Concerns that nitrate contamination of drinking water is linked to increased risk of bowel cancer and preterm birth are not supported by experts in medicine, says the author. Photo / File
Concerns that nitrate contamination of drinking water is linked to increased risk of bowel cancer and preterm birth are not supported by experts in medicine, says the author. Photo / File
Dr Jacqueline Rowarth takes a closer look at the debate surrounding the effect synthetic nitrogen fertiliser has on health.
OPINION:
Over half of the people reading background information supplied to them in a Greenpeace Horizon Poll released last week supported phasing out synthetic nitrogen.
“Some scientific research shows that pollution from the increase in synthetic nitrogen fertiliser and the rise in dairy cow numbers has degraded the water quality of New Zealand rivers and lakes. Medical researchers also say that nitrate contamination of drinking water is linked to increased risk of bowel cancer and preterm birth.”
If the background information had included the fact that synthetic nitrogen fertiliser feeds half the global population and that without it food prices everywhere will escalate because of shortages, the phasing out question might have had a different response.
Except for the health concerns, of course.
Except that the concerns aren’t supported by experts in medicine.
New Zealand’s cancer research experts and Bowel Cancer NZ have stated publicly that:
“Nitrates in drinking water are highly unlikely to increase the risk of bowel cancer in New Zealand, according to the current weight of evidence.”
The research on bowel cancer that stimulated the initial furore in 2018 involved environmental engineers linking water quality over a 30-year period with current colorectal cancer in Denmark.
The fact that Denmark’s population has a long history of eating processed meats, drinking beer and not eating fruit and vegetables in what is considered to be appropriate quantities was not mentioned. Nor was the fact that the average Danish diet is high in fat – 50 per cent more than recommended.
The second health concern mentioned in Greenpeace’s survey was preterm birth. Again, this concern was stimulated by research from overseas.
Key researchers were not from a medical background (the lead researcher is an environmental health scientist) but found a relationship between preterm birth and nitrate in drinking water. They did not correct for ethnicity or any other factor that has been found to be related to preterm births.
Correlation is not causation.
In New Zealand, approximately 7.4 per cent of births are defined as preterm (less than 37 weeks of gestation), lower than 8 per cent in the UK, 8.7 per cent in Australia and 10.5 per cent in the USA, but above the 6.2 per cent in Denmark.
The New Zealand Maternity Clinical Indicators: background document, published in 2020, identifies managing high blood pressure and tobacco use to reduce the likelihood of pre-term babies. Nitrate was not mentioned.
In the Health Status of Children and Young People in New Zealand (an NZ Child and Youth Epidemiology 2015 report), recommendations to reduce preterm birth rates included interventions to reduce smoking and intimate partner violence, improved access to family planning to reduce the number of closely spaced pregnancies, and provision of support to socially disadvantaged women.
Listen to Jamie Mackay interview Dr Jacqueline Rowarth on The Country below:
Further, a check of nitrate in groundwater and wells indicates no relationship between higher nitrate and increased incidence of preterm pregnancies.
Whatever region is examined, very few wells are over the World Health Guideline for nitrate in drinking water (50 mg/l) and few are even above half the guideline recommendation.
In Hawke’s Bay, one of the areas picked out for higher preterm pregnancies, approximately 6 per cent of well samples, most of which were not used for domestic purposes, were between half the drinking water standard and the standard.
Continuing to alarm New Zealanders about health issues that have been allayed by experts is mischievous – it is wasting time and money and creating unnecessary stress. Wasting time is not allowed in courts of law or by the police, yet apparently, it is allowed in media.
We should be focusing time and money on real problems, not those created by activists, however well-meaning.
A second question in the Greenpeace Horizon poll suggested that the Government made laws to lower dairy cow numbers. The result was “increasing support”.
But the fact that only 33 per cent of respondents (up from 25 per cent a year ago) supported the proposal indicates that 67 per cent recognise (or aren’t sure) the importance of the dairy industry for the economy – which side their bread is buttered, as it were.
They’ve listened to the economists.
Now what we need is some listening to the medical experts – they’re different from environmental engineers and environmental health scientists.
Dr Jacqueline Rowarth, Adjunct Professor Lincoln University, has a PhD in Soil Science (nutrient cycling) and is a Director of Ravensdown, DairyNZ and Deer Industry NZ. The analysis and conclusions above are her own. She obtains no revenue from writing; nor does she run a website with “donate” on every page. jsrowarth@gmail.com
