One of the problems with mass spectro technology today is that it can detect
a few molecules of something... and if you take a sample of anything anywhere
in the world, there's a good chance of there being a few molecules of anything
you can name in it.
A lot of the nastier pesticides are oil-soluble (partly good to help make
them stick to plants and not was off) and won't dissolve in a cup, which is
good, but there's some pretty ugly stuff out there and I don't think anyone
really has a good grip on how tiny trace amounts of some of the nastier
organometallics really affect anyone over the long term.