It looks like picking up an existing filter machine means the collected pollution is all returned to the environment. Have you considered adding a way to permanently get rid of it? Currently, once a machine is put down, there's no way to move it without releasing all the pollution, but perhaps a careful engineer could pick it up without producing a giant cloud of toxic waste.
... Never mind. On closer reading (and by experimenting in game) it seems the pollution being absorbed by a filter is combined with the new filters in order to make used filters. It's a pretty small cloud that gets released when an item is picked up.
