I recently switched from Park-lube to a marine grade grease and tried it on a recent build. It is a little thicker and somehow kind of stringy, but seems to work great. I assume it will last longer but only time will tell.
The only way I ever see that getting into the environment is by washing it off my hands or if I wash the shop rag that I was using at the time. In either case it would be bound to a soap molecule (which alows it to become water soluble), and filtered just like everything else we wash down our drain through hundreds of feet of decomposed granite based soil before entering the ground water system. The stuff thats close enough to the surface for plants to pick up doesn't seem to cause any harm because the grass is way greener over the septic lines than anywhere else.