-The Purity of Water, Minerals, Forageables, and Animals all seem to vary across the terrain.
-The Terrain is randomly divided into "purity zones" which blend into each other at the borders resulting in smooth gradients of purity change as you travel, and detectable "Peaks". The north shore of my Lake has Sulphur-rich water, the South has Lead-rich, and the middle of the lake is slightly rich in both Sulphur and Lead.
-The different categories of purity seem to be independent of each other. The purity of a Lilypad Bulb has no relation to the purity of the water it sits on.
-The highest water purity I have seen so far is 35.34 mercury in a stream right next to my enemy's base.

I'm sure there's better stuff out there.
-All animals in a spawning-group have identical purity.
-Plants in one area will all tend to be of similar purity relative to each other. (Do plants spawn in clusters? I once harvested two Devil's worts which had identical purity.)
-The plants and animals around my Sulfur/Lead mine seemed to be rich in Sulfur/Lead. Coincidence?
-All existing trees seem to have 0% purity. Their cuttings, branches and maple-leaves are all 0%.
Questions:
Is the purity of a Mine Node related to the purity of nearby Water, Clay or Lime?