Loftwings and Demons

There's a huge problem with how problems like food contamination (eg. heavy metals) are often communicated: no numbers!  Someone will say some food contains 'a lot' or 'a little' contamination, but this is really not helpful for communicating relative risk.  What are the actual amounts?  What levels should these values be under to be recognized as generally safe?  It's impossible to have no contamination, and it makes a big difference if something is thought to be under safe (or at least negligibly affecting) levels, vs twice that level, vs 200 times that level.  That makes a difference!