The January wildfires left many scars on the city of Los Angeles, from rubble-reduced homes to torched abandoned vehicles. Though cleanup crews quickly cleared much of the debris, one alarming invisible impact lingered over the city for months, a new study suggests.

In late March—more than two months after the flames died out—researchers detected levels of carcinogenic hexavalent chromium (a.k.a. chromium-6) 200 times greater than baseline levels for LA air. If this pollutant sounds familiar, you’re probably thinking of the 2000 film Erin Brockovich , a dramatization of a true story about hexavalent chromium water contamination. Though the levels the researchers detected fell below certain safety thresholds, the particles’ unusually small size immediately raised concerns.

The study is

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