Nitrate fears prompt call
A call has been made for a moratorium on market gardening on the eastern Waimea Plains, near Nelson.
That plea to Tasman District Council is one of six from Water Information Network Inc secretary Lewis Solomon in response to concern about nitrate levels under some areas of the plains.
It comes after the council last week published a report on the nitrate levels in the groundwater. The report, covering the findings of groundwater monitoring and a soil survey on the eastern plains, says the indications are that market gardening is a ‘‘higher risk land use for nitrate leaching’’ compared with the other main land uses in the study area – pasture, pipfruit and viticulture.
The groundwater monitoring shows nitrate levels continued to exceed drinking water standards under some sections of the plains while the soil survey reveals that in subsoil samples, mean nitrate levels were three to four times higher under market gardens than the other land uses.
As well as contemporary land uses, the council report pointed to a former piggery that closed in the 1980s as a possible contributor to the elevated nitrate levels.
Solomon referred to the council report as a ‘‘comprehensive analysis of the pollution of the aquifers’’ under the eastern plains. However, it did not touch on the most important issue for Richmond residents. ‘‘Namely, the high concentration of nitrate in the reticulated water supply.’’
While the concentration of about 5mg/L nitrate-nitrogen in the Richmond supply was below the 11.3 maximum acceptable value in the drinking water standards, it was ‘‘probably the highest of any significant urban area in New Zealand’’, he said.
It was also above a risk level highlighted in a Danish study of 2.7 million people over 33 years. That study, published in February 2019, found nitrates in drinking water may increase the risk of colorectal cancer. It found increased risks at levels above about 1mg/L nitrate-nitrogen.
Solomon raised concern at a Nelson Marlborough District Health Board meeting in July 2019 about the level of nitrates in the Richmond drinking water.
‘‘Concern among medical professionals in New Zealand has been such that the Ministry of Health has assembled a team of scientists under Professor Michael Baker to investigate the relevance of the Danish research to New Zealand,’’ Solomon said this week.
Data on the Health Quality & Safety Commission New Zealand website, showed that for 2008-12, the incidence of colorectal cancer in females in the Nelson Marlborough District Health Board (NMDHB) area was 24 per cent higher than in females in the Canterbury DHB area while the incidence was the same for other cancers combined.
At that time, the concentration of nitrate in drinking water in the NMDHB area varied but was as high as 10mg/L nitrate-nitrogen in Richmond and ‘‘negligible’’ for most of the population in the Canterbury DHB area.
‘‘This result is entirely consistent with the findings of the Danish research,’’ Solomon said.
Councillor Dana Wensley said there might be a lot of reasons for the higher incidence of colorectal cancer in the NMDHB data such as an ageing population and other environmental factors.
‘‘But don’t we have a duty to actually look into this and say: ‘Maybe, when there’s a whole lot of question marks, we need a moratorium on increased intensification in market gardening’.’’
‘‘I think, it’s pretty much the perfect storm – there’s poor soils, high nitrate levels when we know there’s going to be intensification on the plains following the Waimea dam [commissioning] and we also potentially have some new information from the Ministry of Health . . .’’
The council needed to look at the impacts of this and ‘‘how we deliver safe drinking water for our community’’ .
Council environment and planning manager Dennis Bush-King said the council took measures to ensure the water complied with the drinking water standards ‘‘to ensure the people are kept safe’’.
Natural resources policy planner Lisa McGlinchey said work had started on activating a schedule in the Tasman Resource Management Plan ‘‘that will require nutrient management plan information’’ from water permit holders on the Waimea Plains.