We don’t know how the the life of this bear was, but its end came in the darkness, at the bottom of a pit in a narrow Romanian cave. There were no claw marks on the stone, no signs of a struggle, just the silence of a pitfall trap that offered no return. But this brown bear’s death, sometime around the year 845, didn’t mark the end of its story.

A thousand years later, its jaws would tell a toxic tale — one that challenges what we thought we knew about when humans began poisoning the planet.

The Balkan and Carpathian regions contain the oldest known mining and metallurgy sites in Europe. “We know that significant metal pollution occurred in the Balkans as early as 600 BCE, but its impact on wildlife had never been studied before,” explains Sébastien Olive, a researcher at the Belgian Institute of Natural Sciences and co-author of the study.

Metallurgy and a Bear

Among the ancient, extracted metals was lead. Lead was used for making pots, coins, weights, pipelines, and even bullets. We now know making lead pipes and pots isn’t a good idea, but at the time, it was a popular option. Extracting a metal like lead is also polluting to the environment. It can enter the water and soil, accumulating in plants and the animals that eat the plants. But it accumulates even more in the animals that eat other animals.

This seems to be what happened to this bear.

Scientists call the animal “Cl/010,” a reference to its excavation site, but let’s picture it as it was: a stocky male, likely five or six years old, ambling through the Carpathian forests in summer, its powerful nose catching the scent of roots, berries, and carcasses. At the time, medieval forges belched smoke from the nearby Banat mountains. Metallurgists worked lead and silver from deep under the earth, fueling an early boom in mining. Unbeknownst to them — or probably anyone at the time — their pollution was already reaching the wild.

In 2011, researchers exploring a cave found the skeletal remains of three bears. Two of them were chewed, possibly scavenged. However, one mandible was intact and perfect for analysis. That specimen (Cl/010) would become the subject of an unusual forensic investigation.

First, using radiocarbon dating, the team assessed when the bear lived. But the team led by Marius Robu, a Romanian speleologist, wasn’t done. They realized that unlike most tissues, teeth grow incrementally producing layers of dentin and cementum. This means they can offer environmental information, much like annual tree rings.

The Forensics of a Toxic Timeline

In the first molar, researchers found six clear layers of dentin — each corresponding roughly to a summer and winter season. Bears, like many large mammals, “hibernate” through the cold months. Technically speaking, bears don’t actually hibernate, they enter a state of torpor, but it’s still a period of lower activity. That period creates denser, darker tissue layers. Meanwhile, the lighter ones come from the bear’s active months.

It was in the lighter bands that trouble surfaced.

Using laser ablation — an ultra-precise method that vaporizes tiny portions of tissue and reads their chemical composition — the team mapped the presence of lead (Pb), lithium (Li), and zinc (Zn) across the bear’s teeth. The results were striking. Each summer, the bear absorbed a spike of lead. It wasn’t random; it was rhythmic. The concentrations lined up perfectly with the bear’s foraging seasons — five cycles in total. That pattern alone was compelling.

But the final summer was different.

The lead levels in that last layer surged past 15 parts per million, more than 50 times the background rate for wild herbivores and well beyond what’s considered neurotoxic in humans. In modern forensic terms, it would qualify as dangerous exposure. The bear didn’t just live near pollution — it was marinated in it.

“This is the earliest known case of a wild animal suffering from heavy metal poisoning due to human activity,” says Olive. “It is possible that metal pollution had a broader impact on wildlife in medieval Europe, alongside hunting and changes in their habitat.”

The Smoking Gun: Medieval Metallurgy

It’s not clear if the lead pollution actually killed the bear, but it must have affected it. At some point, the bear fell into a natural pit and was unable to escape. Lead is known to be a potent neurotoxin and likely had a big impact on it.

“The poisoning could have been the reason the bear fell into the pit. The lead concentration in its body during its last active summer reached as high as 15.2 ppm (parts per million). This level of lead pollution undoubtedly had negative effects on the bear’s health and brain.” For comparison, in humans, neurological effects occur at just 5 ppm. In wild Romanian bears today, the average lifespan is 20 to 30 years. Cl/010 was dead before reaching six.

The odds are it wasn’t just this particular bear that was affected by the lead pollution. There’s a good chance every creature felt the pain to some extent.

The parallels to our modern world are uncomfortable. Today, we still find lead in wildlife — from scavenging eagles in the American West to Scandinavian brown bears carrying toxic loads in their blood and milk. Even though leaded gasoline and paint have been largely banned, bullets, mining, and old infrastructure continue to leach the metal into food chains. Pollution isn’t a legacy issue — it’s an ongoing threat.

But what’s most striking about Cl/010’s story is how far back that threat reaches. This was no post-industrial bear. It was a medieval omnivore, wandering green mountains centuries before coal smokestacks or chemical plants. And yet, its body already carried the fingerprint of human ambition.

The study “Earliest evidence for heavy metal pollution on wildlife in Middle Age Europe” was published in the journal Environmental Pollution.