Hundreds of children in the city of St. Louis had blood lead levels above 5 micrograms per deciliter, the marker for medical intervention, according to recent state data. Areas in gray indicate no data was available because too few children were tested. Source: Missouri Department of Health and Senior Services.

Andrew Nguyen is a developer for the St. Louis Post-Dispatch.

Janelle O'Dea is a data specialist and reporter for the St. Louis Post-Dispatch.