Urban gardening is a very effective way to get fresh and healthy produce to the people who need it most. But there’s just one sickening caveat. These gardens tend to be next to highways or in close proximity to former waste dumps or industrial sites. This means that the soils in these gardens are at risk of being contaminated with toxic heavy metals. With the staggering rise of backyard and community gardens in cities across the U.S., heavy metal soil contamination is a growing human health concern.
The term “heavy metals” refers to a group of metals that occur naturally in the environment, but are potentially toxic to humans. If these metals accumulate in the body, they can impair major body systems such as the nervous and reproductive systems, they can damage vital organs, and in some cases they may even cause cancer.
Since 1991, the heavy metals arsenic, lead, and mercury have topped the hazardous substance priority list published every 2 years by the Agency for Toxic Substances and Disease Registry (ATSDR) in conjunction with the Environmental Protection Agency (EPA). This list ranks substances based on their frequency and potential for human exposure, in addition to their toxicity. Arsenic, lead, and mercury are found naturally in soil. Like other heavy metals, their distribution in contaminated soil depends in large part on the history of human activities at or near that particular site.
Lead has long been a major environmental health hazard. Until the late 20th century, lead was used routinely in many U.S. products such as pesticides, paint, and gasoline. Although lead has all but disappeared from many of these products, its remnants persist in contaminated plots of land, on the painted surfaces of old houses and buildings, and in urban dust clouds hovering over countless cities. Furthermore, worldwide lead production remains strong, with the U.S. continuing to be one of the top producers.
Although occupational exposure is the primary route for lead poisoning, exposure from soil is a serious health concern, particularly in urban areas. Lead has a broad range of health effects stemming from both acute and chronic exposure; however, it is infamous for its ability to affect the nervous system, and in particular to impair cognitive development in children. Behavioral and physiological differences make children more susceptible to lead and other environmental toxins than adults.
While gardeners may be exposed to lead through inhalation, ingestion is the primary route. Edibles can become contaminated in a variety of ways. Plants can become covered with contaminated garden soil or dust blown in from another location. This is especially true for root vegetables that grow underground and for leafy vegetables whose large surface areas make them easy targets for dust. Plants can also take up the contaminant directly from the soil. Although plants generally do not take up heavy metals very well, certain characteristics of the soil can create the perfect conditions to facilitate increased uptake.
NOFFN’s official position on lead & other heavy metals is that any amount present is potentially harmful. The EPA’s hazard standard for lead present in soil is set at 400 parts per million (ppm). Within our City Farms program, we advise folks that anything above 100ppm is unacceptable in soil where food is grown and where there is regular human contact with soil.
One of the best ways to reduce your risk of lead poisoning from urban gardens is to use raised beds. Raised beds built with concrete blocks or untreated hardwood, placed on fabric separating the bed from ground soil, and filled with uncontaminated soil will go a long way towards protecting the integrity of garden produce (see our guide to starting Raised Bed Gardening). And remember to change the first couple of inches of your soil each year, as a recent study suggests that uncontaminated soil in raised beds can accumulate contaminants over time. Other ways to minimize risk include:
- Covering unused soil with mulch to minimize dust
- Wearing gloves when working in soil
- Cleaning gloves, tools, clothes, and shoes before coming indoors
- Washing hands, particularly underneath nails, before preparing and eating freshly picked produce
- Washing all produce thoroughly, especially the leafy and root vegetables
- Discarding the outer layer of leafy vegetables and peeling root vegetables
Murline Gelin is a writer with a penchant for food justice and environmental causes. She also feels strongly about empowering young people through education and has worked as an instructor to at-risk youth.
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