A week after Environment Canterbury (ECan) declared a nitrate emergency, academics from three universities issued a stark message: central government must tackle "excessively high" dairy cow density in parts of New Zealand to prevent nitrate-riddled drinking water sourced from boreholes.
Other causes in Canterbury, such as septic tanks, were less contributory and treating the water, rather than stopping dairy pollution, would likely incur prohibitive costs, the authors said in a briefing published by the Public Health Communication Centre.
In Otago, the nitrate issue got confrontational. Gore District Council issued a temporary water stoppage due to high nitrate levels, prompting Greenpeace to amend the Welcome to Gore sign to read "Where dirty dairy wrecked the water".
Federated Farmers slammed the environmental organisation and ECan for "scaremongering".
While the dairy industry says it is feeding the world, and that on-farm changes could reduce the amount of nitrate leached from farms, health academics and environmental campaigners say nitrate leaching is only one poor outcome of a global industry contributing to sickness and climate crisis.
At a community level, there is understanding that nitrate testing is important, but differing and unclear advice about danger levels, and confusion about which authority will come to the rescue if nitrate levels spike continues to worsen.
Health risk
Care needs to be taken when trying to understand a borehole’s nitrate reading as it can be described as either nitrate-N (nitrogen atoms that make up a nitrate molecule) or nitrate (nitrogen and oxygen atoms that make up a nitrate molecule).
The World Health Organisation (WHO) maximum advisory limit for nitrate in water is 11.3mg per litre or 50 mg per litre respectively, and was set to prevent babies being poisoned.
However, there are also concerns at lower levels for pregnant women.
The New Zealand College of Midwives advises pregnant women to not drink water that has a nitrate-N level above 5mg per litre — under half the WHO limit — because two international studies have linked nitrate-N above this level to low birth weight and pre-term birth.
There are also observed correlations of nitrate and colorectal cancer. A statistically significant correlation was indicated in a meta-analysis of six epidemiological studies by Auckland, Otago and Massey universities in 2021.
The authors said epidemiological findings must not be over-interpreted, but a biological mechanism was plausible, and 17% of New Zealanders could be at risk.
However, people with agricultural interests have recently flagged a statement, made four years ago by Bowel Cancer NZ, that said the risk of nitrate causing cancer was like correlating ice cream consumption and drownings: they are both higher in summer, but one doesn’t cause the other.
Fed Farmers referenced the Bowel Cancer NZ statement in its press release slamming ECan’s nitrate emergency as a "shameless political stunt".
On the rural podcast REX, Lincoln University agricultural sciences professor Derrick Moot went further.
Referencing the ice cream analogy, he said the colorectal cancer risk from nitrates had "dropped out of favour", the risk of nitrate to unborn babies was also "tenuous" and if people drank nitrate above the limit, then "our bodies would deal with that ... it is not an issue for human health".
When alerted to the use of its statement, Bowel Cancer NZ checked with medical adviser Prof Frank Frizelle and said they stood by the statement, though it was "certainly not our intention for our statement to be used to dismiss concerns about nitrate or to downplay broader environmental or health issues".
Nitrate leaching from dairy
Nitrate leaching from dairy farms is caused when cows urinate in paddocks and when farmers apply cow effluent and synthetic nitrogen fertiliser (urea).
Groundwater moves in slippery ways, but a research paper by Earth Sciences New Zealand senior researcher Dr Karyne Rogers — "Nitrate contamination in New Zealand’s domestic drinking water with a focus on rural groundwater-sourced self-supplies" — described the situation as a "widespread and concerning threat".
About 3800 borehole water samples from Southland, Canterbury and Waikato had the highest nitrate levels. Otago, which has 467 known dairy farms, is defined as an "emerging region of concern".
In Southland, four in 10 samples had exceeded half the maximum limit — compared with three in 10 nationally — and nearly one in 20 exceeded it.
In cow numbers, there is little difference between dairy growth in Canterbury and the South.
Since 1990, both regions have seen more than a 10-fold increase in cow numbers to about 1million, cows in Otago and Southland combined increasing from 81,547 to 986,313.
National, temporary rules that curbed increasing cows numbers ended in January, and Dairy NZ identifies Otago, Southland and Canterbury as among seven regions with most cows per hectare.
Between 2002 and 2019, the use of nitrogen fertiliser in Southland nearly quadrupled and irrigated land more than quadrupled.
Water and exposed earth — for example after cows eat a crop — can contribute to leaching.
University of Otago hydrology expert Dr Sarah Mager says intense storms, which are expected to increase due to climate change, may "exacerbate" nitrate in water and spikes may last a short time or months.
Responsibility for drinking water
Responsibilities for the quality of drinking water are split.
Water regulator Taumata Arowai requires council-run water schemes to test nitrate levels monthly, while smaller schemes are required to test every three months if a result exceeds half the limit.
Regional councils are responsible for managing pollution, including permitting effluent spreading and enforcing farmer rules.
District councils are responsible for supplying drinking water, but not beyond their pipes’ reach.
"This makes me feel small community suppliers would be thrown to the wolves."
Otama Rural Water community scheme chairman and farmer Hamish Mackay says their borehole water is fine, but the expense of chlorination and UV filtering is not.
"The cost is getting quite phenomenal."
The Gore District Council website says the council does not know the cause of the high nitrate levels that led to the recent temporary water stoppage.
"At this stage we do not know. Environment Southland is responsible for investigating."
A decade-old report for Environment Southland says most of the South’s aquifers are not deep, so a significant reduction in nitrate leaching could cause "a vast improvement in groundwater ... in about five years".
Now, council strategy and regulation general manager Hayley Fitchett says she is "aware there are areas of Southland with high nitrate levels in groundwater".
There were 935 permits allowing dairy shed effluent to be discharged to land, and 19 allowing discharges from wintering pads, but "due to the way information is stored on our systems, we cannot respond to how this has changed".
She recommends people using groundwater test it, "particularly in districts of high-intensity land use."
On-farm opportunities
Dairy NZ chief science and innovation officer David Burger said drinking-water challenges "have multiple contributing factors" and urea use had been reduced by a-fifth between 2020 and 2023.
Greenpeace freshwater campaigner Will Appelbe says a maximum cap was slapped on urea usage by the government in 2021 and the reduction only countered a similar urea increase between 2012 and 2019.
Mr Appelbe has written to Gore Mayor Ben Bell inviting him to lobby for stricter water rules, but he is yet to get a reply.
Environment Southland provides annual information about nitrate levels to Land Air Water Aotearoa, but the Otago Regional Council has an online data portal updated every quarter. One Otago borehole, between Kakanui and Oamaru, has nitrate readings above half the limit in an area known for dairy and vegetable farming.
Fonterra supplier Nick Webster, who milks 800 cows on 250ha of his 600ha mixed farm in the area, says some of his farm would not suit dairy.
"There are places where dairy probably shouldn’t happen. We are starting to see a little of that pressure coming on."
His efforts to curb nitrate leaching include fencing waterways and targeted application of effluent and urea.
"It’s in everyone’s interests ... you want to be making small improvements all along the way."
With backing from Dairy NZ, Lincoln University has been testing ways to reduce nitrate leaching by half, including sowing plantain and Italian rye grass and wintering cows on pasture, not crops.
Preliminary results indicate 39% less leaching while maintaining profitability.
Lincoln Associate Prof Racheal Bryant said it was important to "give confidence in the outcome".
Call for a plan
University of Otago environmental epidemiologist Prof Simon Hales, who co-authored the recent public health briefing on nitrate, says nitrate risk needs to be considered as one headache among many others caused by industrial-scale dairy: more plant-based diets could be a healthier, more sustainable global solution.
"Are we really giving people what they need to be healthy?
"And if we are destroying the world in the process, is that a good thing? Surely not."
University of Otago freshwater sciences chairman Prof Ross Thompson says "the risk of picking on a sector is they circle the wagons", but when it comes to nitrate, dairy is the major cause.
"We have not managed environmental concerns [about dairy] and now we are trying to manage public health, too, which is a different magnitude ... a spectacular downward trend.
"For many people there may be a sense of futility.
"We are behind in realising water is a limited resource and drinking out [of] a tap requires significant policy interventions and capital expenditure."
He calls for on-farm best practice to be pushed hard and "a plan for everybody that gives certainty".
"There is no will, globally, to change our economic system, so how can we optimise the best solution within it?
"Personally, I am a fan of something much more disruptive but, professionally, we need to say that while we are waiting for everyone else to catch up and realise we can’t keep living this way, let’s see what we can do within our drivers."
