Big game hunters using lead bullets leave behind fragments that are significantly smaller than regular medical imaging has previously shown, and considerably more widely dispersed.

This finding – which has implications for toxicity – comes from a team of researchers from the Canadian Light Source (CLS) at the University of Saskatchewan and the College of Medicine at USask.

The scientists used synchrotron imaging for the first time to study both the size and spread of bullet fragments in big game and published their results in August in PLOS ONE. Researchers studying this issue usually use medical radiography, which can’t distinguish lead from other materials used in ammunition or accurately measure fragments that small.

Chemist Adam Leontowich, CLS associate scientist and lead author on the study, said while he expected the bullets would produce hundreds of fragments, he was surprised to discover they can be as small as a single human blood cell. These can be more dangerous than larger ones, says Leontowich, pointing to rat studies showing small lead fragments are absorbed more easily during digestion than larger ones.

“That is presumably due to the higher surface area per equivalent weight of particles,” he says. “Also, some animals will actually avoid the largest fragments when eating the remains, so again the smaller particles play a greater role in toxicity.”

Leontowich and his team fired bullets into blocks of ballistic gelatin – the same material used by law enforcement agencies for ballistic testing because it has a similar density to flesh. To better simulate hunting, they also encased deer bone within the gelatin.

Lead rifle bullets are generally 75% lead and 25% copper, which is used as a casing. The researchers thought they would see some copper in their samples, but the particles were almost exclusively lead.

“It’s probably because lead is a lot softer than copper,” says Leontowich. “The copper jacket peels back and remains as one mass.”

Calling it a “very thorough analysis,” University of Guelph professor emeritus Vernon Thomas says it furthers the findings of a 2016 study that used inductively coupled plasma-mass spectrometry to show lead nanoparticles in the range 40 to 750 nm in game meat.

Thomas, an expert in lead toxicity in wildlife, points out that the implications are most serious for frequent consumers of game meat, such as Indigenous subsistence hunters and their families. Lead contamination is also of concern for scavenging wildlife.

In Canada, using lead shot for hunting migratory birds is banned. However, there are no regulations against using lead rifle bullets for hunting big game. Nova Scotia and Prince Edward Island included warnings about the health and environmental risks of lead bullets in their 2021-22 hunting regulation handbooks.

Leontowich, who is a big game hunter himself, says he hopes his findings will help persuade more hunters to switch over to the slightly more expensive copper bullets. “Save the lead bullets for target practice,” he says.