Study of cheetahs and leopards shows lead poisoning threatens wildlife and humans

In the first study of its kind, researchers have assessed lead concentrations in the tibias of 62 cheetah carcasses and 11 leopard carcasses. Lead was detected in all cheetahs studied, with concentrations increasing the longer they had been kept in captivity and fed meat from animals shot with lead-based ammunition.

But it is just the beginning of the story about predators and scavengers in the environment.

The study, conducted by Dr Catherine Hauw for her master’s in wild animal health at the Royal Veterinary College (RVC) in collaboration with Namibian and other international institutions, raised questions.

While the effects of lead on avian species are well documented, its impact on terrestrial mammals, especially carnivores, remains severely underresearched. Despite bans on lead ammunition in some countries around the world, its use is still widespread in biodiversity hotspots around the globe.

This poses a significant threat to conservation efforts, particularly for scavengers and predators at the top of the food chain, which are especially vulnerable to secondary lead poisoning through contaminated prey or carcasses. There are also broader implications for the ecosystem and the meat humans consume.

Hauw, a wildlife veterinarian in the Department of Chemistry at the University of the Witwatersrand and lead author of the study, specialises in this field. She collects bones from predators and scavengers that have died and conducts toxicology research to determine the level of lead in their systems.

She uses predators and some scavengers as sentinels for lead in the environment, since they are susceptible to it.

“Lead was removed from gasoline and paint in Europe in the 1980s, whereas South Africa only phased out leaded petrol in 2006 and is set to ban lead-based paint in 2025. However, the issue persists because lead was never banned in ammunition, nor mines,” she says.

When a hunter that shoots an animal, such as an antelope, the bullet will, upon impact, scatter about 40cm around the wound, causing contamination of micro fragments of lead. Many people cut out this section, but discard it in the environment where it can poison scavengers. If not discarded it is sometimes used for human consumption such as biltong or other processed game meat.

Lead in the environment or in food can affect the brain. “The problem is that it is causing silent poisoning. It is a heavy metal that will stay in your blood for about three weeks, in your kidneys and liver for a couple of months, and then up to 12 years in your bones,” Hauw says.

“So that is why I’m using bones during my study on carcasses of predators or scavengers to show how chronically affected an animal and an environment is.”

A research paper she wrote after she published her master’s thesis showed acute lead poisoning of a cheetah.

Animals in sanctuaries are fed lead-shot meat every so often. If you want to rewild them, you want them to hunt and breed. But the problem is that lead affects cognitive function and reproductive systems.

So, the idea is to work with the management of these wildlife sanctuaries around southern Africa and push for a non-lead transition, which is available.

Thanks to the Cheetah Conservation Fund in Namibia and Dr Laurie Marker, who have kept all the carcasses of cheetahs and leopards that have died since 1991, Hauw had many bones to work on.

This was the basis of her pioneering research. She says many predators do not show clinical signs of lead poisoning until it is too late, yet they have high levels of lead in their bones.

“I’m working in Namibia and South Africa, and I’m going around different NGOs, private game reserves and national parks to collect samples of blood, hair and bones of lions, African wild dogs, brown hyenas, cheetahs, leopards, as well as marine wildlife,” she says.

The next step is to create a contamination map of South Africa and Namibia. If the animals are contaminated, the same will be true of the people in the area.

“Lead poisoning isn’t just a wildlife issue; it’s a One Health crisis. What we feed our animals and what we put into the environment comes back to affect us all. By raising awareness and switching to safer alternatives (non-lead bullets, such as copper or steel), we can protect ecosystems, wildlife and human health at the same time.”

People who want to contact Hauw if they have bones – the tibia of predators – on farms or private reserves can write to catherine.hauw@gmail.com DM