Dozens of California communities have experienced recent rates of childhood lead poisoning that surpass those of Flint, Michigan, with one Fresno locale showing rates nearly three times higher, blood testing data obtained by Reuters shows.

The data shows how lead poisoning affects even a state known for its environmental advocacy, with high rates of childhood exposure found in a swath of the Bay Area and downtown Los Angeles. The figures show that, despite national strides in eliminating lead–based products, hazards remain in areas far from the Rust Belt or East Coast regions filled with old housing and legacy industry.

In one central Fresno zip code, 13.6% of blood tests on children under 6 years old came back high for lead. That compares to 5% across the city of Flint during its recent water contamination crisis. In all, Reuters found at least 29 Golden State neighborhoods where children had elevated lead tests at rates at least as high as in Flint.

“It’s a widespread problem and we have to get a better idea of where the sources of exposure are,” said California Assembly member Bill Quirk, who chairs the state legislature’s Committee on Environmental Safety and Toxic Materials.

Last week, prompted in part by a December Reuters investigation pinpointing thousands of lead hotspots across the country, Quirk introduced a bill that would require blood lead screening for all California children. Now, just a fraction of the state’s children are tested.

The newest zip code–level testing data was released by the California Department of Public Health in response to a longstanding Reuters records request and adds to a limited set of numbers previously disclosed by the state. The numbers offer a partial state snapshot, covering tests conducted during 2012, the most recent year for which information was provided, and in about one–fourth of the state’s more than 2,000 zip code areas.

Unlike other states that provided Reuters with results for all zip codes or census tracts, California withheld data from zip codes where fewer than 250 children were screened, calling such results less reliable. So, the available data, encompassing about 400,000 children tested in 546 zip codes, likely omits many neighborhoods where lead exposure remains a problem but fewer children were screened.

Blood tests can’t determine the cause of a child’s exposure, but potential sources include crumbling old paint, contaminated soil, tainted drinking water or other lead hazards.

In Fresno’s downtown 93701 zip code, nearly 14% of children tested had lead levels at or above 5 micrograms per deciliter of blood, the Centers for Disease Control and Prevention’s current threshold for an elevated reading.

No level of lead exposure is safe, but children who test that high warrant a public health response, the CDC says.

Once common in household paint, gasoline, and plumbing, lead is a neurotoxin that causes irreversible health impacts, including cognitive impairment and attention disorders in children.

In all, Fresno County had nine zip code areas where high lead levels among children tested were at least as common as in Flint. The Reuters article in December documented nearly 3,000 locales nationwide with poisoning rates double those found in the Michigan city along the Flint River.

The city of Fresno battles high poverty rates and problems with substandard housing, both risk factors for lead exposure. Some locals are also concerned with drinking water, after unsafe levels of lead were detected in at least 120 Fresno homes last year.

The exposure hotspots remain outliers. Around 2% of all California children tested in 2012 had lead levels at or above the federal standard, Reuters found.

Yet in the worst–affected zip codes identified statewide, more than 10% of children tested had an elevated lead level.