Safety of a mass driver tug, or lack thereof

"Even the slag left over from the refining operation is useful for shielding, or possibly as reaction mass if mass driver tugs are being used."

I have seen statements of the form "The pellets ejected from a mass driver tug would not measurably alter the number of debris objects in near-Earth space" or words to that effect. Maybe even you have made such a statement; I don't recall.

Perhaps I just need to really understand more deeply, but those words are not very comforting to me. In my mind, pellets ejected from a mass driver tug would go into various orbits around the Sun, more specifically, orbits that intersect with Earth orbit or with Luna's orbit. Furthermore, it is likely that the pellets would be coplanar with Earth's orbit or with the Earth-Luna Trojan points, because that's where the mass driver tugs would be. What goes around would eventually come around, I suspect. Our orbit and the pellet's orbit would have some common synodic period. Shall we just fire off thousands or millions of pellets and just hope that they and we do not occupy the same point in space several years down the road?

I can see firing off pellets of some easily vaporizable material such as ice, solid oxygen, ammonia, or some such. Pellets of these materials would eventually sublimate or vaporize within a few days, weeks, or months. But firing off pellets of slag seems very risky to me because, unless we track the orbit of each such pellet, there would be some risk that we and the pellet might become accidentally re-acquainted at a later date, much to the detriment of both of us.

Can you make me feel more secure about firing off pellets of slag from a mass driver tug? Do you suggest we track the orbits of each pellet fired, and propagate each of those forward for the next 100 years?