If you're writing a research paper, your best bet for sources is scholarly journals, which can usually be found in your school library's databases. You can look for science journals, if that's the slant your paper is supposed to take, or sociology/urban studies, depending on what course this is for. You can also try government websites, which are a good source of information. For example, if I were looking for information in the U.S., the Environmental Protection Agency's website would be a good one, as well as the Centers for Disease Control. I see that you are in the U.K., so you'll have to check to see which governmental agencies there keep track of the environment and its effects on people.
I hope this helps!