Some Cantabrians are seeking alternative drinking water supplies after a study links nitrates to cancer. But thousands of others are seemingly unaware.

Jenny Webster-Brown is an academic but, for her, the issue of nitrates in drinking water isn’t something she considers in the abstract.

The director of the Waterways Centre for Freshwater Management – run jointly by the University of Canterbury and Lincoln University – has installed a still to remove nitrates from the private well at her lifestyle block at West Melton, west of Christchurch.

“I noticed that I was having a lot of stomach issues last year and I went down to Antarctica, as I do every summer, and they went away,” she says. “But as soon as I came back they started happening again.”

Eventually, she hooked up a still she happened to have at home, in case her problems related to drinking water. “Sure enough, as soon as we got rid of the nitrate out of the water, I started feeling a lot better.”

Webster-Brown doesn’t want to blur the personal and professional lines, and she doesn’t want to project what she’s doing on other people. But she also wonders if others might be having similar issues.

There’s something in the water

Nitrates in drinking water have been an increasing problem in Canterbury, and other parts of the country, for years.

The dangers are well understood. Blue-baby syndrome, caused by nitrates being converted to nitrite in the gut, can be life-threatening. In rural Canterbury, ante-natal classes warn about testing drinking water for nitrates.

Council supplies that provide water to more than 100 people are tested, and all practical steps must be taken to meet regulations. But property owners with private bores – the regional council, ECan, says 14,000 of the 32,000 active wells are listed as being used for private domestic supply – are on their own. It’s up to them to test for potential contaminants. (Samples from 306 wells across the region are analysed for water quality by ECan each year.)

Reducing nitrates is one of the main aims of Canterbury’s water management strategy, which divides the province into “zones” in which committees set rules for the likes of farm discharges and river levels.

Not that anything can be done about nitrates immediately. They will continue filtering from land to water for decades. (West Melton’s groundwater is thought to be 30-40 years old while at Lincoln, closer to the coast, is 60-100 years old.)

Fertilisers, industrial waste, and nitrogen-rich, animal-related runoff are typical sources of nitrates. Consider what that means for Canterbury, which had about 1.3 million dairy cattle last year, compared to 560,000 of those animals 15 years ago. The region also has about two-thirds of the country’s irrigated land.

The Danish play

The conversation about nitrates in Canterbury is changing.

That’s mainly because of a Danish study of 2.7 million people published last year in International Journal of Cancer that shows an increased risk of colon and rectal cancer from nitrate in drinking water – even at levels below official guidelines. The current New Zealand threshold is 11.3 milligrams of nitrate per litre of water. But an increased risk of cancer can be seen at a tenth of that level, according to the Danish study.

That would be a big concern in Canterbury, where nitrates in wells are increasing and, every two years, ECan publishes a map showing which areas are at greatest risk.

Webster-Brown: “The risk that I think a lot of people are now thinking about is, well, if I’m drinking this water supply for most of my life, which a lot of them will be, how much have I upped my cancer risk?”

The Christchurch West Melton zone committee – on which Webster-Brown’s partner Kevin Brown sits – wrote to the Ministry of Health in April, asking for further research to be done to understand the link between nitrates and cancer. Canterbury’s medical officer of health Alistair Humphrey told The Press newspaper that new research is urgently needed to prevent a future health emergency.

Ministry of Health group manager of population, health and prevention Sarah Reader tells Newsroom via email that the Danish research is just one study and there’s likely to be further analysis. “Our assessment of the report notes the challenges of separating the impact on health from nitrate from other health hazards including smoking, alcohol or obesity. We continue to monitor research in this area and will respond appropriately to identified risks to public health.”

Not everyone is reassured – including one of Webster-Brown’s neighbours.

“If they knew what we knew we’d be hearing from them.” – Jenny Webster-Brown

Graeme Horrell, a hydrologist, has lived in West Melton for 21 years. It’s never occurred to him to test his water for nitrates until he spoke to Webster-Brown earlier this year.

His bore’s nitrate level is 5.4mg per litre – less than half the danger threshold – but the Danish study has left him quite concerned.

“We aren’t drinking out of it now,” he says. “We use it for cooking and – this is a bit of ignorance on my part – but I’m actually going to a shallower well nearer the river.” He admits he’s yet to check the nitrate levels in that community well.

“I’m just presuming that it’s cleaner water.”

He knows of at least one other person, who lives north of the Waimakariri River, who has abandoned their private bore for drinking water in favour of a community supply.

“I’ve talked to a few neighbours and because they realise I know something about water – but I certainly don’t know anything, really, about nitrates – they’re listening to what I say. They’ll probably go and find alternative water supplies as well.”

Webster-Brown, the university professor, worries that thousands of people with private wells are being blindsided by the potential risks of high nitrates. “The evidence is their silence. We’re not hearing from them. If they knew what we knew we’d be hearing from them.”

New Zealand has high rates of colorectal cancer, so a good response to the Danish study would be to do our own, she says. “We can make a contribution to the global health policy. I think it would be a great thing to get off the ground now.”

Thanks to the application of a chemical reagent, the more intense the orange colour in these nitrate tests the more nitrate is present. Photo: Jenny Webster-Brown

Rural voices agree a New Zealand study would be useful.

Megan Hands, who runs a farm environmental consulting company, is the zone committee co-chair for Selwyn Waihora – an area well-known to have elevated nitrate levels. (She’s pregnant, with her baby due within a week, but is on a community water supply that is regularly tested.) “Most of us around the table are certainly supportive of research that’s relevant for New Zealand, so we do know if there is risk there.”

Asked if more should be done to protect the people of Selwyn from potential harm, district mayor Sam Broughton says studies for health should be funded by the Ministry of Health and district health boards.

Meanwhile, Federated Farmers’ North Canterbury president Cameron Henderson says: “Anything that’s related to human health I guess does deserve further investigation.”

But the dairy farmer, who milks 750 cows near Oxford, and is a member of the Waimakariri water zone committee, pans the Danish study, saying it “had holes picked all the way through”. While admitting he’s no scientist, Henderson says it was a broad study “that used the word potential a lot”.

“I think we’d probably want to know a little bit more around the science before we go and throw too much weight behind just one study with a lot of potential but not a lot of fact.”

Except it’s not one study. There have also been recent studies in Spain and Italy with similar findings. Those at highest risk of colorectal cancer were men who ate high amounts of red meat and had the highest exposure of nitrate from drinking water.

Not all epidemilogical studies have reported the cancer link, however. A female-only cohort in Iowa, United States, observed no association between higher rates of cancer and nitrates in drinking water.

Henderson, of Federated Farmers, says there might be a loose link but the science is far from proven. “Our concern is probably more around the current maximum allowable values for nitrates rather than anything that’s come out more recently.”

Where does the duty of care start and stop?

Science aside, this potential nitrate health nightmare has many worrying assumptions.

Councils publish information on their website about potential risks, assuming people will read it and take action. Property owners assume they will be rational and act on known risks, but many will put it off, especially if the solutions are costly. (Units to strip nitrates from water – something that can’t be done by boiling – can costs thousands of dollars.)

And councils and the Government seem to assume that it will always be acceptable to leave, to the lifestyler with a private bore, the assessment of region-wide problems with drinking water.

If nitrate risks can pass by, even briefly, Webster-Brown, who has a PhD in environmental geochemistry, and Horrell, a hydrologist, then what hope does the general public have?

The Ministry of Health’s Sarah Reader says New Zealand’s nitrate standards are based on recommendations from the World Health Organisation. “The Ministry has not been informed that the WHO intends to review the nitrate limits in light of the Danish study.”

Webster-Brown’s argument is that when WHO reviews its recommendations it’ll need plenty of evidence.

“They’re going to be looking for other areas of the world where this has also been identified. And New Zealand has relatively high rates of colorectal cancer, we’re told. So this makes perfect sense to look at it here.”

Given the “load in the post”, the decades worth of nitrates applied to land that is slowly seeping its way into the groundwater, as well as our rivers and streams, people are going to have to learn to live with high nitrate levels – especially people with private bores.

“I think we have to look after the population in the interim,” Webster-Brown says. That will mean more education about the risks. But she suggests some councils – after all, this is not just a Canterbury problem – should consider subsidising the installation of systems to remove nitrates from drinking water.

“When you’ve got such a vast number of people relying on that for their drinking water I think you, as a country, do have a responsibility to look after them.”

David Williams is Newsroom's environment editor, South Island correspondent and investigative writer.

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