Hi Matilda
One way would be to double-click the number in the Texts column of the
collocate window (e.g the 124 for pollution); that makes Concord order
the concordances to as to move all those concordance lines to the top.
Then way over to the right of that concordance listing you can see the
source text filenames where those hits occurred. Does that answer your
query?
Cheers -- Mike