What are soil contaminants – and how did soil get contaminated?

In its original state, soil was an uncontaminated substance covering the earth. But, humans have intentionally and accidentally poured harmful products onto it in some areas. The waste can hurt the soil and possibly human, plant, and animal health.

The biggest risks for soil contamination are in urban areas, and former industrial sites. However, if you are unsure about the condition of the soil near your home or property, it’s best to have a soil test done to be sure about its safety. Of course, most soil is perfectly safe for play, gardening and recreation, but it’s best to be safe!

Central Park in New York, lake, grassy field and skyscrapers behind
Soils in the city have a risk of contamination due to runoff from pavement, overuse, and other factors. Credit: Barrett Kays

Common contaminates in urban soils include pesticides, petroleum products, radon, asbestos, lead, chromated copper arsenate and creosote. In urban areas, soil contamination is largely caused by human activities. Some examples might be manufacturing/industrial dumping, land development, local waste disposal, and excessive pesticide or fertilizer use. Even heavy car and truck traffic can contaminate soil; have you ever noticed a shiny puddle under your car in the driveway? That’s oil – a petroleum product – and when it rains, that oil could end up in the soil!

Where and how much contamination is added to soils will largely determine how that contamination is spread throughout an area. Type of soil will also play a role in its distribution. For example, certain contaminants may reach ground water sources more easily in sand than clay. This is because of faster infiltration rates of coarse grained sandy soil types. Fine-grained clay soils or organic material in surface soils can hold contaminants tightly, which means the contaminants will accumulate if left undisturbed (e.g. no excavation or tillage).

There are several ways humans can be exposed to soil contaminants. The most common are:

  • Ingesting soil
  • Breathing volatiles and dust
  • Absorbing through skin
  • Eating food grown in contaminated soil

Urban gardens are usually a good idea, but it’s best to know your soil. Many vegetables and herbs can absorb contaminants as they grow. That puts you at risk if you eat them. Also, vegetables and herbs can have dust on them coming from contaminated soil. If not properly washed, you could ingest the contaminants. Some garden beds may also be lined with chemically treated wood. If you did not build your garden beds yourself, it’s best to test your soil because the chemicals can leach into the garden soil.

Urban soil assessment and restoration will be critical in the future to assist in feeding the projected growing population. Depicted here is a student collecting soil samples for analysis with the hopes of generating a restoration plan to improve overall soil health on this urban lot in Columbus, Ohio. Credit: Nall Moonilall

Home yard areas may not be obvious sites for soil contamination. But, during housing construction, soils can get contaminated. Petroleum products from the construction vehicles leak onto them. Paint may spill. Even fibers from roofing products can blow onto soil and disrupt life in soil. These are just a few examples of construction contamination of soils on home sites.

Homeowners may also inadvertently contaminate their soil. Overuse of pesticides or herbicides is the primary culprit. But, sometimes chemically treated wood is used in landscaping. If not used properly, this can contaminate the soil, and the plant and microbial life that it sustains.

My colleagues and I have created additional information on the Soil Science Society of America public information pages, Discover Soils. Visit https://www.soils.org/discover-soils/soils-in-the-city/soil-contaminants to start learning more today!

By Lauren Svejcar, Murdoch University

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