These morphs were always out there. Just look at how long ago Piebalds were around, I think Peter Kahls website says there were reports of a pied back in the 60's and 2 were brought to this country in the 80's.

I think the big thing to remember is that people weren't looking for them. There was no ball python craze, so therefore, no one out there looking for ball python morphs.
Both the VPI and NERD books cover how no one cared about ball pythons initially.

And as far as pollution goes in causing these morphs...that's beyond far fetched. Tons of species are highly variable and carry genetic traits that have nothing to do with external factors. Plus where is this pollution coming from? Out in the middle of the Savannah there is little to no human influence that would be causing anything like this happen.