All of God's creation is pure. It only becomes damaging after it has fallen into the hands of men. Even further, once tainted by mens hands it still is not the cause of becoming unclean. It's how we process what we take in and how we let it settle in our hearts and minds.
Every bit of creation that we have perverted to our own desires or gains comes in to my body with the potential of making me unclean. Seen through my eyes and experiences, I have become desensitized to a lot of what is out there. With this view it becomes a carcinogen, slowly eating away at my mind, heart and soul. Once I can give myself truly to Him, the full benefits of the Spirit can take hold. Working through my conscious, the Spirit can filter out the trash that has made it's way inside of me and destroy it before it can do any permanent damge and before it can escape back out of me to infect someone else.
Lord, use your Spirit in me to cleanse me of all the garbage we have created out of your beautiful creation, to keep my mind clean and to stop me from being a "carrier" of this same garbage.