i independantly came up with this idea also
I don't think this is an absolutely good idea as this would lag most computers and powder would just continuosly fall until the game session has ended.
we could make that particles or waves or etc will be freezed after entering 2 pixels of that chunk to only continue them if that specific chunk is loaded by the screen. we could make this an option for users to toggle if they have lag problems with the chunking system. beefy computers could just handle it. and infinite is impossible but we could limit it to a 16 x16 (or less) chunk field.
about the saving:
only save currently rendered chunk and not all of them
one way to do this theroreticly would to make particles smaller