Nitrates in our water – the doubts remain alarming

EDITORIAL: We cannot yet stand convinced that nitrates in our water have a connection to New Zealand’s high bowel cancer rate.

But we should be unnerved by a study that finds it may be so.

Sufficiently unnerved to seek plausible assurances that a real sense of urgency and disciplined impetus is energising investigations a Ministry of Health task force already has in train. This work must be pursued with more than a sense of frowning curiosity.

It’s scarcely a revelation that freshwater health and human health are related.

The new study, conducted with oversight from Victoria and Otago universities, concludes nitrate in drinking water is “likely to be’’ a significant contributing factor for colorectal cancer rates, which are particularly bad in Canterbury and Southland. However, it acknowledges the results are preliminary, requiring further investigation.

New Zealand does sit the right side of World Health Organisation-mandated safe levels of 11.3mg per litre of water, though the adequacy of that standard is challenged by research, notably a 2018 Danish study which implicated a link with bowel cancer for levels far lower at just 0.87mg.

Some critics attest that rather too much can be made of those findings, particularly since the Danish researchers were not able to correct for lifestyle and dietary factors.

(Speaking of which, the fresh NZ study also found elevated nitrate levels were unlikely to be as significant a risk factor for our bowel cancer rates as obesity or heavy drinking. So we’re likely to find ourselves weighing heavily and sitting unsteadily on our high horses if we’re minded to charge with headlong reproach towards farmers and government bodies at this stage.)

The Danish study scarcely stands alone. A year after it came out a US summary of eight different studies reinforced concerns that the more nitrate exposure you had, the more likely it was that colorectal cancer would develop.

This does not amount to a case-closed conclusion. What it does do, however, is raise the question of what we should do, meantime, in the cause of precautionary measures amidst our landscape of intensified farming.

The Government has no immediate plans to reduce the standard for nitrates in our drinking water beyond the WHO levels in the absence of harder evidence. And with some justification it points to land-use changes already in hand, and the potential for councils to enforce tougher limits if they deem it necessary for river health.

Citing an abundance of caution it may be tempting for us to insist upon emphatic actions, in the knowledge that public health cannot be sacrificed at the altar of agriculture and the economy.

Otago University’s Tim Chambers suggests a more nuanced approach allowing for differences in water supplies.

Granted, it’s often proven folly to conflate emphatic actions with lazily applied broad brush solutions. But safe minimums surely need to be clearly identified, and applied uniformly.

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