Wilson Flower

Lead author Alandra Lopez collecting chromium-rich soil from a serpentine chaparral landscape after the 2020 LNU Lightning Complex fire.

Wildfire frequency and severity are rising under climate change and, with them, health concerns about the potentially harmful contents of smoke and soot.

New research in the journal Nature Communications expands those worries.

The fact that dust and smoke from wildfires near urban margins can hold respiratory carcinogens is well known.

But a new analysis of soils and ash produced from the 2019 and 2020 wildfires across Northern California shows cancer-causing heavy metals can also enter the mix when wildland fires burn the soils that contain them.

Scott Fendorf

Lead author Alandra Lopez preparing dust samplers at McLaughlin Natural Reserve (in California's Napa and Lake counties) in July 2021, the year following the LNU Lightning Complex fire.

Chromium, for example, has a mostly harmless form (trivalent chromium, or Cr(III)) that remains stable in soils. Our bodies even rely on small amounts of it.

But expose it to temperatures of above 390 Fahrenheit, and it changes into an environmental toxin (hexavalent chromium, or Cr(VI)).

What’s more, in dry environments, that noxious dust can persist and potentially become airborne for 10 months following a fire.

Alandra Lopez

Burned grasslands atop the Mayacamas Mountains at Modini Preserve east of Healdsburg, California, after the 2019 Kincade Fire.