The soil of the century lottery

Helen Leach Leach's 1955 Yates' Garden Guide has an alarming method for dealing to brown beetle: "Protective measures include spraying the trees early in November with Arsenate of Lead, one ounce to three gallons of water ... or DDT 50 per cent, one ounce to six gallons of water can be used instead."

The Otago University professor of anthropology and garden historian says that's just one example of how home gardeners have been pouring toxic chemicals on to their properties for years.

The 1955 Yates guide also recommends Aretan (an organic mercurial compound), Hexone (a "new phosphate insecticide"), lindane, and Paris Green (copper acetoarsenite) for slug baits. "For sections with gorse, blackberry or buttercups, it sang the praises of 2,4-D and 2,4,5-T."

Leach says that sort of advice, which continued to the 1970s, adds a new layer to Auckland's soil contamination problems.

The chemicals and heavy metals she's talking about are those found at toxic levels in several Auckland horticultural sites and which may affect thousands of home owners who've built on such locations.

Leach contends that problem is far more widespread. Home gardens all over the country are undoubtedly also contaminated. As you spray, so shall you reap.

"Home gardeners have traditionally been some of the worst users of pesticides," says Meriel Watts, co-ordinator of the Pesticide Action Network. "Because they don't have training and often don't know what they're doing, there's been a tendency to overuse chemicals."

She points out that DDT was still in use under permit until 1989, was used widely on parks and bowling greens, and even though it was banned in 1970 still shows up in household collections by councils of toxic chemicals. "This contamination goes a lot wider than these horticultural soils."

Leach says our chemical dependence spans a century - beginning in the 1890s, when glasshouses were routinely fumigated with cyanide, and arsenic and all manner of horrific substances were in common use.

"That was the period in which chemistry was seen as having the answer to all the gardeners' and farmers' problems."

From World War II the chemicals changed to organochlorines such as DDT, dieldrin and lindane. And while a more organic message can be found in today's gardening guides, it sits alongside one that continues to preach the chemical path.

"There is a long history of chemicals that have been recommended to us as being perfectly okay to use with no after-effects. And then later we are told they are no longer any good or they have unforeseen health consequences."

While Aucklanders worry about the decline of property values resulting from the contamination scare, should they also be worried about their health?

"Overall, it's an issue that is worthwhile dealing with," says Auckland Medical Officer of Health, David Sinclair.

"Particularly in areas where hotspots were found. There could be quite significant levels of exposure."

He says children are most at risk. They are developmentally more susceptible and more likely to be exposed - through play, picking things up off the ground and sometimes eating soil.

He agrees there could be hotspots in home gardens - in places where there have been chemical spills or heavy uses of pesticides, possibly around home glasshouses or garden sheds.

But he points out there are multiple ways people can be exposed to contaminants. Lead exposure, for example, can also come from paint and petrol.

Low-level soil contamination, he says, should be seen in the context of "a general acceptance that we do live in a contaminated environment" - a legacy of the past. "There's not a great deal that we can do about it - it's there and it's adding to our overall exposure from multiple sources."

Just what health effects might occur from exposure to pesticides varies widely - dependent on the person, the level of toxicity, the chemical and a range of other factors. It's a set of variables that make it difficult to prove, or disprove, a causal link between exposure and ill-health.

But as the Auckland City Council points out in its weed management policy, both the World Health Organisation and the United States Environmental Protection Agency do report "a wide variety of known adverse health effects resulting from exposure to herbicides".

The list is daunting: skin and eye irritation, cancer, immune dysregulation, reproductive effects such as miscarriage and birth deformities, developmental and behavioural abnormalities, neurological effects, respiratory disorders, gastrointestinal disorders, heart and blood disorders, kidney failure and liver damage.

In 1997, the Ministries for the Environment and Health set acceptable levels for arsenic (30 milligrams per kilogram of dry weight) and copper (80 mg/kg) in soils. But they have yet to set safe guidelines for many other soil contaminants, including DDT, dieldrin, lead and zinc.

Ingestion, absorption through skin, and inhalation as dust are direct ways soil contaminants can affect humans. The more significant issue, however, is the way pesticides get into the food chain from produce grown on contaminated soil. They are mainly heavy metals, which don't disperse and compounds such as DDT, which take decades to break down.

Our Food Safety Authority sets safe levels - "maximum residue limits" - for such contaminants in food and checks they're being adhered with its total diet survey of the foods we eat. The limits are the basis for further standards - "acceptable daily intakes" or "provisional tolerable weekly intakes" for contaminants.

But co-chair of the Soil and Health Association Steffan Browning says the authority is missing a crucial point. "We think residues full stop are undesirable."

Watts agrees: "We take issue with their attitude that it's actually okay to have contamination." Both say as well as setting safe limits, the authority should be setting targets for reducing residues in food.

Watts believes the Ministry for the Environment, blind to the wider picture, will adopt the same regulatory approach when setting acceptable contaminant levels in soil.

"I'm concerned they're going to develop safe levels that will be juggled to fit with the levels of contamination, so we get rid of the problem by saying it's safe."

Food Safety Authority executive director Andrew McKenzie adopts what might be called a pragmatic position: that pesticide levels in food have been falling and testing techniques have improved - so that if a pesticide has been used, some residue, however small, is likely to be found.

"There's a consumer perception, a fear that pesticides are terrible things," says McKenzie. "DDT was an environmental issue. It wasn't a human health issue. It's not a health risk to humans - not at the levels you find in foods at present, but it does a hell of good job killing mosquitoes in other parts of the world."

Browning strongly disagrees, arguing the authority's attitude is reactive and risky rather than proactive and safe.

Take for example the fungicide chlorothalonil, which in the last total diet survey was found at a level of 0.175mg/kg in celery in Auckland. The authority's maximum residue level is 15mg/kg - so the levels found are insignificant. Not so, says Browning, pointing out that chlorothalonil is a potential human carcinogen, known to affect the kidney and bladder in experimental animals.

"The authority says I'm scaremongering because it's not at dangerous levels, but it is only a matter of time before chlorothalonil will not be allowed in our food for whatever reason."

McKenzie dismisses the argument: "If we thought it [chlorothalonil] was a bit dangerous then we would take it off [the market]".

He says the authority doesn't wait for years until science proves a substance is dangerous, but acts as soon as there are any reasonable concerns.

Meanwhile chlorothalonil stays in our celery and other pesticides stay in our soil. And in the battle between the compost heap and the chemicals, the chemicals are still winning.

As we spray, so shall we eat.