As far as i know, the use of Type 4 has been abandoned in scandinavia due to problems with re-hydration and subsequent frozen elevators...
...and guess what? ...when the Type 4 was gone, so were the above mentioned problems...
I guess Type 1 and 2 will be here for a while longer... The enviroment is one thing, but let's keep aviation safety as the top priority for now...
But no matter what, there is no way Type 4 can replace Type 1 when it comes to de-iceing.. A Type 1-mix packs more heat and pressure for removing snow and ice from the surfaces...
Even when diluted to a 50% mix, the Type 4 has too high viscosity to be efficient in removing anything more than frost... IMHO that is...
As for finding out if it's hydraulic-fluid or de-iceing fluid, you can feel the difference.... The hydraulic-fluid feels dry, while de-iceing fluid is a lot more slippery...