I don't know if it's possible to add polution when dumped

Yes, I'd like to but at the moment I'm not sure how to generate pollution directly from a tile action trigger.

You could duplicate inserters to a poluting variant, each time an inserter is placed or tiles are changed around it it would get replaced to the appropriate version depending if the inserter would dump or not,

To make a poluting inserter, you have to change the energy_source to have emissions_per_minute

I like ecology :-D At least add the pollution with the default value with a multiplier configuration so that everyone can adjust it according to the mod pack