Ann Arbor’s Project Grow is an extremely popular and often over-subscribed program under the auspices of which gardeners without the space (or who may want more space) can pay a fee to have their own little slice of black to grow gardens limited only by imagination (and the Project Grow rules, of course). Gardeners who get a plot through Project Grow must agree to “employ the organic gardening practices accepted by major organic certification agencies, such as the Organic Crop Improvement Association, in all gardens. Any gardener not adhering to organic gardening practices will have their plot revoked and will forfeit their right to garden with Project Grow in the future,” according to the Project Grow web site.

The Project Grow organization strictly prohibits the use of synthetic insecticides, inorganic fertilizers (i.e.5-1-5, Miracle Grow, etc.) and the planting of invasive species, for instance. There is every effort made to keep the soil free of contaminants.

Recent articles in The Boston Globe, The Atlantic Monthly, The Washington Post, as well as a 2009 report by two scientists at UC-Davis suggest that urban gardening, even when done organically, as is the case with Project Grow, may pose health risks. The report by the UC-Davis profs. points out that, “toxins can make their way into crops grown in the city or suburbs.” It’s easy to forget that leaded gas fumes poured out of exhaust pipes of cars for 80 years before leaded gas was banned in the 1980s. Traces of lead can stay in soil for decades.

The County Farm Park in located between Washtenaw and Platt Roads. There are community gardens nestled in the northeast corner of the park. Project Grow has a large presence at the Leslie Science Center. Those garden plots are bordered by Traver Road. Project Grow recently developed a new gardening area on Taylor Street, near Northside School. Food Gathers has a large garden established which produces 20,000+ of pounds of vegetables which are distributed to the county’s residents in need. That 1/2 acre garden is bordered by busy Dhu Varren Road.

According to an op-ed published in The Boston Globe recently titled “The locavore’s dilemma,” “There’s the very real worry that plants grown among the air and soil pollution of the city may actually be dangerously toxic, even as gardeners deliberately avoid chemical fertilizers, insecticides, and herbicides. The AP last month reported that lead had routinely been found in the soil in cities nationwide.”

According to the AP reporting: “[Soil researchers] point to cities like Indianapolis, where nine out of 10 urban gardens tested by one researcher had problems with lead in the soil. Or the Boston area, where a recent study suggests that even clean, trucked-in soil can end up contaminated, perhaps by windblown dust or dirt splattered by rain, in a few short years.”

The op-ed’s author, Edward Glaeser, is the Chair of Boston’s Citizen’s Committee for the Future of Boston, and and professor of economics at Harvard University. The Committee he chaired endorsed urban vegetable gardens. However, Glaeser writes, “But while neighborhoods benefit from the occasional communal garden, it is a mistake to think that metropolitan areas could or should try to significantly satisfy their own food needs. Good environmentalism is smart environmentalism that thinks through the total systemic impacts of any change. Farm land within a metropolitan area decreases density levels and pushes us apart, and carbon emissions rise dramatically as density falls.”

A quick drive up many of Ann Arbor’s busy roads such as Miller Road, Pontiac Trail, Newport, and Maple, and it’s easy to spot the veggie gardens, some in front yards just feet from the edges of the streets, others in backyards, slightly further away. Why worry about growing tomatoes, strawberries, lettuce or peppers in a boulevard garden? One reason is that cadmium from the wear of tires can coat the leaves of plants near roadsides.

The advice from the profs at UC-David? Test your soil. They write, “Not only will it reveal which trace elements are present and their concentrations but also where they are located in the garden. An added benefit of testing the soil is the opportunity to gather information about basic nutrient levels at the site.”

There’s also good news. According to the UC-Davis report, “In most cases potentially hazardous trace elements found in urban garden soils and on plants must be directly ingested to cause harm; usually only small amounts enter the body by inhalation. Plants absorb only minute amounts of lead and then mostly in the roots. However, plants, especially leafy vegetables like lettuce, cabbage, and spinach, can absorb cadmium in roots, leaves, and to some extent in fruits.”

What’s the Urban Gardener to do if the soil test shows higher levels of harmful trace elements such as lead, cadmium and arsenic than expected?

Amend the soil with compost and other organic matter, and cultivate deeply, digging down eight inches is recommended. Mulch with straw, leaves or newspaper to keep down the dust.

Locate vegetable gardens, especially leafy crops, as far away as possible from the street. As much as 75 feet between the street and your Russian kale, spinach and heirloom lettuces is optimal. Use a wall, fence, or hedges, to help to block car exhaust and dust from coming into the site from streets and roads.

Next, when you harvest from your urban garden, even one in which organic growing practices have been used, thoroughly wash all vegetables and fruits and peel root crops like beets, radishes, and carrots before eating. Don’t eat the older, outer leaves of leafy vegetables.

Finally, remember that some trace elements are especially hazardous to children, particularly those under six years of age. According to the UC-Davis report, “Their tolerance levels to these contaminants are lower due to lower body weight and their still developing neurological systems are unusually sensitive to these elements. Also, the type of activity in which children engage, such as playing in the soil with frequent hand-to-mouth contact and even eating soil, allows them to ingest these trace elements directly.”

So if you’re urban gardening with the kids, always wash hands after working or playing in the urban garden. Hand washing is important for kids who are more susceptible to trace elements. Ideally, children who are urban gardening should wear gloves.