Nitrates get closer attention
An old-fashioned scientific disagreement hangs over a vitally important public health issue. Has politics sneaked its way into the debate? Charlie Mitchell reports.
Rising levels of nitrate detected at Te Waikoropupū Springs in Golden Bay has spurred Tasman District Council into action.
Councillors at a meeting of the strategy and policy committee on Thursday approved the development of an action plan.
One aim of the plan is to improve the council’s knowledge of how the hydrogeological system functions including the Tākaka River, Arthur Marble Aquifer and the springs themselves. Another aim is to identify what may be causing the trend of increasing nitrate levels and what actions may be required to tackle the issue if the trend continues.
Te Waikoropupū Springs contain some of the clearest water ever measured. To Māori, the springs are sacred. Ngāti Tama has the role of kaitiaki, or guardian, over the land and the springs.
Ngāti Tama Ki Te Waipounamu Trust was a joint applicant in June 2017 with long-time resident Andrew Yuill for a Water Conservation Order to protect the springs, the aquifer that feeds them and associated water bodies.
That application has been described as ‘‘a close weaving of mātauranga Māori [Māori knowledge], Pākehā science and profound environmental values, which cross cultures’’.
A Special Tribunal in March 2020 released its recommendations to Environment Minister David Parker. It recommended the application for the Water Conservation Order be granted.
Ten parties lodged appeals and an Environment Court hearing is scheduled for next month.
Yuill, who has been collecting water samples from the springs for community conservation group Friends of Golden Bay since February 2016, has long been calling for action, saying there was no room for doubt the trend was upwards for nitrate.
When told after the committee meeting about the councillors’ decision, Yuill said he was pleased to hear about the action plan.
‘‘Even though it’s taken until a month before the Environment Court hearing, finally TDC is saying they would like to do something about it – after six years.’’
Friends of Golden Bay had spent about $30,000 on analysis of the water samples its volunteers had collected, paid by funds donated by the community, Yuill said.
Those results were updated regularly and available publicly on the Friends of Golden Bay website.
The organisation had also sent a ZIP file of almost all of its results to the council, Yuill said.
Those results reveal a trend of increasing nitrate levels in Main Spring and Fish Spring since testing started in February 2016.
Earlier, at the committee meeting, council environmental policy manager Barry Johnson told councillors the Friends of Golden Bay data ‘‘forms part of the data set for water quality’’ and contributed to what would be presented to the Environment Court.
‘‘A lot of the debate around the WCO [Water Conservation Order] at Te Waikoropupū does relate to nitrates, so we’re going to get a lot of information out of the Environment Court case,’’ Johnson said.
Golden Bay ward councillor Celia Butler said Friends of Golden Bay had done a lot of scientifically sound, community-led monitoring, funded by donations.
Fellow Golden Bay ward councillor Chris Hill said the development of an action plan was ‘‘the appropriate thing to do’’.
‘‘It’s quite a complex area.’’ Councillor Dana Wensley said the role the voluntary group had played was interesting.
‘‘I imagine it’s been quite frustrating for them actually.’’
Are hundreds of thousands of New Zealanders drinking water that increases their risk of developing cancer?
It’s a simple question with a complicated answer, best distilled into a single word: maybe.
The stakes of this question are life and death. Everyone drinks water, and many livelihoods – including the export economy – rely on the industry that would be liable.
But in a pandemic era when scientists are expected to hold all the answers, clarity remains frustratingly out of reach, as partisan divides in society complicate an otherwise standard scientific disagreement.
Here’s the problem. Some scientists are worried that nitrates in drinking water can cause bowel cancer, which is already the second-highest killer among cancers in New Zealand.
For a long time, the consensus was that drinking water with nitrates had little to no long-term health effects. The major exception was a link to blue-baby syndrome, a rare but severe illness for infants.
The legal limit for nitrates in drinking water was set specifically to prevent blue-baby syndrome, around 11.3mg/l. This figure comes from World Health Organisation guidelines.
Most people drink water with nitrates well below this level, including the residents of every major city. National data is patchy, but a recent analysis estimated 75 per cent of New Zealanders drink water with nitrate levels lower than 1mg/l.
But in some areas – all of them rural – nitrate levels can approach, or even exceed, 11.3mg/l.
A few years ago, this may have seemed like a manageable problem; the small number of people at risk (anyone who is pregnant or an infant in these areas) could drink bottled water, or find another water source.
Then things changed. In 2018, a massive cohort study from Denmark – one which tracked millions of Danes over many years – found a link between people who drank nitrate-rich water and high rates of bowel cancer (unlike New Zealand, Denmark has a detailed record of nitrate levels in drinking water supplies, allowing such a study).
The cancer risk started to increase with nitrate levels of 0.87mg/l – 13 times lower than the New Zealand limit.
Several other studies have since found this association (and some have not).
If it’s true, it poses a major problem for New Zealand. In recent years, the amount of nitrates – a compound of nitrogen and oxygen molecules that occurs naturally in the environment – has increased, particularly in rural areas.
This is mostly due to nitrogen fertilisers. They either wash off paddocks into rivers and streams, or they fuel the growth of grass to be eaten by cattle, which recycle that nitrogen through their urine, most of which trickles through the ground and into water.
It’s had a dramatic effect on some waterways and is a key driver of the freshwater crisis. Rivers, streams and lakes become thick with algae, choking the oxygen from the water, rendering the habitat unliveable for all but the hardiest of critters.
But what if this environmental problem affected humans more directly? What if all these nitrates were, quite literally, poisoning people?
Leading the charge into
this question is Dr Tim Chambers, an epidemiologist at the University of Otago. Among his research co-authors are fellow epidemiologists Professor Michael Baker and Professor Nick Wilson, and freshwater ecologist Dr Mike Joy.
Chambers and his co-authors have published a flurry of material on this topic. One peerreviewed paper estimated nitrates in water could be causing 100 bowel cancer cases each year, resulting in around 40 deaths. The authors concluded: ‘‘There is sufficient evidence to justify a review of drinking water standards.’’
They have raised the alarm about a potential link between nitrates and adverse birth outcomes, notably premature births.
In another peer-reviewed paper last month, they outlined the (complicated) physical process they think could be responsible for drinking water nitrates causing bowel cancer, and undertook a meta-analysis of other papers which they said shows the association is ‘‘statistically significant’’.
Despite all this, Chambers acknowledges the case is far from closed. Some studies suggest there is a problem, some don’t.
He points out that the studies finding a link between nitrates and cancer tend to be more recent, and better designed – they include more people, over longer periods of time. ‘‘It provides a consistent story,’’ he says, about those studies.
Chambers is well aware of the contentious nature of his research. Even talking about it is sensitive; people are understandably concerned about the implications.
‘‘Making really conclusive claims about it does worry people . . . When I talk publicly about it, I potentially need to preface it by saying this is an emerging evidence base.’’
His work, unsurprisingly, has found a keen audience among environmentalists, who have long warned of the environmental consequences of nitrate pollution.
In a recent joint submission on drinking water standards, Greenpeace, Forest & Bird, and Fish & Game –with the support of other groups – used Chambers’ research as a key plank of their argument to better protect drinking water.
During the recent water reforms, many such groups called (unsuccessfully) for a nitrogen bottom line of 1mg/l in rivers; coincidentally, nearly exactly the point at which the cancer risk in drinking water may start to increase.
‘‘We’ve known for a long time that nitrates in freshwater are really bad for macro invertebrates, fish, and potentially for things like stygofauna that live in our groundwater,’’ says Tom Kay, freshwater advocate for Forest & Bird.
‘‘The levels at which they start to harm those species and native species and native fish such as tuna [eels] are actually really similar to the levels of which they start to affect human health.’’
And now the sceptics
Professor Frank Frizelle is a colorectal surgeon, also at Otago University. He has a longstanding interest in the causes of bowel cancer; his research has focused on the role certain bacteria can play in the process.
Unlike the Otago epidemiologists, who look at population data and high-level trends, Frizelle and his group are looking at the issue up close; they are mostly microbiologists and physiologists.
He doesn’t think drinking water nitrates are causing
bowel cancer; in his view, it may not even be physically possible. ‘‘Almost all of it [nitrates] is absorbed in the proximal small bowel, which means it doesn’t get to your colon at all,’’ he says.
‘‘To say that anything in the water will make a difference is highly unlikely because it doesn’t physiologically have a role in the colon . . . What actually ends up in your colon is about 10 or 15% of what you drink, and any nitrates in it are taken out before it gets there.’’
He accepts that bowel cancer rates are higher in rural areas, as are nitrate levels. But there are plenty of reasons for this, Frizelle says: rural people tend to eat more red meat, and some of the bacteria that can cause cancer come from sheep and cattle.
(Chambers insist there’s a clear biological process. He says it’s called ‘‘endogenous nitrosation’’, which is the same process that makes processed and red meats carcinogenic.)
Frizelle’s view is echoed by Peter Cressey, a senior scientist at the Institute of Environmental Science and Research.
He co-authored 2021 research which looked at Kiwi diets and their exposure to drinking water nitrates.
Cressey concluded there was little reason to worry about the potential connection, describing it as ‘‘highly unlikely’’.
‘‘It’s not really part of epidemiology – it’s more part of toxicology and exposure science,’’ he says. ‘‘You look at what’s happening in the human body and say, is this a plausible method for causation?
‘‘And we looked at all of that information. Looking at the toxicology, there’s so many ifs and buts in there that it really doesn’t hold water.’’
And so we have an oldfashioned scientific disagreement. Researchers from different disciplines looked at an issue using their own methods and came to divergent conclusions.
This is not controversial. You don’t always find consensus in science. It does, however, make sorting out the truth more difficult.
One of the groups supporting the environmentalists’ submission to protect drinking water from nitrates was the Cancer Society, the leading cancer prevention charity.
Its word holds obvious weight on the topic of cancer. Before supporting the submission, the charity had spoken to Chambers about his work, as well as another researcher.
‘‘We acknowledge the uncertainty of the nitrate and cancer link, but remain concerned about the contamination of harmful substances, including known carcinogens, in our drinking water,’’ says chief executive Lucy Elwood.
Then there’s Bowel Cancer New Zealand – unaffiliated with the Cancer Society – which has taken a different approach. In a lengthy position statement, it concluded nitrates ‘‘are highly unlikely to increase the risk of bowel cancer, according to the current weight of evidence’’.
Its view came after a discussion with its chief medical adviser: Professor Frank Frizelle.
While the scientific disagreement is healthy, another pollutant has sneaked into this debate: politics. It has muddied the issue and divided people into camps, which is reflected by growing tensions between the two sides.
On each side of the issue, there are frustrations with how the other side has presented its findings.
Throughout 2021, whilst Chambers’ team produced research regularly being picked up by environmental groups and disseminated through mainstream media – sometimes without the level of caution Chambers himself stresses about the uncertainty of the evidence – critics were gaining traction elsewhere.
When asked by Stuff to respond to Chambers’ findings early last year, Frizelle warned against over-interpreting the research, citing a ‘‘big antidairy lobby and water purity lobby’’ looking to capitalise on such issues.
Later that year, he coauthored an article more directly disputing Chambers’ research. It was published in Ground Effect, the trade magazine of fertiliser company Ravensdown – not the usual forum for scientific debate.
In a note accompanying the article, Ravensdown chief executive Garry Diack said there had been ‘‘misinformation’’ around the nitrate debate: Frizelle and his coauthor were ‘‘eminently more qualified to address this important topic than freshwater ecologists and activists’’.
When Cressey’s research at ESR was published – which also concluded a cancer link was unlikely – critics were quick to point out it had been majorityfunded by Fonterra (Cressey has said Fonterra had no role in the research design or in formulating its conclusions).
Whilst Greenpeace and others highlighted Chambers’ work in their advocacy, the likes of the Fertiliser Association and rural media commentators pointed to Frizelle’s position as a rebuttal.
Since then, the debate has become more pointed.
Chambers and a colleague responded to Cressey’s research with a blog post, which criticised the study at length for what they said were methodical issues and an overly broad conclusion: ‘‘We believe the research aims and analysis were never designed to justify the conclusions in their report or public statements,’’ they wrote.
(Cressey, in response, says: ‘‘A lot of the things he [Chambers] said there were wrong, and this is what happens when somebody tries to critique a study outside their area of expertise.’’)
In their recent peer-reviewed paper, Chambers and his coauthors took the criticisms of their work head-on. ‘‘We disagree with the argument that there is no logical reason for cause and effect, or that it is highly unlikely nitrate could increase risk of cancer,’’ they said.
‘‘Conclusive statements disregarding the potential risk of nitrate contamination in drinking water does a disservice to policymakers and the public attempting to understand the potential risk nitrate poses to health.’’
Unsurprisingly, the sides are also divided about the next steps.
For those who believe there could be a link between drinking water nitrates and bowel cancer, the precautionary principle – the idea that caution should prevail when scientific evidence is lacking – comes into play.
‘‘We think that we should take a precautionary approach towards this issue until we get better evidence, rather than using the existing limited evidence to dismiss it as an issue,’’ Chambers says.
If Chambers and his group are correct, it is likely dozens of New Zealanders are dying each year, with many more becoming severely ill. Most of them would be living in rural areas, and some would be the very farmers working in the industry responsible.
Fixing this problem would require stronger rules around nitrogen pollution, likely to have an economic cost for those same communities. Acting, and not acting, both have consequences.
Andwhat if it’s not correct, and there is no association? It risks distracting from proven contributors to bowel cancer: obesity, excessive alcohol consumption, smoking, and processed and red meat consumption.
Some have already made costly investments to reduce nitrates in their drinking water; others are understandably fearful about the safety of their drinking water.
‘‘I think if you’re going to come out with statements about something as fundamental as drinking water causing something as scary as cancer, the evidence needs to be strong,’’ Cressey from ESR says.
‘‘I don’t like to see politicisation of things like this; only if the evidence is strong. [Nitrate pollution] is clearly an environmental issue, but to use a human health endpoint to fight an environmental fight needs to be done with extreme caution.’’
For Frizelle, his scepticism comes in part from experience – certain topics become fashionable and attract research funding.
‘‘You don’t need much evidence to support things, and people will lock into it. When you’re surrounded by people with theories, you’re really looking for some hard facts to base this on, and that’s what we can’t find.’’
Chambers, naturally, disagrees. ‘‘This is an emerging evidence base, but just because there are some inconsistencies and it’s emerging doesn’t mean that we should dismiss it as a problem.’’