Growing your own vegies healthy once you assess risks involved

Jan Davis suggests a few simple precautions before planting a garden

EVERYONE knows the world’s population is growing rapidly, with predictions it will reach nine billion by 2050. These people need to be fed. This is why food security is on the tip of everyone’s tongues, and why urban agriculture is expanding.

Researchers estimate that 48 per cent of all households in metropolitan areas are now growing some form of edible produce.

However, food security means much more than simply encouraging people to grow their own vegies, keep chooks, go to farmers’ markets, or get involved in urban foraging.

A recent study by RMIT University found that up to 21 per cent of soils tested in inner-city Melbourne gardens had lead levels above the Australian health guideline of 300 milligrams per kilogram of soil. These are not isolated results. A similar survey in Sydney in 2017 found 40 per cent of gardens had soil lead levels above the health guidelines.

As well, about one in seven homes in the sample had levels greater than 1000 mg/ kg.

Lead is naturally present in all soils. In Australia, it generally occurs in the range of 15 to 40 parts lead per million parts of soil, or 15 to 40 mg/kg.

The highest levels are found in homes built more than 80 years ago. This is a result of paint that contained up to 50 per cent lead prior to 1970. Lead in paint was reduced to less than 1000 mg/kg (0.1 per cent) by 1997.

Other sources of contamination include lead water pipes and roofing, leaded petrol and previous industrial emissions.

The highest levels of contamination are within the line of the eaves and in houses on or near major traffic routes.

Although sources of contamination have been greatly reduced, lead in soil tends not to move much and it has an estimated half-life of more than 700 years.

Soil lead poses a risk because contaminated particles can adhere to or get absorbed into edible plants.

An additional pathway of exposure occurs when contaminated soil dust enters homes and is accidentally ingested.

Lead exposure is especially detrimental for children because their neurological and skeletal systems are developing.

Adults are also adversely affected, with studies showing increased blood pressure and hypertension associated with sub-clinical exposures.

Toxicological evidence shows that exposure to high levels of lead reduces semen quality and extends the time to pregnancy.

In short, lead is detrimental to all human systems and exposure should be avoided or minimised at all times.

Scientists and regulators are well aware of these legacy issues, but the general public remains under-informed about the potential risks.

So understanding how to deal with the issue is especially important for people planning on growing their own food. If

you know what you’re facing, then you can take action to reduce the risk of exposure.

In older homes, or where there is reason to believe that lead contamination could be a risk, having the soil tested is a good idea. It’s better to know than not to know.

If you’re growing food in an inner city garden, you’ll want to grow it on fresh, clean soil, which does not contain the legacy of our industrial activities over the past century. Best practice is to choose a garden bed, dig out the old soil, and replace it with fresh quality soil.

Raised garden beds are also very effective. These should be lined with a synthetic geotextile layer and filled with imported clean soil. Don’t use timber treated with copper chrome arsenate though, as this brings a whole new level of risk.

In affected areas, you should steer away from growing vegetables known to accumulate lead. This includes lettuce and root vegetables like carrots, onions, turnips and radishes.

Of course, all produce should be washed thoroughly before eating.

Keeping the dust down with a thick cover of grass or mulch on pathways and other uncultivated areas will reduce the generation of particles that could come into contact with children’s hands.

In addition, everyone should wash their hands after working or playing in the garden and before eating.

So, even if lead levels in your garden exceed the Australian safety guidelines, you don’t have to give up on your visions of a lifestyle like that in the 1970s TV series The Good Life.

Where there’s a will there’s way, so get out there and start planning for spring.

Soil lead poses a risk because contaminated particles can adhere to or get absorbed into edible plants.