Here are a case about workplace exposure where a chemical did great harm. Read: Researchers' Deaths Inspire Actions To Improve Safety , note the quantities involved. When I first read the account of this tragedy, cynical me thought the researcher was probably sloppy for a long time and only admitted to the one accident. I was wrong. Later investigations of trace mercury deposits in her hair demonstrated that those few drops were all Karen Wetterhahn was exposed to - just a few drops on top of standard lab gloves, just once.