Kea. Photo: Tim Norman
Dr Eric Buenz is a biomedical researcher at NMIT, the Nelson Marlborough Institute of Technology. He's also a recreational hunter.
For the past decade Eric and his colleague Professor Gareth Parry have been interested in lead and its impact on human and animal health, with a focus on lead ammunition.
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Every year in New Zealand, recreational hunters shoot more than half a million wild game animals. Eric says three types of ammunition are used with centrefire rifles: lead bullets, lead-free copper bullets, and - most commonly - copper-jacketed bullets with a lead core.
Lead is a very useful metal. It is soft, versatile and cheap. It is also very toxic. The World Health Organisation says that lead affects multiple body systems and it is particularly harmful to young children and women of child-bearing age. There is no level of exposure to lead that is known to be without harmful effects.
Eric Buenz is a hunter who is also interested in the health impacts of lead-based ammunition. Photo: Tim Norman
The hunter with severe lead poisoning
A few years ago, Eric and Gareth met a New Zealand hunter whose main diet was wild game meat that he shot himself. When they suggested he take a blood test to check his lead levels they were astonished when it came back at nearly 75 µg/dL. The World Health Organisation says a blood lead level of 5 or more µg/dL is concerning. His was one of the highest blood lead levels on record.
The hunter switched to non-lead ammunition, and as his blood lead levels began to decline, he quickly regained a significant amount of lost weight and was no longer troubled by a rare type of gout associated with lead poisoning.
How much lead does wild game meat shot in New Zealand contain?
Eric and his colleagues decided to investigate lead levels in hunter-shot deer in New Zealand. They asked the hunting community to send in samples of meat they had shot and received 44 samples of minced wild game meat.
International studies have shown using x-rays that shot animals can contain hundreds of visible metal fragments from a single bullet, much of it lead. There are also many thousands of microscopic fragments that are too small to show up on x-ray.
Each sample sent in for the NMIT study was x-rayed, and a radiologist identified visible metal fragments. Nearly half of the samples contained no visible metal fragments. However, other samples in the NMIT study contained numerous small metal fragments that Eric says look like an image of "a starry night sky." This has also been described in the literature as a "lead snowstorm."
On the left, An x-ray of minced wild game meat – the white highlights are metal bullet fragments including lead. On the right, this x-ray of a goat carcass shows white bullet fragments – much of which is lead – scattered through the body. Photo: NMIT
The Cawthron Institute then used inductively-coupled plasma mass spectrometry to test for lead. This showed that almost half of samples of the wild game mince sent in by hunters contained lead levels exceeding the daily intake benchmarks for children. This included many samples in which no lead had been identified in x-ray screening.
Researcher Eric Buenz using a walking pole to trace the trajectory of a bullet through an animal carcass. Photo: Tim Norman
Eric says that avoiding meat from around the bullet trajectory (he recommends not taking meat within a 30-cm radius of the bullet hole) will lessen the likelihood of eating lead fragments, but he says using non-lead ammunition is the only way to ensure meat harvested for consumption is lead free. This research was published in May 2024.
Lead poisoning in kea
Kea experts and conservationists have known for a long time that kea are at risk of lead poisoning from chewing lead roof flashing and lead-head roofing nails used on back country huts in the South Island high country.
In the last few years, the Kea Conservation Trust and the Department of Conservation (DOC) have attempted to alleviate the risk by removing over 6 tonnes of lead from these huts, as well as buildings in alpine settlements such as Arthur's Pass and Mt Cook village.
Sick kea found at places like Arthur's Pass are taken to the South Island Wildlife Hospital where their blood lead levels are tested and chelation therapy is used as appropriate.
Sick kea including those suffering from lead toxicity are often sent to the South Island Wildlife Hospital for treatment. Photo: Tim Norman
Dr Kerry Weston manages DOC's Kea Recovery Programme. She says that in 2018 researchers collecting blood samples from kea living in remote South Westland, with very limited access to huts with lead roofing material, found that many birds were nonetheless testing positive for lead.
The area was a focus for DOC's tahr culling programme, and groups of kea were observed scavenging on tahr carcasses, raising the possibility that kea were ingesting lead fragments from bullets.
Kea are opportunistic scavengers on wild animal carcasses which can expose them to the risk of lead poisoning from lead-based ammunition. Photo: Tim Norman
Dr Eric Buenz had also become aware of kea scavenging on carcasses shot by hunters and cullers, and this led to a research collaboration with the Kea Conservation Trust, Department of Conservation, South Island Wildlife Hospital, Ngāi Tahu and international expert Professor Myra Finkelstein.
Myra is an adjunct professor in the microbiology and environmental toxicology department at the University of California Santa Cruz, in the United States, and a world-leading researcher in the detection and impacts of lead on human and animal health.
From Californian condor to South Island kea
Myra's pioneering work with California condor has shown that the ingestion of lead from lead-based ammunition is preventing the highly endangered species from recovering.
Worldwide, more than 100 species are affected by lead fragments from ammunition, including bald eagles, golden eagles and white-tailed sea eagles, as well as condors.
More than 80 kea blood samples, collected over several decades, were sent to Myra for stable isotope analysis. She was also sent samples of ammunition used by the DOC tahr culling programme, along with samples of lead flashing and lead-head nails from back country huts.
Myra showed that the lead roofing material has a distinctly different stable isotope profile to the ammunition.
When she tested the kea blood samples, Myra was able to clearly determine the source of the lead they had ingested. The results showed that a third of the kea had eaten lead fragments from bullets, a third had got their lead from roofing material, while the remaining third had got lead from both sources.
Moving away from lead
Dr Kerry Weston says lead poisoning from ammunition is yet another threat facing the nationally endangered kea, whose population may number as few as 1000 breeding birds. Population modelling shows that even a small reduction in deaths caused by lead poisoning could make the difference between kea going extinct or growing in numbers.
DOC began phasing out the use of lead-based ammunition in the tahr control programme back in 2018, as soon as it suspected it might be an issue. Tom Brookman leads DOC's tahr programme and he says work is well underway to move away from lead-based ammunition across all its wild animal control programmes, a move advocated by the Kea Recovery Group.
This is not just an issue for DOC. There is plenty for recreational game hunters to think about. In the published paper, Eric and his colleagues "suggest that an immediate transition to the use of non-Pb ammunition for all forms of shooting within kea habitat will significantly contribute to the recovery of this iconic species and taonga."
There is precedent for this. To help save the condor, California has banned lead-based ammunition. In many countries the use of smaller lead shot to kill waterfowl such as ducks on or near waterways has already been banned. This is because the waterfowl were eating lead shot along with grit they use to help digest their food - this was bad for the birds and bad for the humans eating them. In New Zealand only non-toxic i.e. non-lead shot can be used when hunting waterfowl within 200 metres of water, regardless of the type of gun.
This research was published in October 2024 in a paper by Eric Buenz and others titled "Lead-based ammunition is a threat to the endangered New Zealand Kea."
