In several locations in the game you can find barrels with radioactive warning stickers on them, similar to the ones that appeared in the game Fallout.

There's one in Lothar's house and another in the Tenement of Thugs.

Nuclear waste in a medieval fantasy setting though? It's because the team of programmers that worked on Planescape: Torment included much of the team that made Fallout and Fallout 2