Then in the thesis statement specify one of its kinds? air water ,etc this is what I meant in the previous question.
If you were asked to write about "Pollution," that would be okay. I think that you would help yourself greatly by choosing a more narrow topic, so that your paper will be more focused. However, if you were asked to select a topic under the category of "Pollution" then I would suggest that you get right to the point with the specific topic. That way, you don't waste time or space discussing things in your introduction that you're not going to discuss in the body of your paper.
For instance, if you have chosen "air pollution," starting your paper with a statement like, "Pollution impacts many people in many different ways," would be ineffective. I call that "written throat clearing." In this case, you're more preparing yourself for writing than your audience for what they are about to read.
You'd do better by starting with a statement like, "Air pollution has been linked to many human diseases including emphysema and lung cancer." (Please note that this is just an example. I have no idea whether that is true!) That way you have a better chance of gaining your reader's attention, by creating a focus that is specific and interesting.