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In 29 California neighborhoods, nearly 14 percent of children under the age of six have elevated levels of lead in their blood — these levels are almost three times higher than the contamination experienced by residents in Flint at the peak of the water crisis.

The 2012 data, which comes from the California Department of Health, only accounts for a quarter of the state's zip codes.

Jill Johnston, an assistant professor of preventive medicine at the University of Southern California and director of USC's Environmental Health Centers Outreach Program, explains what the state needs to do to address this issue.