in big cities is a big issue

[blizzy]

Can I say this and does is sound natural?
Environmental pollution in big cities is a big issue which Peter is interested in.
Peter really delved into the subject and became quite knowledgeable.

 

[Tarheel]

Can I say these and do they sound natural?
Environmental pollution in big cities is a big issue which Peter is interested in.
Peter really delved into the subject and became quite knowledgeable.

Rather than a big issue you might just say an issue.