Gord Stewart, is a sustainability consultant with a background in environmental management and economics.
Independent Kiwi scientists suggest that some 800,000 New Zealanders have water supplies with potentially hazardous nitrate levels. Rural residents on bore water supplies are particularly at risk.
Farming leaders tell us there’s not a problem here. Best you decide for yourself.
A high level of nitrate in drinking water was first deemed a risk for “blue baby syndrome”, a condition where transport of oxygen in the baby’s blood is inhibited. This led the World Health Organisation, in 1958, to establish a maximum allowable value (MAV) for nitrate in drinking water.
This level was adopted by the Ministry of Health, and has remained unchanged since then.
Research over the years has shown other possible risks of high nitrate levels, including miscarriage, pre-term birth, low birth weight and some birth defects. (Water high in nitrate is a further risk for formula-fed babies.)
This has led public health scientists to suggest that a safe level of nitrate in drinking water for pregnant women is less than half of the currently accepted MAV. The New Zealand College of Midwives supports this lower limit.
Public health experts in the know say the current MAV is hopelessly out of date, especially as it does not take into account chronic illnesses such as cancer.
An oft-cited Danish study, reported in 2018, followed 2.7 million people over a 23-year period.
Accounting for other risk factors, the study found an increase in colorectal cancer risk with a nitrate level in drinking water less than a tenth of the current MAV.
The 800,000 figure noted above is from a 2022 study reported in the journal Environmental Research.
The same analysis said that nitrate could be attributable to an additional 100 colorectal cancer cases a year and 40 deaths in New Zealand
But the scientists also fairly point out that some studies show a weak association or no association at all.
Examining the health impacts of nitrate is particularly difficult when multiple risk factors are at play.
Colorectal cancer is a perfect example. Known risk factors include obesity, alcohol, red meat, physical inactivity, processed meat and smoking.
Research by leading Kiwi scientists, reported in the Australian and New Zealand Journal of Public Health, confirms that nitrate in drinking water should now be on the list. This has been corroborated in recent work done by scientists overseas.
All of this is of great relevance for New Zealand.
Synthetic nitrogen fertiliser (typically as NO 3 or nitrate) applied for plant growth but not taken up by the plants can leach from the soil, polluting groundwater, rivers and drinking water.
In 2021, Stats NZ, our official data agency, reported a 600% increase in synthetic nitrogen fertiliser use over the past 30 years. This has allowed dairy cow numbers (their excreted urine is an issue as well) to increase from 3.4 million to 6.3 million over the same period.
Dr Alistair Humphrey, former medical officer of health for Canterbury, notes that New Zealand has a relatively high rate of colorectal cancer by world standards. Locally, the highest rates are clustered where people source their water from private bores – rurally and on farms.
The global agrichemical (fertiliser) market is worth nearly $200 billion annually. Its growth has been aided by encouraging farmers to pour excess nitrate on their paddocks. Here in New Zealand, the two major fertiliser companies are farmer-owned co-operatives. The farming community is, thus, both a cause of the problem and a victim of it.
What to do as an individual? For a start, don’t take any chances.
If you are on a household bore, especially if you live near dairy farming, get your water tested (see accompanying “Free testing” information). The Ministry of Health recommends regular testing – at least once a year – so you can track changes over time.
If nitrate levels are unacceptably high, consider rainwater as an alternative source for drinking. There are also filtering systems that target nitrate, although they are expensive.
A revision downward of the MAV is clearly warranted. The government also needs to fund more research on the issue and ensure systematic testing occurs.
The cap on nitrogen fertiliser application to land should to be set at a level that could actually make a difference (some say this level should be zero). It then needs to be properly monitored and enforced.
Livestock farmers need to think long term. Moving to regenerative and organic farming, diversifying away from livestock, or converting entirely to plant-based agriculture where possible are all steps in the right direction.
Such moves would be a win for the environment, for the long-term viability of farming in New Zealand, and for the health and wellbeing of farm workers and their families.
