"They 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 splatted by rain, in a few short years.

"Agriculture and other experts say such problems don't outweigh the benefits of urban gardening, but those growing food should make sure their soil has been tested and take appropriate steps to address pollution so their fruits and vegetables are safe."