What To Know About Soil Contamination

It’s difficult to know what might lurk under your garden and grass. In urban areas like Boston, contaminants like lead are pretty common. In suburban areas, overuse of pesticides and fertilizers are often an issue.

Soil contamination can cause problems like an annoying yellow spot in the lawn, and make you worry about what’s in your vegetables. But to understand its full brunt, it’s also important to understand the role of soils in nature. Sometimes called the kidneys of the natural world, healthy soils balance pH, salts and minerals, and filter out toxins before they reach the groundwater.

“When soils are unhealthy, the waterways are also affected,” says Kathy Glassey, director of renewable services for Monster Tree Service. “Then there’s a chain of events that continue to affect our drinking water, wildlife, habitat, birds, squirrels, fish and so on.”

Here’s what to know about potential soil contamination in your yard.

What Is Soil Contamination?

Soil contamination results from any substance that exceeds naturally occurring levels and poses human health risks. Contaminants include pesticides, petroleum products, asbestos and lead.

Contamination can be limited to a small area from, say, a piece of decomposing treated wood, or widespread from a nearby manufacturing facility.

“But this is not the limit of contamination,” says Judy Daniels, a soil and geospatial scientist at Soil Sage. “Automobiles are also a source of impurities. Cars and trucks leak oil, a petroleum product. And when that oil encounters water, it ends up in the soil.”

Soil Pollution Effects

Soils are complex mixtures of minerals, organic matter, water and life forms.

“Plant biology works synergistically with soil biology,” says Glassey. “The plants and soil all work together to provide the needs of the other. When chemical molecules interact with this symmetry, things can change.”

Some negative effects of soil contaminants on plants include:

• Reduced nutrient uptake, leading to stunted growth, reduced yields and greater susceptibility to insect damage and disease;
• Toxicity, leading to leaf discoloration and wilting, plus inhibiting photosynthesis;
• Soil acidity, with pH levels that are either too low or too high, also affects plants’ ability to absorb nutrients;
• Less diversity in soil microbes, insects and helpful bacteria;
• Ground areas with little to no vegetation;
• Damage to wildlife from diminished habitats and ecosystems;
• Damage to wildlife from toxins contaminating groundwater and the food chain.

Types of Soil Contamination

Soil contamination can come from organic and inorganic sources. Organic ones contain carbon-based compounds usually associated with human activity, such as:

• Petroleum products like gasoline, diesel and oil;
• Plastics;
• Pesticides, including synthetic herbicides and insecticides;
• Chemical detergents;
• Trichloroethylene, used in some solvents, adhesives, wood finishes and paint and stain removers;
• Perchloroethylene, used in some solvents, degreasers and, until recently, dry cleaning;
• Polycyclic aromatic hydrocarbons, found in creosote-treated wood, charcoal and gasoline;
• Volatile organic compounds (VOCs), common in paint, building supplies and cleaning products.

Inorganic soil contaminants don’t contain carbon-based compounds and often stem from industrial activity or naturally occurring sources, such as:

• Heavy metals like lead, arsenic, cadmium, chromium and mercury;
• Salts, including chlorides and sulfates;
• Acids;
• Radionuclides, like uranium and radium.

What Causes Soil Contamination?

Sometimes soil gets contaminated by accident. “If you see that pretty rainbow oil spill on your driveway,” Glassey says, “the oil will move with the next rain event and now it’s moved to the soil.”

But often, we introduce it intentionally, through synthetic fertilizers and pesticides — a practice Daniels and Glassey hope we’ll reconsider.

“Many of these substances that are toxic to plants are also toxic to humans,” says Daniels. “Let’s pause for a moment and contemplate that statement. Humans typically avoid substances that are toxic to them, so why do we intentionally contaminate the soil? It’s a question that is not easily answered.”

How To Know if Soil Is Contaminated?

If you suspect contamination, get your soil analytically tested to determine the type, plus its concentration, depth and radius. You can also ask a soil scientist or soil testing lab for advice.

Glassey recommends biological soil tests because they provide a baseline of microbes and biomass. To find biological soil testing, ask your local cooperative extension service for recommendations.

How To Treat and Prevent Soil Contamination

Treating soil contamination can take time and require different approaches, depending on the type of contaminant. Often soil needs to be removed, although sometimes it can be treated with microorganisms that break them down in place.

Because it’s difficult and time-consuming, prevention is key. Creating healthy soil to begin with, says Glassey, is the best approach.

“I say confidently that if your soils were in good health prior to any contamination event, the soil biology can certainly assist in remediating very quickly,” Glassey says. “However, if you have poor soil health lacking in microbial activity, a contamination can be devastating, requiring much more work to restore the balance.”

To prevent soil contamination

• Reduce or stop using synthetic pesticides, fertilizers and other lawn/garden chemicals.
• If you do use yard chemicals, don’t apply them if rain is in the forecast.
• Use only the amount of chemicals recommended on the labels. Using more won’t create better results. It will stress plants and cause greater soil contamination.
• Use natural alternatives for pesticides.
• Choose green outdoor cleaning products.
• Maintain your mower and other equipment to prevent gas and oil leaks.
• Clean spills and drips immediately by absorbing the liquid and disposing of it appropriately.
• Recycle used motor oil and other hazardous home chemicals at designated waste collection sites.
• Dispose of trash, especially plastics, before it can break down into the soil.
  
• Choose water-based paints.
• Wash road grime off at the car wash, to keep it from entering your soil and storm drain.
• Avoid snow and ice rock salts.
• Use non-treated hardwoods, wood composites or non-wood alternatives for building.
• Never burn products made with chemical-based materials.

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