Strange coincidence (in my head) but my horticulture professor was just mentioning how it is a shame that most American cities are built upon some of the higher quality crop-land, (near rivers or other water, (at least originally) great soil, flat ground, transportation etc.) and how it is a shame we build buildings on top of such great land. Of course each geographic area would have a varying degree of resources and pollution, so these generalizations do not amount to much. Just a thought, but maybe your professor was saying that if you do not spend time on research he doesn't have to either, so he says, bah bad soil pollution, and bad grade?

Or it could be something else entirely, on some bike forum, and as I know nothing about your paper or anything about the situation I couldn't say. If you are serious about improving your grade maybe you could talk to him about a re-write?

One developing area that is really interesting to me is phytoremediation, which uses plants to suck the heavy metals and other pollutants out of the soil. The plants (which become storage for the pollution) can be properly disposed of and the land is left clean. Then we have tons of places to plant food =)