I'd guess the cleaner environments are generally the places farthest from large populations of people and industry. I've heard that the 200 miles surrounding Dayton, Ohio is the most densely populated area of it's size in the US. Each of the ocean coasts are densely populated also. I suspect those areas also have higher than average contamination of soil and water.

Here in the midwest, we have high levels of mercury in the water from all of the coal we burn for electricity. Lots of agricultural run-off around here, too. Still, you can eat alot of bluegills before you need to worry about health effects from eating the fish. Even the little bit of pollution you ingest from eating small fish and game is probably offset by avoiding many of the additives/herbicides/growth hormones, etc. found in commercially processed foods. I don't like eating chemicals any more than you do, but I'm not going to worry a whole lot about it either. Hopefully something else will kill me before environmental pollution makes me sick.

I doubt there's anywhere that pollution hasn't effected to some degree. But the farther you get from the factories and cities I suspect you'll find the pollutants to be less concentrated.