News

Jul 11, 2023

Whose job is it to warn of the risk of nitrates in pregnancy?

The tiny South Canterbury settlement of Glenavy made headlines for all the wrong reasons in late 2022, when Greenpeace and Otago University researchers determined the levels of nitrate in one of the

The tiny South Canterbury settlement of Glenavy made headlines for all the wrong reasons in late 2022, when Greenpeace and Otago University researchers determined the levels of nitrate in one of the Waimate District township's water supplies were the highest they had seen in a registered water supply anywhere in New Zealand.

Water in the Lower Waihao and Waikakahi East rural scheme breached the government’s Maximum Acceptable Value (MAV) for nitrates in August 2022, topping 50 mg/L nitrate (11.3 mg/L nitrate nitrogen) and leaving around 615 households to rely on trucked-in tanks of water for four months.

The local and regional councils pointed to a “significant rain event” the month before as the cause. Waimate District Council signalled its expectation levels would not lower unless dentrification technology was added to a treatment plant, which was expected to come online in mid-2023.

But at the start of December, it announced nitrate levels had dropped to 38mg/L nitrate (NO3) (equivalent to 8.36 mg/L nitrate-nitrogen NO3-N) and the water was deemed “safe to consume”.

READ MORE: * Glenavy residents 'the canaries in the coal mine' of water pollution * Nitrate risk to unborn babies to be measured in $1.2 million study of drinking water * Pollution in the well: 'If you're pregnant you should be told to get your water tested' * Canterbury health officer urges research after study finds link between nitrates and bowel cancer

The New Zealand Drinking Water Standards Maximum Acceptable Value (MAV) for nitrate in drinking water is 50 milligrams per litre (mg/L) of nitrate, also expressed as 11.3mg/L of nitrate-nitrogen.

Campaigners argue the limit – based on 1958 World Health Organisation guidelines for preventing infant death from methaemoglobinaemia (blue baby syndrome) – does not protect from other potential health impacts, as international research points to dangers connected to lower nitrate levels.

With increasing evidence of possible links to adverse birth outcomes related to consuming water above 5mg/L nitrate-nitrogen (during pregnancy – less than half New Zealand’s maximum – there are concerns not enough is being done to warn pregnant people.

A 2021 analysis by Otago University public health researchers of two major international studies showing a link between preterm and underweight births and nitrate-nitrogen levels above 5mg/L called for better reporting of nitrate levels in New Zealand and further research into the link between nitrates and adverse birth outcomes.

Crown research institute GNS Science says the “optimum result” for drinking water is “nitrate levels between 0 to 1 mg/L”, and notes that “more than 80% of New Zealand’s drinking water has nitrate values less than 1mg/L”.

In a May 2021 advisory to members, the New Zealand College of Midwives warned of emerging evidence linking nitrate exposure above 5 mg/L during pregnancy to preterm birth and low birth weight.

It said those on private water supplies, such as bore water, should have their water regularly tested for nitrate, and that – regardless of the 11.3mg/L standard – it is “prudent to take a precautionary approach and consider the lower threshold of 5mg/L (or lower) as safer for pregnant women”.

If nitrate levels were over 5mg/L, “pregnant women should consider accessing an alternative water source such as bottled water, or investigate effective treatment options,” the advisory says.

College of Midwives chief executive Alison Eddy said the 2021 advisory was intended to raise awareness with members and help them discuss the issue with clients.

“Even amongst our members... there's not a lot of public awareness about [nitrate in water].

“All we can do is provide the information, if people choose to read it or not.”

But she said the responsibility to warn pregnant parents did not lie with the college.

“We're not a public health agency. I think this is an area where obviously there's emerging evidence, and I don't think we've got... sufficient evidence yet to say categorically the level should be ‘X’, really.”

Eddy said once Glenavy levels dropped below the 11.3mg/L threshold, the issue becomes safety during pregnancy.

“And that's where the evidence is not clear. It's sort of converging towards concern, but there's not definitive evidence to say categorically it's unsafe.”

The college was considering updating the previous advisory, but Eddy understood more evidence was forthcoming, “so we’re just going to wait and see until we have a clearer picture”.

Canterbury midwives were more likely to be knowledgeable on the matter because of longstanding nitrate issues across the plains, she said.

“There are some midwives who work in the area that are very aware of it, others probably less.”

She said “mostly urban-based” midwives may lack familiarity, but “awareness goes up” when there is a warning, when levels increase, or there are “noted adverse consequences”.

“All we can do is make sure we keep the communication open and raise awareness, so people can be as informed as they are, but it's not our role to criticise the council or contradict them, they've got responsibility for the health and safety of their residents.”

Releasing information to members has met a mixed response.

“We've put out information in the past, and people have said ‘oh, that’s new’, but others have said ‘yes, I’m very aware’, and they routinely discuss it with clients, but mostly it’s the bore water issue – the advice is if you’re on bore water make sure you discuss it, so people know they need to get it tested.”

But the advice did not extend to advising those on reticulated water supplies to be wary of water that meets national standards, but still has levels in excess of 5 mg/L.

“It’s a fine line we tread, really.”

Public Health Association of NZ policy advisor Māori Chris Webber said the lack of centralised messaging on risks was one of the reasons the PHA issued an official policy position on nitrate contamination.

“This underlines exactly the reason why we are expressing the need for a precautionary and proactive approach because you can see… there are gaps you can potentially drive a bus through.”

The PHA is “definitely advocating for lowering” the MAV based on the precautionary approach, said Webber.

He said there are questions as to whether the current limit, which was “established for a certain context” (methaemoglobinaemia) is still the best benchmark, given “new evidence saying there are health implications at lower levels”.

And although some of the evidence is still emerging, there are “some principles which aren't under debate”, such as that even though MAVs are set at a general level, “certain people are more vulnerable” and there is a “dose relationship”.

Councils and public health authorities need to have “hands-on ways to message their communities appropriately”, Webber said.

“If you know the nitrates are high, you need to be communicating that, whether it's through your rates information or other ways.”

After the birth of her second child, Katie** was shocked to discover her family’s bore water measured nearly 16mg/L nitrate nitrogen.

A scientist, she was well aware of the nitrate issue. She knew bore water needed to be tested, and that she was responsible for doing so.

“I knew the science behind it, but not everyone does. I mean, I’m rural and grew up rural and most people have never had their groundwater tested for nitrate.”

She tested the water after the birth of her first child, and intended to again after changing the family’s water source, but it got missed in the hubbub of moving house and a new arrival.

Her second baby stopped growing in the womb and was induced at 37 weeks. When Katie did get to the testing, the water she had been drinking through the latter part of her pregnancy had a nitrate content of 15.9 mg/L nitrate nitrogen.

“I wasn’t even really aware of that 5 [mg/L] until I started looking into it. I was just like, if we’re under 11.3 mg/L, I was going to just assume it was safe, because that’s what the World Health Organisation says, and I was mainly worried about… the risk to feeding a newborn formula, because I fed my first formula.”

But once she did more research, including looking at the Stanford study and the advisory from the College of Midwives, she was disturbed by the risk the family’s drinking water may have posed to her unborn child, and awash with “mum guilt”.

She understands there could have been many other factors, but said she would not have knowingly run the risk.

“You could smoke during pregnancy and your baby could be fine, but why take the risk?”

Katie believes information needs to be made more readily available.

“If you want to drink high nitrate water, knock yourself out, but you should know up front.”

And there need to be more rigorous ways of communicating risk, she said.

“A GP or a midwife needs to mention it to pregnant women… right at the start of the journey, and they should be offered a nitrate test.

“When someone rolls up to the midwife or doctor now, and they’re pregnant, are they identified? Are they asked if they’re on a bore? Do they get offered a nitrate test? It needs to fall back on GPs. A doctor needs to tell you to get your nitrate tested.”

Katie wrote to Associate Health Minister Ayesha Verrall, suggesting such a system, but did not receive a reply.

She has some sympathy for the Waimate District Council.

“It's an issue with the 11.3mg/L, right? And that's when a regulator needs to come and say no, 11.3mg/L is not suitable, it needs to be 5mg/L, because the council can't make up their own rules.

“Council is going back to central government to say, you give us guidelines for what's safe and unsafe.

“...even though it looks like there are suggestions it needs to be lower, until it's actually written down, you can't really blame the council.”

Given national standards are being met, the council could maintain an alternative water source just for pregnant people or those who might become pregnant, she said.

But she would rather err on the side of a precautionary approach.

“You’re setting up a little person for life, why take the risk?”