RvB,
As well as all the nasties from engine oil entering the bleed air, I think it is very likely that the heavy metals you talk about get into the bleed air too. Blood test results from a group of pilots in 2006 showed unusually high levels of Nickel in most of them, and antimony, beryllium and cadmium were also found. Nickel is extensively used in alloys for compressor blades, and I believe the other metals are also to be found in jet engines. If this stuff can get squirted off the compressor blades by water, it seems logical that it can also get sucked into the bleed air.