Heavy Metals in Soils: Urban Gardening

A photo of someone driving a spade into a garden with their foot.
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Impact7G manages lead-based paint inspection and abatement programs in several communities in addition to managing heavy metals in soil and groundwater at brownfield redevelopment sites.  This brochure titled, “Heavy Metals in Soils: Urban Gardening,” provides some helpful information related to heavy metals in some of our urban soils and tips to reduce the risk of being exposed to these substances.

Lead and arsenic are potentially harmful heavy metals which are naturally occurring and commonly found in soil.  Lead and arsenic poisoning is a particular concern for young children (under the age of six) because their rapidly developing bodies are very sensitive to the effects of lead and arsenic, and their play habits tend to increase exposure.  For young children, hand-to-mouth activity is an important exposure route.  For adults, most exposure to lead and arsenic occurs through diet and inhalation.

Major causes of soil lead contamination in populated areas can be from:

  • Pre-1978 constructed structures with lead-based paint which has weathered, chipped, or been sand-blasted off.
  • Vehicle exhaust from now-banned leaded gasoline.
  • Insecticides which contained lead.
  • Lead refineries, industrial sources, and coal-fired power plants.

Soil arsenic contamination can be from:

  • Leaching from decks and fences built with wood that has been treated with arsenic pesticides.
  • Leaching from arsenic-treated wood ties or from pesticide application associated with railways.
  • Insecticides which contained arsenic.

Lead and arsenic pose the greatest human health hazards when particulates are inhaled or ingested.  Garden produce, which has accumulated lead in its tissue or has soil particles adhering to it, can also be a hazard if eaten.  As with most soil contaminants, lead and arsenic tend to stay in the roots with minimal transfer to leaves and fruit.  Root vegetables (carrots, potatoes, turnips, radishes, beets, etc.) growing in lead and arsenic-contaminated soil are more likely to contain these contaminants than fruiting plants (tomatoes, peppers, peas, squash, berries, melons etc.).

Lead and arsenic particles can settle on vegetables grown in lead and arsenic-contaminated soil or in areas where lead or arsenic-laden air pollution settles.  People can be exposed to lead and arsenic by eating unwashed fruits and vegetables.

To reduce your risk of lead or arsenic poisoning, the following is advised:

  • Locate gardens away from old painted structures and heavily traveled roads.
  • Give planting preferences to fruiting crops (tomatoes, squash, peas, sunflowers, corn, etc.)
  • Incorporate organic materials such as high-quality compost, humus, and peat moss.
  • Lime soil as recommended by soil test (a soil pH of 6.5 to 7.0 will minimize lead availability).
  • Wear gloves in the garden.
  • Wash hands immediately after gardening and prior to eating.
  • Peel root crops and wash all produce thoroughly.
  • Be especially careful in washing vegetables that may trap dust, such as leafy greens, broccoli, or cauliflower.  Remove the outer leaves of greens.
  • Protect gardens from airborne particulates using a fence or hedge.  Fine dust has the highest lead and arsenic concentrations.
  • Keep dust in the garden to a minimum by maintaining a well-mulched, vegetated, and/or moist soil surface.

If elevated lead or arsenic levels are present in soil, grow crops in raised beds built with non-contaminated soil and organic amendments.  When building raised beds, the best choices are untreated and rot-resistant wood like redwood, red cedar, or lumber made from recycled plastic.   

Restrict access of children to lead or arsenic-contaminated soils by maintaining dense cover.

Be cautious about placing your garden close to older structures and fencing.

 

References: Healthy Soil: Arsenic and Your Plants: Wisialowski & Goddard, 2018 https://mytapscore.com/blogs/tips-for-taps/healthy-soil-arsenic-and-your-plants Soil Lead: Testing, Interpretation, & Recommendations: UMass Extension https://ag.umass.edu/home-lawn-garden/fact-sheets/soil-lead-testing-interpretation-recommendations    Should I Worry about Heavy Metals in My Garden Soil: Oregon State University Extension Service https://extension.oregonstate.edu/gardening/techniques/should-i-worry-about-heavy-metals-my-garden-soil • Best Practices for Urban Gardening – Lead and Arsenic in Soil: City of Berkeley, 2012

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