LOS ANGELES (CBSLA.com/AP) — A single tar ball that washed up along Manhattan Beach last month has been linked to the Refugio oil spill, authorities said Monday.

Officials with the California Department of Fish and Wildlife (DFW) say an “exhaustive analysis” by chemists at the department’s Office of Spill Prevention and Response (OSPR) Petroleum Chemistry Laboratory determined that a tar ball sample matched the source sample taken from the Refugio incident.

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Chemists also found that the sample “did not match local natural seep oil or oil from vessels in the vicinity around the time of the tarball event,” according to DFW spokeswoman Alexia Retallack.

However, authorities cautioned the findings did not necessarily mean all tar balls found on Manhattan Beach could be attributed to Refugio.

“Although the test results of this tarball sample matched the Refugio Incident oil spill, the source of all tarballs on Manhattan Beach cannot be determined based on one sample,” Retallack said.

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Globs of what initially appeared to be a petroleum-based substance were first reported May 27 along the 2200 block of The Strand in Manhattan Beach.

The discovery was made within days after the ruptured Plains All American Pipeline spilled up to 101,000 gallons of crude oil along a 9-mile stretch of coastline near Refugio State Beach on May 19.

Low levels of tarballs are typically present on Southern California beaches from natural sources, most commonly from offshore seepage from fissures in the seabed, according to scientists.

Plains covered the cleanup costs on those beaches while the oil was tested to make sure it didn’t come from natural seepage, the Associated Press reported.

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