A study showing a link between nitrate levels in drinking water and rates of bowel cancer should concern people living in areas of New Zealand where nitrates are high, write Mike Joy and Michael Baker.
Last year, a Danish study reported a link between nitrate in drinking water and the risk of developing colorectal (bowel) cancer.
This finding could have important implications for New Zealanders.
Recent data show also that drinking water supplies in some parts of New Zealand have nitrate levels more than three times higher than the threshold level for colorectal cancer risk identified in the Danish study.
This study and other research raise an important question about the contribution nitrate exposure through drinking water may be making to New Zealand’s high rates of bowel cancer.
It included 2.7 million people over 23 years and monitored their individual nitrate exposure levels and colorectal cancer rates.
The research found a statistically significant increase in colorectal cancer risk at 0.87ppm (parts per million) of nitrate-nitrogen in drinking water.
One key implication is that the current nitrate standard for drinking water used in most countries, including New Zealand, is probably too high.
The findings are consistent with data from the regional council Environment Canterbury.
In conclusion, surface water in many parts of New Zealand is highly contaminated with nitrates as a result of intensified farming.