Background: Wildfire ashes from the wildland-urban interface (WUI) can contain high levels of toxic metals, such as chromium (Cr), copper (Cu), arsenic (As), and incidental nanomaterials. We hypothesized that the viability of mouse atrioventricular cushion mesenchymal (AVM) cells has a negative dose dependent relationship with WUI wildfire ash.

Methods: Mouse AVM cells were seeded into wells at 5x105 cells/mL. After 24 hours the wells were treated with 42 fire ash supernatants at 0.1, 1, 2, 5, and 7.5 mg/mL. After incubation, a 5 mg/mL MTT (3- (4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) solution was added. The solution was then aspirated and dimethyl sulfoxide was added. The absorbance of each well was then taken at 570 nm. The viability of the treated cells was estimated by comparison to controls on each plate. The desired toxic effect was less than or equal to 50% viability (LD50) after treatment. An unpaired t-test was used to compare the LD50 value to the control.

Results: Of the 42 samples tested, 23 showed a decrease in cell viability, 7 showed a decrease of 50% or more, and 6 showed an increase in cell viability. Over two thirds of the samples that achieved a 50% decrease in viability were structural or vehicular burns, such as those found in the WUI. Sample A-013, collected from a trailer, achieved LD50 at 5 mg/mL (p=0.0034). Sample A-031, collected from burned vegetation, had 46% viability at 7.5 mg/mL (p=0.0011). Sample A-081, collected from a burned oak, had 44% viability at 7.5 mg/mL (p=0.0006). Sample A-092, collected from burned artificial wood, showed 32% viability at 7.5 mg/mL (p=0.0019). Sample A-095, collected from a garage, had 44% viability at 5 mg/mL (p=0.0011). Sample A-096, collected from treated wood and burnt electronics, also had 44% viability at 5 mg/mL (p=0.0035). Sample NCWZ 4-B, collected from a burnt car, had a viability of 45% at 7.5 mg/mL (p=0.0161).

Conclusion: Tested WUI fire ashes showed significant toxicity. Samples with treated wood or trace metals were particularly toxic. These fire ash samples are highly prevalent in the WUI. Regardless, the tested fire ashes supported the hypothesis that the viability of AVM cells has a negative dose dependent relationship with WUI fire ash exposure. These results indicate that WUI fire ashes may cause significant cardiotoxicity in vivo. Further studies on the effects of fire ashes on developmental processes, such as epithelial to mesenchymal transition, will also aid in understanding how exposure may influence heart development.