Lead exposure is a race issue. The crisis in Flint, Michigan, shows why.

On Tuesday, Michigan Gov. Rick Snyder declared a state of emergency over a lead crisis in Flint, Michigan, where 4 percent of children have elevated levels of lead in their bloodstream — twice what the rate was just years ago.

As Vox’s Libby Nelson explained, the root of the crisis is budget problems: Faced with financial constraints, officials made cuts that effectively allowed the city’s water to get contaminated with more lead.

But an overlooked aspect of the crisis is how it represents a common thread in lead exposure issues: Lead often hits black communities hardest. Flint, for one, is nearly 57 percent black, much higher than the state average of 14 percent, according to US Census Bureau data.

Previous research has found big racial disparities in lead exposure. A 2013 study from the Centers for Disease Control and Prevention found that although blood lead levels among US children have dramatically dropped since the late 1990s, average blood lead levels among black children (1 to 5 years old) between 2007 and 2010 were still roughly 38 percent higher than they were among their white peers.

The Flint lead crisis shows how these disparities happen. It’s not that there’s a grand conspiracy to contaminate black children with lead. Instead, centuries of discriminatory and oppressive policies have pushed black people into poor towns and cities that can’t afford the lead abatement programs that wealthier places can.

This has lifetime effects on these communities: Exposure to lead can produce learning disabilities, lower IQs, and impulsivity. The effects are so bad that some researchers believe that the drop in blood lead levels in the past few decades may at least partly explain the United States’ massive drop in crime since the 1990s. As the CDC explained in its study, “No safe blood lead level in children has been identified.”

It’s tragic, then, that lead disproportionately shows up in poor, black communities that are already held down by bad economic circumstances and policies. Flint is a real-time example of that tragedy unfolding.