1 April 2008:
Many home gardeners grow their
own fresh vegetables, believing them to be healthier and cleaner
than market-bought produce – but in some cases home vegies
can be toxic.
‘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,’ says Dr Euan Smith of the
CRC for Contamination Assessment and Remediation of the
Environment.
Scientists at the CRC are
working to quantify the risk to consumers who eat their own
home-grown fresh vegetables, given that residues of arsenic, lead,
cadmium and DDT can linger in the soils for decades after the
industry which left them has disappeared, says CRC CARE
managing director Professor Ravi Naidu.
‘Australians eat quite
large amounts of home-grown produce’, says Professor
Naidu.
‘The last national survey
indicated Australians consume around 150,000 tonnes of garden
vegies every year, with the greatest consumption in regional NSW,
Victoria and Queensland – but there is also considerable
intake in all the main capital cities’, he said.
According to Dr Smith, the aim
of the research is to work out where pollution from a 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 a known contaminated
soil.
The work is based on previous
research carried out by the CRC CARE team 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.
‘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. Arsenic is also a concern in areas of old gold diggings,
such as Victoria’s Golden Triangle, around old rail tracks
and orchards, Professor Naidu says.
DDT was widely used to control
insect pests in orchards from 1950-70, before it was banned, and
the residues of this persistent pesticide linger to this day. 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 which have been treated
with superphosphate fertiliser or sewage solids, or were former
gasworks.
The team has been investigating
silverbeet, lettuce, radish, tomatoes, zucchini, carrots, potatoes
and cabbages to see how much contamination they take into the
edible parts of the plant.
The results are being used by
collaborating scientists at HortResearch, New Zealand, who are
developing a model for predicting the ‘bioavailability’
of the contaminants to humans who eat the vegetables regularly
– that is, the amount of toxic contaminants they would
actually be exposed to.
‘Although it varies a
lot, according to type of vegetable, type of contamination and soil
conditions, in most cases the levels in the diet would be well
within safety limits set under national guidelines’, says Dr
Smith.
However it appears that root
vegetables such as 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’, says Professor Naidu.
However, Dr Smith cautions that
people who grow their own vegetables on a contaminated soil are at
greater risk from breathing in the contaminated dust, or through
skin contact with the soil, than from eating their
produce.
‘This underlines the need
to wash garden vegetables grown in such soils as thoroughly as you
would anything bought from a shop, to remove all traces of
contaminated dust’, says Dr Smith.
‘And, if you’re
planning to grow a lot of vegetables in your garden, then it might
pay to investigate the industrial history of the land your house
now sits on, and work out what sorts of risks you may have to
manage.’
More information:
Dr Euan Smith, CRC CARE, CRC CARE and
University of SA, 08 8302 5042, mob 0437 717 494
Professor Ravi Naidu, Managing Director, CRC
CARE, 08-8302 5041, mob 0407 720 257
Mr Peter Martin 08-8302 3933, mob 0429 779
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www.crccare.com
