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Detection of arsenic and lead contamination in Stream

Te Āti Awa ki Whakarongotai Charitable Trust

Detection of arsenic and lead contamination of watercress in Wharemauku Stream by iwi.

Results from monitoring by local iwi Te Āti Awa ki Whakarongotai of heavy metal contamination of watercress in the Wharemauku Stream in Paraparaumu have now been released, showing concentrations of arsenic in plant material during 2018 reached nine times that of food safety standards, with exceedingly high concentrations of lead also found.

The testing comes from a site that has been of concern to iwi since it was disturbed by the Mackays to Peka Peka Expressway project in 2016 as part of road construction. The land adjacent to the waterway was an old market garden and known to be contaminated. Prior to its disturbance, iwi had conducted their own assessment and predicted that disturbing it would result in contamination of the waterway and the food chain.

Testing of watercress sampled in the tributary of the Wharemauku Stream near Kiwi Road in the Raumati area showed arsenic concentrations in the plant material at 9.3mg/kg. Previous research referred to by the Ministry of Primary Industry suggested that normal arsenic levels in the Wellington region were generally below 0.25 mg/kg, with food safety advice suggesting that concentrations higher than 1 mg/kg pose a risk to human health.

Testing also showed concentrations of lead levels in watercress plant material to be four times food safety standards at the same Kiwi Rd site, and further testing of watercress at two additional sites downstream in the Wharemauku were found to be double the safe level.

The 2018 heavy metal results follow other recent iwi monitoring results identifying the presence of the bug, campylobacter on watercress in the same Wharemauku stream, resulting in the iwi placing a rāhui on the Wharemaukū Stream.

“The results were generated through the monitoring that we have been conducting to identify any potential effects of the Expressway post-construction, as part of an agreement we have with the New Zealand Transport Agency (NZTA)” said Mahina-a-rangi Baker, Pou Takawaenga Taiao, Environmental Manager for the iwi, “the Wharemauku Stream has a range of serious pollution issues that have arisen from a lack of proper regulation of the activities that continue to pollute. In the case of these heavy metal results, we have an opportunity to require NZTA to respond appropriately to an effect of construction and limit any further pollution of an already highly stressed catchment.”

The rāhui remains in place to prevent the public from gathering any food, or having contact with water in the Stream, in order to limit the public health risk. People who consumed watercress or other food from the Stream would be at risk of long-term health effects from arsenic and lead. Long-term exposure to arsenic can cause cancer and skin lesions. Lead is a cumulative toxicant that can affect multiple body systems and is particularly harmful to young children.

Cooking of watercress does not reduce any of the risk posed by heavy metal contamination. Samples were also tested for heavy metal contamination in the Whareroa Stream, several Waikanae River Tributaries, the Waimeha, and the Kākāriki Streams and none of these samples exceeded food safety standards. However, the iwi advise the public to always show caution when harvesting food from public areas and consider the potential for historical or present land use to be a source of pollution.

Baker says, “We cannot allow ourselves to become desensitised to the worsening state of our waterways. There are several examples in New Zealand where complacency around contamination eventually lead to a public health crisis with not just serious economic costs, but potential threats to human life as well, including the Havelock North campylobacter crisis, and the serious chronic health issues attributed to heavy metal contamination in Whakatane.”

“It wasn’t that long ago that the Wharemauku Stream was a place where people could fish, gather food, or even swim. We will not accept a future for our waterways where you can become infected through mere contact with them, or poisoned by consuming the food gathered there.”

The iwi will continue to work with NZTA, Greater Wellington Regional Council, Kāpiti Coast District Council and Regional Public Health to see the contamination issues in the Stream addressed and remediated.


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