If your soil contains high levels of lead, planting in a raised bed can be a good way to avoid the toxic heavy metal element. Credit: Sam Schipani / BDN

There are a number of good reasons to have your soil tested before planting a garden. The results can give you an idea of the nutrients your soil contains and its level of acidity. One result you may not have thought about is the presence and amount of lead in your soil.

Lead is a toxic heavy metal element that naturally occurs in nature and is found in the Earth’s crust. In nature, the levels are often too low to be harmful to humans. But for years, lead was extracted from the ground and used in concentrated levels in products like paint, ceramics, pipes, solder, gasoline, batteries and even cosmetics. In time, thanks to leaking or spilled leaded gasoline, water passing through lead pipes and lead-containing objects being thrown out, that lead eventually found its way back into the soil. In some areas, that amounted to highly concentrated areas of contamination.

Lead is still used commercially, but is now highly regulated in consumer products in the United States and was banned entirely as a paint additive in 1978. But scientists warn it’s still out there in the ground, even here in Maine.

Here’s what you need to know about lead in soil and gardening.

Why is lead a problem?

Lead exposure can lead to adverse health effects for children and adults, according to the United States Centers for Disease Control and Prevention. When children are exposed to high concentrations of lead, it can result in their experiencing brain or nervous system damage, behavioral issues, learning problems and slow growth. For adults, lead exposure can result in neurological issues, heart disease, kidney disease and gastrointestinal problems. It has also been linked to cancer in children and adults.

Lead in soil can contaminate the produce being grown. It is able to bind to the skin of root vegetables like carrots or potatoes or to greens that grow close to the ground like lettuce or spinach. If the lead content in your soil is concentrated enough, it can result in unhealthy lead levels in vegetables grown there.

Always test for lead

There is no way to know for sure if there is lead in your soil simply by looking at it. It can remain in the soil for a very long time. This is why it is crucial to have a soil test before planting your garden in an area for the first time.

“People need to be aware that lead can be in a lot of places,” Damon Yakovleff, environmental planner with the Cumberland County Soil and Water Conservation District, said. “It’s always better to err on the side of caution because maybe your garden spot in the distant past had a building with lead paint that has long been demolished.”

A building like that may have shed lead-based paint flakes into the soil for decades, allowing the heavy metal levels to creep up over time.

Planting near an existing structure that was built before 1978 could also mean you are planting in lead-contaminated soil.

“Lead-based paint was used for a long time to paint the exteriors of houses and barns in Maine,” said Dr. John Jemison, soil and water quality professor with University of Maine Cooperative Extension. “When people would scrape it, it would go into the ground and then years later people might decide to turn that spot into a garden.”

How to garden if you have lead-contaminated soil

If you’ve tested your soil and found that it’s positive for lead, you don’t have to abandon your gardening plans per se. But they will need to be modified for your safety. That might mean not planting directly into the contaminated soil or relocating your garden.

“There will be a gradation [downward] of the lead levels away from the source,” Jemison said. “If you can plant far enough away from that source, you can avoid the contaminated soil.”

If you can’t determine where the source is, or you don’t have the available space to plant far enough from it, a raised bed may be your best option. In this case, you are going to want to lay down black plastic garden cloth or fabric directly on to the ground to block the contaminated soil. Then bring in fresh, clean soil and build your bed up 12- to 18-inches using that.

Once you have taken the steps to safely plant your garden, you are going to want to keep the soil as healthy as possible to further mitigate any lead contamination. According to a publication by Oregon State University Extension Service, adding lime and phosphorus to your soil helps make the lead less soluble and more difficult for plants to absorb that lead. Also adding compost or other organic amendments to your soil is not only a good source of nutrients for your plants, it can help dilute the overall concentration of lead in a garden spot.

“A lot of people want to grow their own or eat locally grown food but they also need to be aware of any risks in the soil so they can do so safely,” Yakovleff said. “To be absolutely sure your soil is safe, we recommend testing and it can be money well spent.”

A soil test costs $18 and can be conducted by the University of Maine’s soil testing service.

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Julia Bayly

Julia Bayly is a reporter at the Bangor Daily News with a regular bi-weekly column. Julia has been a freelance travel writer/photographer since 2000.