White Powder Coming From Air Vents

Hi,

Over the last few months I’ve noticed a very small amount of white power-like substance coming out of my cabin air vents. I thought it was just dust.

However, on Friday I started the engine and a substantial and continuous amount of powder was emitted. It eventually stopped.

I took it to a Toyota dealer who replaced the pollen filter. I'd already cleaned up the mess, so they were not able to examine the powder first hand. They blew through the system and could not see any evidence.

Now, the problem continues. It's not as heavy as Friday, but much worse than it was originally.

I've read something about an anti-mildew coating which is applied to the fins of the fan in the Evaporator unit; which perishes and breaks off.

Does anyone know what is causing this fault? More importantly, is the powder dangerous or damaging to my health??