Emerging evidence suggests that nitrates in some drinking water might be harming unborn babies. Do we err on the side of caution, or do we wait until we know more? KIRSTY JOHNSTON reports.
When Katie’s second baby was born she was tiny. It came as a shock. Her firstborn, a boy, had been a healthy 3.8kg. But her little girl had stopped growing in the womb, and doctors had made the decision to induce Katie at 37 weeks gestation, to give the infant the best start.
“It was really sad,” says Katie, who didn’t want to use her real name in this story. “Ideally I wanted her to be a big healthy baby, but she was so little … she looked like a skeleton.”
Katie blamed herself for the baby’s 2.45kg weight. But the doctors didn’t know what had caused her to stop growing. And once they got home to their house in rural Waikato, the baby put on weight quickly. She got chubby thighs, and fat little cheeks, and Katie pushed her feelings to the back of her mind.
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But then, a few weeks later, Katie got the results of a test she’d ordered on the family’s drinking water.
Health experts advise that farming families on bores - wells drilled deep into the ground - do a nitrate test if they plan to formula feed, to prevent the risk of “blue baby syndrome”, or methaemoglobinaemia. This condition is caused by nitrates limiting oxygen supply in infants’ blood, turning their skin blue, causing seizures and in rare cases, death.
Katie knew about those risks. Her husband was a dairy farmer. She studied methaemoglobinaemia and nitrate - a compound of nitrogen and oxygen molecules that occurs naturally in the environment but has increased in New Zealand with the advent of intensive dairy farming – in her undergrad science papers at Waikato University.
RNZ New research has found there is not enough rain and river water in Canterbury to dilute nitrate pollution from dairy farming to acceptable drinking water standards.
She’d had her water tested after her first baby, and found it safe. But since then, the family had built a new home on a section next door to her parents, moved house, and hooked into their well. Amid the chaos, the nitrate test hadn’t been done. And by the time her daughter was born, Katie had been drinking the bore water for nearly three months.
New Zealand’s allowed nitrate levels, set after blue baby syndrome was discovered, are in line with World Health Organisation guidelines. To be considered safe, drinking water needs under 11.3 milligrams of nitrate-nitrogen per litre (11.3mg/L).
Katie’s bore measured the nitrate at 15.9 mg/L.
Thankfully, Katie says, the baby had been drinking formula made from bottled water, so she’d dodged the risk of blue baby syndrome. But almost immediately, Katie began to wonder about whether nitrates she ingested while pregnant might have affected her daughter’s weight at birth.
“That’s when I went on a Google hunt into the wee hours of the morning,” she says. “I found a couple of studies about nitrates and birth, and began to think ‘oh no, what have I done.’”
UNSPLASH New mums in some areas are warned of the risk of blue baby syndrome if they plan to formula feed.
The studies Katie found showed a strong association between nitrate in drinking water and underweight or premature babies. The most recent, and most robust, evidence had just been published by Stanford University in 2021.
The study involved 1.4 million babies from California, born over a 10-year period. It tracked the nitrate levels women were exposed to in subsequent pregnancies, meaning that while other research had struggled to separate the influence of nitrates from other factors like alcohol, genetics or smoking, for siblings born to the same mother, those factors were likely to be constant.
The results found the risk of early preterm birth (where an infant is born at least nine weeks early) increased by half when nitrates in drinking water were above 5mg/L. If nitrate levels were above 10mg/L - still less than the “safe” level here - the odds of a preterm birth more than doubled. Later preterm births were also associated with elevated nitrate, but the connection was less pronounced. (Babies who are born preterm or at low weight can suffer life-long impacts to their health, social and educational success.)
The study added to a growing body of evidence that suggests nitrates might cause neural tube defects, small gestational age, and low birth weight. Researchers are yet to conclusively determine how nitrates impact babies in the womb, but one way might be that just like with the way blue baby syndrome, nitrates could damage the way oxygen is carried in the foetus' blood.
Reading the studies as a mum, Katie was distraught. But as a scientist, she felt angry.
Effectively, researchers believe the foetus may be starved of blood oxygen if nitrates enter their mothers’ system via contaminated drinking water.
“The way science is communicated is so frustrating,” Katie says. “You shouldn't have to check things out and be so careful and do your own research. You should be told there’s a risk, even if it’s tiny. You should be told: ‘if you’re pregnant, get your water tested’.”
There is no way to prove Katie’s baby was affected by nitrates. All Katie has is a growing pile of studies, and a persistent sense of guilt. To be certain whether nitrates do affect unborn babies, everyone agrees, more research has to be done.
“We need more evidence, and this country should expand the monitoring and reporting of levels of nitrate in drinking water to help to gather that evidence,” said Dr Luling Lin, a postdoctoral fellow from the Liggins Institute, in August last year.
Lin, New Zealand’s authority on pregnancy and baby health, was commissioned by the Ministry of Health to do a review of the evidence on nitrate and birth outcomes after Otago University researchers, the Green Party, Greenpeace, the College of Midwives and Rural Women New Zealand raised concerns last year.
Lin, the study lead, concluded the current evidence was “uncertain” and findings from different studies were “inconsistent”.
“But we can't be complacent,” Lin said. “The lack of conclusive evidence on nitrates does not mean we should not be cautious.”
In raising concerns, Otago University epidemiologist Tim Chambers and his colleagues - including fellow experts Nick Wilson and Michael Baker - had recommended New Zealand should take a precautionary approach to the nitrate issue (they gave the same advice over the association of nitrates with bowel cancer, where growing evidence also points to strong links between the two).
Ross Giblin/Stuff Public health researcher, Professor Tim Chambers, published an analysis of emerging evidence on preterm birth in 2021, drawing New Zealand’s attention to the issue of nitrates and pregnancy.
Chambers said the public should be advised there may be a risk during pregnancy at lower levels than the 11.3mg/L, at least until more evidence was available. The College of Midwives shared this viewpoint, releasing advice to pregnant people that it was “prudent” to consider the lower threshold of 5mg/L (or lower) as safer.
But since the Liggins review, the advice from the Ministry of Health has remained the same - that any water under 11.3mg/L is safe. It told Stuff it was continuing to monitor further evidence, however it had not commissioned such work itself. Separately, Chambers put a funding proposal to replicate the California study in New Zealand to the Health Research Council this year. His team is yet to hear back.
Meanwhile, an increasing number of rural families are drinking water across Aotearoa with levels that are considered unsafe even by current measures - most of it from unregulated, private bores, owned by people who aren’t experts in water management.
For example, Otago University research says 138,000 people nationwide are drinking water with more than 5mg/L - the limit at which Stanford found an association with preterm births. Nitrates are worst in areas with the most intense dairy farming, due to the nitrate from cow urine and synthetic fertiliser running into streams, or leaching through soil to groundwater. Data shows that 8% of wells monitored by the regional council in the cattle-heavy Canterbury plains now exceed the “Maximum Allowed Value” (MAV) for nitrates, up from just 1% in 1992.
“The irony is that the people exposed to the highest levels tend to be people working in the dairy industry drinking from these private bores,” says public health expert Dr Alistair Humphrey. “Sadly, while they benefit from farming in terms of employment, they are also the ones suffering in terms of health.”
JOHN KIRK-ANDERSON/STUFF/Stuff Former Canterbury medical officer of health Dr Alistair Humphrey, a public health expert and long-time water advocate.
Humphrey has been raising the alarm about nitrates for years, with little progress. That’s not unusual: History shows potential population-level health issues almost always take decades to resolve. Problems like lead poisoning, and smoking, each took repeat epidemiological studies before policy changes were made.
“That’s reasonable, but the issue is what you do in the meantime,” writes former Massey University professor Neil Pearce in his book Pesticides and Health. He said often, authorities didn’t want to alarm the public by being honest about the uncertainty. “[But] claiming there is no risk is dishonest and alienates the public.”
Greenpeace water campaigner Steve Abel said in the nitrate space, he believed the vested interests of the dairy industry were being prioritised over the environment.
“The consequence of that is borne by people and people’s health. It seems obvious to say, but everyone no matter where they live has a right of access to safe drinking water,” he says. “No one should have to wonder if their water is making them sick, let alone their baby.”
Andy Jackson/Stuff Greenpeace campaigner Steve Abel says the use of nitrogen fertiliser – and intense stock rates - should be reduced to combat pollution, before water quality worsens and more people are potentially exposed.
Auckland University Māori studies lecturer Daniel Hikuroa (Ngāti Maniapoto, Waikato-Tainui, Ngāti Whanaunga) said the issue was clearly not being considered from a Māori perspective, or there would be more caution.
“The medical approach says we want to be certain that there are elevated levels of nitrates, and they’re unequivocally causing these issues,” he says. “That has benefits, but it has drawbacks. Unequivocal proof often comes decades too late for those who have suffered.”
Dairy New Zealand general manager of sustainable dairy, Dr David Burger, said there was no consensus on nitrates and human health. He agreed more research was needed.
While the industry had been investing in research for two decades to look at ways to reduce nitrogen, Dairy NZ would not be investing in research about drinking water, it said, saying that was for government and medical experts.
Associate Health Minister Ayesha Verrall did not respond to questions about further research, or whether a nitrate working group disbanded in March 2021 would be reconvened to consider the issue.
Katie, who wrote to Verrall in last year, said her hope was that all pregnant women would be offered testing if they were identified as being on bore water, so if their levels were high they could switch to bottled water - or instal a special, expensive filter, which the family have since done.
“Plunket explains the risks of co-sleeping as a matter of course. You don’t drink or smoke when you’re pregnant because you know the risk. Who knows if nitrate made a difference to my baby - but I put this in the same camp,” Katie says.
“You should know, because it’s your right to make an informed decision.”