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Researchers looking at the link between nitrate in drinking water and the impacts on health are being hindered by poor monitoring and data.
A senior research fellow in the University of Otago department of health, Dr Tim Chambers, gave a presentation at the first day of the Environmental Defence Society annual conference in Christchurch yesterday.
Concerns had been raised about the nitrate pollution in some water suppliues which were having long-term impacts.
Dr Chambers said the limits in place now were set on the risk of blue baby syndrome. However, that limit did not consider any other potential health implications.
He acknowledged overseas studies’ conclusions on the risks of increased colorectal cancer and noted the International Agency for Research on Cancer’s finding that “ingested nitrate under conditions that result in endogenous nitrosation is probably carcinogenic to humans”.
That process required three things: the presence of amines, presence of nitrosating agents and the absence of antioxidants.
He said the best evidence for the link between nitrate and pre-term births came out this year; the within-mother analysis showed levels of nitrate over 5mg per litre had a risk increase of 47% for pre-term birth.
While research on the topic within New Zealand was being fleshed out, he said it was difficult to understand the link with colorectal cancer because there was no monitoring data to do a robust study.
“Last year we spent a lot of time and effort trying to collate a nitrate data set for registered drinking water supplies and most district councils don’t have data that goes back further than 10 years.”
There needed to be 15-20 years of data.
Despite these limitations, he said they could instead look at other health outcomes, including child cancer.
Research would look for prenatal exposure to nitrate linked with child cancer, as had been seen overseas.
Pre-term births would be the focus, however, with plenty of data to work with.
A petition created earlier in the year asks the government to lower the allowed level of nitrate in New Zealand’s drinking water.
It was supported by Greenpeace, Forest & Bird, the Environmental Defence Society, Choose Clean Water and Fish & Game.
Last month, Greenpeace visited various towns, including Winton and Riversdale, to test water samples. In Riversdale, levels ranged from 5.19mg per litre to 8.88mg per litre.