ECan asks Govt to prioritise studies of links between nitrates and health

Tuesday, 23 July 2019

Water scientist Dr Mike Joy has been testing the nitrate levels of water around Canterbury. Video first published in November 2018.

Evidence nitrates in drinking water may cause health issues such as cancer is 'inconclusive' but needs investigating, Environment Canterbury (ECan) will say in a letter to Minister of Health Dr David Clark.

ECan is writing a letter to Clark asking for 'well-designed studies' on the relationship between nitrates and health as a Government priority.

It says it can provide 'long-term trends' on the region's freshwater quality to bolster such research and that rising nitrate levels is 'not an issue specific to New Zealand'.

The growth of dairying across the Canterbury Plains has been blamed for the rising nitrate levels in some drinking-water supplies.

The Ministry of Health has already turned down a request from the Christchurch West Melton water management zone committee to examine as a priority the relationship between nitrate levels and colorectal cancer, saying it was unlikely to recommend a change to the maximum acceptable level (MAV) of 11.3 milligrams of nitrate per litre of water, set in the national drinking water standards.

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Environment Canterbury is writing to the Government asking that research into the links between nitrates in drinking water and health be considered a priority.

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'Inconclusive' evidence that nitrates in drinking water may cause cancer and other health issues is behind ECan's call for Government-supported research into the possible links. (File photo)

The leader of a ground-breaking Danish study following 2.7 million Danes from 1978 to 2011, Dr Jörg Schullehner from the department of public health at Aarhus University, said last year those exposed to nitrate levels above 9.3mg/l had a 15 per cent greater risk of getting colorectal cancer compared to those with exposure of less than 1.3 mg/l.

Nitrates can also cause blue-baby syndrome, a potentially fatal condition that stops oxygen getting around the body.

Ministry deputy director-general Deborah Woodley has previously said a 'comprehensive review of standards' was under way, but the Danish study did not fully take into account other risks such as smoking, diet and obesity.

According to ECan's latest annual survey, 95 per cent of Canterbury's monitored wells now have nitrate levels worse or no better than those 10 years ago.

Of the 306 wells sampled for the 2018 groundwater survey, taken in spring last year, only 11 had lower nitrate levels than a decade ago.

On its website, ECan says public drinking water supplies are safe, but the review 'confirms that a few private wells are sometimes below drinking water standards'.

The survey showed samples from 7 per cent of the region's wells had nitrate concentrations above the 11.3mg/l MAV.

Regional councillors were told at their last meeting managing nitrate concentrations in freshwater was a 'key priority' for ECan.

'Considerable resources' had gone into developing rules for farmers for dealing with nitrates from their land, a report said.

'Recently there has been increased community concern about the possible health issues from nitrate concentrations.

'The evidence linking health risks with nitrate concentrations is inconclusive,' the staff report said, pointing to a 2018 paper in the International Journal of Environmental Research and Public Health that stated the number of well-designed studies 'is still too few to draw firm conclusions about risk from drinking-water nitrate ingestion'.

The ministry's response to the zone committee had been it did not consider changes to the drinking-water standards were justified, 'based on existing research'.

Canterbury medical officer of health Dr Alistair Humphrey supported ECan in writing to the minister and said New Zealand would be well placed to undertake a second study to corroborate the Danish study's findings.

'We need to understand why it is we have high levels of colorectal cancer, if it's because of increasing levels of nitrates.

'Certainly the minister could support some such research. It's an important question that we need to answer,' Humphrey said.

Victoria University of Wellington freshwater ecologist Dr Mike Joy told Stuff ECan was 'right to be worried', given Canterbury had some of the highest levels of nitrates in drinking water and the new overseas research.

'ECan has allowed almost unlimited dairy development that resulted in high levels despite many warnings, some as far back as 1986, of the human health risks.

'Playing ignorant now and wanting the ministry to do the research is a bit rich.'