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TFA forms when synthetic chemicals from other "forever chemicals" such as those found in pesticides and refrigerants are partially broken down.

He said the efforts should be prioritized given the area’s high rates of respiratory illnesses, driven partly by toxic lake bed dust laced with pesticides and other pollutants that have accumulated over decades.

Most of the pools are located in Altadena, and the district has so far been able to treat about half of them with pesticides.

Vigilance and quick action are especially important here because Bifano only uses organic control methods, so no chemical pesticides or herbicides.

Diseases such as Usutu are a growing threat to wild birds, amid a host of other pressures, including habitat loss, climate change and pesticide use.