There are some obvious ways to go on this such as air pollution and water pollution. The great thing about this is you can measure it in various scientific ways. In other words, the result is very visible. However, there are other types of pollution. How about noise pollution? I think you can have fun with this. You can show how noise reduces the quality of a person's life, especially if a person lives in an urban area. Image the lack of sleep due to the various noises out there. What does it do to children? How about listening to music loudly on an ipod? Can loss of hearing take place? I think you can combine statistics with a demonstration.
There are plenty of ways to progress with this project. I would suggest identifying a particular aspect that can be explored in a science exhibition format. Perhaps, you are interested in ways that individuals can reduce polluting habits and this can be featured on a posterboard of some type of display format. Another way you can move on this project is to identify a challenge in the realm of pollution and use your science exhibition to display greater understanding of this topic. For example, if you are going to identify major causes of pollution, you are using your exhibition to raise awareness of the problem. I think that you want to focus on one area and project a wide exploration on this topic for your exhibition. In the final analysis, your science fair is meant to display students' findings on the topics selected. Since yours is pollution, it would make sense that if you identified something that you wanted to explore about pollution, making this your focus for your science exhibition might be a good start.
You can take up water polluction and prepare your project on water polluction.You can perform toxicity test of chemicals/metals on fish.
Such tests are performed to screen various chemicals as pesticides and other toxicants for their deleterious enviornmental effects at tentative level.Relative toxicity of these chemicals is studied.Information obtained through such tests is then used for bioasays.
Bioassay is a test in which organisms are used to detect the presence or the effects of any other chemical factor,or any other type of ecological disturbances.Bioassays are very common in polluction studies.Bioassays can be conducted by using any type of organisms.The aim is to find out lethal concentration causing mortality or other effects.
I would recommend that you look at water pollution. Water resources are readily available and fairly easy to collect. Construction sites have run off fences with plastic at the base (the orange plastic fences). Each construction company has someone who has to determine if there are any contaminants in the water. You can easily take some jars and collect water samples from lakes, creeks, construction sites, and even sink water from various areas in the city where you live.
You will need to purchase some Litmus paper. I recommend buying a small pool kit. You will then use the test strips to determine if the water is ph balanced or has acidic qualities.
Another area that you will explore is the turbidity of the water. This basically means whether the water is murky or clear. Water that person's drink is more favorable if it is clear and transparent. Scientists evaluate water turbidity to determine levels of phytoplankton, sediments from erosion (particularly at construction sites),waste, algae growth, and urban runoff.
I have listed a good site where you will be able to learn more about water turbidity.