Up to this point, that's not been a factor considered by anyone in a position of authority.
Starship uses Methane-Oxygen, which burns way cleaner than Kerosene-Oxygen, which is used by Falcon 9.
The thing people should be concerned about are solid rocket boosters, which SpaceX does not use. Solid boosters have polluted every "untouched" alpine lake on the planet. Those have been used by the new Vulcan, Space Shuttle, and a lot of other rockets.
Tim Dodd has an excellent video and write-up on this topic: