Why is "Pollution is dangerous to the environment" not correct?!
That would translate to: La pollution est dangereuse pour l'environnement. The same meaning, but it's not an idiomatic expression, therefore should be translated literally: ĂȘtre un danger - "to be a danger".
Could you say : "for" the environment instead of "to" the environment
Why is 'endangers the environment' not acceptable as an alternative translation?
Your sentence would translate as la pollution met en danger l'environnement. That is a different construction even if the meanings are very similar.