By Mike Joy & Michael Baker. This article is republished from The Conversation under a Creative Commons license. Read the original article.
20 September 2019
A recent Fish and Game New Zealand investigation of drinking water supplies in the Canterbury region found that nitrate levels in drinking water sourced from groundwater in areas of intensive farming and horticulture are already high and rising. The findings are consistent with data from the regional council Environment Canterbury. The latest groundwater report showed that half of the wells they monitor have values greater than 3ppm nitrate-nitrogen, more than three times the Danish study’s trigger level for colorectal cancer risk.
Christchurch City Council data show that of 420 samples collected during five years from 2011 to 2016, 40% exceeded 0.87ppm.
IMPACT ON THE ECOSYSTEMS
When nitrate enters waterways, it accelerates algae growth. Freshwater scientists have long been pushing for nitrate limits to curtail algal proliferation, but restrictions have been slow and in some regions non-existent. An important coincidence is that the Australian and New Zealand guideline for healthy aquatic ecosystems for nitrate is at 0.7mg/l nitrate-nitrogen, close to the level required to stay under the colorectal cancer risk value found in the Danish study.
The Canterbury region exemplifies the problems resulting from the failure of central and local government policy in New Zealand to protect both ground and surface water. These failures cannot be blamed on a lack of awareness as these outcomes were predicted decades ago. For example, in 1986 the Ministry of Works predicted the nitrate contamination we now see as a consequence of regional irrigation schemes. It made it clear that alternative drinking water supplies would have to be found for Canterbury residents.
Apart from health and ecological concerns, another worry is that public fears about drinking water safety will prove a boon for water bottling companies, which have free access to New Zealand’s cleanest water.
While many New Zealanders face significant and increasing costs for water treatment, water bottlers pay virtually nothing. The only cost, apart from bottling costs, is a one-off 35-year regional council consent fee. This anomaly highlights the urgent need for government to put tougher limits on nitrate loss and face up to dealing with water ownership issues in New Zealand.
In conclusion, surface water in many parts of New Zealand is highly contaminated with nitrates as a result of intensified farming. These elevated levels are undoubtedly damaging freshwater ecosystems and biodiversity, and may also be harming human health.
At the very least, public health authorities need to conduct a systematic survey to assess current nitrate levels in New Zealand drinking waters, including those that are not part of the routinely monitored networked system. This information could then be used to provide a quantitative estimate of the colorectal cancer burden in New Zealand that can be attributed to this hazard.
Mike Joy is a senior researcher at the Institute for Governance and Policy Studies at Victoria University of Wellington. Michael Baker is a professor of public health at Otago University.