"I have been thinking about those iridescent shower curtain panels on the corridor trusses and the back wall of the transporter platform. ... Maybe they're an air filtering system. As air passes over these panels, certain impurities are drawn out of the air and trapped onto the panel."
I guess radioactive particles count as impurities and that crap has to go somewhere where it's neutralized, especially when I think of the de-contamination procedure on the transporter platform in "The Naked Time".
This could also explain the strange red glowing effects of the transporter platform panels when they accidentally beamed Gary Seven aboard in "Assignment: Earth". Makes you wonder by what kind of particles he was surrounded during his transport.