#6 Soil Contamination
Contamination in Urban Soils
Farmers wanting to cultivate unfarmed urban soils should be aware of possible soil contamination, whether by physical debris or chemical or other toxins. Physical debris, such as blacktop, glass, and gravel, can be identified and removed much more easily than chemical, heavy metal, or other contamination.
Determining Soil Contamination
Before beginning any urban farming project, it is important to identify soil contaminants by:
- Evaluating your land-use history, as well as the history of nearby properties, and
- Performing a soil test, including a test specifically for heavy metals.
When evaluating your land-use history, some possible starting points are city planning departments, local historical associations, previous owners and older neighbors. Soil tests should be repeated at least yearly, and farmers should consider a plant tissue test to evaluate the amounts of heavy metals (lead, arsenic, and mercury in particular) being taken up by crops.
Soil and Plant Tissue Testing Services
Soil testing services in or near New York State offering heavy metal testing include:
- Cornell University Nutrient Analysis Laboratory, online at cnal.cals.cornell.edu/, Form S on the Forms page (https://cnal.cals.cornell.edu/submission-forms/)
- Brooklyn College Environmental Sciences Analytical Center, online at https://www.brooklyn.edu/usl/
- UMASS Amherst Soil and Plant Tissue Testing Laboratory, online at soiltest.umass.edu/
Farmers should take care to follow the soil sampling procedures provided by each service. For a list of laboratories certified by the NYS Department of Health Environmental Laboratory Approval Program (ELAP), visit wadsworth.org/labcert/elap/comm.html. Farmers should be careful when switching between laboratories, since procedures may differ across labs. A “Guide to Soil Testing and Interpreting Results” is available from the Cornell Waste Management Institute at cwmi.css.cornell.edu/guidetosoil.pdf.
Heavy Metal Levels and Safety Guidelines
Though there are currently no specific regulations or guideline values specifically for garden soils, A&L Eastern Laboratories, Inc. in Richmond, Virginia provides a helpful chart for interpreting soil tests and safety guidelines for gardening in contaminated soils, by type and level of most common urban soil heavy metal contaminants. A PDF containing this chart and other information about heavy metal soil contaminants is available at al-labs-eastern.com/forms/Heavy%20Metal%20Interpretation.pdf.
Heavy Metal Levels and Safety Guidelines (cont’d)
|Heavy Metal||Typical Levels for Non-Contaminated Soils||Unsafe for Leafy or Root Vegetables||Unsafe for Gardens and Contact|
|Arsenic||3 to 12 ppm*||>50 ppm||>200 ppm|
|Cadmium||0.1 to 1.0 ppm||>10 ppm||>50 ppm|
|Copper||1 to 50 ppm||>200 ppm||>500 ppm|
|Lead||10 to 70 ppm||>500 ppm||>1,000 ppm|
|Nickel||0.5 to 50 ppm||>200 ppm||>500 ppm|
|Selenium||0.1 to 3.9 ppm||>50 ppm||>200 ppm|
|Zinc||9 to 125 ppm||>200 ppm||>500 ppm|
*ppm = Parts Per Million
Note that these are general guidelines and that actual toxicity and unsafe levels will be affected by soil texture, pH, and organic matter. For soils with heavy metal levels unsafe for gardening or contact, call your city’s Health Department or the New York State Department of Environmental Conservation (dec.ny.gov/) regarding removal.
Farmer and Community Safety
It is important that farmers keep in mind that people are exposed to soil contaminants primarily by physical exposure to the soil itself, and especially by breathing soil dust. Farmers and urban farm site visitors should follow safety precautions, as outlined in Factsheet #7, Dealing with Contaminated Soils, to minimize exposure.
For More Information
The Cornell Waste Management Institute (CWMI) provides several resources about soil contamination, including “Sources and Impacts of Contaminants in Soils” and “Soil Contaminants and Best Practices for Healthy Gardens,” both available for download from the Institute’s website at cwmi.css.cornell.edu. See also the CWMI Healthy Soils, Healthy Communities website at cwmi.css.cornell.edu/healthysoils.htm and http://cwmi.css.cornell.edu/Soil_Contaminants.pdf , which provides various resources about soil contamination and remediation.
The University of Louisville also offers a practical guide to gardening in contaminated urban soils, including information on the sources and dangers of soil contamination, on soil testing and determining soil safety, and remediation options. This publication, “Urban Agriculture and Soil Contamination: A Guide to Urban Gardening” is available for free download under Practice Guides at louisville.edu/cepm/publications.
The United States Department of Agriculture’s National Resources Conservation Services (NRCS) provides a website about urban soil issues at https://www.nrcs.usda.gov/conservation-basics/natural-resource-concerns/soil/urban-soils. This website includes links to relevant sites and related resources, including the “Urban Soil Primer,” a comprehensive guide to urban soils available for free PDF download. Printed copies of the Primer can be requested by calling (888) 526-3227 or emailing NRCSDistributionCenter@ia.usda.gov.
The United States Environmental Protection Agency’s “Evaluation of Urban Soils: Suitability for Green Infrastructure or Urban Agriculture” (publication number 905R1103, 2011) is a guide to the evaluating the suitability of urban soils and to remediation and coping strategies, available for free download at water.epa.gov/infrastructure/greeninfrastructure/upload/Evaluation-of-Urban-Soils.pdf.
The Resource Centres on Urban Agriculture provides a practical guide to “Soil Contamination and Urban Agriculture,” produced by Alexandra Heinegg, Patricia Maragos, Edmund Mason, Jane Rabinowicz, Gloria Straccini and Heather Walsh and available for download at ruaf.org/sites/default/files/guideonsoilcontamination.pdf
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