Many people grow fresh vegetables in their own backyards, believing them to be healthier and cleaner than market produce. But in some cases these greens can be toxic, says a new study.
Scientists are working to quantify the risk to consumers who eat home-grown vegetables, given that residues of arsenic, lead, cadmium and the pesticide DDT can linger in soil decades, warned researcher Ravi Naidu of Australia's Contamination Assessment and Remediation of the Environment (CARE).
The CARE team has earlier done a similar study into arsenic contamination of the food supply in Bangladesh, where 40 million people are affected by arsenic in the water and food grown or cooked using it.
Seemingly, root vegetables like radishes, like anything grown in the soil, are likely to absorb greater amounts of toxins than leafy plants like spinach or fruit like tomatoes and zucchini.
"This is a new finding given that, until recently, leafy vegetables were considered to be metal accumulators," said Naidu, who is CARE's managing director.
"As our cities and towns grow, they sprawl across old orchards or farms, mine sites and former industrial plants or gasworks which have left residues of toxic contaminants in the soil,' said Naidu's colleague Euan Smith.
Smith said the aim of the study is to work out where pollution from contaminated soil ends up in the vegetable - in the roots, stem, fruit or leaves - and from this develop a model which can predict the risk to people who eat produce grown in contaminated soil.
"In Australia, arsenic was used 100 years ago as a pesticide to control parasites of sheep and cattle - and there are still thousands of toxic dip sites scattered across the landscape, many in areas that have now become suburban," said Smith.
Lead was also used as a pesticide, and is a pollutant commonly found at the sites of old battery factories, former metal mining and smelter sites, and gasworks. Cadmium is in areas that have been treated with super phosphate fertiliser or sewage solids, or were former gasworks.
The team has been investigating silver-beet, lettuce, radish, tomatoes, zucchini, carrots, potatoes and cabbages to see how much contamination they carry into the edible parts of the plant.