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Nearly 300 drinking water wells and other water sources in California have traces of toxic chemicals linked to cancer, new state testing has found.

Testing conducted this year of more than 600 wells across the state revealed pockets of contamination, where chemicals widely used for decades in manufacturing and household goods have seeped into the public’s water supply. An analysis by the Los Angeles Times found that within this class of chemicals, called perfluoroalkyl and polyfluoroalkyl substances, the two most common compounds were detected in 86 water systems that serve up to nine million Californians.

State officials released the water quality results on Monday, the first step in what’s likely to be a years-long effort to track the scale of the contamination and pinpoint its sources. Only a small fraction of California’s thousands of drinking water wells were tested in this initial study. Officials said they planned to examine many more, but have not committed to future statewide testing.

The results offered the clearest picture yet of California’s exposure to a public health crisis that is playing out nationally.

Read the full story on LATimes.com.