Dear aspirant,

As far as your Engineering branch is concerned let me tell you that kindly do that from a renowned college and not from a random private university otherwise you would be having difficulty in your placements.

So, if you think you can handle biology with mathematics then kindly go for it but let me tell you it won't be easy to handle. If you are very sure about environmental engineering then biology in 11th and 12th will help you a bit or rather give you an edge.

Still I feel mathematics with computer will be a better option because no one knows about the future and nowadays there is a great hype for non core area and it companies.