Chemistry

It's all a matter of chemistry.  Chemicals bond, chemicals interact, they evolve.

In Mud Season, full drums of chemicals are abandoned in a dumpsite.  This isn't that odd.  I grew up in Niagara Falls, home to several chemical companies and, in the seventies and eighties, buried drums surfaced in former dumpsites that had not been well documented.  People had moved in, and found these unwanted surprises bordering their property.  Love Canal was just one of these.

Another variable, an important one, is dosage.  So many chemicals, in different doses, do harm and then save lives.  Warfarin (Coumadin) is a well known blood thinner.  In one dose millions of people who've suffered heart attacks can continue living with a reduced risk.  In another dose, warfarin is rat poison (D-Con) and its same effect compels small animals to drown in their own fluids.  Polyethylene glycol is found in anit-freeze.  A much lighter dose is ingested by people preparing for a colonoscopy.

So it's all a matter of dosage.