Toxic Tomatoes: What Urban Gardeners Should Know

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hand with watch reaches for ripe red tomatoes on vine

Treehugger / Sanja Kostic

A report published in the journal "Environmental Pollution" once again reminds us that as the urban gardening boom continues to grow, it is important to teach people tips on how to ensure the food they grow is safe for eating after all their labors of love.

Siting Factors and Vegetable Variations

Researchers from the Technical University of Berlin tested vegetables of various types from gardens across Germany's capital city. Although the risks of contamination of urban gardens has been discussed before, this study attempts to determine what factors favor siting of a safe urban garden and what vegetables might be less susceptible to contamination.The results of the study confirm the potential for vegetables to extract heavy metals from the soils in which they are grown, indicating that merely washing vegetables free of the local soil may be insufficient protection from the toxic effects of high levels of soil contamination. Some of the vegetables tested were found to have lead concentrations above the levels set by European law as safe for foodstuffs. Lead accumulates in the body and can lead to developmental disorders and neurological damage, as well as harm to other organs.

Vegetables sampled include: tomatoes, green beans, carrots, potatoes, kohlrabi, white cabbage, nasturtium, parsley, chard, basil, mint, and thyme. Wide variations in contamination concentrations were seen, so the study does not support the idea that some vegetables may be safer than others for urban gardening.

What the study does conclusively show: gardens nearer to areas with heavy traffic have higher levels of contamination. Barriers between the traffic and the garden, such as thickly vegetated areas or buildings, reduced the levels of cadmium, chromium, lead, and zinc found in the vegetables.

How to Minimize Risk in Urban Gardening

The researchers warn against panic, pointing to the need for more studies before anyone gives up the beneficial effects of an urban garden to go back to supermarket produce. But there are some steps that urban gardeners can take to minimize the risks when growing food in the city.

Picking a Plot

Learn about the land where you intend to garden before you plant the first seed. The city land planning office should be able to help with records of past use. And local health or environmental agencies, or the agricultural extension of a local university, may be able to help with soil testing.

Playing it Safe

If there is any indication of prior land contamination, or the location of your garden lies in highly trafficked areas, or near buildings where leaded paint flakes may have accumulated, try a raised bed garden. Place a sturdy liner on top of the native soil before building the beds, and bring in clean soil for your garden.

The Perfect Eden in the City

Follow the science of this study by planning a wall or thick hedge to help block the potentially contaminated dusts that might otherwise be blown up by traffic.

Michelle Obama's White House Garden set an example for not letting a little lead scare people away: although soil tests showed elevated levels of lead, the contamination risk does not outweigh the benefits of healthy, locally raised vegetables (and that is not even counting the health benefits of activity in the garden!)