What to do about lead contaminated garden soil

Get the lead out — Last year when we were restoring the exterior of our historic net zero energy house, our restoration painter, Chad Pratt, did his best to follow the new EPA rules and mitigate lead contamination.  The house looks gorgeous, and we have no more lead to worry about.  But, despite our efforts to contain the lead dust, our year-and-a-half-old daughter tested for high levels of lead in her blood.  By immediately cleaning up all sources of lead dust, we were able to bring her levels down quickly and she’s fine.

At high concentrations, lead is a potentially toxic element to humans and most other forms of life.  Soil around old buildings and homes with lead-based paint is a common cause of contamination.  The dust tracked into the house can easily wind up in the mouths of vulnerable young children who spend time crawling on floors.  So, it’s really important to take care of any lead in your soil.

Figure 1. Pathways of Lead Exposure in the Home Environment

Lead in garden soils and plants

According to researchers at the University of Minnesota “the most serious source of exposure to soil lead is through direct ingestion (eating) of contaminated soil or dust.” The good news is that plants generally don’t take up lead.  Some lead can be taken up into plants in soil with high lead levels.  It’s generally considered safe to eat food from garden soil with lead levels of less than 300 ppm (parts per million).  The higher the ppm, the higher the risk.  If you are concerned you may have high lead levels in your soil, take it to the local agricultural extension for testing.

Dealing with lead-contaminated soils

1. Keep soil pH levels above 6.5. Lead is relatively unavailable to plants when the soil pH is above this level.
2. Scrape and remove as much of the top layer of soil as practical
3. Add a good layer of compost or clean soil.  This lowers concentrations of lead and helps bind lead to organic material and minimizes uptake into plants.
4. If your soil tests for lead above 100 ppm, and you have children that could ingest the soil from hand to mouth activity, you should not use the soil for gardening and should follow the steps above.  Adults should be safe to eat from garden soil with levels up to 300 ppm.
5. Locate your garden as far away from busy streets or highways and older buildings as possible.

Can you use plants to remove lead from contaminated soil?

In short, not really.  Using plants to draw heavy metals from soil is called bioremediation.  While this method has shown promise for other metals, it does not appear to have value for lead. For now, removing some of the soil, mixing the remaining soil with fresh compost or clean soil, and keeping pH levels high is the best methods available.

Contact your local health department or private physician for information about blood lead testing.

For more information on the abatement of lead, call your local health department or read this paper from University of Minnesota Lead in the Home Garden and Urban Soil Environment.

Matt Grocoff is host of Greenovation.TV, a contributor to The Environment Report on Public Radio and the green renovation expert for Old House Web. His home was honored as one of USA Today’s “Seven Best Green Homes of 2010″.  He has been featured in hundreds of publications and news shows including USA TODAY, Washington Post, Detroit Free Press, Miami Herald, Preservation Magazine, Solar Today, Fox Business News, Huffington Post and more.  Join him on Twitter and Facebook