Nitrates – a Major Environmental and Health Issue

by Rex Gibson

The article on cow deaths from nitrate poisoning (page 3, Agribusiness, July 6 by Gerald Piddock) raises the issue of heavy nitrate leaching into the environment.  Federated Farmers Dairy Vice-Chairman Ben More was quoted as saying “Waikato farmers including himself have had abortions in their herds, which he puts down to nitrate poisoning. He has also heard of cases in Coromandel and on the Hauraki Plains.”  
He further noted “He heard of one bad case that killed 30 cows on a south Waikato farm and another where 130 cows had to be treated by a vet with methylene blue, which helps a cow’s haemoglobin carry oxygen”.
It’s not just cow deaths that should be of concern but the overall effects on the environment of which humans are just one species in the overall ecosystem. Warning
About a year ago, Canterbury’s Medical Officer of Health, Dr Alastair Humphrey warned that, because of high levels of nitrates in drinking water, research is urgently needed to prevent a future human health emergency.
He noted the issue of potentially fatal Blue Baby Syndrome in infants in the Ashburton area linked directly to the nitrate levels; where nitrates block babies haemoglobin’s oxygen carrying capacity.  Dr Humphrey said New Zealand needed to conduct its own study after the findings of a comprehensive Danish study on 2.7 million people study published last year found a high correlation between increased nitrate levels and colorectal (bowel) cancer. The Danish study authors found people exposed to high nitrate levels had a significantly greater risk of getting colorectal cancer. Dr Humphrey’s call was not unsurprisingly ‘side-lined’ by government and some industry spokespeople. 
Danger Figure
The NZ Federation of Freshwater Anglers (NZFFA) also expressed an additional concern about the adverse effect of nitrates on the ecology of rivers and streams regarding young trout, salmon and native fish. Their upper tolerance is the same as the “danger figure” for colorectal cancer i.e.  3.7 mg/L N (= 3.7 milligrams of nitrogen per litre) in the water. But on-going research and sampling by NZFFA is revealing levels in Canterbury waterways such as the Selwyn River and Hart’s Creek to be at least double the 3.7 milligrams of nitrogen per litre bar for many months of the year. At a community nitrate testing day near Ashburton numerous farmers reported the absence of all fish life in irrigation races that for up to half a century had hosted trout and native fish species.
As noted in Agribusiness “In Hawke’s Bay an estimated 120 ewes died from nitrate poisoning on one farm, which Vet Services Hawke’s Bay managing director Richard Hilson believes is a record.
At stake from excess nitrate levels is not only bovine health but also other livestock and both aquatic and human health.
Rex N. Gibson

Note: Rex Gibson is a Scientist and Ecologist and an Executive Member of the Federation of Freshwater Anglers Inc.

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