>> significant, but not large. the biggest amount we found, 44 billionth of a graham. toxic residue has collected from a prior fume event over from gradual accumulation of toxics. >> there is material floating around in the ventilation system and comes out on a regular basis. that's what you are measuring. >> reporter: so even if the flight you are on has not had a fume event, there are toxic fumes in the ventilation system and it's coming out? >> that's the case. >> reporter: he explains when engines are shut down, some oil can leak overnight. when a plane starts up in the morning, a mist of oil can spread through the cabin. >> you don't want to be the first person on the plane in the