City dwellers love to eat their home grown vegetables as much as anyone else. But this private harvest isn't always healthier than produce from the supermarket. Vegetables grown near a busy road are often contaminated with heavy metals such as lead, cadmium or quicksilver. Biologist Ina Säumel of the Berlin Technical University has shown this. In city neighbourhoods with heavy traffic the EU limits for lead were surpassed in 60% of the samples - a leftover from when petrol still contained lead.
But even vegetable that are not grown beside a road aren't always harmless, research by the 'Amt für Umwelt' in Freiburg shows. "Nine out of 27 ground samples contain problematic amounts of heave metals. In two other samples the lead levels were so high the vegetable gardens had to be closed down," says research leader Barbara Gfeller.
The contamination is not just down to the exhaust fumes from traffic and industries. "Previous uses of the land have more influences than its location," says the expert. Many hobby gardeners put the dangerous substances in the ground themselves in the past. For instance due to improper use of compost or by spreading contaminated ashes.
Whoever wants only the best in vegetables, is advised to contact an organisation specialised in soil protection.