Cantabrians may have higher cancer risk from poor drinking water

Monday, 26 November 2018

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

Contaminated drinking water may be increasing the risk of bowel cancer for some Cantabrians.

A citizen science experiment of 114 Canterbury drinking water sources, conducted by Fish and Game New Zealand, revealed some samples from rural areas exceeded a new, lower, cancer-alarm level European authorities are considering following a Danish-led study of 2.7 million people.

Environment Canterbury (ECan) has questioned Fish and Game's figures though, with chief scientist Dr Tim Davie saying there was 'quite a lot missing from a proper analysis and some pretty poor understanding'.

Dr Mike Joy uses a Nico real time nitrate-nitrogen tester to test water samples provided as part of a citizen science project.

Fish and Game is standing by its calculations.

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The organisation joined forces with Victoria University of Wellington freshwater ecologist Dr Mike Joy to test the water brought in by residents earlier this month.

Fish and Game chief executive Martin Taylor said the results showed 'the cows are coming home to roost'.

'Some detractors will say this is scaremongering. It is not.'

Joy used his portable Nico real-time test unit to measure the levels of nitrate-nitrogen in milligrams per litre of water. Each result took about 10 seconds to calculate.

The samples came from Loburn through to Ashburton, including Christchurch city, and as far west as Methven.

Fifty-eight of the 114 registered readings were above the 0.87mg of nitrate-nitrogen per litre threshold for potentially increased cancer risk in the Danish study.

The highest readings were from the Waimakariri district, with 1.86mg/l from bores in North Loburn and Swannanoa. Other samples with high readings included those supplied from Ashburton, Clarkville, Eyreton, Weedons, Marshlands, Tinwald, Hinds and Lake Hood.

Drinking water samples from West Melton, Ohoka, Darfield, Kirwee and Chertsey fell between the 0.87mg and 1.36mg/l levels.

Christchurch city drinking water was well below the nitrate-nitrogen thresholds.

Joy said the sad thing was the results of the random sample came as no surprise.

'It was citizen science. Anyone could have sent off a sample to a lab and paid $100. But this was an opportunity to make it more real for people to think about what is happening to their water in terms of human health.

'That's why I wanted to do this, once I'd read that cancer paper. We would be failing in our duty if we hadn't shared all this information with the people who are affected.'

Davie said during the past eight years, ECan had made progress in curbing contamination of the region's water through setting nitrate limits and encouraging better land-use practices, but it could not be quantified yet.

'It's early days. We are seeing farmers having lower leaching rates. There is less in all parts of the region.'

It was not that ECan was unworried about the Fish and Game study, Davie said.

'This does add something. But it doesn't add anything startlingly new.'

Fish and Game has passed on the list to Canterbury District Health Board medical officer of health Dr Ramon Pink.

Pink said the figures needed to be considered in a broader context, as did the Danish study.

'The health of the environment and us has always been inextricably linked. That is the key thing to take from what Fish and Game are saying. This needs a collaborative effort.'

The study – titled Nitrate in drinking water and colorectal cancer risk: A nationwide population-based cohort study, and led by Aarhus University in Denmark – was published in the International Journal of Cancer in February.

The researchers followed 2.7 million Danes from 1978 to 2011 and nitrate analyses from more than 200,000 drinking water samples.

Study leader Dr Jörg Schullehner, from the department of public health at Aarhus University, said those exposed to nitrate (not nitrate-nitrogen) 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. The increased risk of cancer could be seen at concentrations greater than about 4 mg per litre of water,' he said.

New Zealand's bowel cancer rates are among the highest in the world.

According to the Ministry of Health, bowel cancer is the second highest cause of cancer death in New Zealand, but it can be treated successfully if detected early.