another toxic air incident
 

Air Serbia, and A330. Sorry, I don't have the flight number, or exact date. My brother was on board last week on a flight to Belgrade from JFK. He is a Dr. and responded to a child in the back who passed out from exhaust fumes during ground operations. THey were already at climbout before his response.
He reported a strong exhaust smell in cabin pre taxi.
So, what is a likely cause? APU with cargo door open and an unfavorible wind direction?

Only one person in the cabin affected? Hmmmm . . .

You sometimes get a smell of fuel fumes in the cabin during engine start if the wind is blowing from behind the aircraft.

I have never known it to cause someone to pass out though. I would think there must be another cause?

It will also happen when taxying behind or past other aircraft, if the wind is blowing from the direction of those other aircraft. Taxying in a lengthy queue of aircraft, with the wind coming from in front of you, and you can be breathing the exhaust of several aircraft, for several minutes! Not pleasant, but it is a hazard of the ground portion of aircraft travel. What it isn't, is a toxic air incident, in the generally accepted use of the phrase in aviation.