The idea that bullets can cause lead poisoning might seem obvious to trivia nerds who knew that bullets were made of lead. And to people who knew that the threshold for what constitutes lead “toxicity,” or “poisoning,” has plummeted over the decades. Having 60 micrograms of lead per deciliter of blood used to be the cutoff for what was considered safe. In 1971 that fell to 40, and later to 20, then 10, then five (as of 2015). As lead-exposure data has improved, subtle signs have revealed themselves—to the point that the new consensus on lead poisoning among many experts is that there is no “safe” amount of lead in one’s bloodstream.

A person’s lead levels can be quantifiably increased by minor exposures. Eating the tiniest paint chips (even only on special occasions) can do it, but drinking slightly contaminated water is widely believed to be the most common cause of lead toxicity. The people of Flint, Michigan, have already reported more than 8,000 documented cases, costing hundreds of millions of dollars and unknowably many IQ points. And these people are far from alone. In December, a Reuters investigation found 3,000 areas where at least 10 percent of people had lead poisoning.

So it could seem obvious that it’s risky to leave an actual chunk of lead inside a person’s body. Why is this a report that’s being issued in 2017 instead of, say, 1977? Lead was phased out of paint and gasoline when the dangers of exposure became undeniable almost half a century ago.

The challenges to understanding the problem are many, starting with the fact that NRA lobbyists have rendered the CDC effectively forbidden from studying gun violence.

Add to that the multiple variables that come with being a human in the world that make it difficult to discern the exact and primary causes of lead poisoning. People who are most likely to get shot––people from poor, minority populations—are also the most likely to already have lead poisoning from other exposures. The amount of lead in an American’s body tends to be a quantifiable proxy for socioeconomic status—the two could almost be used interchangeably.

In the current study, researchers used cutoff for “toxicity” at 10 micrograms of lead per deciliter of blood. Fewer than 1 percent of people with that level of lead appeared to be due to bullet fragments. But at higher levels of 80 micrograms (severe poisoning), almost 5 percent of people had retained bullets. Many other people carrying around lead could have lower levels in their blood and be suffering mild cognitive impairments that go long or forever undiagnosed.

So until more is known, the CDC researchers report, “These data should be considered minimum estimates of the magnitude of the problem.”

In the meantime, if a person is having vague symptoms and they’re carrying around a bullet, health professionals are urged to promptly consider a diagnosis of lead poisoning. Similarly, people with lead poisoning should be asked about bullets. Extraction should be considered, and the CDC advises counseling on the symptoms of lead poisoning and regular testing. A single negative test is insufficient since the fragments can migrate within the body. For example, a person who was shot a decade ago could become acutely ill if a bit of lead moves into a joint space.

There is also an impractical approach that’s worth mentioning. Much suffering and cost could be prevented if all people had clean drinking water and did not shoot one another.