In Gaia, there's no such thing as pollution. The rules of the game are that any species that produces something noxious that affects the environment, is doomed. Imagine there's some green bug... that decides it would be a neat trick to make chlorine. That bug is not going to succeed. If it doesn't kill itself off, it will certainly kill off its progeny, and destroy the environment around it and have no food to eat.
"The Man Who Named the World"