Traffic pollution a threat to a backyard garden?
I'm thinking of establishing a backyard garden at our house located on a main thoroughfare in Ann Arbor. We tend to get a substantial layer of a soot-like substance out on the street-facing porch, presumably from the consistently high level of passing traffic; presumably this is accumulating on everything else in the yard as well. Should I be concerned about this "soot" accumulation in evaluating whether to establish a garden here?
Washtenaw County Michigan
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High traffic zones are an area with increased risk for soil contamination. Two notable, potential contaminants in high traffic zones are lead and PAHs (polyaromatic hydrocarbons), as mentioned in the article Sources and Impacts of Contaminants in Soils from the Cornell Waste Management Institute.
To really know whether soil contamination is a problem in your yard, you would have to get the soil tested for contaminants. The Soil and Plant Nutrient Laboratory (SPNL) at Michigan State University (MSU) recommends contacting the following labs, outside of MSU, to inquire about testing for soil contaminants:
Element Materials Technology
Please ask these labs for guidance in deciding what contaminants to test for, if you’d like to go that route. Just so you know, contaminant testing can be expensive.
You can purchase a home lawn and garden "Soil Test Kit Self-Mailer" from MSU for $25, but this does NOT include testing for soil contaminants, unless testing for lead or arsenic is requested for an extra fee.
As mentioned in the "Don't guess - soil test! ..." article from MSU Extension, the home lawn and garden soil test mailer results will determine your soil type, pH, level of organic matter and provide you with a reading for nutrients including phosphorus, potassium, calcium and magnesium. The results will also provide a recommendation for nitrogen and will determine how much lime should be applied based upon the type of plant you specify.
The pH of the soil is one factor that determines the bioavailability of certain contaminants, such as heavy metals, to plants, so having an accurate reading of your soil pH from a lab soil test is helpful for managing any contamination present, as well as to manage general plant health.
The level of organic matter in the soil also determines bioavailability of contaminants, with a greater amount of organic matter reducing the bioavailability of certain contaminants.
For an extra $28 dollars EACH, you can request that the soil sample you send with the MSU Soil Test Kit Self-Mailer be tested for lead or arsenic as well. You can write which tests you want on the soil test kit form and include a check made out to MSU. The regular soil results will be received first, and about a week later, the lead and/or arsenic results will follow.
Visit http://www.msusoiltest.com/ for more information about home soil testing at MSU.
Even if there is contamination in your yard soil, certain precautions can be taken to avoid extra exposure.
Unfortunately, leafy greens have a larger surface area for collecting soil and particles from the air, so you might want to avoid planting them in areas with potential soil or air pollution. Food crops grown for their seeds and fruit are more appropriate in contaminated areas. Still, wash all produce carefully before eating.
I would highly recommend reading the article Soil Contaminants and Best Practices for Healthy Gardens, again from Cornell Waste Management Institute. Cornell seems to have some great resources related to this question topic on their “Healthy Soils, Healthy Communities” website. See the following webpages from Cornell:
There’s also a nice article from Minnesota called Urban Gardens and Soil Contaminants.
A couple more related articles:
Soil contamination can be a deterrent to urban agriculture from MSU Extension
How might Flint’s water contamination affect garden soils? Part 1 from MSU Extension
Please let me know if you have any further questions.