The leading causes of nitrate contamination in drinking water comes from the application of synthetic nitrogen fertilisers and animal effluent on farms. Photo: Stephen Jaquiery Southern councils have not responded to new research which reveals nitrate pollution in drinking water is associated with an increased risk of premature births in humans. Environment Southland, the Gore District Council and the Ministry of Health were all contacted by the Otago Daily Times yesterday and asked if they were concerned about the new research, and if consideration needed to be given to changing the nationwide standards for nitrates in drinking water. None responded by deadline. The leading causes of nitrate contamination in drinking water comes from the application of synthetic nitrogen fertilisers and animal effluent on farms. Excess nitrogen not absorbed by crops leaches through the soil into groundwater aquifers. The research, by the Universities of Otago, Canterbury and Massey, found a small but consistent increase in the risk of preterm births as nitrate concentrations increased - even at levels well below the present drinking water standards. Research lead author and University of Canterbury environment health researcher Associate Prof Tim Chambers said the study analysed 735,831 single baby births between 2008 and 2021, linking gestational age with estimated nitrate concentrations in drinking water at the mother’s usual residence. About one in 15 babies in New Zealand are born preterm - before 37 weeks - which increases the risk of health problems at birth and later in life. ‘‘Our study found that the risk of preterm birth increased by about 1% for every 1mg per litre increase in nitrate concentration in drinking water,’’ he said. The researchers noted the study was ‘‘observational’’ and did not prove that nitrate caused preterm birth. However, the findings were consistent with several previous large cohort studies that have reported similar associations, he said. ‘‘If the relationship is causal, nitrate exposure could contribute to around 120 preterm births each year, or about 4% of all preterm births in New Zealand.’’ The present New Zealand drinking water standard of 11.3mg nitrate-nitrogen per litre of water was established to protect against infant methaemoglobinemia (blue baby syndrome), rather than preterm birth. Denmark recently decided to lower its drinking water standard for nitrates to 1.3mg/litre, based on an international expert assessment of increased risk of colorectal cancer. Other studies have shown that in New Zealand, up to 100 cases of bowel cancer and 40 deaths a year could be caused by nitrate contamination in drinking water. Most public drinking water supplies in New Zealand have low nitrate concentrations, with the majority below 1mg/litre. However, contamination is more common in private shallow groundwater bores, a national survey finding 20.8% exceeded half the present drinking water standard and 3.7% exceeded the standard. Two municipal supplies, Gore and Waimate, were highlighted in the study because they recently breached the existing standard for nitrates in drinking water. The researchers found higher nitrate concentrations were associated with small but consistent increased risks of preterm births and the findings remained consistent across a range of sensitivity analyses, including sibling cohort models. Assoc Prof Chambers said the results strengthened the case for a review of drinking water standards. ‘‘While the increase in risk is likely to be small for the great majority of communities supplied by public water systems, this study adds further urgency to reassessing regulatory limits for nitrate in drinking water.’’ The researchers also said greater emphasis was needed on protecting drinking water sources, with stronger action by national and local government to reduce nitrate contamination and safeguard drinking water quality. john.lewis@odt.co.nz
