with an overhead system, some of the water will splash up from the soil onto the plant, thus depositing some lead onto the plant.

That’s why using drip irrigation or applying the water at the base of the plants is the best way to cut down on soil and water splash, thus reducing risk. Hand watering is another option as long as the water is applied carefully so it only touches the base of the plant.

According to a new study done by researcher Sara Perl Egendorf and her team at Cornell University, placing some mulch around plants such as lettuce, greens, and other crops that could get “splashed,”  or using hoop houses, or small greenhouses, are effective ways to reduce lead contamination simply because they keep contaminated particles away from the plants.

Rain barrels?
While there is a lot of interest in collecting water in rain barrels or cisterns to be used to water a garden, some precautions are in order.

For example, what about water runoff from a roof? Factors to be considered in this sort of situation are the climate, the age of the roof, the roofing materials, air quality, and the slope of the roof. Roofs with metal surfaces require more water-safety considerations, which would include the type of coating used on the metal. In addition, nonmetal gutters and downspouts should be installed.

As for using rainwater in barrels, it should be tested to make sure it doesn’t test positive for pathogenic E. coli or other foodborne pathogens. If it does, it should never touch the edible part of crops, although it can be just fine for watering ornamental plants.

Lead
The most common type of contaminant in urban soil is lead. Elevated lead in urban soil generally comes from the historic use of leaded gasoline and lead paint. Lead in exhaust from cars when leaded gasoline was still in use will have contaminated the soil.

The soil in an urban garden is most likely to be contaminated with lead if the site is next to a very busy, high-traffic road that has existed for more than 40 years.

Lead is a neurotoxin that can damage multiple organ systems and can pose a dire threat to children especially.

“It is incredibly important to know if urban gardeners are being exposed to lead when they consume their produce,” says Cornell researcher Egendorf, lead author of a new study showing that washing lettuce grown in urban gardens can remove most lead contamination.

The study, “Effectiveness of washing in reducing lead concentrations in lettuce,”  was published in the Journal of Environmental Quality.

Egendorf and her colleagues grew lettuce in an urban community garden in Brooklyn, NY, and in a rural field site in Ithaca, NY. They focused on lettuce because predicting lead levels in leafy greens like lettuce can be tricky.

“Leafy greens often have intricate surfaces,” says Egendorf. These surfaces can trap lead-containing soil particles that may be hard to wash off. “We really didn’t know if washing lettuce could effectively remove contaminated soil.”

The lettuce was grown in soils containing either high or low levels of lead in an urban community garden in Brooklyn and in a rural field site in Ithaca.

Some unwashed lettuce grown in low-lead soils had elevated lead levels. All unwashed lettuce grown in high-lead soils had lead levels above government standards. However, washing the lettuce reduced lead levels to below these guidelines in all cases.

The researchers tested different washing strategies: rinsing with tap water, soaking in water, soaking in vinegar, or soaking in a commercial vegetable wash solution.

The conclusion, according to a press release about the study: Washing effectively removed lead contamination from lettuce leaves.

“All the wash methods we tested worked,” says Egendorf. “We also found that washing lettuce grown in low-lead soils was still important to reduce lead levels before consuming. Some unwashed lettuce grown in low-lead soils had elevated lead levels. All unwashed lettuce grown in high-lead soils had lead levels above government standards. Washing reduced lead levels to below these guidelines in all cases.”

Using mulch or covers over the lettuce can work to prevent soil splash and lead deposition on the plants. But even more effective is combining these practices and washing the lettuce gave the best result.

For example, according to the study, mulching alone reduced lead levels in unwashed lettuce by 76 percent while washing alone reduced levels by 85 percent. Better yet, says the study, mulching, and washing combined reduced lead levels found on the lettuce by almost 97 percent.

Egendorf says reducing exposure to lead is of the utmost importance.

Children are especially at risk from lead exposure because lead can cause major harm to brain development. In adults, long-term exposure to lead can cause many issues, which include kidney damage and a decline in cardiovascular and nervous system health. Lead exposure has been shown to cause more than 400,000 premature deaths per year in the United States.

Children can be exposed to lead in soil by swallowing or breathing in lead-contaminated soil while playing.

Lead-contaminated soil particles can also be brought inside as lead dust or on shoes, clothing, or pets.

Egendorf and colleagues are sharing their findings with organizations, agencies, and extension specialists.

“We want to encourage urban gardeners to keep doing their important work,” says Egendorf. “We also want to make sure they have access to strategies for safe and effective gardening.”

Strategies
Here are some tips from the Soil Science Society of America:

Remember this: Lead stays where it lands.

°If you have an older home with a high potential for lead paint, plant your vegetable garden away from your home’s drip line. The lead contamination is almost certain to be highly localized — right under your house. Move away from the drip line and you move away from the high-lead area.

°If you live near a busy street, the easiest thing to do is to plant your garden a few feet away from the curb. The farther you are from the street, the lower the soil lead concentration will be.

°Till your soil. Because lead typically lands on the top of the soil, it’s likely that high concentrations will be limited to the top inch or two of your soil. Mixing the soil with a hand tiller wi ll reduce the lead concentration by mixing the contaminated soil on top with the lower-lead soil on the bottom.

Researchers also recommend putting a layer of compost on top of lead-contaminated soil, which significantly dilutes the lead concentration, according to several previous studies. In some instances, compost will actually render the lead insoluble, meaning it’s unlikely to be absorbed into the bloodstream if eaten.

°Add fertilizers to your soil. Remember that urban soils are often neglected soils. Adding fertilizers, especially phosphorus fertilizers, will help your plants grow. Phosphorus will also bind the lead and make it much less dangerous over time. The EPA has tested adding phosphorus to Superfund sites as a way to take away the hazard while still leaving the lead in place.

What about other crops?
According to research done at the University of Washington, while lead might get into the roots of plants such as lettuce and other greens, it usually doesn’t go past the roots.

However, root crops such as potatoes, carrots, turnips, and beets can have a slightly higher lead content when grown in an urban garden. If soil testing shows that the soil does have lead, many root crops can be grown in containers using new topsoil. Go here (How to grow potatoes in containers YouTube) and (How to grow carrots in containers YouTube) to see how it can be done.

Crops such as tomatoes and tree fruit will be fine since they’re so far up from the soil.

Even so, the rule of thumb is to wash all produce with running cold water.

“The real danger is in the soil, not in items grown in the soil,” say researchers.

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