Below is a summary of a paper by scientists Marnie Prickett, a Research Fellow in the Department of Public Health, University of Otago and fellow scientists Adam Canning, Tim Chambers, Michael Baker, Simon Hales. While it relates to human needs for safe drinking water, nitrates can be very toxic to fish and the aquatic ecosystem in general.
Many communities across Canterbury are facing increasingly difficult decisions as nitrate pollution of drinking water sources worsens. Some water supplies in the region have already breached drinking water standards for nitrate pollution and publicly available information suggests more could follow.
Last year, Canterbury saw its highest-ever number of dairy cattle, the primary source of nitrate pollution in the region. Furthermore the area under irrigation, also linked to increased nitrate pollution, has continued to increase. As nitrate levels rise, associated costs are climbing for Canterbury’s communities.
Nitrates to Worsen?
Environment Canterbury (ECan), the regulator responsible for protecting drinking water sources in this region, has said nitrate pollution will get worse before it gets better and is a “legacy issue”. However, drawing together information on cattle numbers, irrigation, current state of drinking water and trends not only demonstrates failure by ECan to protect drinking water from nitrate contamination but also suggests the regulator’s recent decisions are likely to be making the situation worse.
Some communities and households in Canterbury are already grappling with nitrate levels above the drinking water standards (the Maximum Allowable Value or MAV, 11.3mg/L
as nitrate-nitrogen). Publicly available information suggests the problem of drinking water supplies breaching national standards for nitrate in Canterbury could get significantly worse, meaning more communities face the same, with costs escalating.
Environment Canterbury (ECan) is the regional council responsible for controlling nitrate pollution and protecting sources of drinking water in the region. Our analysis of water policy in place over at least the last decade (if not earlier), demonstrated that in many instances it would have been possible for ECan to use bylaws and planning, in a way that protected or reduced pollution of communities’ source water. Failure to do so means the cost of treating nitrate polluted drinking water falls on those downstream – households on private supplies and ratepayers.
Allowing drinking water contamination at the levels detected in Canterbury amounts to serious regulatory failure. Communities and households now face escalating costs as their once potable water breaches health standards.
Before there can be confidence that nitrate pollution will reduce, ECan must clearly demonstrate to its communities, and its district and city councils, that it is not continuing to add to the ‘legacy issue’ of nitrate pollution through decisions it is making now.
Central Government’s Role
Central government also has an essential regulatory role in the protection of communities’ drinking water sources. We have highlighted in previous briefings that the current Government should not weaken existing protection for drinking water sources, as well as stressed the greater role that Taumata Aroma, the national drinking water regulator should take in source water protection.
Editor’s Note:
Note that freshwater ecological health is affected with nitrate levels above 1.0 mg/L NO3-N, while salmonid eggs and fry show toxic effects from 3.5 mg/L.
Central government needs to step up its act and get involved. National has to forget John Key’s disastrous state grab of ECan in 2008 to let his corporate dairying mates set up their mega farms and forge a new path in the interests of not only public health but the public’s freshwater ecosystem too.
Full marks to the scientists for speaking out.
A 2017 Danish study reported a link between nitrate in drinking water and the risk of developing colorectal (bowel) cancer. New Zealand has one of the highest bowel cancer rates in the world.
I was told South Canterbury and/or Canterbury has the highest bowel cancer rate.
C’mon Minister of Health Shane Reti, how about government fronting up? People are dying.
The 1.0 mg/L nitrate value is the toxicity trigger. Nitrate has an ecological impact at far lower concentrations than when organisms start to turn up their toes. The triggers for nitrate as a stressor (i.e. to prevent algal blooms) are almost never mentioned. They are here:
https://environment.govt.nz/assets/Publications/Files/Establishment-of-reference-conditions-and-trigger-values-for-chem-phys-micro-biol-indicators-in-NZ-rivers-2013.pdf
It is a bit hard to follow, but we are interested in the “80%ile” column in Table (I) of Appendix I. The trigger varies depending on climate and water type, which makes sense as we expect a higher water quality in the backcountry than lowland streams. Nevertheless, the highest trigger is 0.265 mg/L and the lowest is 0.011 mg/L. The data comparisons are slightly different, but the allowable concentrations required to avoid algal blooms etc are almost always lower than the 1 mg/L toxicity trigger and a small fraction of the 11.3 mg/L human health trigger. If you are serious about protecting the environment from nitrate, these are the concentrations you need to achieve.